A Holocene Sedimentary Record and the Impact of Sea-Level Rise in the Karst Lake Velo Blato and the Wetlands on Pag Island (Croatia)

Abstract

Lakes in coastal lowland areas represent a critically vulnerable environment as a transitional space between freshwater and seawater environments. The paleoenvironmental reconstruction and anthropogenic impact are assessed through the lake sediment cores from Velo, Malo, and Kolanjsko Blato using multi-proxy analyses (sedimentological, mineralogical, geochemical, 137Cs and ostracod analyses, and AMS 14C radiocarbon dating). The freshwater lake Velo Blato was formed at 8100 cal yr BP due to rising groundwater levels as a consequence of sea-level rise. The brackish conditions in Lake Velo Blato started at 7100 cal yr BP, giving the index point for the sea-level curve of 7-m lower than present. Lead concentrations showed slightly increased values in the last 1800 cal yr BP, while the spike in Malo Blato lake sediments probably derived from bird hunting with lead bullets. Kolanjsko Blato sediment core archives the sediment record of the last 2050 years, which represents a shallow brackish coastal wetland under marine influence. Enrichment factors showed the accumulation of Cu, Hg, P, Pb, S, and Zn in the sediments from Kolanjsko Blato in the last 650 cal yr BP, which coincides with the high organic carbon content, and in sediments from Malo Blato after the lake’s formation (from the depth of 20 cm upwards). Anthropogenic Cu introduced into the Kolanjsko Blato sediments is the highest in the surface sample. Surficial sediments from Velo Blato are characterized by the high organic carbon, S, P, and N content, indicating high productivity and eutrophication which led to occasional anoxic conditions on the lake bottom in the last 200 years.