Why I built a wetland not a dam
How high up on our priority list should biodiversity be? For Mara Ripani, her family and fellow wetland-lovers, it’s crucial—and there are practical benefits too. Mara explains.
This article was first published in issue 145 (Oct-Dec 2018) of Renew magazine.
It never occurred to my partner Ralf and I to build a dam—it was always going to be a wetland. The sale of our home in Melbourne in 2015 afforded us the chance to act on our dream. After purchasing 15 acres in Blampied, Victoria, we set about constructing our very own wetland.
There are many different types of wetlands. There are natural wetlands such as damplands, sumplands, ephemeral wetlands, springs, marshes and swamps, rivers and streams, floodplains and billabongs, and artificial wetlands such as sewage ponds, rice paddies and constructed habitat ponds, just to name a few.
The definitions in Nick Romanowski’s book, Aquatic and Wetland Plants, illustrate the differences in water levels between the different types. For example, he defines damplands as having water mostly underground, but rising with seasonal rains to just below the surface in wetter months. Sumplands are similar, but here the water rises higher so that the ground is waterlogged at times and pools of standing water are common.
Having the water level just below, just above or flooding the soil determines the type of vegetation that will thrive and the type of animals, insects and amphibians that will make the wetland their home.
Our wetland is a ‘constructed habitat pond’ that collects a body of water in low-lying ground. It is flooded in winter, but in summer the water level drops. It’s often extremely low, say ankle-high, with some patches of soil completely exposed. It was designed to wet and dry in a way that mimics natural wetlands in the surrounding landscape, to provide habitat for the local flora and fauna.
Ralf and I were introduced to the beauty and ecological importance of wetlands back in our 20s, when we both worked for a revegetation company, Australian Ecosystems, that specialised in wetland ecology.
Our job involved collecting seed from grasslands, marshes and swamps, propagating the seed harvested, and planting out seedlings in newly constructed wetlands. Our employers at the time, Damien Cook and Brendan Condon, were two young men just a few years older than us who were passionate about the role wetlands play in supporting fauna and flora biodiversity.
Their passion was infectious. When we bought our acreage, at the very top of our list of reasons for constructing a wetland instead of a dam was biodiversity.
A dam serves a single purpose
The primary objective of a dam is to store as much water as possible in a given area of land, so that this water can then be used for irrigation or drinking water for stock. Hence, dams have steep gradients and deep centres to maximise the amount of water captured. And, as their purpose is water storage, they are rarely planted with trees or aquatic plants.
Where a dam is on pasture land, cattle and other grazing animals are almost always given access to the whole dam for drinking water. As a result, the dam edges get highly compacted and the soil is constantly disturbed, making it difficult for plants to establish. The water quality in dams used by animals can also be poor; the water can get very turbid due to the constant disruption of soil by hooves, so little, if any, aquatic life survives. (To prevent this, dams can be fenced so that grazing animals only have access to a small area, or water can be pumped to a drinking trough.)
What changes in a wetland
A wetland, however, can serve a multitude of purposes and values. At the core of these values are ‘ecosystem services’: the direct and indirect benefits humans experience from living in a well-functioning environment. These include such things as clean air and water, mental and spiritual wellbeing, and access to a range of food plants, pollinated by bees for free.
A wetland can do this by changing one crucial factor: the gradient.
By designing for a shallow gradient, you increase the area that wets and dries as the water level goes up and down. Thus, it is possible to plant a broader diversity of trees, sedges, reeds, rushes and aquatic plants, and provide a greater diversity of habitats.
These varied plant groups need differing levels of soil moisture to grow. Some, such as grasses and sedges, thrive on the very fringe of the wetland. Others, such as azolla, a floating fern, sit on the surface of the water. The tuberous-rooted water ribbons in the genus Cycnogeton can be found growing in waters 50 cm deep.
In between are a variety of plants providing highly valuable habitat both above and below the water. These include sedges in the genus Baumea, such as the twig-rushes, or those in the genus Bolboschoenus. Carex, a large genus of grass-like sedges, grow mostly in drier damplands, but some are found in waterlogged soils. Juncus rushes and the club-rushes also grow in waterlogged areas.
Each plant community provides a specific habitat or feeding role. Together they support a lush ecosystem of invertebrates, frogs, fish and animals. Think of each plant community as having its own architect and the architecture of that community catering to the specific needs of particular animals. The establishment of a vegetation community of sedges, rushes, grasses and trees and its supporting wetland is a direct invitation to the amphibians, birds and invertebrates that thrive in that specific combination.
When the black swans arrived
In our case, by constructing the wetland and establishing a vegetation community, we have created conditions for the arrival of black swans, pobblebonk frogs, dragonflies, swallows, herons and masked lapwings to name a few.
Our wetland is still only a baby; all our plantings are no more than three years old. As the vegetation grows and swells, the number of birds, insects and animals coming to visit will increase as more habitat and shelter is created and as our trees develop expansive canopies.
What is its value? How can I explain the feeling I get when I see swallows feeding at dawn and dusk on insects hovering over the water’s surface, or the pleasure and pride I feel when I hear our choir of frogs? And when the black swans arrived, these large indigenous birds, and made their home with us for a few weeks, how full of joy and happiness I was.
In choosing biodiversity, we chose not to use our wetland as a drinking hole for grazing animals, even though we plan to graze pigs. Instead, we will provide drinking troughs for them. We have fenced off the wetland to prevent access: the wetland is closed off to pigs on the east, west and south, but open to the north, so wildlife still has easy access. Damien Cook, my previous employer, now both a friend and a well-established botanist, suggested I leave a ‘flight path’ open for visiting birds, so on the north side I am only planting indigenous grasses.
Planting it out
I am doing the plantings in stages. Once the initial aquatic and terrestrial plants have established, I will go back and plant a greater diversity of vegetation. I save up to purchase tree guards, stakes and plants. Then, with my best friend, the mattock, I plant.
In summer, I water, as I don’t want to lose plants to our unreliable rain patterns, after all the work I’ve done. The plant roots are small and shallow in the first few years. So, with our very old ute, a 1000 L water tank and the help of visiting ‘workaways’, I water as often as I can, which is about three times during the summer months. I can’t manage more—there are too many trees. Why not install irrigation? In the near future, the trees won’t need the support I am giving them now, so the cost of materials, labour and time for a short-term goal is not worth it to us.
Other wetland values
The other wetland values for us are fire protection, irrigation for our kitchen garden and fruit orchard if our 220,000 litre rainwater tank and bore dry out (we limit this because if we use it too much for irrigation we will lose wetland vegetation), recreation, swimming, aesthetics and as a cooling microclimate.
I can’t believe I have my own wetland; its aesthetic value is priceless. The sunset colour bleeds into the water’s surface to create vast beauty. It is a joy to walk around the wetland to observe the changing colours of the aquatic plants—they go from a lush green to a fantastic copper colour—and to observe visiting birds and dragonflies and discover indigenous colonising wildflowers.
At the beginning of summer when the water level is still high, I love to swim there. Flat on my back, looking up into the big open sky, I feel such happiness. I sneak up on dragonflies to admire their colour. The water is clear compared to neighbouring dams as the aquatic plants help to stabilise the soil. Decomposing plant matter further protects the soil by forming a thick protective layer over it, and this in turn reduces turbidity. No crystal-clear swimming pool could ever bring me this much joy.
In the peak of summer, the combination of water and plants creates a cooling microclimate. Trees transpire releasing water from leaves into the atmosphere. The water body itself acts as a heat sink as water has a high specific heat capacity: it takes a lot of heat to increase the temperature of water by one degree Celsius. Hence, in summer, when the soil surface temperatures are high, the wetland temperature in comparison remains low and that difference in temperature is experienced by us.
I am so glad, so pleased, so ecstatic that we built a wetland instead of a dam!