Whale burial and organic matter impacts on biogeochemical cycling in beach aquifers and leachate fluxes to the nearshore zone

摘要

Coastal managers are increasingly faced with the challenge of disposing of stranded whale carcasses on beaches. Direct burial in the beach is often used as a cost effective method of disposal. However, whale burial management plans are often met with public resistance owing to the perceived risk of shark attraction to burial leachate that may discharge from the seabed. A reactive transport model was combined with a numerical variable-density groundwater flow model to assess buried whale leachate plume formation, transport, influence on beach aquifer reactivity, and discharge to coastal surface water for a range of burial setback distances, depths, and whale sizes. A second set of simulations was performed to evaluate aquifer nitrate removal efficiencies for a range of buried wrack scenarios and to evaluate the role of organic carbon source on beach reactivity. A sensitivity analysis was performed for both sets of models across ten physical and reaction parameters. Simulations using the best estimate parameter set showed that whale burials can produce DOC and ammonium leachate plumes in the beach aquifer that are transported to and discharge near the low tide line in water depths of 0.4-2.4 m. DOC and ammonium concentrations in discharging whale leachate werel.6 and 26 times higher than typical surf zone concentrations, respectively. Of the factors tested, the burial distance inland from the high tide line was the most important factor affecting leachate fluxes to surface water. Burials placed farther inland led to smaller DOC fluxes to surface water, but increased ammonium fluxes. Burial depth also affected whale leachate to the subtidal zone, with deeper burials resulting in smaller fluxes of DOC. Leached DOC from whale decomposition and from buried wrack can fuel denitrification hotspots within beach sediments. The sensitivity analysis showed that nitrate removal supported by buried wrack and whale leachate fluxes are highly dependent on beach properties, hydrologic forcing, and reaction parameters. The wrack model results have implications for beach scraping and the whale burial models show that whale leachate can be delivered to the shallow subtidal zone via groundwater discharge pathways, with potential implications for shark attraction and whale burial management practices.