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Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated, causing more bioavailable nitrogen to enter groundwater and surface waters. Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from(More)
Nitrous oxide (N(2)O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N(2)O via microbial denitrification that converts N to N(2)O and dinitrogen (N(2)). The fraction of denitrified N that escapes as N(2)O rather than(More)
We measured denitrification rates using a field 15 N–NO { 3 tracer-addition approach in a large, cross-site study of nitrate uptake in reference, agricultural, and suburban–urban streams. We measured denitrification rates in 49 of 72 streams studied. Uptake length due to denitrification (S Wden) ranged from 89 m to 184 km (median of 9050 m) and there were(More)
We measured uptake length of 15 NO { 3 in 72 streams in eight regions across the United States and Puerto Rico to develop quantitative predictive models on controls of NO { 3 uptake length. As part of the Lotic Intersite Nitrogen eXperiment II project, we chose nine streams in each region corresponding to natural (reference), suburban–urban, and(More)
Agricultural and urban land use increase nitrogen (N) concentrations in streams, which can saturate biotic demand by plants, algae, and bacteria via assimilative uptake, and by nitrification and denitrification. We studied six streams per year in each of three land-use categories (agricultural, urban, and forested) for 3 yr (n 5 18 streams), and we compared(More)
Experience with implementing agricultural phosphorus (P) strategies highlights successes and uncertainty over outcomes. We examine case studies from the USA, UK, and Sweden under a gradient of voluntary, litigated, and regulatory settings. In the USA, voluntary strategies are complicated by competing objectives between soil conservation and dissolved P(More)
Carbon (C) and nitrogen (N) are strongly coupled across ecosystems due to stoichiometrically balanced assimilatory demand as well as dissimilatory processes such as denitrification. Microorganisms mediate these biogeochemical cycles, but how microbial communities respond to environmental changes, such as dissolved organic carbon (DOC) availability, and how(More)
In streams, benthic bacterial communities are integral to multiple aspects of ecosystem function, including carbon and nitrogen cycles. Variation both in terms of bacterial community structure (based on taxonomic and/or functional genes) and function can reveal potential drivers of spatiotemporal patterns in stream processes. In this study, the abundance(More)
Denitrifiers remove fixed nitrogen from aquatic environments and hydrologic conditions are one potential driver of denitrification rate and denitrifier community composition. In this study, two agriculturally impacted streams in the Sugar Creek watershed in Indiana, USA with different hydrologic regimes were examined; one stream is seasonally ephemeral(More)
Most nitrogen (N) assimilation in lake and marine ecosystems is often subsequently released via autochthonous dissolved organic nitrogen (DON) production, but autochthonous DON production has yet to be quantified in flowing waters. We measured in-stream DON production following 24 h 15 N-nitrate (NO { 3) tracer additions in 36 headwater streams, a subset of(More)