TY - JOUR
T1 - Metal fate and partitioning in soils under bark beetle-killed trees
AU - Bearup, Lindsay A.
AU - Mikkelson, Kristin M.
AU - Wiley, Joseph F.
AU - Navarre-Sitchler, Alexis K.
AU - Maxwell, Reed M.
AU - Sharp, Jonathan O.
AU - McCray, John E.
N1 - Funding Information:
This research was supported by the U.S. National Science Foundation ( WSC-1204787 ), the USGS-National Institute of Water Resources (No. 2011CO245G Subaward G-2914-1 ) through the Colorado Water Resources Research Institute , the Office of Science (BER) U.S. Department of Energy ( DE-SC0006997 ), and the U.S. Environmental Protection Agency (EPA) STAR Fellowship no. FP91735401 .
Publisher Copyright:
© 2014 Elsevier B.V.
PY - 2014/10/5
Y1 - 2014/10/5
N2 - Recent mountain pine beetle infestation in the Rocky Mountains of North America has killed an unprecedented acreage of pine forest, creating an opportunity to observe an active re-equilibration in response to widespread land cover perturbation. This work investigates metal mobility in beetle-impacted forests using parallel rainwater and acid leaches to estimate solid-liquid partitioning coefficients and a complete sequential extraction procedure to determine how metals are fractionated in soils under trees experiencing different phases of mortality. Geochemical model simulations analyzed in consideration with experimental data provide additional insight into the mechanisms controlling metal complexation. Metal and base-cation mobility consistently increased in soils under beetle-attacked trees relative to soil under healthy trees. Mobility increases were more pronounced on south facing slopes and more strongly correlated to pH under attacked trees than under healthy trees. Similarly, soil moisture was significantly higher under dead trees, related to the loss of transpiration and interception. Zinc and cadmium content increased in soils under dead trees relative to living trees. Cadmium increases occurred predominantly in the exchangeable fraction, indicating increased mobilization potential. Relative increases of zinc were greatest in the organic fraction, the only fraction where increases in copper were observed. Model results reveal that increased organic complexation, not changes in pH or base cation concentrations, can explain the observed differences in metal partitioning for zinc, nickel, cadmium, and copper. Predicted concentrations would be unlikely to impair human health or plant growth at these sites; however, higher exchangeable metals under beetle-killed trees relative to healthy trees suggest a possible decline in riverine ecosystem health and water quality in areas already approaching criteria limits and drinking water standards. Impairment of water quality in important headwater streams from the increased potential for metal mobilization and storage will continue to change as beetle-killed trees decompose and forests begin to recover.
AB - Recent mountain pine beetle infestation in the Rocky Mountains of North America has killed an unprecedented acreage of pine forest, creating an opportunity to observe an active re-equilibration in response to widespread land cover perturbation. This work investigates metal mobility in beetle-impacted forests using parallel rainwater and acid leaches to estimate solid-liquid partitioning coefficients and a complete sequential extraction procedure to determine how metals are fractionated in soils under trees experiencing different phases of mortality. Geochemical model simulations analyzed in consideration with experimental data provide additional insight into the mechanisms controlling metal complexation. Metal and base-cation mobility consistently increased in soils under beetle-attacked trees relative to soil under healthy trees. Mobility increases were more pronounced on south facing slopes and more strongly correlated to pH under attacked trees than under healthy trees. Similarly, soil moisture was significantly higher under dead trees, related to the loss of transpiration and interception. Zinc and cadmium content increased in soils under dead trees relative to living trees. Cadmium increases occurred predominantly in the exchangeable fraction, indicating increased mobilization potential. Relative increases of zinc were greatest in the organic fraction, the only fraction where increases in copper were observed. Model results reveal that increased organic complexation, not changes in pH or base cation concentrations, can explain the observed differences in metal partitioning for zinc, nickel, cadmium, and copper. Predicted concentrations would be unlikely to impair human health or plant growth at these sites; however, higher exchangeable metals under beetle-killed trees relative to healthy trees suggest a possible decline in riverine ecosystem health and water quality in areas already approaching criteria limits and drinking water standards. Impairment of water quality in important headwater streams from the increased potential for metal mobilization and storage will continue to change as beetle-killed trees decompose and forests begin to recover.
KW - Bark beetle infestation
KW - Forested ecosystem regulation
KW - Metal mobility
KW - Soil chemistry
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U2 - 10.1016/j.scitotenv.2014.07.052
DO - 10.1016/j.scitotenv.2014.07.052
M3 - Article
C2 - 25089693
AN - SCOPUS:84905439714
SN - 0048-9697
VL - 496
SP - 348
EP - 357
JO - Science of the Total Environment
JF - Science of the Total Environment
ER -