LAUSR

Abstract Lowland lotic ecosystems are under increasing pollution pressure. In this study, we analyzed the plankton community responses to environmental changes, including natural ones and those related to anthropogenic activities, to finally determine their optimums in natural conditions. In four dates, seven streams were sampled, and a total of twenty-one physical-chemical variables were measured or estimated (including metals and pesticides). Partial redundancy analyses were performed, as well as, General Linear Models (GLM) considering Reynolds Functional Groups (RFG) for phytoplankton, and families for zooplankton as response variables. Finally, the optimum concentration of these plankton groups was estimated. Results indicated that phytoplankton was dominated by diatoms belonging to functional groups B, C, and TB, being chlorophytes (J) and cyanobacteria (M) the subdominant groups. Zooplankton was dominated by Bdelloidea, Brachionidae, and Copepoda nauplii. For almost all groups of phytoplankton, except M, chemical oxygen demand (COD) and high nutrients concentrations contribute to explain their variations. However, the explanation percentages increased when other variables like temperature and light extinction coefficient were included. For zooplankton, chromium and biochemical oxygen demand (BOD5) explained variation of almost all groups. Variance explanation of Lecanidae, Gastropodidae, Trochosphaeridae, and Trichocercidae increased when conductivity and pH were included. Finally, both plankton groups had in general high maximum tolerance for COD, BOD5, and metals concentrations. We conclude that the plankton assemblages of these highly modified lowland streams could tolerate the anthropogenic disturbance, with organic pollution and eutrophication, as the most relevant.