Papers by A. Scott Andres
Journal of Environmental Quality, 2019
Noxious cyanobacterial blooms are common in many ponds in the mid‐Atlantic Coastal Plain. In Dela... more Noxious cyanobacterial blooms are common in many ponds in the mid‐Atlantic Coastal Plain. In Delaware, blooms normally occur between July and October, yet no in‐depth analyses of the causes and predictors exist. A study using commercially available, high‐frequency, continuous, and automated biogeochemical sensors at Coursey Pond, Delaware, a pond known for perennial summer blooms, was conducted to investigate how hydrophysical and hydrochemical conditions affect bloom dynamics. Cyanobacterial abundance (based on the in vivo phycocyanin fluorescence and phycocyanin/chlorophyll fluorescence ratios) increases during periods of high water temperatures (up to 32°C), low discharge through the pond (mean hydraulic residence time ≥5 d) with evaporative concentration of dissolved solids, and decreasing NO3− concentrations (reaching <0.1 mg L−1, the detection limit). These conditions lead to the uptake and depletion of bioavailable N in the pond surface waters and provide a competitive adv...
2 color plates To understand the effects of projected increased demands on groundwater for water ... more 2 color plates To understand the effects of projected increased demands on groundwater for water supply, a finite-difference, steady-state, groundwater flow model was used to simulate groundwater flow in the Coastal Plain sediments of southern New Castle County, Delaware. The model simulated flow in the Columbia (water table), Rancocas, Mt. Laurel, combined Magothy/Potomac A, Potomac B, and Potomac C aquifers, and intervening confining beds. Although the model domain extended north of the Chesapeake and Delaware Canal, south into northern Kent County, east into New Jersey, and west into Maryland, the model focused on the area between the Chesapeake and Delaware Canal, the Delaware River, and the Maryland- Delaware border. Boundary conditions for these areas were derived from modeling studies completed by others over the past 10 years.
The Seaford area geologic mapping project (Andres and Ramsey, 1995) was conducted by Delaware Geo... more The Seaford area geologic mapping project (Andres and Ramsey, 1995) was conducted by Delaware Geological Survey (DGS) staff and focused on the Seaford East (SEE) and Delaware portion of the Seaford West (SEW) quadrangles (Fig. 1). Data evaluated in support of mapping from these quadrangles and surrounding areas are documented in this report.
GIS analysis combined with simple groundwater models provide an efficient and effective screening... more GIS analysis combined with simple groundwater models provide an efficient and effective screening tool to identify suitability of land for rapid infiltration basin systems (RIBS) and other forms of land based wastewater disposal in the State of Delaware. Existing, published, or publically distributed GIS-ready data of suitable spatial resolution are available to evaluate hydraulic and other natural and cultural criteria in the context of compliance with regulation defined isolation distances from the water table, wells, bodies of surface water, and property boundaries. This process addresses suitability in terms of compliance with regulatory requirements but does not evaluate risks for contamination of groundwater, water supply wells, and surface waters. Work in progress is addressing these issues. GIS analysis does not replace the need for competent site specific evaluation for design and permitting of new facilities. However, because the spatial resolution of data is based on a 30...
Journal of Environmental Quality, 2006
A detailed study of water and nitrogen (N) discharge from a small, representative subwatershed of... more A detailed study of water and nitrogen (N) discharge from a small, representative subwatershed of Rehoboth Bay, Delaware, was conducted to determine total N loads to the bay. The concentrations of ammonium (NH 4 +), nitrate + nitrite (NO 3-+ NO 2-), and dissolved and particulate organic N were determined in baseflow and storm waters discharging from Bundicks Branch from October 1998 to April 2002. A novel hydrographic separation model that accounts for significant decreases in baseflow during storm events was developed to estimate N loads during unsampled storms. Nitrogen loads based on gauged flows alone (7100-19,100 kg/yr) significantly underestimated those based on land use-land cover (LULC) and estimated N export factors from different classes of LULC (32,000-40,600 kg/yr). However, when ungauged underflow and associated N loads were included in the total loads (25,500-33,800 kg/yr), there was much better agreement with LULC export models. This suggests that in permeable coastal plain sediments, underflow contributes significantly to N fluxes to estuarine receiving waters, particularly in drier years. Based on the similarity in LULC, N loads from the Bundicks Branch subwatershed were used to estimate upland loads to the entire Rehoboth Bay Watershed (259,000-316,000 kg/yr). These N loads from the watershed were much greater than those from direct atmospheric deposition (49,000-64,500 kg/yr) and from a local wastewater treatment plant (9700-13,700 kg/yr). While the watershed was the principal source of N at all times during the year, the relative contributions from the watershed, wastewater, and direct atmospheric deposition varied predictably with season.
Estuarine, Coastal and Shelf Science, 2012
... Jennifer A. Volk a , 1 , E-mail The Corresponding Author , Joseph R. Scudlark a , E-mail The ... more ... Jennifer A. Volk a , 1 , E-mail The Corresponding Author , Joseph R. Scudlark a , E-mail The Corresponding Author , Karen B. Savidge a , A. Scott Andres b , E-mail The Corresponding Author , Robert J. Stenger c , E ... (1977), Glibert and Loder (1977), and Solorzano and Sharp ...
Journal of Environmental Quality
Scientific Investigations Report, 2006
Biogeochemistry, 2018
Although many climate predictions suggest that the frequency and intensity of large storm events ... more Although many climate predictions suggest that the frequency and intensity of large storm events might increase in the coming decades, few studies document the full impact of such events along their path. Here, we synthesize information on the impact of Hurricane Irene (formed August 21 2011) and Tropical Storm Lee (formed August 30, 2011) on erosion and sediment transport, lake metabolism, riparian hydrology and biogeochemistry, and stream water quality, from North Carolina to Maine. In almost all cases, these storms generated unprecedented changes in water quality (concentrations, loads), from tenfold increases in DOC and 100-fold increases in POC in Maryland, to 100-fold increases in TSS concentrations in Pennsylvania. Overbank flooding and up to 200-year streamflow events were recorded in New York and Vermont. In many cases, particulate loads (e.g. POC, PP, TSS) occurring during Irene and Lee represented more than 30% of the annual load. The dominance of particulate exports over solutes during Irene and Lee is consistent with the mobilization of normally immobile sediment pools, and
Ground water, May 1, 2018
Current national stormwater policy may have adverse effects on public and private water supplies.... more Current national stormwater policy may have adverse effects on public and private water supplies. Shallow groundwater, which is increasingly being relied on for drinking water, irrigation, stream baseflow, and drought relief, is now becoming a sink for unwanted stormwater contaminants to avoid direct discharge to surface water. This policy of infiltration without properly considering implications for groundwater quality should be improved so that society's contaminants are not transferred from one water resource to another just to avoid paying the full cost of today's stormwater management. Stormwater regulatory programs and green infrastructure practices focus first on reducing pollutant loads to surface water, with minimal consideration of pollutant load diverted to groundwater. Best management practices, which provide direct recharge, such as porous pavement, retention ponds, shallow injection wells, as well as agricultural and roadway drains, are commonly used. Frequently the only design criterion for stormwater infiltration is the infiltration rate. Infiltrated stormwater can carry pollutants (nitrogen; pesticides; metals, oil, and grease from road surfaces and gas stations; hazardous waste spills; and salts used in road deicing) as well as cause hydraulic problems (mounding, slope stability, and subsurface flooding of infrastructure). Governmental and professional organizations, including the National Research Council (https://doi.org/ 10.17226/12465), USEPA Underground Injection Control Program, and Water Environment & Reuse Foundation (www.werf.org), have examined the groundwater impact issue, but issued often vague, general cautions about the risks. For instance, the guidance for the
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Papers by A. Scott Andres