HR: 0800h
AN: H41E-0340    [Abstracts]
TI: Controls on inorganic monomeric aluminum release from soils after a clearcut in southeastern New York State, USA
AU: * McHale, M R
EM: mmchale@usgs.gov
AF: U.S. Geological Survey, 425 Jordan Road, Troy, NY 12180 United States
AU: Murdoch, P S
EM: pmurdoch@usgs.gov
AF: U.S. Geological Survey, 425 Jordan Road, Troy, NY 12180 United States
AU: Burns, D A
EM: daburns@usgs.gov
AF: U.S. Geological Survey, 425 Jordan Road, Troy, NY 12180 United States
AU: Lawrence, G B
EM: glawrenc@usgs.gov
AF: U.S. Geological Survey, 425 Jordan Road, Troy, NY 12180 United States
AB: A 24 ha catchment in the Catskill Mountains of southeastern New York was clearcut during the winter of 1996-97. Soil water from the O-, upper B-, and lower B horizons was examined for interactions between inorganic monomeric aluminum (Al$_{im}$) and nitrate (NO$_{3}$$^{-}$), dissolved organic carbon (DOC), pH, and base cations to discern how Al$_{im}$ was released from soils to stream water after the disturbance. Al$_{im}$ at concentrations greater than 2 $\mu$moles l$^{-1}$ can be toxic to some fish species and can inhibit the uptake of calcium by tree roots thereby decreasing tree tolerance to stress. Al$_{im}$ was strongly correlated with NO$_{3}$$^{-}$ in upper and lower B-horizon soil water (r$^{2}$ = 0.67 and 0.68 respectively), but the relation was much weaker in O-horizon soil water (r$^{2}$ = 0.40). O-horizon soil water had the lowest pH values despite having lower NO$_{3}$$^{-}$ concentrations than were measured in the B-horizon; high DOC concentrations in O-horizon soil water suggest that the acidity was partly due to organic acids. The O-horizon also had higher exchangeable base cations than the B-horizon that buffered the inorganic acidity produced by NO$_{3}$$^{-}$ after the clearcut. The high organic content of the O-horizon also allowed for organic complexation of Al as indicated by the strong correlation between DOC and organic monomeric Al (r$^{2}$ = 0.67). Al$_{im}$ concentrations were much higher and DOC concentrations were much lower in B-horizon soil water than in the O-horizon and in the B-horizon the high Al$_{im}$ concentrations persisted for a year longer after the clearcut. Al$_{im}$ concentrations in groundwater seeps were consistently low because mineral dissolution of base cations provided a high buffering capacity; as a result water with high NO$_{3}$$^{-}$ concentration was buffered by base cations rather than by Al$_{im}$. In contrast, B-horizon soil water, which had low buffering capacity and low DOC concentration, contributed large amounts of Al$_{im}$ to stream water, especially at NO$_{3}$$^{-}$ concentrations above 100 $\mu$moles l$^{-1}$, an apparent threshold above which Al$_{im}$ was needed to buffer acidity that exceeded the buffering capacity of base cations within the B-horizon. In conclusion, DOC concentration and base-cation availability were major controls on Al$_{im}$ release from soils after the clearcut, yet, Al$_{im}$ concentrations in stream water draining the catchment greatly exceeded the 2 $\mu$moles l$^{-1}$ toxicity threshold during the first 2 years after the clearcut. An increase in exchangeable Al and a decrease in exchangeable base cations in the soil after the clearcut caused a decrease in the soil Ca:Al ratio; this decrease has been shown to cause tree stress, inhibit regrowth, and result in long-term forest decline.
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
DE: 1615 Biogeochemical processes (4805)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting