Environmental changes induced by human activities in the Northern Curonian Lagoon (Eastern Baltic): diatoms and stable isotope data

A sediment core collected from the northwestern part of the Curonian Lagoon, which was deposited approximately during 1800-2002, was analysed for several proxy records. Changes in diatom assemblages and carbon, nitrogen and oxygen stable isotopes (delta C-13, delta N-15 and delta O-18) revealed two periods, which are characterized by differences in the sedimentation rate, sediment type and trophic state of the northern part of the Curonian Lagoon. Low delta N-15 values in organics and prevailing fresh brackish benthic diatoms indicate low enrichment in the shallow, freshwater lagoon during the period 1800-1955. The eutrophic conditions in this shallow lagoon are reflected by a high abundance of planktonic diatoms common in nutrient-rich basins and increased delta N-15 values in organics of the sediments since 1955. Starting approximately in the 1960s, decreased freshwater run-off and increased brackish-water inflow into the lagoon were observed. These changes were likely caused by the construction of the hydropower station (and a reservoir) near the Nemunas River and the artificial deepening of the Klaipeda Strait during 1960-1962 and later, also by the rising sea level in the SE Baltic. The changed river run-off and the artificially deepened strait significantly influenced the fresh-brackish water circulation and environmental conditions in the northern part of the Curonian Lagoon in the last decades.