Amazing Nature

Wetland Engineers

Aug 2022
Author: Green Power
Sha Lo Tung, a large man-made wetland, is a noted dragonfly treasury in Hong Kong.

Freshwater wetlands are unique ecosystems. Covering just 1% of the earth's surface, freshwater wetlands nurture 10% of all known animal species. Apart from being key water sources, wetlands' geomorphology and structure are important factors for keeping them in good shape. Artificial technologies of hydrological and geological engineering are widely deployed around the world to upgrade wetland habitats. Sha Lo Tung, the dragonfly paradise of Hong Kong, is a typical example. By recovering the irrigation system of the agricultural land, an ecologically rich, man-made wetland has been created. In nature, there are many “engineers” too. They work relentlessly – without much publicity – and generate diverse wetland habitats.

“surales” wetland habitat
Giant earthworms Andiorrhinus sp. create “surales”, a labyrinth-like earth-mound wetland habitat.

Mound Engineers - Earthworms

In South America, there is a special type of freshwater wetland which scientists have termed “surales”. The mystery of the labyrinth-like earth-mound landscape had been little studied until recent years. Researchers found that giant earthworms Andiorrhinus sp. inhabiting the water-logged soil have a unique habit of returning to the same spot to deposit their excrement, in time forming towers of mound where the underground creatures can breathe. Meanwhile, the mounds also provide habitats for a variety of wetland flora and fauna.

The dam built by beavers
By building dams along streams, beavers enhances the water holding capacity of wetlands.
© Franklin Vera Pacheco

River Bank Architects - Beavers

Beavers are good divers. To hide away from predators, they build dams with tree twigs and logs that raise the depth of water. They will even carry out maintenance work to prevent leakage of the dams. Their work enhances the water storage capacity of the wetlands and provides stable habitats for other relatively deep water species. In addition, with water staying in the wetland for a longer time, more sediments are deposited, containing essential nutrients for many wetland species. The dam-building behaviour of beavers is of great value not only to themselves but also to other wetland species as well as the whole ecosystem.

Beavers had been extinct in England for over 400 years due to over-hunting of the species. Conservation biologists have reintroduced beavers into some areas, and proven successful in upgrading the biodiversity of natural freshwater wetlands.

Water buffalo
The activities of water buffaloes create many water pools favourable to the survival of freshwater wetland creatures.

Pool Making - Water Buffaloes

Water buffaloes (Bubalus bubalis) enjoy wallowing in mud. The thick coating of mud allows them to reduce heat absorption from the sun. Owing to their large size and heavy weight, they often create water pools of various sizes as they wallow. The water pools are important microhabitats for many species. Researchers have found that, in some restored wetlands of Hong Kong, those visited by water buffalo herds were richer in freshwater invertebrates than those without, indicating the significance of the water pool microhabitats to wetland ecosystems.

On the other hand, as water buffaloes wallow in the mud and compress the soil, they increase the soil viscosity and water holding capacity of the wetland, preventing the wetland from drying up due to water seepage. In addition, water buffaloes are herbivores which help keep vegetation from over-shadowing wetlands. In Hong Kong’s Mai Po Nature Reserve, water buffaloes were introduced in 2006 to keep weeds under control and to enhance the ecological complexity of the area. Today there are ten “water buffalo engineers” working in the reserve.