Estimates of nitrate loads and yields from groundwater to streams in the Chesapeake Bay watershed based on land use and geology

Terziotti, Silvia; Capel, Paul D.; Tesoriero, Anthony J.; Hopple, Jessica A.; Kronholm, Scott C.

doi:10.3133/sir20175160

Cited by 7 publications

(10 citation statements)

References 4 publications

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“…Nitrate movement to and within aquifers occurs in many areas of the watershed but is enhanced in areas of carbonate rocks (Lizarraga, 1997;Miller et al, 1997) or permeable well-drained sediments (Ator & Denver, 2012;Böhlke & Denver, 1995;Hirsch et al, 2010;Sanford & Pope, 2007;Sanford & Pope, 2013) where oxic conditions are common. Such areas of the Chesapeake Bay watershed often support intensive agriculture, and elevated nitrate in groundwater (Greene, LaMotte, & Cullinan, 2005;Terziotti, Capel, Tesoriero, Hopple, & Kronholm, 2018) and receiving streams in such areas may reflect years of nitrogen applications exceeding removal rates (Parris, 1998;Spiertz, 2010).…”

Section: Legacy Nutrientsmentioning

confidence: 99%

Factors driving nutrient trends in streams of the Chesapeake Bay watershed

Ator¹,

Blomquist²,

Webber³

et al. 2020

J of Env Quality

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Despite decades of effort toward reducing nitrogen and phosphorus flux to Chesapeake Bay, water-quality and ecological responses in surface waters have been mixed. Recent research, however, provides useful insight into multiple factors complicating the understanding of nutrient trends in bay tributaries, which we review in this paper, as we approach a 2025 total maximum daily load (TMDL) management deadline. Improvements in water quality in many streams are attributable to management actions that reduced point sources and atmospheric nitrogen deposition and to changes in climate. Nutrient reductions expected from management actions, however, have not been fully realized in watershed streams. Nitrogen from urban nonpoint sources has declined, although waterquality responses to urbanization in individual streams vary depending on predevelopment land use. Evolving agriculture, the largest watershed source of nutrients, has likely contributed to local nutrient trends but has not affected substantial changes in flux to the bay. Changing average nitrogen yields from farmland underlain by carbonate rocks, however, may suggest future trends in other areas under similar management, climatic, or other influences, although drivers of these changes remain unclear. Regardless of upstream trends, phosphorus flux to the bay from its largest tributary has increased due to sediment infill in the Conowingo Reservoir. In general, recent research emphasizes the utility of input reductions over attempts to manage nutrient fate and transport at limiting nutrients in surface waters. Ongoing research opportunities include evaluating effects of climate change and conservation practices over time and space and developing tools to disentangle and evaluate multiple influences on regional water quality.

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Section: Legacy Nutrientsmentioning

confidence: 99%

Factors driving nutrient trends in streams of the Chesapeake Bay watershed

Ator¹,

Blomquist²,

Webber³

et al. 2020

J of Env Quality

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“…Improved understanding of the spatial and temporal patterns of streamflow can help describe the timing of loads to the bay. Groundwater discharge can be an important factor in nitrogen transport to streams in the Chesapeake Bay Watershed (Terziotti et al 2018), and typically is the source of streamflow during low‐flow conditions. Changing patterns in low flows may contribute to observed changes in nitrogen transport to the bay (Ator and Denver 2015).…”

Section: Sites and Datamentioning

confidence: 99%

Spatial and Temporal Patterns of Low Streamflow and Precipitation Changes in the Chesapeake Bay Watershed

Fleming

Archfield

Hirsch

et al. 2020

J American Water Resour Assoc

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Spatial and temporal patterns in low streamflows were investigated for 183 streamgages located in the Chesapeake Bay Watershed for the period 1939–2013. Metrics that represent different aspects of the frequency and magnitude of low streamflows were examined for trends: (1) the annual time series of seven‐day average minimum streamflow, (2) the scaled average deficit at or below the 2% mean daily streamflow value relative to a base period between 1939 and 1970, and (3) the annual number of days below the 2% threshold. Trends in these statistics showed spatial cohesion, with increasing low streamflow volume at streamgages located in the northern uplands of the Chesapeake Bay Watershed and decreasing low streamflow volume at streamgages in the southern part of the watershed. For a small subset of streamgages (12%), conflicting trend patterns were observed between the seven‐day average minimum streamflow and the below‐threshold time series and these appear to be related to upstream diversions or the influence of reservoir‐influenced streamflows in their contributing watersheds. Using multivariate classification techniques, mean annual precipitation and fraction of precipitation falling as snow appear to be broad controls of increasing and decreasing low‐flow trends. Further investigation of seasonal precipitation patterns shows summer rainfall patterns, driven by the Atlantic Multidecadal Oscillation, as the main driver of low streamflows in the Chesapeake Bay Watershed.

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“…The base flow nitrate data sets were developed in a previous study 16 from surface water data collected by the USGS and partnering agencies throughout the Chesapeake Bay watershed with the purpose of quantifying the annual median base flow nitrate concentrations at the local scale. 27,28 Data selection criteria to capture local base flow conditions 16 were imposed on the full database, which led to a final set of annual median nitrate concentrations calculated for each of 156 sites (Figure S-1). 16 The criteria specified that selected sites have drainage areas less than 1300 km 2 and samples collected over the 1970−2013 period.…”

Section: Methodsmentioning

confidence: 99%

“…27,28 Data selection criteria to capture local base flow conditions 16 were imposed on the full database, which led to a final set of annual median nitrate concentrations calculated for each of 156 sites (Figure S-1). 16 The criteria specified that selected sites have drainage areas less than 1300 km 2 and samples collected over the 1970−2013 period. A base flow index (BFI) value was estimated for each stream using a digital filter for hydrograph separation; 16 details of the base flow calculations are provided elsewhere.…”

Section: Methodsmentioning

confidence: 99%

“…15 Recently, base flow nitrate concentrations were estimated in the Chesapeake Bay watershed by relating measured nitrate concentrations during base flow to land use and geology characteristics of each catchment using multiple linear regression. 16 Machine learning methods, such as random forest and boosted regression trees (BRTs), began to be more commonly used in environmental science in the 2000s, 17,18 with the number of applications increasing dramatically in the last decade. 19 For example, random forest and boosted regression have recently been used to improve predictions of redox conditions and contaminant concentrations under groundwater 20−23 and ecological conditions.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Factors Affecting Nitrate Concentrations in Stream Base Flow

Wherry

Tesoriero

Terziotti

2020

Environ. Sci. Technol.

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Elevated nitrogen concentrations in streams and rivers in the Chesapeake Bay watershed have adversely affected the ecosystem health of the bay. Much of this nitrogen is derived as nitrate from groundwater that discharges to streams as base flow. In this study, boosted regression trees (BRTs) were used to relate nitrate concentrations in base flow (n = 156) to explanatory variables describing nitrogen sources, geology, and soil and catchment characteristics. From these relations, a BRT model was developed to predict base flow nitrate concentrations in streams throughout the Chesapeake Bay watershed. The highest base flow nitrate concentrations were associated with intensive agricultural land use, carbonate geology, and sparse riparian canopy, which suggested that reduced nitrogen inputs, particularly over carbonate terrane, are critical for limiting nitrate concentrations. The lowest nitrate concentrations in the BRT model were associated with extensive riparian canopy, high levels of organic carbon in soils, and suboxic conditions at shallow depths, which suggested that denitrification in the subsurface, particularly in the riparian zone, is limiting base flow nitrate concentrations. Nitrate transport from aquifers to streams can take decades to occur, resulting in decades-long lag times between the time when a land-use activity is implemented and when its effects are fully observed in streams. Predictive models of base flow nitrate concentrations in streams will help identify which portions of a watershed are likely to have large fractions of total stream nitrogen load derived from pathways with significant lag times.

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Estimates of nitrate loads and yields from groundwater to streams in the Chesapeake Bay watershed based on land use and geology

Cited by 7 publications

References 4 publications

Factors driving nutrient trends in streams of the Chesapeake Bay watershed

Factors driving nutrient trends in streams of the Chesapeake Bay watershed

Spatial and Temporal Patterns of Low Streamflow and Precipitation Changes in the Chesapeake Bay Watershed

Factors Affecting Nitrate Concentrations in Stream Base Flow

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