By Olivia Rose
The San Francisco Bay Watershed connects communities across more than 75,000 square miles throughout the state of California, and just tickles the southeast corner of Oregon. From the Sierra Nevada mountains down to the San Francisco Bay and ocean, this watershed provides drinking water for more that 25 million people, and is home to countless numbers of nonhuman living plants, insects, birds, fish, and animals. So how can we ensure that these communities, connected by water, are thriving and healthy? Well first, as with any good relationship, we need to check in first to see how things are going. Lucky for us, there’s an easy and fun way to investigate your local creek, stream, or river’s health using insects called benthic macroinvertebrates. These creatures are typically found dwelling at the bottom (benthic meaning bottom-dwelling) or along the sides of flowing bodies of water. Benthic macroinvertebrates are an essential part of the food web, and can help us understand the health of our watershed.
Rivers throughout our watershed are teeming with our benthic macroinvertebrate friends, who are playing two key roles in the food web. Firstly, as primary consumers, they eat living plant material from producers and provide food to the secondary consumers that may munch on these insects for a snack, like fish, turtles, and frogs. Secondly, as detritivores, macroinvertebrates provide a necessary service of eating and breaking down dead and decaying plants, therefore giving nutrients back to the water and the soil around it.
Aquatic macroinvertebrates are often the same insects we’re familiar with buzzing around on land, but in the water we’re just seeing them in an earlier part of their life cycle. For example, mosquitos live most of their life in water. Three out of four of the mosquito’s life cycle stages are spent in water, from egg to larva, to pupa. Only when it’s an adult does it sprout wings and try to bite you. It’s a similar story with our dragonfly, damselfly, mayfly, and beetle friends, among many others. Although their life cycle stories might be similar, each species of macroinvertebrate reveals a different story for the health of the water it calls home. Some macros are sensitive to water pollution, such as the caddisfly, while others are very tolerant to water pollution, like the mosquito. Benthic macroinvertebrates thrive on a scale of pollution tolerance, which means that if we can find and identify benthic macroinvertebrates in a local creek, stream, or river, we’ll be able to find out how healthy that body of water is, and therefore the community that surrounds it.
We do this with a few simple tools (see pictured below). The most “scientific” tool is a net of some kind. This could be a minnow net or a larger net, just something with fine enough mesh that the macros won’t slip through. You’ll also need a frisbee or a bucket, a spoon, an ice cube tray, and a dichotomous key. Once you’re at the body of water you hope to investigate, fill your frisbee or bucket with water from the stream and set it in a safe place where you can easily revisit it throughout the investigation. While searching for macroinvertebrates, be sure to check under rocks, in the areas with aquatic plants, and along dead logs or sticks. Then, you’re going to take your net and use the “dunk, dunk, dunk, SWOOP” method, running your net along the bottom or the sides of the creek or stream. Once you have a netful, head back to your bucket or frisbee, invert the net, and rinse to wash the macros off your net and into your frisbee or bucket. You’ll want to do this between 3 and 5 times to get a good sample.
Once you have completed your sampling, fill your ice cube tray with water, and begin sorting macroinvertebrates. Using your spoon, scoop out one macro at a time and place it in one section of the ice cube tray with others that look the same. Once all your macros are sorted, you can begin identifying them using the dichotomous key below. When you’ve identified each different type of macroinvertebrate, you’ll need to figure out their individual pollution tolerance. This can be done with just a quick Google search. As you discover pollution tolerance, use the guide below to tally how many fall into group #1) pollution sensitive, group #2) somewhat pollution tolerant, or group #3) pollution tolerant. Then, conduct the quick math necessary to determine stream health! Congratulations! Now you have a better understanding of where the stream’s health is at, and can better support our watershed with your knowledge.
Why do we care about the health of our local creeks, streams, and rivers? Well, checking in on the health of these flowing bodies of water is a lot like checking our pulse. When we check our pulse, we’re tuning in with our blood flow, and with our heart as it pumps blood throughout our bodies. Water, as it moves throughout the planet, is much like the circulatory system in our bodies. All the blood in our body is connected, and so is all the water on earth. So if flowing bodies of water are like the circulatory system, what’s the heart that pumps and moves water around the planet? Any guesses? THE OCEAN! So by checking the health of our local flowing bodies of water, we’re tapping into a much larger system, and ensuring the health of our ocean, the heart of our big blue planet.