Mark Rasmussen | Leopold Center for Sustainable Agriculture Director
We humans seem to have an affection and fascination with the color green—the green of money, the green grass of spring after a long winter, the green of a Christmas tree or the expanse of leaves in a deciduous forest.
But there are some forms of green that we look upon with suspicion or have grown to dislike—the green water of an algae bloom or the pond scum that covers the surface of our favorite beach. We tend to lump different forms of life under the general term “algae” (including cyanobacteria, also referred to as blue-green algae, which are technically not algae at all!), so our relationship with algae can be confusing and somewhat complicated.
As photosynthetic organisms, algae use energy from sunlight to produce oxygen. Over many eons of time, they are responsible for much of the oxygen in the atmosphere, and they are the original source of fossil carbon transformed deep in the earth into crude oil and natural gas. Algae are also the basis of many food chains in aquatic environments.
We look upon algae with favor when they are used to produce biofuels and nutrient rich dietary supplements. But then there are the “other” algae that are more suspect—blue-green algae. (Remember, the blue-green algae are technically not algae at all, but early taxonomists used the term and it stuck.) We especially need to be concerned with the blue-green algae that produce toxins as we enter another growing season here in Iowa.
Cyanobacteria, or blue-green algae, tend to do well in warm, slow-flowing, or stagnant water when both nitrogen and phosphorus are abundant and available. These nutrients, along with sunlight and temperature are the primary drivers of their growth. Some species can grow very rapidly in what is called a bloom. In a pond they can be part of the natural process of turning a water body eutrophic when dense growth can cause a reduction in animal life due to the absence or limitation of oxygen. In our agricultural world, blue-green algae growth can be the result of poor nutrient management when high levels of nutrients get into surface waters and stimulate growth.
Along with rapid growth, the production of harmful toxins from certain species of blue-green algae is of great concern. Children and small pets with less body mass are highly susceptible. The toxins can also impact wildlife when they drink contaminated water. Dried biomass on shore can also be toxic if inhaled as dust. Research has discovered that people who live or spend a lot of time near contaminated water have a greater risk of health effects just from being near this kind of water.
Toxin production in critical species is also stimulated by increased water temperature. Therefore, we see more problems later in the summer as bodies of water warm. Iowa began testing surface water in 2000, and every summer, beach closings and alerts are issued for water that has elevated levels of algae toxins. Climate change and hot summers which warm the water faster also stimulate toxin production and can be expected to increase the problem.
It is difficult and expensive to purify water for drinking when water sources are contaminated, and most water treatment plants do not have that kind of purification capacity. Last year the water in the Des Moines River in central Iowa was not useable for many weeks as a primary source due to the high level of toxins contained in the water. Once contaminated, dilution with cleaner water is about the only solution.
Given that we can expect this problem to get worse, we must redouble our effort to keep nutrients out of the water. We can’t control the water temperature nor the hours of sunlight, but we can do something about the nutrient loading in our surface waters. Unless we do more, we can expect there to be more problems with water quality in Iowa.