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.
Highlights
Diverting freshwater from the Mississippi River into adjacent coastal wetlands and estuaries is one approach to the comprehensive restoration plan being implemented in coastal Louisiana to reduce delta degradation [1,2]
Water conductivity indicates how much of these changes may be related to mixing with higher salinity water in lower Breton Sound as the near field station ranged from 264 to 473 μS/cm compared to the higher value of 1605 μS/cm at FF-2 in March 2004
The fate of NO3− input from river-pulse events associated with diversion operations is a function of how diverted water is distributed over subtidal and intertidal habitats
Summary
Diverting freshwater from the Mississippi River into adjacent coastal wetlands and estuaries is one approach to the comprehensive restoration plan being implemented in coastal Louisiana to reduce delta degradation [1,2]. The concept of reconnecting the river to its floodplain as a means of restoring wetlands is rooted in the river-pulse concept of enhancing biological productivity and maintaining diversity in a river-floodplain ecosystem [3,4,5,6] This idea evolved from the river continuum concept [7], which describes the development of the structure and function of biotic communities along a longitudinal gradient in dynamic equilibrium with the physical environment [8]. The largest sediment diversion project being designed for the mid-Barataria coastal basin is rated at 2124 m3/s, which will be one of the largest river diversion projects in the country These diversions are part of a comprehensive approach to utilize the river-pulse of the Mississippi River to reduce wetland losses in Mississippi River Delta [14]
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