| 1. |
- Burrows, Ryan, et al.
(författare)
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Nitrogen limitation of heterotrophic biofilms in boreal streams
- 2015
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 60:7, s. 1237-1251
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient limitation of the biofilm is fundamental to stream ecosystem processes, as microbial activity shapes the biological availability and biogeochemical cycling of carbon and nutrients. We used nutrient-diffusing substrata (NDS) to investigate heterotrophic nutrient limitation of microbial respiration (MR) across 20 streams draining boreal landscapes in northern Sweden. We also explored variation in microbial biomass and community structure of biofilms that developed on NDS using phospholipid fatty acid (PLFA) biomarkers. Limitation was determined as a significant response of MR and biomass production on cellulose surfaces to enrichment with nitrogen (N), phosphorus (P) or N+P, relative to controls. Microbial respiration was N-limited, with an average 3.3-fold increase on N-amended NDS. Nitrogen limitation decreased, and control rates of MR increased, with greater background concentrations of inorganic N across the sites. In contrast to MR, microbial biomass was primarily N-limited but was greatest for the N+P NDS. Accordingly, differences in respiratory versus biomass responses to nutrient addition resulted in significantly greater biomass-specific MR on N-amended NDS compared to all other treatments. In addition, PLFA biomarkers indicated distinct microbial communities on N and N+P NDS compared to controls and/or P NDS. Greater MR and biomass, and the development of distinct microbial communities, when supplied with inorganic N suggest that factors which alter aquatic N loading during autumn may have important implications for ecosystem processes and the biogeochemistry of boreal streams and rivers. Our findings add to a growing body of evidence that the productivity of Fennoscandian boreal landscapes is constrained by N availability.
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| 2. |
- Creed, Irena F., et al.
(författare)
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Global change-driven effects on dissolved organic matter composition : Implications for food webs of northern lakes
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:8, s. 3692-3714
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Forskningsöversikt (refereegranskat)abstract
- Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.
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| 3. |
- Gómez-Gener, Lluís, et al.
(författare)
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Integrating Discharge-Concentration Dynamics Across Carbon Forms in a Boreal Landscape
- 2021
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Ingår i: Water resources research. - : John Wiley & Sons. - 0043-1397 .- 1944-7973. ; 57:8
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Tidskriftsartikel (refereegranskat)abstract
- The flux of terrestrial carbon across land-water boundaries influences the overall carbon balance of landscapes and the ecology and biogeochemistry of aquatic ecosystems. The local consequences and broader fate of carbon delivered to streams is determined by the overall composition of carbon inputs, including the balance of organic and inorganic forms. Yet, our understanding of how hydrologic fluxes across different land-water interfaces regulate carbon supply remains poor. We used 7 years of data from three boreal catchments to test how different land-water interfaces (i.e., forest, wetland, and lake) modulate concentration-discharge (C-Q) relationships for dissolved organic carbon (DOC), carbon dioxide (CO2), and methane, as well as the balance among forms (e.g., DOC:CO2). Seasonal patterns in concentrations and C-Q relationships for individual carbon forms differed across catchments. DOC varied between chemostasis and transport limitation in the forest catchment, between supply limitation and chemostasis in the wetland catchment, and was persistently chemostatic in the lake outlet stream. Carbon gases were supply limited overall, but exhibited chemostasis or transport limitation in the forest and wetland catchments linked to elevated flow in summer and autumn. Unique C-Q relationships for individual forms reflected the properties of different interfaces and underpinned changes in the composition of lateral carbon supply. Accordingly, DOC dominated the carbon flux during snowmelt, whereas gas evasion increased in relative importance during other times of the year. Integrating the C-Q dynamics of individual carbon forms provides insight into the shifting composition of lateral export, and thus helps to predict how hydrologic changes may alter the fate of carbon supplied to streams.
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| 4. |
- Hamdan, Mohammed, et al.
(författare)
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An experimental test of climate change effects in northern lakes : Increasing allochthonous organic matter and warming alters autumn primary production
- 2021
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Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 66:5, s. 815-825
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Tidskriftsartikel (refereegranskat)abstract
- Climate changes are predicted to influence gross primary production (GPP) of lakes directly through warming and indirectly through increased loads of allochthonous coloured dissolved organic matter (cDOM) from surrounding landscapes. However, few studies have investigated this combined effect.Here we tested the effects of warming (elevated 3celcius) and cDOM input (three levels of humic river water addition) on GPP in autumn (2 months including open water and ice-covered periods) in experimental pond ecosystems.The cDOM input decreased whole-ecosystem GPP at natural temperature conditions mainly as a result of lower benthic GPP not fully counteracted by an increase in pelagic GPP, while warming increased whole-ecosystem GPP due to a positive response of mainly pelagic GPP at all levels of cDOM input.Warming delayed autumn ice cover formation by 2 weeks but did not affect light availability in the water column compared to ambient ice-covered treatments. Gross primary production during this period was still affected by warming and cDOM.The results stress the importance of accounting for multiple climate drivers and habitats when predicting lake GPP responses to climate change. We conclude that climate change may shift whole-ecosystem GPP through different responses of habitat-specific GPP to increasing cDOM inputs and warming.
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| 5. |
- Hamdan, Mohammed, et al.
(författare)
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Carbon dioxide stimulates lake primary production
- 2018
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Gross primary production (GPP) is a fundamental ecosystem process that sequesters carbon dioxide (CO2) and forms the resource base for higher trophic levels. Still, the relative contribution of different controls on GPP at the whole-ecosystem scale is far from resolved. Here we show, by manipulating CO2 concentrations in large-scale experimental pond ecosystems, that CO2 availability is a key driver of whole-ecosystem GPP. This result suggests we need to reformulate past conceptual models describing controls of lake ecosystem productivity and include our findings when developing models used to predict future lake ecosystem responses to environmental change.
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| 6. |
- Hamdan, Mohammed, 1978-
(författare)
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Effects of temperature and terrestrial carbon on primary production in lake ecosystems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate warming is predicted to affect northern lake food webs in two ways: (1)directly via changes in water temperature and ice conditions, and (2) indirectlyvia changes in catchment characteristics and processes that influence input ofallochthonous coloured dissolved organic matter (cDOM) and nutrients. Input ofcDOM increases carbon dioxide (CO2) availability, causes brownification andreduced light conditions, and may increase nutrient availability especially forpelagic primary producers. Increased water temperature and light penetrationand longer ice-free periods affect metabolic rates. These changes are expected toinfluence gross primary production (GPP) and growth of higher trophic levels.However, majority of studies focus on pelagic processes and net effects at wholelake scale is not well understood. Consequently, the lack of knowledge of whatfactors control benthic GPP makes predictions of net effects of climate change onwhole-ecosystem GPP spurious. The aim of this thesis was to experimentally testeffects of warming and increased input of allochthonous cDOM on habitatspecific and whole-ecosystem GPP in lakes. First, by manipulating the CO2concentrations in large scale pond ecosystems, we showed that increased CO2stimulated whole-ecosystem GPP. In a separate incubation study with naturallake sediments in a boreal lake, we tested the role of CO2 as a limiting factor forbenthic GPP under different light levels. The results showed that CO2 supplystimulated benthic GPP at high but not at low light availability, suggesting thatbenthic GPP can be CO2-limited. In the same experimental pond ecosystems, thecombined effect of increased allochthonous cDOM and warming (+3.5°C) on GPPwas studied. The results showed that cDOM input decreases whole-ecosystemGPP, mainly as a result of decreased benthic GPP due to light limitation not fullycounteracted by an increase in pelagic GPP under ambient conditions. Warmingon the other caused a hump shaped increase in whole-ecosystem GPP withincreasing cDOM input mainly due to a positive response in pelagic GPP due torelaxed nutrient limitation. Finally, by manipulating the fish consumer biomassin the same experimental pond ecosystems we showed that whole-ecosystem GPPcan be controlled by top-down effects under warm (+ 3.0°C) but not ambienttemperature conditions. The decline in whole-ecosystem GPP was mainlyattributed to a warming-stimulated consumer-driven trophic cascade in thepelagic habitat and top-down control by zooplankton on phytoplankton growth,while no corresponding cascade was evident in the benthic habitat.Taken together, the results suggest that climate change impacts, as increasinginputs of cDOM, warming and changes in food webs, have different effects onhabitat specific GPP and alone or in combination have impacts on whole-lakeGPP. This thesis offers important insights to better understand the factors thatcontrol lake GPP and to predict future lake ecosystem responses to environmentalchange.
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| 7. |
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| 8. |
- Hotchkiss, Erin, et al.
(författare)
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Modeling priming effects on microbial consumption of dissolved organic carbon in rivers
- 2014
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 119:5, s. 982-995
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Tidskriftsartikel (refereegranskat)abstract
- Rivers receive and process large quantities of terrestrial dissolved organic carbon (DOC). Biologically available (unstable) DOC leached from primary producers may stimulate (i.e., prime) the consumption of more stable terrestrially derived DOC by heterotrophic microbes. We measured microbial DOC consumption (i.e., decay rates) from contrasting C sources in 10 rivers in the western and Midwestern United States using short-term bioassays of river water, soil and algal leachates, glucose, and commercial humate. We added inorganic nutrients (ammonium and phosphorus) to a subset of bioassays. We also amended a subset of river, soil, and commercial humate bioassays with glucose or algal leachates to test the hypothesis that unstable DOC primes consumption of more stable DOC. We used prior measurements of source-specific DOC bioavailability, linked with a Bayesian process model, to estimate means and posterior probability distributions for source-specific DOC decay rates in multisource bioassays. Modeled priming effects ranged from a -130 to +370% change in more stable DOC decay when incubated with unstable DOC. Glucose increased modeled river DOC decay by an average of 87% among all rivers. Glucose and algal leachates increased soil leachate and commercial humate decay by an average of 25% above background rates. Inorganic nutrient additions did not have consistent effects on DOC decay, likely because most of the study rivers had high ambient background nutrients. Our results demonstrate that the priming effect can augment DOC decay in rivers. In addition, Bayesian models can be used to estimate mechanisms driving aquatic ecosystem processes that are difficult to measure directly.
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| 9. |
- Hotchkiss, Erin R, et al.
(författare)
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Linking calcification by exotic snails to stream inorganic carbon cycling.
- 2010
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 163:1, s. 235-44
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Tidskriftsartikel (refereegranskat)abstract
- Biotic calcification is rarely considered in freshwater C budgets, despite calculations suggesting that calcifying animals can alter inorganic C cycling. Most studies that have quantified biocalcification in aquatic ecosystems have not directly linked CO(2) fluxes from biocalcification with whole-ecosystem rates of inorganic C cycling. The freshwater snail, Melanoides tuberculata, has achieved a high abundance and 37.4 g biomass m(-2) after invading Kelly Warm Springs in Grand Teton National Park. This high biomass suggests that introduced populations of Melanoides may alter ecosystem processes. We measured Melanoides growth rates and biomass to calculate the production of biomass, shell mass, and CO(2). We compared Melanoides biomass and inorganic C production with ecosystem C pools and fluxes, as well as with published rates of CO(2) production by other calcifying organisms. Melanoides calcification in Kelly Warm Springs produced 12.1 mmol CO(2) m(-2) day(-1) during summer months. We measured high rates of gross primary productivity and respiration in Kelly Warm Springs (-378 and 533 mmol CO(2) m(-2) day(-1), respectively); CO(2) produced from biocalcification increased net CO(2) production in Kelly Warm Springs from 155 to 167 mmol CO(2) m(-2) day(-1). This rate of CO(2) production via biocalcification is within the published range of calcification by animals. But these CO(2) fluxes are small when compared to ecosystem C fluxes from stream metabolism. The influence of animals is relative to ecosystem processes, and should always be compared with ecosystem fluxes to quantify the importance of a specific animal in its environment.
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| 10. |
- Hotchkiss, Erin R., et al.
(författare)
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Whole-stream 13C tracer addition reveals distinct fates of newly fixed carbon
- 2015
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Ingår i: Ecology. - : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 96:2, s. 403-416
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Tidskriftsartikel (refereegranskat)abstract
- Many estimates of freshwater carbon (C) fluxes focus on inputs, processing, and storage of terrestrial C; yet inland waters have high rates of internally fixed (autochthonous) C production. Some fraction of newly fixed C may be released as biologically available, dissolved organic C (DOC) and stimulate microbial-driven biogeochemical cycles soon after fixation, but the fate of autochthonous C is difficult to measure directly. Tracing newly fixed C can increase our understanding of fluxes and fate of autochthonous C in the context of freshwater food webs and C cycling. We traced autochthonous C fixation and fate using a dissolved inorganic C stable isotope addition (13CDIC). We added 13CDIC to North Fork French Creek, Wyoming, USA during two days in August. We monitored changes in 13C pools, fluxes, and storage for 44 d after the addition. Two-compartment flux models were used to quantify net release of newly fixed 13CDOC and 13CDIC into the water column. We compared net 13C fixation with tracer 13CDIC removal and gross primary production (GPP) to account for the mass of tracer fixed, released, lost to the atmosphere, and exported downstream. Much of the fixed C turned over rapidly and did not enter longer-term storage pools. Net C fixed was 70% of GPP measured with O2. Algae likely released the remaining 30% via 13CDOC exudation and respiration of newly fixed C. Primary producers released 13CDOC at rates of up to 16% per day during the 13C addition, but exudation of new labile C declined to near zero by day 6. DIC production from newly fixed C accounted for 21% of ecosystem respiration the day after the 13C addition. All measured organic C (OC) pools were enriched with 13C 1 d after the tracer addition. 20% of fixed 13C remained in benthic OC by day 44, and average residence time of autochthonous C in benthic OC was 62 d. Newly fixed C had two distinct fates: short-term (<1 week) exudation and respiration or longer-term storage and downstream export. Autochthonous C in streams likely fuels short-term microbial production and biogeochemical cycling, in addition to providing a longer-term resource for consumers.
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| 11. |
- Jonsson, Micael, et al.
(författare)
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Climate change modifies the size structure of assemblages of emerging aquatic insects
- 2015
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Ingår i: Freshwater Biology. - : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 60:1, s. 78-88
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is expected to not only raise water temperatures, but also to cause brownification of aquatic ecosystems via increased inputs of terrestrial dissolved organic matter. While efforts have been made to understand how increased temperature and brownification separately influence aquatic food webs, their interactive effects have been less investigated. Further, although climate change effects on aquatic ecosystems likely will propagate to terrestrial consumers via changes in aquatic insect emergence, this has rarely been studied. We investigated the effect of climate change on aquatic insect emergence, in a large-scale outdoor pond facility where 16 sections - each containing natural food webs including a fish top-consumer population - were subjected to warming (3 degrees C above ambient temperatures) and/or brownification (by adding naturally humic stream water). Aquatic insect emergence was measured biweekly over 18weeks. We found no effect of warming or brownification on total emergent insect dry mass. However, warming significantly reduced the number of emergent Chironomidae, while numbers of larger taxa, Trichoptera and Ephemeroptera, remained unchanged. On average, 57% and 58% fewer Chironomidae emerged from the warmed clear and humic pond sections, respectively. This substantial decrease in emergent Chironomidae resulted in a changed community structure and on average larger individuals emerging from warm sections as well as from humic sections under ambient conditions. There was also a weak influence of fish biomass on the size structure of emergent aquatic insects, with a positive relationship between individual insect size and total fish biomass, but effects of fish were clearly subordinate to those of warming. Climate change impacts on aquatic systems can have widespread consequences also for terrestrial systems, as aquatic insects are ubiquitous and their emergence represents an important resource flow from aquatic to terrestrial environments. While we found that neither warming nor brownification quantitatively changed total aquatic insect emergence biomass, the warming-induced decrease in number of emergent Chironomidae and the subsequent increase in average body size will likely impact terrestrial consumers relying on emergent aquatic insect as prey.
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| 12. |
- Klaus, Marcus, et al.
(författare)
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Listening to air–water gas exchange in running waters
- 2019
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Ingår i: Limnology and Oceanography. - : Association for the Sciences of Limnology and Oceanography. - 1541-5856. ; 17:7, s. 395-414
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Tidskriftsartikel (refereegranskat)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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| 13. |
- Solomon, Christopher T., et al.
(författare)
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Sediment size and nutrients regulate denitrification in a tropical stream
- 2009
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Ingår i: Journal of The North American Benthological Society. - : University of Chicago Press. - 0887-3593 .- 1937-237X. ; 28:2, s. 480-490
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Tidskriftsartikel (refereegranskat)abstract
- Landuse changes might alter N cycling in tropical aquatic ecosystems, but understanding of N cycling in tropical streams is limited. We measured actual and potential denitrification rates during the dry season in Rio Las Marias, a 4(th)-order Andean piedmont stream in Venezuela. Our objectives were to describe spatial and temporal variation in denitrification, quantify the effects of nutrient availability and substratum particle size on denitrification, and explore potential effects of anthropogenic sedimentation on denitrification. In 4 experiments, actual and potential denitrification rates ranged from 0 to 160 and from 0 to 740 mu g N(2)O-N m(-2) h(-1), respectively. Rates were distributed approximately log-normally because of spatial variation. During a 1-mo period, actual denitrification rates decreased exponentially from 37 +/- 39 to 5 +/- 7 mu g N(2)O-N m(-2) h(-1) (mean +/- SD), probably because of a decline in water-column NO(3)-N concentration from 41 +/- 14 to 12 +/- 3 mu g NO(3)-N/L. The texture (particle size) of stream substrata markedly affected denitrification rates. Actual rates were low in cobble, gravel, and fine sediments (< 5 mm), but in fine sediments, rates increased in response to addition of excess NO(3)-N and organic C. In a 3-km stream reach, actual (but not potential) denitrification rates increased with the proportion of fine sediments (< 2 mm) in mixed substrata. This increase was nonlinear, and the threshold value occurred at 37% fine particles, above which actual denitrification rates were almost always high. An experiment simulating the effects of anthropogenic sedimentation showed that topsoil inputs resulted in denitrification rates similar to 8x higher than rates in trials where excess NO(3)-N and organic C were supplied. Denitrification is a small but potentially significant sink for available N in this N-limited system. Anthropogenic sedimentation associated with landuse change might significantly increase denitrification rates in streams.
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