A Disconnect in the SQT Pyramid: When Geomorphology Doesn’t Predict Biology in Spring-Fed Headwater Systems
Hailee Bates
Beaver Creek Hydrology
Lexington, KY
Authors: Hailee Bates, Leslie J. White PhD, Amy Schultz, PE
Many districts have adopted versions of the Stream Quantification Tool (SQT) originally created by Stream Mechanics for the use of stream mitigation banking. District-specific SQT assessments require a subset of the pyramid-approach including Hydrology, Hydraulics, Geomorphology, Physiochemical, and Biology functional categories to assess existing degraded stream systems and a guide for proposed performance standards used throughout the required monitoring period. The Biology category often includes assessment of macroinvertebrates to calculate functional lift. In Tennessee, the macroinvertebrate sample is an index tool, the Tennessee Macroinvertebrate Index (TMI). The TMI produces a score based on macroinvertebrate species’ quality and diversity. The TMI score is typically used as the biology function-based parameter, with scores ranging from 36-42 considered “functioning” according to the SQT in all Bioregions other than 73a or 73b.
Based on the pyramid structure, it’s assumed that functioning Biology is a result of the functioning categories at the base of the pyramid, including functioning Geomorphology of a stream system. Here we detail two case studies where this is not evident. Two headwater sites, both located in Tennessee, experienced anthropogenic disturbances: the first, a 331-acre previously logged bedrock system; the second, a 425-acre cattle farm with both stream channelization and wetland drainage. While both sites had stream reaches assessed as not-functioning or functioning-at-risk for the Geomorphology parameters of floodplain connectivity, lateral migration, riparian vegetation, and bed form diversity, each site had high TMI scores, resulting in a functioning Biology category. The author proposes that excellent water quality (due primarily to spring-fed streams in headwater systems) have led to this seeming disconnect. We use these two case studies to show the pyramid-approach, that is Geomorphology of the stream should predict Biology, is not always the case in headwater systems.
This presentation will detail the potential disconnect between the SQT pyramid approach when assessing degraded headwater streams. If existing Biology is functioning under degraded Geomorphology conditions, can restoration focused on functional lift of Geomorphology lead back to functioning Biology? We argue there should be more leniency surrounding restoration decisions when considering these types of systems, especially when the Biology and Geomorphology are seemingly un-connected.
About Hailee Bates
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