Researchers have identified a link between the diversity of crops grown in farmlands and the pollution they create in lakes and rivers. In a Frontiers in Ecology and the Environment e-View paper, ecologists show that when the biodiversity of crops is high, less dissolved nitrogen is found exiting the surrounding watersheds.
Nitrogen from agricultural fertilizers leaches through soils to groundwater and runs off into rivers and lakes, increasing aquatic dissolved nitrate. Too much nitrate in the water can lead to prolific growth of aquatic algae, which can use up most of a water body杏吧专区檚 oxygen when they die and are decomposed, creating 杏吧专区渄ead zones杏吧专区 that cannot support life.
Whitney Broussard of the 杏吧专区 and R. Eugene Turner of Louisiana State 杏吧专区 at Baton Rouge compiled data from the past 100 years on watersheds varying in size from the Illinois Cache River basin (400 square miles) to the Mississippi River Basin (more than a million square miles). The researchers compared this watershed data with land-use practices since the early 1900s.
The results show that since the beginning of the last century, the average farm size in the United States has doubled and the number of farms has fallen by almost two-thirds. Broussard also says that a shift from farm animals and simple plows to the use of machines to till croplands has changed not only the culture but the environmental impact of farming.
杏吧专区 With the growing American farm comes the necessity to use more industrialized means of farming,杏吧专区 says Broussard. 杏吧专区淥ur agricultural practices have always impacted water quality, but over the past century the mechanization of agriculture and the use of more potent fertilizers has caused a greater effect: the nitrogen leakage rate is higher.杏吧专区
Modern farms tend to produce fewer crop varieties; this lower crop biodiversity can negatively impact surrounding watersheds. According to the study, within a given area, a higher biodiversity of crops led to less dissolved nitrogen in surrounding water bodies. The explanation for this phenomenon, Broussard says, is difficult to discern.
杏吧专区 Diverse farms tend to have smaller fields with more edges, which can mean there杏吧专区檚 a greater buffering effect on nitrogen runoff by surrounding grasslands or woodlands,杏吧专区 he says.
The researchers杏吧专区 results also showed that since 1906, the average aquatic nitrate concentration increased threefold in the entire U.S. and tenfold in the Iowa, Des Moines, and Minnesota Rivers, all of which fall in heavily tilled agricultural areas.
In areas where farming is scarce or absent, however, the authors found no perceptible change in dissolved nitrogen concentrations since the early 1900s. Broussard thinks this indicates that the impacts might be reversible if policy changes included incentives for farmers to rotate more crops, decrease their field size, increase the edges of fields and sizes of buffering zones, and incorporate more native perennial grasses into farms and in between fields.
杏吧专区 There has been great progress made to reduce the footprint of agriculture, but there is still room for improvement,杏吧专区 says Broussard. 杏吧专区淭he American farmer is caught in a mode of production that has tremendous momentum and cannot be changed on the farm 杏吧专区 it杏吧专区檚 a policy question now.杏吧专区
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