Trace elements in the sediments of Lake Forsyth/Wairewa

Abstract

In support of initiatives to restore Wairewa/Lake Forsyth and improve its water quality, this report investigates trace element concentrations in the lake sediments. Field sampling and chemical analyses for key contaminant trace elements were undertaken, and the data analysed with respect to correlations between elements and comparison to other lake sediments and sediment quality guidelines for the protection of aquatic life. Surface sediment samples were collected at 20 sites on the lake, and then dried and separated into two size fractions; <63μm and <2mm. These were analyzed for chromium (3.7-12.8mg/kg), manganese (90-795 mg/kg), nickel (2.3-10.4 mg/kg), copper (1.3-11.6 mg/kg), zinc (19-55 mg/kg), arsenic (0.2-3.2 mg/kg), cadmium (0.02-0.08 mg/kg) and lead (3.4-16.4 mg/kg) using ICP-MS, and for iron (1.0-3.2 wt%) using AAS. Organic matter (2.6-13.6 wt%) was determined from LOI in a muffle furnace. All of the trace element concentrations were close to natural background levels, and seemingly unaffected by anthropogenic inputs. Concentrations were below those anticipated to adversely affect aquatic life (i.e., below ANZECC interim sediment quality guidelines) and low relative to the sediments of Te Waihora and Lake Taupo.