Hydrologic and nutrient dynamics of a coastal bay and wetland receiving discharge from the Atchafalaya River

This article synthesizes several studies carried out at Fourleague Bay and connecting waterways of the western Terrebonne interdistributary basin of the Mississippi River delta plain, which is strongly impacted by the Atchafalaya River. Hydrologic and nutrient fluxes were measured over two tidal cycles in February, April, and September of 1982. Synoptic water quality sampling of nutrients, sediments, salinity, and chlorophyll a was carried out from April 1986 to August 1991 (17 events), during 1994 (12 events), and from 2000 to 2002 (8 events). Hydrology and nutrient dynamics of the region were controlled by winds associated with cold fronts and Atchafalaya River discharge during winter-spring, and tidal forces during summer-fall. Less than 5% of the water discharged from the Atchafalaya River entered Fourleague Bay, but nonetheless was the dominant source of nutrients, especially nitrate + nitrite (NO (x) ), and sediments. Nitrate + nitrite concentrations entering Fourleague Bay ranged from 33.3 to 118.0 mu M, with highest levels occurring during peak river discharge. Fourleague Bay was a sink for DIN, with retention rates ranging from 184.4 to 704.2 mu g-at m(-2) h(-1), but both a source and sink for DIP, with retention rates ranging from -2.7 to 14.9 mu g-at m(-2) h(-1). Concentrations of DIN and DIP in the bay ranged from below detection limits to 49.0 and 29.1 mu M, respectively, while chlorophyll a ranged from 6.1 to 49.4 mu g/l. In the wetlands surrounding Fourleague Bay, chlorophyll a generally mirrored NO (x) and TSS, and generally peaked 2-15 km from riverine sources.