Effects of nutrient load from St. Jones River on water quality and eutrophication in Lake George, Florida

Abstract

Nutrient contamination in surface waters can pose a health risk for humans and aquatic life. The influx of Nitrogen and Phosphorus can cause an increase in algal blooms resulting in eutrophication of the water body. Eutrophication describes the trophic state or the health of a water body as it relates to the level of algae biomass. Water quality for this research is represented by the presence of chlorophyll a (Chl-a) which is an indicator of the activity within the water body. In this study, trophic state analysis and relations between Chl-a and nutrients in Lake George, Florida, have been conducted. Three zones within Lake George are established to prepare a succinct analysis of the existing monthly and seasonal averages across the water body. Statistical analyses, including multiple regression analysis, were used in this study to establish the relationship between Chl-a and nutrients, Total Nitrogen (TN) and Total Phosphorus (TP). Traditional single-variable regression analysis shows good correlations between the Chl-a and TN loading and poor relationship with TP, which indicate that TN loading is the controlling factor. Single-variable regression was also used to compare the inlet load contributions to the lake loading which was found to be conclusive. Multivariate regression analysis for all three zones were conducted to obtain acceptable to good relationship between Chl-a and nutrient (TN, TP) with the monthly R values for zones 1, 2, 3, are 0.72, 0.82, and 0.80 respectively, indicating nutrient is the dominant factor for eutrophication in the lake. Multivariate regression equations between Chl-a and nutrient (TN,TP) were used to investigate scenarios to reduce nutrient load at the inlet so as to control Chl-a concentrations in the lake to avoid eutrophic conditions. It was found that the TN inlet loading would have to be reduced by more than 75% for zone 1, 65% in zone 2 and less than 25% for zone 3 in order to not exceed the current EPA approved numeric criteria for Florida Lakes. It was also determined that both TN and TP concentrations are co-limiting in the lake based on Carlson’s criteria. Assessments by both Trophic State Index (TSI) method and Total Nutrient Status Index (TNI) methods indicate eutrophic conditions in the lake under current conditions.