A Science Nerd Learns About P

The first time I visited the St. Croix Watershed Research Station in Marine I was a little awestruck. I toured the station with other members of the Minnesota Naturalist Association, a group of self-professed nature nerds, and we totally geeked-out learning about the high-tech methods the scientists there were using to track water pollution. At the time, the researchers were using a combination of lead-210, cesium-137 and radiocarbon dating to measure the rate of sediment and phosphorus accumulation in Lake St. Croix from 1850 until today. As we learned with fascination, they could even use these methods to determine if a particle of dirt at the bottom of the river came from a farm field or a stream bank. These scientists were doing real life CSI-style investigations at an idyllic setting near the banks of the St. Croix River and many of us in the room yearned for similar jobs.

Eight years later and now working in the St. Croix Valley, I’ve still got a bit of a science-nerd crush on the folks at the Watershed Research Station. At the 11th Annual Protecting the St. Croix Conference, held yesterday in River Falls, I joined more than 100 attendees to hear about cutting-edge research that’s helping us to protect the places we love. The St. Croix River is struggling today as an influx of phosphorus from farm fields, residential areas and wastewater treatment plants gradually changes our treasured river from blue to green. As a result, it was officially listed as impaired in 2008, proving that even Wild and Scenic Rivers can become polluted.

Chemistry geeks like myself can appreciate the humor of an element with the symbol P that makes a blue river green.  Not surprisingly, the audience guffawed when Jim Almendinger, senior scientist with the watershed research station, told us that Hennig Brand discovered phosphorus in 1669 by distilling his own urine.  Funny as it may be to talk about P in the water, however, the consequences are serious for the St. Croix River as well as countless cherished lakes throughout our region.

Both nitrogen and phosphorus are limiting nutrients, meaning they are less abundant that other natural elements in our soil and water. Farmers apply phosphorus to their fields to help seeds grow in the spring and then nitrogen throughout the summer to keep the plants growing taller and larger. Unfortunately, both nutrients have the same impact on aquatic plants. In freshwater lakes and rivers, extra phosphorus helps algae and other plants in the water to grow and spread. In the Gulf of Mexico, a saltwater system, nitrogen entering from the Mississippi River feeds toxic algae, resulting in a dead zone the size of New Jersey where nothing else can live.

If only there were a giant spigot somewhere that we could turn off, it would be easy to keep excess nutrients out of our lakes, rivers and the ocean. Unfortunately, the St. Croix watershed covers approximately 7,760 square miles of land in Minnesota and Wisconsin, and there are a million nutrient sources both large and small within this area. Some nutrients originate from fertilizers that are added to the soil on farm fields, residential lawns, golf courses and community parks. To address this problem, Minnesota passed a law in 2006 requiring all homeowners to use phosphorus-free fertilizer on their lawns. Wisconsin followed suit with a similar law last year. It turns out that our northern soils are already rich in phosphorus, so we don’t need any more from fertilizers to grow healthy lawns. Farmers have also begun to reduce the amounts of nitrogen and phosphorus they use on their fields so that they can continue to grow abundant crops without sending extra nutrients into our waterways.

A bigger challenge, however, is comes from sediment and organic debris. Phosphorus clings to soil particles, so when dirt from farm fields, construction sites and residential yards washes into nearby lakes and streams, it not only makes the water muddy, but also rich in nutrients. Because we have been using artificial fertilizers for years, our soil has nearly twice as much phosphorus in it as it used to, making the problem even worse. There is also phosphorus in organic debris like grass clippings and leaves. If the debris stays on our property, it is no big deal, but if rain or melting snow washes those leaves and grass clippings into streets and streams, our water can quickly turn green.

A collaboration of local and state government entities as well as researchers and citizens is currently developing a plan to turn the St. Croix River from green back to blue. This plan builds on years of research from places like the St. Croix Watershed Research Station as well as on-the-ground work being done by Soil and Water Conservation Districts and others. Although the St. Croix Basin is huge, we know that we can make a difference with simple practices like raingardens and buffer strips that keep sediment and phosphorus out of our waterways. Scheduled for completion in June 2011, the plan will identify the biggest sediment and nutrient sources for the river, as well as strategies for keeping it all out of our water. If you want the one-sentence summary, it’s simple. It’s up to all of us to stop runoff and erosion from our own properties, otherwise in ten years, we’ll be swimming in P.