Benthic Nutrient Fluxes across Subtidal and Intertidal Habitats in Breton Sound in Response to River-Pulses of a Diversion in Mississippi River Delta

Abstract

We measured benthic fluxes of dissolved nutrients in subtidal sediments and intertidal soils associated with river-pulse events from Mississippi River via the operation of a river diversion structure at Caernarvon, LA. Experiments measuring benthic fluxes in subtidal habitats were conducted during the early spring flood pulse (February and March) each year from 2002 to 2004, compared to benthic fluxes of intertidal habitats measured in February and March 2004. Nitrate (NO3−) uptake rates for subtidal sediments and intertidal soils depended on overlying water NO3− concentrations at near-, mid-, and far-field locations during river-pulse experiments when water temperatures were >13 °C (NO3− removal was limited below this temperature threshold). NO3− loading to upper Breton Sound was estimated for nine river-pulse events (January, February, and March in 2002, 2003, and 2004) and compared to NO3− removal estimated by the subtidal and intertidal habitats based on connectivity, area, and flux rates as a function of NO3− concentration and water temperature. Most NO3− removal was accomplished by intertidal habitats compared to subtidal habitats with the total NO3− reduction ranging from 8% to 31%, depending on water temperature and diversion discharge rates. River diversion operations have important ecosystem design considerations to reduce the negative effects of eutrophication in downstream coastal waters.