Study of altitudinal lapse rates of δ18O in precipitation/river water with seasons on the southeast Tibetan Plateau

Seasonal δ18O variation in water on the southeast Tibetan Plateau has been studied, showing the consistent variation pattern of δ18O with altitude indicative of relevant atmospheric circulation processes. Study shows a similar variation pattern of fixed-site river water δ18O with that of the precipitation δ18O in southeast Tibet. δ18O in regional rivers in southeast Tibet demonstrates a gradual depletion with increasing altitude, though the rates vary seasonally. The most depleted river 18O occurs during the monsoon period, with the lowest δ18O/altitude lapse rate. The river 18O during the westerly period is also depleted, together with low δ18O/altitude lapse rate. The pre-monsoon rivers witness the most enriched 18O with least significant correlation coefficient with the linear regression, whilst the post-monsoon rivers witness the largest δ18O/altitude lapse rate. Different coherence of seasonal δ18O variation with the altitude effect is attributed to different moisture supplies. Though sampling numbers vary with seasons, the δ18O-H linear correlation coefficients all reach the 0.05 confidence level, thus witnessing the variation features of δ18O in seasonal river water due to the influence of atmospheric general circulation and land surface processes revealed from the altitudinal lapse rates.