Protection of water resources is one of today’s most significant environmental challenges. One key component in effectively implementing pollution abatement is the identification and assessment of pollution sources. Proper source evaluation is needed to target best management practices, develop watershed restoration plans, and assess human health risk.
The majority of US waterbodies do not meet water quality standards. Pathogens are the leading cause of water quality impairment in US rivers and streams, impairing 16% of river/stream miles. When a waterbody is classified as impaired, watershed restoration plans must be developed and implemented.
Computer models have historically been used to assess bacteria sources and loads in impaired watersheds. However, prior data deficiencies caused wildlife contributions to be underrepresented and other non-point sources (i.e. livestock) to be over-allocated in watershed planning efforts.
To provide better data on the predominant sources of bacteria impacting recreation, Texas initiated a bacterial source tracking (BST) program in 2003. BST is a valuable tool for identifying human and animal sources of fecal pollution. BST provides watershed planners bacteria source data not previously available. DNA fingerprinting methods selected for use were enterobacterial repetitive intergenic consensus sequence-polymerase chain reaction (ERIC-PCR) and riboPrinting® (RP). These methods required development of a BST Library. Since 2003, the library has been populated with almost 1,800 E. coli isolates collected from over 1,500 different samples and representing in excess of 50 animal classes.
Using the statewide BST library, comprehensive BST has been completed to identify the source of bacterial impairments in over 15 Texas watersheds. The BST Library has performed well, particularly for identifying broad source categories. A 100% rate of correct classification has been achieved when identifying relative contributions of human, domestic animals, and wildlife. For most studies, the majority of tested isolates were source-delineated with only a small proportion of isolates (~12%) unidentifiable.
Throughout these studies, wildlife contributions have been found to be the predominant source of bacteria, contributing 23-65% of the isolates identified, with non-avian wildlife being a primary contributor. Similarly, recent evaluations of small watershed and edge-of-field runoff from grazed and ungrazed pastures have found median background concentrations ranged from 3,500 to 5,500 cfu/100 mL. When compared to the concentration allowable (126 cfu/100 mL), these background concentrations are significant.
Background loading is not currently adequately addressed in most water quality models, watershed restoration strategies, or other water quality management efforts. This causes serious implications to application of water quality standards, particularly when applied to storm events where background runoff naturally exceeds water quality standards, as well as to watershed restoration plans where ignoring background concentrations may lead to inaccurate load allocations and reductions as well as incongruence of modeling and BST results.
This presentation will summarize the findings from watershed scale BST and small watershed runoff studies completed to date and discuss the implications of these findings on regulatory and non-regulatory water quality programs.