A version of this article first appeared in the Coffs Coast Advocate on 12.11.10.
Aquaponics in Coffs Harbour
Last weekend I was at the Sustainable Living Festival at the Coffs Harbour Botanical Gardens. I was there with Kirsten Larsen, Research Manager of the Victorian Eco-Innovation Lab (VEIL), which is run out of Melbourne University.
VEIL have produced some quality research over recent years around food-sensitive urban planning and design, and food supply scenarios assuming certain policy settings and priorities, e.g. ‘business-as-usual’ vs. local and government adaptations taking changed circumstances into account.
In its submission to the Federal Government on the proposed National Food Plan, VEIL stated that ‘substantial, unavoidable and imminent changes in our food supply systems require fundamental shifts in how we manage land and resources for food production and other critical needs’. The combination of a series of key drivers, including increasing constraints in the availability of oil and fresh water, climate instability, soil degradation, and the ongoing loss of farmers and good farmland, led VEIL to conclude that ‘our existing systems of food production and distribution [are] increasingly brittle’.
All of which means, as Kirsten pointed out last weekend, that we are entering a period of probably large volatility, in which there is no guarantee that the future will look like the past or the present.
Those listening to Kirsten certainly took this message to heart, and many were motivated, like thousands more around the country and around the world, to start taking matters into their own hands.
As I’ve written previously in this column, the coordinator of the new Coffs Harbour Community Garden at Combine Street, Steve McGrane, is a pioneer in showing what can be achieved in a small urban setting.
Steve’s latest project is aquaponics: the combination of small-scale (i.e. back-yard) aquaculture with the hydroponic growing of vegetables. His system involves three ponds, each raised above the other, connected by halved lengths of long-lasting PVC pipe in which the vegies grow on a base on gravel, drawing their nutrients from the fish waste. Depending on the numbers of fish, plant growth can be remarkable: ‘as much as seven times faster than vegies grown in ordinary soil’, according to Steve.
The water flow, whose purpose is also to return adequate amounts of dissolved oxygen to the fish, is regulated by a 20-watt pump, powered from a 40-watt solar panel, with four lithium batteries of 4 watts each. Running at lower rates of intensity, these can last for as long as 40 years. The entire micro-energy system cost $500 to set up.
The system runs with special software that controls the maximum input and output of each battery, to prevent overheating. The time the pump runs is determined according to the amount of sunlight: on cloudier days, the fish are less active, and so there will be less need for oxygen. On average, the pump runs for 10 mins every 20-30 minutes, leaving 15 minutes for the trays to empty.
Steve’s largest pond is 1500 litres, and over the summer he plans to stock it with up to 30 silver perch fingerlings, which will take approximately 12 months to reach an edible size of 500 grams. He’s also looking at installing a slightly larger system, in which he can raise up to 100 fish per year. About half of the total water surface area of the large pond, where the fish are raised, needs to be covered with plants such as water lillies, to return oxygen to the water.
Like conventional aquaculture, Steve’s fish depend on fish-meal, though he’s also looking at home-grown sources of protein like meal worms and comfrey. The fish may not grow as fast, but that’s not the point. For Steve, being sustainable means greater self-reliance:
“I’m all about not leaving your block to eat, having your food at your back door.”