Look closely and you might see two giant water scorpions, several dozen dragonfly and damselfly nymphs, a spoonful of nematodes, one fat pumpkinseed, thirty thin fry, a squadron of scuds, and eleventy-hundred tadpoles of varying shapes and sizes. Explore the smaller side of nature and you’ll be surprised to find a world in miniature, teaming with life, in little more than a bucket of water.
Aquatic scientists use a variety of techniques to measure the health of rivers, lakes and streams. The water monitoring team at the Washington Conservation District works on behalf of area watershed management organizations to monitor water quality in 80 lakes and more than 40 streams each year. They collect water samples to analyze levels of dissolved oxygen, phosphorus, chlorophyll-a, and minerals and nutrients such as chlorides and nitrogen. In addition, staff and volunteers routinely collect information about water levels, temperature, and water clarity (measured by lowering a secchi disk into the water until it can no longer be seen). Measuring the physical and chemical properties of our local lakes and streams only tells part of the story, however.
A healthy lake is a thriving ecosystem, alive with millions of organisms in an assortment of colors and sizes. Phytoplankton form the basis of aquatic food webs; these tiny, single-celled organisms produce food through photosynthesis, using carbon-dioxide and energy from the sun. In addition to phytoplankton, aquatic plants (also called macrophytes) grow in and on the water, providing food turtles, birds and other animals. Zooplankton are the tiniest animals in the water, and they feed on the phytoplankton. Next up are the aquatic invertebrates, such as insects, snails, leeches, worms, freshwater shrimp, and water fleas. These become food for small fish, which in turn become food for large fish.
We can learn a lot about the health of a lake or stream by examining its tiniest inhabitants. As part of Minnesota’s Volunteer Stream Monitoring program, students from Stillwater Area High School work with Conservation District staff to search for and collect aquatic invertebrates in Brown’s Creek and Valley Creek. Some species, like caddisfly larvae, stonefly nymphs, and riffle beetles can only tolerate cool, clean water. Others, like midges and pouch snails can live in fairly polluted water. In recent years, Brown’s Creek has struggled with warm water and high levels of copper that periodically kill species of aquatic invertebrates that trout in the stream depend on. The Brown’s Creek Watershed District has now completed a number of buffer plantings and stormwater treatment projects aimed at cooling the water and protecting the stream’s ecosystem.
This summer, the East Metro Water Resource Education Program held a series of family-friendly “pond dipping” events throughout Washington County to help people explore the smaller side of nature in their local lakes and ponds. During the programs, we used highly scientific equipment (clear plastic containers, fish-tank nets, and plastic spoons) to collect water samples and look for aquatic critters. It was a fun way to get outside, and an easy activity for children to replicate on their own after the programs. Now, in the dog-days of summer, most of the insect nymphs have emerged and flown away and tadpoles have turned into frogs. Even so, the water’s edge is still alive, waiting for explorers.