Hydrologic fragmentation-induced eutrophication in Dove Sound, Upper Florida Keys, USA

Anthropogenic impacts to island systems can have deleterious effects on coastal aquatic ecosystems. These effects can alter water quality, primary production as well as habitat. Land development often fragments hydrologic connectivity within aquatic ecosystems forcing alterations in nutrient transport and increases the potential for eutrophication. Dove Sound, a tidal lagoon located in the Upper Florida Keys on Key Largo, has been subjected to anthropogenic influences of land development during the last century. To investigate these influences a short sediment core was collected from within Dove Sound and investigated using Pb-210 dating, stable isotopes of carbon and nitrogen, and sedimentary pigments. Results indicated that Dove Sound has undergone eutrophication and the primary producer community structure has shifted from dominantly macrophytic to a system that supports substantial algal production. While septic waste was a possible source for eutrophication, low delta N-15 did not support this conclusion. However, the timing of the shifts in Dove Sound along with indicators of anoxia leads to the conclusion that fragmentation caused by the construction of a railroad was the root cause. The hydrologic fragmentation reduced the flushing rates, thereby enhancing anoxic conditions in the system and increasing the internal nutrient loading.