Document Type

Report

Publication Date

12-2017

Pages

136 pp.

Abstract

Executive Summary

This report summarizes the ecological condition of the subtidal macrobenthic communities off Money Point in the Southern Branch of the Elizabeth River based upon quantitative sampling in summer 2016. The designated Money Point study area was part of a sediment contaminant remediation effort. The primary objectives were to: (1) characterize the biological health of the benthos of Money Point comparing pre-remediation condition (2010) to post-remediation condition in 2013 and again in 2016, and (2) assess the effectiveness of the sediment contamination remediation efforts with respect to the ecological condition of the Money Point benthos.

Prior to sediment contaminant remediation, Dauer (2011) characterized the benthic community condition off Money Point as consistent with previous characterizations of the Elizabeth River watershed: (1) benthic community species diversity and biomass were below reference condition levels; (2) abundance often above reference condition levels and considered excessive; and (3) community composition was unbalanced with levels of pollution indicative species above, and levels of pollution sensitive species below, reference conditions.

Compared to previous characterizations of the benthos of the Elizabeth River, the Money Point benthos as sampled in 2010 had (1) the lowest average B-IBI value, 2.0, a level characterized as severely degraded; (2) relatively high abundance levels, exceeding 6,000 individuals per m2; (3) the lowest Shannon Diversity Index value; and (4) the lowest biomass level. The low level of biomass was probably indicative of poor ecological value of the benthos as a food source for higher trophic levels, i.e. fish, crabs, birds, etc.

In 2013 after sediment contaminant remediation (Dauer 2014), the benthic community showed (1) a significant increase in the value of the B-IBI from 1.8 to 2.1; (2) a highly significant reduction in abundance levels from 6,012 to 2,640 individuals per m2; (3) a highly significant increase in the Shannon Diversity Index value from 1.62 to 2.33; and (4) a highly significant increase in the level of biomass from 0.35 to 0.85 AFDW g C per m2 (142% increase). The increase in the species diversity (H’) was due to both an increase in species richness (the species per sample increased significantly from 9.48 to 11.96) and lower dominance by two pollution indicative polychaete species (Mediomastus ambiseta and Streblospio benedicti) from a combined level of 4,956 individuals per m2 in 2010 to 1,244 individuals per m2 in 2013. Those levels of these two species represented, respectively, 82.4% of the individuals in 2010 and only 47.1% of the individuals in 2013.

Benthic data collected in 2016 (this report) showed that at Money Point the B-IBI, abundance, biomass and species richness all decreased and were significantly lower than levels at Blows Creek. The declines in the BIBI, abundance, biomass and species richness at Money Point were most likely due to factors such as poor larval recruitment, low post-larval survivorship, increased mortality associated with predation, etc. This conclusion is based on the observed patterns of benthic community condition at two long-term benthic monitoring stations – one located downstream of Money Point (SBE2) and the other upstream of Money Point (SBE5). These two fixed point stations of the Chesapeake Bay Benthic Monitoring Program have been sampled yearly since 1989. The long-term patterns of the BIBI and its metrics at the fixed stations (SBE2 and SBE5) indicate that over time at larger spatial scales (e.g. for the entire Southern Branch) patterns of recruitment and survivorship may have overwhelmed the signal of the initial remediation improvement of benthic community condition at Money Point shown in the 2013 data.

In contrast there were positive aspects of changes in benthic community composition at Money Point after remediation in the 2013 data that continued in the 2016 data. Specifically (1) the continued decline of the two pollution indicative polychaete species, Mediomastus ambiseta and Streblospio benedicti, at Money Point; (2) the larger body size of species at Money Point; (3) continued lowered level of pollution indicative abundance; and the (4) slightly higher level of pollution sensitive abundance. All these metrics collectively indicate that the very positive improvement in benthic community composition quantified after remediation in the 2013 sampling has continued in 2016.

Continued periodic sampling at Money Point and Blows Creek will provide further assessment of the apparent beneficial effects of the remediation on the benthic community condition.


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Included with kind permission from the author(s).

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