The most common feature of wetlands in the coastal plain around Perth is their disappearance. Since European settlement over 60% of wetlands, swamps and lakes have been removed from the map. Perth city was built on a series of wetlands that were drained and filled from the earliest days of the Swan River colony.
Pumps were constantly working to keep the foundations of the old Boans Perth store (now the Myer centre) from being permanently waterlogged. It was built on the site of a wetland area. Most of the league football ovals around the city are built on drained swamps, including Perth, Leederville, Subiaco and Bassendean.
Wetlands habitats play many important roles in our environment and a change of thinking has occurred just in time to save the remaining metropolitan swamps and lakes. This is the story of the largest wetland habitat on the plain - Herdsman Lake just 7 kilometres from central Perth
What is a habitat? It’s a place in which animals, plants and insect live. It offers protection and a source of food.
Looking at food chains allows you to see right inside how a wetlands environment works. Essentially plants are at the bottom and provide the vast bulk. Plant consumers such as aquatic insects, snails and birds come next and these are followed by the animal eaters.
As is the case in all food chains plants are the basic fuel of this watery habitat. The stringy pondweed (Potomogeton crispus) is one of four plant species on which the success of Herdsman is based. It is a favourite food of the coot, a common waterbird and they dive down to pull up the long strands.
The other critical plants are water dwelling algae, bulrushes (Typha orientalis) that live in shallow water and lawns planted around the edge. All are grazed extensively. For an example you can see hundreds of the same black coots nibbling away on any area of lawn surrounding the lake every day of the year. They are also capable of pushing their strong beak into the bulrushes to harvest the tender, sweet leaf bases
At the top of one food chain at Herdsman is a raptor, the Harrier. In order to survive it needs to consume 90 Coots in any year. To keep 90 Coots fed the equivalent of 27,000 plant will be consumed. In order to maintain an equilibrium and be able to afford the sacrifice of 90 excess birds there needs to be a community of around 1000 coots The plant number just shot up to 30 million to feed them.
With other predators of the coots such as snakes and pelicans actual numbers need to be around 5000 in order to remain in balance.
Predators are a very necessary part of a habitat. Tiger snakes for example ensure that frog numbers don't explode to the point where they could wipe out dragon flies. The whole ecosystem is kept in a state of dynamic balance by these competing interests.
Herdsman lake is one of a handful of remnant suburban wetlands. Covering 400 hectares it is characterised by extensive reed beds and limited open water areas. Today it is a haven for wildlife and a wonderful example of conservation.
Since European settlement the lake has suffered massive interference including draining, agriculture, feral animals and introduced weeds, housing development, industry, heavy metals pollution, frequent bushfires and garbage disposal.
Today we recognise the pivotal role that wetlands play as part of a unique corridor of life that runs along the sandy coastal plain of WA.
Each wetland is a unique habitat because of plant communities, water quality and depth etc. Each one supports a different suite of plants, insects and animals.
What is their significance today? Wetlands are a vital part of the whole coastal plain ecosystem. Many animals and birds cannot live without these areas of swamp or lakes. For example there are 10 species of reed dependent birds at Herdsman. None of these birds can nest in nearby wetlands because they need an extensive area of reedbeds for each breeding pair.
Lake side vegetation of paperbark trees (Melaleuca rhaphiophylla) together with rushes and sedges act as water filters. In combination they remove nutrients and pollutants from road run off as well as salt arriving from on the wind from the nearby coast. Every year some 240 kg of salt lands on each hectare of the lake. Plants recycle this material and stop its accumulative threat.
Migratory birds from the Artic Circle call into Herdsman on their epic global journeys. Not only does it offer safe haven but food sources to sustain them for the next long leg of their journey.
The size of Herdsman is important because all animals must have a certain amount of room to live. Reed warblers for example need 300 square metres for one breeding pair. A pair of Harriers need 400 hectares of bulrush swamp so this means there is only space enough for one pair in the whole of Herdsman.
Wetlands provide places for people to come face to face with nature in a quiet placid location. On any day you can witness the enjoyment of visitors to nearby Lake Monger as thousands come to feed, photograph or look at the birds. The education centre at Herdsman gives 7000 children per year a first hand look at an ecosystem.
Herdsman was originally an open water lake. In the 1920’s, under the Soldier Settlement Scheme, the lake was drained resulting in a permanent 2 metre drop in water level. Farms established on the former lake bed failed as a result of poor soil.
Bulrushes produce prodigious quantities of seed but conditions for germination are very exacting. These abandoned farms became flooded in winter and this provided the perfect set of conditions for bulrush germination. You could say with some truth that the plants seized this opportunity with both hands.
It’s the proliferation of bulrushes that has created a new habitat. When it was an open lake it supported a limited range of bird species. Now it is home to a amazing 75 species. This is in stark contrast to next door Lake Monger, an open water lake, where only 20 species of bird are found.
It’s ironic that human intervention has completely altered the habitat at Herdsman and created just the sorts of living spaces needed to support birds displaced from other disappearing suburban wetlands.
WA’s Dept of Parks and Wildlife have taken this lake under it’s protective wing and it is now designated as a Regional Park which will ensure it’s protection as part of our natural heritage.
This change in attitude has come just in time to preserve wetlands. These doorstop wilderness areas are full of more unique wonders that you could see in a month of Sundays.