Geographical and seasonal patterns in the carbonate chemistry of Narragansett Bay, RI.

This study examined geographical and seasonal patterns in carbonate chemistry and will facilitate assessment of acidification conditions and the current state of the seawater carbonate chemistry system in Narragansett Bay. Direct measurements of total alkalinity, dissolved inorganic carbon, dissolved oxygen percent saturation, water temperature, salinity and pressure were performed during monthly sampling cruises carried out over three years. These measurements were used to calculate the following biologically relevant carbonate system parameters: total pH (pHT), the partial pressure of carbon dioxide in the gas phase pCO2, and the aragonite saturation state ΩA. The information provided by carbonate chemistry analysis allowed for the characterization of acidification events which have the potential to disrupt the species composition and ecological functioning of coastal biological communities and threaten commercially important aquatic life. We found very robust relationships between salinity and total alkalinity Radjusted2=0.82 and between salinity and dissolved inorganic carbon Radjusted2=0.81 that persisted through all regions, seasons, and depth-layers with mixing of coastal waters with freshwater entering in the upper bay being an important driver on alkalinity and dissolved inorganic carbon distributions. We compared the metabolically linked calculated carbonate system parameters with dissolved oxygen (DO) saturation and found high correlation, with DO percent saturation exhibiting robust correlation with the calculated carbonate system parameters total pH (r=0.70) and with partial pressure of carbon dioxide in the gas phase (r=-0.71). Using a statistical model to correct for the confounded effects of time and space that are a common challenge in marine survey design, we found that acidification events occurred in the Northern Region of the bay, primarily during the Summer and Fall, and likely due to a combination of microbial respiration and stratification. These acidification events, especially in the Northern Region, have the potential to adversely impact aquatic life.

Tracking the dynamic ecological history of a tropical urban estuary as it responds to human pressures.

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.

Ciudades costeras en los trópicos generalmente se encuentran localizadas en lugares de baja elevación y vulnerables a los efectos de tormentas e inundaciones. San Juan, Puerto Rico es un buen ejemplo de esto. Esta ciudad fue construida alrededor de un sistema de lagunas y canales que se conoce como el Estuario de la Bahía de San Juan. Un canal crítico en este sistema es el Caño Martín Peña que en el pasado fue rellenado con sedimentos causando inundaciones en las comunidades vecinas. Estas aguas de escorrentía incluyen aguas residuales y aumentado el riesgo a problemas de salud pública y del ambiente. Análisis de los sedimentos indican que porciones de este sistema funcionan como lagunas de sedimentación. Gran flujo de aguas residuales y escorrentía urbana hacia el Caño aportan nitrógeno (N), pero el análisis de sedimentos y nutrientes por isótopos estables indica que esta escorrentía también aumenta las condiciones por procesos acoplados de reducción de sulfato y fijación de nitrógeno. La cantidad de 'nuevo' N biodisponible creado del gas nitrógeno inerte atmosférico podría lograr o exceder esa fijación del nitrógeno derivado de la escorrentía hacia el Caño. Las consecuencias ecológicas de esto parecen extenderse más allá de este canal estancado afectando así la calidad del agua en el Estuario, mayor aún que los contaminantes encontrados en la escorrentía pluvial por sí sola.