Anthropogenic and climatic stressors impact the health of coastal ecosystems, but the synergistic effects of both kinds of stressors are not well understood. Long-term (2000 – 2008) water quality and biological data were collected from three shallow lagoons in the Perdido Bay system, Florida. These lagoons have similar physical and hydrological characteristics but cover a wide gradient of human watershed development, i.e. one lagoon is pristine (State Park, SP), another one is moderately developed (Kee’s Bayou, KB), and the third one is highly developed (Gongora Canal, GC). Here we examine (1) long-term (2000 – 2008) water quality (i.e. nutrients, oxygen) and biotic (i.e. algae, seagrass, benthic fauna) trends and responses to increasing watershed developments, and (2) the interactions between the urban stress and climatic events (i.e. 16 storms and hurricanes that made landfall in the systems during the study period).

Results/Conclusions

Nutrient (total dissolved nitrogen, nitrite, and phosphate) concentrations increased with higher urban development in the studied lagoons. In addition, during the period 2002 – 2005, nitrate and ammonia concentrations increased in all the lagoons following the passage of storms. In particular, high concentrations of nitrate (e.g., nitrate > 4 mg/L) were observed in the moderately (KB) and highly (GC) developed lagoons after the 2003 and 2004 tropical storm seasons and mean ammonia concentration increased to 14 mg/L in the highly urbanized GC lagoon after the passage of tropical storm Bonnie and Hurricane Ivan in 2004. Higher concentrations of chlorophyll a in both water column and bottom were found with increased urban development. No seagrass was observed in the highly developed GC lagoon, most likely due to elevated shading by high water column chlorophyll a concentrations. Seagrass was healthiest in the pristine SP lagoon and displayed the highest abundance of benthic fauna over the whole study period. Our results show that climatic events increased nutrients stress from the watersheds but did not shift the overall biological trends. Yet, longer term monitoring is needed to fully detect the interactions of urban development and other longer-term climatic alterations such as sea level rise.