Assessment of present and future nitrogen loads, water quality, and seagrass (Thalassia testudinum) depth distribution in Lemon Bay, Florida

Nitrogen loads into Lemon Bay, Florida were modeled to have increased ca. 59% between pre-development (i.e., 1850) estimates (5.3 kg TN ha(-1) yr(-1)) and estimates for the year 1995 (8.4 kg TN ha(-1) yr(-1)). By the year 2010, nitrogen loads are predicted to increase an additional 45% or 58%, depending upon progress being made toward replacing older septic tank systems with centralized sewerage (nitrogen loads of 12.2 and 13.3 kg TN ha(-1) yr(-1), respectively). Using 1995 estimates, nonpoint sources (stormwater runoff) are thought to be responsible for ca. 76% of the annual nitrogen load, folllowed by septic tank systems (14%), rainfall (10%), and an insignificant load from baseflow. Based on an empirically-derived nitrogen load:chlorophyll a relationship developed for a portion of nearby Tampa Bay, a 45% increase in nitrogen loads into Lemon Bay could result in a 29% increase in annual average chlorophyll. a concentrations. Using the estimate of a 29% increase in future chlorophyll a concentrations, an empirically-derived optical model for Lemon Bay suggests that light attenuation coefficients in the bay would increase ca. 9%, and the average depth limit of Thalassia testudinum in Lemon Bay would decrease by ca. 24%.