Headwater streams in an urbanizing world

Abstract

Headwater streams are critical to the integrity of the stream network, yet they are being rapidly degraded, channelized, or lost through land-cover and land-use change, particularly in urbanizing areas. We refined the definition of a headwater stream, reviewed the headwater stream ecosystem literature using examples from southeastern Australia and globally, and identified 4 critical knowledge gaps that are hampering the management of these unique systems: 1) inadequate high-resolution mapping and, thus, low-accuracy estimates of headwater stream locations and extents within catchments; 2) insufficient characterization of headwater stream typologies across varying geological, topographical, climatic, and anthropogenic conditions; 3) incomplete quantification of headwater stream structure, function, and ecosystem services across varying scales; and 4) limited understanding of the effects of urbanization on headwater streams against a backdrop of climate change. We propose a series of research questions to address these gaps and, finally, hypothesize and discuss the most effective ways to protect headwater streams in urbanizing environments given our current state of understanding. Of particular importance are the need to 1) shift perceptions of these systems as dry, insignificant depressions in the landscape; 2) manage both the headwater stream catchment and the channel; and 3) prioritize protection of the natural flow regime.