Matt Charette and Meagan Gonneea.
Non-point sources of pollution like submarine groundwater discharge represent a significant, yet poorly quantified threat to the ecology of coastal systems throughout the world. Tropical systems may be particularly endangered due to the ongoing and future shifts in land use and coastal management practices. Pollutants such as macronutrients and trace metals must traverse subterranean estuaries, the zone where fresh groundwater mixes with intruding salt water, before discharging into the ocean.
There is a growing body of literature suggesting that biogeochemical transformations within subterranean estuaries play a significant role in modulating material fluxes to the coastal ocean, however, they remain largely unexplored, particularly in tropical regions. We propose to study the geochemistry of trace metals and nutrients in geologically contrasting tropical subterranean estuaries: one in western Panama (Liquid Jungle Lab), and another on the Yucatan Peninsula of Mexico.
This exploratory research will allow us to gain insight into the workings of tropical subterranean estuaries, which in turn will provide key information on an important endmember for global fluxes of nutrients and metals from coastal groundwater systems.
We will visit each site once during the dry season, when the likelihood of a well developed salinity structure in the STE is highest (March 2008). During each visit we will map the subterranean estuary mixing zone by drilling 10 m piezometer profiles along a shore perpendicular transect. We will collect samples for nutrients, trace metals including Ba, Sr, U, Mn, As and Fe, radon and radium, in addition to measuring ancillary water chemistry such as salinity, pH and dissolved oxygen.
We will also collect samples along a shore perpendicular transect, which will provide information about how groundwater associated constituents are mixed and attenuated in the coastal ocean. In the laboratory, we plan on modeling geochemical reactions from each STE by using our flow through reactors with sediment collected at each site.
These laboratory experiments augment the field sampling by allowing us to mimic seasonal changes in water level, and thus see how salt-driven and redox-driven reactions control trace metal dynamics and their potential influence on coastal ocean budgets of these elements.