Colorado mountains

Altitudinal gradient of dissolved organic carbon in headwater streams of the Wuyi Mountains in China

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honghua ruan
Wei Huang
Xiaoming Zou
William H. McDowell

Dissolved organic carbon (DOC) in stream water is positively correlated with soil organic carbon (SOC) at regional scales in which climate and vegetation are relatively invariant. Does this correlation hold when variations of temperature, precipitation and vegetation are large across altitudinal gradient? We examined patterns of headwater stream DOC concentrations in relation to SOC contents, temperature, soil C:N ratio, and stream dissolved nitrogen concentrations along an altitudinal gradient in the Wuyi Mountains, China where variation in temperature, precipitation, and vegetation are remarkable across the altitudinal gradient. We found that headwater stream DOC concentrations decreased and SOC contents increased with increasing altitude. Stream water DOC concentrations correlated positively with temperature along the altitudinal gradient. In addition, stream DOC concentrations peaked in February at the end of the dry season and were lowest in August at the end of the rainy season. Seasonal variation of stream DOC concentrations correlated positively with stream water nitrate concentrations in the antecedent two months. Our findings suggest that concentrations of DOC in headwater streams are not solely controlled by SOC contents. Factors influencing the decomposition of SOC, such as temperature, as well as the dilution of stream DOC source by precipitation, can also play an important role in determining DOC concentrations in headwater streams along an altitudinal gradient that across vegetation types. Furthermore, annual mean values in headwater stream DOC can be largely predicted by temperature alone across the altitudinal gradient, and seasonal variation in stream DOC levels can be predicted by stream nitrate concentrations two months in advance.

Key words: altitudinal gradient; dissolved organic carbon (DOC); nitrate; precipitation; soil organic carbon (SOC); stream; temperature.

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Background Photo by: Nicole Hansen - Jornada (JRN) LTER