What time period is covered by the NAWQA study?
This study is primarily based on results from NAWQA’s first decade of water-quality assessments, which were completed on a rotational schedule from 1992 to 2001 in 51 major hydrologic systems across the country—referred to as Study Units—as well as the High Plains Regional Groundwater Study, using a nationally consistent study design. Assessments were conducted in 20 Study Units during 1992–1995; in 16 during 1996–1998; and in 15 Study Units during 1998–2001. (Go to the NAWQA web site for a map of Study Units.) In addition, selected streams and groundwater were sampled through 2004 to assess the effects of nutrient enrichment on stream ecosystems (2003 – 2004) and to assess trends in nutrient concentrations in streams (1993 – 2003) and groundwater (first sampled once during 1988-1995, re-sampled once during 2000 – 2004).
