By Hannah Corsini, Kingfisher Writer

Published March 13th, 2024

Agriculture is a major driver of land-use changes and can intensify the impacts of climate change on temperature and groundwater. The loss of riparian cover or vegetation can affect the ecosystem’s health of the Mississippi River Basin in the Midwestern US, particularly the fish population.

Freshwater ecosystems are among those most threatened on the planet. Humans depend on freshwater for many reasons, but water as a resource is becoming increasingly scarce due to overexploitation, pollution and climate change.

Not only does this spell disaster for us but also for the species that rely on freshwater at the core of their ecosystems. Freshwater fish exhibit the highest extinction rates, with freshwater species as a whole showing an 83% decline since 1970.

Chemical inputs used on farms can drain off into waterways where they can accelerate plant growth to the point that algal blooms form. Algal blooms are caused by eutrophication, and when the algae die, their decomposition uses all of the available oxygen in the water, creating what is known as a ‘dead zone.’

A study published in 2023 suggests that although climate change will increase the severity of harmful algal blooms (HABs), full implementation of conservation practices can help offset their occurrence, suggesting that these practices may function best as a type of damage control for the effects of climate change.

Dead zones, being devoid of oxygen, are uninhabitable for plant and animal life. A 7,829 square mile dead zone in the Gulf of Mexico now exists as a direct result of nutrient runoff from Midwestern farms into the Mississippi River basin, which has seen its nitrogen levels triple since the 1950s due to agricultural pesticide and fertiliser use.

‘Climate change will increase the severity of harmful algal blooms.’

The reduction of riparian cover around the riverbanks of the Mississippi River basin has also led to negative impacts on fish communities downstream from the river. The loss of riparian cover can increase solar radiation exposure, alter river flow patterns and reduce habitat complexity.

Researchers recommend building wooded riparian zones to recover the river’s sinuosity. The riparian zone can also help buffer between aquatic communities and terrestrial agricultural production. Although there is uncertainty in farming communities the economic benefits from recovering riparian cover can be quantified.

Further remedies: Best Management Practices

‘Best Management Practices’ (BMPs) are voluntary practices with which farmers aim to maximise both productivity and sustainability. A key aim of several BMPs is to reduce eutrophication, either by reducing the amount of chemicals applied to farms, or reducing nutrient leaching: i.e. the amount of nitrogen and phosphorus draining off into waterways.

One example of such practices is conservation tillage, where the residue from the previous year’s crops is left on the ground, as opposed to conventional tillage, where the soil is completely inverted with a tractor-pulled plough and then smoothed over before the new crops are planted.

The stated benefits of this are improved soil health and reduced nutrient leaching. A UK study disputed this claim, finding no benefit to soil quality or local freshwater biodiversity over five years of using conservation tillage, whilst evidence from a 15-year study taking place in Switzerland supported it, finding an increase in topsoil carbon and both microbial biomass and activity when the farm ceased ploughing and switched to conservation tillage.

‘Conservation tillage, where the residue from the previous year’s crops is left on the ground.’

Other BMPs have similar uncertainties behind them, perhaps owing to a lack of thorough research in this field, and the fact that different techniques work for different areas. During seven years of monitoring, scientists in Illinois found that despite high uptake of BMPs such as grassed waterways, strip tillage and stream buffers, there were no changes in nitrate-nitrogen or dissolved phosphorus content observed in the studied watershed.

A 2020 study of Lake Erie suggested that implementing conservation practices would likely be outweighed by the effects of climate warming since smaller, benthic (bottom-feeder) species will be better suited to warmer waters than larger, cool-bodied species that swim in open water.

These small species—which feed on dead organic matter—can disturb sediment deposits, which could lead to an increase in nutrient flow through the lake and therefore an increase in eutrophication.

The United States Department of Agriculture (USDA) makes payments worth billions of dollars to farmers every year in indemnities, easing the burden of some farmers. But these payments are largely unequally distributed—with some regions receiving millions of dollars worth of funding each year, and some receiving none at all—and do little to address the real issue at hand: an inbuilt lack of resilience in the Western farming system.

The USDA has promised to address this issue—their National Institute of Food and Agriculture is now funding a five-year project called ‘Diverse Corn Belt: Resilient Intensification through Diversity in Modern Agriculture’ in Illinois, Indiana and Iowa.

The major point of the scheme is to grow a range of crops to replace the dominance of soy and corn, increasing both environmental and economic stability. But with the future of Midwestern agroecology looking the way it does—this may merely be another sticking plaster.

Recently, another group of scientists have assessed the effect BMPs could have on the Kaskaskia River watershed. This vast tributary to the Mississippi River spans 14,880 kilometres squared, a sizable 10.2% of the state of Illinois. Before the arrival of European settlers in the 18th century, this land consisted of sweeping prairies and forests alongside bodies of water. Now, like much of the Midwest, it contains little more than corn and soybeans. Many of its meandering streams and rivers have been channelised and dredged.

The scientists sampled fish from 91 sites across the Kaskaskia watershed to assess whether or not BMPs had an impact on the biodiversity of the freshwater fish. They modelled four key practices: crop rotation, cover crops, reduced tillage and reduced fertiliser application.

Contrary to other studies, they found that BMPs could reduce the nutrient and sediment input into the river. Local nitrate levels were predicted to reduce by up to 40% and 30% in the years 2020-2029 and 2030-2039 respectively. However when the scientists modelled the actual diversity of the fish, not a single conservation scenario was able to prevent the predicted decrease in biodiversity.

The most prominent species richness loss predicted at any single site was 22% from the year 2019 to 2049. The average loss predicted was 6%. The agricultural conservation scenarios made little to no difference—in every modelled scenario, the impact on freshwater biodiversity was less than 1%.

‘Best Management Practices could reduce the nutrient and sediment input into the river.’

On a more local scale, algal blooms present a problem for Midwestern waterways. Some algal blooms secrete toxins, which produce side effects in the unlucky few who swim in or drink this water.

These can include rashes, gastrointestinal symptoms like nausea and diarrhoea, muscle weakness and even kidney and liver damage. Multiple research centres in the US monitor the region’s HABs, which can be found, for example, in the Illinois River, Mozingo Lake, and the Mississippi River basin.

Along with creating dead zones, HABs secrete neurotoxins, which are capable of paralysing the central nervous system of fish and therefore causing death by asphyxiation, whilst others secrete hemolytic compounds which destroy blood cells, rupturing fish gills and starving them of oxygen. With cyanobacterial blooms exceeding WHO thresholds in Midwestern lakes, it is clear that both ecological and human health are under threat.

What is the future of farming in the Midwest?

Over the next two decades, the owners of 70% of the USA’s farmland are set to retire. However, the vast majority of this land will end up not in the hands of the next generation of farmers, but in those of property developers.

What’s more, climate events like floods and droughts—set to worsen as the world warms—and supply-chain issues like the global pandemic or the war in Ukraine jeopardise farmers’ livelihoods under the current agricultural system.

‘With cyanobacterial blooms exceeding WHO thresholds in Midwestern lakes, it is clear that both ecological and human health are under threat.’

The future for farming in the Midwest, therefore, may seem bleak. Although often maligned by environmentalists, it is important to recognise that farmers and farmworkers will be left vulnerable by these turbulent socio-economic and environmental conditions. According to the Purdue University horticultural architecture expert Linda Prokopy, farmer suicides and bankruptcies have risen in the last several years.

According to the Endangered Species Committee of the American Fisheries Society (AFS), 40% of American freshwater fish species are either endangered or already extinct. Declines are visible across America in species such as freshwater mussels and pallid sturgeon, but for the most part, the changes to freshwater ecology are out of sight.

Why are freshwater species declining?

Agriculture is responsible for 70% of freshwater consumption, and some estimates suggest that agricultural water consumption could increase by 50% by 2050.

Water stress occurs when a community has insufficient access to water due to a lack of supply or inadequate infrastructure. It is estimated by the Food and Agriculture Organization (FAO) that around 10% of the global population lives in water-stressed areas. In the vast majority of these areas, agriculture is the primary cause of water consumption.

Consequently, organisations such as the United Nations (UN) and the FAO have advised agricultural policy shifts and information campaigns to make agriculture more sustainable and far less water-intensive.

‘Agriculture is responsible for 70% of freshwater consumption.’

A sizeable percentage of the money spent on conservation by the United States Department of Agriculture (USDA) goes to states in the midwest, (Illinois, Indiana, Iowa, Michigan, Mississippi, Missouri, Ohio and Wisconsin), often referred to as the corn belt due to its vast agricultural production, which totals a $76 billion industry and 127 million acres of land, of which 75% of which is made up of corn and soybeans.

The Midwest is dominated by farmland, having the highest concentration anywhere in the United States, and consequently, less than 0.1% of the original Midwestern prairie remains.

So in the battle fought by BMPs to preserve fish biodiversity in the Kaskaskia watershed, it looks like climate change will win. They say never to bring a knife to a gunfight, and global warming is a behemoth that will take a lot more than individual conservation actions to confront.

However, that does not mean that these conservation actions have no value. As stated, in certain studies they were found to be of benefit to local ecology, and even in the Kaskaskia watershed, they were predicted to decrease nitrate levels, something which may aid fish abundance if not diversity.

The takeaway is that there is no one-size-fits-all approach to conservation and that mitigating global warming by ending the global fossil fuel hegemony should be one of our key priorities as ecologists.

If the latter proves impossible, conservation can salvage some of the ruins: the scientists studying the Kaskaskia watershed recommend prioritising key species and the cool-water species which will be most negatively affected by warming waters. With mass extinction and biodiversity loss looming on the horizon, conservationists may have to make more of these decisions.

Featured Image: Gary Leavens | Flickr

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