Toxic algal blooms are now ubiquitous in lakes and oceans around the world, risking human health and sucking up so much oxygen they suffocate fish and other animals. Dangerous blooms have been documented from the Gulf of Mexico to the Baltic Sea. In North America’s Great Lakes, algal blooms have emerged as the most unhealthy, unsightly, and urgent water quality problem.
The Great Lakes are the largest source of fresh surface water in the world. They are essential for cities, industries, and agriculture in eight states in the United States and one province in Canada. Heavily polluted in the 1960s, state, federal and international action — including the 1972 Clean Water Act in the United States and the 1978 Great Lakes Water Quality Agreement between the U.S. and Canada — restored the Lakes to health by the mid-1980s. While these efforts greatly reduced the amount of phosphorus, a key pollutant, that was released by industrial activities and city wastewater plants, they did little to address phosphorus runoff from agricultural fields and urban areas. Failure to take these sources, often called non-point source pollution, into account led to a reemergence of the algal blooms by the late 1990s. Today, algal blooms are closing beaches and harming aquatic ecosystems. Just last year, they forced an Ohio drinking water plant to shut down for the first time in history, making them an urgent threat to water quality and public health.
Focusing on Ohio, home to Lake Erie’s largest tributaries and one of the most productive agricultural areas in the Great Lakes region, Circle of Blue’s Choke Point: Index data team set out to make connections using “big data.” The visualizations below were made by combing through thousands of pages of documents, scientific reports, and university database from a multitude of sources, such as federal, state, and local non-profit agencies.
While phosphorus overall has declined in Lake Erie and its tributaries, the amount of dissolved reactive phosphorus — a form that is more easily used by algae — has grown since the 1990s. The numbers show a steep increase in the percentage of DRP washing into Ohio’s Maumee River watershed, which is Lake Erie’s largest tributary and a primary contributor of the phosphorus that drives the largest and most problematic blooms in the Great Lakes. While DRP comes from a range of sources, such as fertilizers, sewage, soaps and detergents, scientists at universities throughout the Great Lakes region believe that changing agricultural practices and climate change are behind the recent increases. Together, these trends are creating larger algal blooms. Researchers are now exploring which farming practices could reduce phosphorus runoff, and stakeholders from conservationists to municipal water managers are urging governments to take legal action to address the problem.
Click the images below to launch the infographics and read the descriptions below to put them in context. Data were gathered from Heidelberg University, the National Oceanic and Atmospheric Administration, Ohio State University, and the U.S. Geological Survey.
Dissolved reactive phosphorous (DRP) as a percentage of total phosphorous (TP) in the Maumee River is nearing levels during the 1970s when algal blooms occurred in Lake Erie. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
Of the total phosphorus in Ohio’s Maumee River, Lake Erie’s largest tributary, the percentage of dissolved reactive phosphorus (DRP) is on the rise. The Maumee River contributes most of the phosphorus that feeds toxic algal blooms in the lake.
DRP as a percentage of total phosphorus was about 35 percent in the Maumee River during the mid-1970s, when algal blooms first became a problem in Lake Erie. That percentage decreased to about 15 percent in the mid-1990s, following federal and international efforts to reduce phosphorus that corresponded with the decline in algal blooms that were observed in Lake Erie. The percentage of DRP in the Maumee River again reached about 30 percent in 2010, one year before the largest algal bloom ever recorded on Lake Erie.
The average concentration of dissolved reactive phosphorous (DRP) in the Maumee River is nearing levels during the 1970s after a period of lower concentration during the 1980s and 1990s. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
Scientists say the rise in DRP is due primarily to changing agricultural practices.
Crop acres of corn, soybeans, and wheat that were harvested in northern Ohio over the last half-century show a significant increase in soybeans, which are often no-tiled and can result in phosphorous loading. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
Overall, the number of acres of crops harvested in Ohio’s portion of the Lake Erie watershed has not increased significantly since the 1950s — from a little more than 3 million acres to about 4.6 million acres harvested today — and the percentage of land that is used for agriculture in Ohio’s Lake Erie watershed has actually decreased. The biggest area of growth has been in soybeans, not corn, however, which may have implications for phosphorus runoff because soybeans are more often no-tilled than corn. No tilling means the farmers do not turn the soil over, reducing erosion but also concentrating phosphorus fertilizers in the top layer of soil where they are more likely to wash off during large storms. Whereas total crops have increased by less than 50 percent since the 1950s, soybeans have increased by about 250 percent.
Land use in the northern Ohio counties that are located within the Lake Erie watershed. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
Land use changes have been minimal since the 1980s in the northern Ohio counties that are located within the Lake Erie watershed. Overall, the percentage of land used for agriculture has actually decreased, though it is still the largest land use type when compared to urban areas and forested land. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
The amount of phosphorus, in pounds, flowing through the Maumee River each year is highly variable from year to year. This variation is largely due to differences in precipitation within the basin.
Since the 1990s, the highs and lows of seasonal precipitation changes have been more extreme. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
When there is more rainfall, the likelihood for phosphorous to run off the surface of the ground and into water bodies increases. But yearly rain accumulations are not nearly as important as extreme events, because it is the pulse of phosphorus that spurs the growth of algae. Scientists expect climate change to increase the likelihood of extreme events within the Great Lakes region.
On average, there have been more precipitation events that exceeded one-inch after 1991 than before 1991 for every month of the year. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
Using datasets from the National Oceanic and Atmospheric Administration (NOAA), Circle of Blue’s data team was able to graph how the likelihood of extreme rainfall events has changed over time. Counting any event where more than 1 inch of rain falls in a 24-hour period, we found that the likelihood of an extreme rainfall event is noticeably higher after 1991 when compared with years before 1991. This is especially true during the spring and fall months. In April, for example, there was a weighted average of 0.4 extreme events before 1991, but 0.75 extreme events after 1991. Scientists have determined that extreme rain events — which flush phosphorus off the land and into the water in a big pulse — are most likely to affect the size of summer algal blooms if they occur in late spring.
The concentration of total phosphorous (TP) in the Maumee River increased with higher annual levels of precipitation. Image © Robbie Queen for Circle of Blue. Click image to enlarge.
Many holes remain in the data that are available for the Great Lakes, especially databases tracking agricultural practices and land use. It was surprisingly difficult, for example, to find land-use data at the county level in Ohio. The USDA keeps comprehensive statistics on crop acreage, but to find urban and forested land-use data, our researchers had to use a variety of sources, like Ohio State University and the USGS. These data were not collected at regular time intervals. There are also little publicly available data on farm practices, such as how many farm acres are no-tilled, what time of year farmers are applying fertilizer, and what kinds of fertilizers they are applying. The USDA is starting to collect this information in more detail, but we were unable to find long-term data sets about these topics.
However, there is a very comprehensive dataset on water quality in Lake Erie tributaries, which is available from Heidelberg University in Ohio. They have been measuring phosphorus levels and other water-quality parameters in northern Ohio rivers since the 1970s.
Do you have data that pertains to crops, fertilizers, land use, rainfall, phosphorous levels, or toxic algal blooms in Ohio an Lake Erie, or any of the other Great Lakes and their neighboring states or provinces? We’d love to see it. Check out our compiled data in Google Fusion Tables here.
These graphics were created by Robbie Queen, a student with the Columbia Water Center in New York City. Contributors include Sheng Long, another Columbia student, as well as Codi Yeager-Kozacek and Aubrey Ann Parker of Circle of Blue, with assistance from Sreeram Balakrishnan of Google Fusion Tables. Columbia interns overseen by Upmanu Lall and Margo Weiss. Reach Circle of Blue’s data team at [email protected]/~circl731.
Choke Point: Index is produced in collaboration with Google Research, Qlikview, and the Columbia Water Center and with financial support from the Rockefeller Foundation.
