design for algal communities uses an approach that provides a common spatial scale (a defined sampling reach) to assess biological communities and habitat characteristics. This design also considers seasonal and hydrologic conditions that affect the algal communities. Other collection methods and equipment for algae sampling are described by Patrick and Reimer (1966), Weber (1973), Pryfogle and Lowe (1979), Stevenson and Lowe (1986), Britton and Greeson (1988), and Aloi (1990).
A variety of sample-collection methods focuses on qualitative multihabitat and quantitative targeted-habitat periphyton samples. The methods used depend on the type of sample to be collected, physical conditions in the sampling reach, and the relevance of the measurement to study-unit and national objectives. Forms for recording sampling data are provided.
The scheme for processing algal samples stresses preservation methods, preparation of subsamples, and labeling. Samples sent to contract laboratories for processing are monitored according to established quality-assurance and quality-control criteria.
The NAWQA sampling design emphasizes a multidisciplinary approach using physical, chemical, and biological tools to provide multiple lines of evidence with which to evaluate water-resource conditions. The NAWQA Program focuses on a broad spectrum of attr ibutes and sampling approaches to collect data in relation to (1) benthic invertebrate, fish, and algal communities; (2) stream habitats; (3) water-column measures of inorganic constituents (major ions, trace elements, nutrients), physical characteristics (suspended sediment, conductance, temperature), radionuclides, and organic compounds; (4) trace elements and organic compounds in bed material and aquatic biota; and (5) hydrology. Study-unit investigations consist of four main components: (1) retros pective analysis and reconnaissance, (2) occurrence and distribution assessment, (3) assessment of long-term trends and changes, and (4) source, transport, fate, and effect studies.
Retrospective analyses and reconnaissance efforts provide information used to focus NAWQA issues and aid in the design of NAWQA studies. Retrospective analyses are designed to provide historical perspectives of water-quality conditions and biota within a study unit and to assist in the identification of major natural and human factors that control water quality in that study unit. Analysis of retrospective information also provides baseline information to assist with the identification of candidate sampling locations. Sampling locations are chosen following a reconnaissance and evaluation of candidate sampling locations.
A reconnaissance consists of a rapid site assessment, including evaluations of stream access, stream habitat conditions, proximity of major natural or human stream influences, and methods and equipment appropriate for conducting various types of sampling at that location. A reconnaissance is conducted to familiarize project personnel with watershed features of the study unit and to evaluate and select candidate locations for subsequent sampling of biological, chemical, and physical characteristics of streams. This subsequent, integrated sampling effort is known as an occurrence and distribution assessment.