Despite rather quiet media attention over the last six years, Lake Erie’s algae problem hasn’t improved since Toledo’s 2014 nationally-known water crisis; each summer, the water is as green as ever. After such a publicized public health emergency, one would expect consolidated efforts to mitigate the issue. And there have been on some level: city officials, farmers and environmentalists alike have advocated for better water quality. Yet many of the major factors for the bloom remain largely unchanged, one of them being agricultural land use in the Maumee River watershed. Ohio is a historically agricultural state, and much of its economic, cultural and social standing depend upon farming; thus, it is especially important to investigate and understand the complexity of the factors that lead to the algal blooms, and to work toward balanced solutions to mitigate negative impacts.
Algal blooms in the Western Basin of Lake Erie are fed by excess phosphorus runoff from its many connecting tributaries in the U.S. and Canada. Nonpoint source pollution—runoff pollution that comes from many diffuse sources—contributes most of the nutrient pollution (phosphorus & nitrogen) into Lake Erie. Fertilizer and animal waste used in agricultural fields represent a significant portion of nonpoint source pollution. The Maumee River is one of the largest sources of nonpoint source pollution to Lake Erie, contributing almost half of the total phosphorus between 2011-2013.
The Maumee River Watershed includes part of Ohio, Michigan and Indiana, which utilize large portions of their land for agriculture. The whole watershed drains over 4.2 million acres of land with roughly 72% of it used in agriculture. Major crops grown in the watershed include corn, soybean, hay and wheat. And among these, soybeans and corn are the most prominent, utilizing about 33-40% and 12-26% of land in the Maumee River watershed respectively within the past 10 years. Both require additional fertilization, with corn requiring the higher proportion of phosphate application: in a 2019 USDA report, the average annual phosphate application rates on soybean and corn fields were about 52 and 71 lbs per acre. Whereas phosphate was applied to about a third of all soybean fields, over 80% of corn fields annually receive phosphate application.
Thus, the Midstory Water Project team looked at the agricultural land use for three major crops grown in the Maumee River watershed: soybeans, corn and winter wheat. We animated the crop-planting area in the watershed each year, using data maps from the USDA National Agricultural Statistics Service from 2010 to 2019. We also graphed phosphorus load from the Maumee River watershed, estimated using an analytical template and Maumee River watershed data from Heidelberg University’s National Center for Water Quality Research.
In the past 10 years, the planting area of the major crops has remained relatively steady, with an increase of soybean growing from 1.382 to 1.671 million acres between 2012 and 2017. These increases and relative utilization of land for soybeans may be explained by a 27% price increase of soybeans in early 2012 from the previous year and increasing export demand mostly from China in following years. Between May and July of 2019, increased precipitation (24.3 inches of rain in 2019 versus a ten-year average of 18.7 inches) greatly disrupted planting in the Maumee River watershed. The USDA Farm Service Agency annually reports on the acres of land planted and prevented from being planted (often due to environmental circumstances). In 2018, the state of Ohio reported 24,756 prevented acres of corn (~3.4 million acres planted of corn) while in 2019, that number was over 37.5 times larger at 928,742 acres prevented.
Phosphorus runoff depends on a number of factors, a major one of which is land use for agriculture. Crop coverage maps show that agricultural land takes up a considerable portion of land use in this region, but smaller fluctuations in yearly agricultural land use (considering the overall large amount of the watershed used for agricultural purposes) do not seem to be the most influential contributor to the amount of phosphorus runoff to the lake, which suggests that how we manage the use of existing agricultural land is key to mitigating the algal bloom issue. For example, even though in 2019, the crop planting area was dramatically reduced due to precipitation, the phosphorus runoff was the third-highest year in the past 10 years. The severity of Lake Erie’s algal blooms aren’t as simple as they seem, with many factors impacting the runoff going into Lake Erie, including levels of precipitation, application of fertilizer on crop lands and conversion of swamp lands.
The research and media presented here were made possible in part through a grant from the First Solar Corporate Charitable Fund. Read more here.