.|  Baltimore Ecosystem Study
Increased salinization of fresh water due to suburban and urban growth
Recent work based at the BES suggests that chloride concentrations are increasing at a rate that threatens the availability of fresh water in the mid-Atlantic U.S. (Kaushal et al. 2005). In streams of the Baltimore LTER site, we have observed chloride concentrations up to 25% the concentration of seawater during winters, and chloride concentrations unexpectedly remaining up to 100 times greater than forest streams during summers. Our work shows that mean annual chloride concentration increases as a function of impervious surface and can exceed tolerance for freshwater life in suburban and urban watersheds (Kaushal et al. 2005). Increased salinity can impair ecosystem functions relelvant to water quality maintenance including denitrification (Hale and Groffman 2006). Our work in the Baltimore region along with collaborators at the Baltimore Department of Public Work, U.S. Forest Service, and U.S.G.S., and U.S. EPA indicate that widespread increases in roadways and deicer use are now salinizing fresh waters, degrading habitat for aquatic organisms, impacting critical ecosystem functions, and also impacting large supplies of drinking water for humans. We are now investigating the effects of increasing salinity on ecosystem functions in streams draining urbanizing landscapes, long-term storage of salt in ground water, and use of isotopic techniques for “fingerprinting” of sources of salt to ground and surface waters.

Figure 1. Salt crystals on a storm drain that enters a major drinking water supply for the Baltimore, MD metropolitan area. Photo: Ken Belt.

Figure 2. Relationship between impervious surface and mean annual concentration of chloride in BES streams during a five-year period (R2 = 0.81). Sites are located along a gradient of urbanization. Dashed lines indicate thresholds for damage to some land plants and for chronic toxicity to sensitive freshwater life (Kaushal et al. 2005).

Hale, R.L., and P.M. Groffman. 2006. Chloride effects on nitrogen dynamics in forested and suburban stream debris dams. Journal of Environmental Quality 35: 2425-2432.
Kaushal, S.S., P.M. Groffman, G.E. Likens, K.T. Belt, W.P. Stack, V.R. Kelly, L.E. Band, and G.T. Fisher. 2005. Increased salinization of fresh water in the northeastern United States. Proceedings of the National Academy of Sciences of the United States of America 102: 13517-13520.

This research was supported by funding from the NSF Long-term Ecological Research (LTER) Program. This material is based upon work supported by the National Science Foundation under Grant No. 1637661. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.