Using Freshwater Invertebrates in River Monitoring
By: Damon Mullis
In the summer of 2014, we implemented a quarterly macroinvertebrate sampling regime to complement our continuous water quality monitoring programs on the Savannah and Ogeechee Rivers. Macoinvertebrates are any of a wide variety of invertebrates that live in aquatic habitats and are large enough to be seen without the aid of a microscope. Examples include crayfish, snails, segmented worms, and insects. The tolerance level of these diverse, localized populations to environmental stressors varies widely. As a result, their community structures are reliable indicators of changing environmental conditions over time and space. This characteristic makes macroinvertebrate assemblages ideal indicators of aquatic ecosystem health and quality. In addition, macroinvertebrates play an important role in freshwater food webs, serving as prey for other organisms including fish, amphibians, and wading birds. However, their role in processes like breaking down organic matter and nutrient cycling is likely their most significant contribution to the ecosystem. In fact, we initiated these biomonitoring projects because of the ecological importance and environmental utility of macroinvertebrate communities.
We collect macroinvertebrates by deploying Hester-Dendy multiplate samplers tied to floats that suspend them approximately 2 feet below the water’s surface. These samplers do not trap invertebrates; rather, they supply a stable substrate for them to inhabit. Fungus and bacteria start to grow on the samplers soon after they enter the water. This growth encourages the presence of species of macroinvertebrates that feed on these colonies. Other species use the stable substrate as a place to attach and filter food out of the flowing water. Predatory macroinvertebrates soon show up to feed on these other groups. After 30 days, the samplers are retrieved and the macroinvertebrates are identified, measured, counted, and classified into groups based on their ecological roles and tolerances to pollution. This data allows us to calculate abundance and biomass. We also use it to estimate diversity, biotic integrity, and functional roles for each community. Using this information in conjunction with data collected from our continuous monitoring stations allows us to detect changes in water quality and see how these changes directly impact biological communities.