From hippopotami, platypuses and otters, to beavers, minks and river dolphins, freshwater mammals around the world are under threat. (Image: Chris Stenger/Unsplash)
Freshwater ecosystems like marshes, streams and lakes cover just a sliver of our planet, but they’re powerhouses of diversity. Nearly 10 percent of all animal species are found in these blue oases — a charismatic group of freshwater mammals that includes charging hippopotami, curious platypuses and frolicking otters.
Unfortunately, freshwater systems are one of the most threatened places on Earth. Over two-thirds of our wetlands have vanished since 1900. Similarly, nearly a third of freshwater mammals are threatened, and their numbers are declining faster than other furred and lactating creatures.
However, we can help the beavers, minks and river dolphins of the world with changes in an unexpected area: agriculture. Even in an industry that often harms freshwater systems, mitigating the impacts of the agriculture sector on our planet’s tranquil pools and bubbling waterways is possible.
Threats to freshwater mammals
Agriculture harms freshwater mammals in multiple ways. While hunting, fishing and logging weigh in as the main risks to freshwater mammals, agriculture is a close second.
An obvious impact of agriculture is habitat destruction. In fact, a major driver of wetland conversion is food production. Besides outright habitat destruction, agriculture also degrades freshwater habitats.
“A big thing we're still dealing with is the sins of the past where wetland loss occurred throughout the history of agriculture,” said Brian Jennings, a fish and wildlife biologist at the U.S. Fish and Wildlife Service. “Back in the '50s and the '60s, they were going in and ditching and draining wetlands and then actively farming them. In Delaware and other places on the coastal plain, the problem was you didn't have enough elevation to get the water off the field. So, they started channelizing streams to lower the elevation and drain the [agricultural] lands. But they didn't take into consideration the natural channel function, so you get a lot of sediment issues and bank erosion from these channelized streams.”
In addition to these issues, runoff from agriculture is a main source of pollution for rivers, lakes and wetlands. Excess nutrients from fields can be washed into nearby waterways, potentially fueling dead zones, fish kills and algal blooms. Finally, agriculture is also the largest consumer of freshwater globally, competing directly with these ecosystems.
Besides the threats across the crop world, urban development, invasive species, pollution, climate change, dams and water management systems menace freshwater mammals. It’s no wonder 44 percent of their species are declining.
The benefits of buffer zones
Fortunately, there are many ways to reduce the harmful effects of agriculture. First of all, maintaining buffer zones — or strips of land and vegetation along the banks of water bodies, also called riparian areas — is important for wildlife.
“The whole riparian area acts as travel corridors for different species, whether it's birds, mammals, amphibians or reptiles,” Jennings said.
Buffers with native vegetation improve habitat for animals by filtering and cleaning the water, stabilizing stream banks, mitigating floods, reducing and regulating water temperatures, and uptaking carbon.
Yet agricultural livestock prefer riparian areas because they provide abundant food, water and shade. They can degrade these sensitive areas — changing stream channels, trampling banks, increasing erosion, and reducing plant and animal diversity.
A simple solution to this problem is keeping livestock away from these areas. Fencing can protect riparian areas, while supplying alternative water sources can attract livestock away from streams. This can lead to dramatic habitat improvements. For example, excluding livestock from riparian areas in Oregon substantially improved the diversity and abundance of native vegetation.
While buffers are good for the environment, farmers may oppose giving up otherwise usable land, Jennings explained. A forested buffer can also interfere with irrigation systems, and shading may affect nearby crops. However, incentive payments, like those offered by the U.S. Department of Agriculture’s Conservation Reserve Program, can encourage farmers to adopt conservation practices on their land.
Improving water quality
Buffers aren't the only way farmers can help protect freshwater habitats and their furred inhabitants. For instance, farmers can reduce pollution from their farms by adopting best management practices for nutrients. These involve applying the correct type of fertilizer at the right time, place and amount.
Planting cover and perennial crops to reduce soil erosion can also be helpful. Another method is conservation drainage techniques, which involves filtering water through trenches filled with wood chips to remove nutrients and modifying ditches and drainage systems.
For instance, best management practices on agricultural lands in Florida reduced phosphorus pollution entering the Everglades by an average of 55 percent. These practices included leveling fields to reduce soil erosion, constructing berms (or raised banks) along ditches and canals to reduce runoff, and cleaning sediments out of canals, among other actions.
Reducing water use
Tamping down on water use is another way to shrink the oversized reach of agriculture into freshwater ecosystems. For example, drip irrigation, where tubing is placed on or under the soil, reduces evaporation, as does scheduling irrigation for cooler parts of the day. Sensors that detect soil moisture can reduce unnecessary water use on farms, too.
In addition, cover crops and mulch cool the soil, reducing evaporation. They also lock up nutrients in the soil and allow for reduced fertilizer use, saving farmers money, Jennings explained.
Along with no-till practices (or not plowing the soil) and compost, these methods increase organic matter in the soil, and in turn, improves its ability to hold water. However, no-till practices may require spraying herbicides since mechanical treatments to suppress weeds aren’t an option.
A similar problem exists with organic production. “The big problem with organic farming is you have to turn the soil over since that's your weed control,” Jennings said. “There are no approved organic herbicides that are really effective on weed control.”
In the quest for more sustainable agriculture and healthier ecosystems, some tradeoffs are inevitable.
Safeguarding freshwater mammals
All this effort may sound laborious, but after all, freshwater mammals are a valuable group. For instance, the industrious beaver creates wetlands, improves water quality, reduces erosion, increases plant and animal diversity, and minimizes the risk of flooding. Hippos, perhaps better known for their aggression, also transfer silicon into rivers and lakes. Silicon, in turn, is a vital nutrient for diatoms (or algae) that make up the base of the food chain feeding aquatic insects and fish.
While the threats to freshwater mammals are numerous, there are nearly as many ways to protect them. Changing agricultural practices is one major step forward.
Ruscena Wiederholt is a science writer based in South Florida with a background in biology and ecology. She regularly writes pieces on climate change, sustainability and the environment. When not glued to her laptop, she likes traveling, dancing and doing anything outdoors.