State Water Resources Research Institute Program

Project ID: 2008GU165B
Title: Baseline Study of Coastal Discharge of Groundwater on Guam
Project Type: Research
Start Date: 2/27/2009
End Date: 2/28/2010
Congressional District:
Focus Categories: Groundwater, Hydrogeochemistry, Hydrology
Keywords: Groundwater discharge, Groundwater quality
Principal Investigator: Jenson, John
Federal Funds: $ 10,316
Non-Federal Matching Funds: $ 0
Abstract: At its September 12, 2008 meeting, the Guam Water Resources Advisory Council identified "Baseline studies to help identify the locations and levels of key contaminants impacting Guam's ground and surface resources, and the processes that might explain their presence" as one of its research priorities under "Ground, surface, and coastal waters."

We still know very little about how the total volume of aquifer discharge is distributed across the coastal zone or how much the flux may vary over time at any given discharge point in response to storms or seasonal variations in rainfall. We also lack baseline data on the concentrations of nutrients or toxins that may come from any given discharge feature and how concentrations might vary with seasonal or other changes in rainfall intensity. The proposed research would provide new and heretofore unattainable baseline information on the mass flux distribution and concentrations of nitrogen in the groundwater that discharges into the coastal waters surrounding the limestone plateau of northern Guam. This information is needed by managers and regulators of Guam's fresh water and coastal resources, including the Guam Waterworks Authority, Guam Environmental Protection Agency, and Department of Aquatic and Wildlife Resources.

Two naturally-occurring tracers of coastal groundwater discharge will be used to quantify the groundwater and associated nutrient flux to the coastline of Guam: radium isotopes and radon-222. Nutrients will be collected from groundwater using piezometers (wells) installed on the beach, from visible seeps, in stream waters (where applicable), and from coastal seawater. To evaluate the current and future impact of coastal groundwater discharge-derived nutrient flow on the coastal marine ecosystem, we will (1) examine natural abundance stable nitrogen isotopic signature of marine biota and (2) construct a nitrogen loading model (NLM) that can be applied to other Pacific Island marine ecosystems.

The proposed research would constitute a baseline study to identify not only the spatial and temporal distribution of the discharging groundwater mass, but also to provide insight into the source locations and levels of a key contaminant, nitrogen, impacting Guam's groundwater, and the processes that might explain its presence. It will also provide some new insight into the e

Progress/Completion Report, 2008, PDF
Progress/Completion Report, 2009, PDF

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