Water quality lab preparation

Contents of this module

In this lab activity, we will get some practice interpreting temporal patterns in water quality associated with precipitation response hydrographs. While the specific mechanisms governing the interactions of water quality and quantity in watersheds are quite complex, two basic patterns in the alignment of changes in concentration with respect to changes in flow tend to occur, resulting in evidence of either a flushing pattern or a dilution pattern. You will be developing a calibration curve to estimate the changes in concentrations of dissolved solids at a gauge based on measurement of specific electrical conductivity. Then, you will be comparing the times series data of discharge, concentration, and load to look for patterns typical of flushing or dilution phenomena in storm and seasonal precipitation responses (17:58 min).

Here is a spreadsheet template you may want to download to follow along with the following exercises.

Click to download the Excel spreadsheet

To build a calibration relationship between total dissolved solids (TDS) and specific electrical conductivity, we will need to learn how to download water quality sampling data for a gauge where we would like to estimate TDS over time (10:00 min).

Here is a review of using the legacy Excel data import tool to make the downloaded data available in a spreadsheet (6:35 min).

The more powerful (and newer) power query tool in Excel can also be used to import the data (7:14 min).

Electrical conductivity is frequently used as a linear indicator of total dissolved solids. Assumption that this relationship is consistent through a precipitation event may be problematic because the specific constituents of TDS might vary and thus have an inconsistent relationship with electrical conductivity. In fact, the relationships you will likely see in this exercise will demonstrate a fairly rough relationship between TDS and conductivity. Despite the roughness of the estimates, there is no difference in the practice of interpreting patterns in these data than a more robust racer, and collecting the high frequency concentration measurements of a more robust tracer necessary for this type of time series analysis is often impractical (9:12 min).

Using the calibration above, we can now derive the time series of concentrations and loads accompanying storm and seasonal hydrographs (7:34 min).

Finally, we can explore the full complement of bivariate relationships among discharge, concentration, and load to seek evidence of flushing or dilution in watershed behavior (14:00 min).

Click this link to download the MS Powerpoint file

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