Specific Conductance
In the last post I talked about the stream temperature, discharge, and gage height and the importance of knowing the stream conditions before leaving on your trip to better prepare yourself for a more enjoyable time on the water. In the next part we are going to take a look at the water quality data that is taken at some of the sites.
These water quality parameters help keep track of the health of the waterway and can be an early warning sign for trouble if these parameters show up at unsafe levels to support aquatic life. If you have been following along from the beginning than you already know how to find the information for a particular stream and hopefully understand how to read and interpret the temperature, discharge, and gage height graphs. Hopefully you also have a good idea on how to use these graphs to help plan your adventures on the water as well.
There are 3 water quality data sets the USGS collects. They are the specific conductance, dissolved oxygen, and PH. Let’s take a look at the graphs for Kettle Creek in north central PA.
Specific conductance is a measure of the ability of water to pass an electrical current. Now I’m sure you know that water does pass an electrical current so how does that correlate to water quality? Well, if you take a glass of pure water and pass an electrical current through it the current is going to stay constant as long as everything stays equal. But if I were to drop say some lead into the glass or some other metal or perhaps dissolve some salt in the water then the amount of current the water is able to conduct will increase. If I were to put oil in the glass then the conductance will decrease.
In our waterways things like road salt, fertilizer, urban runoff, and raw sewage all have an effect on the conductance of our waterways. Rainfall can also effect the conductance of a waterway. Rainfall does not contain salts so it will dilute the waterway when it enters but at the outset of a heavy rain the initial runoff could contain fertilizers and other pollution that will drive up the conductance.
Once this initial pollution works its way through the waterway during a rain storm the conductance falls. However, if the conductance changes and there is no rainfall then that could be a good indicator that a significant polluting event occurred in the waterway. The conductance of a waterway stays within a fairly constant band. If over time we see the conductance either slowly increasing or decreasing then we would need to investigate to see why this would be occurring.
I will be talking about dissolved oxygen in the next post so please stay tuned.
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