SPATIAL AND TEMPORAL VARIATIONS IN DISSOLVED ORGANIC MATTER COMPOSITIONS OF STREAM WATER INFLUENCED BY PERMAFROST MELTING IN A SMALL ALPINE WATERSHED OF QINGHAI-TIBETAN

Climate warming induced permafrost melting in low altitude alpine environment is expected to influence the concentration and characteristics of dissolved organic matter (DOM) in stream water. To what extent such changes can be used to provide warnings for permafrost melting that can benefit from better understanding of spatial and temporal patterns of DOM characteristics. Stream (n=35) and thermokarst pool (n=26) waters collected in July 2012, April, July and Sept of 2013 from a small (area 25 km2), low latitude (99⁰50' – 99⁰54' E，38⁰12' – 38⁰17' N) alpine (elevation 2960 – 4820m) watershed, Hulugou, in the NE Qinghai-Tibetan Plateau were analyzed for 18O and D, concentrations of cations, anions and DOM, and DOM optical properties including specific UV absorbance (SUVA254) and fluorescence index (FI), and 13 DOM components obtained by PARAFAC modeling of fluorescence spectra. In three tributaries and the main stream, concentrations of DOM reached maximum in July of 2012 and 2013, with optical characteristics of DOM suggesting input of DOM with a source similar to thermokarst pool waters and also waters equilibrated with soil (15 ml add to 5 g wet soil) from 0 – 100 cm depth. Concentrations of DOM in one tributary, Red Gully (elevation 3059 – 3248 m) are much higher than in the other two (elevations 3155 – 3622 m and 3184 – 3413 m). Not only were the DOM concentrations of Red Gully water the highest at 4 sampling times (7.2 – 13.3 mg/l), the DOM also displayed the highest SUVA254 (2.3 – 3.2 L mgC-1 m-1), the lowest FI (1.34 – 1.43) and the highest protein components (36%-68%) that would not have been possible without influences of permafrost melting because these characteristics are similar to thermokarst pool waters and that the DOM characteristics of the two other branches are different. The influence of the Red Gully on the main stream DOM through mixing is evident from the stable isotope data and the correlation between SUVA254 and FI. Therefore, changes in concentration and composition of DOM are easily detected in stream water at the lowest altitude of the Hulugou watershed where degradation of permafrost is presumably the most. Seasonality of DOM in stream water is useful to delineate the spatial heterogeneity and the degree of permafrost melting in low attitude alpine environment sensitive to warming.