Soil degradation mobilizes soil nutrients placing Canadian Prairie wetlands at risk

Depressional wetlands in the Canadian Prairies are experiencing degradation due to intensive agricultural practices in adjacent upland areas. Depressional wetlands within cropland are particularly affected, as increased sedimentation and runoff elevate nutrient levels within these ecosystems. This study assessed soil organic carbon (SOC) and soil particulate phosphorus (SPP) stocks, fluxes, and balances within the contributing catchment area to depressional wetlands. Catchment-scale sediment tracing using ¹³⁷Cs and budgeting methods was employed to examine the interactions between soil degradation, sediment movement, and nutrient redistribution. Analysis of 165 soil/sediment cores from eight wetland catchments revealed spatial heterogeneity in SOC and SPP stocks across upper-, middle-, and lower-slope and depression topographical sequences. SOC levels ranged from 6.9 to 104.1 kg m⁻², while SPP varied from 0.06 to 1.9 kg m⁻² within soil depth profile. Riparian areas at slope bottoms emerged as key accumulation sites for sediment, SOC, and SPP, underscoring their role as natural filters that intercept sediment and nutrients before they reach wetlands. These findings highlight the vulnerability of Canadian Prairie depressional wetlands to sediment and nutrient loading, emphasizing the need for soil erosion control strategies—such as the conservation of riparian buffers—to mitigate the adverse effects of agricultural activities on these vital ecosystems.