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USGS2010

Flow path studies in forested watersheds of headwater tributaries of Brush Brook, Vermont

An investigation was undertaken into how headwater tributaries of Brush Brook, Vermont, could have average p H differences of almost two units (4.75 and 6.7). Sampling along four tributaries revealed that most of one tributary, below an area of seeps, had consistently higher p H, Ca 2+ , Mg 2+ , and K + , and lower Al than other sites. Bedrock mapping showed numerous fractures in vicinity of the seeps. A portion of this tributary's watershed and a portion of an acid tributary's watershed were intensively mapped for soil depth. Sampling showed the widespread existence of dense basal till in the watershed of the acid tributary but none in that of the near-neutral stream. Lateral flow, found above the dense till, was chemically similar to that of the acid tributary and to solutions sampled from soil B horizons. There were no differences in the average p H of nonseep soils sampled from either watershed. Flow paths are hypothesized to be through the B horizons in the acid tributaries and from below the soil profile in the near-neutral tributary. The acid catchment should be more sensitive to environmental change.

Vermont↗

USGS1996

Exchangeable hydrogen explains the pH of spodosol Oa horizons

The chemistry of extremely acid Oa horizons does not conform to traditional pH, Al, and base saturation relationships. Results from two separate studies of northeastern U.S. forested soils were used to investigate relationships between pH in water or dilute salt solutions and other soil characteristics. In Oa horizons with pH below 4, soil pH in dilute CaCl 2 solution was correlated with exchangeable H + measured either by titration ( r = −0.88, P = 0.0001, n = 142) or by electrode ( r = −0.89, P = 0.0001, n = 45). Exchangeable H + expressed as a percentage of the cation-exchange capacity (CEC) was linear with pH and showed similar slopes for data from both studies. For all samples, pHw = 4.21 − 1.80 × H + /CEC ( R 2 = 0.69, n = 194). The reciprocal of the H + /CEC ratio is base saturation with Al added to the bases. Because of the low pH, exchangeable Al does not appear to behave as an acid. Exchangeable H + remains an operationally defined quantity because of the difficulty in separating exchange and hydrolysis reactions. In a variety of neutral-salt extractants, concentrations of H + were correlated with 0.1 M BaCl 2 -exchangeable H + ( r > 0.91, P = 0.0001, n = 26) regardless of the strength of the extract. Nine successive extractions with 0.33 m M CaCl 2 removed more H + than was removed by single batch extractions with either 1 M KCl or 0.1 M BaCl 2 (average H + of 70, 43, and 49 mmol kg −1 , respectively for 26 samples). The data showed little difference in the chemical behavior of Oa horizons from a variety of geographical sites and vegetation types.

Maine, New Hampshire, New York, Vermont↗