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Nutrient dynamics in an urban tropical estuary before significant restoration
Citation:
Hanson, Alana, A. Oczkowski, I. Cappielo Cosme, M. Molina, D. Katz, M. Schwartz, AND E. Huertas. Nutrient dynamics in an urban tropical estuary before significant restoration. Coastal & Estuarine Research Federation Conference 2023, Portland, OR, November 12 - 16, 2023.
Impact/Purpose:
Tropical urban estuaries are understudied in the field of environmental research. In San Juan, Puerto Rico lies the San Juan Bay Estuary which has been heavily impacted from urban development. It is also heavily impacted by anthropogenic inputs that lead to dangerous water quality conditions to the detriment of the estuary and nearby communities. Working with people living in these underserved communities is essential to completing robust environmental studies in these urban areas. The data presented will represent an analysis of samples collected monthly across the estuary since 2021 looking at a range of anthropogenic driven ecological indicators, including fecal bacteria indicators, inorganic nutrients, and stable isotopes. The audience for this presentation is a group of technical experts in the ecological field, with whom the agency can benefit from sharing the results of this study.
Description:
The San Juan Bay Estuary (SJBE) is an estuarine system situated in highly developed and urbanized San Juan, Puerto Rico. Due to increased residential development in the 1950s, the Caño Martín Peña (CMP), a channel which connects lagoons to the bay has increasingly restricted water flow through the estuary. The flow restrictions combined with direct sewage inputs from dense urban areas without wastewater treatment along the channel have resulted in very high surface water fecal coliform and enterococci counts, far exceeding EPA limits for recreational water. However, cleanup of the CMP started recently and dredging of the entire channel soon commence. We have been collecting monthly surface water samples across the SJBE since 2021 to measure water quality parameters, inorganic nutrients, particulate stable isotopes, and fecal bacterial indicators. Monthly samplings will continue throughout the duration of the dredging, and we will quantify the changes in the system as water exchange between the bay and the lagoons increases. Currently we observe very small seasonal differences in dissolved inorganic nitrogen (DIN) concentrations, but large differences between sites, with significantly higher concentrations seen in CMP sites than any other site across the bay or lagoons. Similar differences are observed in enterococci counts, with significantly higher counts in CMP water samples than the other SJBE sites, supporting the notion that direct sewage inputs being discharged into the channel are negatively impacting it. However, results are less clear in δ15N data with CMP samples showing trends of lower values than other sites, thus presenting confounding results that will require further microbial analysis to explain.
