Document Type

Article

Publication Date

8-2006

Pages

173 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 seventh year of sampling in 2005. 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 2005 areal estimate of degraded benthic bottom was the same as 2004, i.e., highest level recorded since the beginning of this program in 1999. 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, and 84 ± 12.7% in 2005. Average B-IBI values for the Elizabeth River watershed were 2.7, 2.6 , 2.7, 2.4, 2.3, 2.2 and 2.2 respectively for the years 1999-2005.

Trend analyses were conducted using the data from the 14 fixed point stations for the period 1999-2005. Four stations showed trends in the B-IBI at p< 0.05 with two stations showing improvements (LFB1, ELD1) and two stations deterioration (EBB1, WBB1). 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 (2003-2005). No station had a B-IBI value over 3.0, ELD1was Marginal and all other fixed-point stations had a degraded or severely degraded status. Of the 29 significant trends in individual B-IBI metrics, 21 were improving trends and only 8 were degrading trends. Of the eight degrading trends, seven were in the diversity index metric.

In general for the Elizabeth River watershed, 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.

The water quality of the Elizabeth River can be generally characterized as follows: (1) nutrients have a poor status indicating high concentration levels, (2) there were improvements in long-term trends in surface total nitrogen levels (STN) and inorganic nitrogen levels (SDIN), and (3) widespread improvements in long-term trends in surface total phosphorus levels (STP).

Nutrient levels of the Elizabeth River exceed those of the lower section of the James River (Table 9). Nitrogen levels are highest in the Southern Branch with smaller differences between the branches of the river for phosphorus levels. The nutrient level in the Elizabeth River are more comparable to levels in the upper reaches of the James River in oligohaline and tidal freshwater regions (Dauer et al. 2003a,b; 2005). Chlorophyll levels, indicative of algal blooms when high, are good in both the Eastern Branch and Southern Branch in spite of high nutrient levels and good water clarity. Chlorophyll levels are fair in the Western Branch but there is an improving long-term trend. Bottom dissolved oxygen are fair to good in all branches.


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