Role of Seasonal Melt Streams in Heavy Metal and Nutrient Transport from an Antarctic Penguin Colony

Abstract

Despite the perception that Antarctica is pristine, concentrations of heavy metals and persistent organic pollutants have been recorded at increasing levels. Heavy metals may be present within the Antarctic terrestrial environment through natural geologic processes, long-range atmospheric transport, anthropogenic point sources, and biological transport. While the biological transport of contaminants remains frequently overlooked, in the Arctic, it has been shown to rival atmospheric fluxes of contaminants. Adélie penguins are known vectors for transporting heavy metals and nutrients from within the marine environment and depositing them on the land through guano, feathers, eggshells, and whole carcasses. The incorporation of this material in deep ornithogenic soils has resulted in Adélie penguin colonies being identified as sites of heavy metal and nutrient accumulation. Despite seasonal glacial melt streams that erode these colony soils, their role in heavy metal and nutrient transport is largely under-researched. Therefore, this study evaluated the redistribution of heavy metals and nutrients via melt streams. Stream discharge and load, in addition to soil heavy metal and nutrient content, were also assessed. Five sites along two streams, one flowing through an Adélie penguin colony (P1 to P5) and a control stream with no penguin influence (C1 to C5), were compared throughout this research. Melt water within the Adélie penguin colony had elevated arsenic, cadmium, and lead (p<0.05), with total heavy metal concentrations exceeding New Zealand freshwater guidelines for ecological health up to 37, eight, and two times, respectively. Cadmium and lead were found mostly in particulate form (dissolved cadmium <22 % and dissolved lead <11 %), however, there was a relatively higher portion of arsenic (up to 72 %) that was dissolved (<45 m). This indicates increased bioavailability and concern for toxicity of arsenic. Nutrient anions (ammonium, nitrate, and phosphate) were also elevated in penguin-influenced water compared to the control stream (p<0.05), surpassing water quality guidelines up to 1038, 1017, and 551 times. When accounting for differences in discharge, stream loads of heavy metals and nutrients were significantly higher within the Adélie penguin colony (p<0.05), with nitrate and phosphate exhibiting the most prominent differences (p<0.01). In both streams, discharge exhibited large fluctuations on both diurnal and daily time scales (P3 16.7 L s-1 to 53.3 L s-1; C3 10.8 L s-1 to 14.7 L s-1) and was correlated strongly with air temperature (P3 R=0.88, C3 R=0.81). The pH of all stream sites was circumneutral to basic (6.86 to 8.07). This research suggests that seasonal melt streams play a critical role in redistributing potentially toxic levels of heavy metals and nutrients from penguin colonies into the Southern Ocean. Ornithogenic soil samples from the penguin colony had up to 27, 71, and six times higher arsenic, cadmium, and lead compared to two sampled control soils (p<0.05). Ammonium, total nitrogen, and total carbon were also significantly more enriched with up to 5727, 2454, and 484 times higher concentrations than the control soils (p<0.05). These enrichments were particularly significant with the upper 44 cm. Concentrations of arsenic in the topsoil (0 - 2 cm) and cadmium at soil depths 0 – 44 cm were present in concentrations that exceeded the Canadian ecological quality guidelines for soil. The pH of all soils was neutral to basic (7.78 to 9.86) reflecting the basic basalt parent material. These findings support previous research that ornithogenic soils are sites of heavy metal and nutrient accumulation. Given the fluctuating nature of melt streams, both daily and seasonally, results are likely to be variable over longer time scales and therefore, more research is suggested to quantify this. Moreover, climate change disproportionately affects polar regions with expected temperature rises. Thus, understanding how melt streams intensify in flow, duration, and transport capacity is an essential area of investigation, to which this research provides important baseline data.