Urban-rural gradients in the distribution of trace metals in sediments within temperate mangroves (New Zealand)

Abstract We investigated the sequestering capacity of mangrove sediments through better understanding of trace metal distributions within a temperate estuary. We selected two mangrove stands within Manukau Harbour, New Zealand, based on proximity to contaminant sources. Organic matter (OM), pH, and metal (Cd, Co, Cr, Cu, Fe, Mn, Pb, Zn) concentrations in sediments were analysed. Positive correlations between OM and most trace metals, and metals themselves suggest common contamination sources and sequestering capacity of organic sediments. Higher trace metals in urban versus rural mangrove sediments indicate that contamination source is a major factor controlling metal distribution in these temperate intertidal ecosystems. Specific seasonal trends in metal distributions were not observed due to complex weather patterns and possible fluctuations in anthropogenic inputs. Overall, we suggest that metal dynamics in mangrove sediments are controlled by interacting factors, and that mangroves modulate the ultimate distribution and magnitude of these inputs within temperate estuaries.