Submarine groundwater discharge of nutrients and copper to an urban subestuary of Chesapeake Bay (Elizabeth River)

Abstract

We investigated the role submarine groundwater discharge (SGD) plays in the delivery of nutrients and copper to the Elizabeth River (Virginia) estuary, a major subestuary of lower Chesapeake Bay. Using an approach based on radium isotopes, we concluded that two distinct sources of groundwater were equally impacting the estuary: a surface (marsh) aquifer and deep aquifer source each with a unique 228 Ra/ 226 Ra activity ratio. Considering each of these sources, we calculated an SGD flux of 1 ϫ 10 6 m 3 d Ϫ1 (Ϯ10%), which represented ϳ6% of the SGD flux for the entire Chesapeake Bay and ϳ5% of the James River, a major source of freshwater to lower Chesapeake Bay. SGD-derived dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) fluxes averaged 4.5 (Ϯ4.6) and 0.16 (Ϯ0.17) mmol m Ϫ2 d Ϫ1 , respectively, and compared well with area-normalized fluxes to Chesapeake Bay. In contrast, SGD-derived Cu input of 730 (Ϯ390) kg yr Ϫ1 was a relatively small source of Cu (ϳ3%) to the Elizabeth estuary given that surface water inputs, such as antifouling paints associated with naval operations, are a major component of the Cu budget for this system. These findings were in general agreement with prior studies of SGD for this region.Submarine groundwater discharge (SGD) is often ignored when constructing geochemical budgets for elements in nearshore environments, mainly because the volume flux is difficult to estimate. However, many studies indicate that SGD may carry significant quantities of nutrients and trace metals to the ocean Moore 1996;Krest et al. 2000;Montlucon and Sanudo-Wilhelmy 2001). In the case of nutrients, SGD has been the principal mechanism for eutrophication in many coastal embayments throughout the world (e.g., Valiela et al. 1990).Various approaches for quantifying SGD include water budgets, seepage meters, and natural tracers (see review by Burnett et al. 2001). The water budget approach, which attempts to balance aquifer inputs (precipitation) with losses (evapotranspiration), often results in a large uncertainty, since SGD is the difference between two very large numbers (e.g., Cambareri and Eichner 1998). Seepage meters, though useful for understanding local-scale patterns of SGD, are labor intensive and therefore require significant effort for quantifying SGD on large spatial scales (e.g., Michael et al.

Denitrifier Community Composition along a Nitrate and Salinity Gradient in a Coastal Aquifer

“…Nitrate concentrations ranged from 0.5 M at station A to 331 M at station D, indicating a pronounced nitrate gradient across the study site (Table 1). Ammonium concentrations ranged from a low of 9.2 M at station A to a maximum of 160 M at station C. Although the ammonium concentrations were high compared to those in typical estuarine and marine water columns, they are not atypical of porewaters (8,11,17), which have reported concentrations in excess of 1 mM. Salinity increased in the cross-shore direction as nutrient concentrations decreased and ranged from 8 practical salinity units (psu) at station E to 33 psu at station A.…”

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

“…Again, the mobilization of these metals in groundwater was attributed to the Fe and Mn redox cycles and the suspected low pH of the groundwater as it passed through the sediment deposits left behind from mining activities. Charette and Buesseler [2004] studied copper (Cu) fluxes in SGD near a naval base on the eastern coast of the United States, but found that this source was minor compared to that from Cu-based antifouling paints used on boat hulls. Beck et al [2009] compared SGD-derived metal inputs to those from treated wastewater inputs to a surface estuary near New York City.…”

An evaluation of submarine groundwater discharge along the continental shelf of Louisiana using a multiple tracer approach

“…However, the use of multiple tracers should alleviate many of the complexities associated with assessing groundwater in the system. Many studies have utilized natural geochemical tracers to quantify groundwater in coastal systems [Cable et al, 1996a;Moore, 1998;Corbett et al, 2000;Top et al, 2001;Charette and Buesseler, 2004], which are found in elevated concentrations relative to surface waters [Davis et al, 1980]. This study incorporates 222 Rn and 4 He/ 3 He/ 3 H as natural tracers of groundwater.…”