Nitrogen inputs drive nitrogen concentrations in U.S. streams and rivers during summer low flow conditions
Ecological and human health impairments related to excess nitrogen (N) in streams and rivers remain widespread in the United States (U.S.) despite recent efforts to reduce N pollution. Many studies have quantified the relationship between N loads to streams in terms of N mass and N inputs to watersh...
Saved in:
| Published in: | The Science of the total environment Vol. 639; pp. 1349 - 1359 |
|---|---|
| Main Authors: | , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Netherlands
Elsevier B.V
15-10-2018
|
| Subjects: | |
| Online Access: | Get full text |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | Ecological and human health impairments related to excess nitrogen (N) in streams and rivers remain widespread in the United States (U.S.) despite recent efforts to reduce N pollution. Many studies have quantified the relationship between N loads to streams in terms of N mass and N inputs to watersheds; however, N concentrations, rather than loads, are more closely related to impacts on human health and aquatic life. Additionally, concentrations, rather than loads, trigger regulatory responses. In this study, we examined how N concentrations are related to N inputs to watersheds (atmospheric deposition, synthetic fertilizer, manure applied to agricultural land, cultivated biological N fixation, and point sources), land cover characteristics, and stream network characteristics, including stream size and the extent of lakes and reservoirs. N concentration data were collected across the conterminous U.S. during the U.S. Environmental Protection Agency's 2008–09 National Rivers and Streams Assessment (n = 1966). Median watershed N inputs were 15.7 kg N ha−1 yr−1. Atmospheric deposition accounted for over half the N inputs in 49% of watersheds, but watersheds with the highest N input rates were dominated by agriculture-related sources. Total N input to watersheds explained 42% and 38% of the variability in total N and dissolved inorganic N concentrations, respectively. Land cover characteristics were also important predictors, with wetland cover muting the effect of agricultural N inputs on N concentrations and riparian disturbance exacerbating it. In contrast, stream variables showed little correlation with N concentrations. This suggests that terrestrial factors that can be managed, such as agricultural N use practices and wetland or riparian areas, control the spatial variability in stream N concentrations across the conterminous U.S.
[Display omitted]
•Summer N concentrations were predicted from N inputs to the landscape and land cover.•Atmospheric deposition, agriculture, and sewage contribute to aquatic N loading.•Climate and stream characteristics explained little spatial variability in stream N.•At a national scale, nitrogen inputs drive concentrations, but interact with land cover.•Aquatic nitrogen impairment may be mitigated by managing inputs and land cover. |
|---|---|
| ISSN: | 0048-9697 1879-1026 |
| DOI: | 10.1016/j.scitotenv.2018.05.008 |