Toward Explaining Nitrogen and Phosphorus Trends in Chesapeake Bay Tributaries, 1992–2012. (24th May 2019)

• Record Type: Journal Article
• Authors: Ator, Scott W.; García, Ana Maria; Schwarz, Gregory E.; Blomquist, Joel D.; Sekellick, Andrew J.
• Is Part Of: Journal of the American Water Resources Association. Volume 55:Number 5(2019)
• Page Start: 1149
• Page End: 1168
• Publication Date: 2019-05-24
• Subjects: nutrients -- SPARROW modeling -- watershed management, time series analysis -- Chesapeake Bay -- stream chemistry; Water-supply -- Periodicals; Hydrology -- Periodicals; Water resources development -- Periodicals; Water resources development -- Environmental aspects -- Periodicals; 333.9100973
• DOI: 10.1111/1752-1688.12756
• Languages: English
• ISSNs: 1093-474X

Abstract

Abstract: 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% to 127, 000 Mg (metric tons) between 1992 and 2012, due primarily (more than 80% of the decline) to reduced point sources. The remainder of the decline was due to reduced atmospheric deposition (13%) and urban nonpoint 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 nonpoint inputs were relatively unchanged. Annual phosphorus delivery to the bay increased by 9% to 9, 570 Mg between 1992 and 2012, however, due mainly to reduced retention in the Susquehanna River at Conowingo Reservoir. Abstract : Research Impact Statement : Point‐source reductions account for more than 80% of the decline in nitrogen flux to Chesapeake Bay between 1992 and 2012, but were offset by rising phosphorus inputs from the Susquehanna River.