Bulletin Board

EOR + Biotic Impairments / Biotic TMDLs

Biotic Impairments:
A biotic impairment means that your stream is not supporting the type of aquatic organisms it should. The challenge is in determining the ‘stressors’ (conditions affecting the biota). The EPA has a defined protocol for the identification of these stressors and, for each identified primary stressor, a Total Maximum Daily Load (TMDL) analysis must be conducted.

Guidance for the Red River Basin biotic impairment assessments developed.

data collection for biotic assessment

Developed for the MPCA, as guidance for conducting future biotic TMDLs in the Red River Basin, EOR's assessment represents one of the first applications of the Watershed Assessment of Riverine Stability and Sediment Supply (WARSSS) in Minnesota. This work contributes to a better understanding of the relationship between geomorphology and biotic impairment.

Main project components include:
• Compilation and organization of existing Red River monitoring data
• Technical literature review
• Rosgen WARSSS assessment of the South Branch Buffalo River
Comparison of WARSSS to USDA's Rapid Geomorphic Assessment (RGA)
• Preparation of Red River Basin Biotic TMDL guidance document
• Recommendations for Red River Basin Biotic TMDL Implementation Plans


Hardwood Creek Impaired Biota (Fish) & Low DO TMDL approved by EPA.

impaired biota data collection

EOR is the only Minnesota-based organization to have completed a biotic TMDL in the state. EOR's Hardwood Creek TMDL was developed as one of Minnesota's first TMDL studies addressing a biotic impairment. The primary stressor identified was altered habitat and altered hydrology linked to excessive sedimentation.

Main project components include:
• Evaluation of in-stream habitat
• Collection of fish and macroinvertebrate data
• Completion of a Rosgen Level III assessment
• Stressor identification process, identifying primary causes of impairment
• CONCEPTS modeling for in-stream sediment
• Implementation Plan - for MS4 stormwater runoff & drainage maintenance


Multiple stressors, including copper, temperature, and sediment
identified in the Brown's Creek TMDL.

TMDL data collection

The Brown's Creek TMDL was initiated to address two biological impairments, lack of a cold water species assemblage (trout) and a poor quality macroinvertebrate community. The impairments are based on what types of aquatic life should be expected in a cold water stream. Using EPA's CADDIS, EOR identified the primary stressors to include high water temperature, suspended sediments and copper concentrations.

Main project components include:
• Identification of lack of shading & stormwater as causes of high water temperatures
• Identification of algaecides & fungicides as copper sources
• P8 modeling of subwatersheds and restoration scenarios
• Load duration curves & TMDL allocations for 3 primary stressors
• Implementation activities designed per identified primary stressors

For more info. on EOR's TMDL projects contact: TMDLs@eorinc.com