Methods 



Periphyton samples were collected following standard operating procedures of the 

 MDEQ Planning, Prevention, and Assistance Division. Using appropriate tools, microalgae 

 were scraped, brushed, or sucked from natural substrates in proportion to the importance of those 

 substrates at each study site. Macroalgae were picked by hand in proportion to their abundance 

 at the site. All collections of microalgae and macroalgae were pooled into a common container 

 and preserved with Lugol's (IKI) solution. 



The samples were examined to estimate the relative abundance and rank by biovolume of 

 diatoms and genera of soft (non-diatom) algae according to the method described in Bahls 

 (1993). Soft algae were identified using Smith (1950), Prescott (1962, 1978), John et al. (2002), 

 and Wehr and Sheath (2003). These books also ser\'ed as references on the ecology of the soft 

 algae, along with Palmer (1969, 1977). 



After the identification of soft algae, the raw periphyton samples were cleaned of organic 

 matter using sulfuric acid, potassium dichromate, and hydrogen peroxide. Then permanent 

 diatom slides were prepared using Naphrax, a high refractive index mounting medium, following 

 Standard Methods for the Examination of Water and Wastewater (APHA 1998). At least 400 

 diatom cells (800 valves) were counted at random and identified to species. The following were 

 the main taxonomic references for the diatoms: Krammer and Lange-Bertalot 1986, 1988, 

 1991a, 1991b; Lange-Bertalot 1993, 2001; Krammer 1997a, 1997b, 2002; Reichardt 1997, 1999. 

 Diatom naming conventions followed those adopted by the Academy of Natural Sciences for 

 USGS NAWQA samples (Morales and Potapova 2000) as updated in 2003 (Dr. Eduardo 

 Morales, Academy of Natural Sciences, digital communication). Van Dam et al. (1994) was the 

 main ecological reference for the diatoms. 



The diatom proportional counts were used to generate an array of diatom association 

 metrics. A metric is a characteristic of the biota that changes in some predictable way with 

 increased human influence (Barbour et al. 1999). Diatoms are particularly usefiil in generating 

 metrics because there is a wealth of information available in the literature regarding the pollution 



