Have you ever noticed small creatures crawling on rocks in streams? These organisms are called benthic macroinvertebrates. Often referred to as macros, these creatures are visible invertebrates that live in the sediment of aquatic habitats, including aquatic insect larvae, crustaceans, snails, worms and other arthropods.
These organisms are important to the stream ecosystem as they decompose organic matter, provide vertebrates with a source of food and impact other populations of macroinvertebrates and young vertebrates (tadpoles and small fish). Since these organisms spend most of their life cycle in the water, their community structure can show the cumulative impacts of pollution. The presence and abundance of certain pollution-tolerant species, for example, can indicate specific environmental stresses on a stream ecosystem.
In Nine Mile Run, non-biting midge larvae and black fly larvae are heavily dominant in the macro community. These two species are extremely tolerant to pollution and indicate the presence of sewage pollution. Due to the aging storm and sewer infrastructure within the watershed, even small amounts of precipitation can – and does – cause sewage to overflow into Nine Mile Run. By collecting data on these creatures, we can determine if the health of the stream is improving over time.
Dr. Mary Kostalos