Benthic algal distribution and abundance

Proximate factors that may influence benthic algae include light, temperature, current, substrate, scouring by floods, water chemistry, and grazing. Biggs (1996) proposed that regional and catchment features such as topography, geology, land use, vegetation, and climate affect these proximate variables, which directly regulate the accrual and loss of benthic algal biomass. Light and nutrients, interacting with temperature, influence biomass accrual while disturbance (substrate turnover and transport, high current velocities) and grazing lead to the dislodgement of algae and biomass loss (Figure 6.2).

The abundance or biomass of benthic algae can be measured in several ways (Stevenson and Smol 2003, Steinman et al. 2006). Typically a known area of substrate is sampled using a brush to dislodge algae. Some researchers favor a suction device constructed by fitting a brush inside a cylinder to which a side port is added to withdraw the slurry by suction. The resultant slurry can then be filtered onto a filter paper and the cells counted, the biomass determined, or the chlorophyll pigment extracted and assayed using a spectrophotometer. Artificial

TABLE 6.1 Representation of major periphyton taxa in collections where all habitats were sampled, and from studies emphasizing epipelic and epiphytic assemblages. Patrick's (1961) data are from one time of year and include only those species represented by a minimum of six specimens in a very large sample (a count of 8,000 individuals). Inclusion of rarer species would at least double the species list. The studies of Moore (1972) and Chudyba (1965, 1968) probably represent close to the entire flora for the site.

Number of taxa

TABLE 6.1 Representation of major periphyton taxa in collections where all habitats were sampled, and from studies emphasizing epipelic and epiphytic assemblages. Patrick's (1961) data are from one time of year and include only those species represented by a minimum of six specimens in a very large sample (a count of 8,000 individuals). Inclusion of rarer species would at least double the species list. The studies of Moore (1972) and Chudyba (1965, 1968) probably represent close to the entire flora for the site.

Number of taxa

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