Source and Delivery of Nutrients to Receiving Waters in the Northeastern and Mid-Atlantic Regions of the United States1

The SPARROW (SPAtially Referenced Regressions On Watershed attributes) model was used to evaluate the spatial distribution of total nitrogen (TN) sources, loads, watershed yields, and factors affecting transport and decay in the stream network of California and portions of adjacent states for the year 2002. The two major TN sources to local catchments on a mass basis were fertilizers and manure (51.7%) and wastewater discharge (15.9%). Other sources contributed < 12%. Fertilizer use is widespread in the Central Valley region of California, and also important in several other regions because of the diversity of California agriculture. Precipitation, sand content of surficial soils, wetlands, and tile drains were important for TN movement to stream reaches. Median streamflow in the study area is about 0.04 m3/s. Aquatic losses of nitrogen were found to be most important in intermittent and small to medium sized streams (0.2‐14 m3/s), while larger streams showed less loss, and therefore are important for TN transport. Nitrogen loss in reservoirs was found to be insignificant, possibly because most of the larger ones are located upstream of nitrogen sources. The model was used to show loadings, sources, and tributary inputs to several major rivers. The information provided by the SPARROW model is useful for determining both the major sources contributing nitrogen to streams and the specific tributaries that transport the load.

“…450.12 kg/km 2 /year, respectively, as shown in Table ). These coefficients are comparable to results from other SPARROW models (Moore et al ., ; Rebich et al ., ; Wise and Johnson, ).…”

Section: Resultsmentioning

confidence: 98%

SPARROW Modeling of Nitrogen Sources and Transport in Rivers and Streams of California and Adjacent States, U.S.

Saleh

Domagalski

2015

“…It was found that the model coefficients performed well at explaining observed variation in the 2001 flux dataset; the r 2 value was 0.90 (Figure ). We also looked at past SPARROW studies and found that our baseline model resulted in calibrated parameters that are similar to those reported in other studies (Smith et al ., ; Alexander et al ., ; Hoos and McMahon, ; Najjar et al ., ; Brown et al ., ; Moore et al ., ; Rebich et al ., ; Robertson and Saad, ; Wise and Johnson, ; Alam and Goodall, ). Based on these past studies, we found a consistent negative relationship between N loading and mean annual T and a positive relationship between N loading and mean annual P .…”

Section: Resultsmentioning

confidence: 99%

The Impact of Projected Climate Change Scenarios on Nitrogen Yield at a Regional Scale for the Contiguous United States

Alam

Goodall

Bowes

et al. 2017

Improved understanding of the potential regional impacts of projected climatic changes on nitrogen yield is needed to inform water resources management throughout the United States (U.S.). The objective of this research is to look broadly at watersheds in the contiguous U.S. to assess the potential regional impact of changes in precipitation (P) and air temperature (T) on nitrogen yield. The SPAtially Referenced Regression On Watershed attributes model and downscaled P and T outputs from 14 general circulation models were used to explore impacts on nitrogen yield. Results of the analysis suggest that projected changes in P and T will decrease nitrogen yield for the majority of the contiguous U.S., including the watersheds of the Chesapeake Bay and Gulf of Mexico. Some regions, however, such as the Pacific Northwest and Northern California, are projected to face climatic conditions that, according to the model results, may increase nitrogen yield. Combining the projections of climate‐driven changes in nitrogen yield with projected changes in watershed nitrogen inputs could help water resource managers develop regionally specific, long‐term strategies to mitigate nitrogen pollution.

“…Regional models, however, indicate that these processes typically result in a net loss of nitrogen in streams (Alexander et al. , 2007; Moore et al. , 2011) of generally <20%, attributable primarily to the loss of nitrate through benthic denitrification (Howarth et al.…”

Section: Methodsmentioning

confidence: 99%

Estimating Contributions of Nitrate and Herbicides From Groundwater to Headwater Streams, Northern Atlantic Coastal Plain, United States¹

Ator

Denver

2012

Groundwater transport often complicates understanding of surface-water contamination. We estimated the regional flux of nitrate and selected herbicides from groundwater to nontidal headwater streams of the Atlantic Coastal Plain (New Jersey through North Carolina) based on late-winter or spring base-flow samples from 174 streams. Sampled streams were selected randomly, and flux estimates are based on resulting population estimates rather than on empirical models, which have been used previously for similar estimates. Base-flow flux in the estimated 8,834 headwater streams of the study area are an estimated 21,200 kg ⁄ day of nitrate (as N) and 5.83, 0.565, and 20.7 kg ⁄ day of alachlor, atrazine, and metolachlor (and selected degradates), respectively. Base-flow flux of alachlor and metolachlor is <3% of the total base-flow flux of those compounds plus degradates. Base-flow flux of nitrate and herbicides as a percentage of applications is typically highest in well-drained areas and lowest in areas with abundant poor drainage and anoxic conditions. In Coastal Plain watersheds of Albemarle and Pamlico Sounds, <2% of applied nitrogen reaches headwater streams as base flow. On the Delmarva Peninsula part of the Chesapeake Bay watershed, however, more than 10% of such applications are transported through groundwater to streams, and base-flow nitrate flux represents 70% of total nitrogen flux in headwater streams.(KEY TERMS: base-flow contaminant flux; surface water ⁄ groundwater interactions; nonpoint source pollution; nutrients; pesticides ⁄ herbicides; total maximum daily load (TMDL); groundwater discharge.) Ator, Scott W. and Judith M. Denver, 2012. Estimating Contributions of Nitrate and Herbicides from Groundwater to Headwater Streams, Northern Atlantic Coastal Plain, United States.