Do waterbody classifications predict water quality?

• Class B waters had higher levels of some nutrients, ions, and solids than Class AA.
• Class B watersheds had less forest cover and more development and impervious cover.
• Water quality is more closely associated with land cover than classification.
• Some Class B waterbodies have water quality similar to Class AA waterbodies.
• Incorporating land cover could improve waterbody classification systems.

Many states classify waterbodies according to groups of designated uses, which suggests that classifications may be correlated with water quality. The primary assessments of water quality in the United States (the Biennial Integrated Water Quality Reports) do not consider classification, so the relationship between classification and water quality is untested. Additionally, water quality has been shown to be influenced by watershed land use; however, land use is not typically part of waterbody classification systems. To determine the relationships between waterbody classification, water quality, watershed land cover, and forest fragmentation, we analyzed existing water quality data for the State of Connecticut from the United States Geological Survey and the Connecticut Department of Energy and Environmental Protection and land cover data from the National Land Cover Dataset. Connecticut uses a unique classification system that includes separation of drinking water sources (Class AA) and waterbodies receiving waste water discharges (Class B). Using a comparison of multiple means, we found that Class B waters had higher levels of nitrogen, solids, chloride, sodium, dissolved copper, total iron, and dissolved manganese than Class AA waters. Watersheds upstream of Class B segments had less forest cover, more development and more impervious cover than watersheds upstream of Class AA segments. Class A sites had some similarities in water quality and land cover with Class AA sites and some with Class B sites. The subset of Class B waterbodies with “Class AA-like” water quality also had “Class AA-like” land cover. Based on this and a multiple linear regression analysis, we found that water quality is more closely related to watershed land cover and forest fragmentation than to waterbody classification. Our results suggest that watershed land cover likely is a better proxy for water quality than waterbody classification.