| 1. |
- Alikas, Krista, et al.
(author)
-
Robust remote sensing algorithms to derive the diffuse attenuation coefficient for lakes and coastal waters
- 2015
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 13:8, s. 402-415
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Journal article (peer-reviewed)abstract
- In this study, empirical and semianalytical algorithms are developed and compared for optically complex waters to retrieve the diffuse attenuation coefficient of downwelling irradiance (Kd(lambda)) from satellite data. In the first approach, a band ratio algorithm was used. Various sets of MERIS band ratios were tested to achieve the best estimates for K-d(490) based on the in situ dataset which was measured in Nordic lakes (oligotrophic to eutrophic conditions). In the second approach, K-d(490) was expressed as a function of inherent optical properties which were retrieved from MERIS standard products. The algorithms from both approaches were tested against an independent data set and validated in optically complex coastal waters in the Baltic Sea and in Nordic lakes with high concentrations of coloured dissolved organic matter (0.3 < a(cdom)(442) m(-1) < 4.5), chlorophyll a (Chl a) (0.7< C-Chl a(mg m(-3))< 67.5) and total suspended matter (TSM) (0.5 < C-TSM(g m(-3)) < 26.4). MERIS-derived K-d(490) values showed reliable estimates in case of both methods. The results indicate that for band ratio algorithms, the root mean square error (RMSE) decreases and the coefficient of determination (R-2) increases when using longer wavelengths in the visible spectrum as a reference band. It was found that the best estimates were retrieved from MERIS data when using the ratio of R-rs(490)/R-rs(709) for coastal waters (K-d(490) < 2.5 m(-1)) and the ratio R-rs(560)/R-rs(709) for more turbid inland waters (Kd(490) > 2.5 m(-1)). As a result, a combined band ratio algorithm was developed, which provides a promising approach R-2 = 0.98, RMSE= 17%, N = 34, p < 0.05) for estimating K-d(490) over a wide range of values (0.3-6.1 m(-1)).
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| 2. |
- Atamanchuk, Dariia, 1987, et al.
(author)
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Performance of a lifetime-based optode for measuring partial pressure of carbon dioxide in natural waters
- 2014
-
In: Limnology and Oceanography : Methods. - : Wiley. - 1541-5856. ; 12, s. 63-73
-
Journal article (peer-reviewed)abstract
- This article reports the performance of an improved, newly developed, compact, low power, lifetime-based optical sensor (optode) for measuring partial pressure of dissolved CO2 gas (pCO2) in natural waters. The results suggest that after preconditioning, these sensors are stable in water for time periods longer than 7 months. The wide dynamic range of about 0-50000 μatm opens possibilities for numerous applications of which some are presented. In normal marine environments with pCO2 levels of 200-1000 μatm, the best-obtained precision was about ±2 μatm, and the absolute accuracy was between 2-75 μatm, depending on the deployment and the quality of the collected reference water samples. One limitation is that these sensors will become irreversibly poisoned by H2S and should thus not be deployed in sulphidic environments.
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| 3. |
- Baden, Susanne P., 1952, et al.
(author)
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Relative importance of trophic interactions and nutrient enrichment in seagrass ecosystems: A broad-scale field experiment in the Baltic-Skagerrak area.
- 2010
-
In: Limnology and Oceanography. - 1541-5856. ; 55:3, s. 1435-1448
-
Journal article (peer-reviewed)abstract
- The interaction of eutrophication and predation in structuring seagrass Zostera marina L. ecosystems was assessed in a field experiment in three regions along an estuarine salinity gradient, from southern Finland to the Skagerrak area of the Swedish west coast. All regions are considered to be affected by eutrophication and overfishing but differ in the abundance of intermediate predators (e.g., small fish, shrimp, and crabs), mesograzers, and the biomass of epiphytic algae. Using transplanted Zostera (eelgrass), nutrient levels and intermediate predator abundance were manipulated in a full-factorial cage experiment. On the Swedish west coast, where ambient densities of mesograzers are very low, epiphytic algae responded strongly to nutrient enrichment, resulting in significantly reduced growth of eelgrass. At the Baltic sites however, where ambient densities of mesograzers are high, no significant growth of epiphytic algae was detected, and only grazer biomass responded to nutrient enrichment. Predation from small fish, shrimp, and crabs decreased the biomass of mesograzers by . 98% on the Swedish west coast, but natural predators had no significant effect on mesograzers biomass at the Baltic sites. Predation and nutrient enrichment interacted to affect the growth of eelgrass by controlling the biomass of mesograzers and nuisance algae. The differing effect of nutrient enrichment and grazing in the three regions may therefore be a result of the prevailing low and high predation pressure on mesograzers in Zostera. This absence or presence of predation may derive from interregional changes in trophic interactions, possibly caused by a combination of eutrophication and overfishing.
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| 4. |
- Barão, Lúcia, et al.
(author)
-
Alkaline-extractable silicon from land to ocean: A challenge for biogenic silicon determination
- 2015
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; , s. n/a-n/a
-
Journal article (peer-reviewed)abstract
- The biogeochemical cycling of silicon (Si) along the land-to-ocean continuum is studied by a variety of research fields and for a variety of scientific reasons. However, there is an increasing need to refine the methodology and the underlying assumptions used to determine biogenic silica (BSi) concentrations. Recent evidence suggests that contributions of nonbiogenic sources of Si dissolving during alkaline extractions, not corrected by standard silicate mineral dissolution correction protocols, can be substantial. The ratio between dissolved Si and aluminum (Al) monitored continuously during the alkaline extraction can be used to infer the origin of the Si fractions present. In this study, we applied both a continuous analysis method (0.5 M NaOH) and a traditional 0.1 M Na2CO3 extraction to a wide array of samples: (1) terrestrial vegetation, (2) soils from forest, cropland and pasture, (3) lake sediments, (4) suspended particulate matter and sediments from rivers, (5) sediments from estuaries and salt marshes and (6) ocean sediments. Our results indicate that the 0.1 M Na2CO3 extraction protocol can overestimate the BSi content, by simultaneously dissolving Si fractions of nonbiogenic origin that may represent up to 100% of the Si traditionally considered as biogenic, hampering interpretation especially in some deeper soil horizons, rivers and coastal oceanic sediments. Moreover, although the term amorphous Si was coined to reflect a growing awareness of nonbiogenic phases we show it is actually inappropriate in samples where silicate minerals may account for a large part of the extracted Si even after linear mineral correction.
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| 5. |
- Bianco, Giuseppe, et al.
(author)
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Plankton 3D tracking: the importance of camera calibration in stereo computer vision systems
- 2013
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In: Limnology and Oceanography: Methods. - : Wiley. - 1541-5856. ; 11, s. 278-286
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Journal article (peer-reviewed)abstract
- Computer vision applications are very useful to study animal movements, but due to their intrinsic complexity they are challenging to design, implement, and use properly. We here describe a calibration procedure for a laboratory stereo vision system for tracking zooplankton in three dimensions (3D). We demonstrate the crucial importance of using a correct calibration for proper interpretation of animal swimming tracks. We also address the effect of the air-water shift phase in the calibration procedure. Actually, not performing a proper calibration caused an average positional error of more than 25 body-lengths in the investigated animal Daphnia magna. Furthermore, we evaluate the different outcomes of using 2D and 3D tracks obtained with a calibrated stereo vision system and show that although 2D tracking might be sufficient in some cases, the method was in our study unable to give information of swimming path geometry and underestimated the speed by 25%. Finally, we discuss consequences for biologically relevant questions when an incorrect methodology is used and strongly recommend that future studies provide detailed descriptions of the framework used for calibration to allow for comparisons between different studies.
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| 6. |
- Blackburn, Nicholas, et al.
(author)
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The use of an automated organism tracking microscope in mesocosm experiments
- 2022
-
In: Limnology and Oceanography. - : John Wiley & Sons. - 1541-5856. ; 20:12, s. 768-780
-
Journal article (peer-reviewed)abstract
- A method for automatically counting and measuring sizes and motility behavior of zooplankton and phytoplankton in water samples is presented. Two video cameras are focused on separate optical chambers of different sizes. The chambers are filled and emptied repeatedly by synchronized pumps. Real-time motion analysis is performed by computer on the respective video feeds. Fluorescence from chlorophyll a (Chl a) is imaged at single pixel resolution. Measured parameters for individual organisms include size, swimming velocity, motility patterns, and chlorophyll fluorescence density. The system was tested during a mesocosm experiment where it was mounted on one of several mesocosm columns. The results were validated against Chl a measurements and microscopy counts. A sampling interval of 1 per day revealed detailed dynamics of chlorophyll activity as well as shifts in both the phytoplankton and zooplankton community structure over the course of a month. A helix coefficient, a metric related to organism motility behavior, showed substantial variation over time, consistent with changing plankton communities. Sampling rates as frequent as 1 per hour enables detailed analysis of diurnal vertical migration and similar phenomena at fixed sampling points.
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| 7. |
- Block, Benjamin D., et al.
(author)
-
The unique methodological challenges of winter limnology
- 2019
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In: Limnology and Oceanography. - : Wiley-Blackwell. - 1541-5856. ; 17:1, s. 42-57
-
Research review (peer-reviewed)abstract
- Winter is an important season for many limnological processes, which can range from biogeochemical transformations to ecological interactions. Interest in the structure and function of lake ecosystems under ice is on the rise. Although limnologists working at polar latitudes have a long history of winter work, the required knowledge to successfully sample under winter conditions is not widely available and relatively few limnologists receive formal training. In particular, the deployment and operation of equipment in below 0 degrees C temperatures pose considerable logistical and methodological challenges, as do the safety risks of sampling during the ice-covered period. Here, we consolidate information on winter lake sampling and describe effective methods to measure physical, chemical, and biological variables in and under ice. We describe variation in snow and ice conditions and discuss implications for sampling logistics and safety. We outline commonly encountered methodological challenges and make recommendations for best practices to maximize safety and efficiency when sampling through ice or deploying instruments in ice-covered lakes. Application of such practices over a broad range of ice-covered lakes will contribute to a better understanding of the factors that regulate lakes during winter and how winter conditions affect the subsequent ice-free period.
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| 8. |
- Chu, S. N., et al.
(author)
-
Field evaluation of a low-powered, profiling pCO2 system in coastal Washington
- 2020
-
In: Limnology and Oceanography: Methods. - : Wiley. - 1541-5856. ; 18:6, s. 280-296
-
Journal article (peer-reviewed)abstract
- Summertime upwelling of deep, corrosive waters on the continental shelf of the northern California Current System can exacerbate ocean acidification conditions, providing unsuitable environments for development of calcifying organisms and finfish that are important to the local economy. To better understand the carbonate system in this dynamic region, two recently developed technologies were combined with other sensors to obtain high-frequency carbon profile data from July 2017 to September 2017. The compact, low-power sensor package was composed of an optical sensor for partial pressure of carbon dioxide (pCO2 optode, Aanderaa model #4797) integrated onto a wave-powered PRofiling crAWLER (PRAWLER). The PRAWLER profiled from 3 to 80 m, stopping at fixed depths for varying lengths of time to allow for pCO2 equilibration. pCO2 derived from a regional empirical algorithm was used to correct optode drift using data at 80 m. Near-surface adjusted optode pCO2 agreed within 6 ± 42 μatm to surface pCO2 from a nearby Moored Autonomous pCO2 instrument. Throughout the water column, optode pCO2 compared to algorithm pCO2 within −28 ± 66 μatm. Overall, optode uncertainty was 35–72 μatm based on root-mean-square errors from all comparison data sets. Errors are attributed to optode calibration, adjustment, algorithm uncertainty, and environmental variability between optode and reference data. Improvements for optode performance within this profiling application include using more stable sensing foils, in situ calibration, and pumped flow over the sensing foil. Additionally, the study revealed undersaturated (corrosive) waters with respect to aragonite below 60 m throughout the deployment that reached up to 40 m by mid-September. © 2020 The Authors. Limnology and Oceanography: Methods published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography.
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| 9. |
- Cole, Jonathan J, et al.
(author)
-
Multiple approaches to estimating air-water gas exchange in small lakes
- 2010
-
In: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 1541-5856. ; 8, s. 285-293
-
Journal article (peer-reviewed)abstract
- The rate of gas exchange between air and water is an essential quantity in a number of contexts, from mass balances to the calculation of whole-system metabolism. The exchange of a gas between water and the atmosphere is controlled by differential partial pressures of gases in air and in water (both straightforward to measure) and by the amount of turbulent energy exchange between the air-water interface, the measurement of which is neither simple nor direct. This physical exchange is often expressed as a piston velocity (k). We compared four methods for estimating k in a series of small (0.3 to 45 ha), low-wind (mean wind < 3 m s–1) lakes: 1) floating chambers using ambient CH4; 2) whole-lake SF6 additions; 3) three wind-based models from the literature; and 4) C mass balances constrained by whole-lake 13C additions. All of the methods, with the exception of one windbased model, converged on values for k600 of between 0.35 and 0.74 m d–1 with no biases among methods. The floating chambers, if designed properly, are a cost-effective way of obtaining site-specific values of k for low wind lakes over fairly short time frames (hours).
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| 10. |
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| 11. |
- Gorokhova, Elena
(author)
-
A single-step staining method to evaluate egg viability in zooplankton
- 2010
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 8, s. 414-423
-
Journal article (peer-reviewed)abstract
- A simplified method for viability analysis of zooplankton eggs by staining of nonviable eggs with a fluorescent nucleic acid stain TO-PRO-1 iodide is proposed here as a further development of fluorescence-based egg viability assays. This is one-step analysis with no intermediate steps for chorion removal. The method was calibrated using predetermined mixtures of viable and nonviable eggs (rotifers and copepods), and validated using hatching experiments (copepods) and egg development assay (cladocerans) as reference measurements. In these tests, eggs of several zooplankton species, Brachionus plicatilis (Rotatoria), Daphnia magna (Cladocera), Nitocra spinipes (Harpacticoida), Acartia tonsa (Calanoida), were used. Moreover, staining efficiency was not affected by storage of samples for up to 1 month in -80 degrees C, making the assay suitable for egg viability assessment in field and laboratory studies. To illustrate usefulness of the method, it was applied to evaluate how absence of re-mating affects production of viable eggs in females of A. bifilosa (Calanoida). In females separated from males, proportion of sterile eggs increased in 3 d after the separation and no viable eggs were produced after 5 d. The effects of mating frequency on egg viability are important to understand when designing egg production experiments and interpreting field data on egg viability in populations with skewed sex ratios.
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| 12. |
- Gross, Susanna, 1982, et al.
(author)
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Optimization of a high-throughput phenotyping method for chain-forming phytoplankton species
- 2018
-
In: Limnology and Oceanography : Methods. - : Wiley. - 1541-5856. ; 16:2, s. 57-67
-
Journal article (peer-reviewed)abstract
- Modern equipment facilitates phenotyping of hundreds of strains of unicellular organisms by culturing and monitoring growth in microplates. However, in the field of phytoplankton ecology, automated monitoring of growth is not often done and this method has not been tested for many species. To meet the demand for a high-throughput technique for monitoring growth of chain-forming phytoplankton species, we have assessed and optimized a method commonly used for other microorganisms. Skeletonema marinoi is a pelagic chain-forming diatom, and we have acquired growth patterns in four different treatments (i.e., low and high light, low and high nutrient concentrations) when cultured in multi-well plates. Due to the unexpected heterogeneity in growth rates and maximum cell densities observed between wells (spatial) and runs (temporal), a set of models was fitted to the obtained phenotypic data to correct for these biases. Models were tested for robustness on two replicate multi-strain experiments including 23 different strains. Using the model accounting for temporal and spatial bias, we could reliably determine changes in growth rate caused by nutrient treatments as well as differences in cell density as a response to nutrient availability and light treatment. This method can facilitate high-throughput phenotyping of hundreds of strains, which is often a bottleneck in characterizing the ecology and capacity for adaptation of chain-forming phytoplankton.
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| 13. |
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| 14. |
- Gustafsson, Ö., et al.
(author)
-
Evaluation of the collection efficiency of upper ocean sub-photic-layer sediment traps : A 24-month in situ calibration in the open Baltic Sea using 234Th
- 2004
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 2:2, s. 62-74
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Journal article (peer-reviewed)abstract
- The collection efficiency of cylindrical sediment traps of common design was assessed in situ for more than 2 y in an offshore shelf regime using the 234Th proxy and simultaneously collected hydrological and biogeochemical parameters. The traps were found to systematically record an undertrapping bias of 234Th by, on average, a factor of three (range 0.8 to 10). Seasonal variations in trapping efficiency were related to the seasonally varying ballasting properties of the settling particle pool. Sediment trap 234Th fluxes agreed within a factor of two of the estimated 234Th export from the overlying surface waters in the winter-spring periods in both 1999 and 2000 and appeared related to a particle pool that included, presumably rapidly sinking, mineral particles and diatom tests acting as ballast. In contrast, discrimination against slowly settling organic-rich aggregates of apparent exudate origin resulted in undertrapping of 234Th by factors of three to ten throughout the summerfall seasons. These data are consistent with hydrodynamic predictions that the collection efficiency of sinking particles is inversely related to their intrinsic settling velocities. Recognition of changing particle composition along a settling velocity spectrum combine with carbon mass balance restrictions to suggest that these 234Th-based collection efficiencies, ranging from 0.1 to 1, may not be directly applicable to "correct" sediment trap fluxes of other components, such as organic carbon. However, the 234Th-derived insights of settling-velocity-related undertrapping may beneficially be taken into account when interpreting trap records both in studies of biogeochemical element fluxes and in phytoplankton ecology
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| 15. |
- Hawkes, Jeffrey A., et al.
(author)
-
An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry : Are we getting the same answer?
- 2020
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 18:6, s. 235-258
-
Journal article (peer-reviewed)abstract
- High-resolution mass spectrometry (HRMS) has become a vital tool for dissolved organic matter (DOM) characterization. The upward trend in HRMS analysis of DOM presents challenges in data comparison and interpretation among laboratories operating instruments with differing performance and user operating conditions. It is therefore essential that the community establishes metric ranges and compositional trends for data comparison with reference samples so that data can be robustly compared among research groups. To this end, four identically prepared DOM samples were each measured by 16 laboratories, using 17 commercially purchased instruments, using positive-ion and negative-ion mode electrospray ionization (ESI) HRMS analyses. The instruments identified similar to 1000 common ions in both negative- and positive-ion modes over a wide range of m/z values and chemical space, as determined by van Krevelen diagrams. Calculated metrics of abundance-weighted average indices (H/C, O/C, aromaticity and m/z) of the commonly detected ions showed that hydrogen saturation and aromaticity were consistent for each reference sample across the instruments, while average mass and oxygenation were more affected by differences in instrument type and settings. In this paper we present 32 metric values for future benchmarking. The metric values were obtained for the four different parameters from four samples in two ionization modes and can be used in future work to evaluate the performance of HRMS instruments.
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| 16. |
- Holmborn, Towe, 1979-, et al.
(author)
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Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)
- 2009
-
In: Limnology and Oceanography. - Waco : American society of limnology and oceanography. - 1541-5856. ; 7:11, s. 785-794
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Journal article (other academic/artistic)abstract
- Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA: DNA ratio, RNA: protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0-1200 mu g C L-1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA: protein ratio, whereas correlations with spAARS and RNA: DNA ratio were weaker or nonsignificant. However, when RNA: DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.
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| 17. |
- Holtappels, Moritz, et al.
(author)
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Measurement and interpretation of solute concentration gradients in the benthic boundary layer
- 2011
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In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 9, s. 1-13
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Journal article (peer-reviewed)abstract
- The coastal ocean is characterized by high exchange rates of organic matter, oxygen, and nutrients between the sediment and the water column. The solutes that are exchanged between the sediment and the overlying water column are transported across the benthic boundary layer (BBL) by means of turbulent diffusion. Thus, solute concentration gradients in the BBL contain valuable information about the respective fluxes. In this study, we present the instrumentation and sampling strategies to measure oxygen and nutrient concentration gradients in the BBL. We provide the theoretical background and the calculation procedure to derive ratios of nutrient and oxygen fluxes from these concentration gradients. The noninvasive approach is illustrated at two sampling sites in the western Baltic Sea where nutrient and oxygen concentration gradients of up to 5 and 30 mu M m(-1), respectively, were measured. Nutrient and oxygen flux ratios were used to establish a nitrogen flux balance between sediment and water column indicating that 20% and 50% of the mineralized nitrogen left the sediment in form of N(2) (station A and B, respectively). The results are supported by sediment incubation experiments of intact sediment cores, measuring denitrification rates, and oxygen uptake. The presented flux ratio approach is applicable without knowledge of turbulent diffusivities in the BBL and is, therefore, unaffected by non-steady-state current velocities and diffusivities.
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| 18. |
- Infantes, Eduardo, et al.
(author)
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Making realistic wave climates in low-cost wave mesocosms: A new tool for experimental ecology and biogeomorphology
- 2021
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In: Limnology and Oceanography-Methods. - : Wiley. - 1541-5856. ; 19:5, s. 317-330
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Journal article (peer-reviewed)abstract
- Wave flume facilities that are primarily designed for engineering studies are often complex and expensive to operate, and hence not ideal for long-term replicated experiments as commonly used in biology. This study describes a low-cost small wave flume that can be used for biological purposes using fresh- or seawater with or without sediment. The wave flume can be used as a mesocosm to study interactions between wave hydrodynamics and benthic organisms in aquatic ecosystems. The low-costs wave maker (< 2000 USD) allows for experimental setups which can be easily replicated and used for longer term studies; hence the term wave mesocosm. Waves were generated with a pneumatic piston and wave heights ranged between 3 and 6 cm. Maximum orbital flow velocities ranged between 10 and 50 cm s(-1) representing shallow coastal areas with a short fetch. The system can generate both regular waves (i.e., the wave period and orbital velocity remains constant), using a wave absorber, and irregular waves (i.e., varying wave period and orbital velocity) using a fast push and slow pull motion of the wave paddle. This wave mesocosm system is particularly useful in biogeomorphology to quantify interactions between organisms, sediment, and hydrodynamics and for aquatic ecologist aiming to simulate realistic bed shear stress where short- and long-term experiments (weeks-months) can be replicated.
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| 19. |
- Jansson, Pär, et al.
(author)
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A new numerical model for understanding free and dissolved gas progression toward the atmosphere in aquatic methane seepage systems
- 2019
-
In: Limnology and Oceanography : Methods. - : Wiley. - 1541-5856. ; 17:3, s. 223-239
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Journal article (peer-reviewed)abstract
- © 2019 The Authors. Limnology and Oceanography: Methods published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography. We present a marine two-phase gas model in one dimension (M2PG1) resolving interaction between the free and dissolved gas phases and the gas propagation toward the atmosphere in aquatic environments. The motivation for the model development was to improve the understanding of benthic methane seepage impact on aquatic environments and its effect on atmospheric greenhouse gas composition. Rising, dissolution, and exsolution of a wide size-range of bubbles comprising several gas species are modeled simultaneously with the evolution of the aqueous gas concentrations. A model sensitivity analysis elucidates the relative importance of process parameterizations and environmental effects on the gas behavior. The parameterization of transfer velocity across bubble rims has the greatest influence on the resulting gas distribution, and bubble sizes are critical for predicting the fate of emitted bubble gas. High salinity increases the rise height of bubbles; whereas temperature does not significantly alter it. Vertical mixing and aerobic oxidation play insignificant roles in environments where advection is important. The model, applied in an Arctic Ocean methane seepage location, showed good agreement with acoustically derived bubble rise heights and in situ sampled methane concentration profiles. Coupled with numerical ocean circulation and biogeochemical models, M2PG1 could predict the impact of benthic methane emissions on the marine environment and the atmosphere on long time scales and large spatial scales. Because of its flexibility, M2PG1 can be applied in a wide variety of environmental settings and future M2PG1 applications may include gas leakage from seafloor installations and bubble injection by wave action.
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| 20. |
- Klaus, Marcus, et al.
(author)
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Listening to air–water gas exchange in running waters
- 2019
-
In: Limnology and Oceanography. - : Association for the Sciences of Limnology and Oceanography. - 1541-5856. ; 17:7, s. 395-414
-
Journal article (peer-reviewed)abstract
- Air–water gas exchange velocities (k) are critical components of many biogeochemical and ecological process studies in aquatic systems. However, their high spatiotemporal variability is difficult to capture with traditional methods, especially in turbulent flow. Here, we investigate the potential of sound spectral analysis to infer k in running waters, based on the rationale that both turbulence and entrained bubbles drive gas exchange and cause a characteristic sound. We explored the relationship between k and sound spectral properties using laboratory experiments and field observations under a wide range of turbulence and bubble conditions. We estimated k using flux chamber measurements of CO2 exchange and recorded sound above and below the water surface by microphones and hydrophones, respectively. We found a strong influence of turbulence and bubbles on sound pressure levels (SPLs) at octave bands of 31.5 Hz and 1000 Hz, respectively. The difference in SPLs at these bands and background noise bands showed a linear correlation with k both in the laboratory (R2 = 0.93–0.99) and in the field (median R2 = 0.42–0.90). Underwater sound indices outperformed aerial sound indices in general, and indices based on hydraulic parameters in particular, in turbulent and bubbly surface flow. The results highlight the unique potential of acoustic techniques to predict k, isolate mechanisms, and improve the spatiotemporal coverage of k estimates in bubbly flow.
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| 21. |
- Koehler, Birgit, 1980-, et al.
(author)
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Inter-laboratory differences in the apparent quantum yield for the photochemical production of dissolved inorganic carbon in inland waters and implications for photochemical rate modeling
- 2022
-
In: Limnology and Oceanography. - : John Wiley & Sons. - 1541-5856. ; 20:6, s. 320-337
-
Journal article (peer-reviewed)abstract
- Solar radiation initiates photochemical oxidation of dissolved organic carbon (DOC) to dissolved inorganic carbon (DIC) in inland waters, contributing to their carbon dioxide emissions to the atmosphere. Models can determine photochemical DIC production over large spatiotemporal scales and assess its role in aquatic C cycling. The apparent quantum yield (AQY) spectrum for photochemical DIC production, defined as mol DIC produced per mol chromophoric dissolved organic matter-absorbed photons, is a critical model parameter. In previous studies, the principle for the determination of AQY spectra is the same but methodological specifics differ, and the extent to which these differences influence AQY spectra and simulated aquatic DIC photoproduction is unclear. Here, four laboratories determined AQY spectra from water samples of eight inland waters that are situated in Alaska, Finland, and Sweden and span a nearly 10-fold range in DOM absorption coefficients. All AQY values fell within the range previously reported for inland waters. The inter-laboratory coefficient of variation (CV) for wavelength-integrated AQY spectra (300-450 nm) averaged 38% +/- 3% SE, and the inter-water CV averaged 63% +/- 1%. The inter-laboratory CV for simulated photochemical DIC production (conducted for the five Swedish lakes) averaged 49% +/- 12%, and the inter-water CV averaged 77% +/- 10%. This uncertainty is not surprising given the complexities and methodological choices involved in determining DIC AQY spectra and needs to be considered when applying photochemical rate modeling. Thus, we also highlight current methodological limitations and suggest future improvements for DIC AQY determination to reduce inter-laboratory uncertainty.
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| 22. |
- Kothawala, Dolly, et al.
(author)
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Inner filter correction of dissolved organic matter fluorescence
- 2013
-
In: Limnology and Oceanography: Methods. - : Wiley. - 1541-5856. ; 11:DEC, s. 616-630
-
Journal article (peer-reviewed)abstract
- The fluorescence of dissolved organic matter (DOM) is suppressed by a phenomenon of self-quenching known as the inner filter effect (IFE). Despite widespread use of fluorescence to characterize DOM in surface waters, the advantages and constraints of IFE correction are poorly defined. We assessed the effectiveness of a commonly used absorbance-based approach (ABA), and a recently proposed controlled dilution approach (CDA) to correct for IFE. Linearity between corrected fluorescence and total absorbance (ATotal; the sum of absorbance at excitation and emission wavelengths) across the full excitation-emission matrix (EEM) in dilution series of four samples indicated both ABA and CDA were effective to an absorbance of at least 1.5 in a 1 cm cell, regardless of wavelength positioning. In regions of the EEMs where signal to background noise (S/N) was low, CDA correction resulted in more variability than ABA correction. From the ABA algorithm, the onset of significant IFE (>5%) occurs when absorbance exceeds 0.042. In these cases, IFE correction is required, which was the case for the vast majority (97%) of lakes in a nationwide survey (n= 554). For highly absorbing samples, undesirably large dilution factors would be necessary to reduce absorbance below 0.042. For rare EEMs with ATotal > 1.5 (3.0% of the lakes in the Swedish survey), a 2-fold dilution is recommended followed by ABA or CDA correction. This study shows that for the vast majority of natural DOM samples the most commonly applied ABA algorithm provides adequate correction without prior dilution. © 2013, by the American Society of Limnology and Oceanography, Inc.
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| 23. |
- Lau, Danny C P
(author)
-
Preservation effects on C/N ratios and stable isotope signatures of freshwater fishes and benthic macroinvertebrates
- 2012
-
In: Limnology and Oceanography: Methods. - : Wiley. - 1541-5856. ; 10, s. 75-89
-
Journal article (peer-reviewed)abstract
- This study examined the effects of fluid preservatives on carbon and nitrogen stable isotopes (δ13C and δ15N) and C/N ratios of freshwater animals. Brotia hainanensis snails, Caridina cantonensis and Macrobrachium hainanense shrimps, and Pseudogastromyzon myersi, Liniparhomaloptera disparis, and Ctenogobius duospilus fishes were collected from seven Hong Kong streams, so as to incorporate natural variations in isotopic signals among conspecifics. Samples were preserved with 10% formalin, 70% ethanol, or formalin-ethanol solution (fixation in formalin then storage in ethanol). We compared sample molar C/N, δ13C, and δ15N with frozen conspecifics after 30, 60, 90, 180, and 360 d. Increases in C/N were evident in formalin-fixed shrimps and fish only, whereas ΔC/N attributable to ethanol and formalin-ethanol preservation was insignificant in all species. Chemical preservation generally caused δ13C depletion in fishes and Δδ13C significantly declined over time in formalin-ethanol-preserved L. disparis. Formalin-induced δ13C shifts were observed in shrimps (C. cantonensis: -1.54‰; M. hainanense: -0.80‰) and snails (-0.25‰) and were relatively consistent when preservation was ≤ 60 d. The influence of formalin-ethanol on C/N and δ 13C was smaller than that of formalin for all species and more consistent than ethanol preservation. δ 15N of all species was unaffected (within ±1‰) by chemical preservation. Effects on isotopic signals were more predictable among fishes than shrimps or snails. Corrections of +1.11‰ and +1.24‰ should be applied to δ13C of fishes preserved with formalin and formalin-ethanol (respectively) during trophic analysis. We recommend using formalin-ethanol for macroinvertebrates to limit isotopic shifts, especially those preserved for > 60 d.
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| 24. |
- Lucia Santoro, Ana, et al.
(author)
-
Simultaneous measurements of dark carbon fixation and bacterial production in lake sediment
- 2013
-
In: Limnology and Oceanography. - : Association for the Sciences of Limnology and Oceanography (ASLO). - 1541-5856. ; 11, s. 298-303
-
Journal article (peer-reviewed)abstract
- Carbon fixation by chemoautotrophic bacteria represents an autochthonous source of organic matter, and may be of particular importance close to redox boundaries. Despite the known sediment chemoautotrophic potential, the quantitative role and the importance of dark carbon fixation (DCF) in lake sediments are still unknown. We provide here a method to measure DCF and bacterial production simultaneously in stratified sediment cores, using C-14 labeled dissolved inorganic carbon ((DIC)-C-14) and H-3-leucine incorporation. Beyond the total activity, the method allows measurements of the processes over depth, as a profile into the sediment. DCF increased with depth in our profiles, indicating a predominance of anoxic processes. In addition, the method can yield information about the extent (DIC)-C-14 was allocated into the bacterial proteins (DCFp). Slurry and stratified core incubations were compared and yielded similar results for total DCF activity.
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| 25. |
- Mörth, Carl-Magnus, et al.
(author)
-
Practical steps for improved estimates of calcium carbonate concentrations in deep sea sediments using coulometry
- 2011
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 9, s. 565-570
-
Journal article (peer-reviewed)abstract
- Coulometric titration is a commonly used method for determination of carbonate carbon, and hence calcium carbonate concentrations, in geological materials. Analyzes of 460 samples of pure CaCO3 powder demonstrate that the coulometer output data need to be recalculated using a multi-point regression analysis. These analyses also demonstrate that to generate a precision of +/- 0.8%, at least 7 mg of 100% calcite is needed. A precision of +/- 0.5% requires 12 mg pure calcite. We recommend that 35 mg samples are used for most deep sea sediment samples, which gives a precision of +/- 0.8% down to 20% calcite contents in the sample. Calcite contents <10% in samples require multiple runs to improve precision.
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| 26. |
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| 27. |
- Nondal, Gisle, et al.
(author)
-
Optimal evaluation of the surface ocean CO2 system in the northern North Atlantic using data from voluntary observing ships
- 2009
-
In: Limnology and Oceanography : Methods. - 1541-5856. ; 7, s. 109-118
-
Journal article (peer-reviewed)abstract
- This work evaluates whether an accurate calculation of the entire CO2 system in the northern North Atlantic can be carried out using a combination of in situ fugacity of CO2 (fCO2) and ancillary data often measured on Voluntary Observing Ships (VOS), i.e., sea surface temperature (SST) and sea surface salinity (SSS), as well as nitrate (NO3 –). Two approaches are tested: (I) determination of At from SSS and then calculating Ct from measured fCO2 and estimated At; and (II) determination of Ct from SSS, SST, and NO3 – and then calculating At from measured fCO2 and estimated Ct. The optimal approach was found to be determination of At from SSS and then calculating Ct from measured fCO2 and estimated At. This allowed At to be determined with a mean bias of –1.8 μmol kg–1 and root mean square (rms) deviation 6.2 μmol kg–1 and then Ct to be calculated with a mean bias of –1.0 μmol kg–1 and standard error of calculation of 7.4 μmol kg–1, as validated using independent data sets.
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| 28. |
- O'Malley, Brian P., et al.
(author)
-
An underwater video system to assess abundance and behavior of epibenthic Mysis
- 2018
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 16:12, s. 868-880
-
Journal article (peer-reviewed)abstract
- The application of remote video technologies can provide alternative views of in situ behavior and distribution of aquatic organisms that might be missed with traditional net‐based techniques. We describe a remote benthic video camera system designed to quantify epibenthic density of the macroinvertebrate Mysis diluviana. We deployed the camera multiple times during the day and night at a 60‐m depth site in Lake Champlain and quantified Mysis density from the footage using basic methods and readily available software. Density estimates from the video were on average 43 times higher than concurrent estimates from benthic sled tows, suggesting sleds may be inefficient at sampling mysids. Deployment caused initial scattering of individuals, resulting in low densities immediately after deployment that slowly increased. On some occasions, Mysis densities on video fluctuated greatly over several hours, consistent with organisms that have a patchy distribution on the lake bottom. The camera system provided novel insights on behavior and distribution of Mysis on benthic habitats, demonstrating potential for use as a tool to study partial diel vertical migration and predator–prey interactions.
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| 29. |
- Pierson, D. C., et al.
(author)
-
An automated method to monitor lake ice phenology
- 2011
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 9, s. 74-83
-
Journal article (peer-reviewed)abstract
- A simple method to automatically measure the date of ice-on, the date of ice-off, and the duration of lake ice cover is described. The presence of ice cover is detected by recording water temperature just below the ice/water interface and just above the lake bottom using moored temperature sensors. The occurrence of ice-on rapidly leads to detectible levels of inverse stratification, defined as existing when the upper sensor records a temperature at least 0.1 degrees C below that of the bottom sensor, whereas the occurrence of ice-off leads to the return of isothermal mixing. Based on data from 10 lakes over a total of 43 winter seasons, we found that the timing and duration of inverse stratification monitored by recording temperature sensors compares well with ice cover statistics based on human observation. The root mean square difference between the observer-based and temperature-based estimates was 7.1 d for ice-on, 6.4 d for ice-off, and 10.0 d for the duration of ice cover. The coefficient of determination between the two types of estimates was 0.93, 0.86, and 0.91, respectively. The availability of inexpensive self-contained temperature loggers should allow expanded monitoring of ice cover in a large and diverse array of lakes. Such monitoring is needed to improve our ability to monitor the progression of global climate change, and to improve our understanding of the relationship between climate and ice cover over a wide range of temporal and spatial scales.
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| 30. |
- Ploug, Helle, et al.
(author)
-
A novel method to measure particle sinking velocity in vitro, and its comparison to three other in vitro methods
- 2010
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 8, s. 386-393
-
Journal article (peer-reviewed)abstract
- We introduce a novel, simple method to measure sinking velocity of particles and aggregates in roller tanks. Using this noninvasive method, it is possible to follow changes in sinking velocities on the same aggregates during time and to make paired measurements of aggregate sinking velocity and composition. Particles and aggregates are video recorded in roller tanks, and their sinking velocity is derived from the orbital trajectories. This new method is compared with three other methods (using roller tanks, a vertical flow system, and a sedimentation column), which have not previously been inter-calibrated. Agar spheres and diatom aggregates were used as model particles in all experimental systems. No method showed significantly different sinking velocities of agar spheres compared with those calculated by theory. Paired measurements showed that sinking velocities from 70 to 700 m d(-1) were linearly correlated between different methods. Highest sinking velocities were measured in a sedimentation column followed by those measured in roller tanks and in the vertical flow system, respectively. The average difference of sinking velocity measured with the different methods ranged from 8% to 11% for agar spheres, and up to 20% for diatom aggregates.
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| 31. |
- Ray, Nicholas E., et al.
(author)
-
A review of how we assess denitrification in oyster habitats and proposed guidelines for future studies
- 2021
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 19:10, s. 714-731
-
Research review (peer-reviewed)abstract
- Excess nitrogen (N) loading and resulting eutrophication plague coastal ecosystems globally. Much work is being done to remove N before it enters coastal receiving waters, yet these efforts are not enough. Novel techniques to remove N from within the coastal ecosystem are now being explored. One of these techniques involves using oysters and their habitats to remove N via denitrification. There is substantial interest in incorporating oyster-mediated enhancement of benthic denitrification into N management plans and trading schemes. Measuring denitrification, however, is expensive and time consuming. For large-scale adoption of oyster-mediated denitrification into nutrient management plans, we need an accurate model that can be applied across ecosystems. Despite significant effort to measure and report rates of denitrification in oyster habitats, we are unable to create such a model, due to methodological differences between studies, incomplete data reporting, and inconsistent measurements of environmental variables that may be used to predict denitrification. To make a model that can predict denitrification in oyster habitats a reality, a common sampling and reporting scheme is needed across studies. Here, we provide relevant background on how oysters may stimulate denitrification, and the importance of oyster-mediated denitrification in remediating excess N loading to coastal systems. We then summarize methods commonly used to measure denitrification in oyster habitats, discuss the importance of various environmental variables that may be useful for predicting denitrification, and present a set of guidelines for measuring denitrification in oyster habitats, allowing development of models to support incorporation of oyster-mediated denitrification into future policy decisions.
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| 32. |
- Robertson, Elizabeth, 1987, et al.
(author)
-
Application of the isotope pairing technique in sediments: use, challenges and new directions.
- 2019
-
In: Limnology and Oceanography : Methods. - : Wiley. - 1541-5856. ; 17:2, s. 112-136
-
Journal article (peer-reviewed)abstract
- Determining accurate rates of benthic nitrogen (N) removal and retention pathways from diverse environments is critical to our understanding of process distribution and constructing reliable N budgets and models. The whole‐core 15N isotope pairing technique (IPT) is one of the most widely used methods to determine rates of benthic nitrate‐reducing processes and has provided valuable information on processes and factors controlling N removal and retention in aquatic systems. While the whole core IPT has been employed in a range of environments, a number of methodological and environmental factors may lead to the generation of inaccurate data and are important to acknowledge for those applying the method. In this review, we summarize the current state of the whole core IPT and highlight some of the important steps and considerations when employing the technique. We discuss environmental parameters which can pose issues to the application of the IPT and may lead to experimental artifacts, several of which are of particular importance in environments heavily impacted by eutrophication. Finally, we highlight the advances in the use of the whole‐core IPT in combination with other methods, discuss new potential areas of consideration and encourage careful and considered use of the whole‐core IPT. With the recognition of potential issues and proper use, the whole‐core IPT will undoubtedly continue to develop, improve our understanding of benthic N cycling and allow more reliable budgets and predictions to be made.
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| 33. |
- Ryder, Elizabeth, et al.
(author)
-
Reply to a comment by Watras et al. (2014) on temperature compensation method for field measurements of CDOM fluorescence
- 2015
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 13:10, s. 527-528
-
Journal article (peer-reviewed)abstract
- The recent comment by Watras et al. (2014) clarifies the calculation of the temperature correction coefficient (rho) in Watras et al. (2011). Based on this clarification, we accept that the equation to compensate for temperature quenching of chromophoric dissolved organic matter (CDOM) fluorescence presented in Ryder et al. (2012) and the equation proposed in Watras et al. (2011) are mathematically equivalent.
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| 34. |
- Ryder, Elizabeth, et al.
(author)
-
Temperature quenching of CDOM fluorescence sensors : temporal and spatial variability in the temperature response and a recommended temperature correction equation
- 2012
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 10, s. 1004-1010
-
Journal article (peer-reviewed)abstract
- Field-based instruments measuring chromophoric dissolved organic matter (CDOM) fluorescence are often used as a proxy for dissolved organic carbon concentrations in lakes and streams. CDOM fluorescence yield is, however, affected by water temperature at the time of measurement, a factor which varies on both diel and seasonal timescales. A temperature correction must therefore be applied to these data. We present data on temporal and site-specific variability in temperature quenching of CDOM fluorescence for water from a humic lake and one of its main inflows in the west of Ireland. In addition, we present a temperature compensation equation and show that this equation is an improvement on methods previously proposed.
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| 35. |
- Scharnweber, Kristin, 1983-, et al.
(author)
-
Comprehensive analysis of chemical and biological problems associated with browning agents used in aquatic studies
- 2021
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 19:12, s. 818-835
-
Journal article (peer-reviewed)abstract
- Inland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. However, manipulative studies, especially at ecosystem scale, require large amounts of dissolved organic matter with optical and chemical properties resembling indigenous organic matter. Here, we compared the impacts of two leonardite products (HuminFeed and SuperHume) and a freshly derived reverse osmosis concentrate of organic matter in a set of comprehensive mesocosm- and laboratory-scale experiments and analyses. The chemical properties of the reverse osmosis concentrate and the leonardite products were very different, with leonardite products being low and the reverse osmosis concentrate being high in carboxylic functional groups. Light had a strong impact on the properties of leonardite products, including loss of color and increased particle formation. HuminFeed presented a substantial impact on microbial communities under light conditions, where bacterial production was stimulated and community composition modified, while in dark potential inhibition of bacterial processes was detected. While none of the browning agents inhibited the growth of the tested phytoplankton Gonyostomum semen, HuminFeed had detrimental effects on zooplankton abundance and Daphnia reproduction. We conclude that the effects of browning agents extracted from leonardite, particularly HuminFeed, are in sharp contrast to those originating from terrestrially derived dissolved organic matter. Hence, they should be used with great caution in experimental studies on the consequences of terrestrial carbon for aquatic systems.
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| 36. |
- Tengberg, A., et al.
(author)
-
Evaluation of a lifetime-based optode to measure oxygen in aquatic systems
- 2006
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 4:FEB, s. 7-17
-
Journal article (peer-reviewed)abstract
- In this article, we evaluate the performance of a commercially available lifetime-based optode and compare it with data obtained by other methods. We performed a set of 10 different tests, including targeted laboratory evaluations and field studies, covering a wide range of situations from shallow coastal waters and wastewater treatment plants to abyssal depths. Our principal conclusion is that, owing to high accuracy (+/- 2 mu M), long-term stability (more than 20 months), lack of pressure hysteresis, and limited cross-sensitivity, this method is overall more suitable for oxygen monitoring than other methods.
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| 37. |
- Urrutia-Cordero, P., et al.
(author)
-
SITES AquaNet: An open infrastructure for mesocosm experiments with high frequency sensor monitoring across lakes
- 2021
-
In: Limnology and Oceanography-Methods. - : Wiley. - 1541-5856. ; 19:6, s. 385-400
-
Journal article (peer-reviewed)abstract
- For aquatic scientists mesocosm experiments are important tools for hypothesis testing as they offer a compromise between experimental control and realism. Here we present a new mesocosm infrastructure-SITES AquaNET-located in five lakes connected to field stations in Sweden that cover a similar to 760 km latitudinal gradient. SITES AquaNet overcomes major hindrances in aquatic experimental research through: (i) openness to the scientific community, (ii) the potential to implement coordinated experiments across sites and time, and (iii) high-frequency measurements (temperature, photosynthetic photon flux density, turbidity and dissolved oxygen, chlorophyll a and phycocyanin concentrations) with an autonomous sensor system. Moreover, the infrastructure provides operational guidance and sensor expertise from technical staff, and connections to a multi-layered monitoring programme ("SITES Water") for each lake. This enables ecological observations from whole lake ecosystems to be compared with experimental studies aiming at disentangling major drivers and mechanisms underlying observed changes. Here we describe the technical properties of the infrastructure along with possibilities for experimental manipulations to tackle pressing issues in aquatic ecology and global change science. As a proof of concept, we also present a first mesocosm experiment across all five field sites with a cross-factorial design to evaluate responses of the sensor measurements to press/bottom-up (constant light reduction) and pulse/top-down (temporary fish predation) disturbances. This demonstrates the suitability of the infrastructure and autonomous sensor system to host modularized experiments and exemplifies the power and advantages of the approach to integrate a network of mecsocosm facilities with manageable costs across large geographic areas.
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| 38. |
- Verpoorter, Charles, et al.
(author)
-
Automated mapping of water bodies using Landsat multispectral data
- 2012
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 10, s. 1037-1050
-
Journal article (peer-reviewed)abstract
- The assessment of the role of lakes and impoundments at regional and global scales, e.g., in biogeochemical cycles, requires good estimates of the areal extent and shape of water bodies. Upscaling to large regions, except in limited areas where precise maps are available, so far depends on statistical estimates of the number and size of lakes, which explains why estimates are poor. We present an automated procedure that allows mapping of the actual number, size, and distribution of lakes at large scale. Landsat 7 Enhanced Thematic Mapper Plus (ETM +) mosaics from the GeoCover Circa 2000 dataset covering the Earth land surfaces with 14.25 m spatial resolution were used as input data. We developed an approach called GWEM (GeoCoverTM Water bodies Extraction Method) that combines remote sensing and GIS to extract water bodies and study their abundance and morphometry. All water bodies greater than 0.0002 km2 were taken into account as lakes. The accuracy of the method was tested on Sweden, where detailed maps of lakes, based on in situ data and orthophotos, exist for the whole country. The proposed method produced accurate results. The largest sources of errors are shadows of mountains and clouds, since the GeoCover mosaics are not absolutely cloud free.
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| 39. |
- Vikström, Kevin, et al.
(author)
-
Improved accuracy of optode-based oxygen consumption measurements by removal of system drift and nonlinear derivation
- 2019
-
In: Limnology and Oceanography-Methods. - : Wiley. - 1541-5856. ; 17:3, s. 179-189
-
Journal article (peer-reviewed)abstract
- This method evaluation aimed to improve the accuracy and precision of the previously published method to measure oxygen consumption using optodes with integrated temperature and salinity correction in dark incubations. Significant short-term system drift currently requires a correction to remove the drift, thus reducing the precision of the oxygen consumption rates. Frequent nonlinear declines in oxygen concentration with time also call for improved data analysis and identification of its origin. Optodes in titanium casings (Aanderaa (TM) model 4330) with low oxygen binding properties showed no significant system drift in autoclaved seawater. Nonlinear oxygen dynamics fitting a quadratic polynomial occurred in 28% of 230 field samples, independent of season and water depth. Polynomial curve fit resulted in 64% higher respiration rates when derived within 1 h of the quality assured incubation, than obtained when using linear fit. Carbon substrate limitation explained the nonlinearity of oxygen decline during dark incubations. Pretreatment of the optode attached to stoppers with 0.3 mol dm(-3) hydrochloric acid resulted in the most stable performance of the sensor and simultaneously provided proper cleaning of the equipment. A conservative detection limit of 0.97 mu mol O-2 dm(-3) d(-1) was calculated for the titanium optodes, matching other methods for oxygen consumption reported in the literature. Thus, we recommend the use of model 4330 optode pretreated with HCl and the derivation of initial respiration rates by a quadratic polynomial function for best accuracy and precision of oxygen consumption in oxygenated surface waters.
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| 40. |
- Vogel, Hendrik, et al.
(author)
-
Quantification of biogenic silica by means of Fourier transform infrared spectroscopy (FTIRS) in marine sediments
- 2016
-
In: Limnology and Oceanography. - : Wiley-Blackwell. - 1541-5856. ; 14:12, s. 828-838
-
Journal article (peer-reviewed)abstract
- Due to the major role played by diatoms in the marine biological pump, opal/biogenic silica (bSi) has a strong potential as a proxy for paleoproduction reconstructions. Here, we present a detailed evaluation of the independent Fourier transform infrared spectroscopy (FTIRS) calibration introduced by Meyer-Jacob et al. (2014a), which is based on synthetic sediment mixtures with known concentrations of bSi and the application of partial least squares (PLS) regression, for the determination of bSi in marine sediments. To test the robustness of the FTIRS calibration for marine samples we selected 199 globally distributed samples, with available wet chemically inferred bSi concentrations and compared the results of both methods. We observe that the spectral characteristics in marine samples are comparable to those reported for a synthetic FTIR spectrum composed solely of spectral features in quartz, biogenic silica, and calcite. FTIRS-inferred and wet-chemically measured bSi concentrations for the set of 199 marine sediment samples are strongly correlated (R-2 = 0.87; RMSE = 5.27%). Together with the high reproducibility of bSi values by the independent calibration our results corroborate the applicability of the independent FTIRS bSi calibration for quantification in marine samples. This together with the succinct sample preparation procedure, rapid analysis, reduced consumable and machine maintenance costs makes FTIRS a powerful and robust alternative for the quantitative analysis of bSi in marine sediments.
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| 41. |
- West, Johannes, 1991-, et al.
(author)
-
Dimethylmercury in natural waters—analytical and experimental considerations
- 2023
-
In: Limnology and Oceanography. - 1541-5856. ; 21:12, s. 837-846
-
Journal article (peer-reviewed)abstract
- Mono- and dimethylmercury (MMHg and DMHg, respectively) are the two primary organic forms of mercury (Hg) found in natural waters. While experimental approaches to characterize the environmental behavior of MMHg and inorganic forms of Hg are widely used today, few laboratories conduct experimental studies entailing the use of DMHg. In this paper, we have evaluated and developed different analytical and experimental approaches to quantify and use DMHg in laboratory studies. We demonstrate that DMHg can be analyzed from samples where MMHg is derivatized using sodium tetraethyl borate and where the matrix effects of dissolved sulfide are masked using copper sulfate. Tests, where the calibration curves of MMHg and DMHg were used, showed that MMHg may be used to calibrate for DMHg. For the pre-concentration of DMHg, both traps filled with Tenax® TA and Bond Elut ENV were found suitable. We observed good recoveries of DMHg added to different types of natural waters or purified water containing aquarium salt, sodium chloride and dissolved sulfide, iron sulfide, and cadmium sulfide at DMHg : sulfide molar ratios > 10−6. In addition to evaluating these analytical aspects, we present suitable subsampling techniques for DMHg-containing solutions, the recovery of DMHg when filtering DMHg through different types of filters, and experimental data on the long-term stability of DMHg added to different types of waters and stored at different temperatures. Finally, we present and discuss a new synthetization protocol for preparing aqueous solutions containing DMHg free of organic solvents and where handling DMHg in a pure form is prevented.
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| 42. |
- Wikner, Johan, 1961-, et al.
(author)
-
Precise continuous measurements of pelagic respiration in coastal waters with Oxygen Optodes
- 2013
-
In: Limnology and Oceanography. - : Association for the Sciences of Limnology and Oceanography. - 1541-5856. ; 11, s. 1-15
-
Journal article (peer-reviewed)abstract
- An analytical setup for respiration rate measurements was developed and evaluated in pelagic water samples using a commercially available optical oxygen sensor (Optode (TM)). This setup required the development of a gas tight stopper to connect the sensors to a 1 dm(3) glass sample bottle, precise temperature control (+/- 0.05 degrees C), and proper stirring of samples. The detection limit and precision of the method was 0.3 mmol O-2 m(-3) d(-1). This was similar to the detection limit for the high-precision Winkler titration method reported in field studies. When compared with the Winkler method, the Optode sensor enabled operator-independent, high temporal resolution measurement of respiration, better coverage of plankton groups and detection of non-linear oxygen decline, without the need for wet chemistry. Respiration rates measured by the Optodes showed good accuracy when compared with measurements made with the Winkler titration method (3% deviation), followed the expected temperature response (Q(10) = 3.0), were correlated with chlorophyll a and were congruent with earlier reported values in the literature. The main source of uncertainty was a necessary correction for system drift during the incubation period, due to oxygen release from the plastic components. Additionally, less stringent temperature control on board research vessels during rough seas reduced the precision. We conclude that the developed Optode system can be used to measure respiration in productive coastal waters. Samples from cold or deep waters were, however, often below the detection limit.
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