Factors influencing algal biomass in hydrologically dynamic salt ponds in a subtropical salt marsh

Abstract

The interface between land and water is often a dynamic zone that responds to relatively short-term climatic and hydrologic forces. Coastal salt marshes occupy this zone between land and sea and typically are comprised of vegetated marsh intersected by channels and shallow ponds that are subject to flooding by winds, tides, and storm surges. Coastal salt marshes are widely regarded as zones of high macrophyte productivity. However, microalgae may contribute more to salt marsh productivity than previously realized, underscoring the importance of understanding algal dynamics in such systems. Benthic and planktonic chlorophyll-a (surrogate for total algal biomass), sediment AFDW, total suspended solids, salinity, and nutrients were examined in marsh ponds in the subtropical Guadalupe Estuary, TX, USA to determine the effects of hydrologic connections on algal biomass in this system. From May 2005 – May 2006 there were several pond connection, disconnection, and desiccation events. During periods of disconnection, algal biomass was higher in both the benthos and the water column than during connection events when supposed flushing occurred. Connection events also flushed out high NH4 accumulating in pond surface waters, but did not increase NOx. Therefore, the primary source of DIN seemed to be nutrient cycling within the ponds. There was a temporal effect on surface water salinity, which increased throughout the sampling period as bay water levels and subsequent pond connections decreased, demonstrating interannual variability and the link between seasons (wet vs. dry) and marsh inundation patterns (high water periods vs. low water periods) in this estuary.