Our local catchment has one major lake, but many wetlands. Wetlands are usually known locally in Western Victoria as swamps. The word 'swamp' can be difficult to define, but here it means a place where you can get bogged in a vehicle, and sometimes there can be shallow water up to about one metre depth in a very wet year. Locally, a wetland might refer to a deeper pool of water. However, this is ambiguous, and this difficulty of definition is an indicitative characteristic of many of the attributes of a swamp. The edge is not defined, and depends on how wet it is in a particular season. It is a place where nothing might happen for a long stretch of time, and then is a riot of growth, noise and activity once the rains come. One of the attractive things about wetlands is that they are complex systems which have an intricate array of interactions between their species and the environment. This is especially true of our wetlands, because the filling sequence is largely unpredictable.
The species that live here are adapted to a life of extremes. They avoid or tolerate hot dry summers, including intense grass fires, and are waiting, ready to thrive and breed when the water returns. The array of life forms includes microalgae, bacteria and fungi, insects, crustraceans and other invertebrates, plants, amphibians, birds and mammals.
A filling event from localised rains initiates a cascade of life cycles. Algal populations boom then are replaced by herbivores. Plants grow, frogs emerge and birds arrive from other regions. Life then becomes a race to complete a life cycle before the start of the next dry period.
Many wetlands wet up then dry again
There are more than 1200 wetlands in the H11 H12 catchments. Some the characteristic features of our wetlands are that in general they are endorheic (having no drainage outlet), they are temporary (wet in winter, dry in summer), and the majority of them are freshwater rather than salty. Their shallow temporary nature means that they do not have a well defined boundary. It is not uncommon for them to remain dry for a number of years.
Wetlands in the H11 H12 catchments are among those that have been recognised as having high biodiversity values. One recent study (Casanova and Powling, 2014 – pdf) found 150 microalgae taxa from one swamp alone, plus a further 81 angoisperm and charophyte species were reported as having been identified from local swamps. This is let alone considering animal, fungi or any other life form. In 2012 temporary wetlands were included under the Federal Government's listing of Seasonal Herbaceous Wetlands (Freshwater) of the Temperate Lowland Plains under the Environment Protection and Biodiversity Conservation (EPBC) Act. They were assessed as having met the listing criteria as being critically endangered ecological communities. Threat abatement and recovery plans are an area of current interest.
Are you familiar with tadpole shrimps (Lepidurus apus)? These ancient crustaceans have been around since the time of the dinosaurs. They grow to about 2 cm long, and are very well adapted to life in our wetlands. They mature quickly in spring, just in time to be eaten as food by nesting brolgas. Their eggs can survive dried out for years. See Wikipedia for more information.
'Brolga' from 'Corroboree' (2001) 'Brolga' is inspired by totemic systems in Australian Aboriginal culture.
Long distance visitors – snipe, which migrate each year between southern Australia and northern Japan.
Our wetlands from a global perspective
How do our wetlands compare with those from around the world? Wetlands such as our are special and are actually becoming quite rare. There are a few systems elsewhere that share similar characteristics to those in Western Victoria. Many international wetlands are either permanent, or are frozen in winter and have free water during summer. Winter filling, temporary wetlands, like those that we have here, are usually referred to as occuring where there is a mediterranean type climate. Overseas they commonly they occur in areas of high human population density, and have been drained over recent centuries and decades.
Wetlands are disappearing on each continent. Seasonally dry, inland wetlands are the most affected. This figure is derived from 189 reports from around the world, and shows the estimated global decline in the number of wetlands since 1700 (from Davidson 2014).
Temporary wetlands in temperate climates around the world are often found in areas of high human population density. Some of the major regions where they still exist include in the Mediterranean basin from (southern France to northern Africa – Algeria, Tunisia, Morocco) and in southern United States of America (Texas and California). There are some major organisations in these areas that have been researching the management of threatened wetlands for a number of decades.
This video shows the different types of wetlands in Algeria in north Africa. At the 3:00 minute mark, there is a graphic that describes the location of their varous types of their wetlands, extending from estuary swamps at the Mediterranean Sea to chotts (salt lakes) and osases in the Sahara desert. Like us, they experience hot summers and winter rainfall, so this makes a useful wetland contrast to what we have here in Australia.