Urbanisation affects ecosystem functioning more than structure in tropical streams

Fabienne Wiederkehr,Clare L Wilkinson,Yiwen Zeng,Darren C.J Yeo,Robert M Ewers,Eoin J O'Gorman

doi:10.1016/j.biocon.2020.108634

Fabienne Wiederkehr, Clare L Wilkinson + Show 4 more

Open Access

https://doi.org/10.1016/j.biocon.2020.108634

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Abstract

Urbanisation poses a clear threat to tropical freshwater streams, yet fundamental knowledge gaps hinder our ability to effectively conserve stream biodiversity and preserve ecosystem functioning. Here, we studied the impact of urbanisation on structural and functional ecosystem responses in low-order streams in Singapore, a tropical city with a mosaic landscape of protected natural forests, managed buffer zones (between forest and open-country habitats), and built-up urban areas. We quantified an urbanisation gradient based on landscape, in-stream, and riparian conditions, and found an association between urbanisation and pollution-tolerant macroinvertebrates (e.g. freshwater snail and worm species) in litter bags. We also found greater macroinvertebrate abundance (mean individuals bag−1; forest: 30.3, buffer: 70.1, urban: 109.0) and richness (mean taxa bag−1; forest: 4.53, buffer: 4.75, urban: 7.50) in urban streams, but similar diversity across habitats. Higher levels of primary productivity (measured from algal accrual on ceramic tiles) and microbial decomposition (measured from litter-mass loss in mesh bags) at urban sites indicate rapid microbial activity at higher light, temperature, and nutrient levels. We found that urbanisation affected function 32% more than structure in the studied tropical streams, likely driven by greater algal growth in urban streams. These changes in ecological processes (i.e. ecosystem functioning) possibly lead to a loss of ecosystem services, which would negatively affect ecology, society, and economy. Our results point to possible management strategies (e.g. increasing vegetation density through buffer park creation) to reduce the impacts of urbanisation, restore vital ecosystem functions in tropical streams, and create habitat niches for native species.

Highlights

Habitat loss is increasing rapidly across the globe and represents one of the largest environmental threats to fresh waters and their biodi versity (Dudgeon et al, 2006; Vörösmarty et al, 2010)
We found that urbanisation affected function 32% more than structure in the studied tropical streams, likely driven by greater algal growth in urban streams
Most of the extensively-described manifestations of the urban stream syndrome were reflected in our urbanisation gradient

Summary

Introduction

Habitat loss is increasing rapidly across the globe and represents one of the largest environmental threats to fresh waters and their biodi versity (Dudgeon et al, 2006; Vörösmarty et al, 2010). The expanding human population as well as developments in infrastructure, agriculture, and industry threaten stream ecosystems by causing landscape modifications (channelisation of streams), pollu tion (surface runoff), and introduction of invasive species (Haddad et al, 2015; Pickett et al, 2011). These threats exert a dis proportionately high impact on the native species within such water ways through reduction in available habitat niches, high nutrient loads, and simplified food webs, resulting in species loss and causing worldwide conservation issues (Peralta et al, 2019; Pickett et al, 2011). Intact lotic systems provide numerous benefits to society such as regulating (e.g. flood control), provisioning (e.g. drinking water), supporting (e.g. habitat), and cultural (e.g. recreation)

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