aquaponics

aquaponics, system of agriculture that combines aquaculture and hydroponics to cultivate both plants and aquatic animals. Aquaponics setups cycle nutrients through a closed circuit of bacteria, fish, and crop plants. The system uses nitrifying bacteria to convert fish waste into nitrates for plants, which in turn purify the water for the fish.

History

Some consider ancient agricultural practices by the Maya and Aztecs to be early examples of aquaponics. The Aztecs built floating gardens called chinampas atop freshwater lakes, and nitrogen cycling within the water bodies supplied nutrients to the plants. Other early predecessors of aquaponics emerged in Far Eastern regions, where farmers have long grown rice in paddies rife with aquatic life in order to fertilize their crops.

Modern aquaponics systems arose in the 1970s and ’80s, when aquaculture research was on the rise. The New Alchemy Institute, a research center founded in 1969, designed a structure in partnership with Solsearch Architects called the “Ark” that incorporated fish and vegetable cultivation into a residential home on Prince Edward Island. Scientists from North Carolina State University constructed the first successful closed-loop aquaponics circuit in the 1980s, and the first commercial aquaponics facility appeared that same decade in Amherst, Massachusetts. In the early 21st century the concept continued to gain popularity, especially in Australia and Canada, and both commercial systems and backyard aquaponics kits became more available.

Setup

Aquaponics systems rely on the interplay between fish, plants, and bacteria. The system imitates the natural cycles of aquatic ecosystems and their nutrient exchanges, albeit in a simplified form. A common aquaponics setup houses fish in a tank that is connected to crop beds through a pump. The pH value of the water in the system must be in the neutral range, between about 6.8 and 7.2. At improper pH values, the fish face the risk of death, and the plants cannot successfully integrate nutrients. Common varieties of fish used for freshwater aquaponics include carp, catfish, and tilapia. The fish consume feed, which contains nitrogen, and excrete waste that is rich in the chemical compound ammonia. Water from the fish tank, which is laden with waste matter, ammonia, and uneaten fish feed, flows into biofiltration structures containing nitrifying bacteria. Often, the biofilters are incorporated directly into the media used to grow the plants, though some setups rely on additional pumps and filters. Various kinds of nitrifying bacteria convert the ammonia into nitrite and then into nitrate, the form of nitrogen that plants can consume, and thus the water nourishes the crops.

The newly nitrate-rich water travels to the soilless plant beds, which can take a number of forms depending on the plants and the size of the setup. Small leafy vegetables such as lettuce, spinach, and kale lend themselves well to aquaponics, as do many herbs. In the popular deep water culture or raft system of aquaponics, a thin buoyant sheet sits across a tank of water, and plants stretch their roots through the material. This method involves constant circulation of the water between the fish tank and the separate plant chambers. Other arrangements, such as ebb and flow systems, vary the amount of water available at a time and provide different substrates on which the plants can anchor themselves. In all setups, as water flows through the channel, plants absorb nitrate as fertilizer, and the purified water travels back to the fish tank. Because of this cyclical design, an aquaponics system reuses between 95 and 99 percent of the water it initially receives, with small losses occurring as a result of evaporation from the tanks and transpiration by the plants.

Saltwater aquaponics, a less common variant of the technique, functions similarly to freshwater aquaponics but relies on fish and plants that thrive in a more saline environment.

Advantages and disadvantages

Aquaponics has a number of environmental advantages over its progenitors, hydroponics and aquaculture, as well as over traditional agriculture. Aquaculture systems often crowd fish into densely packed pools that yield a significant amount of waste-contaminated water. Aquaponics systems recycle and filter the water, and thus wastewater treatment and disposal is not necessary. While hydroponics systems require costly nitrogen fertilizers to sustain plants, aquaponics systems obtain these nutrients from fish. Finally, inefficient irrigation in conventional agriculture is a major source of water waste, with significant amounts of precious fresh water being lost to evaporation or runoff before reaching crop roots. In contrast, closed aquaponics systems have little water loss and can grow crops efficiently with little water waste. Other advantages of aquaponics systems include their ability to produce fish and plants year-round and their minimal need for herbicides and pesticides. Aquaponics systems can be certified organic, which can increase the market value of the crops and fish they produce.

One of the major disadvantages of aquaponics is the cost. Expense has been a major barrier to commercial aquaponics endeavors, with both initial investment and later operating costs—such as fish feed and electricity for the pump—being prohibitive for some farmers. Systems are also labor intensive, requiring daily maintenance and a knowledge of both fish and plant cultivation. Research has suggested that aquaponics systems are not as profitable as traditional agriculture, though some proponents of aquaponics counter that such findings were based on nascent aquaponics setups that had not yet achieved profitability and argue that aquaponics can be profitable when housed in large enough facilities.