Ecological Indicators of Restoration Success: Zooplankton as Indicators of Lake Change in a Dredged Southwest Florida Lake

Eutrophication, caused by excess inputs of nutrients in lakes, rivers, estuaries, and coastal oceans, is a worldwide problem. Although the addition of nutrients may lead to abrupt increases in eutrophication, immediate decreases of such inputs do not always cause rapid or complete reversal of eutrophic conditions. Internal nutrient loading will often drive the eutrophication status of the lake and delay its recovery. Internal loading can often be vastly decreased by sediment removal through sediment dredging, which has been used in many lake restoration projects as an eco-engineering technology. However, it is still a controversial technique.;Biological assessments are currently the chief method used to determine the integrity or "bio-integrity" of an ecosystem. Aquatic invertebrates are an integral part of freshwater biotic communities and can be used to indicate disturbance or recovery of aquatic systems. Zooplankton is a major contributor to the importance of invertebrates within aquatic systems. Zooplankton have potential value as indicators of changing trophic state since community structure and composition are greatly affected by disturbed conditions such as eutrophication. The objectives of this study were to: i) examine the spatial and temporal patterns of zooplankton in Lake Trafford, ii) explore possible controlling factors for changes in the zooplankton community (including water parameters and phytoplankton), and iii) evaluate the potential use of zooplankton community characteristics as a measure of lake health in a post dredged southwest Florida lake.;Our findings indicate spatial distribution of zooplankton is highly variable within Lake Trafford and the influence of wind and wind driven waves seem to be the driving factors for this water body. Seasonal patterns of zooplankton abundance are opposite of the normal summer peaks and winter lows. In addition the seasonal peaks appear to be becoming less severe over time thus, potentially indicating a more stable lake ecosystem subsequent to dredging. The stabilization and indication of the altered community structure is apparent and may be a precursor to major lake change. It appears that a transitional period is taking place and continued monitoring should ideally reveal a definitive lake change. Temperature was shown to be the most important abiotic factor driving zooplankton abundance. Zooplankton was indeed negatively correlated with temperature in Lake Trafford. Water temperature and conductance were key factors during the spring and summer seasons while other abiotic factors (DO, pH, light penetration, and wind) were more important in the winter and fall. A significant correlation between phytoplankton and zooplankton was found; however, their relationship is weak. Further study into alternative bottom-up control is suggested.;Unique spatial and temporal patterns of zooplankton abundance exit in Lake Trafford. Continued monitoring of zooplankton may help illuminate post-dredging biotic dynamics and guide management decisions. A deeper understanding of Lake Trafford dynamics may help inform management decision on other eutrophic subtropical lakes.