Periphyton is commonly defined as the community of microorganisms that are attached to or live upon submerged surfaces. This analysis considers algal growth only. The upper Strawberry Creek watershed channels were surveyed for algal growth on July 30, 1987. Visible algal growth was sampled at a dozen different representative locations (Figure 14). The unpreserved algal samples were taken immediately to University Herbarium personnel for identification. Results are presented in Table 19.
Due to the ephemeral (intermittent) nature of the upper canyon reaches of the creek, no algal growth was observed. Hamilton Creek did not support visible algal growth because of its shaded channel conditions. All of the sites sampled had fairly little canopy cover and exhibited quite shallow flow conditions. Most of the substrates were epilithic (rock), but some organic substrates consisting of wood or plant materials were also sampled for algal growth. All of the algae identified in Strawberry Creek were green algae (Chlorophyceae) and all were branched filamentous algae except for the coccoid colonial alga Chlorella sp., found in the North Fork at North Gate.
The most abundant alga found in the watershed was Cladophora glomerata. This,was observed at nine of the twelve sites sampled in both forks of Strawberry Creek. This alga is generally indicative of "clean" waters, but may produce a septic odor when abundant (Palmer, 1977). Cladophora glomerata is symptomatic of eutrophication (nutrient enrichment) of surface waters. Large growths such as those observed in the creek are found only in waters that have a relatively high nutrient content (Whitton, 1970). Cladophora glomerata growths also usually indicate low heavy metals content of the water (James and Evison, 1979). These observations correlate well with the results of the baseline water quality results (Section 4.1.2). Another more coarsely-branched species of Cladophora was found in Chicken Creek and in the North Fork below University Drive. Vaucheria sp., a "clean" water alga, was found in the South Fork Botanical Garden stream channel.
Chlorella sp., an alga commonly observed in organically enriched areas, was found in the North Fork at North Gate. This alga is the most common and widespread alga seen in sewage ponds .and may produce a musty odor when abundant (Palmer, 1977). Its presence in the North Fork correlates with the baseline water quality data (Section 4.1.2). Spirogyra sp., a slime-producing alga also observed in sewage ponds, was found in a branch of the South Fork just north of the Botanical Garden. This alga may produce a grassy odor when abundant.