John S. Eaton

‘Acid rain’, dissolved aluminum and chemical weathering at the Hubbard Brook Experimental Forest, New Hampshire

Abstract Contemporary ‘acid rain’ in the Hubbard Brook ecosystem has induced a series of geochemical responses. Neutralization is accomplished in essentially a 2-step process. Initially, hydrogen ion acidity is neutralized by the dissolution of reactive alumina primarilly found in the soil zone. In the Hubbard Brook area this reactive alumina has solution properties much like natural gibbsite. Aluminum-rich surface waters with a pH of 4.7 5.2 are typical of this neutralization stage. In a second step, both hydrogen ion acidity and aluminum acidity are neutralized by the chemical weathering of primary silicate minerals, i.e. by the alkali and alkaline earths contained in the bedrock and glacial till of the watershed. The chemical weathering reaction is much slower than the alumina dissolution reaction, so that the aluminum acidity stage (pH 4.7 5.2) may persist for substantial periods. Typically, however, in the Hubbard Brook area the aluminum acidity has been neutralized and a pH > 5.2 is obtained before surface waters reach a third-over stream channel. Because of the relatively low pHs throughout the soil zone and in the streamwater, carbonic acid reactions are essentially absent at the present time in the Hubbard Brook system. Water pathlength (or residence time) in the soil zone is the crucial factor in the state of acid rain neutralization, aluminum chemistry and chemical weathering. As measured by the losses of alkali and alkaline earths from the ecosystem, chemical weathering rate in the Hubhard Brook area at the present time is not especially high relative to other areas.

Carbon Flow in Four Lake Ecosystems: A Structural Approach

Direct and indirect carbon fluxes in lakes Marion (British Columbia), Findley (Washington), Wingra (Wisconsin), and Mirror (New Hampshire) are compared, using budgets and input-output analysis. Overall differences in carbon flow between the lakes are shown with cycling indices of .031, .108, .572, and .661, respectively. The results suggest that lake ecosystems may be considered unique aggregatins of similar components.

Chemistry of precipitation, streamwater, and lakewater from the Hubbard Brook Ecosystem Study: a record of sampling protocols and analytical procedures

The Hubbard Brook Ecosystem Study (HBES), begun in 1963, is a long-term effort to understand the structure, function and change in forest watersheds and associated aquatic ecosystems at the Hubbard Brook Experimental Forest in New Hampshire. Chemical analyses of streamwater and precipitation collections began in 1963, and analyses of lakewater collections began in 1967. This publication documents these collection methods, sites, and analytical techniques, providing a complete record to ensure the integrity of HBES data.

Hydrogen ion input to the hubbard brook experimental forest, New Hampshire, during the last decade

Being downwind of eastern and midwestern industrial centers, the Hubbard Brook Experimental Forest offers a prime location to monitor long-term trends in atmospheric chemistry. Continuous measurements of precipitation chemistry during the last 10 yr provide a measure of recent changes in precipitation inputs of H ion. The weighted average pH of precipitation during 1964–65 to 1973–74 was 4.14, with a minimum annual value of 4.03 in 1970–71 and a maximum annual value of 4.21 in 1973–74. The sum of all cations except H ion decreased from 51 μeq 1−1 in 1964–65 to 23 μeq 1−1 in 1973–74 providing a significant drop in neutralizing capacity during this period. Based upon regression analysis, the input in equivalents of H ion and nitrate increased by 1.4-fold and 2.3-fold respectively, from 1964–65 to 1973–74. Input of all other ions either decreased or showed no trend. Based upon a stoichiometric formation process in which a sea-salt, anionic component is subtracted from the total anions in precipitation, SO4=, contribution to acidity dropped from 83% to 66%, whereas NO3− increased from 15% to 30% during 1964–65 to 1973–74. The increased annual input of H ion at Hubbard Brook during the past 10 yr is highly correlated with the increased input of nitrate in precipitation.

Chemical Concentrations in Cloud Water from Four Sites in the Eastern United States

Event samples of cloud and fog water were collected in 1984 and 1985 as part of the Cloud Water Project, a large-scale network designed to chemically analyse cloud and rain water from ten sites in North America. The data presented here are from four sites in the eastern United States that ranged in elevation from 5 m to 1534 m, and in geographic location from Virginia to Maine.

Wet and Dry Deposition of Sulfur at Hubbard Brook

In recent years ecologists and others have become increasingly interested in chemical inputs to natural ecosystems, not only in wet deposition (rain and snow), but also in the form of particulate and gaseous deposition. This interest is illustrated by several recent conferences and symposia relative to the subject of “acid precipitation” and its effects (e.g. Dochinger and Seliga,1; AMBIO,2. Most of the available data pertain to wet deposition, however, the importance of dry deposition in some ecosystems is increasingly recognized (e.g. Whitehead and Ferth,3; White et al.,4; Elwood and Henderson,5; Likens et al.,6).

Variations in Precipitation and Streamwater Chemistry at the Hubbard Brook Experimental Forest during 1964 to 1977

In 1975 at the First International Symposium on Acid Precipitation and the Forest Ecosystem in Ohio, we summarized the changes relative to sulfur, nitrogen and hydrogen ion input in precipitation during 1964 to 1974 for the Hubbard Brook Experimental Forest in New Hampshire (Likens et al. 1), In some ways this paper is an update of those data.

Trace metal loss following whole-tree harvest of a northeastern deciduous forest, U.S.A.

We examined changes in the biogeochemistry of trace metals following a commercial whole-tree harvest (WTH) at the Hubbard Brook Experimental Forest in New Hampshire. Within 6 months after completion of the WTH, maximum streamwater concentrations of Ni, Cd, Ba, Sr, Mn, Zn and Fe increased two- to nine-fold. Streamwater concentration of Cu remained unchanged after harvest. Streamwater pH decreased from 5.2 to 4.5 after the harvest, and correlated strongly with trace metal concentrations except for Fe. The decrease in pH apparently resulted from increased nitrogen mineralization and nitrification following harvest. All streamwater metal concentrations (except Mn and Fe) in the disturbed watershed increased prior to the decrease in streamwater pH, suggesting that the loss of readily exchangeable metals, not increased mineral dissolution, was responsible for the initial increase in streamwater trace metal concentrations. In contrast, streamwater Mn concentrations did not increase until streamwater pH dropped to 4.5, due in part to increased mineral dissolution. Although pH related strongly to trace metal concentrations in the harvested watershed, it did not account for much of the variation in metal concentrations in the reference (W6) watershed. Annual flux of trace metals increased two- to eight-fold following WTH. Annual losses of Mn and Sr were 14% and 12%respectively of the forest floor pool for each element, and less than 10% of forest floor pools for all other elements. Except for Cd and Cu, annual trace metal losses in streamwater exceeded annual inputs in bulk precipitation.

The Northern Hardwood Ecosystem at Hubbard Brook in Relation to Other Forested Ecosystems in the World

Forests and woodlands cover some 57 × 106 km2, which is about 38% of the total continental area or 11% of the earth’s surface. Despite this relatively small area, 92% of the earth’s plant biomass and 46% of its annual net primary production come from forests (Table 21). The 79.9 billion metric tons of dry plant matter produced (net) each year by forests exceeds the total net primary production of the oceans, even though the oceans are more than six times larger in area. The animal biomass in these forests represents 68% of the total found on continental land masses (Whittaker and Likens, 1973).