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Long-term analysis of Hubbard Brook stable oxygen isotope ratios of streamwater and precipitation sulfate

Miles, Gretchen R., Mitchell, Myron J., Mayer, Bernhard, Likens, Gene, Welker, Jeffrey
Biogeochemistry 2012 v.111 no.1-3 pp. 443-454
ambient temperature, atmosphere, chemical precipitation, climate, climate change, drainage, emissions, forests, freshwater, isotopes, models, organic sulfur compounds, oxygen, pollution control, seasonal variation, streams, sulfates, sulfur, watersheds, winter, Northeastern United States, Ontario
In response to decreasing atmospheric emissions of sulfur (S) since the 1970s there has been a concomitant decrease in S deposition to watersheds in the Northeastern U.S. Previous study at the Hubbard Brook Experimental Forest, NH (USA) using chemical and isotopic analyzes ([Formula: see text]) combined with modeling has suggested that there is an internal source of S within these watersheds that results in a net loss of S via sulfate in drainage waters. The current study expands these previous investigations by the utilization of δ¹⁸O analyzes of precipitation sulfate and streamwater sulfate. Archived stream and bulk precipitation samples at the Hubbard Brook Experimental Forest from 1968–2004 were analyzed for stable oxygen isotope ratios of sulfate ([Formula: see text]). Overall decreasing temporal trends and seasonally low winter values of [Formula: see text] in bulk precipitation are most likely attributed to similar trends in precipitation [Formula: see text] values. Regional climate trends and changes in temperature control precipitation [Formula: see text] values that are reflected in the [Formula: see text] values of precipitation. The significant relationship between ambient temperature and the [Formula: see text] values of precipitation is shown from a nearby site in Ottawa, Ontario (Canada). Although streamwater [Formula: see text] values did not reveal temporal trends, a large difference between precipitation and streamwater [Formula: see text] values suggest the importance of internal cycling of S especially through the large organic S pool and the concomitant effect on the [Formula: see text] values in drainage waters.