Declining nitrate-N yields in the Upper Potomac River Basin: What is really driving progress under the Chesapeake Bay restoration?. (December 2016)

• Record Type: Journal Article
• Authors: Eshleman, Keith N.; Sabo, Robert D.
• Is Part Of: Atmospheric environment. Volume 146(2016)
• Page Start: 280
• Page End: 289
• Publication Date: 2016-12
• Subjects: Atmospheric N deposition -- Nonpoint-source pollution -- Nitrate pollution -- Chesapeake Bay -- Potomac River watershed; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2016.07.004
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Reducing nutrient pollution of surface and coastal waters in the U.S. and elsewhere remains a major environmental and engineering challenge for the 21st century. In the case of the Chesapeake Bay restoration, we still lack scientific proof that watershed-based management actions have been effective at reducing nonpoint-source nutrient loads from the land to this estuary in accordance with restoration goals. While the conventional wisdom is that implementation of best management practices (BMP's) and wastewater treatment have turned the tide against nutrient pollution, we examined long-term (1986-present) nitrate-N trends in streams and major tributaries of the Upper Potomac River Basin (UPRB) and found that: 1) dramatic reductions in annual discharge-weighted mean nitrate-N concentrations and yields across the UPRB can be almost universally attributed to reductions in atmospheric N deposition as opposed to on-the-ground management actions such as implementation of BMP's; 2) observed water quality changes generally comport with a modified kinetic N saturation model (MKNSM); 3) the MKNSM can separate the nitrate-N yield that is responsive to atmospheric deposition from a "non-responsive" yield; and 4) N saturation from atmospheric N deposition appears to be an inherently reversible process across most of the landscape. These unanticipated region-wide water quality benefits can be attributed to NOx emission controls brought about by the 1990 Clean Air Act Amendments (and subsequent U.S. NOX control programs) and reflect a water quality "success story" in the Chesapeake Bay restoration. Highlights: U.S. NOx emission control programs were shown to be the primary driver of improving water quality across most of the UPRB. The MKNSM explained large proportions of the variation in annual nitrate-N yield through time and among the watersheds. The MKNSM allowed the annual nitrate-N yield to be separated into "responsive" and "non-responsive" components. NOx emission controls have rapidly reversed nitrogen saturation across most of the UPRB.