Excess fertilizers and raw human waste spell trouble for Lake Erie. New research suggests that in order to eradicate the problem, large-scale changes need to be made to current agricultural practices.
The issue is phosphorus runoff from farms and nearby watersheds feeds an oxygen-depleted "dead zone" in the lake, as well as toxin-producing algal blooms, such as the 2014 event that contaminated the drinking water of more than 400,000 people near Toledo, Ohio, for two days.
This study follows a goal established last month by U.S. and Canadian governments to reduce this contamination by 40 percent from 2008 levels. Multi-institution computer modeling led by researchers at the University of Michigan revealed that meeting this goal requires the widespread use of strong fertilizer-management practices, significant conversion of cropland to grassland and more targeted conservation efforts.
"Our results suggest that for most of the scenarios we tested, it will not be possible to achieve the new target nutrient loads without very significant, large-scale implementation of these agricultural practices," said Don Scavia, lead author of the study and director of the Graham Sustainability Institute. "It appears that traditional voluntary, incentive-based conservation programs would have to be implemented at an unprecedented scale or are simply not sufficient to reach these environmental goals, and that new complementary policies and programs are needed."
After consulting with agricultural and environmental experts, researchers created a list of potentially effective cropland management practices, including various options for fertilizer application, tillage operations, crop rotations and land conversion.
Researchers then created 12 scenarios that were each tested using six computer models. The watershed models, for example, tested the ability of each scenario to achieve the proposed 40 percent phosphorus-reduction target. Each scenario addressed both the total amount of phosphorus, known as TP, and the amount of dissolved reactive phosphorus (DRP) - the form of the nutrient that facilitates toxic algal blooms.
"The most promising scenarios included widespread use of nutrient management practices - especially subsurface application of phosphorus-based fertilizers - along with substantial conversion of cropland to grassland and extensive use of buffer strips," explained Jay Martin, study co-author from Ohio State University.
However, seven of the 12 management scenarios did not meet the 40 percent reduction goal. One of the five capable scenarios - scenario 6 - requires taking nearly 30,000 acres of cropland out of production and putting more than 1.5 million acres under strict conservation regulation. This, researchers say, is equivalent to impacting more than 6,300 farms, as the average farm is about 235 acres.
"While there may be a temptation to select one model based on 'superior performance,' there is no one way to evaluate model performance," said Margaret Kalcic, study co-author from the University of Michigan. "Instead, we chose to use multiple models because together they represent the range of reasonable representations of the real world."
In other words, improved conservation requires the right mix of land and water management practices, deployed in the right place and amount. Even still, reducing phosphorus runoff is no easy feat, and meeting federal-imposed goals has proved difficult for other troubled areas, such as the Gulf of Mexico and the Chesapeake Bay.
A full report, titled "Informing Lake Erie Agriculture Nutrient Management Via Scenario Evaluation," can be found online.
