A water quality model for the Patuxent estuary: Current conditions and predictions under changing land-use scenarios

Lung, Wu‐Seng; Bai, Sen

doi:10.1007/bf02695966

Cited by 35 publications

(31 citation statements)

References 9 publications

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“…2) of the estuary model (Lung 1992). Later versions of the estuary model (Lung and Bai 2003) require watershed inputs for a more detailed 42-segment scheme (Fig. 2).…”

Section: Statistical Nonpoint Source Modelsmentioning

confidence: 99%

“…Weekly material fluxes were divided by water discharge to recover the average material concentrations for each segment and week. We supplied weekly results for all 42 segments to the estuarine modelers (Lung and Bai 2003), but we aggregated results for concise presentation in this paper by summing weekly predicted discharges to estimate annual fluxes, 2-yr average fluxes, and flow-weighted average concentrations for larger sections of the watershed (Table 1).…”

Section: Statistical Nonpoint Source Modelsmentioning

confidence: 99%

“…The Chesapeake Bay agreements have provided further impetus for reductions in nutrient discharges (Boesch et al 2001). Large reductions in wastewater nutrient discharges have been achieved, but have not produced dramatic improvements in water quality in the Patuxent estuary, suggesting a need to also reduce nonpoint source (NPS) nutrient discharges (D'Elia et al 2003;Lung and Bai 2003). Continued development of the watershed seems inevitable (Maryland Office of Planning [MOP] 1993[MOP] , 1995Tassone et al 1998;Bockstael and Irwin 2003).…”

Section: Introductionmentioning

confidence: 99%

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Effects of land-use change on nutrient discharges from the Patuxent River watershed

et al. 2003

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ABSTRACT:We developed an empirical model integrating nonpoint source (NPS) runoff, point sources (PS), and reservoir management to predict watershed discharges of water, sediment, organic carbon, silicate, nitrogen, and phosphorus to the Patuxent River in Maryland. We estimated NPS discharges with linear models fit to measurements of weekly flow and 10 material concentrations from 22 study watersheds. The independent variables were the proportions of cropland and developed land, physiographic province (Coastal Plain or Piedmont), and time (week). All but one of the NPS models explained between 62% and 83% of the variability among concentration or flow measurements. Geographic factors (land cover and physiographic province) accounted for the explained variability in largely dissolved material concentrations (nitrate [NO 3 ], silicate [Si], and total nitrogen [TN]), but the explained variability in flow and particulates (sediment and forms of phosphorus) was more strongly related to temporal variability or its interactions with land cover and province. Average concentrations of all materials increased with cropland proportion and also with developed land (except Si), but changes in cropland produced larger concentration shifts than equivalent changes in developed land proportion. Among land cover transitions, conversions between cropland and forest-grassland cause the greatest changes in material discharges, cropland and developed land conversions are intermediate, and developed land and forest-grassland conversions have the weakest effects. Changing land cover has stronger effects on NO 3 and TN in the Piedmont than in the Coastal Plain, but for all other materials, the effects of land-use change are greater in the Coastal Plain. We predicted the changes in nutrient load to the estuary under several alternate land cover configurations, including a state planning scenario that extrapolates current patterns of population growth and land development to the year 2020. In that scenario, declines in NPS discharges from reducing cropland are balanced by NPS discharge increases from developing an area almost six times larger than the lost cropland. When PS discharges are included, there are net increases in total water, total phosphorus, and TN discharges.

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“…2) of the estuary model (Lung 1992). Later versions of the estuary model (Lung and Bai 2003) require watershed inputs for a more detailed 42-segment scheme (Fig. 2).…”

Section: Statistical Nonpoint Source Modelsmentioning

confidence: 99%

Section: Statistical Nonpoint Source Modelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of land-use change on nutrient discharges from the Patuxent River watershed

et al. 2003

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“…In one major tributary of Chesapeake Bay, the Patuxent River estuary, point-source P and N loads decreased abruptly in 1986 and 1991, respectively (Lung and Bai 2003). Reductions in P loads began with a statewide ban on phosphate-based detergents in 1984, followed by subsequent upgrading of the sewage treatment facilities.…”

Section: Introductionmentioning

confidence: 99%

Long-Term Changes in Water Quality and Productivity in the Patuxent River Estuary: 1985 to 2003

Testa

Kemp

Boynton

et al. 2008

Estuaries and Coasts

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We conducted a quantitative assessment of estuarine ecosystem responses to reduced phosphorus and nitrogen loading from sewage treatment facilities and to variability in freshwater flow and nonpoint nutrient inputs to the Patuxent River estuary. We analyzed a 19-year dataset of water quality conditions, nutrient loading, and climatic forcing for three estuarine regions and also computed monthly rates of net production of dissolved O 2 and physical transport of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) using a salt-and waterbalance model. Point-source loading of DIN and DIP to the estuary declined by 40-60% following upgrades to sewage treatment plants and correlated with parallel decreases in DIN and DIP concentrations throughout the Patuxent. Reduced point-source nutrient loading and concentration resulted in declines in phytoplankton chlorophyll-a (chl-a) and light-saturated carbon fixation, as well as in bottomlayer O 2 consumption for upper regions of the estuary. Despite significant reductions in seaward N transport from the middle to lower estuary, chl-a, turbidity, and surfacelayer net O 2 production increased in the lower estuary, especially during summer. This degradation of water quality in the lower estuary appears to be linked to a trend of increasing net inputs of DIN into the estuary from Chesapeake Bay and to above-average river flow during the mid-1990s. In addition, increased abundance of Mnemiopsis leidyi significantly reduced copepod abundance during summer from 1990 to 2002, which favored increases in chla and allowed a shift in total N partitioning from DIN to particulate organic nitrogen. These analyses illustrate (1) the value of long-term monitoring data, (2) the need for regional scale nutrient management that includes integrated estuarine systems, and (3) the potential water quality impacts of altered coastal food webs.

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“…Patuxent River water quality and the physical structure of the water column are both affected by changes in nutrient loading rates from the Patuxent River watershed, Chesapeake Bay water quality at the downstream boundary, and inter-annual variability in rainfall , Lung & Bai 2003, Fisher et al 2006, Lung & Nice 2007. Land use in the Patuxent River watershed has changed dramatically over the past 150 yr, from primarily agricultural (~85% agriculture and 15% forested) in the 1850s to a mix of forested (51.6%), agriculture (28.5%), residential (15.5%), and urban (4.3%) in 1994 (D'Elia et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Simulating the effect of hypoxia on bay anchovy egg and larval mortality using coupled watershed, water quality, and individual-based predation models

Adamack

Rose²,

Breitburg³

et al. 2012

Mar. Ecol. Prog. Ser.

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Greater nutrient loads since the 1950s have increased the extent and duration of hypoxic conditions in the Patuxent River and the Chesapeake Bay (Maryland, USA). We linked watershed, water quality, and individual-based predation models to predict how changes in local (Patuxent River watershed) and regional (bay-wide) nutrient loading rates would affect bay anchovy Anchoa mitchilli egg and larval mortality rates in the lower region of the Patuxent River. Nutrient loadings affected hypoxic volume and the degree of spatial overlap between anchovy and their predators. Mortality rates were simulated during June and July under combinations of a wet or dry year, reduced and increased nutrient loadings from the Patuxent River watershed, and increased and decreased nutrient loadings into the Patuxent River at the Chesapeake Bay boundary. Chesapeake Bay water quality at the downstream boundary had a much larger effect on egg and larval mortality rates than nutrient loading rates from the Patuxent River watershed, and these responses were consistent with the downstream boundary condition having a greater effect on hypoxia. Water column structure, year type (wet/dry), and location within the lower Patuxent River had smaller effects on egg and larval mortality. Due to indirect effects, the effect of the Chesapeake Bay boundary condition on larval mortality rates during June was opposite to that predicted for egg mortality rates. Our results illustrate that statements and justifications about the benefits of nutrient loading reductions on estuarine ecosystems should avoid oversimplification, be specific, and recognize that species responses to changes in environmental conditions can be complex and variable.

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A water quality model for the Patuxent estuary: Current conditions and predictions under changing land-use scenarios

Cited by 35 publications

References 9 publications

Effects of land-use change on nutrient discharges from the Patuxent River watershed

Effects of land-use change on nutrient discharges from the Patuxent River watershed

Long-Term Changes in Water Quality and Productivity in the Patuxent River Estuary: 1985 to 2003

Simulating the effect of hypoxia on bay anchovy egg and larval mortality using coupled watershed, water quality, and individual-based predation models

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