Written by Skyline High Interns Elise, Ariella, and Amy.
Sometimes it may be hard to decide whether a stream is healthy or not, you cannot judge solely on the way that it looks. A main factor of determining stream healthiness is by taking a look at the insects within the water and seeing if there is biodiversity. If there is, then this means there are conditions in which many different species can survive. It is good to find that there are predatory insects because this can tell you that there are smaller ones for it to eat, otherwise they would not be present. Sometimes streams that aren’t in a beautiful surrounding area can be very healthy because no human interference would affect life within the creek. It is a good idea to consider the water source and the tributaries it flows through because it can tell us what will be affecting the stream. For example, if the stream goes under or near a freeway or a busy city then we know it is affected by the car pollutants and harmful chemicals in the atmosphere of a city.
In Oakland’s Sausal Creek, my group EarthTeam has been doing water tests and kick-samples to examine the water and life in the creek. In our findings, there is plenty of different species flourishing in the creek. Based on physical appearance, I’d say that it is healthy since you cannot see obvious litter or pollutant in or near the water. – Elise
Benthic macro-invertebrates are the small animals or bugs living among stones, logs, sediments and aquatic plants on the bottom of a body of water, in this case Sausal Creek. They are large enough to see with the naked eye (macro) and do not possess a backbone (invertebrate). The process of sampling for benthic macro-invertebrates involves four major parts – taking a kick sample, obtaining a leaf pack, collecting and transferring all the bugs, and identifying and enumerating them.
- To do the kick sample, we had to find a riffle (a shallower area with faster-flowing water and larger sediments), then hold a special bug-collecting net upright in the riffle to collect bugs. While holding the net we would pick up rocks and wipe them off in the water, and run the mud and pebbles from the bottom through our hands to get as many bugs as possible into the net.
- To obtain a leaf pack, we had to look for clumps of leaves that had fallen into the creek and accumulated behind rocks or other obstructions, and simply scoop it up. We would then add this to the stuff we had collected with the net to sift through for bugs.
- After taking multiple kick samples and obtaining a leaf pack, we had to transfer it all into a white tub, then begin sifting through it and taking out the mud, sticks and leaves to find the bugs.
- Finally, we had to pour the water in the tub through a sieve and pick out the bugs with entomology forceps. We used an ice cube tray to separate the bugs by species. Then we had to identify and enumerate them, recording how many of each species we found.
In practice, this process was pretty complicated, but once we learned how to do each step it got easier. It was interesting getting to see all the different types of bug species in Sausal Creek, and having the opportunity to work with a scientist to collect data. A lot of the process was trial and error until we understood how to do it correctly, but we all had fun watching the bugs with a magnifying lens. We learned about how the different bugs and their sensitivity to pollution can indicate how healthy the creek is. – Ariella
Water bugs are important parts of a creek ecosystem as they provide predators with food, herbivores can feed on the algae that grows on rock in the creek and dead leaves that fall into the creek, everything is a part of this ecosystem. For instance, if there was too much herbivores and not enough predators them most of the plants and algae on the rock will be eaten. This can lead to an imbalance in dissolved oxygen, that could lead to species being unable to receive oxygen to breathe through their gills. Thus most species will die until the oxygen level returns to a state that it can be functional for life again.
Many of the bugs or insects were larva of flying insects like a damselfly or a mayfly, many of these larvas have gills on their abdomens and three tails. The difference is that mayfly have feather like gills and damselfly tails are plate like. There was a really cool dragonfly larva and the way the body is designed is so that water goes into the gills and shoot out from the back as a way for the insect to shoot forward quickly. The shrimp were clear in color and very small, the snails very small as well, it was probably because they were immature ones. The humpless casemaker was very interesting because the cocoon was made of dirt sediment and pieces of plant when it begins to make it’s case. I wonder if the insect can be killed in the case. -Amy