Ostracod palaeolimnological analysis reveals drastic historical changes in salinity, eutrophication and biodiversity loss in a coastal Mediterranean lake

Abstract

The Albufera of Valencia, one of the largest oligohaline coastal lagoons of the Iberian Peninsula, has suffered hydrological and landscape modifications since medieval times. This paleolimnological study clears up the controversy about the factors, which drove the lake to its present state. Lithological descriptions, ostracod paleoassemblages and Cyprideis torosa (Jones, 1850) shell morphological variations and geochemistry (δ18O, δ13C and Sr/Ca) have been used to reconstruct the lake ecosystem evolution during the last two centuries. The sandy sediments at the bottom of L’Antina core (63 cm) presented a typical assemblage of brackish water ostracods, with shell-derived δ18O values, inferred salinity and Sr/Cawatercharacteristic of waters with marine influence. However, 10 cm above, coinciding with a drastic change in lithology, ostracod palaeoassemblages and decreased shell δ18O indicated a shift to freshwater influences. At the top of the sequence, inferred salinity suggests oligohaline waters and ostracods have almost disappeared. The early brackish conditions of Lake Albufera changed at the beginning of the 19th century when important hydrological modifications were undertaken for irrigation and started the major period of rice field expansion. Later, with the change of traditional rice farming to a more technological agriculture, together with increased domestic and industrial sewage inputs, the Albufera became a highly eutrophicated system 50 years ago. Eventually, the loss of macrophyte cover, cyanobacteria blooms and the increase of grazing by fish forced the loss of ostracod communities, currently almost inexistent.