Earth’s soils are crucial study systems in light of the two major environmental challenges of the 21st century: anthropogenic climate change and ecosystem alteration. We depend on soils for anchoring plants, for water filtration/storage, and for nutrient cycling (including decomposition). Soil organisms control these processes, yet surprisingly little is known about their activities and community dynamics, let alone how these organisms are affected by anthropogenic stressors, such as the addition of contaminants like plastics, to the system.
This study examined the effect of plastic surface litter on underlying invertebrates in urban soils, using abundance, diversity, and community structure as response variables. We collected 50 paired soil samples (one from underneath plastic surface litter and the other from underneath natural surface coverings) across five public parks in the Bronx, New York City. Invertebrates from all 100 samples were extracted, counted, and identified, and background soil characteristics (including microbial biomass, soil carbon, pH, water holding capacity, gravimetric moisture, and bulk density) were measured. Response variables were compared between treatment and control samples using t-tests and ANOVA, and generalized linear models were constructed to predict invertebrate abundance and diversity using all measured variables.
Results/Conclusions
Our results suggest that plastic surface trash does not affect abiotic soil properties or microbial biomass in ways that significantly influence invertebrate presence or diversity; instead, drivers of invertebrate diversity included temperature, soil density, and water holding capacity, while significant predictors of invertebrate abundance included all abiotic and microbial variables – except the presence of surface plastic. Communities differed significantly across study sites, mirroring the trends in invertebrate community structure observed across large-scale ecosystem types. Overall, data suggests that urban soil fauna are adapted to their environment and that climate variables and vegetation regime, not anthropogenic habitat alteration, drive community diversity and abundance.
In the context of global change, it is important to consider ecosystem resiliency together with the possibility of ecosystem collapse. Although our results suggest that invertebrate communities are resilient to soil plastics – in this system and at these loadings – further research is warranted to explore potential toxicity thresholds for soil organisms, and the applicability of our results to other soil ecosystems. Current and future research by the PI explores the community dynamics resulting from urban soil contamination and addresses practical questions about resilience and tipping points that can be applied to management and policy.