Sand and gravel extraction from aquatic ecosystems is a known driver of freshwater habitat degradation, sediment disturbance, and turbidity. Lough Neagh, the UK and Ireland's largest freshwater lake, supports internationally important habitats, biodiversity, and fisheries, but has recently experienced severe cyanobacterial harmful algal blooms (HABs), intensifying scrutiny of additional stressors. This study provides the first integrated geomorphological and hydrodynamic assessment of commercial sand dredging impacts across this relatively shallow lake. A combination of high-resolution multibeam echosounder bathymetry, Earth observation imagery, GIS mapping, and modelling of propeller-wash scour was used to quantify both excavation impacts and fleet-scale operational disturbances. Multibeam bathymetry within part of the licensed extraction zone revealed extensive pockmarked deformation and depressions, lowering the local lakebed by 12-17 m, with an estimated 2 million tonnes of sand mined from within only 0.5 km2. Satellite imagery captured dredger hopper overflow and extraction-associated sediment plumes extending up to 1.2 km at the surface, while offloading and shoreline runoff at landing sites generated plumes extending up to ∼2 km offshore. Analysis of Sentinel-2 and Landsat imagery identified extensive propeller-wash tracks forming persistent turbidity corridors covering 49% of the lake. Hydrodynamic modelling suggested propeller-vortex near-bed shear stresses of 5.9-8.4 kPa (≡ kN m-2) in shallow waters, exceeding mud and fine-sand erosion thresholds by four to five orders of magnitude, implying potential local bed scour of up to ∼1.3 m depth, while mid-lake stresses remained sufficient for sediment resuspension. Collectively, these findings indicate that sand dredging is associated with sustained, lake-wide physical disturbance and sediment redistribution, with plausible implications for nutrient remobilisation, water quality, biodiversity, and HAB dynamics. These findings support the inclusion of extraction activity, vessel-induced disturbance, and shoreline sedimentation within future monitoring, management, and licensing frameworks for sand mining in lake ecosystems.
Reid et al. (Wed,) studied this question.