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Coastal loss in southern Louisiana is dependent upon sediment accumulation; the speed at which this sediment accumulates or erodes is largely dependent upon microbially-driven decomposition rates. This project studied decomposition in Lake Pontchartrain Basin wetlands, in combination with measurements of microbial activity and community structure.

Decomposition in these wetlands is slow, and there are limiting factors on microbial activity. This suggests that changes in water flow and nutrient concentrations associated with restoration efforts will have major impacts on microbial processes. For example, freshwater diversion efforts might bring in nutrients and oxygenated water that, by all predictions, would likely stimulate the plant community. It is assumed that greater plant growth would result in more organic matter accrual in sediments and reduce wetland loss rates. But what if the microbial decomposer community is also stimulated, so that this additional input of organic matter is decomposed rather than accumulates?  Surveys of bacterial communities indicate that these wetlands also contain many different species of microorganisms, some of which are likely new to science.

More on this study:

Development of an Index of Biological Integrity for Lake Pontchartrain Basin Wetlands PI: Bossart, Jackson, Abdelghani Determining the Potential for Algal Bloom in Lake Maurepas: Effects of Changing Nutrient Load from Freshwater Diversion and Changes in Human Population PI: Voegel, Pinckney, Passey

Our microcosm studies show that salinity depresses microbial enzyme activity, and the decomposition study shows that this enzyme activity directly correlates with decomposition rate. Reduced salinity levels may have the opposite effect – stimulating microbial activity, which in turn would accelerate the decomposition process. Estimating decomposition activity relative to diversion-delivered sediment and plant growth will be an important part of Louisiana’s restoration efforts.

The development of the enzyme models that relate decomposition to enzyme activity is probably the most profound impact of this project. Because such models allow the rapid monitoring of decomposition, the approach would have broader management implications. A project that is about to be initiated as part of the Phase V program will monitor microbial enzyme activities in sediments around Lake Maurepas, with a particular focus on sites that are likely to be impacted by Mississippi River diversion efforts. In collaboration with Dr. Janice Bossart (Southeastern), the enzyme activities will be combined with studies of aquatic invertebrate community structure and diversity to develop holistic biotic indices for environmental quality in this system. Such indices have great value in evaluating both the short and long-term impacts of environmental perturbations.