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Synthesis of long-term water quality and modern biogeochemical sediment data in the San Juan Bay Estuary
Citation:
Hanson, Alana, A. Oczkowski, E. Santos, R. Martin, H. Buffum, E. Huertas, E. Watson, AND C. Wigand. Synthesis of long-term water quality and modern biogeochemical sediment data in the San Juan Bay Estuary. ASLO 2019 Aquatic Sciences Meeting, San Juan, Puerto Rico, PUERTO RICO, February 23 - March 02, 2019.
Impact/Purpose:
Tropical urban mangroves 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. Particularly, a channel that lies in its center (Caño Martín Peña) has nearly completely blocked water flow between the western and eastern sides due to urban development and infilling. It is also heavily impacted by human driven inputs that lead to dangerous water quality conditions to the detriment of the estuary and nearby communities. This study synthesized pre-existing data and compared data from the 1970s with data from 2015-2017. Parameters studied include fecal coliform counts, nitrogen concentrations in water and sediment, and other recreational water quality data. The data presented will add to the limited data pool for tropical urban ecosystems, and hopefully encourage other researchers to study similarly understudied environments.
Description:
The San Juan Bay Estuary (SJBE) is located in the middle of highly developed and urbanized San Juan, Puerto Rico. Due to heightened 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 longer residence times in the estuary due to the flow restriction along with direct inflow of sewage from dense urban areas alongside the channel have led to very high water column fecal coliform counts. Based on our synthesis of data compiled from the PR Environmental Quality Board, SJBE Program and other agencies fecal coliform levels have been found to exceed the EPA water quality standard of 200CFU/100mL in 90% of samples collected at nearby USGS sampling sites since the 1970s. Although high concentrations of fecal coliform have been measured, the levels of nitrogen (N) in water samples have not been near expected concentrations from a highly impacted system. In addition to synthesizing pre-existing data dating back to the 1970s, we collected mangrove cores, subtidal cores and sediment surface grabs from the SJBE during 2015-2017 to quantify spatial and temporal differences in N throughout the estuary. While trends in sediment N content were consistent with the observations from the water quality data, there is some emerging evidence that additional biogeochemical dynamics may be a substantial source of bio-available N to the most impacted region of the estuary (the CMP). Here we document the far-reaching ecological impacts of the closure of the CMP on the tropical and urban SJBE.