Characterization of the salinity profile of the Arecibo River estuary, a Caribbean island ecosystem
Estuaries are unique, dynamic environments that harbor fauna associated with both marine and fresh water environments. We chose the salt-wedge estuary of the Río Grande de Arecibo in Puerto Rico, USA, as our study site. This estuary is important because it is the site of recruitment for post-larval amphidromous fishes and because it supports valuable sport and subsistence fisheries.
In wedge estuaries salinity and other physicochemical parameters are affected by ocean connectivity, tidal action and river discharge Understanding how these drivers affect stratification and mixing of water masses is critical for understanding the formation of microhabitats and the ecosystem as a whole.
A Garmin GPS was used to establish nine fixed sampling stations on a longitudinal transect that began at the estuary mouth and ended at a low-head dam located 2,949m upstream. Sampling dates and times were selected using tide height data from tide-forcast.com to include high, mid, and low tide events. Data collected at each station were water salinity, pH, depth, temperature, dissolved oxygen, and conductivity. These measurements were made using an YSI 556 multiparameter water quality meter at three locations in the water column: the surface, bottom and mid-column.
The size and shape of the salt wedge of the Río Grande de Arecibo estuary varied with tide height. Salt water did not reach station seven until our first high tide sampling on July 17th, when we observed water of 27ppt at the bottom of the river. Water salinity never exceeded that of brackish water at station eight, and water salinity never exceeded that of freshwater at station nine. At its maximum length the saltwater wedge of this the estuary extended from the mouth of the river to a location 1735 meters upstream. We also observed a saltwater pool, a deep area at station three that held high salinity water even when stations one and two (downstream) had relatively low salinities throughout the water column.
Our research enhances the knowledge of estuarine ecology by describing tidal influence on the dynamic boundaries of an economically and ecologically important estuarine zone. We also observed stable, saline microhabitats that could serve as physiological refugia for estuarine fauna. This knowledge is useful for estuarine conservation and management and can be applied by state, commonwealth, or federal natural resource agencies in the Caribbean region or other tropical estuarine systems.