Citation:

Oczkowski, A., E. Santos, A. Gray, K. Miller, E. Huertas, Alana Hanson, R. Martin, E. Watson, AND C. Wigand. Tracking the Dynamic Ecological History of a Tropical Urban Estuary as it Responds to Human Pressures. ECOSYSTEMS. Springer, New York, NY, 23:231-245, (2020). https://doi.org/10.1007/s10021-019-00399-1

Impact/Purpose:

Here we assess how the urbanization of San Juan, Puerto Rico has impacted the San Juan Bay Estuary. A critical channel in the estuary, the Caño Martín Peña, has filled in and now frequently floods the adjacent communities with sewage-enriched waters. We traced the anthropogenic history of the estuary via the geochemistry of a series of dated sediment cores. Our analyses indicated that deposition rates and the amount of organic matter and nutrients in the sediment have recently increased throughout the estuary. Portions of the system are now functioning as settling basins. Stable isotope and sediment nutrient measurements suggest that while high urban and sewage runoff to the Caño contributes nitrogen (N), it may also enhance conditions for biogeochemical processes that fix additional bioavailable N from inert dinitrogen gas. This source of ‘new’ N may meet or exceed that from urban runoff. The ecological consequences extend beyond the ponded Caño and are contributing to the poor water quality of the SJBE. This work supports observations that the closure of the Caño Martín Peña is negatively impacting the San Juan Bay Estuary.

Description:

Coastal cities in tropical areas are often low-lying and vulnerable to the effects of flooding and storms. San Juan, Puerto Rico, is a good example of this. It is built around a lagoon-channel complex called the San Juan Bay Estuary (SJBE). A critical channel in the estuary, the Caño Martín Peña, has filled in and now frequently floods the surrounding communities with sewage-enriched waters, causing a series of human health and ecological problems. Sediment core analyses indicate that portions of the SJBE now function as settling basins. High urban and sewage runoff to the Caño contributes nitrogen (N), but stable isotope and sediment nutrient analyses indicate that this runoff may also enhance conditions for coupled sulfate reduction-nitrogen fixation. The amount of ‘new’ bioavailable N created from inert atmospheric N2 gas may meet or exceed that from the runoff into the Caño Martín Peña. The ecological consequences of this appear to extend beyond the ponded channel, potentially contributing to the poor water quality of the SJBE, greater than contaminated runoff alone.

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