Periphyton and phytoplankton monitoring

Phytoplankton, or free-floating algae, is the base of most aquatic food webs, and fish production is linked to phytoplankton primary production. Excessive nutrient and organic inputs from human activities lead to eutrophication, characterized by increases in phytoplankton biomass, macrophyte biomass, nuisance algae blooms, loss of water clarity from increased primary production, and loss of oxygen in bottom waters. From a human perspective, eutrophication problems might include loss of aesthetic appeal, decreases in desirable gamefish, loss of accessibility due to increased macrophyte production, and increased cost of treating drinking water.

Periphyton, the algae growing on solid substrates (rock, wood, sediment, macrophytes), have a long history of use in bioassessment of streams (Patrick 1949). Ecology of periphyton is much like other algal assemblages: they respond to nutrient enrichment; they are cropped by grazers; and their species composition is affected by pH, metal concentrations, trace elements, and contaminants. In addition, periphyton are affected by the physical and chemical characteristics of their substrate. Like phytoplankton, periphyton is subject to changing water chemistry and seasonal succession.

Phytoplankton were sampled at each site with a 1-liter grab sample. Each grab sample was wrapped in foil, placed on ice in a closed cooler, and either filtered in the Agency's mobile field laboratory or transported to the EPA's laboratory at 4°C in the dark until processing. The samples were filtered through 47 mm, 0.7 µm glass fiber filters and frozen until further processing was performed. EPA Region 7 standard operating procedure (SOP) 2334.22A was followed for extraction and analysis, which involved fluorometric determination on acetone extracts.

Periphyton samples were taken from each of the 5 transects at a site. Five rocks with relatively flat surfaces were selected from at or near each transect. A delimiter with known surface area was placed on the rock with downward pressure to seal in the sample. Within the delimiter the rock surface was scoured with a stiff bristle brush while rinsing the rock surface with de-ionized water. The dislodged periphyton and de-ionized water were aspirated into a sample vial. This procedure was repeated three times or until the sample vial was approximately three quarters full. For detailed sampling methods see Description and Protocol for Two Quantitative Periphyton Samplers Used for Multihabitat Stream Sampling (Bouchard and Anderson, 2001). Five separate samples were collected at each stream site to account for within site variability, labeled, wrapped in foil and either field filtered or transported to the laboratory at 4°C in the dark until processing. For sampling and processing see EPA Region 7 SOP 2334.22A.