Project at a Glance
Title: Monitoring of wet deposition in alpine areas in the Sierra Nevada
Principal Investigator / Author(s): Melack, John M
Contractor: Marine Science Institute, UC Santa Barbara
Contract Number: A932-081
Topic Areas: Acid Deposition, Monitoring
The quantity and chemical composition of precipitation in the Sierra Nevada was monitored at high elevation stations during the period of 1990 through 1995. From 1990 through 1993, eleven sites were included in the network. For 1994 the number was seven and during the spring of 1995, the snowpack was sampled at six Stations. During the course of the study a total of 1,546 snow samples were collected from 225 snowpits and an additional 514 non-winter precipitation events were sampled. All major solutes in wet deposition were measured and a rigorous quality assurance-quality control protocol was followed.
The amount of winter precipitation during the study was variable (range ca. 250 to 3,000 mm). Winter precipitation accounted for the majority of the input of water to high elevations of the Sierra Nevada. Non-winter precipitation events ranged in size from trace amounts to over 100 mm. The annual amount of non-winter precipitation in the Sierra Nevada varied widely (range ca. 10 to 200 mm).
Snow chemistry was similar among the six years of study and among the sampling stations. Samples from the spring snowpack had pH levels typically between 5.3 and 5.6 (hydrogen concentration, 2 to 4 µEq L -1). After hydrogen ion the most abundant solutes were anunonium and nitrate with concentrations usually 1.5 to 4.5 µEq L -1. Sulfate concentrations ranged from ca. 1.0 to 3.0 µEq L -1. Organic anions (acetate and formate) were usually found in low concentrations (i.e. < 0.5 µEq L -1). The specific conductance of snow in the Sierra Nevada was usually between 2 and 4 I.1S cm-l.
The mean pH of summer rain in the Sierra Nevada measured during the study period was 4.65. The lowest pH measured during this period was 3.86. The range of pH in spring and autwnn stonns was 4.4 to 6.0 with mean values of 5.05 for spring storms and 5.00 for autumn storms.
Spring stOn11S had a mean ammonium concentration of 18.9µEq L -1 (standard deviation (Sm), 14.2; N = 67)) and range of 1.1 to 80 µEq L -1. The mean ammonilU11 concentration in summer stOn11S was 36.5 µEq L -1 (Sm, 27.1; N = 365) and ranged up to ca. 160 µEq L -1. Mean ammonium concentration in autumn storms was 28.1 µEq L -1 (Sm, 33.8; N = 82) and ranged from ca. 1.0 to 160 µEq L -1.
Mean nitrate concentration in summer rain was 36.4 µEq L -1 (sm, 26.3) and samples with levels over 40 µEq L -1 were common. Nitrate concentrations in autumn
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