The foundation for quality natural waters research begins with superior sampling methods. Even the best analytical measurements are unusable if the sample was improperly collected or was contaminated. A variety of considerations are important to collecting quality samples including where the sample is collected, conditions during sample collection, and specific sampling techniques.
When choosing the sampling location, a few general guidelines should be followed. Primarily, the chosen sampling location should be relevant to the specific parameters being tested. For example, if data are desired about water flowing into a certain area, samples should be taken there as well as upstream of that area. Additionally, the sample should be taken at an area where natural turbulence provides for good mixture of the water. This is important to ensure that the sample accurately represents the concentrations of the components in the entire body of water.
Among other factors, weather conditions are very important to consider in determining when samples should be collected. Temperature has a large effect on aquatic organisms, for example, if water temperature is extremely low, microbial activity would be at a minimum. These conditions would not be preferred by a researcher interested in microbial behavior. Additionally, rainfall is an important consideration as well, as it has the potential to affect turbidity, pH, dissolved oxygen, etc. As a result, the research goals must be the basis for choosing the best time to collect samples.
There are several different ways to take sets of samples that exist for different research purposes. The basic sample type is known as a grab sample, which is defined as an individual sample collected over a period of time no greater than 15 minutes. More specific types of grab samples exist such as: surface grab samples, subsurface grab samples, and integrated grab samples which are a mixture of grab samples collected from different points in a short period of time.
As always, avoiding contamination of the samples is of the upmost importance and measures tailored to the specific research goal should be used. Consider rinsing before water collection. When collecting samples to be analyzed for inorganic compounds, the sampling container should be rinsed with the sample water; however, samples to be analyzed for organics should not be rinsed. When analyzing pH, using grab samples is the proper collection method. Further examples of goal-specific collection techniques can be found in the Manual of Ohio EPA Surveillance Methods and Quality Assurance Practices.
Content on this web page authored by Michael Irwin, Kris Roser, Jackie Smith & Courtney Timmons.