Document Type

Report

Publication Date

7-2007

Pages

42 pp.

Abstract

Executive Summary

Macrobenthic communities of the Elizabeth River watershed have been quantitatively sampled since summer 1999. This report presents the data from the eigth year of sampling in 2006. 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 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. The areal extent of degraded bottom in 2006 was 80 ± 15.7%. 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, 72 ± 17.6 % in 2002, 80 ± 15.7 % in 2003, 84 ± 12.7% in 2004, 84 ± 12.7% in 2005, and 80 ± 15.7% in 2006. Average B-IBI values for the Elizabeth River watershed were 2.7, 2.6, 2.7, 2.4, 2.3, 2.2, 2.2 and 2.4 respectively for the years 1999-2006.

Trend analyses were conducted using the data from the 14 fixed point stations for the period 1999-2006. A single station in the Lafayette River showed an improving trend in the BIBI (LFB1). Using the approach of the Chesapeake Bay Program, the status of each of the 14 fixed-point stations was characterized using the median value of the B-IBI for the last three years (2004-2006). A single station had a B-IBI value over 3.0 (ELD1), one station was Marginal (ELC1) and all other fixed-point stations had a degraded or severely degraded status. Of the 26 significant trends in individual B-IBI metrics, 19 were improving trends and seven were degrading trends. Of the seven degrading trends, four were in the diversity index metric.

In general for the Elizabeth River watershed, benthic community species diversity and biomass remain below reference condition levels while abundance was often above reference condition levels and considered excessive. Community composition was unbalanced with levels of pollution indicative species above, and levels of pollution sensitive species below, reference conditions.


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