The influence of environmental parameters on the phytoplankton community of two tropical reservoirs

Abstract

Previous studies have indicated certain environmental variables such as rainfall, nutrient concentrations and mixing events can be strong drivers of the phytoplankton community structure in reservoirs. Shifts in the phytoplankton community composition of Puerto Rican reservoirs, however, are not well understood. The present study identified the spatial and temporal changes in the phytoplankton community structure of two reservoirs in Puerto Rica, and which environmental parameters determined the structure. Whether or not the main environmental variables varied on the basis of the initial trophic status of the reservoirs was also explored. Two Puerto Rican reservoirs, one classified as mesotrophic and the other as eutrophic, were sampled on three sampling dates, with the reservoirs into three zones (dam; transition; riverine). Physical parameters were recorded at each sampling site, nutrient concentrations were measured, and the phytoplankton community biomass and diversity were determined. A canonical correspondence analysis (CCA) was run for each reservoir to explore which variables determined the phytoplankton community composition. Temperature, pH and total phosphorus concentration were the main drivers of the phytoplankton community composition for the mesotrophic reservoir, while specific conductance, pH, total phosphorus and nitrate were the main explanatory variables. Although the driving variables changed between the reservoirs, the temporal shifts observed in the phytoplankton community structure were consistent for both reservoirs regardless of their trophic status. The findings of the present study suggest that, although shifts in the phytoplankton community structure are similar in reservoirs with differing initial trophic status, the environmental variables driving community composition may nevertheless vary. Accordingly, tropical reservoirs managers should consider a reservoir's initial trophic status when evaluating what environmental parameters may lead to changes in its phytoplankton community structure. The present study represents a first step at examining the variables driving phytoplankton community structure in Puerto Rican reservoirs.