engleski

Urbanization reduces trophic redundancy and alters resource flow through stream food webs

The exact nature of the effects of catchment urbanisation on the structure and function of stream food webs is currently unknown. To characterize these patterns, we compared the consumer-resource integrations and resource flow through stream food webs in relation to the resource availability and abiotic characteristics at agricultural, woodland and urban sites in the Zagreb region of Croatia. Urbanised sites had lower trophic redundancy with fewer interactions between trophic levels, indicating a more fragile system. Increased loading and altered composition of nutrients, lower water discharge and higher light availability at urban sites likely promoted the contribution of aquatic macrophytes to diets of primary consumers. Macroinvertebrate predators relied more on detritivores and less on shredder prey at urban compared to woodland and agricultural sites. There was no effect of land use on isotopic variation of basal resources, primary consumers or macroinvertebrate predators, but all these trophic groups in urban and agricultural sites were enriched in nitrogen stable isotope ratios relative to their counterparts in woodland stream food webs. The physical and chemical ecosystem characteristics associated with intensive land use altered the resource availability, trophic redundancy and the flow of energy to upper trophic levels, with potentially negative consequences for community dynamics and ecosystem functioning. These empirical findings indicate that reducing nutrient pollution, agricultural runoffs and maintaining riparian vegetation can mitigate the impacts of land use on structure and function of stream ecosystems.

urban streams, stable isotopes, macroinvertebrates, consumers

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