Abstract
The Central Wetlands Unit (CWU), covering 12,000 hectares in St. Bernard and Orleans Parishes, Louisiana, was once a healthy baldcypress–water tupelo swamp and fresh and low salinity marsh before construction of levees isolated the region from Mississippi River floodwaters. Construction of the Mississippi River Gulf Outlet (MRGO), which funneled saltwater inland from the Gulf of Mexico, resulted in a drastic ecosystem change and caused mortality of almost all trees and low salinity marsh, but closure of the MRGO has led to decreases in soil and surface water salinity. Currently, the area is open water, brackish marsh, and remnant baldcypress stands. We measured hydrology, soils, water and sediment chemistry, vegetation composition and productivity, accretion, and soil strength to determine relative health of the wetlands. Vegetation species richness is low and above- and belowground biomass is up to 50% lower than a healthy marsh. Soil strength and bulk density are low over much of the area. A baldcypress wetland remains near a stormwater pumping station that also has received treated municipal effluent for about four decades. Based on the current health of the CWU, three restoration approaches are recommended, including: (1) mineral sediment input to increase elevation and soil strength; (2) nutrient-rich fresh water to increase productivity and buffer salinity; and (3) planting of freshwater forests, along with fresh and low salinity herbaceous vegetation.
Highlights
The Pontchartrain Basin is a 1.2 million-ha coastal watershed in southeast Louisiana and southwestMississippi
Conductivity, which is directly related to salinity, showed similar trends to salinity. pH was similar among all sites and fluctuated primarily between 7.0 and 8.0
total dissolved solids (TDS), total suspended solids (TSS), and volatile suspended solids (VSS) concentrations were higher near the 40 Arpent Canal, and generally decreased when moving towards the Mississippi River Gulf Outlet (MRGO) levee (Table 3)
Summary
The hydrology of the Basin has been extensively altered due to construction of levees along the Mississippi River, closure of old distributaries [1,2,3,4,5,6], dredging of canals for navigation and oil and gas development [4,7,8,9], drainage of upland areas Gulf and Outlet (MRGO) [5,12,13] These hydrologicofalterations decreased area), creation of River spoil banks impoundments [10,11], and construction the Mississippi. IncreasedThese saltwater intrusion, along with changing the way thatand water moves Gulf. Hydrologic alterations decreased freshwater input increased through intrusion, the Basin. Freshwater wetland species, such As as a result, baldcypress saltwater along changingmany the way that water moves through the Basin
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