- In the Strathbogie Ranges, most wetlands occur where groundwater comes to the surface and where soils are seasonally or permanently saturated.
- Though healthy wetland habitat is now rare, it was once widespread and covered roughly 15-20% of the Strathbogie Tableland.
- Extensive clearing of wetland habitat occurred by the early 20th C, enabling agricultural production, but has had a high environmental cost.
- Re-establishing wetland habitat has multiple benefits.
Wetland vegetation on the Tableland occurs where soils are reliably damp, or even water-logged, for most of the year. Not that some wetland sites don’t dry out occasionally, or even regularly/seasonally, but the distinctive vegetation that makes up these areas (variously known as spring-soaks, swamps, bogs, tea-tree scrub, sphagnum moss beds) is specialized to cope with saturated soils, often clay or humus-rich, that have developed where ground water discharges – seeps out of the soil (as distinct from wetlands on the plains which usually occur where water pools, from run-off, at low points in the landscape). In the Ranges, these wetland sites are referred to as ‘ground water dependent’ ecosystems, because they only occur where groundwater reliably seeps out of the ground. Although these wetlands are considered to be a particularly important environmental and cultural feature of the catchment, there is a near complete lack of these wetlands on state databases. The lack of accurate mapping of these wetlands is considered a hindrance to management (Strathbogie Groundwater Management Area LMP, GMW, 2013, p. 10.).
Mapped wetlands in north east Victoria. Colours refer to primary water source. Location of this study area (Seven Creeks catchment) and the broader Strathbogie Ranges (which contain extensive groundwater dependent ecosystems) are shown. Note the complete lack of mapped wetlands within the Strathbogie Ranges.
This image gallery shows the variety of wetlands found on the Tableland, many of which are now fragmented and degraded.
As is abundantly clear when you drive through the Strathbogie landscape, most of the native vegetation has been cleared and replaced with farm land. It’s not always easy to say where wetlands once occurred, though there are often tell-tale signs. Rushes, reeds and tea-tree indicate a wetland, even if most of it has been cleared. Most streams and drainage lines are fed by and flanked by wetlands, where you can still find Mountain Swamp Gum (Eucalyptus camphora) and Blackwood Wattle (Acacia melanoxylon). It’s even more obvious from space! Wetlands also have characteristic clay soils (see below). If you know what to look for, satellite images are an ideal tool for identifying wetlands, even if the original vegetation is gone.
Here’s a Google Earth satellite image of the Seven Creeks catchment above Polly McQuinn’s. The degree to which native vegetation has been lost is quite startling – more than 80% of the native vegetation in the entire catchment has been cleared. This figure increases to about 95% if we look only at private property (excluding the non-arable, mountainous public land) – that’s a staggering degree of clearing and makes all native habitat in the catchment extremely valuable.
The type of vegetation a wetland can support depends on several factors: the extent and duration of water-logging, the type and depth of soil, site history, surrounding topography and geology. Some sites support trees, others are far too wet for trees and are dominated by water-loving shrubs (like tea-tree), sedges and rushes. These different types are technically described as, for example, Spring-soak Woodland (EVC 85), Perched Boggy Shrubland (EVC 185) and Swampy Riparian Woodland (EVC 83) (The floristics of wetlands in the Strathbgie Ranges (p. 2)). As often as not, these vegetation types intermingle and exist as a patchwork, or mosaic. When wetland vegetation is cleared, all this diversity and complexity, and the habitat itself, disappears. It’s little wonder that animals like the Long-nosed Bandicoot (Perameles nasuta) that rely on dense ground-layer vegetaton, now only occurs in isolated pockets and is on the verge of local extinction (personal observation).
So, how much wetland and riparian vegetation once occurred on the Tableland? The image below maps all groundwater discharge areas in the catchment above Polly’s – the total comes to some 2700 ha! [notes on mapping, below] So, wetland and riparian vegetation once comprised a staggering 15-20% of this landscape – it must once have truly been a Wetland Wonderland!
Much of the focus of this Bogies and Beyond project has been on monitoring how groundwater levels change seasonally and from year to year (eg here) and better understanding what influences groundwater in the ranges, but it’s important to recognize that this unique wetland habitat (eg here and here), though once widespread and quite common, has been largely cleared and most is now significantly degraded.
Historically, these wetlands, acting like sponges, held onto water, slowed its passage through the landscape – storing water and releasing it slowly throughout the drier months, ensuring that the Seven Creeks at Strathbogie and Euroa had a year-round flow.
Today, perhaps as little as 500 ha of the original 2700 ha of wetland habitat remains. Whilst there are still some fantastic wetland sites, much of what remains, as already stated, is fragmented and degraded.
Early farmers cleared land where they could and, in many instances, were required to clear a certain amount each year in order to maintain their selection, as well as create arable land for grazing and crops. By the early 20th Century, the Tableland came to resemble what it is today – a largely tree-less landscape. With most of the original forest and wetland vegetation cleared, the hydrological system has drastically changed and we are the poorer for it. The days of guaranteed summer flow in the Sevens at Strathbogie and Euroa are gone.
What can a healthy wetland look like?
The value of plentiful, high quality groundwater on the Strathbogie Tableland can’t be underestimated – for nature and humans. ‘Spring-fed dams’ are present in almost every paddock and groundwater bores are becoming increasingly important for farming and domestic water security. The rub is, we still don’t really know that much about how the groundwater system functions, nor what will happen to water tables and wetland habitat as rainfall patterns change.
There have been a number of studies into the unique wetlands of the Strathbogie Ranges. Over the past 18 months, the Bogies and Beyond project, coordinated by the Goulburn Broken Catchment Management Authority and funded by the Victorian Government, has re-focused attention on groundwater and wetland habitat.
Why do wetland soils hold water?
Granitic soils are sandy and friable – they contain lots of quartzite/sand and silt, but relatively little clay (particle size <0.002 mm). Granitic soils in the Starthbogies are usually reddish-orange in colour due to the presence of oxidized metals like iron and aluminium. These soils, being friable and often deep, are pretty good for growing trees, but not at all good for building good dams. That’s why virtually all dams are built in or near wetlands, where the soil has a higher clay content.
Granitic soils prone to water logging turn from reddish, through yellow, to grey, or even white, in colour. This colour change is a result of reduced oxidation (of metals like aluminium and iron) and also indicates a higher proportion of clay particles in the soil. Physical and chemical weathering of feldspar and mica results in the formation of clay minerals (eg. kaolin), which have excellent water-holding capacity and are good dam building material. As the feldspar and mica breaks down, the tiny clay particles are carried by water to ever lower parts of the landscape. Some of the particles end up in streams and leave the catchment, but over the millennia, much of the clay has been deposited where groundwater discharges. Once deposited, these clay soils usually support wetland vegetation with extensive, fibrous root systems that bind the soil/clay particles.
Mapping the previous extent of wetland habitat can be done by recognizing groundwater discharge sites from aerial images, based on the texture and colour of the vegetation. Polygons are then drawn to enclose the discharge areas, to calculate area.
Further Information- investigations into groundwater and groundwater dependent ecosystems:
- Wetland implementation plan – peatland and spring-soaks wetlands, Strathbogie Ranges (Car et. al. Ecology Australia 2006)
- The hydrology of wetlands in the Strathbogie Ranges – report (Stewardson, University of Melbourne 2009)
- The Floristics of Wetlands in the Strathbogie Ranges (Coates et. al. DELWP 2010)
- Strathbogie Groundwater Management Area, Local Management Plan (Goulburn Murray Water 2013)
Posts relating to wetlands and groundwater in the Strathbogie Ranges:
- Strathbogie groundwater update – January 2020 (Feb. 1, 2020)
- Groundwater – where does it come from, where does it go? (Sept. 5, 2019)
- Little Mt Wombat walk – eagle nest, wetland, fire (April 8, 2020)
- Strathbogie groundwater update – June 2019 (July 1, 2019)
- Spring Soak and Bog Management Trials (May 16, 2011)
- Creek Junction Wetland Walk (Feb. 20, 2011)
- Flying Dragons (Feb. 18, 2011)
- Snipe found in Strathbogie wetlands (Dec. 21, 2010)
- Bluetailed Damselfly (Dec. 7, 2010)
- White-eared Honeyeater nest & pregnant lizard (Nov.9, 2010)
- Roadside wetland plants- what have we got and what are we losing? (Nov. 7, 2010)
- Water Ribbons (Aug. 30, 2010)
The Bogies and Beyond Groundwater Monitoring Project is supported by the Victorian Government and the Goulburn Broken Catchment Management Authority.
For more information contact Bertram Lobert email@example.com 5790 8606, 0409 433 276 or go to: https://strathbogierangesnatureview.wordpress.com/?s=groundwater