Monitoring Design Water Quality Monitoring and Human Health


parameters, sampling locations would be identified at varying depths as well as horizontal locations. Lakes often have a primary source of inflow and outflow, which are often sampled.


The most representative or average conditions in a lake are usually found where the lake is deepest. In natural lakes with a roundish shape, the deepest section is usually near the middle. Some lakes are not round of course, but may have a number of different fingers or bays. In these cases, it may be important to sample the deepest section in each bay, because each may have its own unique water quality characteristics.


Grab samples may be collected from a specific depth in the water column. This is the method most often used in citizen monitoring programs. Composite Samples are sometimes used where equal portions of samples from different depths are combined. Deeper sampling is accomplished using a special device; two of the most common are called Kemmerers and Van Dorns. The devices are basically cylindrical tubes with rubber stoppers at each end. They are lowered to the depth where a sample is desired; a weight is released that slides down the rope holding the devise. When the weight reaches the devise it triggers the stoppers to close and collect a sample from that depth. The sampler is then brought back to the surface (usually in a boat or on a bridge) and the sample is poured into a container.


When: Time of day and year


There are a number of factors to take into account that affect when you sample. The “when” in sampling refers to the time of day; the frequency of sampling, and the time of year. Some water quality conditions change with either the time of day or time of year or both.


Fish need oxygen just like we do, fish “breathe” through their gills and obtain oxygen that is dissolved in water. If there’s not enough dissolved oxygen in water, fish die. Dissolved oxygen levels in water are usually lowest first thing in the morning that’s when we would want to sample – when levels are at their lowest!


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