Our Uviiii; Rcsinincs — Hinmiii Influences 



421 



In mSl ;i long-term, cooperative study of 

 ecosystems in the southern Siena Nevada was 

 begun to address concerns over high levels of 

 air pollutants. Atmospheric pollutants are gen- 

 erated throughout California and because of 

 topography, wind patterns, and a Meditenanean 

 climate, they eventually concentrate in the San 

 Joaquin Valley, west of the study area. Baseline 

 ecosystem data — chemical and biological — 

 were collected to determine basic system struc- 

 ture and function. This collection was followed 

 by long-term measurements of pollutants to 

 assess their present and potential effects on ter- 

 restrial and aquatic ecosystems. Studies includ- 

 ed measurement of precipitation chemistry, dry 

 deposition, stream hydrology, aquatic chemistry 

 and biology, soil chemistry, meteorology, nutri- 

 ent fluxes, watershed response to fire distur- 

 bance, and vegetation structure and dynamics. 



Methods 



Research was designed to take advantage of 

 the striking elevation gradient by including 

 measurements at three core areas: 



Elk Creek is a low-elevation. 75()-m (2.460- 

 ft) foothill site dominated by chamise chaparral 

 (Adenosumui fascictdatuni). Precipitation aver- 

 ages 66 cm (36 in) annually, nearly all falling as 

 rain in winter Precipitation chemistry and vol- 

 ume are collected weekly from a site at Ash 

 Mountain, 3 km ( 1.9 mi) south of the site. An 

 intermittent first-order tributary, Chamise 

 Creek, is sampled when possible. 



Log Creek is a mid-elevation 2,100-m 

 (6,890-ft) montane mixed conifer forest site 

 dominated numerically by white fir (Abies con- 

 color); however, giant sequoia (Sequoiadendnm 

 giganteiim) contribute the greatest basal area. 

 Mean annual precipitation is 100 cm (39.4 in); 

 more than 85% falls as snow during the winter 

 Precipitation chemistry and volume are collect- 

 ed weekly. Paired watersheds. Tharp's and Log 

 creeks, are sampled biweekly. 



Emerald Lake is a subalpine 3.000-m 

 (9,840-ft) cirque {see glossary), largely treeless 

 but including lodgepole pine (Pinus contorta), 

 western white pine {Pinus monticola), foxtail 

 pine (Pinus halfouriana). and red fir (Abies 

 magnifica). Annual precipitation varied 

 between 70 cm (28 in) and 300 cm (118 in) in 

 the past decade, nearly all as snow during the 

 winter Precipitation depth is estimated by using 

 snow-water equivalents; precipitation chemistry 

 is collected as the opportunity arises. 



Inputs 



Precipitation and discharge at all three sites 

 vary greatly from year to year As a result, annu- 



al ion input and export also vary considerably in 

 each watershed. There was a general increa.se in 

 precipitation and a decrease in ion concentra- 

 tion with elevation. Most precipitation falls dur- 

 ing the winter as snow above 1 ,800 m (.5.900 fi ). 

 LInlike the eastern United States, where the 

 major source of acidification of lakes and 

 streams is sulfur deposition, the southern Sierra 

 Nevada is considered to be most exposed to 

 nitrogen. At the Log Creek and Elk Creek sites, 

 over the sampling period the mean loading of 

 nitrogen, expressed as NO, . was 16.77 kg ha'' 



yr' 



with 74% contributed from wet deposi- 



tion. The mean loading of sulfur (S). expressed 

 as S0_^- . was 5.24 kg ha" ' yr' ' . with bl% con- 

 tributed by wet deposition (Table). The dry 

 deposition input estimates are conservative 

 because the dry deposition sampling site 

 appears more shielded from pollutant inputs 

 than the wet sampling site. 



The mean precipitation pH at the Log Creek 

 site was 5.25. and at the Elk Creek site 5.37; 

 there is not a chronic acid rain problem in the 

 area. The frequency and volume of summer 

 storms were fairly constant. Wet-deposition ion 

 loading at Log Creek and Elk Creek was simi- 

 lar Elk Creek, a somewhat more polluted site, 

 received 57% as much precipitation as Log 

 Creek, but ions were proportionately more con- 

 centrated (Blanchard and Tonneson 1993), 

 yielding equivalent loading. Dry deposition 

 loading in the Elk Creek site was not measured. 



Emerald Lake received about 99% of its pre- 

 cipitation in the form of snow, with a mean pH 

 of 5.3. meaning the site is only slightly acidic. 

 Concentrations of individual ions were 

 extremely dilute, usually less than 5 pEq L'. 

 Mean wet deposition loading of nitrogen and 

 sulfur, expressed as NO, and SO^- . was 2.15 

 kg ha' ' yr" ' and 0.78 kg ha" ' yr" ' . respectively 

 (estimated from Dozieret al. 1987). No reliable 

 estimate of annual dry deposition tTux is avail- 

 able at Emerald Lake. Like Log Creek. Emerald 

 Lake has no chronic acid precipitation problem. 



Atmospheric 

 Deposition 

 and Solute 

 Transport in a 

 Montane 

 Mixed-Conifer 

 Forest System 



by 



Daniel A. Everson 



David M. Graber 



National Biological Service 



Table. Log Creek site inputs of 

 nrtrogen and sulfur (lig ha"' yr''). 



Hydrologic year is October 1 to September 30 



Wet deposition from National Atmospheric Deposition Program site. 



Dry deposition from Wolverton National Oceanic and Atmosptieric Administration site. 



' Dry deposition N is HNO-^ and NO-^ reported as NO-^. 



* Dry deposition S is SO^ and SO'' reported as SO''. 



