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Water Quality Meter
During each quarterly sampling period for pad sites and surface bottles sites (thrice yearly for reservoir sites), field personnel use a Hanna combination meter (see Figure 1) to measure pH, temperature, electrical conductivity, and total dissolved solids (TDS) in water.
For pad sites, the meter is placed into an available pool or stream of water. For bottle sites, the meter is placed directly into the stream where the bottle sample was taken. Each meter used in the field is calibrated periodically to ensure that pH and conductivity readings are accurate. The field TDS measurement is simply a calculated value from the electrical conductivity measurement, which usually differs from the TDS value measured in the laboratory via a gravimetric method.
From approximately March to October or November of each year, the project installs and maintains a continuous stream monitoring device known as a Levelogger. This device is suspended in a stream and anchored to a tree or other sturdy support and left in the field to collect data every 15 minutes. Periodically, project personnel visit each Levelogger site and download the information from the logger to a laptop computer.
While the Levelogger does not provide as much information as the Hanna field meter, it does provide a continuous record of stream quality parameters over the sampling period. By reviewing the data, we can determine if there were any times during deployment that the stream was affected by an event to cause a dramatic increase in temperature or conductivity. Increased conductivity can usually be attributed to an increase in total dissolved solids (TDS). In addition to these field measurements, we compare the average daily conductivity values to recorded precipitation events. It is noted that there is a fairly good inverse relationship between precipitation and TDS. Higher rainfall usually causes TDS values to decrease (dilution), whereas long periods of no or little precipitation causes TDS values to increase (concentration).
- Reservoir samples are taken three times per year at different intervals than pad and surface bottle sites because the boat needed to gather these samples is removed from the lake between November and March. Reservoir samples are also timed to avoid effects arising from the seasonal overturn of thermal layers in the reservoir.