Cadmium distribution and inventories at a pre-European seabird breeding site on agricultural land, Banks Peninsula, New Zealand

Abstract

Cadmium distribution was determined at a hill country agricultural site with no history of fertiliser application, but where pre-European seabird breeding occurred. Total Cd concentrations were measured in 2 depth profiles on the ridgeline, and in surface soil (0–15 cm; 15 ridgeline and 7 sideslope transects). Concentrations were low (range 0.04–0.13 mg/kg) for New Zealand agricultural soils. Concentrations were independent of stock camps (locations frequented by grazing animals), altitude, soil depth, organic matter, and N and P concentrations. Surface Cd concentrations on the sideslope were significantly higher than the ridgeline. Inventories from the 2 ridgeline profiles (29.9 ± 2.4 mg/m²; 18.4 ± 1.5 mg/m²) were higher than the 16 mg/m² and 7 mg/m², respectively, predicted from the loess and basalt parent material concentrations; surface soil concentrations also exceeded those predicted from parent materials. Together, these results suggest that agricultural activity has not significantly redistributed Cd, and that external sources have contributed a large proportion of soil Cd. Atmospheric input was too low to explain all of the observed enrichment. Instead, Cd distribution was consistent with seabird input concentrated in the deeper soils of the sideslope rather than the relatively thin soils of the ridgeline.