Determination of Trace elements and Major Ions in Environmental Matrices from Rano Raraku Lake (Easter Island)

Abstract

In the southern Pacific Ocean Easter Island is located famous for its megalithic statues named moai. Two lakes Rano Raraku (RR) and Rano Aroi (RA) are central water resources currently used by the local population for agricultural and breeding activities. The objective of this study is to determine the trace and rare earth elements as well as major ion contents in water and sediments of these lakes to obtain information about the water quality and to provide additional insights on transport mechanism inside the lake basin. The analysis was carried out by using Inductively Coupled Plasma –Mass Spectrometry, Isotope Ratio Mass Spectrometry and Ion Chromatography. The results showed that RR water contains high amounts of sodium and chlorine due to high evaporation rate in conjunction with a likely marine input. These values make the water undrinkable and unsuitable for agricultural purposes, although the level of metals in the water is not alarming. The rare earth element analysis suggested that strong winds activity, favored by the high deforestation rate occurred several centuries ago, is the main factor that influenced transport dynamics inside the basin. Potential warning for the water quality of RR is due to the unregulated management of the wild horses, as the dead body of the animals that oftentimes left near lakeshore. RR and RA are found to enrich in Ag, Fe, and Zn but they are deficient in many elements like Cs, Pb, V, Ni. This is explained as Island does not have industrial activities. Moreover, although the water of Rano Aroi is not polluted by metals and the presence of dead animals was not observed, the recent plantation of the eucalyptus forest in its neighborhood is a serious thread that may cause significant drop in the level of water in the next future.