Biogeochemical Influence of Chinese Privet in Riparian Forests in West Georgia and the Influence of Oyster Harvesting in Apalachicola Bay, Florida

Abstract

In the Southeastern U.S., urbanization influences nutrient availability, species composition, and water quality among other ecosystem processes. This study examined the influence of invasive species spread, facilitated by urbanization; and the influence of oyster harvest due to changes in water quality/quantity resulting from urbanization in Apalachicola Bay, FL. First, Chinese privet (Ligustrum sinense Lour.) was studied to document biogeochemical changes as it becomes more abundant in riparian forests in Georgia. To determine Chinese privet’s influence on biogeochemistry, decomposition rates, litterfall nutrient dynamics, nutrient use efficiency (NUE), nitrogen mineralization rates, and microbial biomass were assessed. Study sites were divided into three different classes (severely invaded>80%, moderately invaded 25-79%, and uninvaded 0%) based on percent of Chinese privet in understory. Two decomposition studies were conducted: one with site specific litter on different microsites and one with predetermined litter bag composition on a single microsite. Both studies indicated Chinese privet increased the rate of decomposition. Chinese privet litter quality was higher than that of native species, because it had lower concentration of the recalcitrant materials lignin and cellulose and high nutrient concentrations. Litterfall had greater mass, carbon content, and N content in moderately invaded sites than in uninvaded or severely invaded sites. Land use had a greater influence on N-NUE than Chinese privet did and urban sites had inefficient N-NUE. N-mineralization was greater in moderately and severely invaded sites for summer collections and microbial biomass tended to be higher in moderately and severely invaded sites. Results from this study indicate that Chinese privet alters nutrient cycling processes in riparian forests. In the second study, water quality/quantity and economic influence of oyster harvest were examined in relation to land use conversion in Franklin and Gulf counties neighboring Apalachicola Bay, FL. There was a negative relationship between % of the Bay closed and quantity of oysters harvested. There was significant negative relationship between discharge of the Apalachicola River at the Blountstown gauging station and quantity of oysters harvested. Water quality, as measured by fecal coliform abundance, was not significantly influenced by the land use changes in Franklin and Gulf counties from 1995-2005. Closures of <25% harvestable area resulted in an unrealized value >$45,000 per month. Land use change in the entire watershed may have greater influence on discharge and water quality entering the Bay but was not included in this study.