Document Type

Report

Publication Date

11-2003

Pages

56 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 fourth year of sampling in 2002. 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 characterized in this report by combining the Benthic Index of Biotic Integrity (B-IBI) developed 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. The 1999 intensive data set is used as a benchmark for comparison with data in collected in succeeding years. Beginning in 2000 a single stratum, the entire Elizabeth River watershed, will be sampled with 25 random samples.

Based upon probability-based sampling the estimate of benthic bottom not meeting the benthic restoration goals was 64 ± 10.1 % in 1999, 72 ± 17.6% in 2000, 52 ± 19.6% in 2001, and 76 ± 16.7 % in 2002. Average B-IBI values for the Elizabeth River watershed were 2.7 in 1999 (area weighted for the five strata (Dauer 2000), 2.6 in 2000 (Dauer 2001), 2.7 in 2001 (Dauer 2002) and 2.4 in 2002 (this report).

In general for the Elizabeth River watershed, species diversity and biomass were below reference condition levels while abundance 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.


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