Environmental impact propagated by cross-system subsidy: Chronic stream pollution controls riparian spider populations

Abstract

Abstract. Resource subsidies between habitats are common and create the potential for the propagation of environmental impacts across system boundaries. However, recent understanding of the potential for subsidy-mediated cross-system impact propagations is limited and primarily based on passive flows of nutrients and detritus or short-term effects. Here, we assess the effects of sustained alterations in aquatic insect emergence (active subsidy pathway), due to chronic stream pollution, for riparian spiders. The sustained reduction in aquatic insect densities at the polluted reaches resulted in a marked decline in web spider population density and a shift in spider community composition. Our results provide the first evidence that stream pollution can control populations and community structure of terrestrial predators via sustained alterations in aquatic subsidies, emphasizing the role of subtle trophic linkages in the transmission of environmental impacts across ecosystem boundaries.

Importance of Riparian Zone: Effects of Resource Availability at Land-water Interface

“…human-provided foods to predators, artificial light, and novel ecosystems), which are becoming more common and may have large impacts on aquatic and riparian ecosystems [143,[189][190][191], and think more about their effects on subsidy quality, quantity, and fluctuation intensity/frequency [10,36]. Also, we should not ignore the dark side of cross-ecosystem subsidies [117,152], which may also influence riparian biodiversity and ecosystem functioning through interactions of resource subsidy fluxes, consumer communities and their ecological feedbacks [192]. Future research should also consider metacommunity framework [193] to understand crossecosystem dynamics of subsidy flux in materials and energy influenced by food-web species traits through top-down and bottom-up control in riparian and aquatic ecosystems.…”

“…While the importance of available water is established, the quality of the water should also be taken into consideration. Polluted river conditions can also have an impact on the riparian community, as it has been shown to decrease stream arthropod populations, thereby removing a subsidy for terrestrial consumers, who show clear preference for these aquatic insects [152].…”

“…Not all cross-system subsidies are beneficial to recipient ecosystems, as subsidies can also propagate pollutants [116,117,152] and pathogen [178] to consumers, and lower ecosystem stability [179]. Contaminants in aquatic ecosystems such as heavy metals and polychlorinated biphenyls (PCBs) can be accumulated in terrestrial predators through directly feed on emerging aquatic insects.…”

“…Consequently, total metal transported by insects was least at the streams with heaviest contamination, 96% reduction among sites. Therefore, spiders were affected the prey biomass reduction [152], but not by the metal exposure or metal flux to land by aquatic insect adults [116]. Interestingly, adult insect emergence may be more sensitive to reflect the impact of low metals concentrations on the communities of aquatic insect when compared to larvae, mainly because adult insect emergence is co-restricted by larval survival and other factors that limit successful emergence [182].…”

Aquatic prey subsidies to riparian spiders in a stream with different land use types

“…In the riparian zone, aquatic and terrestrial ecosystems are linked through fluxes of energy and nutrients, also termed subsidies (Rowe and Richardson, 2001;Baxter et al, 2005;Post et al, 2007;Richardson et al, 2010). Studying the linkages between these ecosystems is crucial to understand how environmental impacts on one ecosystem can propagate to the adjacent ecosystem (Knight et al, 2005;Paetzold et al, 2011). Aquaticterrestrial food chains or webs are crucial connections and may offer a pathway of propagation of environmental impact across these ecosystem boundaries (Polis et al, 1997).…”