Ecologist Val English presented us with a talk on mound springs at the November meeting. Having joined the Department of Parks & Wildlife in 1994, Val was responsible for setting up the flora survey database of endangered/threatened species; she is now Principal Ecologist with the Species and Communities Section.
Mound springs are special sites, small in area, that are covered in dense vegetation and where, as the result of having a continuous discharge of groundwater, decomposing plant material produces peat. All designated mound spring sites in WA have peat.
Often the seepage zones form a raised area due to upwelling water pushing up the peat and at some, permanent pools have developed. Some springs also have a moated area. As their occurrences are widely scattered in the state, flora and fauna and local ecology will vary from one to another.
There are eleven mound spring sites in WA. Closest to Perth are those of the Swan Coastal Plain in the Bullsbrook area and at Three Springs, near Eneabba. Other sites are in the north of the State. In the north Pilbara/ southern Kimberley area are two groups (Dragon Tree soak and the Mandora springs) and in the northern and coastal regions of the Kimberley are Bunda Bunda, Lolly Well, Disaster Bay and Big Springs, a group known as the north Kimberley mound springs, the Durack Ranges and the Victoria-Bonaparte Wetlands.
The source of the water at spring sites is controlled by geological factors; the causes vary and include faults and differing permeability of the local lithologies, but not all sites have been studied in sufficient detail. As sites of permanent water, mound springs have a particular biota adapted to the moist conditions. As a result they are zones of specialised habitats and plant refugia where flora typically has adapted to permanent moist environment and where there will often be significant vegetation and invertebrate assemblages. At one of the Kimberley sites, for example, a rare new discovery of the “spiral” orchid Spiranthes sinensis, known only from coastal areas in the Eastern States, has been made.
Ages of mound springs will vary and it is considered that some will have developed over long periods. Mandora Spring (in the Kimberley) for example, is estimated to have established about 7000 years ago.
All mound springs are under threat and all are categorised to reflect their state as priority, endangered, vulnerable or threatened. Many factors pose threats to mound spring sites: changes in water input; weeds and their control; fires resulting in the loss of peat, cattle and other domestic and feral animals causing soil compaction through trampling and grazing; and water extraction for local agricultural projects. Where springs are located on pastoral stations such as some in the North Kimberley, some of these factors are more prevalent. In the south west Kimberley lack of rainfall is not the main threat but grazing and trampling by camels and donkeys is of concern. Some of the management measures include buffer zones, fire breaks to isolate the mound spring sites; and buffer zones created by land purchases that can be controlled through Departmental interventions. Recovery planning is based on ongoing monitoring and reporting.
Four of the eleven mound spring sites of WA, at the Swan Coastal Plain (north of Perth), Three Springs, Mandora (SW Kimberley) and North Kimberley (NE Kimberley), were described in some detail.
The Swan Coastal Plain mound spring on the Gnangara mound, west of the Ellen Brook and the Darling Scarp is situated over a series of aquifers (including the Yarragadee) from which some of Perth’s potable water is extracted in drought times. This mound spring site has broad zones of peat ~100m wide and has eight vegetated springs over an area covering 21ha from Bullsbrook to Mundijong.
The varied vegetation has a tree storey of Swamp Banksia (Banksia littoralis), Paperbark (Melaluca preissiana) and Flooded Gum (Eucalyptus rudis) with lower storeys comprised of ferns and sedges, and amongst the non-vascular plants are bog clubmosses and liverworts (refer to the excursion report on page 2 for further details of species and local observations). Rich invertebrate life is established including seed shrimp crustaceans (Ostracods), unsegmented worms (Nematoda), swimming crustaceans (Cladocera), oar feet crustaceans (Copepoda), water mites (Acarina) and other invertebrates. Here, the fern Cyclosorus interruptus is established. This is an outpost occurrence as it is noted only from several sites in the Kimberley area.
Research into the nature of peat at mound spring sites provides information on their ages, the flora species that contribute to its formation and whether these plants are remnants of past climates. A project, commenced in 2015 by hydrogeologist J. Rutherford, is based on examining peat core and its pollen grain record (from Light and SEM photomicrographs and imaging and 14C dating).
This talk was an interesting introduction to these generally little known special sites and whilst some mound springs have small pool oases attracting water birds, being small areas, they are not generally well known as tourist sites and this is a preservation advantage.
Susan Stocklmayer
See Page 2 for Plant Species list from excursion to Neaves Road