Relating major ions and nutrients to watershed conditions across a mixed-use, water-supply watershed

350 210 Stroud Water Research Center

Dow, C.L., D.B. Arscott, and J.D. Newbold. 2006. Journal of the North American Benthological Society 25(4):887–911.



Stream inorganic chemistry was sampled under summer baseflow conditions from 2000 to 2002 at 60 sites as part of a large-scale, enhanced water-quality monitoring project (the Project) across New York City’s drinking-water-supply watersheds. The 60 stream sites were evenly divided between regions east and west of the Hudson River (EOH and WOH, respectively). EOH sites had generally higher ionic concentrations than WOH sites, reflecting differences in land use and geology. Within each region, variability in inorganic chemistry data between sites was far greater than annual variability within sites. Geology was an important factor controlling underlying baseflow chemistry differences within and between regions. However, after taking into account geological controls, anthropogenic land uses primarily defined ion and nutrient baseflow chemistry patterns at regional and watershed levels. In general, watershed-scale landscape attributes had either the strongest relationships with analytes or had relationships with analytes that did not differ fundamentally from relationships of riparian- or reach-scale landscape attributes. Individual analyses indicated no dominant watershed-scale landscape attribute that could be used to predict instream inorganic chemistry concentrations, and no single ion or nutrient was identified as the best indicator of a given anthropogenic land use. Our results provide a comprehensive baseline of information for future water-quality assessments in the region and will aid in examining other components of the Project.