Toward Explaining Nitrogen and Phosphorus Trends in Chesapeake Bay Tributaries, 1992–2012

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.

Multi-decadal improvement in U.S. lake water clarity

“…Our results are consistent with recent studies showing regional (46,47) and national (41,42) improvements to U.S. streams and rivers (41,42,46,47) and lakes (42) in nutrient loads, they have shown declines in suspended sediments, consistent with improved sediment management practices (41). These recorded improvements in streams and rivers provide a mechanism for increasing lake water clarity, as changes in fluvial systems often equate to changes in sediment and nutrient inputs to lakes (48).…”

Land‐use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments

“…Substantial increases in forest standing stock are common in Finland, Sweden and Norway (de Wit, Austnes, Hylen, & Dalsgaard, 2015; Luyssaert et al, 2010) suggesting that increased nitrogen uptake by forests may affect NO 3 leaching from forested catchments elsewhere in the Nordic region. In Chesapeake Bay, USA, a watershed with considerably higher proportion of agriculture and developed areas than the Nordic countries, declines in atmospheric N deposition were found to be the second‐most important factor responsible for the decrease in N export to the bay (Ator, Garcia, Schwarz, Blomquist, & Sekellick, 2019).…”

Demand for bio-based fertilizers from dairy manure in Washington State: a small-scale discrete choice experiment

“…In the USA, most of this manure is land applied, and regulations discourage application rates that might exceed what plants can take up. Handling, storage and application of this manure and the associated nutrients to soils have contributed to impairment of air and water quality (US-EPA, 2012; Harter et al ., 2017; LCBP, 2018; Ator et al ., 2019). Meanwhile, most cropland is fertilized with imported synthetic fertilizers.…”