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APPLICATION OF TREE‐RING ISOTOPIC ANALYSES TO RECONSTRUCT HISTORICAL WATER USE OF RIPARIAN TREES
Author(s) -
Alstad Karrin P.,
Hart Stephen C.,
Horton Jonathan L.,
Kolb Thomas E.
Publication year - 2008
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/06-1969.1
Subject(s) - riparian zone , environmental science , xylem , dendrochronology , hydrology (agriculture) , streamflow , ecology , riparian forest , biology , geology , geography , habitat , botany , drainage basin , paleontology , geotechnical engineering , cartography
Historical patterns of water source use by trees inferred from long‐term records of tree‐ring stable isotopic content could assist in evaluating the impact of human alterations to natural stream flow regimes (e.g., water impoundments, stream flow diversions, and groundwater extraction). Our objective was to assess the utility of the hydrogen stable isotopic composition (δD) of tree rings as an index of historical water source use by riparian trees. We investigated the influence of site conditions that varied in climate and hydrology on the relationship between δD of Populus xylem water (δD xyl ) and tree‐ring cellulose (δD cell ). δD xyl and δD cell were strongly correlated across sites ( r 2 = 0.89). However, the slope of this relationship was less than 1, indicating that factors other than δD xyl influenced δD cell . Inverse modeling with an isotopic fractionation model for tree‐ring cellulose suggested that the lack of one‐to‐one correspondence between δD xyl and δD cell was due to the influence of the hydrogen isotopic content of the atmospheric water vapor (δD atm ). Empirically measured values of δD cell were typically within the seasonal range of δD cell predicted from the fractionation model. Sensitivity analyses showed that changes in δD xyl generally had a greater influence at high‐elevation montane sites, whereas δD xyl and δD atm had about equal influence on δD cell at low‐elevation desert sites. The intrasite relationship between δD cell and δD xyl among individual trees was poor, perhaps because of the within‐site spatial variation in hydrologic conditions and associated tree physiological responses. Our study suggests that historical variation in δD cell of Populus provides information on historical variation in both time‐integrated water source use and atmospheric conditions; and that the influence of atmospheric conditions is not consistent over sites with large differences in temperature and humidity. Reconstruction of xylem water sources of Populus in riparian ecosystems from δD cell will be more direct at higher elevation mountain sites than at low‐elevation desert sites.