Water areas are some of the most difficult parts of the environment to measure.  Many water-based ecosystems are constantly changing, causing data from scientific experiments to vary greatly.

Because water ecosystems are so dynamic, environmental problems that spread to the water rapidly intensify.  For example, when the Exxon Valdez spill occurred, the oil was carried for hundreds of miles.

A Stream.  Photo Credit: ClickART Image Pak.

There are several types of environments based on water.  Oceans, streams, lakes, reservoirs, and groundwater are all water-based ecosystems that are studied frequently.  Of course, water plays an important role in every ecosystem, so scientists' interest in performing experiments on water may stretch well beyond the few ecosystems listed above.

Within a body of water, there can be significant variation.  Different temperatures, densities, chemical compositions, gases, and pollution levels might be noted in different areas and at different depths.

As a result of the differences between different parts of the same body of water, sampling must be performed carefully.  This is especially true when one is measuring pollution in a water body, because pollution is seldom spread evenly throughout.

Other difficulties in measuring water samples exist.  Since some pollutants are highly volatile, meaning they can turn into gas quickly, tests must be performed immediately.  Also, water samples can easily become contaminated, ruining the results of an experiment.

In the process of a water experiment, other issues that affect accuracy arise.  For example, if water is filtered to remove some undesired elements, the sample will likely lose some components that need to be measured.  As a result, water analysis is very difficult, and must be performed with great care and accuracy.