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(29) Thurman, E. M.; Malcolm, R. L. Environ. Sci. Technol. 1981,15,463-466. (30) Ertel, J. R.; Hedges, J. I. In Aquatic and Terrestrial Humic
Thurman, E. M. Organic Geochemistry of Natural Waters; Martinus Nijhoff/Junk The Hague, The Netherlands, 1985; pp 304-312.
Materials; Christman, R. F.; Gjessing, E. T., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; pp 143-163. (31) Giddings, J. C.; Karaiskakis, G.; Caldwell, K. D.; Myers, M. N. J. Colloid Interface Sei. 1983, 92, 66-80. (32) Tanford, C. Physical Chemistry of Macromolecules;Wiley: New York, 1961; Chapter 6.
Thurman, E. M.; Wershaw, R. L.; Malcolm, K. L.; Pinckney, D. J. Org. Geochem. 1982,4, 27-35. Giddings, J. C. Sep. Sci. Technol. 1984,19, 831-847. Wahlund, K.-G.; Winegarner, H. S.; Caldwell, K. D.; Giddings, J. C. Anal. Chem. 1986,58, 573-578. Giddings, J. C.; Yang, F. J.; Myers, M. N. Anal. Chem. 1976, 48,1126-1132.
Yang, F. J.;Myers, M. N.; Giddings, J. C. Anal. Chem. 1977, 49,659-662.
Malcolm, R. L.; Thurman, E.M.; Aiken, G. R. Trace Subst. Environ. Health 1977, 11, 307-314.
Received for review July 8,1986. Accepted November 10,1986. Financial support was obtained from Department of Energy Contract DE-AC02-79EV10244.
Composition of Snowmelt and Runoff in Northern Michigan Steven H. Cadle" and Jean M. Dasch Environmental Science Department, General Motors Research Laboratories, Warren, Michigan 48090
Robert Vande Kopple University of Michigan Biological Station, Pellston, Michigan 49769
Snowmelt and runoff were studied during the 1982-1983 and the 1983-1984 winters at the University of Michigan Biological Station, which is located near the northern tip of Michigan's lower peninsula. The first 50% of the snowpack acidity was released in meltwater and rainwater equal to 25% of the original snowpack water content. Interaction between the meltwater and the litter layer produced large changes in the concentrations of most species. Runoff to two streams had high Sod2and very low NO3- concentrations. It is concluded that most of the NO3- is either biologically utilized or retained in the watershed, even during the early snowmelt period at this site.
Introduction The acidification of aquatic ecosystems by acid deposition occurs in two forms: long-term acidification and short-term, episodic acidification. Long-term acidification is believed to be due primarily to sulfuric acid deposition (1). Nitric acid is less important because it can be utilized in the environment by processes that produce alkalinity (2). Episodic events can be caused by runoff from the spring snowmelt. Nitric acid may be a significant contributor to those events for three reasons. First, nitric acid concentrations in wet deposition show little seasonal variation, while sulfuric acid concentrations are highest in the summer and lowest in the winter (3,4). Therefore, nitric acid can be the dominant acid in snow. Second, the ionic constituents of snow are released in the early meltwater (5). Thus, the nitric acid concentration in the water entering the ecosystem can be significantly higher than normal. Third, the biological processes that utilize nitrate may be inactive during the melt period. Therefore, the nitric acid may be present in the runoff (2). Overall, this process is of concern because it occurs at a sensitive time in the life cycle of aquatic species (1). Several studies have investigated the importance of nitric acid during the snowmelt period in eastern North America. Both Stottlemyer (6) and Hemond and Eshleman (7) found almost complete NO3- retention in Lake Superior basin watersheds and Bickford Reservoir, MA, watersheds, respectively. Jeffries and Snyder (8) and Jeffries and Semkin (9)found small sustained increases 0013-936X/87/0921-0295$01.50/0
in NO< in some streams in Ontario. In contrast, Likens et al. (IO),Galloway et al. (II), and Driscoll and Schafran (12) have reported large NO3- pulses at Hubbard Brook and various Adirondack Lakes. All of these studies reported that significant amounts of SO-: are exported to streams and lakes during the snowmelt period. Further investigations of episodic events are needed in order to characterize the regional differences in the importance of NO3-. In this study the relative importance of NO3- to the acidity of snowmelt and runoff at a site in northern Michigan has been determined. Comprehensive studies of wet deposition and dry deposition to the snowpack at as has an this site have been reported elsewhere (4,13), earlier study of snowmelt and runoff (14,15).
Experimental Section Site. The study was conducted during the 1982-1983 and 1983-1984 winters at the University of Michigan Biological Station, which is located near the tip of Michigan's lower peninsula. Snow-core samples were collected in a 0.2-ha open field surrounded by deciduous forest. Lysimeter samples were collected at a location under a deciduous canopy 30 m from the edge of the open field. The soil at this location is a spodosol (Rubicon Series). Streamwater samples were collected from Beavertail and Van Creeks. Beavertail Creek is a small cold-water creek with a 534-ha watershed. Stream length from the headwaters to the sampling site was 4.4 km. Total vertical rise in the watershed is 25 m. Most of the watershed is forested with a coniferous canopy adjacent to the stream and a deciduous canopy of sugar maple and aspen in the uplands. Van Creek is a cold-water creek that drains a 2643-ha watershed. Stream length from the headwaters to the sampling site was 13.3 km. Total vertical rise in the watershed is 58 m. Most of this watershed is also forested. There are tag alder and coniferous swamp areas along the stream course while the uplands are almost exclusively mixed aspen and sugar maple stands. In addition, seven pools were sampled. These included five beach pools around Douglas Lake and two woodland pools. The continuous canopy over the woodland pools is mostly red maple.
0 1987 American Chemical Society
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Sampling. Snow cores were collected with a 10.2 cm i.d. Plexiglas tube on a weekly basis. Cores were transferred to polyethylene beakers and allowed to melt at room temperature. The triplicate cores collected each weak were analyzed separately. Wet and dry deposition samples were collected on a weekly basis with either Aerochem Metrics or Wong samplers. Weekly measurements of dry deposition to snow were also made. These measurements have been discussed elsewhere (13). Lysimeters were fabricated from 38-cm sections of 7.6 cm i.d. PVC pipe. Twenty lysimeters were used: eight on the surface, six under the litter and organic layer at an average depth of 3.25 cm, and six under the E horizon at an average depth of 12.5 cm. Daily samples were collected and analyzed individually. Multiple samples from the same day and level were averaged on a volume-weighted basis. Streamwater samples were collected weekly before and after the snowmelt period and daily during the major portions of the melt. Stream velocity measurements were taken with a Teledyne Gurley 625 pygmy current meter. The first pool water samples were collected as soon as the ice melted back from the edge of the pools-i.e., close to the end of the snowmelt period. Analysis. All samples were filtered thru 0.4 pm pore size Nuclepore filters shortly after collection. SO:-, NO3-, and C1- were determined with a Dionex Model 2110i ion chromatograph. Ca2+and Mg2+were determined with a Perkin-Elmer 403 atomic absorption spectrometer after addition of La20,. Na+ and K+ were determined on the same spectrometer after addition of LiC1. NH4+was determined with a Lachet Quik Chem flow-injectionanalyzer.
Results and Discussion Snowpack. During the 1983-1984 winter there was 3.12 m of snowfall resulting in a maximum snow depth of 0.74 m. The snowpack was stable with most temperatures below freezing until an early February thaw. The major spring melt commenced in mid-March. The 1982-1983 winter was unusually mild with a total snowfall of 0.90 m and a maximum snow depth of 0.38 m. Some data from the 1981-1982 winter (15) are also presented in this paper for comparison purposes. Total snowfall and snow depth during this winter were 2.36 and 0.77 m, respectively. Thus, the results are from three very different winters: a heavy precipitation winter with a February thaw, an unusually mild winter, and an average precipitation winter. The average concentrations of H+, SO:-, and NO< in the snowpack immediately preceding the first melt period were 42,24, and 37 pequiv/L, respectively. NO3- was the dominant acid anion in the snowpack. Snowmelt. The snowmelt and meltwater were monitored by collecting weekly snow cores and daily lysimeter samples. The snow-core samples provided information on the loss of species from the snowpack. This information was combined with measurements of wet and dry deposition to calculate average meltwater concentrations. A direct determination of the meltwater or meltwater/rainwater concentrations was made from the surface lysimeter samples. (a) Snowpack Changes. Table I gives the percent loss of SO?-, NO,, and H+from the snowpack during the first week of melt for all three winters. The average percent loss of all measured ionic species for the first week of melting was 35 i 9%, 59 f 8%, and 52 i 9% for the 1983-1984,1982-1983, and 1981-1982 winters, respectively. The loss of ionic species during the first week of melting in 1983-1984 is significantly lower than that of the previous 296
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Table I. Percent Loss of Water and Ionic Species from the Snowpack during the First Week of Snowmelt species water
so:-
NO
