Spatiotemporal distribution of phycotoxins and their co-occurrence within nearshore waters.

Harmful algal blooms (HABs), varying in intensity and causative species, have historically occurred throughout the Chesapeake Bay, U.S.; however, phycotoxin data are sparse. The spatiotemporal distribution of phycotoxins was investigated using solid-phase adsorption toxin tracking (SPATT) across 12 shallow, nearshore sites within the lower Chesapeake Bay and Virginia's coastal bays over one year (2017-2018). Eight toxins, azaspiracid-1 (AZA1), azaspiracid-2 (AZA2), microcystin-LR (MC-LR), domoic acid (DA), okadaic acid (OA), dinophysistoxin-1 (DTX1), pectenotoxin-2 (PTX2), and goniodomin A (GDA) were detected in SPATT extracts. Temporally, phycotoxins were always present in the region, with at least one phycotoxin group (i.e., consisting of OA and DTX1) detected at every time point. Co-occurrence of phycotoxins was also common; two or more toxin groups were observed in 76% of the samples analyzed. Toxin maximums: 0.03 ng AZA2/g resin/day, 0.25 ng DA/g resin/day, 15 ng DTX1/g resin/day, 61 ng OA/g resin/day, 72 ng PTX2/g resin/day, and 102,050 ng GDA/g resin/day were seasonal, with peaks occurring in summer and fall. Spatially, the southern tributary and coastal bay regions harbored the highest amount of total phycotoxins on SPATT over the year, and the former contained the greatest diversity of phycotoxins. The novel detection of AZAs in the region, before a causative species has been identified, supports the use of SPATT as an explorative tool in respect to emerging threats. The lack of karlotoxin in SPATT extracts, but detection of Karlodinium veneficum by microscopy, however, emphasizes that this tool should be considered complementary to, but not a replacement for, more traditional HAB management and monitoring methods.

Base flow nutrient discharges from lower delmarva peninsula watersheds of virginia, USA.

Proper management of shallow coastal systems, which are vulnerable to nutrient enrichment, requires knowledge of land use impacts on nutrient discharges. This study quantified base flow nutrient concentrations and yields for 1 yr (May 2001-April 2002) from 14 first-order streams on the Virginia Eastern Shore (VaES) on the Delmarva Peninsula and assessed their relationships with land cover and soil drainage class in their watersheds. Base flow water discharge rates (1.4-31.5 cm yr(-1)) were likely lower than the long-term average due to a severe drought. Seasonal mean nitrate concentrations were higher in winter, while mean dissolved organic carbon and ammonium concentrations were higher in summer. Annual base flow-weighted mean total dissolved nitrogen (TDN) concentrations were positively related to percent (%) agricultural land cover (r(2) = 0.43; p = 0.02) and % very poorly drained soils (r(2) = 0.51; p = 0.009) and negatively related to % forested land cover (r(2) = 0.54; p = 0.005). Patterns of base flow TDN yields were similar to those of concentrations but were also positively related to % developed land cover (r(2) = 0.40; p = 0.03). Agricultural and developed land covers, together with very poorly drained soil, accounted for 91% of the variability of TDN yields (p = 0.0001). Using a multiple regression model, the base flow TDN loading rate to a coastal lagoon on the VaES, a system vulnerable to nutrient enrichment, was estimated to be 28,170 kg N yr(-1).

Ground water flow analysis of a mid-Atlantic outer coastal plain watershed, Virginia, U.S.A.

Models for ground water flow (MODFLOW) and particle tracking (MODPATH) were used to determine ground water flow patterns, principal ground water discharge and recharge zones, and estimates of ground water travel times in an unconfined ground water system of an outer coastal plain watershed on the Delmarva Peninsula, Virginia. By coupling recharge and discharge zones within the watershed, flowpath analysis can provide a method to locate and implement specific management strategies within a watershed to reduce ground water nitrogen loading to surface water. A monitoring well network was installed in Eyreville Creek watershed, a first-order creek, to determine hydraulic conductivities and spatial and temporal variations in hydraulic heads for use in model calibration. Ground water flow patterns indicated the convergence of flow along the four surface water features of the watershed; primary discharge areas were in the nontidal portions of the watershed. Ground water recharge zones corresponded to the surface water features with minimal development of a regional ground water system. Predicted ground water velocities varied between < 0.01 to 0.24 m/day, with elevated values associated with discharge areas and areas of convergence along surface water features. Some ground water residence times exceeded 100 years, although average residence times ranged between 16 and 21 years; approximately 95% of the ground water resource would reflect land use activities within the last 50 years.