From the Dead Zone to the Buffer Zone

Algae blooms, eutrophication, and dead zones are a problem in many of the world’s oceans. Runoff from the Mississippi River contributes to a dead zone in the Gulf of Mexico that, in some years, exceeds the size of a smallish state, and last summer an algae bloom in the Pacific stretched from California to Alaska, the largest ever recorded in the region. They’re a problem in the Great Lakes and in our rivers, too, and several Midwest states are starting to do something about it.

Algae blooms occur when excess nutrients—nitrogen and phosphorus—enter the waterways and fuel their growth. Agricultural runoff is a big contributor, both from the fertilizers applied to crops and from livestock manure, but urban stormwater runoff, leaking septic tanks, and other sources also contribute. As the algae grows, dies, and decomposes, it reduces the oxygen levels in the water, causing dead zones. This article from Stormwater magazine gives an overview of the process. At their worst, dead zones kill aquatic life and wreak havoc on the fishing industry. Milder blooms have an economic effect as well, because the water is unappealing for recreational activity, which can hurt areas that depend on tourism and, in the long term, can lower real estate values.

Two years ago, a toxic algae bloom in Lake Erie cut off the water supply for the City of Toledo; that and other less-reported incidents have led Midwestern states to take steps to protect the Great Lakes and other water bodies. (This article from Stormwater looks at monitoring efforts in the Great Lakes, particularly Lake Erie.) As reported here, last year Minnesota began requiring a 50-foot buffer of vegetation between cropland and water bodies. At first the rule included not only lakes, rivers, and wetlands, but also private drainage ditches. However, after protests from the ag community, the ditches were written out of the rule. Wisconsin, the same article reports, has the strictest limits in place and is spending money—$2 million over 20 years, contributed by local governments—to curb phosphorus. Ohio just drafted a multiyear plan of its own; Iowa, which has experienced numerous beach closures, has not yet enacted any new limits.

Although buffers are effective at stopping the migration of nutrients and pesticides, recent research from the University of Missouri indicates tree buffers can impede crop growth by providing too much shade and by competing with the crops for water. Researchers are now recommending buffers for the buffer zones: for example, if trees in the existing buffer zone are 20 feet high, farmers should leave 6 to 9 feet of space between the cultivated land and the trees.

Several voluntary conservation programs—many designed to help farmers control both erosion and excess nutrients in runoff—are funded through the USDA’s Natural Resources Conservation Service. Other than these voluntary programs, what measures are in place in your area to limit nutrients? Do local water bodies have total maximum daily loads in place for nitrogen or phosphorus?