Description of Study
The objective of this study was to define specific conductance in stream water under low streamflow conditions in Central New York. The study area covers parts of six counties in the Southern Tier region of New York State (fig. 1). This survey covered a range of watershed areas and land use types, and specifically targeted low-flow periods during the summer as the flow would be mostly derived from groundwater discharge at this time and represents the upper limit of conductance that can currently be expected. This study was funded by the New York State Department of Environmental Conservation.
Methods
The network of sites sampled was created using ARCMAP software. Over 280 sites were selected at locations where roadways crossed over streams, covering a range of stream sizes with drainage areas from less than 1 square mile to 38 square miles. Specific conductance measurements were collected between July 23 and July 26, 2012. Locations of sample sites were verified in the field using global positioning system units, and the mapped locations shown in fig. 1 reflect field-verified locations. Of the 280 sites selected for sampling, 262 contained enough water for specific conductance measurements.
Measurements were made using a multimeter that was calibrated at the beginning of each day using standards similar to expected specific conductance values. Field measurements and meter calibration were performed using methods outlined in Wilde and others, variously dated. Stream temperature was measured at all sites and stream pH was measured at some sites. In order to conduct measurements on baseflow conditions, streams receiving any flow from rain events were avoided until available streamflow data from local stream gages indicated that streams had returned to baseflow. In order to assess specific conductance variability during the study, specific conductance was measured over three consecutive days at two sites. The difference between the maximum and minimum specific conductance values for these two sites were between 7 and 12 percent, indicating minimal changes in specific conductance at these sites during the study period.
Results
Specific conductance measurements ranged from 34 to 923 micro-Siemens per centimeter (µS/cm), with a median of 195 µS/cm for the 262 sites. The data set (fig. 2) shows a trend of increasing conductance from east to west across the study area, as indicated by a lowess plot of specific conductance and longitude. The lowest specific conductance measurements were recorded in the eastern portion of the study area, as the median specific conductance for the samples collected east of -75.7 degrees longitude was 93, and 90% of these samples had specific conductance less than 200 µS/cm.
When the specific conductance is graphed over longitude, all but 2 of the 170 specific conductance measurements collected west of -75.7 degrees W are greater than 100 µS/cm. The highest specific conductance measurements were primarily collected in the central region of the study area, between -75.7 degrees W and -76.3 degrees W. This central region of the study area also displayed a wider range of specific conductance measurements, from around 100 µS/cm to the highest measurement recorded of 923 µS/cm. The western portion of the study area had specific conductance measurements primarily between 120 and 400 µS/cm, with one measurement of 660 µS/cm. This east to west increasing trend was also evident when the data were plotted by hydrologic unit.
Summary
Specific conductance was measured at over 262 stream sites across the study area during baseflow conditions in the Southern Tier of New York State in July 2012. The 262 sites sampled included a range of stream sizes and land-use conditions. Specific conductance measurements ranged from 34 to 923 µS/cm. The data indicate an increasing trend in specific conductance in streams from east to west. The lowest specific conductance values were present in the eastern portion of the study area.
References
Wilde, F.D., ed., variously dated, Field Measurements: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A6, accessed from http://pubs.water.usgs.gov/twri9A/ on January 25, 2013.
Project Location by County
Broome County, NY, Tioga County, NY, Delaware County, NY, Chemung County, NY
