Cw. Martin et al., Changes in streamwater chemistry after 20 years from forested watersheds in New Hampshire, USA, CAN J FORES, 30(8), 2000, pp. 1206-1213
Citations number
29
Categorie Soggetti
Plant Sciences
Journal title
CANADIAN JOURNAL OF FOREST RESEARCH-REVUE CANADIENNE DE RECHERCHE FORESTIERE
Long-term patterns of streamwater chemistry provide valuable evidence of th
e effects of environmental change on ecosystem biogeochemistry. Observation
s from old-growth forests may be particularly valuable, because patterns sh
ould not be influenced by forest succession. Water samples were collected b
iweekly from four streams in, and near, the old-growth forest watershed of
the Bowl Research Natural Area in the White Mountains of New Hampshire from
May 1973 through October 1974, and from June 1994 through June 1997. Avera
ge NO3- concentrations, which ranged from 40.8 to 46.1 mu equiv..L-1 in 197
3-1974, declined significantly to averages of 14.9-20.1 mu equiv..L-1 durin
g 1994-1997. Concentrations of the base cations, Ca2+ and Mg2+, also declin
ed in stream water between the two sampling periods. The northeastern Unite
d States, including the study area, has been subjected to elevated atmosphe
ric deposition of sulfur and nitrogen for more than 40 years. This observat
ion has led to the concern that mature forest ecosystems may exhibit N satu
ration and depletion of Ca2+ from exchangeable soil pools. While the Bowl e
xhibits a pattern of elevated concentrations of NO3- throughout the year, s
uggestive of conditions of N saturation, concentrations have declined marke
dly over the last 20 years. Concentrations of Ca2+ have also declined sugge
sting possible depletion from the exchangeable soil pool, but the acid neut
ralizing capacity of stream water has remained constant or increased, indic
ating resistance to additional acidification.