THE ENVIRONMENTAL HISTORY OF A MOUNTAIN-LAKE (LAGO-PAIONE-SUPERIORE, CENTRAL ALPS, ITALY) FOR THE LAST C.100 YEARS - A MULTIDISCIPLINARY, PALEOLIMNOLOGICAL STUDY

A palaeoecological study of an oligotrophic alpine lake, Paione Superi ore (Italy), provided a record of historical changes in water quality. Historical trends in lake acidification were reconstructed by means o f calibration and regression equations from diatoms, chrysophycean sca les and pigment ratios. The historical pH was inferred by using two di fferent diatom calibration data sets, one specific to the alpine regio n. These pH trends, together with the record of sedimentary carbonaceo us particles and chironomid remains, indicate a recent acidification o f this low alkalinity lake. Concentration of total organic matter, org anic carbon, nitrogen, biogenic silica (BSiO2), chlorophyll derivative s (CD), fucoxanthin, diatom cell concentration and number of chironomi d head capsules increased during the last 2-3 decades. When expressed as accumulation rates, most of these parameters tended to decrease fro m the past century to c. 1950, then all except P increased to the pres ent day. A marked increase in sedimentary nitrogen may be related to a tmospheric pollution and to the general increases in output of N in Eu rope. High C/N ratios indicate a prevailing allochthonous source of or ganic matter. Finally, the increase in measured air temperature from t he mid-1800's appeared to be related to lake water pH before industria lization: cold periods generally led to lower pH and vice-versa. The m ore recent phenomenon of anthropogenic acidification has apparently de coupled this climatic-water chemistry relationship.