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Dilution and the Elusive Baseline
journal contribution
posted on 2016-02-21, 14:28 authored by Gene E. Likens, Donald C. BusoKnowledge of baseline conditions is critical for evaluating
quantitatively
the effect of human activities on environmental conditions, such as
the impact of acid deposition. Efforts to restore ecosystems to prior,
“pristine” condition require restoration targets, often
based on some presumed or unknown baseline condition. Here, we show
that rapid and relentless dilution of surface water chemistry is occurring
in the White Mountains of New Hampshire, following decades of acid
deposition. Extrapolating measured linear trends using a unique data
set of up to 47 years, suggest that both precipitation and streamwater
chemistry (r2 >0.84 since 1985) in
the
Hubbard Brook Experimental Forest (HBEF) will approximate demineralized
water within one to three decades. Because such dilute chemistry is
unrealistic for surface waters, theoretical baseline compositions
have been calculated for precipitation and streamwater: electrical
conductivity of 3 and 5 μS/cm, base cation concentrations of
7 and 39 μeq/liter, acid-neutralizing capacity values of <1
and 14 μeq/liter, respectively; and pH 5.5 for both. Significantly
large and rapid dilution of surface waters to values even more dilute
than proposed for Pre-Industrial Revolution (PIR) conditions has important
ecological, biogeochemical and water resource management implications,
such as for the success of early reproductive stages of aquatic organisms.