Over the last few weeks we've spent several hours at the Intrepid Pond with the AP Biology students from Grosse Ile High School. Their teacher, Ms. Jean Alred, and some of the students donned waders to collect water samples as part of a pre-assessment of the water quality. Their first visit was focused on physical and chemical determinations: pH, turbidity, temperature and dissolved oxygen. On their second visit they were excited to observe tadpoles and several bullfrogs. Now we know why an egret has been spending a lot of time there....good feeding grounds.
The purpose of the visit was to determine the diversity of macroinvertebrates present. They are the little animals without backbones that are visible without magnification. This assessment was important since macroinvertebrates are excellent indicators of overall water quality, especially over a period of time. Chemical analyses are snapshots of present conditions, while a macroinvertebrate assessment provides information over a longer period of time. Some of those critters are very sensitive to pollution while others are not.
So, simply put, if you find lots of different types of these critters, e.g. mayflies, stoneflies, damselflies you have a pretty healthy system. If you only find aquatic snails, worms, and leeches, it may be an indication of past and/or present pollution.
If you want to learn more about macroinvertebrates, click here: The Stream Study.