The relationship between landscape functional patch type and soil ecotoxicity along a pollution gradient

Abstract

Anthropogenic stressors such as mining and smelting disrupt soil processes and degrade landscape functionality, creating long-term barriers to ecological rehabilitation. The Landscape Function Analysis (LFA) model is widely used to monitor landscape recovery. It works by delineating a fixed portion of the landscape into regions of resource accumulation (patches) and areas of resource loss (interpatches). Each region is then visually and physically assessed for its soil-surface attributes, which relate to indices of landscape function (stability, infiltration, and nutrient cycling). However, the LFA model is field-based, so it cannot directly capture landscape function in terms of chemical and ecotoxicological degradation, and these are integral aspects of ecosystem function. This study aimed to determine whether complementing soil physicochemical and ecotoxicological indicators with LFA metrics could improve the assessment of ecosystem function in contaminated environments. This research was conducted along a heavy metal pollution gradient at an area next to a smelter complex, using the Trigger–Transfer–Reserve–Pulse (TTRP) model as a conceptual foundation. Three complementary approaches were applied: (1) measuring soil properties and deriving LFA indices in patches and interpatches; (2) assessing the toxicity of soil leachates to the euryhaline cladoceran Daphnia magna (D. magna) and the marine bacterium Aliivibrio fischeri (A. fischeri); and (3) evaluating soil and leachate phytotoxicity using vascular plant bioassays. The results indicated significant variation in soil chemistry along the gradient, with decreasing organic matter (p = 0.003) under higher contamination. The correlations between the LFA indices and soil parameters were weak, indicating that surface indicators were insufficient to reflect subsurface chemical impairment. For toxicity to D. magna and A. fischeri, the results revealed significant toxicity in leachates from highly contaminated sites, with increased immobilisation of D. magna (p = 0.021) and inhibition of A. fischeri luminescence (p < 0.001) corresponding to higher concentrations of Cu, Zn, and Pb. Some leachates from areas with moderate LFA scores still exhibited strong toxicity, indicating that the visual surface condition may underestimate chemical stressors. The vascular plant bioassays revealed strong inhibition of germination (p < 0.05) and root growth (p < 0.05) in soils and leachates from highly contaminated areas, with root elongation being the most sensitive endpoint. These vascular plant patterns were consistent with aquatic bioassay results and correlated with elevated metal concentrations and electrical conductivity (r = 0.67 and r = 0.92, respectively). Differences between patch and interpatch soils diminished with increasing contamination. Collectively, these findings showed that heavy metal contamination and salinity decouple surface structure from subsurface processes, disrupting the TTRP feedback that maintains landscape resilience. This study proposes an expanded LFA framework for smelter contaminated sites, incorporating chemical and ecotoxicological diagnostics alongside traditional surface metrics. The integrated approach captures both visible and latent dimensions of ecosystem function, offering a more mechanistic and sensitive tool for monitoring rehabilitation and ecological recovery in degraded areas.