Summary 



During the 2003 field season, six periphyton samples were collected from four sites on 

 the Shields River for the purpose of assessing whether this river is water-quality limited and in 

 need of TMDLs. Four of the samples were grab samples of conspicuous macroalgae and were 

 collected for identification only. Two samples from two sites (Johnstone's and Near Mouth) 

 were composite samples collected following MDEQ standard operating procedures, processed 

 and analyzed using standard methods for periphyton, and evaluated following modified USEPA 

 rapid bioassessment protocols for wadeable streams. 



Since the Shields River begins in a mountain ecoregion and flows for most of its length 

 through a prairie ecoregion, diatom metrics generated from the two standard TMDL samples 

 were compared to criteria developed for both mountain streams and plains streams. 



Diatom metrics indicate good biological integrity, minor impairment, and full support of 

 aquatic life uses at both sites where composite samples were collected in 2003. An assessment 

 of minor impairment resulted from a comparison of metrics to biocriteria for both mountain and 

 plains streams. Diatoms dominated the periphyton at both sites in September. Cladophora was 

 a co-dominant near the mouth but was missing at Johnstone's. 



The only apparent deviation from excellent biological integrity at Johnstone's and near 

 the mouth was a few abnormal diatom valves at each station and slightly elevated percentages of 

 Achnanthidium minutissimiim, which indicates chemical, physical, or biological disturbance. 

 The stress causing this disturbance and the abnormal diatom valves may be natural in origin. The 

 two sites were virtually identical in terms of diatom floristics and ecological conditions. 



The majority of diatoms at Johnstone's and near the mouth were non-motile nitrogen 

 autotrophs that exert a continuously high demand for dissolved oxygen. The majority of diatoms 

 at both sites also indicate fresh, alkaline waters with only a small amount of BOD loading. Most 

 diatoms at Johnstone's indicate eutrophic waters that are rich in inorganic nutrients. The modal 

 category for trophic state near the mouth was "variable". Diatoms in this category can prosper 

 under a wide range of nutrient regimes from oligotrophic to hypereutrophic. 



Grab samples of macro-algae indicate cool, nutrient-rich waters at Coal Camp Road in 

 September and Elk Creek Road in August. The filamentous green alga Cladophora was 

 abundant at the lowermost bridge in July and August, as well as in September. 



