Surface Water Quality Is Improving due to Declining Atmospheric N Deposition

Abstract

We evaluated long-term surface water nitrate and atmospheric nitrogen (N) deposition trends for a group of nine predominantly forested Appalachian Mountain watersheds during a recent multidecadal period (1986-2009) in which regional NOx emissions have been progressively reduced. Statistical analysis showed unexpected linear declines in both annual surface water nitrate-N concentrations (mean =46.4%) and yields (mean =47.7%) among the watersheds corresponding to comparable declines in annual wet N deposition (mean =34.4%) resulting from U.S. NOx emission control programs during the same time period. Nitrate-N concentration trends were robust across a large geographical region and appeared insensitive to watershed size across several orders of magnitude-suggesting that the improvements in water quality are probably propagated to surface and estuarine waters downstream. Surface waters are thus responding to declining atmospheric N deposition in much the same way they responded to declining sulfur deposition-although only one watershed showed a 1:1 relationship. Application of a kinetic N saturation model indicated that all nine forested watersheds are exhibiting signs of N saturation as evidenced by a limited, but variable, efficiency of demand for N. Further reductions in N deposition would be expected to produce additional reductions in streamwater N loads.

Long‐Term Trends of Nutrients and Sediment from the Nontidal Chesapeake Watershed: An Assessment of Progress by River and Season

“…In other words, these nine human‐disturbed watersheds may have responded to reductions of atmospheric input in more complex ways than the upland forest watersheds analyzed by Eshleman et al . ().…”

“…Similarly, DP has shown decreases in these rivers since the 1980s (Figures B2c, B3c, B4c, and B9c). The nontidal Patuxent is particularly remarkable in terms of the degree of reduction, largely owing to historical management controls on point source inputs (specifically the P‐detergent ban and WWTP upgrade) (Boynton et al ., ) and, as recently reported elsewhere in the watershed, decreases in N loading from AD (Eshleman et al ., ; Linker et al ., ). In fact, these efforts would be expected to achieve more apparent loading reduction in Patuxent than in the other tributaries, because Patuxent has been more dominated by point, urban, and atmospheric sources than the other tributaries (collectively representing 70% of N and 80% of P inputs).…”

Methylmercury Bioaccumulation in an Urban Estuary: Delaware River, USA

“…Throughout the last century, urban rivers and waterways in the northeastern US have faced numerous challenges to ecosystem health; yet they have also experienced substantial improvements in water quality, with documented reductions in sulfate, phosphorus, organic loading, and metal pollutants (Burns et al 2006; Eshleman et al 2013; Sanudo-Wilhelmy and Gill 1999; Skjelkvale et al 2005) across water bodies. Coastal rivers and estuaries continue to be affected by current stressors and both organic and inorganic legacy contamination.…”

Atmospheric N Deposition Increases Bacterial Laccase-Like Multicopper Oxidases: Implications for Organic Matter Decay

“…Although rates of N deposition have recently declined in parts of North America and Europe, global rates of N deposition are expected to increase through the next century (1)(2)(3). The extent to which N deposition affects terrestrial C storage has fueled much scientific discourse (4)(5)(6)(7), and it is the focus of this work.…”