LTREB Renewal at Hubbard Brook: Hydrologic-nutrient cycle interaction in small, undisturbed and human-manipulated ecosystems

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The records of precipitation and stream water amount and chemistry collected at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire are now the longest continuous biogeochemical records of this type in the world. As such, they represent a treasure trove of information relevant to current environmental problems, such as acid rain, nitrogen deposition, forest growth, and rising levels of atmospheric carbon dioxide. The first five years of this decadal project focused primarily on the effect of disturbance and environmental change, including the continued decline in acid rain and the changing climate within the Hubbard Brook Valley. A number of surprises have emerged, including the disappearance of an early climate change effect on stream water temperature, decreased ice cover duration on Mirror Lake, and the impacts of acid rain on soil chemical changes that are now affecting forest growth. A major surprise seen from a synthesis and extrapolation of long-term trends in precipitation and stream water chemistry was that a relentless dilution of surface waters is occurring throughout the Hubbard Brook Valley and that surface waters are likely to approximate demineralized (extremely dilute) water in the near future. This suggests that future baseline conditions may be more dilute than thought for the time before the industrial revolution, apparently because of the depletion of soil nutrients by acid rain and the impacts of federal air pollution regulations on precipitation chemistry. This has important implications for the structure, function and management of northern hardwood forests and their associated aquatic ecosystems in the near future. It is expected that important answers to many of the questions pursued during the past five years will be obtained or made clearer during the final five years of this long-term project.For researchers and decision makers grappling with solutions to major environmental issues, such carefully documented and synthesized, long-term data are essential for providing an accurate and quantitative perspective on chemical changes in our atmosphere and in our forest and aquatic ecosystems, as well as to advance the theoretical underpinnings of ecology. In addition, numerous students are engaged in this research and the data are made freely available for other uses.