Seawater Circulation in Coastal Aquifers: = Processes and Impacts| Research Project Database | NCER | ORD

Seawater Circulation in Coastal Aquifers: Processes and = Impacts

EPA=20 Grant Number: F07B30483
Title: Seawater Circulation in = Coastal=20 Aquifers: Processes and Impacts
Investigators: Karam,=20 Hanan N.
Institution: Massachusetts=20 Institute of Technology
EPA Project = Officer: Cobbs,=20 Gladys M.
Project Period: January 1, 2007 through January = 1, 2010=20
RFA: STAR=20 Graduate Fellowships (2007)
Research Category: Aquatic=20 Ecology and Ecosystems , Fellowship=20 - Hydrology , Fellowship=20 - Groundwater Dynamics in Coastal Aquifers , Academic=20 Fellowships

Description:

Objective:

In coastal aquifers, groundwater has two origins, inland meteoric = recharge=20 and seawater. Hence, subsurface flow dynamics are driven by unstable = density=20 variations and by hydraulic head gradients, which are subject to = time-varying=20 forcings at both the terrestrial (e.g. seasonally varying recharge) and = marine=20 (e.g. tides and waves) boundaries of these aquifers. These forcings = drive a=20 circulation of seawater in the subsurface of potentially great = ecological=20 significance: it increases subsurface mixing between fresh groundwater = and=20 seawater and provides a mechanism to continuously flush submarine = sediments,=20 enhancing chemical exchange between the aquifer and the overlying water = column;=20 additionally, it may play a role in the breakdown of marine-derived = organic=20 matter, and hence contribute fundamentally to the nutrient cycle of = coastal=20 ecosystems. However, seawater circulation in coastal aquifers is still = poorly=20 understood: its characteristic spatial and temporal scales and the = relative=20 importance of various forcings are unclear. The goal of this project is = to=20 quantitatively model the rates and patterns of this circulation, = capturing its=20 most important spatial and temporal scales and their relationship to = various=20 landward and seaward forcings, and elucidating its control on the extent = of=20 subsurface mixing between fresh groundwater and seawater.

Approach:

High-resolution, long-term data will be collected describing the = groundwater=20 system at the head of Waquoit Bay, located on the south shore of Cape = Cod, MA.=20 The effects of forcings with different timescales (hours to seasons) on=20 groundwater dynamics will be analyzed. Differential pressure sensors and = a=20 fiber-optic temperature sensing cable will be used to monitor exchanges = between=20 the subsurface and the water column. The pressure sensors will provide = time=20 series of head gradients across the bay floor, which can be used to = infer the=20 direction and rate of water flux across the water-sediment interface. = The=20 fiber-optic cable will provide time series of bay bottom temperatures, = which=20 will also be used to calculate water fluxes through heat transport = modeling.=20 Additionally, electrical resistance tomography (ERT) data on subsurface=20 resistivity will be used to understand the evolution of salt = distribution in the=20 coastal aquifer over a year=E2=80=99s duration, particularly the mixing = patterns of=20 fresh groundwater and seawater and the movement of fresh-saline mixing = zones in=20 response to the various forcings. The field data will be used to develop = and=20 constrain a numerical model of the local groundwater dynamics, which = will then=20 be generalized to investigate other coastal systems.

Expected Results:

To provide new understanding of patterns and rates of seawater = circulation in=20 coastal aquifers, which will contribute to research on seawater = contamination of=20 fresh coastal aquifers, groundwater-transported pollution of marine=20 environments, and nutrient cycling in these environments.

Supplemental Keywords:

coastal groundwater, marine pollution, seawater intrusion, heat = transport=20 modeling, electrical resistance tomography (ERT), numerical = modeling, ,=20 Scientific Discipline

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The perspectives, information and conclusions = conveyed in=20 research project abstracts, progress reports, final reports, journal = abstracts=20 and journal publications convey the viewpoints of the principal = investigator and=20 may not represent the views and policies of ORD and EPA. Conclusions = drawn by=20 the principal investigators have not been reviewed by the = Agency.

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Seawater Circulation in Coastal Aquifers: Processes and = Impacts

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