Research articleHabitat complexity influences fine scale hydrological processes and the incidence of stormwater runoff in managed urban ecosystems
Introduction
Urban ecosystems provide numerous environmental, socio-economical and ecological benefits to cities and towns (Bolund and Hunhammar, 1999, Chiesura, 2004, McPherson et al., 1997). As extreme precipitation events are likely to increase with climate change (Yilmaz et al., 2014), the effective management of hydrological processes and related ecosystem services such as stormwater drainage, runoff mitigation, soil water storage and purification is becoming increasingly important to create more sustainable and resilient cities and towns (Bolund and Hunhammar, 1999, Cunningham et al., 2010, Pauleit and Duhme, 2000, Nouri et al., 2013).
The traditional approach in evaluating hydrological processes and benefits within urban areas has focused on mapping and modelling the hydrology of urban land cover types at large landscape scales, such as the city or catchment scale (Pauleit and Duhme, 2000, Perry and Nawaz, 2008, Sjomana and Gill, 2014, Tratalos et al., 2007, Whitford et al., 2001). These models have then been applied to estimate changes in hydrological processes under climate change scenarios (Gill et al., 2007) or calculate economical benefits associated with runoff reduction (Zhang et al., 2012). However, these models can be problematic as soil hydrological properties are likely to vary with soil physical properties which are highly variable at a very fine scale (Pickett and Cadenasso, 2009). Currently, very few studies have investigated the variability of soil hydrological properties in urban ecosystems through empirical measurements (e.g. Gregory et al., 2006, Yang and Zhang, 2011).
Together with soils, other habitat components, such as litter and vegetation layers, are likely to exert significant effects on the hydrology of urban ecosystems (Nouri et al., 2013). The absolute amount of these habitat components (e.g. volume, surface area) also define the overall complexity of habitat patches (McCoy and Bell, 1990, Byrne, 2007), and may influence the presence of organisms, such as plant and invertebrates, able to affect hydrological processes at a fine scale (Bartens et al., 2008, Colloff et al., 2010). The hydrological impact of vegetation has been previously assessed in a few urban ecosystem studies. For example, throughfall and stemflow have been measured in some urban forests and under isolated trees and related to the complexity of vegetation layers (e.g. Guevara-Escobar et al., 2007, Inkiläinen et al., 2013, Livesley et al., 2014). Nevertheless, to date there have been no studies specifically investigating the hydrology of litter layers in urban ecosystems.
Management practices (or lack of) can alter directly or indirectly each of these system components, determining changes in the overall complexity of urban habitats (Byrne, 2007, Gaston et al., 2013), and therefore directly impacting on the local hydrological processes (Fig. 1).
Building on this bi-directional interaction, this study aims to holistically investigate the effects of management-driven differences in habitat complexity upon hydrological properties for each habitat component (soil, litter and vegetation). We addressed the following research questions:
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How do soil physical and hydrological properties vary in urban habitats characterized by different levels of habitat complexity?
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What is the hydrological role of each habitat component (soil, litter, vegetation)?
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How can our findings inform ecologically-sensitive urban habitat management to optimize urban water conservation and retention?
Section snippets
Study area
The study was conducted in the south-eastern Melbourne metropolitan area, Australia. The geology of the study area was restricted to quaternary and tertiary sandstones and therefore sandy soils, such as Podosols and Tenosols (sand > 89%). The study area was also confined to a single ecological vegetation class, herb-rich, heathy woodland (The State of Victoria, Department of Environment and Primary Industries, 2013), so that differences in soil properties amongst habitat types were brought
Soil properties
Soils in the three habitat types had similar mean bulk density (BD) but values ranged between 0.4 and 1.6 g/cm3 (Table 1). Nevertheless, soil penetration depth (PEN) was significantly reduced in low-complexity parks, as compared to high-complexity parks and remnants (Table 1), indicating a higher soil strength of soils in low-complexity systems. Total porosity (St) was similar in low-complexity parks and high-complexity parks, and 15% greater than in high-complexity remnants. Conversely, soil
Soil physical and hydrological properties
Soils with BD > 1.5 g/cm3 are considered compacted, as root growth is physically impeded, therefore soils investigated in this study were not generally compacted. In some LCP patches the turf thatch impeded to precisely establish the start of the mineral soil when taking cores for bulk density analysis. Therefore an underestimation of some BD values might be possible. Contrary to our expectations, the age since establishment of low- and high-complexity parks did not significantly affect soil
Conclusions
In the present study we evaluated fine scale hydrological properties of urban habitat patches differing for complexity and management history, which affect the hydrology of urban ecosystem at larger scale. We found that water permeability is dependent upon the habitat complexity, with low-complexity patches providing surfaces with reduced permeability compared to high-complexity ones. The presence of soil macropores exerted a positive effect in enhancing water infiltration and reducing surface
Acknowledgements
This project was funded by the Australian Research Council (ARC LP 110100686), the Australian Golf Course Superintendent Association (AGCSA), the Australian Centre for Urban Ecology (ARCUE) and the Frank Keenan Fund Trust. AO is supported by MIFRS and MIRS scholarships. AKH would like to acknowledge salary support from the Baker Foundation. None of the funding sources was involved in the design, data collection, analysis and writing phases of this manuscript. We thank Prof. Tim Fletcher and the
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