Macrobenthic community structure before, during, and after implementation of the Clean Water Act in the Neches River estuary (Texas)

Community structure of macrobenthos in the industrialized, tidal Neches River was studied 12 years after implementation of phase III of the Clean Water Act (CWA). Result were compared with a 1971-72 study conducted before implementation of the CWA and a 1984-85 study conducted after implementation of phases I & II of the CWA. The permitted BOD waste load decreased 93% between the 1971-72 and 1984-85 studies, then increased 19% between 1984-85 and the current study. A total of 50 taxa were collected during the 1971-72 study, 104 during the 1984-85 study, and 110 during the current study. Numbers of taxa per collection at each station increased by a factor of at least two between the 1971-72 and 1984-85 studies and were significantly different at the 0.0001 level. Numbers of taxa per collection at each station were not significantly different between the 1984-85 and the current study (p=0.286). Minimum collection densities in 1984-85 were higher than maximum densities in 1971-72 and were significantly different at the 0.0001 level. Collection densities were not significantly different between the 1984-85 study and the current study (p=0.374). Shannon's annual and station collection diversity values significantly increased (p=<0.05) between the 1971-72 and 1984-85 studies, but not between the 1984-85 and the current study (p=>0.05). Dendrograms of Sorenson's similarity index between all pairs of stations were more alike between the 1971-72 and the current study than between the 1984-85 and the current study. Evidence of some organic enrichment at the upper stations was indicated by the dominance of Limnodrilus hoffmeisteri and depressed oxygen concentrations. Environmental quality in the river has greatly improved since implementation of the CWA in 1972. Most of the improvments were due to phases I & II of the CWA, with little apparent change since implementation of phase III.