Understanding the Past, Current and Future Transport and Fate of Semi-Volatile Organic Compounds in A Remote Alpine Glacier-Fed Lake in New Zealand

Abstract

Persistent semi-volatile organic compounds (SVOCs) undergo atmospheric transport and accumulate in cold ecosystems, and their fates are intimately linked to those of the snowpack and glaciers into which they become trapped. As glacial melting occurs, SVOCs that have been stored in glaciers for many decades may undergo release to the environment. While glacial melting in cold ecosystems is projected to accelerate due to increases in mean atmospheric temperatures, enhanced release of SVOCs from glaciers to the surrounding environment is also expected. In this study, the historic, current and future distribution, transport and fate of current-use and historic-use pesticides, a group of SVOCs, were studied in a remote mountainous glacier-fed lake environment in New Zealand, a Southern Hemisphere country.

The behaviour of semi-volatile pesticides over the course of one year was investigated. Pesticides were quantified in air, lake water, glacial melt water, and stream water in the catchment of Lake Brewster, an alpine glacier-fed lake located in the Southern Alps of New Zealand. Two historic-use pesticides (endosulfan I and hexachlorobenzene (HCB)) and three current-use pesticides (dacthal, triallate, and chlorpyrifos) were frequently found in both air and water samples from the catchment. Regression analysis indicated that the pesticide concentrations in glacial melt water and lake water were strongly correlated.

A multimedia environmental fate model containing four compartments (air, lake water, sediment and ice cover) was developed for these five chemicals in Lake Brewster for understanding chemical behaviour and predicting their fate under future climate changes. The measured concentrations in air, the glacial melt water and stream water were used as inputs to the model. Modelled pesticide concentrations in lake water agreed well with the measured concentrations. Modelling results indicated that seasonal lake ice cover melt, and varying contributions of input from glacier melt and stream water, created pulses in pesticide concentrations in lake water. Under future climate scenarios, glacier melt water made increasing contributions to the input of pesticides to the lake and significant shifts in timing and other alterations in pesticide concentration pulses were observed.

Sediment cores were collected at two lakes located in the Southern Alps of New Zealand: the glacier-fed Lake Brewster and the non-glacier-fed Lake Christabel. The concentrations of current- and historic-use pesticides were quantified in two cores to understand their historic deposition pattern and to probe the contribution of glacial melt water to the sediment profile. Nine pesticides were detected in the Brewster core. Both the total pesticide import values and the Brewster Glacier elevations showed significant correlations with some of the pesticide fluxes in sediments, suggesting the contributions of long-range atmospheric transport and deposition as well as glacial melt water input to these pesticides in the lake cores. Significant correlations were also found between endosulfan I, endosulfan II and endosulfan sulphate concentrations, as well as between alpha-hexachlorocyclohexane (α-HCH) to beta-hexachlorocyclohexane (β-HCH) in the Brewster core. Four pesticides were detected in the Christabel core. The fluxes of the pesticides in the Christabel core peaked in the 1970s and decreased after the mid-1970s, which happened to be in accordance with their usage and ban time in New Zealand. This study is the first time that current- and historic-use pesticides in mountain lake sediment cores were investigated in New Zealand, furthermore, in the Southern Hemisphere.