What Do Crop Diversity and Ocean Dead Zones Have In Common?

Photo Nicholas_T @ flickr

Biodiversity – like change – is the spice of life. It’s what keeps our ecosystems healthy, resilient to stress and able to provide valuable services such as clean air, water, and/or food. However, we are increasingly becoming a monoculture society. We plow under our diverse ecosystems and plant a monoculture (single species) in its place. Now instead of a lovely patchwork of crops; we have fields of one crop as far as the eye can see. This affects the insects that visit; the variety of pollinators that can survive here; the nutrient ratios in the soil; increased chances of species-specific disease; increased soil runoff; higher fertilizer requirements; and, ultimately ocean dead zones.

image NASA

Louisiana State University has new research that shows that industrialized farming leads to ocean dead zones. One of the techniques that could be used to lower nitrogen runoff is to plant a variety of crops. Studies show that where the biodiversity of crops is high, there is less dissolved nitrogen found in surrounding watersheds. Eventually the water from the watersheds (along with all the pollutants it may carry) makes it way to the ocean and is dispersed many thousands of miles from where it first originated.

Nitrogen from agriculture fertilizers (produced from fossil fuel) winds up increasing the local aquatic dissolved nitrate. The increase in fertilizer is necessary because we are now growing single species crops which leach the soil of select nutrients only. Instead of replacing those nutrients naturally through crop rotation and times of laying fallow (unplanted), we pump the soil full of artificial nutrients and nitrogen. The increased nitrate leads to the growth of algae, which uses up the available oxygen in the water, creating dead zones.

The number of marine dead zones has doubled every 10 years since the 1960s, which corresponds nicely with the increase of these industrialized farming technologies.

image US DEP

Whitney Broussard, who received a Ph.D. in oceanography and coastal sciences from Louisiana State University is now at the University of Louisiana at Lafayette, and R. Eugene Turner of LSU, 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 the average farm size has approximately doubled from 60 ha in 1900 to 180 ha in 2002. An additional result of survey is that corn has been proven to be probably not the best biofuel out there and now there may be a link between the corn farming itself and increased nitrogen runoff.

"These results are important because they highlight the need to address land use in order to reduce both the size of the low oxygen zone off Louisiana and the negative effect of nutrients on coastal wetland restoration efforts," said Turner.

"With the growing American farm comes the necessity to use more industrialized means of farming," said Broussard. "Our 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…. Diverse farms tend to have smaller fields with more edges, which can mean there's a greater buffering effect on nitrogen runoff by surrounding grasslands or woodlands."

The good news is that the impacts of nitrogen pollution due to industrialized farming practices might be reversible if incentives were developed for farmers to increase biodiversity, decrease field size, increase buffering zones, and incorporate more native landscapes between fields.

"There has been great progress made to reduce the footprint of agriculture, but there is still room for improvement," said Broussard. "The American farmer is caught in a mode of production that has tremendous momentum and cannot be changed on the farm – it's a policy question now."