How much would reducing phosphorus improve water quality in the Lower Great Miami River?
That question led the Miami Conservancy District (MCD) and 15 regional communities and wastewater treatment providers to undertake an extensive scientific modeling project examining nutrients and river conditions.
Completed in 2017 by LimnoTech, the Lower Great Miami River Nutrient Management Project developed a water quality model to evaluate how changes in nutrient loading could affect algae and dissolved oxygen in the Lower Great Miami River.
The study provides important scientific information for communities making complex and potentially costly decisions about nutrient reduction and water quality.
Nitrogen and phosphorus occur naturally and are essential to aquatic ecosystems. Excessive amounts, however, can stimulate algae growth and contribute to water quality problems.
Nutrients reach the Great Miami River from multiple sources, including municipal wastewater discharges, runoff from urban and agricultural land, agricultural drainage, and groundwater.
Understanding how those nutrients behave after entering a large river is complicated. Nutrient concentrations alone do not necessarily explain how algae grow or how dissolved oxygen changes.
That is why MCD and its partners invested in a scientific model capable of evaluating the relationships among nutrient loading, algae, dissolved oxygen, river flow and other environmental conditions.
Ohio EPA had identified portions of the Lower Great Miami River as impaired and had begun establishing phosphorus limits for major wastewater treatment facilities.
However, a model had not yet been developed to estimate how reducing phosphorus loads would affect the river conditions associated with nutrient enrichment.
Fifteen communities and wastewater treatment providers joined MCD to fund development of that model.
The partnership included communities and wastewater providers from throughout the Lower Great Miami River corridor.
MCD contracted with LimnoTech to develop the Lower Great Miami River water quality model.
Researchers assembled extensive information about the river and used monitoring data representing a range of flow and environmental conditions to calibrate and evaluate the model.
The model examined factors including:
Nitrogen and phosphorus
Dissolved oxygen
Algae suspended in the water
Algae attached to the riverbed
River flow, depth and velocity
Wastewater treatment plant nutrient loads
Nonpoint-source nutrient loads
Different nutrient-reduction scenarios
The result was a scientific tool capable of testing how different nutrient management strategies could influence conditions in the Lower Great Miami River.
The modeling demonstrated that the relationship among nutrients, algae and dissolved oxygen in the Lower Great Miami River is complex.
One of the study's important findings was that large reductions in phosphorus discharged by major wastewater treatment facilities were not predicted to produce correspondingly large improvements in algae or dissolved oxygen conditions.
Even modeling scenarios involving very substantial reductions in point-source phosphorus produced relatively small changes in predicted river conditions.
This finding demonstrated why nutrient management decisions need to consider the complete river system rather than assuming that reducing a single nutrient source will necessarily produce a proportional environmental response.
The study also examined benthic algae—algae attached to rocks and other surfaces on the riverbed.
Modeling indicated that benthic algae played an important role in the daily fluctuations in dissolved oxygen observed in the Lower Great Miami River.
During daylight, algae produce oxygen through photosynthesis. At night, algae and other organisms consume oxygen. Large amounts of algae can therefore contribute to significant differences between daytime and nighttime dissolved oxygen levels.
Understanding these processes is important when evaluating both river health and potential nutrient management strategies.
Field observations also demonstrated another challenge in characterizing a large river: water quality conditions are not necessarily uniform from bank to bank.
Measurements collected during the project found substantial differences in dissolved oxygen across the river channel at the same time.
That means where and when a water quality measurement is collected can matter when interpreting river conditions.
The study does not conclude that nutrients are unimportant or that nutrient reductions are unnecessary.
Instead, it demonstrates something more useful: effective nutrient management requires understanding how the entire river system responds to different sources and different reduction strategies.
Nitrogen and phosphorus enter the Great Miami River from point and nonpoint sources. River flow, physical habitat, algae, sediment, sunlight, temperature and other factors can influence what happens after those nutrients reach the river.
The model gives scientists, regulators and communities another tool for evaluating which strategies are most likely to produce measurable improvements.
Wastewater treatment improvements can require significant public investment. Those costs ultimately affect communities, businesses and utility customers.
At the same time, protecting water quality is essential to healthy rivers, communities and ecosystems.
MCD supports using sound science to understand the causes of water quality problems and evaluate the environmental benefits of potential solutions before major investments are made.
The Lower Great Miami River Nutrient Management Project provides scientific information that can help support those decisions.
The 2017 study is part of a much larger body of MCD research into nutrients and water quality in the Great Miami River Watershed.
MCD's published research includes work examining:
Nutrient concentrations and loads
Long-term nitrogen and phosphorus trends
Benthic phosphorus
Nitrate sources
Surface water and groundwater relationships
Nutrient management and water quality modeling
MCD has also operated a surface water monitoring program focused on nutrients since 2006, providing long-term data about nitrogen and phosphorus conditions in the Great Miami, Stillwater and Mad rivers.
Explore MCD Water Studies and Research
It is a scientific modeling study completed in 2017 to evaluate how different nutrient-reduction scenarios could affect water quality in the Lower Great Miami River.
The Miami Conservancy District and participating regional communities and wastewater treatment providers contracted with LimnoTech to develop the water quality model and complete the study.
The research examined nitrogen and phosphorus and their relationship to algae, dissolved oxygen and other river conditions.
Dissolved oxygen is oxygen present in water and available to aquatic organisms. Its concentration naturally changes, but very low concentrations can stress or harm aquatic life.
Benthic algae are algae that grow attached to surfaces on the bottom of a river or stream. The Lower Great Miami River study found that benthic algae were important to understanding daily changes in dissolved oxygen.
No. The study found that the relationship between phosphorus reductions and river response was more complex than a simple one-to-one relationship. The modeling evaluated how different nutrient reductions could affect algae and dissolved oxygen and found that substantial reductions in point-source phosphorus alone were not predicted to produce similarly substantial changes in those conditions.
Long-term monitoring and scientific research help MCD and regional partners understand water quality trends, identify potential sources and evaluate strategies for protecting the Great Miami River and its tributaries.
Lower Great Miami River Nutrient Management Project
LimnoTech | February 28, 2017
Lower Great Miami River Nutrient Management Project (2017)
The Lower Great Miami River Nutrient Management Project is a modeling study of the potential effects of nutrient load reduction on water quality in the Great Miami River.
Nutrient Pollution, Nutrient Loading
Program - Great Miami River Watershed Nutrient Trading Program
Nutrient Concentrations in the Upper Great Miami River (2024)
Dual Isotope Tracing of Nitrate Contaminant Source in Surface and Groundwater in the Great Miami River Watershed, Southwestern Ohio (2019)
An investigation of sources of nitrate in water using stable isotopes of nitrate.
Summary of Nutrient Loads, Yields, and Mean Concentrations in the Great Miami River Watershed (2006 – 2016)
A summary of nutrient loads, yields, and mean concentrations in the Great Miami River Watershed.
Lower Great Miami River Nutrient Management Project (2017)
The Lower Great Miami River Nutrient Management Project is a modeling study of the potential effects of nutrient load reduction on water quality in the Great Miami River.
Benthic Phosphorus Fluxes in the Lower Great Miami River (2016)
The Benthic Phosphorus Fluxes in the Lower Great Miami River quantifies fluxes of phosphorus from sediment at locations along the Lower Great Miami Rivers.
Nutrients in the Great Miami River Watershed (2012)
Nutrients in the Great Miami River Watershed reviews nitrogen and phosphorus concentrations and loads in the Great Miami River Watershed from 2005 to 2011.
Nitrate Concentrations and Sources in the Elk Creek Watershed (2006)
Nitrate concentrations and sources in surface water and groundwater in the Elk Creek Watershed during 2003 and 2004.
