20 research outputs found

    Dilution and the Elusive Baseline

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    Knowledge 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 (<i>r</i><sup>2</sup> >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

    Eurycea_bislineata_AFLP_Data

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    AFLP data for Eurycea bislineata individuals at downstream and upstream sites in 6 streams in the Hubbard Brook Watershed, New Hampshire, USA

    Appendix A. A table showing descriptive statistics for amplified fragment length polymorphism variation at 18 sites in the Hubbard Brook watershed, New Hampshire, USA, where Gyrinophilus porphyriticus tissue samples were collected.

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    A table showing descriptive statistics for amplified fragment length polymorphism variation at 18 sites in the Hubbard Brook watershed, New Hampshire, USA, where Gyrinophilus porphyriticus tissue samples were collected

    Gyrinophilus_porphyriticus_AFLP_Data

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    AFLP data for Gyrinophilus porphyriticus individuals at downstream and upstream sites in 6 streams in the Hubbard Brook Watershed, New Hampshire, USA

    Increased River Alkalinization in the Eastern U.S.

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    The interaction between human activities and watershed geology is accelerating long-term changes in the carbon cycle of rivers. We evaluated changes in bicarbonate alkalinity, a product of chemical weathering, and tested for long-term trends at 97 sites in the eastern United States draining over 260 000 km<sup>2</sup>. We observed statistically significant increasing trends in alkalinity at 62 of the 97 sites, while remaining sites exhibited no significant decreasing trends. Over 50% of study sites also had statistically significant increasing trends in concentrations of calcium (another product of chemical weathering) where data were available. River alkalinization rates were significantly related to watershed carbonate lithology, acid deposition, and topography. These three variables explained ∼40% of variation in river alkalinization rates. The strongest predictor of river alkalinization rates was carbonate lithology. The most rapid rates of river alkalinization occurred at sites with highest inputs of acid deposition and highest elevation. The rise of alkalinity in many rivers throughout the Eastern U.S. suggests human-accelerated chemical weathering, in addition to previously documented impacts of mining and land use. Increased river alkalinization has major environmental implications including impacts on water hardness and salinization of drinking water, alterations of air–water exchange of CO<sub>2,</sub> coastal ocean acidification, and the influence of bicarbonate availability on primary production

    Estimated regression coefficients.

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    <p>Estimated regression coefficients (with standard errors) in the fitted relationship between abundance of three species of marsupial and abundance of hollow-bearing trees, plotted over time, together with the associated mean numbers per site of hollow-bearing trees, and of each species of arboreal marsupial.</p

    Comparison of models using log-transformed counts of the explanatory variables.

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    <p>Comparison of models using log-transformed counts of the explanatory variables (LP abundance of Leadbeater’s Possum, HBT abundance of hollow-bearing trees) fitted individually in negative binomial models for both target species in all four datasets (GG Greater Glider; MBP Mountain Brushtail Possum); the deviance is the change in –2 log(likelihood); the non-linear effect is the difference between a cubic smoothing spline with 2 d.f. and a linear model on the log scale; p-values are approximate because they are based on asymptotic properties.</p

    Comparison of negative binomial models for species richness.

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    <p>The comparison uses log-transformed counts of the explanatory variables (LP abundance of Leadbeater’s Possum, HBT abundance of hollow-bearing trees) fitted individually.</p

    Observed and expected abundance of Greater Glider and Mountain Brushtail Possum.

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    <p>Observed and expected abundance, from the model with transformed counts of hollow-bearing trees as the explanatory variable, for all four datasets. Only one observation was greater than 7 animals, and this is indicated as an abundance of 11 Mountain Brushtail Possums in Dataset 1.</p
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