Benthic algae (periphyton) and phytoplankton communities are characterized in the U.S. Geological Survey's National Water-Quality Assessment Program as part of an integrated physical, chemical, and biological assessment of the Nation's water quality. This multidisciplinary approach provides multiple lines of evidence for evaluating water-quality status and trends, and for refining an understanding of the factors that affect water-quality conditions locally, regionally, and nationally. Water quality can be characterized by evaluating the results of qualitative and quantitative measurements of the algal community. Qualitative periphyton samples are collected to develop of list of taxa present in the sampling reach. Quantitative periphyton samples are collected to measure algal community structure within selected habitats. These samples of benthic algal communities are collected from natural substrates, using the sampling methods that are most appropriate for the habitat conditions. Phytoplankton samples may be collected in large nonwadeable streams and rivers to meet specific program objectives. Estimates of algal biomass (chlorophyll content and ash-free dry mass) also are optional measures that may be useful for interpreting water-quality conditions. A nationally consistent approach provides guidance on site, reach, and habitat selection, as well as information on methods and equipment for qualitative and quantitative sampling. Appropriate quality-assurance and quality-control guidelines are used to maximize the ability to analyze data locally, regionally, and nationally.
The collection of algal samples is designed to complement the collection of physical and chemical data at National Water-Quality Assessment (NAWQA) Program basic fixed sites and at stream locations chosen for synoptic surveys and case studies. The sampling methods and procedures described are intended to provide guidance to personnel collecting algal samples as part of the NAWQA Program.
The U.S. Geological Survey's (USGS) NAWQA Program is designed to assess the status and trends of the Nation's water quality and to develop an understanding of the major sources and factors that affect the observed water-quality conditions and trends (Hirsch and others, 1988; Leahy and others, 1990; Gurtz, 1993). The NAWQA Program is organized into 60 study units on the basis of hydrologic systems (major river basins and large parts of aquifers). Personnel in each study unit conduct water-quality investigations for 4 to 5 years, followed by 5 years of low-level monitoring, with the cycle then repeated (Hirsch and others, 1988; Leahy and others, 1990). Activities are staggered so that approximately one-third of the study units are in an intensive data-collection phase each year.