Meanwhile, waiting patiently in the back corner of the dome is the 3200gl water tank. It plays an essential role in regulating temperatures in the dome acting as a thermal mass in winter to capture heat during the day and as a cooling mass in summer to keep the dome from overheating. But in true permaculture spirit, the tank can serve dual, even triple purposes….permaculture likes when you stack systems and cycle different eco-services.
One of the dual functions that the water tank will serve is for Aquaponics. I’m just learning about this technique but I’m already fascinated by its potential. Both aquaponics and hydroponics grow plants without soil. The plant is suspended in a tray allowing only its roots to touch nutrient rich water that is being circulated. Hydroponics uses nutrient additives to feed the plants where as aquaponics generates its own nutrients between a symbiotic relationship between fish and plants. The fish poop then microbes in the water convert the amonia-rich waste into nitrates making it available to the plants to absorb as food. The plants then filter the water as it passes through the system and back to the fish. It’s a closed loop, organic system unlike hydroponics which takes a lot of inputs many of which can be synthetic.
Tilapia is a common aquaponics fish and they eat water based plants like duckweed or watercress that float on the water’s surface. At full capacity, a 3200gl water tank could hold enough fish to grow food for three 900sqft domes. But in our system, aquaponics is an added value not the primary growing style. Soil-based farming is our focus and the water tank’s primary role is to regulate temperature in the dome. Aquaponics allows us to stack an additional function on the water tank and by running it at a quarter of its aquaponics capacity, we can use the nutrient-rich water to not only feed the aquaponic plants but irrigate the crops in the gardens beds as well. By building a trellis above the the water tank, we can take advantage of the open space above the garden beds that would otherwise go unused.