Nutrient and mercury deposition and storage in an alpine snowpack of the Sierra Nevada, USA

Abstract

Abstract. Biweekly snowpack core samples were collected at seven sites along two elevation gradients in the Tahoe Basin during two consecutive snow years to evaluate total wintertime snowpack accumulation of nutrients and pollutants in a high-elevation watershed of the Sierra Nevada. Additional sampling of wet deposition and detailed snow pit profiles were conducted the following year to compare wet deposition to snowpack storage and assess the vertical dynamics of snowpack nitrogen, phosphorus, and mercury. Results show that, on average, organic N comprised 48 % of all snowpack N, while nitrate (NO − 3 -N) and TAN (total ammonia nitrogen) made up 25 and 27 %, respectively. Snowpack NO − 3 -N concentrations were relatively uniform across sampling sites over the sampling seasons and showed little difference between seasonal wet deposition and integrated snow pit concentrations. These patterns are in agreement with previous studies that identify wet deposition as the dominant source of wintertime NO − 3 -N deposition. However, vertical snow pit profiles showed highly variable concentrations of NO − 3 -N within the snowpack indicative of additional deposition and in-snowpack dynamics. Unlike NO − 3 -N, snowpack TAN doubled towards the end of winter, which we attribute to a strong dry deposition component which was particularly pronounced in late winter and spring. Organic N concentrations in the snowpack were highly variable (from 35 to 70 %) and showed no clear temporal, spatial, or vertical trends throughout the season. Integrated snowpack organic N concentrations were up to 2.5 times higher than seasonal wet deposition, likely due to microbial immobilization of inorganic N as evident by coinciding increases in organic N and decreases in inorganic N in deeper, aged snow. Spatial and temporal deposition patterns of snowpack P were consistent with particulate-bound dry deposition inputs and strong impacts from in-basin sources causing up to 6 times greater enrichment at urban locations compared to remote sites. Snowpack Hg showed little temporal variability and was dominated by particulate-bound forms (78 % on average). Dissolved Hg concentrations were consistently lower in snowpack than in wet deposition, which we attribute to photochemically driven gaseous re-emission. In agreement with this pattern is a significant positive relationship between snowpack Hg and elevation, attributed to a combination of increased snow accumulation at higher elevations causing limited light penetration and lower photochemical re-emission losses in deeper, higher-elevation snowpack. Finally, estimates of basin-wide loading based on spatially extrapolated concentrations and a satellite-based snow water equivalent reconstruction model identify snowpack chemical loading from atmospheric deposition as a substantial source of nutrients and pollutants to the Lake Tahoe Basin, accounting for 113 t of N, 9.3 t of P, and 1.2 kg of Hg each year.

Mercury in arctic tundra snowpack: temporal and spatial concentration patterns and trace–gas exchanges

“…Louis et al, 2005;Steffen et al, 2002). The low concentrations we measured result in very small pool sizes of Hg diss stored in the snowpack during wintertime compared to temperate studies (Pearson et al, 2015). At Toolik, snowpack pool sizes amounted to 26.9 and (Figure 7).…”

“…We also suggest largely an absence of re-emission losses or elution losses from snow melt as occurs in temperate snowpacks (discussed in Faïn et al (2013) and Pearson et al (2015)). Elution losses are unlikely given that no temperatures above freezing were present in the Arctic until May, and atmospheric re-emissions losses of volatile Hg 0 gas were not important in this arctic snowpack for most of the season as discussed above.…”

Mercury in the Arctic tundra snowpack: temporal and spatial concentration patterns and trace gas exchanges

“…Louis et al, 2005;Steffen et al, 2002). The low concentrations we measured result in very small pool sizes of Hg diss stored in the snowpack during wintertime compared to temperate studies (Pearson et al, 2015). At Toolik, snowpack pool sizes amounted to 26.9 and 19.7 ng m −2 during peak snowpack and prior to the onset of snowmelt in 2014-2015 and 2015-2016, respectively.…”

“…Hence, we suggest no significant additional deposition of Hg (e.g., by dry deposition of gaseous or particulate Hg) to exposed older snow consistent with the lack of correlation to pollution tracers and NO − 3 ). We also suggest an absence or minor importance of re-emission losses or elution losses from snowmelt as occurs in temperate snowpacks (discussed in Faïn et al, 2013, andPearson et al, 2015). Elution losses are unlikely, given that no temperatures above freezing were present in the Arctic until May, and atmospheric re-emissions losses of volatile Hg 0 gas were not important in this Arctic snowpack for most of the season as discussed above.…”

Winter atmospheric nutrients and pollutants deposition on West Sayan mountain lakes (Siberia)

“…It also takes an intermediate position relative to the Alps: lower than in Tyrolean Alps (308 µg NO3- Felip et al 1995) but higher than most sampling points in the French Alps (Dambrine et al, 2018). Finally, nitrate concentration in Ergaki snow was in between that of the Bothnian Bay of the Baltic sea (480 ±130 µg NO3-N•l -1 , Rahm et al 1995) and the lake Tahoe basin in Sierra Nevada (14-138 µg NO3-N•l -1 , Pearson et al 2015). Note that, paradoxically, the former is considered a low atmospheric nitrogen deposition region (Bergström and Jansson, 2006) whereas the latter has been reckoned as an airborne nutrient enriched area (Sickman et al, 2003) where atmospheric nitrogen deposition has shifted phytoplankton limitation from N and P colimitation to persistent P limitation (Jassby et al, 1994).…”