Assessing the effects of increased summer flooding in an impounded mangrove with the use of remote sensing

Mangrove impoundments on the Indian River Lagoon, Florida, were constructed as a method for mosquito control. Artificial dikes were built up around the marsh areas to keep the mangroves continuously flooded as the black salt marsh mosquito, which is common in the area, will not oviposit in standing water. By 1959 over 3,240 ha of wetlands were impounded in the Indian River Lagoon (Rey et al., 2012). Continuous impounding is known to have negative effects on the health of mangrove vegetation. A simple change in water management: using a rotational impoundment management (RIM), was hypothesized to prevent the adverse consequences of continuous impounding, while at the same time allowing for noxious insect control. RIM involves the pumping of estuarine water into the impoundments to raise the water by 30 cm in spring and summer, the reproductive season of the black salt marsh mosquito. With this thesis I assessed the effects of the RIM strategy in an impounded mangrove in Florida, five years after the implementation of RIM. More specifically I examined whether there have been changes in the spatial distribution and state of the dominant black mangrove vegetation on the scale of the impoundment, before and after the implementation of RIM by making use of aerial photographs and high resolution satellite data. To follow distribution and extent of the mangrove vegetation I performed a land-cover classification with different classes of vegetation on color infrared aerial photographs from 2008 and 2010 and a Worldview-2 satellite image from 2014. In addition I created a map of leaf area index (LAI) by linear regression of vegetation indices and in situ collection of LAI to assess the current productivity of the vegetation on the scale of the mangrove impoundment. I found that an increase in mangrove vegetation took place after implementation of RIM in the mangrove impoundment and that the productivity of the vegetation measured by NDVI increased by 8% over the whole impoundment. The greatest shifts took place in areas without vegetation cover or with stunted mangrove vegetation, associated with hypersaline conditions. Productivity measured by NDVI in those regions increased on average by more than twofold. The succession towards denser classes of vegetation at the hypersaline interior indicated that re-establishment of mangrove vegetation took place. However, I found that current productivity over the whole impoundment, years after implementation of RIM, nonetheless remained lower than that of mangrove vegetation that was not impounded