The fusion of aquaculture with hydroponics results in what could be a promising future for sustainable agriculture. Not only does aquaponics promise circular recycling, whereby wastewater feeds plants and then returns, detoxified, to grow more fish, but its double cropping could be key to food security for global coastal agriculture.
Aquaponics, in one form or another, has been practiced throughout history. Bloomberg notes that both Chinese and Aztec farmers knew the benefits of growing crops and fish together. In essence, it’s the result of a symbiotic environment; fish or other aquaculture species produce nitrogenous waste into the water, which is then circulated as fertilizer for the plants. The Food and Agriculture Organization of the United Nations (UN FAO) describes it as a three-living-organism arrangement. Fish, plants and nitrogen-fixing bacteria in the plant roots support themselves, which turns the waste into fertilizer for the crops. The system also cleanses the water by filtering out particulates and removing fish waste before it builds up to toxic levels. The water is left fresh and clean enough to support fish growth, and so the cycle begins again.
Salmon and Salad for Sustainable Agriculture
In its simplest form, aquaponics is growing a tray of salad greens balanced over a self-cleaning aquarium tank of guppies on the kitchen counter. Modern commercial projects fill warehouses with high-tech, high-yield farms. Historical versions of this practice have included flooded rice paddies populated with carp or floating rafts of veggies in a fish pond. All, however, feature sustainability in reducing water consumption and maximizing nutrient recycling. Nothing goes to waste. There is even research into more sustainable foods to feed the fish, with mealworms as part of the menu according to USDA’s SARE (Sustainable Agriculture Research and Education) project.
According to the University of Maryland’s Sustainability blog, aquaponics uses only 10% of the water required by conventional agricultural practices for crop growing. Compared to traditional arable farming, the soilless conditions used for growing the plant crops also reduces pesticide and fertilizer use. The closed ecosystem minimizes or avoids disease and pest infestations. The UN FAO also notes that plants are grown much closer together. The increased stocking density or capacity per square foot is much greater than land-based farms, so facilities generally produce bigger yields in a much smaller area.
The system also optimizes output by cultivating plant crops especially suited to soilless cultivation. Microgreens and other salad vegetables grow quickly and are harvested earlier than traditional crops. They are also nutrient dense. Bloomberg profiles Edenworks, a business growing baby greens and microgreens over salmon, shrimp and striped bass within an urban indoor facility. Early in its startup, the company switched to the higher value crops with short growth cycles.
It’s also possible to scale this venture upwards and outwards. The Coolist describes how vertical farming enterprises optimize available space to maximize crop yields. Meanwhile, SeaGrant, a federal-university partnership maintained by the National Oceans and Atmospheric Administration (NOAA) describes how to grow 160,000 pounds of fish annually, and 30,000 heads of lettuce per day from 40,000 square feet of fish ponds and a 123,000-square-foot greenhouse.
Sustainable Agriculture and Food Security for Coastal Communities
For developing countries, where agricultural land is marginal and resources limited, aquaponics could be the answer to feeding communities and solving food security.
Science Direct describes a low-tech solution that uses readily available resources to optimize food production in coastal Bangladesh. Floating vegetable rafts above fish cages on existing homestead ponds brings food to villages in a way that is both sustainable and socially relevant. Not only can families move the rafts to follow available sunlight and improve crop growth, but the cages stop fish from escaping during rainy season floods.
Another potential for sustainable agriculture in coastal regions is to use saltwater. Project Feed 1010 describes how versatile these systems could be. Not only is saltwater widely available, and in areas where agriculture already struggles, but the salinity could support more fish species for consumption and preserve wild stocks. Although salad greens would struggle, plants that are salt-tolerant show potential for oil production or biofuels.
It is also possible that harnessing wave energy could power this agriculture. As an alternative energy source for desalination and electricity, this could bring freshwater systems as sustainable agriculture to arid coastal regions around the world. Aquaponics could not only feed communities but also produce a valuable crop to sell.
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