EFFECTS OF 2 LOUISIANA MARSH MANAGEMENT PLANS ON WATER AND MATERIALS FLUX AND SHORT-TERM SEDIMENTATION

The impact of two coastal Louisiana marsh management plans on water and materials flux, shortterm sedimentation, and several soil parameters was evaluated between May 1989 and January 1990. The study was carried out in the Fina-Laterre Marsh Management Area and the Rockefeller State Wildlife Refuge in managed and unmanaged areas. Water and material flux was measured each two hours during twelve 48 h flux studies, and net fluxes per m(2) of drainage area were calculated for water, total suspended sediments, salinity, NO3+NO2, PO4, and NH4. Short-term sedimentation was measured as the weight of material deposited over 2-4 week intervals on petri dishes placed on the marsh surface. The managed sites experienced considerable reductions in total water exchange, leading to reductions in net material exchanges. when expressed on a per m(2) basis, the managed wetlands are much less tightly coupled to the surrounding estuary compared to unmanaged areas. Within the context of a general decrease of exchange, the two managed areas on average export materials to the estuary. In the managed areas, the results suggest that management can lead to reduced salinity and a loss of sediments and nutrients. Short-term sedimentation was less at the managed areas; expressed as g m(-2)d(-1), total sedimentation rates were 0.57 for Fina managed, 1.02 for Fina unmanaged, 1.68 for Rockefeller managed, and 3.82 for Rockefeller unmanaged. Soil P was lower and soil organic matter was higher at the managed areas. Organic matter in the soil was low compared with recently deposited material, suggesting that most organic matter deposited on the surface of the marsh is lost through decomposition. Reduction of flooding during storm events is the likely mechanism leading to reduced sedimentation on the marsh surface in the managed areas.