By Mike Ekberg, manager of water monitoring and analysis
Drastically reducing nutrient discharges from wastewater treatment plants won’t be enough to further improve water quality in the Great Miami River from Troy to just downstream of Fairfield, Ohio. That’s what a study, funded by 15 regional wastewater treatment plants and cities, showed.
Excessive nutrients in water (nitrogen and phosphorus) fuel excessive growth of algae and are a leading cause of impairment to biological communities in rivers and streams. Nutrients above natural levels in rivers and streams come from human sources, primarily agricultural fertilizers and municipal sewage.
The Miami Conservancy District (MCD) and the 15 partners chose LimnoTech, an environmental science and engineering firm headquartered in Ann Arbor, Michigan to complete the study. The company developed a water quality model and ran scenarios to look for potential improvement to river quality, specifically from decreased phosphorus discharges.
The model relied on many sources of data including water-quality data collected by MCD’s hydrology team. In addition, the model incorporated a Hydrologic Simulation Program — FORTRAN (HSPF) model, developed by the United States Geological Survey and MCD, to simulate tributary watershed flows.
An important objective of the project was to ensure that the model developed to represent water quality in the Great Miami River was scientifically sound. Three internationally recognized water-quality monitoring experts reviewed the model and endorsed it as “state of the science.”
Treatment plant upgrades won’t do enough
LimnoTech’s modeling study suggests that technology upgrades to 13 municipal wastewater treatment plants would reduce phosphorus levels in the Great Miami River downstream of Troy. But the improvements wouldn’t be enough to stop excessive algal growth which can cause large swings in oxygen levels and threaten aquatic life in the river.
Another important finding of the study is that no dissolved oxygen measurement collected at a single point in the river is representative of the entire river channel. There is wide variability across the channel and at different upstream and downstream places. Therefore, no single point measurement should be relied on to determine overall river health or to set water quality goals.
River quality high but more improvements challenging
Excessive algal growth negatively affects the river’s health. Even when the model simulates drastic reductions from wastewater treatment plants, algal levels in the river remain too high to show significant improvement.
The study results don’t point to a realistic, cost-effective solution to improve the river.
It appears there’s no silver bullet, no single step that will fix the problem.
It’s likely some combination of reductions in nutrients from agricultural fertilizers and wastewater treatment plants will be necessary to resolve excessive growth of algae in the Great Miami River and reduce nutrient loads delivered downstream to the Ohio River and ultimately the Gulf of Mexico.
MCD is working with Limnotech to further the research to determine the amount of phosphorus and nitrogen reductions necessary to reduce algal communities in the Great Miami River.
MCD facilitated the study, and provided technical support and water quality data. The partnership also included: the cities of Dayton, Englewood, Fairfield, Franklin, Hamilton, Miamisburg, Middletown, Springboro, Troy, Union, and West Carrollton; Tri-Cities Wastewater Authority on behalf of the cities of Huber Heights, Vandalia, and Tipp City; and Montgomery County.