Rio Grande water and sediment quality data affecting benthic macrofaunal community obtained from 2000-10-24 to 2005-08-06

The lower Rio Grande is a river-dominated estuary that serves as the border between Texas, USA and Tamaulipas, Mexico. River estuaries encompass the section of the river influenced by tidal exchange with the Gulf of Mexico, but the connection with the Rio Grande is intermittent and can be temporarily open or closed. During the 4.8-year study period, the river mouth was closed 30% of the time, mostly during average or dry climatic conditions, with the temporary closing of the river mouth being linked to hydrology. When the Rio Grande estuary is closed, salinity is low, nitrate plus nitrite are low, and ammonium is high, but chlorophyll is similar. Benthic macrofaunal abundance and biomass are higher when the river mouth is closed than open. Benthic macrofaunal community structure divided into two groups: chironomid larvae and Oligochaeta dominated when the river mouth was closed, whereas polychaetes Mediomastus ambiseta and Streblospio benedicti dominated when the river mouth was open. The implications of these results for managing freshwater flows are that the open and closed conditions each have a characteristic benthic macrofaunal community that is strongly influenced by system hydrology.