Dissolved Organic Carbon In Precipitation Research Articles

Dissolved organic carbon fractionation in wet deposition and its potential impact on radiative forcing in the central Tibetan Plateau

As an important component of carbonaceous matters, dissolved organic carbon (DOC) can absorb and scatter the solar radiation at ultraviolet and blue wavelengths. The wet deposition process has great impact on the concentration and light absorption ability of precipitation DOC, affecting the climatic effect caused by DOC in the atmosphere. In this study, light absorption and fluorescence characteristics of precipitation DOC was investigated in the central Tibetan Plateau (TP). The results showed that the mean DOC concentration and mass absorption cross-section measured at 365 nm (MAC365) in Tanggula (TGL) station were 0.59 ± 0.42 mg/L and 0.37 ± 0.19 m2/g, respectively, while both values showed much higher volatilities than those of aerosols. DOC concentrations had significant negative correlation with the precipitation amount, while MAC365 values increase with the precipitation amount in TGL station. Therefore, DOC with high light-absorbing ability was preferred to be retained in the atmosphere during wet deposition. In this study, precipitation DOC contained three fluorescent components (one humic-like component and two tyrosine-like components) mainly from local biomass burning sources. DOC concentration showed a negative relationship with MAC365 value in TGL station. The wet deposition of DOC with low light-absorbing ability can reduce the strong negative radiative forcing caused by secondary organic aerosol due to high proportion of DOC in secondary organic carbon. Similar phenomenon was also found in Nam Co, Lulang and Everest stations of previous study, which may have a potential impact on radiative forcing in the atmosphere of TP.

Rapid decline in atmospheric organic carbon deposition in rural Beijing, North China between 2016 and 2020

Atmospheric deposition of dissolved organic carbon (DOC) is equivalent to the magnitude of riverine export of organic carbon (OC) to the oceans. Interpreting the fluctuations of DOC in precipitation is therefore essential in understanding the global carbon balance. This study measured DOC in 137 rain events collected from November 2016 to November 2020 at a rural site in agricultural areas of Beijing on the North China Plain. Concentrations of DOC ranged from 0.09 to 19.69 mg C L−1 with a volume weighted mean value of 2.76 ± 0.27 mg C L−1, which is comparable with those measured in North China a decade ago (3.0 ± 0.4 mg C L−1) and the global mean level (2.64 ± 2.04 mg C L−1). While differences in these values were small, their overall mean values were statistically different (p < 0.05). When classified via air mass back-trajectories, precipitation events with trajectories from south demonstrated higher DOC concentrations than those from north, matching with the spatial distribution of OC emission in the region. The annual precipitation DOC fluxes varied from 6.60 to 15.85 kg C ha−1 yr−1, with an average of 11.05 ± 3.83 kg C ha−1 yr−1 in this study. Both the annual mean concentrations and fluxes of precipitation DOC decreased by approximately 60% between 2017 and 2020, coinciding with the declining trend in OC emissions and aerosol OC concentrations due to the clean air actions. These unique data will allow for a better understanding of current status of rainwater DOC deposition on the global scale and will be critical for evaluating the impacts of future changes, e.g., replacing coal with natural gas, on atmospheric composition.

Seasonal Variations in Dissolved Organic Carbon in the Source Region of the Yellow River on the Tibetan Plateau

Rivers as the link between terrestrial ecosystems and oceans have been demonstrated to transport a large amount of dissolved organic carbon (DOC) to downstream ecosystems. In the source region of the Yellow River (SRYR), climate warming has resulted in the rapid retreat of glaciers and permafrost, which has raised discussion on whether DOC production will increase significantly. Here, we present three-year data of DOC concentrations in river water and precipitation, explore the deposition and transport processes of DOC from SRYR. Results show that annual mean concentrations of riverine DOC ranged from 2.03 to 2.34 mg/L, with an average of 2.21 mg/L. Its seasonal variation is characterized by the highest concentration in spring and summer (2.65 mg/L and 2.62 mg/L, respectively), followed by autumn (1.95 mg/L), and the lowest in winter (1.44 mg/L), which is closely related to changes in river runoff under the influence of precipitation and temperature. The average concentration of DOC in precipitation (2.18 mg/L) is comparable with riverine DOC, while the value is inversely related to precipitation amount and is considered to be the result of precipitation dilution. DOC deposition flux in precipitation that is affected by both precipitation amount and DOC concentration roughly was 86,080, 105,804, and 73,072 tons/year from 2013 to 2015, respectively. DOC flux delivered by the river ranged from 24,629 to 37,539 tons/year and was dominated by river discharge. Although permafrost degradation in SRYR is increasing, DOC yield is not as significant as previously assumed and is much less than other large rivers in the world.

Characteristics of dissolved organic carbon and nitrogen in precipitation in the northern Tibetan Plateau

Dissolved organic carbon (DOC) and nitrogen (N) play essential roles in global C and N cycles. To address the possible role of DOC and N in precipitation and enrich the related global database, the characteristics of DOC and N in precipitation were investigated in a typical remote permafrost region (upper Heihe River Basin) of the northern Tibetan Plateau (TP) from February 2019 to March 2020. The results demonstrated that the average DOC and total dissolved N (TDN) concentrations in the precipitation were 1.41 ± 1.09 μg mL−1 and 0.84 ± 0.48 μg mL−1, respectively, with relatively lower concentrations in the summer. The annual DOC and TDN fluxes were estimated to be 6.42 kg ha−1 yr−1 and 3.39 kg ha−1 yr−1, respectively, indicating that precipitation was a significant factor in C and N deposition. The light-absorbing properties of precipitation DOC from the SUVA254 and spectral slope revealed that precipitation DOC containing more aromatic components and lower molecular weights mostly was present during the summer; the mass cross-section (at the wavelength of 365 nm) ranged 0.26–1.84 m2 g−1, suggesting the potential impact of DOC on climatic forcing in the area. The principal component analysis combined with air mass backward trajectories indicated that the air masses from west Siberia, Central Asia, and northwestern China most significantly influenced the precipitation C and N in the study area. The WRF-Chem simulations and aerosol vertical distributions further illustrated the air mass transport pathways, demonstrating that dust and anthropogenic emissions could be transported over the studied area by westerlies and monsoonal winds. In the study basin, the precipitation deposition of DOC and N contributed largely to the riverine DOC and N exportation during the summer and had potential ecological effects. These results highlight the importance of DOC and N deposition from precipitation in the northern TP.

High dissolved organic radiocarbon in precipitation during winter and its implication on the carbon cycle

Radiocarbon (14C) analysis is a powerful tool for tracing carbon in the global carbon cycle. Precipitation is a component of the global carbon cycle through which dissolved organic carbon (DOC) enters terrestrial and aquatic ecosystems from the atmosphere. In previous studies, the Δ14C of DOC in rain or snow was negative indicating an input of relatively old organic carbon including fossil fuels, with only a few positive values up to +108‰ showing the signal of recent photosynthesis. However, here we report surprisingly high Δ14C-DOC in bulk precipitation, more than 1000‰ in Seoul, South Korea, especially when the Northwesterly wind blows during winter. In contrast, Δ14C of particulate organic carbon (POC) in bulk precipitation was negative, indicating that the sources of POC and DOC were different. Although the sources of the high Δ14C-DOC are not clear and future studies on them are required, the relatively high Δ14C-DOC in a nearby headwater stream suggests that precipitation DOC has the potential to affect the local carbon cycle, and that stream DOC derived from terrestrial ecosystems could be older than previously thought. The analysis of Δ14C-DOC of precipitation in many other locations is necessary to understand how long carbon stays in terrestrial ecosystems.

Atmospheric wet deposition of dissolved organic carbon to a typical anthropogenic-influenced semi-enclosed bay in the western Yellow Sea, China: Flux, sources and potential ecological environmental effects

Dissolved Organic Carbon (DOC) is a key organic compound in wet precipitation, but few data are available in China marginal seas. To probe the concentration, deposition flux, seasonality, source and potential ecological environmental effects of precipitation DOC, in this study, one-year precipitation samples were collected at Jiaozhou Bay (JZB), a typical anthropogenic-influenced semi-enclosed bay in the western Yellow Sea for the first time from June 2015 to May 2016. The concentrations of DOC in precipitation were highly variable with a volume-weighted mean (VWM) concentration of 3.63 mg C L−1, which was mostly higher than those in other areas. DOC concentrations were lower in wet season than that in dry season due to the dilution from more amount of rainfall. The wet deposition flux of DOC was calculated to be 3.15 g C m−2 yr−1 with 68.7% of which occurred in wet season mainly owing to the promoting of more rainfall amount. Besides, local emissions together with the long-range transport of pollutants were other factors controlling precipitation DOC. Fossil fuel combustion particularly coal burning was considered to be the leading source of precipitation DOC based on correlation analysis with some generally accepted indicators. Wet deposition dominates the external input of DOC at JZB by comparison with riverine input with a percentage of 54%. Heavy storm may exert enrichment effect on DOC levels in the surface water of JZB, and then promote the secondary productivity. This study emphasizes that wet deposition is an important process that should be seriously considered in the models of global/regional carbon biogeochemical cycling.

Water-soluble ions and oxygen isotope in precipitation over a site in northeastern Tibetan Plateau, China

A total of 30 precipitation samples were collected at a remote site of Qinghai Lake in the northeastern Tibetan Plateau, China, from June to August 2010. All samples were analyzed for major cations (NH4+, Na+, K+, Ca2+, and Mg2+) and anions (F−, Cl−, NO3−, and SO42−), electric conductivity (EC), pH, dissolved organic carbon (DOC), and oxygen isotopic composition (δ18O). The volume-weighted mean (VWM) values of pH and EC in the precipitation samples were 7.2 and 19.0 μs cm−1. Ca2+ was the dominant cation in precipitation with a VWM of 116.9 μeq L−1 (1.6–662.9 μeq L−1), accounting for 45.7% of total ions in precipitation. SO42− was the predominant anion with a VWM of 32.7 μeq L−1, accounting for 47.1% of the total anions. The average precipitation DOC was 1.4 mg L−1, and it shows a roughly negative power function with the precipitation amount. The values of δ18O in the rainwater in Qinghai Lake varied from −13.5‰ to −3.9‰ with an average of −8.1‰. The enrichment factor analysis indicates that crustal materials from continental dust were the major sources for Ca2+ in the precipitation samples. The high concentration of Ca2+ in the atmosphere played an important role in neutralizing the acidity of rainwater in Qinghai Lake area. Cluster analysis of air-mass trajectories indicates that the air masses associated with northeast and east had high values of NH4+, SO42−, and NO3−, whereas large Ca2+ loading was related to the air mass from west.

Deposition and light absorption characteristics of precipitation dissolved organic carbon (DOC) at three remote stations in the Himalayas and Tibetan Plateau, China

The concentrations, depositions and optical properties of precipitation DOC at three remote stations (Nam Co, Lulang and Everest) were investigated in the Himalayas and Tibetan Plateau (HTP). The results showed that their volume-weighted mean DOC concentrations were 1.05±1.01mgCL−1, 0.83±0.85mgCL−1 and 0.86±0.91mgCL−1, respectively, close to those of other remote areas in the world and lower than those of typical polluted urban cities. Combined with precipitation amounts, the DOC depositions at these three stations were calculated to be 0.34±0.32gCm−2yr−1, 0.84±0.86gCm−2yr−1 and 0.16±0.17gCm−2yr−1, respectively. The annual DOC deposition in the HTP was approximately 0.94±0.87TgC, the highest and lowest values appeared in the southeastern and northwestern plateau, respectively. The sources of DOC in the precipitation at these three stations were remarkably different, indicating large spatial heterogeneity in the sources of precipitation DOC over the HTP. Nam Co presented combustion sources from South Asia and local residents, Lulang showed biomass combustion source from South Asia, and Everest was mainly influenced by local mineral dust. The values of the MACDOC at 365nm were 0.48±0.47m2g−1, 0.25±0.15m2g−1, and 0.64±0.49m2g−1, respectively, for the precipitation at the three stations. All of these values were significantly lower than those of corresponding near-surface aerosol samples because precipitation DOC contains more secondary organic aerosol with low light absorption abilities. Additionally, this phenomenon was also observed in seriously polluted urban areas, implying it is universal in the atmosphere. Because precipitation DOC contains information for both particle-bound and gaseous components from the near surface up to the altitude of clouds where precipitation occurs, the MACDOC of precipitation is more representative than that of near-surface aerosols for a given region.

Variability of dissolved organic carbon in precipitation during storms at the Shale Hills Critical Zone Observatory

AbstractOrganic compounds are removed from the atmosphere and deposited to the Earth's surface via precipitation. In this study, we quantified variations of dissolved organic carbon (DOC) in precipitation during storm events at the Shale Hills Critical Zone Observatory, a forested watershed in central Pennsylvania (USA). Precipitation samples were collected consecutively throughout the storm during 13 events, which spanned a range of seasons and synoptic meteorological conditions, including a hurricane. Further, we explored factors that affect the temporal variability by considering relationships of DOC in precipitation with atmospheric and storm characteristics. Concentrations and chemical composition of DOC changed considerably during storms, with the magnitude of change within individual events being comparable or higher than the range of variation in average event composition among events. Although some previous studies observed that concentrations of other elements in precipitation typically decrease over the course of individual storm events, results of this study show that DOC concentrations in precipitation are highly variable. During most storm events, concentrations decreased over time, possibly as a result of washing out of the below‐cloud atmosphere. However, increasing concentrations that were observed in the later stages of some storm events highlight that DOC removal with precipitation is not merely a dilution response. Increases in DOC during events could result from advection of air masses, local emissions during breaks in precipitation, or chemical transformations in the atmosphere that enhance solubility of organic carbon compounds. This work advances understanding of processes occurring during storms that are relevant to studies of atmospheric chemistry, carbon cycling, and ecosystem responses.

Atmospheric inputs of organic matter to a forested watershed: Variations from storm to storm over the seasons

The objectives of this study were to determine the quantity and chemical composition of precipitation inputs of dissolved organic carbon (DOC) to a forested watershed; and to characterize the associated temporal variability. We sampled most precipitation that occurred from May 2012 through August 2013 at the Susquehanna Shale Hills Critical Zone Observatory (Pennsylvania, USA). Sub-event precipitation samples (159) were collected sequentially during 90 events; covering various types of synoptic meteorological conditions in all climatic seasons. Precipitation DOC concentrations and rates of wet atmospheric DOC deposition were highly variable from storm to storm, ranging from 0.3 to 5.6 mg C L−1 and from 0.5 to 32.8 mg C m−2 h−1, respectively. Seasonally, storms in spring and summer had higher concentrations of DOC and more optically active organic matter than in winter. Higher DOC concentrations resulted from weather types that favor air advection, where cold frontal systems, on average, delivered more than warm/stationary fronts and northeasters. A mixed modeling statistical approach revealed that factors related to storm properties, emission sources, and to the chemical composition of the atmosphere could explain more than 60% of the storm to storm variability in DOC concentrations. This study provided observations on changes in dissolved organic matter that can be useful in modeling of atmospheric oxidative chemistry, exploring relationships between organics and other elements of precipitation chemistry, and in considering temporal changes in ecosystem nutrient balances and microbial activity.

Dissolved organic carbon concentrations under conditions of different forestcomposition

The study deals with the monitoring of dissolved organic carbon (DOC) concentrations in seepage water sampled from differently managed forest plots in the Drahanská vrchovina Upland. Simultaneously, the input of DOC in precipitation and throughfall is evaluated. Preliminary results show higher mobility level of carbon substances in forest soil in a pure spruce stand compared to mixed stand or a pure beech stand. DOC can be one of suitable characteristics to evaluate the conversion effectiveness of spruce monocultures.

Carbon isotopic characterization of dissolved organic carbon in rainwater: Terrestrial and marine influences

This study presents the first published 14C and 13C isotopic data for dissolved organic carbon (DOC) in rainwater. The 14C fraction modern ( Fm) values for rain DOC ranged from 0.9051 to 1.0569. Between 4% and 24% of the rainwater DOC was of fossil fuel origin based on a two end member calculation assuming biogenic carbon has the same 14C content as the contemporary atmosphere ( Fm=1.11–1.19) and fossil fuel carbon is devoid of 14C. The δ 13C content of rain DOC ranged from −21.8‰ to −28.2‰ spanning the terrestrial and fossil fuels average (∼−26‰) to marine (−18‰ to −20‰) values. Rain events with more continental influences had δ 13C values closer to the terrestrial and fossil fuels signal and higher concentrations of fossil fuel derived DOC. Rain events with stronger oceanic influences had δ 13C values shifting towards those typical of marine systems and had lower concentrations of fossil fuel derived DOC. The influence air mass back trajectory has on the terrestrial and marine characteristics of rainwater DOC identifies air mass recent history as an important factor controlling the sources of DOC in precipitation. It also indicates water soluble volatile organic carbon (VOC's) have relatively short residence times on the order of days with minimal global transport. However, residence times of days, and the presence of both marine and terrestrial DOC in rainwater, suggests that precipitation represents an important exchange of carbon between land and the oceans especially in coastal regions.

Dissolved organic carbon and nitrogen in precipitation, throughfall and stemflow fromSchima superba andCunninghamia lanceolata plantations in subtropical China

Despite growing attention to the role of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in forest nutrient cycling, their monthly concentration dynamics in forest ecosystems, especially in subtropical forests only were little known. The goal of this study is to measure the concentrations and monthly dynamics of DOC and DON in precipitation, throughfall and stemflow for two plantations ofSchima superba (SS) and Chinese fir (Cunninghamia lanceolata, CF) in Jianou, Fujian, China. Samples of precipitation, throughfall and stemflow were collected on a rain event base from January 2002 to December 2002. Upon collection, all water samples were analyzed for DOC, NO3 −−N, NH4 +−N and total dissolved N (TDN). DON was calculated by subtracting NO3 −−N and NH4 +−N from TDN. The results showed that the precipitation had a mean DOC concentration of 1.7 mg·L−1 and DON concentration of 0.13 mg·L−1. The mean DOC and DON concentrations in throughfall were 11.2 and 0.24 mg·L−1 in the SS and 10.3 and 0.19 mg·L−1 in the CF respectively. Stemflow DOC and DON concentrations in the CF (19.1 and 0.66 mg·L−1 respectively) were significantly higher than those in the SS (17.6 and 0.48 mg·L−1 respectively). No clear monthly variation in precipitation DOC concentration was found in our study, while DON concentration in precipitation tended to be higher in summer or autumn. The monthly variations of DON concentrations were very similar in throughfall and stemflow at both forests, showing an increase at the beginning of the rainy season in March. In contrast, monthly changes of the DOC concentrations in throughfall of the SS and CF were different to those in stemflow. Throughfall DOC concentrations were higher from February to April, while relatively higher DOC concentrations in stemflow were found during September–November period.

Dissolved organic carbon in a northern boreal landscape

I examined concentrations and fluxes of dissolved organic carbon (DOC) in precipitation, upland forest throughfall, stemflow and soil water, peatland pore water, beaver ponds, and streams from May to September 1994 in the BOREAS Northern Study Area, near Thompson, Manitoba, Canada. Concentrations of DOC in precipitation were large (8 mg L−1) compared to other boreal locations, possibly associated with a high incidence of local forest fires. DOC concentrations increased in throughfall, stemflow, and soil organic horizons and decreased in subsoil pore water, associated with DOC sorption. Pore water of fens and bogs contained large DOC concentrations (seasonal average 20 to 40 mg L−1), similar to that observed in beaver ponds (seasonal average 19 to 38 mg L−1). Streams draining three small (30 to 420 km2) catchments contained DOC concentrations generally from 15 to 30 mg L−1, with a negative correlation with discharge. For the May to September period, it was estimated that precipitation imported ∼2 g DOC m−2, increasing to 3 to 6 g DOC m−2 with passage through forest vegetation and organic horizons. DOC export in streams was estimated to be ∼3 g DOC m−2, controlled mainly by contributions from wetlands and beaver ponds before reaching streams. Although DOC concentrations are large, compared to other landscapes, the hydrologic pathways and the paucity of mineral subsoils for DOC sorption, and the small runoff (average 125 mm, May to September 1994 to 1996) in this continental climate (precipitation 535 mm yr−1) environment results in a small export of DOC from the land surface to water bodies.