The role of precipitation events in the water quality of a buffer urban ecosystem

Non-point source pollution from stormwater runoff has become one of the main contributors to pollution in urban water bodies. In this study, we aimed to quantify changes in limnological variables (including nutrients), pollutants (heavy metals, microplastics, hydrocarbons), and microbial communities (coliform bacteria and phytoplankton), with particular emphasis on precipitation events in an urban drainage reservoir. To achieve this, we sampled three urban runoff channels that drain water from two main areas of Santa Fe City (Argentina) over an entire hydrological year, including four rainfall events. The results revealed differences among the drainage channels, with hydrocarbons and nitrogen contamination predominating in channel 1, organic matter in channel 2, and eutrophic conditions in channel 3. In all cases, coliforms bacteria and Escherichia coli levels exceeded permitted limits for most of the year, and phytoplankton communities were dominated by species indicative of organic matter pollution and eutrophication. Precipitation events only significantly affected dissolved inorganic nitrogen forms (positive correlation) and hydrocarbons (negative correlation). These findings highlight the importance of integrated stormwater management to reduce pollutant loads, with different management strategies tailored to each runoff channel and urban area.