DOI: 10.26188/30038539.v1
title: 24.3 Headwaters streams.pdf

description: This research sought to increase our understanding of the ecological values and services provided by headwater streams in the Melbourne Water management region. The research also aimed to contribute to the effective management and protection of headwater streams through a clear business case and appropriate policy and design guidelines. The work comprised two parts—1) a literature review and 2) a monitoring program featuring five headwater sites to the west of Melbourne.The literature review defined headwater streams as the point in the landscape where catchment runoff first accumulates sufficiently to create overland flow paths. The review found that headwater streams are dominant and critical features of many landscapes. They are the primary sources of streamflow, important sources of organic matter and biota (e.g. invertebrates and frogs) to downstream waters, and act as hot spots for retention and transformation of nutrients such as nitrogen and carbon. Their contribution to regional aquatic biodiversity is disproportionately large. For example, several studies have shown that headwater streams provide extensive habitat, with up to ~one-third of aquatic invertebrate species being unique to these running waters. Headwater streams are also the first source of aquatic life in the transition from hillslopes to the river network and thus can be an important source of colonists to lower reaches. The contribution of headwater streams to regional biodiversity and downstream ecological processes is not yet known in the Melbourne region.The monitoring program collected data on hydrology, water quality, and ecological structure and function. In general, flow behavior at the sites was highly seasonal, with surface flow only occurring during the wetter months. Water draining from the sites was of a very high quality (e.g. filterable reactive phosphorus concentrations less than 0.01 mg/L). Leaf breakdown rates—an indicator of stream decomposition—were found to be lower in the headwater forested sites compared to nearby agricultural streams. The slow rates are indicative of healthy ecosystem function in Melbourne’s largely undistributed, forested headwaters. Bores in the stream substrate sampled for groundwater-dwelling aquatic animals (stygofauna) revealed few individuals.Our results highlight the overarching and critical role that headwater streams play in maintaining downstream river and bay health. These systems however, are particularly vulnerable to degradation or loss in rapidly urbanizing cities such as Melbourne. Even small changes in land-use in the catchments of headwater streams are likely to elicit significant consequences to hydrology, water quality and ultimately stream structure and function.Further work is required to develop a clear business case and appropriate policy and design guidelines for headwater stream protection.<br><b>Recommendations</b>• Consistent with Regional Performance Objective 16 in the Healthy Waterway Strategy, headwater streams should be protected from urban development. The use of the new stream network layer—which now includes headwater stream extents—will help identify where this Performance Objective needs to be met.• Quantify the loss of headwater streams to date and estimate the length of headwater streams that are vulnerable to urban development. In doing so, determine the implications for regional hydrology, water quality, biodiversity, and relevant targets set (for key values) within the Healthy Waterways Strategy.• In locations where urban development occurs, appropriately designed stormwater control measures (SCMs) can ensure headwater stream protection is achieved. The SCMs must be designed in ways that mimic natural flow and water quality regimes.Develop guidelines for the protection or restoration of headwater streams in urban developments based on project outcomes, along with data and knowledge from other related studies (e.g. stream monitoring for the Sunbury Integrated Water Management project, Ideas for Aitken Creek project).