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Description: This layer includes tidal Benthic Index of Biotic Integrity (B-IBI) data for fixed stations in the Choptank River (1984-2014). Data were collected by the Chesapeake Bay Program/Versar (http://www.versar.com/, http://www.chesapeakebay.net/data/downloads/baywide_benthic_database). At fixed stations, a 0.025 m2 hand operated box corer is used to sample benthic organisms in the nearshore shallow habitats, while a 0.0225 m2 Wildco box corer is used in the deepwater (>4 m) habitats (see Llansó et al., 2013 for more details). Multiple metrics are used in the calculation of the overall B-IBI, including Shannon-Weiner species diversity index, total species abundance, total species biomass, and others (Llansó, 2002). Summary statistics for each metric are scored on a ranking of 1, 3, or 5, with least disturbed sites receiving a 5 and severely degraded sites receiving a 1. The scoring is done by comparing observed metrics with established thresholds derived from reference data (Llansó, 2002). The overall B-IBI score is then calculated by averaging the scores for all individual 1-5 metrics. The Chesapeake Bay Benthic Monitoring Program classifies benthic community condition into four levels according to the following breakpoints: “meets restoration goals” (≥3.0), “marginally degraded” (2.7-2.9), “degraded” (2.1-2.6), and “severely degraded” (≤2.0) (CBP, 2012; Llansó, 2002). The mean ± standard error (SE) B-IBI was calculated for each fixed station and sampling date and values were coded for condition based on these criteria. |