SEDIMENT ARCHIVE OF SEAGRASS DYNAMICS IN NORTHERN INDIAN RIVER LAGOON, FL

Seagrasses are an integral part of nearshore and estuarine environments in Florida, serving not only as a potential carbon sink, but also providing a food source for fish, waterfowl, and other herbivorous species. Unfortunately, Florida’s seagrass beds have experienced significant historical declines. Seagrass decline and intense algal blooms are likely two of the biggest environmental problems facing Florida’s estuaries and the two problems are related. Algal blooms reduce sunlight penetration and are a factor contributing to seagrass loss. A sediment probe survey was undertaken to identify the depth and age of organic sediment deposits within seagrass beds in Mosquito Lagoon, a sub-lagoon of the northern part of the Indian River Lagoon, FL. Basal ages of six cores were obtained through radiocarbon dating and the deposits ranged from modern to ~700 cal yrs BP. Two of the cores were sub-sampled and analyzed for bulk density, carbon to nitrogen ratios, and stable carbon isotope ratios. Preliminary results from the analyses suggest an increase in microalgal or phytoplankton markers towards the top of the cores, highlighting the presence of recent, intense blooms in the lagoon. However, the age control required to determine exact timing of this increase is lacking. Average carbon sequestration rates were determined for these cores and ranged from 2.0 to 3.6 x 10^-3 g C cm^-2 yr^-1. There was significant decomposition with depth. Our work shows that these seagrass beds contain an archive of paleoenvironmental information on the scale of hundreds of years and that they rapidly sink carbon.