Managing freshwater inflow to estuaries in northeastern Puerto Rico
Smith, Katherine LeConte
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Estuaries in northeastern Puerto Rico provide critical habitat for diadromous, estuarine, and marine species. While freshwater abstraction has been recognized as a threat to riverine species in this region, the issue of decreasing inflow to estuaries has received very little research or management attention. To address this research gap, the ecological importance of freshwater inflows to estuaries in northeastern Puerto Rico and the management framework for this resource are examined in this dissertation. The ecological importance of freshwater inflow was examined in two studies: (1) a comparison of salinity and fish community data collected from the Espiritu Santo estuary in 1977 and 2004, before and after the 1984 construction of an upstream low-head dam and water intake structure and (2) a stable isotope and gut content analysis of the contribution of freshwater organic matter to estuarine fishes in the Espiritu Santo and Mameyes. Results of the first study illustrate the potential importance of freshwater inflow to estuarine fish communities. 2004 sampling yielded lower fish species richness and abundance than 1977 sampling. Freshwater-oriented species demonstrated the greatest decline, with only 25% of freshwater-oriented species redetected in 2004 versus redetection of more than 50% for marine and euryhaline species. Results of the second study illustrate the contribution of riverine organic matter to estuarine fish diet. While riverine organic matter was of limited (<33%) importance to three of four fishes sampled (Centropomus pectinatus, Bairdiella ronchus, and Mugil curema), stable isotope analyses indicated that it potentially contributed as much as 69% of the diet of one species, Diapterus rhombeus. Gut content analysis of these four and eleven other common fishes collected from the two estuaries demonstrated the importance of riverine-derived organisms, specifically juvenile diadromous freshwater shrimps, to fish diet. Freshwater shrimps were frequently encountered (in 37% and 39% of guts examined) and composed an average of 18% and 22% of the gut content material of omnivorous fishes sampled in the Espiritu Santo and Mameyes estuaries, respectively. After assessing the ecological importance of freshwater inflow to estuaries, the management framework for this resource was examined via a legal analysis and manager interviews. The primary legal and policy authorities with relevance to inflow management in northeast Puerto Rico are the Clean Water Act, the Rivers and Harbors Act, and the Puerto Rico Water Law. Inflow management actions under these authorities, however, have focused on riverine, rather than estuarine, inflow needs. Results of manager interviews illustrate the role of several key factors in limiting management of inflow to estuaries: low priority of inflow to estuaries, lack of relevant scientific information, lack of a champion pushing the issue, programmatic limitations, as well as issues related to Puerto Rico’s wider institutional and political environment that affect natural resource management in general. Based on the results of these three studies, management and future research recommendations are provided.