ARE STABLE ISOTOPES OF LACUSTRINE CARBONATE A GOOD TRACER OF LAKE HYDROLOGY AND LAKE LEVEL VARIABILITY? THE LAKE LEDRO CASE (NORTHERN ITALY).

Oxygen and carbon isotopes were analysed on bulk samples and carbonate concretions from Lake Ledro, northernItaly, with the aim to assess their suitability as reliable proxy of the hydrological changes in the lake. For this purpose, isotopiccomposition of bulk marls and concretions were compared to lake level reconstruction obtained with sedimentological approach.The delta13Cbulk record mostly mirrors the delta 18Obulk record, while carbon and oxygen isotopes from concretions are not correlated. Wefound that there is a statistically significant correlation between the oxygen and carbon isotopic record of the bulk carbonate andlake level changes, with the positive changes in lake level corresponding to lower values on delta 18Obulk and delta 13Cbulk and vice versa.Assuming that most of the bulk carbonate is formed by bio-induced calcite precipitation, this means that this kind of carbonatereflects the local hydrological condition of the lake water better than lacustrine concretions, which instead are more affected bylocal conditions of precipitation like biological plant activity.