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- Casas-Ruiz, Joan P., et al.
(författare)
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A tale of pipes and reactors : Controls on the in-stream dynamics of dissolved organic matter in rivers
- 2017
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 62, s. S85-S94
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Tidskriftsartikel (refereegranskat)abstract
- The potential for rivers to alter the flux of dissolved organic matter (DOM) from land to ocean is widely accepted. Yet anticipating when and where rivers behave as active reactors vs. passive pipes of DOM stands as a major knowledge gap in river biogeochemistry, resulting in uncertainties for global carbon models. Here, we investigate the controls on in-stream DOM dynamics by evaluating changes in DOM concentration and composition along several reaches of a medium-sized river network over one full hydrological year. Roughly half of the observations over time and space showed active reactor conditions and, among these, similar pro-portion of gains and losses was measured. High water residence times promoted the active over passive behavior of the reaches, while DOM properties and nitrate availability determined whether they supplied or removed DOM from the river. Among different DOM fractions, protein-like DOM both of terrestrial and aquatic origin seemed to drive bulk DOM patterns. Our study emphasizes the role of water residence time as a physical constraint for in-stream processes, and provides new insights into the key factors governing the net balance between in-stream gains and losses of DOM in rivers.
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| 2. |
- Casas-Ruiz, Joan P., et al.
(författare)
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Drought-induced discontinuities in the source and degradation of dissolved organic matter in a Mediterranean river
- 2016
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 127:1, s. 125-139
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Tidskriftsartikel (refereegranskat)abstract
- The composition of dissolved organic matter (DOM) in rivers results from the different sources and in-stream transformations along the land to ocean aquatic continuum. Riverine DOM sources are highly dependent on the hydrological connection between the river channel and the surrounding terrestrial ecosystems, but how the lack of this connectivity (e.g., during drought episodes) affects the sources and biodegradation of DOM in rivers remains unclear. Here we identified the DOM sources as well as the different DOM pools that are respired along a Mediterranean river during drought by combining absorbance-fluorescence spectroscopy, size-exclusion chromatography, biodegradation assays, and stable and radiocarbon isotopes. DOM composition was highly heterogeneous along the river in response to different sources and in-stream processes in each distinct aquatic environment (i.e., isolated water pools, running waters, and impounded waters in weirs). The reduced hydrological connectivity with terrestrial ecosystems promoted the influence of autochthonous DOM sources. Still, tree leaves from overhanging canopies stood out as an important terrestrial DOM source, especially in sites where water residence time was high such as isolated pools and weirs. Degradation of leaf leachates was a relevant process in these sites, whereas autochthonous DOM and groundwater millennial DOM (> 1300 year B.P.) seemed to be degraded in running waters. Overall, our results highlight that the drought-induced hydrological disconnection entails a great spatial heterogeneity in the sources of DOM, which at the same time determines the different DOM pools that are respired in each environment along the river.
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| 3. |
- Catalan, Nuria, et al.
(författare)
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Carbon dioxide efflux during the flooding phase of temporary ponds
- 2014
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Ingår i: LIMNETICA. - 0213-8409. ; 33:2, s. 349-359
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Tidskriftsartikel (refereegranskat)abstract
- Small water bodies, such as temporary ponds, have a high carbon processing potential. Nevertheless, despite the global occurrence of these systems, the carbon effluxes from such water bodies have been largely overlooked. In this study, we examined the intra- and intersystem variability of carbon dioxide (CO2) effluxes from a set of Mediterranean temporary ponds during the flooding phase, a hot-spot for biogeochemical cycling in temporary systems. The CO2 effluxes showed higher variability among the various sections of each pond (i.e., inundated, emerged-unvegetated and emerged-vegetated) than among the ponds. The emerged-vegetated sections showed the highest CO2 effluxes per unit area and tended to drive the total effluxes at the whole-ecosystem scale. The mean CO2 efflux (121.3 +/- 138.1 mmol m(-2) d(-1)) was in the upper range for freshwater ecosystems. The CO2 effluxes were not related to catchment properties but rather to the organic content of the sediments, especially in the emerged sections of the ponds. Our results indicate that temporary ponds, especially their emerged sections, are important sources of CO2 to the atmosphere, highlighting the need to include the dry phases of these and other temporary aquatic systems in regional carbon budgets.
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| 7. |
- Donis, Daphne, et al.
(författare)
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Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer
- 2021
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:12, s. 4314-4333
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Tidskriftsartikel (refereegranskat)abstract
- To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L-1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4 degrees C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature.
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| 8. |
- Gómez-Gener, Lluís, et al.
(författare)
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Effect of small water retention structures on diffusive CO2 and CH4 emissions along a highly impounded river
- 2018
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Ingår i: Inland Waters. - : Taylor & Francis. - 2044-2041 .- 2044-205X. ; 8:4, s. 449-460
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Tidskriftsartikel (refereegranskat)abstract
- The impoundment of running waters through the construction of large dams is recognised as one of the most important factors determining the transport, transformation, and outgassing of carbon (C) in fluvial networks. However, the effects of small and very small water retention structures (SWRS) on the magnitude and spatiotemporal patterns of C emissions are still unknown, even though SWRS are the most common type of water retention structure causing river fragmentation worldwide. Here we evaluated and compared diffusive carbon dioxide (CO2) and methane (CH4) emissions from river sections impounded by SWRS and from their adjacent free-flowing sections along a highly impounded river. Emissions from impounded river sections (mean [SE] = 17.7 [2.8] and 0.67 [0.14] mmol m(-2)d(-1), for CO2 and CH4, respectively) never exceeded those from their adjacent free-flowing river sections (230.6 [49.7] and 2.14 [0.54] mmol m(-2)d(-1)). We attribute this finding to the reduced turbulence in impounded river sections induced by SWRS compared to free-flowing river sections (i.e., physical driver). Likewise, the presence of SWRS favoured an increase of the concentration of CH4 in impounded waters, but this increase was not sufficient to cause a significant influence in the CH4 efflux from the downstream free-flowing river sections. By contrast, this influenced the larger-scale longitudinal patterns of dissolved CH4, which exhibited a dear shifting pattern along the study stretch, modulated by variables associated with the presence of SWRS, such as higher water residence times, higher sedimentation rates, and higher temperatures. Overall, our results show that the presence of SWRS can modify the concentrations of C gases in highly impounded rivers but exerts a minor influence on diffusive C emissions.
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| 9. |
- Gómez-Gener, Lluís, et al.
(författare)
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Hot spots for carbon emissions from Mediterranean fluvial networks during summer drought
- 2015
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 125:3, s. 409-426
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Tidskriftsartikel (refereegranskat)abstract
- During summer drought, Mediterranean fluvial networks are transformed into highly heterogeneous landscapes characterized by different environments (i.e., running and impounded waters, isolated river pools and dry beds). This hydrological setting defines novel biogeochemically active areas that could potentially increase the rates of carbon emissions from the fluvial network to the atmosphere. Using chamber methods, we aimed to identify hot spots for carbon dioxide (CO2) and methane (CH4) emissions from two typical Mediterranean fluvial networks during summer drought. The CO2 efflux from dry beds (mean ± SE = 209 ± 10 mmol CO2 m−2 d−1) was comparable to that from running waters (120 ± 33 mmol m−2 d−1) and significantly higher than from impounded waters (36.6 ± 8.5 mmol m−2 d−1) and isolated pools (17.2 ± 0.9 mmol m−2 d−1). In contrast, the CH4 efflux did not significantly differ among environments, although the CH4 efflux was notable in some impounded waters (13.9 ± 10.1 mmol CH4 m−2 d−1) and almost negligible in the remaining environments (mean <0.3 mmol m−2 d−1). Diffusion was the only mechanism driving CO2 efflux in all environments and was most likely responsible for CH4 efflux in running waters, isolated pools and dry beds. In contrast, the CH4 efflux in impounded waters was primarily ebullition-based. Using a simple heuristic approach to simulate potential changes in carbon emissions from Mediterranean fluvial networks under future hydrological scenarios, we show that an extreme drying out (i.e., a four-fold increase of the surface area of dry beds) would double the CO2 efflux from the fluvial network. Correspondingly, an extreme transformation of running waters into impounded waters (i.e., a twofold increase of the surface area of impounded waters) would triple the CH4 efflux. Thus, carbon emissions from dry beds and impounded waters should be explicitly considered in carbon assessments of fluvial networks, particularly under predicted global change scenarios, which are expected to increase the spatial and temporal extent of these environments.
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| 10. |
- Gomez-Gener, Lluis, et al.
(författare)
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When Water Vanishes : Magnitude and Regulation of Carbon Dioxide Emissions from Dry Temporary Streams
- 2016
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 19:4, s. 710-723
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Tidskriftsartikel (refereegranskat)abstract
- Most fluvial networks worldwide include watercourses that recurrently cease to flow and run dry. The spatial and temporal extent of the dry phase of these temporary watercourses is increasing as a result of global change. Yet, current estimates of carbon emissions from fluvial networks do not consider temporary watercourses when they are dry. We characterized the magnitude and variability of carbon emissions from dry watercourses by measuring the carbon dioxide (CO2) flux from 10 dry streambeds of a fluvial network during the dry period and comparing it to the CO2 flux from the same streambeds during the flowing period and to the CO2 flux from their adjacent upland soils. We also looked for potential drivers regulating the CO2 emissions by examining the main physical and chemical properties of dry streambed sediments and adjacent upland soils. The CO2 efflux from dry streambeds (mean +/- A SD = 781.4 +/- A 390.2 mmol m(-2) day(-1)) doubled the CO2 efflux from flowing streambeds (305.6 +/- A 206.1 mmol m(-2) day(-1)) and was comparable to the CO2 efflux from upland soils (896.1 +/- A 263.2 mmol m(-2) day(-1)). However, dry streambed sediments and upland soils were physicochemically distinct and differed in the variables regulating their CO2 efflux. Overall, our results indicate that dry streambeds constitute a unique and biogeochemically active habitat that can emit significant amounts of CO2 to the atmosphere. Thus, omitting CO2 emissions from temporary streams when they are dry may overlook the role of a key component of the carbon balance of fluvial networks.
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