Diatom assemblages from short-lived jökulhlaup-formed kettle lakes in a proglacial outwash plain, south-east Iceland

Abstract

ABSTRACTLittle is known about the ecological implications of high-magnitude, low frequency jökulhlaup events in proglacial systems. This study highlights how kettle lakes produced by jökulhlaups in proglacial areas create short-lived ecosystems and increase biodiversity. This research also demonstrates that as ice-margins retreat, creating new proglacial lakes and aquatic habitats, these sites may be increasingly important as sites of biogeochemical cycling and carbon fixing. Using diatoms from the base of former kettle hole lakes formed during the November 1996 jökulhlaup on Skeiðarársandur, south-east Iceland, we investigate the record of changing conditions of these lakes over their short (∼15 year) life span. Diatom assemblages were investigated in sediment sections up to 0.36m deep from the base of two kettle holes, and across a profile of surface sediments in one kettle hole. The diatom assemblages across all kettle holes are dominated by small benthic species (e.g. Achnanthes, Navicula, Nitzschia and Fragilaria spp.), with planktonic species (Cyclostephanos, Stephanodiscus spp.) present in only one kettle hole. The diatom assemblages are characterized by species with high nutrient and alkalinity optima. The variation in the diatom assemblages between different sedimentary units in the kettle holes’ basal stratigraphy reflect changes in the proportion of available habitat type (e.g. benthic, planktonic and littoral) resulting from changes in water levels, and changes in water chemistry relating to variations in sediment input (e.g. aeolian accumulation, slumping and re-working) and source of water (e.g. precipitation, ground water, snow melt). A conceptual model for typical kettle lake development in proglacial environments is also presented.