Document Type

Report

Publication Date

10-2004

Pages

88 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 fifth year of sampling in 2003. 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 2003 areal estimate of degraded benthic bottom was the 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, and 80 ± 15.7 % in 2003. Average B-IBI values for the Elizabeth River watershed were 2.7, 2.6 , 2.7, 2.4 and 2.3 respectively for the years 1999-2003. For the first time since the program began the pollution sensitive bivalve Macoma balthica was listed as a density dominant as the sixth mot abundant species at 115 individuals per m-2. There appeared to be successful recruitment of this species particularly in the Western Branch, Eastern Branch and Lafayette River.

Trend analyses were conducted for the first time using the data from the 14 fixed point stations for the period 1999-2003. The present trend analyses have limited statistical power due to the number of years of the program. No stations showed a trend in the B-IBI at p< 0.05. However, at this probability level there were mixed improving and degrading trends in five individual B-IBI metrics. At p< 0.10 level there was a single improving trend in the B-IBI at Station LFA1 in the Lafayette River and 23 trends in individual metrics. Of these 23 metric trends, five were degrading trends and 18 were improving trends. Of the five degrading trends, three were due to trends in community abundance to excessive levels. Improving trends were seen in community biomass at both stations in the Western Branch, Station EBB1 in the Eastern Branch and Station SBC1 in the Southern Branch. The remaining improving trends were in community composition (balance between pollution sensitive and pollution indicative species) and included Station ELD1 in the Mainstem, three stations in the Southern Branch (SBB1, SBC1, SBD2), both stations in the Western Branch (WBB1, WBB5) and the single station in the Eastern Branch (EBB1). 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 (2001-2003). Only one station, ELD1 in the Mainstem, had a B-IBI value over 3.0 and was considered to have met the Benthic Restoration Goals of the B-IBI. A second station in the Mainstem, ELD1, had a marginal value. All other fixed-point stations had a degraded or severely degraded category.

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 widespread 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). 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 (Appendix B, Fig. B3). Chlorophyll levels are poor in the Western Branch but there is an improving long-term trend. Bottom dissolved oxygen are fair to good in all branches with improving trends in all branches except the Mainstem.


Rights

Included with kind permission from the author(s).

Comments

Erratum (January 2005): In this edition Appendix B- Summary of water quality status and trends for the Elizabeth River has been updated. Several nutrient trends previously reported as having improving trends had non-significant patterns. The appropriate figures and tables of the appendix were corrected.

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