Document Type

Report

Publication Date

7-2001

Pages

30 pp.

Abstract

Executive Summary

A study of the macrobenthic communities of the Elizabeth River watershed was initiated in summer 1999. This report presents the data from the second year of sampling in 2000. The three objectives of the Benthic Biological Monitoring Program of the Elizabeth River watershed are: (1) To characterize the health of the tidal waters of the Elizabeth River watershed as indicated by the structure of the benthic communities. ( 2) To conduct trend analyses on long-term data at 14 fixed-point stations to relate temporal trends in the benthic communities to changes in water and/or sediment quality. Trend analyses will be updated annually as new data are available. (3) To produce an historical data base that will allow annual evaluations of biotic impacts by comparing trends in status within probability-based strata and trends at fixed-point stations to changes in water and/or sediment quality.

The health of the benthic communities of the Elizabeth River watershed is characterize by combining previously developed benthic restoration goals, the Benthic Index of Biotic Integrity (BIBI) for the Chesapeake Bay and probability-based sampling. A probability-based sampling design allows calculation of confidence intervals around estimates of condition of the benthic communities and allows estimates of the areal extent of degradation of the benthic communities. In summer 1999 a spatially intensive sampling occurred. The Elizabeth River watershed was divided into five sampling strata - the Mainstem of the river, the Lafayette River, the Southern Branch, Western Branch and Eastern Branch. Within each stratum 25 samples were randomly allocated in a probability-based sampling design. In 2000 and in succeeding years a single stratum, the entire Elizabeth River watershed, will be sampled with 25 random samples.

Based upon probabilty-based sampling the estimate of benthic bottom not meeting the benthic restoration goals was 72.0 % in 2000 compared to a value of 64.3 % in 1999. In general for the Elizabeth River watershed, species diversity and biomass were below reference condition levels while abundance values was above reference condition levels. Community composition was unbalanced with levels of pollution indicative species above and levels of pollution sensitive species below reference conditions. Of the 25 random samples 10 received a score of “1" indicating degraded conditions. For 9 of these 10 the score of “1"was due to level of abundance higher than the benthic restoration goal levels. The high level of abundance exceeded the benthic restoration goals and is considered an indication of degradation because abundance levels are too high. The increased densities were due to opportunistic annelids - the polychaete species Mediomastus ambiseta and Streblospio benediciti and the oligochaete taxa Tubificoides heterochaetus and Tubificoides spp. Group I. In the 1999 sampling these four taxa accounted for 1,863 individuals m-2 and for 5,259 individuals m-2 in 2000.


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Included with kind permission from the author(s).

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