Arsenic, cobalt and chromium food web biodilution in a Patagonia mountain lake

Mussels, Diplon chilensis, from Lake Moreno, a double-basined mountain lake in southern Argentina, is known to have elevated concentrations of chromium (Cr, > 25 μg g⁻¹ dry weight DW) and arsenic (As, 35 μg g⁻¹ DW), attributed to untreated sewage. To further understand the trophodynamics of Cr, As and cobalt (Co), we investigated concentrations and transfer throughout the food web in each basin of Lake Moreno. Each basin differs in morphology in that the gently-sloping Lake Moreno West has more littoral habitat than deeper Lake Moreno East with its higher proportion of pelagic habitat. Despite the morphological differences, both basins share similar water quality parameters and species assemblages. As a result, Lake Moreno provides an exceptional opportunity to compare trophodynamics of elements that enable us to hypothesize pelagic-littoral habitat coupling in response to lake morphology as the underlying factor influencing both Cr pathway and Co and As trophodynamic modeling. Using stable isotopes of nitrogen (δ¹⁵N) and carbon (δ¹³C) to characterize metals trophodynamics in each basin, biodilution of As, Cr and Co were indicated by negative regressions. This is confirmed by elevated As, Co and Cr concentrations in phytoplankton (11.3±5.7, 7.4±4.9, 44.5±40.7 μg g⁻¹ DW respectively), while zooplankton and biofilm had the next elevated concentrations. Those elevated concentrations are in contrast with lower concentrations in sport fish such as rainbow trout (0.5±0.5, 0.2±0.3, 1.8±1.2 μg g⁻¹ DW). Higher concentrations of Cr in fish were associated with higher proportion of benthic/littoral prey items in western basin, and were confirmed by significant correlation with δ¹³C values. Arsenic, Co and Cr concentrations in fish, while elevated, do not post health risks to human or wildlife consumers.