Document: AMA-3-59-17

The effect of groundwater contamination by domestic sewage on dissolved inorganic nitrogen fluxes in a Bermudian mangrove bay.

CUNDIFF, A.*

University of California, Berkeley, CA 94704 ¹

Abstract:
Cesspit seepage has been shown to contaminate Bermudian groundwater. However, the ecological significance of this pollution on the mangrove forest and the ocean has not been determined. Water samples from the mangrove forest at Hungry Bay, Bermuda and nearby groundwater were analyzed to test whether outwelling groundwater is a significant source of inorganic nitrogen to the bay and inshore waters. Sea and freshwater mixing were tracked along the tidal inundation gradient to calculate the flux of incoming groundwater in October and November 1999. To construct an inorganic nitrogen budget for the forest, samples were taken over four weeks from house wells in the drainage area, the standing water and creek system in the forest at high and low tide, interstitial forest water, and the bay. Approximately 79.6m3 groundwater enters the forest per hour, carrying between 202 and 238g inorganic nitrogen, virtually all in the form of nitrate. The mean concentration of inorganic nitrogen in ebbing water is 12.33mM. Thus, the flux of inorganic nitrogen from the forest to the bay is 1468g per tidal cycle. In addition to the nitrogen that leaves the forest on the ebb tide, between 2114 and 3014g inorganic nitrogen from groundwater are absorbed by the forest per day. The additional inorganic nitrogen deposited in the bay due to human sources may have adverse eutrophication effects on nearby coastal reef ecosystems. These data suggest that the mangrove forest may sequester excess nitrogen, thereby buffering inshore waters from excess nitrogen loading.

Keywords: inorganic nitrogen, mangrove, groundwater

This abstract is being presented at: 3:15 PM in session:
Oral Session #49: Linkages Between Land and Streams.