Watershed Assessment
In addition to reach-specific assessments (VSA) of stream ecological integrity based on quantitative community and habitat data, INSTAR classifies watershed (i.e., 6th order hydrologic units or HUCs) integrity using a modified Index of Biotic Integrity (mIBI). Watershed assessments include a broader range of validated qualitative (e.g. species lists) biotic data from various sources, including state and federal agencies. These data are used to generate regionally calibrated scores for six metrics (see above) and an overall mIBI score for each of Virginia’s 1275 watersheds. Scores range between 6 and 30; watersheds with mIBI scores > 16 are associated with generally high watershed integrity.
How is watershed integrity calculated?
All stream-dependant living resources data are compiled for each watershed in Virginia. The data are then ran against 6 different metrics (variables) and a scoring scenario created for each drainage basin. A watershed could score a value of 1, 3, or 5 for a total score ranging from 6-30. There are a few watersheds, particularly in southeast Virginia that are predominantly estuarine and do not currently have any data. These watersheds would receive a 'Not Scored' value.
The 6 metrics (variables) that are used for Watershed Integrity are:
Native Species Richness (total number of species indigenous)
Number of Rare, Threatened, or Endangered Species (data from VA DGIF and VA DCR-NH included here)
Number of Non-indigenous Species (number of introduced species, see list)
Number of Significant Species (ecologically or economically important)
Number of Tolerant Species (species that are tolerant to pollution, sedementation, or habitat alteration)
Number of Intolerant Species (species that are intolerant to degraded stream conditions) as this number is high, high watershed integrity can be inferred)
Not all drainage basins have the same number of species, so scoring schemes/criteria was created for each drainage basin within Virginia.
