Rivermouth alteration of agricultural impacts on consumer tissue δ 15 N

James H. Larson; William B. Richardson; Jonathan M. Vallazza; J. C. Nelson

doi:10.1371/journal.pone.0069313

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Rivermouth alteration of agricultural impacts on consumer tissue δ 15 N

James H. Larson·William B. Richardson·Jonathan M. Vallazza·J. C. Nelson

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Abstract

Terrestrial agricultural activities strongly influence riverine nitrogen (N) dynamics, which is reflected in the δ 15 N of riverine consumer tissues. However, processes within aquatic ecosystems also influence consumer tissue δ 15 N. As aquatic processes become more important terrestrial inputs may become a weaker predictor of consumer tissue δ 15 N. In a previous study, this terrestrial-consumer tissue δ 15 N connection was very strong at river sites, but was disrupted by processes occurring in rivermouths (the ‘rivermouth effect’). This suggested that watershed indicators of N loading might be accurate in riverine settings, but could be inaccurate when considering N loading to the nearshore of large lakes and oceans. In this study, the rivermouth effect was examined on twenty-five sites spread across the Laurentian Great Lakes. Relationships between agriculture and consumer tissue δ 15 N occurred in both upstream rivers and at the outlets where rivermouths connect to the nearshore zone, but agriculture explained less variation and had a weaker effect at the outlet. These results suggest that rivermouths may sometimes be significant sources or sinks of N, which would cause N loading estimates to the nearshore zone that are typically made at discharge gages further upstream to be inaccurate. Identifying definitively the controls over the rivermouth effect on N loading (and other nutrients) will require integration of biogeochemical and hydrologic models.

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Source-reported bounding extent: 41.38° to 48.85° latitude; -92.11° to -76.3° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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James H. Larson, William B. Richardson, Jonathan M. Vallazza, J. C. Nelson. 2013-07-31. Rivermouth alteration of agricultural impacts on consumer tissue δ 15 N. https://doi.org/10.1371/journal.pone.0069313

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