Significance

The headwater streams of the Australian Alps provide a substantial proportion of the water yield of the Murray-Darling Basin (est. 30 – 70% of base flows) from a very small relative catchment area (2.5%). Stream flows in the Alps are maintained by groundwater sources (springs), recharged from rain and snowmelt. Associated with many of these groundwater sources are small isolated bryophyte pools, which feed into larger peatlands that attenuate extremes in stream flows and modify headwater stream chemistry.

Also found in these aquatic environments are distinct communities of aquatic macroinvertebrates, with mayflies, stoneflies, caddisflies, beetles and dragonflies dominating the insect fauna of streams and the amphipods (crustaceans) more abundant in the pools. Previous taxonomic studies have identified numerous species which are endemic to the Australian Alps and highly restricted in distribution. Included among these is the endangered predatory stonefly (Thaumatoperla alpina) which is only found on the Bogong High Plains. However, the invertebrate fauna of the Alps is largely under-described with respect to taxonomic associations and life cycles.

What we know about these systems:

Through long-term (multi-year) base-flow and storm response studies we have established the key hydro-chemical processes that occur in alpine aquatic ecosystems.

We now know that groundwater is critical to the viability of alpine peatlands, sustaining moisture levels over long summer months. This groundwater has a composition very similar to rain (and snow) due to the highly weathered nature of the alpine regolith and short period of time that groundwater spends in the aquifers, effectively providing a year-round supply of ‘rainwater’  (McCartney et al. Australian Journal of Botany 2013, 61, 566).

Our long-term studies have shown that peatlands seasonally regulate the export of nutrients and organic carbon to downstream aquatic ecosystems, and increase the buffering capacity of headwater streams. This provides the nutrients and energy that drive biogeochemical processes, and makes them more resilient to both natural and human disturbance (Silvester Environmental Chemistry 2009, 6, 424).

During storm events peatlands have a particularly important role in moderating stream water composition and flow. In response to such events peatlands retain rainfall, releasing it slowly in the following days to weeks. More surprisingly, despite the extremely low salt content of rain, the water released by peatlands during these events has a near-constant composition, providing a stream aquatic physico-chemical environment that is largely unaffected by the rain event (Karis et al. Journal of Hydrology 2016, 542, 317).

Current research:

Our current research in aquatic biogeochemistry and aquatic ecology of the Australian Alps is in the following areas:

• The re-charge mechanisms of groundwater sources, particularly the relative roles of rain, snow and seasonality of precipitation in groundwater recharge. This work will be critical to understanding the future viability of the groundwater dependent bryophyte pools and peatlands.
• Measurement of evapotranspiration rates from alpine peatlands using the eddy-covariance flux technique to establish a water budget for these systems. Combined with stream chemical data, this will allow a detailed hydro-chemical model of peatland and headwater stream regulation processes to be developed. The work will also allow an estimate of the ground water inflows to these systems.
• The response of headwater streams to extreme rain events. Our work has shown that peatlands are a strong regulator of stream water composition under high flow conditions; this work is now focused on the effects of closely spaced extreme events and directed towards understanding peatland function in a changing climate.
• Physical and chemical drivers of vegetation patterns in alpine peatlands. This work includes: (i) understanding the mechanisms underlying the extreme sensitivity of groundwater dependent mosses to desiccation and (ii) characterizing the exchange (calcium uptake) properties of Sphagnum moss using synchrotron-based IR microspectroscopy.