PLANKTON DYNAMICS IN AN URBAN, SUBTROPICAL LAKE PRIOR TO LAKE RESTORATION

This research assessed plankton dynamics in two urban, subtropical lakes (University Lake and City Park Lake) shortly before a proposed and approved lake restoration project. Plankton dynamics were determined in University Lake by the dilution method to attempt to quantify growth rates of phytoplankton and grazing rates of zooplankton. Landry and Hassett’s (1982) dilution method has been widely used in marine systems to estimate rates of growth and grazing. In many marine systems, nutrients must be added to prevent nutrient limitation. However, it is assumed, due to the hypereutrophic conditions, that nutrients would not be a limitation in University Lake. From October 2018 to March 2020, the average initial chlorophyll concentration was 231.7 µg L−1 and the average temperature was 20.1 ºC. The average net growth from dilution experiments was 0.02 d−1. The expected result is that dilution will influence grazing, and net growth rates should increase with increasing dilutions, but 14 cases did not change with dilution. In four cases, growth rates were estimated and average 1.55 d−1. Additionally, zooplankton sampling was conducted in University Lake and City Park lake from October 2019 to March 2020 to evaluate zooplankton composition over time. The largest quantities and species diversity were collected in City Park Lake near the interstate. The difference between composition and quantity in University Lake may be due to the differences in depth at the sampling sites.