Abstract
Urban activities and related infrastructure alter the natural patterns of stream physical and chemical conditions. According to the Urban Stream Syndrome, streams draining urban landscapes are characterized by high concentrations of nutrients and ions, and might have elevated water temperatures and variable oxygen concentrations. Here, we report temporal and spatial variability in stream physicochemistry in a highly urbanized watershed in Puerto Rico. The main objective of the study was to describe stream physicochemical characteristics and relate them to urban intensity, e.g., percent impervious surface cover, and watershed infrastructure, e.g., road and pipe densities. The Rio Piedras Watershed in the San Juan Metropolitan Area, Puerto Rico, is one of the most urbanized regions on the island. The Rio Piedras presented high solute concentrations that were related to watershed factors, such as percent impervious cover. Temporal variability in ion concentrations lacked seasonality, as did all other parameters measured except water temperature, which was lower during winter and highest during summer, as expected based on latitude. Spatially, stream physicochemistry was strongly related to watershed percent impervious cover and also to the density of urban infrastructure, e.g., roads, pipe, and building densities. Although the watershed is serviced by a sewage collection system, illegal discharges and leaky infrastructure are probably responsible for the elevated ion concentration found. Overall, the Rio Piedras is an example of the response of a tropical urban watershed after major sewage inputs are removed, thus highlighting the importance of proper infrastructure maintenance and management of runoff to control ion concentrations in tropical streams.
Highlights
Human activities have greatly transformed the environment and the planet, creating new conditions in which human systems are major factors (Ellis 2011)
Study watershed The Río Piedras Watershed drains a large portion of the San Juan Metropolitan Area (SJMA) in Puerto Rico
The signature of human activities on the watershed is clearly reflected in the water chemistry of streams draining the Río Piedras
Summary
Human activities have greatly transformed the environment and the planet, creating new conditions in which human systems are major factors (Ellis 2011). Urban areas are a type of extreme manifestation of human presence as they severely alter the natural landscape. As the human population increases its presence in cities, urban areas become important sources of ecosystem alteration (Alberti et al 2003). Streams are vulnerable because they integrate the landscape, and stream water physicochemical characteristics reflect both the geological setting that they drain and inputs from the surrounding watershed (Allan 2004). Urban streams show particular physicochemical signals that reflect the higher amounts of inputs they receive from the surrounding watershed (Hatt et al 2004). Urban stream water chemistry can be used to gauge the effects that human activities have on the environment
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