Changes in algal communities in different habitats and environmental variables during an atypical drought period in a marginal lake to a river

Abstract

Climate change is changing the duration and intensity of dry and rainy periods, influencing the dynamics of algal communities in freshwater ecosystems. We evaluated the phytoplankton, metaphyton, epipelon, and epiphyton chlorophyll-a in a shallow marginal lake during a prolonged drought with a loss of river–lake connectivity in an artificial wetland system. We relate algal chlorophyll-a changes in different habitats to environmental conditions during the gradual lake volume reduction. Water and algal community samplings were performed monthly in pelagic, sublittoral, and eulittoral zones during a severe drought due to low rainfall in the summer. We used the chlorophyll-a concentration as a proxy for algal biomass. Differences in nutrient concentrations, water transparency, and depth were determined for two limnological phases. TP and light were significant predictors of algal chlorophyll-a. Lake volume continuously decreased and lost connectivity with the river. The drought increased the trophy, evidencing the tenuous threshold between mesotrophy and eutrophy in a subtropical lake. On a temporal scale, we observed the loss of chlorophyll-a in phytoplankton and epiphyton. The chlorophyll-a concentration fluctuated in the epipelon and increased in phytoplankton-metaphyton, especially in the eulittoral. The results showed a close connection between the pelagic and littoral zones. The phenomena that affect the morphometric variables, such as changes in the precipitation regime, can change trophic state lakes and algal community dynamics in marginal lakes. Our findings suggest that mesotrophic marginal lakes can become eutrophic due to the loss of river–lake connectivity, favoring high phytoplankton-metaphyton growth in wetland systems.