Lithological controls on lake water biogeochemistry in Maritime Antarctica

Although the Antarctic lakes are of great importance for the climate and the carbon cycle, the lithological influences on the input of elements that are necessary for phytoplankton in lakes have so far been insufficiently investigated. To address this issue, we analyzed phytoplankton cell concentrations and chemical compositions of water samples from lakes, ponds and a stream on Fildes and Ardley Islands of King George Island in the South Shetland Archipelago. Furthermore, lake sediments, as well as soil and rock samples collected from the littoral zone were analyzed for their mineralogical/petrographic composition and pollutant contents of polycyclic aromatic hydrocarbons (PAHs). In addition, leaching experiments were carried out to with the lithologic samples to investigate the possible changes in pH, alkalinity, macronutrients (N, P, Si), micronutrients (e.g. Fe, Zn, Cu, Mn), anions (S, F, Br), and other cations (e.g. Na, K, Mg, Ca, Al, Ti, V, Cr, Co, Ni, As, Se, Pb, Sb, Mo, Ag, Cd, Sn, Ba, Tl, B). Our results showed that phytoplankton levels varied between 15 and 206 cells/mL. Chlorophyll-a concentrations showed high correlations with NH₄, NO₃. The low levels of PO₄ (<0.001 mg/L) indicated a possible P-limitation in the studied lakes. The composition of rock samples ranged from basalt to trachybasalt with variable major oxide (e.g. SiO₂, Na₂O and K₂O) contents and consist mainly quartz, albite, calcite, dolomite and zeolite minerals. The concentrations of total PAHs were below the toxic threshold levels (9.55-131.25 ng g^-1 dw). Leaching experiments with lithologic samples indicated major increase in pH (up to 9.77 ± 0.02) and nutrients, especially PO₄ (1.03 ± 0.04 mg/L), indicating a strong P-fertilization impact in increased melting scenarios. Whereas, toxic elements such as Pb, Cu, Cd, Al and As were also released from the lithology, which may reduce the phytoplankton growth.