Project overview
Stormwater ponds have long served as a best management practice to reduce flooding and filter pollutants. Thousands exist across Minnesota, but as more are built and older ones lose efficiency, traditional monitoring which is often costly and time-consuming has become harder to maintain. This highlights the need for a faster, more cost-effective way to assess pond performance and target maintenance.
This project tested and refined the Pond Assessment Tool, which uses spatial, water quality, and pond data to estimate risks like high phosphorus, sediment phosphate release, and anoxia. A beta version was well received by the Technical Advisory Panel, though further workshops were needed for refinement.
To ensure the Tool meets practitioner needs, the project included three key components: (1) additional analysis to develop a pond water balance feature; (2) validation using ponds with sufficient data; and (3) workshops to gather feedback and improve usability and outputs.who contributed intensive pond data collection to develop the Tool and test its components.
Data collection & synthesis included:
- Comprehensive survey (50+ sites)
- Intensive field sampling (35+ sites)
- High frequency monitoring (35+ sites)
- Laboratory studies (35+ sites)
- Leveraging existing datasets (200+ sites)
Research questions
- How well can a diagnostic tool assess the function of stormwater ponds for phosphorus removal (e.g., water column phosphorus concentration, sediment phosphate release potential, and oxygen status) from readily-available pond and watershed parameters?
- How does pond water balance affect retention of phosphorus (and other pollutants) and what indicators can be used to predict hydrologic function of stormwater ponds?
- What monitoring and maintenance options can be reliably linked to an assessment indicators of pond function (water column phosphorus, sediment phosphate release, anoxia, and water balance)?
Research findings
The updated Pond Assessment Tool can help pond managers organize the assessment of ponds at risk of high phosphorus concentration and sediment phosphorus release. Summary of the research and Tool updates:
- New Feature: A scoring and ranking feature was added to the Tool and the ability to compare multiple ponds.
- Model Improvements: Predictive relationships of the Tool’s sub-models were strengthened and new ones were added, resulting in wider range of conditions than in the previous version of the Tool. A Guidance Document was created on the range of input parameters used to develop the models.
- Model Limitations: As the models were unable to predict the wide range in TP or anoxia in some of the testing datasets, a broader set of parameters may be needed in the future to better describe total phosphorus and dissolved oxygen in ponds.
- Key Inputs: Anoxic factor and duckweed cover are crucial parameters for both screening and prediction assessment goals and more information on their determination is provided in the Guidance Document.
- Vegetation’s Role: Aquatic vegetation (especially submerged macrophytes) significantly affects TP and oxygen, and emerged as a potentially important driver of pond phosphorus and oxygen dynamics.
- Water Balance Data Gaps: Insufficient data limited development of water level indicators for the Tool, but the initial analyses of water level fluctuation could serve as a starting point for future work.
Key innovations/contributions
This project produced a faster, more cost-effective way to assess pond performance and prioritize pond maintenance and pond retrofits.
What does this mean for Minnesota?
The updated Pond Assessment Tool will help stormwater managers in Minnesota understand the likelihood of ponds at risk of poor phosphorus water quality functionality so that they can better prioritize pond management activities which could save resources involved in full-scale assessment or maintenance.
“Ponds are unique. They are complex but not all ponds are bad and we will continue to study more ponds.”
Poornima Natarajan, University of Minnesota
Project assets
Reports and Presentations
- Research brief 2025 .pdf
- Final Report 2025