The main cations in the lake water include Na+, K+, Ca2+, Li+ and Mg2+, while Cl−, SO, HCO are the main anions. The Na+ and Cl− concentration is roughly four times the concentration of natural seawater. Sodium ions are at slightly higher concentration in the south compared to the north of the lake, which could result from the shallower depth in the south, and a higher net evaporation rate. The lake is divided into north and south, separated by the Urmia Lake Bridge and its associated causeway, which was completed in 2008. The bridge provides only a gap in the embankment, allowing little exchange of water between the two sections. Due to drought and increased demands for agricultural water in the lake's basin, the salinity of the lake has risen to more than 300 g/L during recent years, and large areas of the lake bed have been desiccated. Ecology Palaeoecology A palynological investigation on long cores from Urmia Lake has revealed a nearly 200 kyr record of vegetation and lake level changes. The vegetation has changed from the Artemisia/grass steppes during the glacial/stadial periods, to oak-juniper steppe-forests during the interglacial/interstadial periods. The lake has had a complex hydrological history and its water levels have fluctuated greatly in geological history. Very high lake levels have been suggested for some time intervals during the two last glacial periods, as well as during both the Last Interglacial as well as the Holocene. The lowest lake levels have occurred during the last glacial periods. Modern ecology Based on the latest checklists of biodiversity at Lake Urmia in 2014 and 2016, it is home of 62 species of archaebacteria and bacteria, 42 species of microfungi, 20 species of phytoplankton, 311 species of plants, five species of mollusca, 226 species of birds, 27 species of amphibians and reptiles and 24 species of mammals (47 fossils have been recorded in the area). Lake Urmia is an internationally registered protected area as both a UNESCO Biosphere Reserve and a Ramsar site. The Iranian Dept. of Environment has designated most of the lake as a National Park. The lake is marked by more than a hundred small, rocky islands, which serve as stopover points during the migrations of a number of bird species, including flamingos, pelicans, spoonbills, ibises, storks, shelducks, avocets, stilts, and gulls. A recent drought has significantly decreased the annual amount of water the lake receives. This