Posted by Angie Hong | Posted in Keeping water clean | Posted on 21-10-2013
At last month’s Children’s Water Festival in St. Paul, I used a groundwater model to talk with fourth grade students about how surface and groundwater resources connect and how we can keep them both clean. In one demonstration, I used food coloring to illustrate how fertilizer from a farm field could pollute nearby wells and streams. Afterwards, a parent asked me an interesting question, “If fertilizer is potentially harmful, do local government agencies support using GMO [genetically modified] crops to reduce fertilizer use?”
In a recently released paper, Nitrogen in Minnesota Surface Waters: Conditions, trends, sources and reductions, the Minnesota Pollution Control Agency (MPCA) reported that nitrate concentrations in the Mississippi River have increased by 87-283% (depending on location) between 1976 and 2010 and they attributed 70% of that nitrogen to agricultural sources. Too much nitrogen in the water can harm fish and aquatic life and, once it leaves Minnesota via the Mississippi River, contributes to the oxygen-depleted “dead zone” in the Gulf of Mexico. Meanwhile, in southern Minnesota where sandy soils and sink holes are common, the Minnesota Department of Health has found that many private and community wells have unhealthy levels of nitrates due to fertilizers leaching down into the groundwater; this puts pregnant women and infants at risk of developing “blue-baby syndrome.”
For the past several years, local and state agencies have primarily focused on keeping another nutrient – phosphorus – out of our water because it can cause toxic algae blooms and deplete oxygen levels in lakes and rivers. Phosphorus is a natural element in leaves, grass clippings and soil that is also an important component of fertilizer used to grow crops. Rural and agricultural areas contribute 70-80% of the phosphorus to the Mississippi, Minnesota and St. Croix Rivers.
Given these stats, it is obvious that we need to make changes in our agricultural systems to protect groundwater resources and restore our lakes, rivers and streams to good health. Since most Minnesotans are not farmers, however, it is not always obvious what kinds of changes would help.
To begin, it’s important to understand that nitrogen and phosphorus are natural elements and also vital to plant growth. Nitrogen is water soluble, meaning it dissolves into water and will stay in that water as it soaks into the ground or runs over the land. The MPCA’s nitrogen study found that 30% of the nitrogen entering the Mississippi River comes from groundwater underneath cropland, 37% comes from tile lines used to drain cropland, and 5% comes from farm field runoff; most of this comes from fertilizer. Some of the phosphorus in our rivers also comes from fertilizer, but a lot is adhered to soil particles that end up in the water when there is erosion on the land or in rivers and streams.
Whether or not a farmer uses GMO crops has little to no impact on how much fertilizer they need. For example, Roundup Ready® crops can survive herbicide applications, but still require the same amount of nutrients to grow. Practicing organic farming prevents environmental impacts due to pesticides, but doesn’t reduce the need for fertilizers either and organic fertilizers also contain nitrogen and phosphorus.
Since farmers can’t stop using fertilizers (without severely impacting their crops), many put together nutrient management plans that outline how much fertilizer they need to apply and when. This helps to keep excess nutrients from washing away or leaching down into the groundwater. The Nutrient Management Initiative, led by the Natural Resources Conservation Service (NRCS) and Minnesota Department of Agriculture, allows farmers to fine tune their optimal fertilizer application rates by setting up test comparison plots on their land. They receive $1,408 for participating in the program and often save money on fertilizer purchases in the long run as well.
Locally, the Washington Conservation District (WCD) and NRCS have worked with farmers since the 1940’s to reduce runoff and erosion. Most local efforts focus on phosphorus since it has the biggest impact on our lakes, streams and rivers. Common strategies include using cover crops to hold the soil in place during the winter, building sediment basins that temporarily hold back runoff water and allow sediment to settle out, planting buffers of native or perennial plants along lakes and streams, and creating grassed waterways in high-flow areas of farm fields. In other parts of the state where tile lines have dramatically changed the landscape, the NRCS and Conservation Districts are installing control structures that let farmers adjust water levels in their tile lines, building woodchip trench bioreactors and saturated buffers to take nitrogen out of tile line drainage, and sometimes even removing drain tile to restore natural wetlands. Each new practice gets us a little bit closer to our goal of healthy lakes and rivers and clean drinking water for all.
Local NRCS staff can also provide information about funding and other assistance programs. Contact Matt Scharr or Lucas Altwegg in southern Washington and Dakota County (651-463-8665) or Jason Rehn in northern Washington and Chisago County.