Nutrient Cycles

Applying Nutrient Cycles

Water, carbon, nitrogen, and phosphorus are strongly tied to agriculture. Our agricultural industry is responsible for providing us with the food we eat. Modern agriculture makes extensive use of inorganic fertilizers without which we could not feed the world’s rapidly growing population. However, this dependence on inorganic fertilizers and other synthetic agricultural chemicals has led to some unsustainable agricultural practices. These practices have created environmental and health problems. They also disrupt the natural flow of the nutrient cycles.

One damaging agricultural practice is the excessive use of manure and fertilizer. Nutrients from these sources contain both nitrogen and phosphorous compounds. The nutrients that are not absorbed by plants may enter runoff or seep into groundwater. This nutrient pollution eventually enters rivers, lakes, and estuaries. The excess of nutrients can cause algae in these ecosystems to rapidly reproduce, which leads to hypoxic or anoxic conditions in the water. Other organisms in the food chain are often negatively affected. In fact, when nutrient runoff from farms along the Mississippi River washes into the Gulf of Mexico, large hypoxic dead zones can result, leaving fisheries in dire straits.

Environmental scientists have engineered solutions to the problem of nutrient runoff from agricultural fields. One solution is what is known as a denitrifying bioreactor. Designs vary, but these are usually large open pits filled with wood chips or other organic matter placed between the drainage outlet of a field and any nearby waterways. Bacteriaglossary term (opens in a new window) occupying small pores in the wood chips convert the nitrate in the drainage water into harmless N₂ gas, which enters the atmosphere. With nitrogen content greatly reduced by this process, the water can safely drain into streams.

STEM and Nutrient Cycles

Carbon dioxide and methane are greenhouse gases. Under normal circumstances, Earth’s surface is warmed by incoming solar radiation, and Earth emits infrared radiation outward toward space. The greenhouse gases that are present in the atmosphere trap the infrared radiation and then re-emit the radiation back to Earth. This potentially warms average temperatures on Earth and disrupts weather patterns.

Most climate scientists today argue that human-produced greenhouse gases in the atmosphere contribute to global warming. The burning of fossil fuels generates large amounts of CO₂. Plants cannot uptake the huge amounts of CO₂ released by motor vehicles, power plants, and factories all over the world. Furthermore, millions of acres of forest have been destroyed to make space for land development and agriculture. These forest trees were a vital absorber of carbon dioxide.

While some debate surrounds the exact contribution increased CO₂ levels from human activities have upon global warming, burning fossil fuels clearly has a negative impact on the natural balance of the carbon cycles it adds various forms of potentially harmful carbon gases and metal particulates to the atmosphere. Most people agree that the answer to this problem lies in the use of renewable energy sources rather than fossil fuels. These sources include solar, wind, and thermal energy, as well as biofuels. Biofuels are composed of, or produced from, renewable biological materials such as animal waste and plants. The largest source of plant-based biofuel currently is corn, which can be converted into ethanol. However, plant breeders are busy developing dedicated biofuel crops—such as perennial grasses and fast-growing trees—which can be grown on marginal land, leaving the prime agricultural land for food production. Bioengineers have developed technologies to convert cellulose from biofuel crops, and new biorefineries are being built around the country.