Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012
Understanding trends in stream chemistry is critical to watershed management, and often complicated by multiple contaminant sources and landscape conditions changing over varying time scales. We adapted spatially-referenced regression (SPARROW) to infer causes of recent nutrient trends in Chesapeake Bay tributaries by relating observed fluxes during 1992, 2002, and 2012 to contemporary inputs and watershed conditions. The annual flow-normalized nitrogen flux to the bay from its watershed declined by 14 percent to 127,000 Mg (metric tons) between 1992 and 2012, due primarily (more than 80 percent of the decline) to reduced point sources. The remainder of the decline was due to reduced atmospheric deposition (13 percent) and urban non-point sources. Agricultural inputs, which contribute most nitrogen to the bay, changed little, although trends in the average nitrogen yield (flux per unit area) from cropland and pasture to streams in some settings suggest possible effects of evolving nutrient applications or other land management practices. Point sources of phosphorus to local streams declined by half between 1992 and 2012, while non-point inputs were relatively unchanged. Annual phosphorus delivery to the bay increased by 9 percent to 9,570 Mg between 1992 and 2012, however, due mainly to reduced retention in the Susquehanna River at Conowingo Reservoir.
Citation Information
| Publication Year | 2019 |
|---|---|
| Title | Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012 |
| DOI | 10.1111/1752-1688.12756 |
| Authors | Scott Ator, Ana M. Garcia, Gregory E. Schwarz, Joel Blomquist, Andrew Sekellick |
| Publication Type | Article |
| Publication Subtype | Journal Article |
| Series Title | Journal of the American Water Resources Association |
| Index ID | 70203385 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | Maryland Water Science Center |
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Inputs and Selected Predictions of the CBTN_v5 and CBTP_v5 SPARROW Models for the Chesapeake Bay Watershed
The CBTN_v5 and CBTP_v5 SPARROW models were developed to support inferences about causes of observed changes in nitrogen and phosphorus (respectively) fluxes in Chesapeake Bay tributaries between 1992 and 2012. Model inputs and outputs are included in three files, which are described below. Detailed documentation of the SPARROW modeling technique is available at https://pubs.er.usgs.gov/publicatio - Connect
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