The blog has been on hiatus for a while, partly because we’ve had so many exciting things going on. One of our current projects involves investigating the feasibility of using hydroponic gardens to improve water quality in a local urban lake (Saint Paul’s Como Lake), turning a waste product (nutrient pollution) into a product of value (locally grown food).
The rationale is simple: many of our urban lakes suffer from excess phosphorus, which comes from our lawns and gardens, pet waste, and leaves. Phosphorus is necessary for all life–it serves as the backbone of DNA, for example–but in lakes it fuels the growth of excess algae. The decomposing algae can use up a lake’s dissolved oxygen, causing fish kills, and algae-covered lakes are less desirable for recreation. Many different initiatives have focused on reducing phosphorus inputs to Como Lake, through increasing stormwater infiltration (through rain gardens or underground trenches) and from neighborhood leaf cleanup initiatives. While these initiatives have reduced P inputs, the problem is that there is a huge amount of phosphorus stored in the lake sediments, which is the main contributor to lake water phosphorus. To achieve any improvement in lake water quality, somehow we have to address this hidden source of phosphorus to the lake.
My students and I have conducted experiments with our 600-gallon aquaponics system for the last few years, in which vegetables grow hydroponically while removing nutrients from fish waste. We wondered about using similar technology to clean urban lakes, and received a grant through EPA’s People, Prosperity, and the Planet Student Design Competition for Sustainability.
Last summer Jessica Brown conducted the first phase of this work, funded by a Young Scholars grant through the UST Grants and Research Office. Jessica’s study focused on measuring the maximum rates that different plant species could remove phosphorus from lake water, and on identifying limitation by other nutrients (like nitrogen and iron) that limit plant growth in lake water. Her research showed that legumes (such as peas and beans) can partially compensate for low nitrogen in the lake water by “fixing” atmospheric nitrogen, but the plants require additional nutrition to thrive. Currently my Environmental Problem Solving class is designing an experiment to find the best solution to this problem. The class will also be exploring the effects of hydroponic gardens on lake water quality by building on the lake ecosystem model begun by research student Quinn Niederluecke.
In mid-April, a team of our students will travel to Washington D.C. to present our project at the National Sustainable Design Expo and compete for a Phase II award. We’ll be posting updates on the project periodically throughout this semester.