Abstract
Urban lakes are important environmental assets that contribute significant ecosystem services in urbanised areas around the world. Consequently, urban lakes are more exposed to anthropogenic pressures. Zooplankton communities play a central role in lake processes and, as such, are very sensitive to the impacts of human activities both through in-lake and catchment processes. Understanding their ecological function in urban lakes and how they respond to urbanisation is essential for environmental sustainability. In this study, we investigated the reliability of zooplankton size structure as indicators of anthropogenic stressors in urban lakes. We examined the relationship between environmental variables and zooplankton community size spectra derived as mean body size, density, and biomass. Our study showed that the overall mean body size was within the small size group ranged from 416 to 735 µm equivalent spherical diameter (ESD). Despite no significant difference in total zooplankton density between lakes, there was variability in the total density of the five different size classes. Total biomass was characterised by a significant proportion of size >750 µm. As the specific parameter of normalised biomass size spectra (NBSS), the slopes of the NBSS varied from moderate (−0.83 to −1.04) for a community with higher biomass of the larger size zooplankton to steeper slopes (from −1.15 to −1.49) for a community with higher biomass of smaller size. The environmental variables, represented by total phosphorus (TP) and chlorophyll a (chl-a), had a strong effect on zooplankton biomass and NBSS, where TP and chl-a were significantly correlated with the increase of total biomass and corresponded well with a less negative slope. Our results indicated that the community metric was sensitive to nutrient input and that size-based metrics have the potential to serve as key indicators for the management of urban lakes.
Highlights
Freshwater ecosystems are increasingly under stress from urbanisation, and this is likely to increase as it is projected that more than 60% of the global population will live in cities by 2050 [1]
A principal component analysis (PCA) ordination using all environmental variables (Figure 2) revealed that ~30% of the variability in environmental characteristics was explained by eutrophication indicators including chl-a, total phosphorus (TP), pH, and Secchi depth, while ~26% was explained by other variables including suspended solids, temperature, dissolved oxygen (DO), mean depth, salinity, and conductivity
Regardless of the degree of variation of environmental stressors identified across studied lakes, we were able to document a clear relationship between environmental variables and the dynamics of zooplankton community structure in urban lakes in Perth metropolitan and regional areas
Summary
Freshwater ecosystems are increasingly under stress from urbanisation, and this is likely to increase as it is projected that more than 60% of the global population will live in cities by 2050 [1]. A key challenge for local city governments, communities, and scientists is to protect and maintain the ecological integrity of aquatic systems in the urbanscape [2,3]. The trends in urban densification due to population growth are projected to lead to a threefold increase in the urban land cover, leading to a disproportionately higher impact on environmental assets [2,4]. Effective conservation and management of urban ecosystems will increasingly rely on our ability to satisfy the demands of the growing population while maintaining the ecological integrity, maintaining the sustainable delivery of ecosystems services well beyond 2030. As stated by Seto, et al [3], “cities can no longer be uncoupled
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