Patterns in the Biogeochemistry at the Hubbard Brook Experimental Forest, New Hampshire, USA

Abstract

The small watershed approach, in which bulk precipitation inputs and stream outputs are measured, has been used to assess patterns of element cycling at the Hubbard Brook Experimental Forest (HBEF), NH, USA since 1963. In recent years the monitoring program has been expanded to include dry deposition, throughfall, litterfall, vegetation, soil and soil solutions. Detailed element budgets have been compiled. Atmospheric deposition at the HBEF is markedly acidic (pH = 4.2 for the period 1964–1990). Detailed element budgets reveal that atmospheric inputs of SO4 2- are largely transported conservatively through the watershed to surface water. These inputs have a marked effect on drainage water quality. Soil at the HBEF is characterized by low percent base saturation and limited release of basic cations. Thus, high SO4 2- inputs result in acidic soil solutions and streamwater with elevated concentrations of inorganic monomeric Al. Concentrations and fluxes of SO4 2- in precipitation and streamwater at Hubbard Brook have decreased simultaneously with declines in atmospheric emissions of SO2 in the eastern U.S. While precipitation pH has increased slightly in recent years, stream pH has remained below 5.0 and has not shown recovery from declining inputs of acidic deposition.