1. Characteristics of Algal Assays
Algal assays consist of three steps:
• selection and measurement of appropriate factors or conditions during the assay (e.g., biomass indicators, such as measured or calculated dry weight);
• presentation and statistical analysis of measurements; and
• interpretation of results.
Interpreting the results involves assessing receiving water to determine its nutritional status and its potential sensitivity to change, the effects of chemical constituents on algal growth in receiving waters, effects of changes in waste treatment processes on algal growth in receiving waters, impact of nutrients in tributary waters on algal growth in lakes and confluent receiving waters, and effects of measures used in lake restoration and advanced waste treatment.
The maximum standing crop and the maximum specific growth rate are responses that can be estimated from growth measurements. The maximum standing crop described in this method is proportional to the initial amount of limiting nutrient available. The maximum specific growth rate is related to the concentration of rate-limiting nutrient present.
The algal test procedure for determining a water sample’s primary productivity is based on Liebig’s law of the minimum, which states that growth is limited by the substance that is present in minimal quantity in respect to the organism’s need. Biostimulants are substances that increase algal growth or the potential for algal growth.
Algal species used in biostimulation tests are selected to allow for a standardized test of growth response using a well-characterized organism under standard laboratory conditions. See Sections 10010, 10200, and 10300 for methods appropriate to field studies.
The effects of various substances on maximum crop of selected algal species cultured under specified conditions are measured in this test. Results are assessed by comparing growth in the presence of selected nutrient and chelator additions to growth in controls. Experimental designs must incorporate sufficient replication to permit the statistical evaluation of results.
A method for growth inhibition tests with algae has been published.1