Water Chemistry Field Sampling
38
Range of Colorado (Baron et al. 1994, Williams et al. 1996); the Allegheny
Mountains of West Virginia (Gilliam et al. 1996); the Catskill Mountains of
New York (Murdoch and Stoddard 1992, Stoddard 1994); and the Great Smoky
Mountains in Tennessee (Cook et al. 1994).
The mobility of SO 4
2− is an important factor governing the extent to which
S deposition contributes to soil and water acidification, BC depletion, and
Al mobilization, each of which can harm sensitive ecosystems. Sulfur deposition moves through watershed soils and into surface waters as SO 4
2− . Sulfate is
the most important anion contributed by acidic deposition in most, but not all,
parts of the United States. In some regions (including the glaciated Northeast,
Upper Midwest, and West), much of the deposited S moves readily through
soils into streams and lakes. Thus, SO 4
2− has been classified as a mobile anion
(Seip 1980). However, SO 4
2− is less mobile in areas having older, more weathered
and nonglaciated soils, most notably the southeastern United States.
One of the most important effects of acidic deposition on watersheds
has been increased mobilization of Al from soils to surface waters (Cronan
and Schofield 1979). Aluminum, which occurs naturally in soils, has a pHdependent solubility in water. Solubility increases dramatically at pH values
below about 5.5. Aluminum concentrations in acidified drainage waters are
often an order of magnitude higher than in circumneutral waters. Effects of
Al mobilization to surface and soil waters include toxicity to aquatic biota
(Driscoll et al. 1980, Muniz and Levivestad 1980, Schofield and Trojnar 1980,
Baker and Schofield 1982); toxicity to terrestrial vegetation (Ulrich et al. 1980);
alterations in nutrient cycling (Dickson 1978, Eriksson 1981); and pH buffering effects (Driscoll and Bisogni 1984). Inorganic monomeric Al concentrations
often reach potentially toxic concentrations (> about 2 μM) in surface drainage
waters having pH less than about 5.5.
There can be substantial leeway in terms of selection of parameters to
measure in a field study of surface water acidification. Analytical costs must
be weighed against the value contributed by each constituent that one may
choose to analyze in the laboratory. In general, we recommend that the
parameters in Table 2.2 be considered the core for inclusion in the suite of
analytes to be measured in any study of surface water acid-base chemistry. When budgets allow, all of the parameters listed in Table 2.2 that are
designated as having high importance should be included in the list of analytes, plus DOC. If pH is below about 5.5, we also recommend analyzing for
total monomeric Al (Al m ) and Al o . The concentration of the potentially toxic
Al i is then obtained by subtracting Al o from Al m . Although DOC should be
measured in all acid-base chemistry studies, color could be substituted as
an inexpensive alternative if necessary. Measurement of dissolved inorganic carbon (DIC) should be considered optional; this measurement can
be used in estimating HCO 3
− concentration, which is important as part of
38
Range of Colorado (Baron et al. 1994, Williams et al. 1996); the Allegheny
Mountains of West Virginia (Gilliam et al. 1996); the Catskill Mountains of
New York (Murdoch and Stoddard 1992, Stoddard 1994); and the Great Smoky
Mountains in Tennessee (Cook et al. 1994).
The mobility of SO 4
2− is an important factor governing the extent to which
S deposition contributes to soil and water acidification, BC depletion, and
Al mobilization, each of which can harm sensitive ecosystems. Sulfur deposition moves through watershed soils and into surface waters as SO 4
2− . Sulfate is
the most important anion contributed by acidic deposition in most, but not all,
parts of the United States. In some regions (including the glaciated Northeast,
Upper Midwest, and West), much of the deposited S moves readily through
soils into streams and lakes. Thus, SO 4
2− has been classified as a mobile anion
(Seip 1980). However, SO 4
2− is less mobile in areas having older, more weathered
and nonglaciated soils, most notably the southeastern United States.
One of the most important effects of acidic deposition on watersheds
has been increased mobilization of Al from soils to surface waters (Cronan
and Schofield 1979). Aluminum, which occurs naturally in soils, has a pHdependent solubility in water. Solubility increases dramatically at pH values
below about 5.5. Aluminum concentrations in acidified drainage waters are
often an order of magnitude higher than in circumneutral waters. Effects of
Al mobilization to surface and soil waters include toxicity to aquatic biota
(Driscoll et al. 1980, Muniz and Levivestad 1980, Schofield and Trojnar 1980,
Baker and Schofield 1982); toxicity to terrestrial vegetation (Ulrich et al. 1980);
alterations in nutrient cycling (Dickson 1978, Eriksson 1981); and pH buffering effects (Driscoll and Bisogni 1984). Inorganic monomeric Al concentrations
often reach potentially toxic concentrations (> about 2 μM) in surface drainage
waters having pH less than about 5.5.
There can be substantial leeway in terms of selection of parameters to
measure in a field study of surface water acidification. Analytical costs must
be weighed against the value contributed by each constituent that one may
choose to analyze in the laboratory. In general, we recommend that the
parameters in Table 2.2 be considered the core for inclusion in the suite of
analytes to be measured in any study of surface water acid-base chemistry. When budgets allow, all of the parameters listed in Table 2.2 that are
designated as having high importance should be included in the list of analytes, plus DOC. If pH is below about 5.5, we also recommend analyzing for
total monomeric Al (Al m ) and Al o . The concentration of the potentially toxic
Al i is then obtained by subtracting Al o from Al m . Although DOC should be
measured in all acid-base chemistry studies, color could be substituted as
an inexpensive alternative if necessary. Measurement of dissolved inorganic carbon (DIC) should be considered optional; this measurement can
be used in estimating HCO 3
− concentration, which is important as part of