Journal
ENVIRONMENTAL RESEARCH LETTERS
Volume 8, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1748-9326/8/1/014039
Keywords
nitrate; ammonium; trends; stream; forested catchment; reference catchments
Funding
- USDA Forest Service Research and Development
- National Council on Air and Stream Improvement
- American Reinvestment and Recovery Act [PNW/OSU 10-JV-11260489-026]
- USDA Forest Service
- National Science Foundation
- Direct For Biological Sciences [1019522] Funding Source: National Science Foundation
- Direct For Biological Sciences
- Division Of Environmental Biology [0814280, 0823380] Funding Source: National Science Foundation
- Direct For Biological Sciences
- Division Of Environmental Biology [823293, 1256696, 1114804] Funding Source: National Science Foundation
- Division Of Environmental Biology [1019522] Funding Source: National Science Foundation
- EPSCoR
- Office Of The Director [1101245] Funding Source: National Science Foundation
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To examine whether stream nitrogen concentrations in forested reference catchments have changed over time and if patterns were consistent across the USA, we synthesized up to 44 yr of data collected from 22 catchments at seven USDA Forest Service Experimental Forests. Trends in stream nitrogen presented high spatial variability both among catchments at a site and among sites across the USA. We found both increasing and decreasing trends in monthly flow-weighted stream nitrate and ammonium concentrations. At a subset of the catchments, we found that the length and period of analysis influenced whether trends were positive, negative or non-significant. Trends also differed among neighboring catchments within several Experimental Forests, suggesting the importance of catchment-specific factors in determining nutrient exports. Over the longest time periods, trends were more consistent among catchments within sites, although there are fewer long-term records for analysis. These findings highlight the critical value of long-term, uninterrupted stream chemistry monitoring at a network of sites across the USA to elucidate patterns of change in nutrient concentrations at minimally disturbed forested sites.
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