Chloride in Urban Streams in Maine Thomas Parr Prepared for Salt Management Group Meeting 09/13/2011

Chloride in the Baltimore Long-Term Ecological Research (LTER) site freshwater aquatic organisms and their uses should not be affected unacceptably if-the four-day average concentration of dissolved chloride, when associated with sodium, does not exceed 230 mg/L more than once every three years on the average and if the one-hour average concentration does not exceed 860 mg/L more than once every three years on the average. This criterion probably will not be adequately protective when the chloride is associated with potassium, calcium, or magnesium, rather than sodium. – EPA 1988 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(Kaushal et al. 2005). Dashed lines indicate thresholds for damage to some land plants and for chronic toxicity to sensitive freshwater life (EPA 1988) http://www.beslter.org/frame4-page_3f_08.html

Tracking Chloride Sources Cl- source was tracked in Fishkill Creek, NY using elemental ratios (Jin et al. 2011) Cl:Br <2000 indicates marine influences (Mullaney et al. 2009) Na:Cl - 1:1 indicates road salt influences and direct flowpaths. Other deicers will be different Cl- from road salt 85% Cl- from home water softeners 12%

Maine Chloride – Conductivity 04/28/2011-5/14/2011 This method required dilution of samples. Also note that chloride in maine streams is below the 250 ppm threshold noted by Kaushal et al 2005. Should be noted that this is information that the long creek requested in its 2010 RFP for monitoring. Also this is very close to the slope obtained from preparation of SC in DI water in the lab.

Maine Chloride Conductivity 8/17/2011-09/03/2011 ~30 sites + brunswick are post irene.

2 Season Conductivity Relationship Fall conductivity is 3 times higher than it is in the spring. This is likely due to application of deicers in the late fall

-Spring 2011 Cl- is 1.52 times greater than fall 2010 Cl- British Columbia US EPA Long Creek Sites The setting of a chloride standard is very murky. Some states (iowa) have proposed a multiple stressors model in which the allowable toxicity of chloride varies in the presence of other compounds (e.g. presence of sulfate would allow for a higher Cl value). -Spring 2011 Cl- is 1.52 times greater than fall 2010 Cl- -Only two sites consistently exceed the 230 ppm chronic toxicity threshold, and one reaches that threshold seasonally. -Conductivity Cl- is likely higher during spring snowmelt. -Cl- was estimated for fall 2010.

Chloride Impervious cover relationship Fall 2010 My larger survey includes lands that are clearly proximally influenced by agriculture, forestry or some other land use. These sites represent a subset of sites I will be using for other studies that I have identified as “urban.” The large scatter above 10% is likely due to effective imperviousness.

Chloride impervious cover relationship – Spring 2011

Attainment class Chloride Spring 2011 (ppm) Correlative association among imperviousness, chloride, and Maine DEP attainment class. % watershed total imperviousness

Conclusions Chloride increases in the spring likely due to winter deicers. Sources of Cl- can be tracked using ion ratios specific to deicer composition. A minority of low order streams seem to exceeding or approaching chronic toxicity thresholds. Little is known about acute chloride concentrations in Maine. Chloride increases with increase in extent of impervious cover (IC). This relationship is stronger at lower levels of IC and weaker at higher levels. The specific pattern and purpose of high IC is likely a key predictor of Cl in the waterways 10% IC seems to be the threshold where the relationship becomes more scattered More information on effective imperviousness is needed