Document Type
Report
Publication Date
8-2020
Pages
95 pp.
Abstract
Executive Summary
A study of the macrobenthic communities of the Elizabeth River watershed was conducted in summer 1999 and again in summer 2019 – a 20-year span. The primary objective of the Benthic Biological Monitoring Program of the Elizabeth River watershed was to characterize the ecological condition of regional areas of the tidal waters of the Elizabeth River watershed as indicated by the structure of the benthic communities. These characterizations are based upon application of the Benthic Index of Biotic Integrity (BIBI) developed for the Chesapeake Bay to five primary 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.
Comparing 1999 data with 2019 data the best benthic community condition was in the Mainstem of the river. The Mainstem had the highest average B-IBI value in both 1999 and 2019; the B-IBI value did not change (B-IBI = 2.8). The area of degraded benthic community condition declined from 52% (1999) to 44% (2019). The Southern Branch was the only stratum to show a significant improvement in benthic community condition compared to the 1999 data. The 1999 average B-IBI value of 2.0 significantly increased to 2.5 in 2019. This B-IBI value is near the marginal category for the Chesapeake Bay of 2.6 – 2.9. In addition, the area of degraded benthic community condition declined from 96% (1999) to 64% (2019). Especially significant was the decline in the Southern Branch of severely degraded bottom from 64% (1999) to 36% (2019). The Lafayette River average B-IBI declined significantly from 2.6 (1999) to 2.1 (2019) and the area of degraded benthic community condition increased from 72% (1999) to 92% (2019). The Eastern Branch average B-IBI declined significantly from 2.3 (1999) to 1.8 (2019) and the area of degraded benthic community condition increased from 80% (1999) to 100% (2019). The Western Branch average B-IBI declined slightly from 2.3 (1999) to 2.2 (2019) and the area of degraded benthic community condition decreased slightly from 84% (1999) to 80% (2019).
The general pattern of increased degradation in the Elizabeth River watershed comparing the 1999 data to the 2019 data was also found outside the watershed. The polyhaline benthic communities of the Elizabeth River watershed are most comparable to the benthic communities of the lower James River and to the Virginia Mainstem. Both regions showed a similar increase in levels of degraded benthic community condition comparing 1999 to 2019 using the Chesapeake Bay random monitoring program data.
In summary, the increased benthic community degradation seen in the 2019 data also occurred outside of the Elizabeth River watershed. Clearly larger scale drivers of ecosystem condition affected the patterns observed in the Elizabeth River watershed comparing 1999 and 2019. Further analyses of large-scale and long-term patterns in water column parameters (e.g. bottom dissolved oxygen, salinity, temperature, suspended solids and nutrients) are required.
Rights
Included with kind permission from the author(s).
Repository Citation
Dauer, Daniel M., "Benthic Biological Monitoring of the Elizabeth River Watershed (1999 and 2019)" (2020). Elizabeth River Reports. 4.
https://digitalcommons.odu.edu/chesapeakebay-archive_eriver_reports/4
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