Throughfall Dissolved Organic Carbon Research Articles

Canopy Phenology and Meteorology Shape the Seasonal Dynamics in Hydrological Fluxes of Dissolved Organic Carbon in an Evergreen Broadleaved Subtropical Forest in Central Japan

Seasonal variabilities in hydrological fluxes of dissolved organic carbon (DOC) and their driving factors in the evergreen broad-leaved forest are inadequately understood. To aid this understanding, we conducted a three-year study to examine seasonal changes in DOC concentration and flux in throughfall, stemflow, and litter leachate in an evergreen broad-leaved subtropical forest in central Japan. We specifically addressed (1) how DOC in different hydrological fluxes vary on a monthly to seasonal basis, and (2) how canopy phenology and meteorology shape the DOC concentration and flux of throughfall, stemflow, and litter leachate trends in this evergreen forest. Clear seasonal changes were found in throughfall and stemflow DOC concentration but not in litter leachate DOC concentration; the highest throughfall DOC concentrations were observed in spring (10.03 mg L−1 in 2017 and 9.59 mg L−1 in 2018, respectively) and the highest stemflow DOC concentrations were observed in summer (13.95 mg L−1 in 2017 and 16.50 mg L−1 in 2018, respectively). Correlation analysis revealed the monthly throughfall DOC concentration to be positively related to the dry weight of fallen leaves (r = 0.72, p < 0.05) and flowers (r = 0.91, p < 0.05). In addition, Random Forest models predicted that the dry weight of flowers was a primary driver of throughfall DOC concentration and that the DOC concentrations of stemflow and litter leachate were constrained by the throughfall DOC concentration. DOC fluxes in different hydrological flux were significantly positive related to bulk precipitation amounts and temperature. Moreover, the throughfall DOC concentration had a considerable effect on throughfall and litter leachate DOC fluxes. Over 75% of annual net tree-DOC (throughfall + stemflow) fluxes and more than 70% of the annual litter leachate DOC fluxes were produced in the flowering season. Thus, we speculated that the seasonal phenological canopy changes (leaf emergence, fallen leaves, flowering, and pollen) and the sufficient rainfall had great impacts on the amount and quality of DOC concentrations in the evergreen forest; and, furthermore, that the DOC from different forest hydrological fluxes was a significant fraction of the carbon that accumulates in soils.

Evaluation of the factors governing dissolved organic carbon concentration in the soil solution of a temperate forest organic soil

The widespread increase of dissolved organic carbon (DOC) in northern hemisphere surface waters have been generally attributed to the recovery from acidic deposition and to climatic variations. The long-term responses of DOC to environmental drivers could be better predicted with a better understanding of the mechanisms taking place at the soil level given organic forest soils are the main site of DOC production in forested watersheds. Here, we assess the long-term variation (25 years) of DOC concentration in the solution leaching from the soil organic layer (DOCOL) of a temperate forest. Our results show that DOCOL increased by 32 % (p < 0.001) during the period of study while the lake outlet DOC concentration did not show any changes. Weekly and annual models based on a simple set of explicative variables including throughfall DOC, throughfall precipitation, temperature, litterfall amounts and organic layer leachate calcium concentration (CaOL, taken as a proxy for soil solution ionic strength) explain between 17 and 58 % of the variance in DOCOL depending on model structures and temporal scales. Throughfall DOC and CaOL were both positively related to DOCOL in the models describing its variations at the weekly and annual scale. Temperature was positively correlated to DOCOL, probably due to increased microbial activity, while precipitation had a negative effect on DOCOL (only at the weekly scale), most probably due to a dilution effect. Contrary to our expectations, annual litterfall inputs had no impacts on annual DOCOL variations. Overall, the results shows that DOCOL control is a complex process implicating a set of environmental factors that are acting in different ways while no single variable alone can explain a large part of the variation in both, weekly or annual DOCOL variations.

ORCHILEAK (revision 3875): a new model branch to simulate carbon transfers along the terrestrial–aquatic continuum of the Amazon basin

Abstract. Lateral transfer of carbon (C) from terrestrial ecosystems into the inland water network is an important component of the global C cycle, which sustains a large aquatic CO2 evasion flux fuelled by the decomposition of allochthonous C inputs. Globally, estimates of the total C exports through the terrestrial–aquatic interface range from 1.5 to 2.7 Pg C yr−1 (Cole et al., 2007; Battin et al., 2009; Tranvik et al., 2009), i.e. of the order of 2–5 % of the terrestrial NPP. Earth system models (ESMs) of the climate system ignore these lateral transfers of C, and thus likely overestimate the terrestrial C sink. In this study, we present the implementation of fluvial transport of dissolved organic carbon (DOC) and CO2 into ORCHIDEE (Organising Carbon and Hydrology in Dynamic Ecosystems), the land surface scheme of the Institut Pierre-Simon Laplace ESM. This new model branch, called ORCHILEAK, represents DOC production from canopy and soils, DOC and CO2 leaching from soils to streams, DOC decomposition, and CO2 evasion to the atmosphere during its lateral transport in rivers, as well as exchange with the soil carbon and litter stocks on floodplains and in swamps. We parameterized and validated ORCHILEAK for the Amazon basin, the world's largest river system with regard to discharge and one of the most productive ecosystems in the world. With ORCHILEAK, we are able to reproduce observed terrestrial and aquatic fluxes of DOC and CO2 in the Amazon basin, both in terms of mean values and seasonality. In addition, we are able to resolve the spatio-temporal variability in C fluxes along the canopy–soil–water continuum at high resolution (1°, daily) and to quantify the different terrestrial contributions to the aquatic C fluxes. We simulate that more than two-thirds of the Amazon's fluvial DOC export are contributed by the decomposition of submerged litter. Throughfall DOC fluxes from canopy to ground are about as high as the total DOC inputs to inland waters. The latter, however, are mainly sustained by litter decomposition. Decomposition of DOC and submerged plant litter contributes slightly more than half of the CO2 evasion from the water surface, while the remainder is contributed by soil respiration. Total CO2 evasion from the water surface equals about 5 % of the terrestrial NPP. Our results highlight that ORCHILEAK is well suited to simulate carbon transfers along the terrestrial–aquatic continuum of tropical forests. It also opens the perspective that provided parameterization, calibration and validation is performed for other biomes, the new model branch could improve the quantification of the global terrestrial C sink and help better constrain carbon cycle–climate feedbacks in future projections.

Long-term changes in acidity and DOC in throughfall and soil water in Finnish forests.

The main objective of this study was to examine if any detectable trends in dissolved organic carbon (DOC), sulphate (SO4-S) concentrations and acid neutralizing capacity (ANC) in throughfall (TF) and soil water (SW) could be found during 1990-2010 and to relate them to recent changes in decreased acid deposition. The study was conducted in seven boreal coniferous forest sites: four of which are managed and three unmanaged forests sites. Generally, temporal trend showed a significant decrease in SO4-S concentrations in bulk precipitation (BP), TF and SW. At some of the sites, there was an increasing tendency in BP and TF in the DOC concentrations. This feature coincides with decreasing SO4-S concentration, indicating that SO4-S may be an important driver of DOC release from the canopy. However, a slightly increased temperature, larger senescing needle mass and consequently increased decaying activity in the canopy may partly explain the increasing trend in DOC. In SW, no consistent DOC trend was seen. At some sites, the decreased base cation concentrations mostly account for the decrease in the ANC values in SW and TF.

Decomposition pathways of 13C-depleted leaf litter in forest soils of the Swiss Jura

Decomposition of leaf litter and its incorporation into the mineral soil are key components of the C cycle in forest soils. In a 13C tracer experiment, we quantified the pathways of C from decomposing leaf litter in calcareous soils of a mixed beech forest in the Swiss Jura. Moreover, we assessed how important the cold season is for the decomposition of freshly fallen leaves. The annual C loss from the litter layer of 69–77% resulted mainly from the C mineralization (29–34% of the initial litter C) and from the transfer of litter material to the deeper mineral soil (>4 cm) by soil fauna (30%). Although only 4–5% of the initial litter C was leached as dissolved organic carbon (DOC), this pathway could be important for the C sequestration in soils in the long term: The DOC leached from the litter layer was mostly retained (95%) in the first 5 cm of the mineral soil by both physico-chemical sorption and biodegradation and, thus, it might have contributed significantly to the litter-derived C recovered in the heavy fraction (>1.6 g cm−3) at 0–4 cm depth (4% of the initial litter C). About 80% of the annual DOC leaching from the litter layer occurred during the cold season (Nov–April) due to an initial DOC flush of water-soluble substances. In contrast, the litter mineralization in winter accounted for only 25% of the annual C losses through CO2 release from the labelled litter. Nevertheless, the highest contributions (45–60%) of litter decay to the heterotrophic soil respiration were observed on warm winter days when the mineral soil was still cold and the labile litter pool only partly mineralized. Our 13C tracing also revealed that: (1) the fresh litter C only marginally primed the mineralization of older SOM (>1 year); and (2) non-litter C, such as throughfall DOC, contributed significantly to the C fluxes from the litter layer since the microbial biomass and the DOC leached from the litter layer contained 20–30% and up to 60% of unlabelled C, respectively. In summary, our study shows that significant amounts of recent leaf litter C (<1 year) are incorporated into mineral soils and that the cold season is clearly less important for the litter turnover than the warm season in this beech forest ecosystem.

The effects of phytophagous insects on water and soil nutrient concentrations and fluxes through forest stands of the Level II monitoring network in the UK

The effects of insect defoliators on throughfall and soil nutrient fluxes were studied in coniferous and deciduous stands at five UK intensive monitoring plots (1998 to 2008). Links were found between the dissolved organic carbon (DOC), nitrogen (N) and potassium (K) fluxes through the forest system to biological activity within the canopy. Underlying soil type determined the leaching or accumulation of these elements. Under oak, monitored at two sites, frass from caterpillars of Tortrix viridana and Operophtera brumata added direct deposition of ~ 16 kg ha −1extra N during defoliation. Peaks of nitrate (NO 3–N) flux between 5 and 9 kg ha −1 (×5 usual winter values) were recorded in consecutive years in shallow soil waters. Synchronous rises in deep soil NO 3–N fluxes at the Grizedale sandy site indicate downward flushing, not seen at the clay site. Under three Sitka spruce stands, generation of honeydew (DOC) was attributed to two aphid species ( Elatobium abietinum and Cinara pilicornis) with distinctive feeding strategies. Throughfall DOC showed mean annual fluxes (6 seasons) ~ 45–60 kg ha −1 compared with rainfall values of 14–22 kg ha −1. Increases of total N in throughfall and NO 3–N fluxes in shallow soil solution were detected — soil water fluxes reached 8 kg ha −1 in Llyn Brianne, ~ 25 kg ha −1 in Tummel, and ~ 40 kg NO 3–N ha −1 in Coalburn. At Tummel, on sandy soil, NO 3–N leaching showed increased concentration at depth, attributed to microbiological activity within the soil. By contrast, at Coalburn and Llyn Brianne, sites on peaty gleys, soil water NO 3–N was retained mostly within the humus layer. Soil type is thus key to predicting N movement and retention patterns. These long term analyses show important direct and indirect effects of phytophagous insects in forest ecosystems, on above and below ground processes affecting tree growth, soil condition, vegetation and water quality.

Dynamics of dissolved organic 14C in throughfall and soil solution of a Norway spruce forest

Dissolved organic carbon (DOC) is an important component of the C cycle in forest ecosystems, but dynamics and origin of DOC in throughfall and soil solution are yet poorly understood. In a 2-year study, we analyzed the radiocarbon signature of DOC in throughfall and soil solution beneath the Oa horizon and at 90 cm depth in a Norway spruce forest on a Podzol soil. A two-pool mixing model revealed that throughfall DOC comprised mainly biogenic C, i.e. recently fixed C, from canopy leaching and possibly other sources. The contribution of fossil DOC from atmospheric deposition to throughfall DOC was on average 6% with maxima of 8–11% during the dormant season. In soil solution from the Oa horizon, DO14C signature was highly dynamic (range from −8‰ to +103‰), but not correlated with DOC concentration. Radiocarbon signatures suggest that DOC beneath the Oa horizon originated mainly from occluded and mineral associated organic matter fractions of the Oa horizon rather than from the Oi or Oe horizon. Relatively old C was released in the rewetting phase following a drought period in the late summer of 2006. In contrast, the DO14C signature indicated the release of younger C throughout the humid year 2007. In soil solutions from 90 cm depth, DO14C signatures were also highly dynamic (−127‰ to +3‰) despite constantly low DOC concentrations. Similar to the Oa horizon, the lowest DO14C signature at 90 cm depth was found after the rewetting phase in the late summer of 2006. Because of the variation in the DO14C signatures at this depth, we conclude that DOC was not equilibrated with the surrounding soil, but also originated from overlaying soil horizons. The dynamics of DO14C in throughfall and soil solution suggest that the sources of DOC are highly variable in time. Extended drought periods likely have a strong influence on release and translocation of DOC from relatively old and possibly stabilized soil organic matter fractions. Temporal variations as well as the input of fossil DOC needs to be considered when calibrating DOC models based on DO14C signatures.

Fluxes of dissolved organic carbon in two tropical forest ecosystems of East Kalimantan, Indonesia

Leaching of dissolved organic carbon (DOC) from the organic horizon is an important process involved in translocation and stabilization of organic matter in forest soils. Despite there being many studies on the DOC fluxes in temperate forest soils, very little information is available in tropical forest soils. The roles of DOC leaching in soil organic carbon cycle were evaluated by quantifying the fluxes of DOC in throughfall and soil solution in the Ultisols under tropical secondary and pristine forests in East Kalimantan, Indonesia. The fluxes of DOC in the soil profiles are highest from the O horizon (470–562 kg C ha − 1 yr − 1 ), decreasing markedly in the A and B1 horizons of the two Ultisols studied. DOC fluxes from the O horizon are comparable to those of temperate forests because of the greater amounts of precipitation, substantial C input (3.7–4.3 Mg C ha − 1 yr − 1 ) and its rapid decomposition (4.2–5.4 Mg C ha − 1 yr − 1 ). The proportion of DOC leaching to C input in the O horizon (12.7–13.2%) is similar to Spodosols under boreal and temperate forests. DOC leached from the O horizon appears to be an important carbon source into mineral soils, even in tropical regions. At the same time, DOC leaching contributed to eluviation of Al and Fe from the O horizon and their illuviation in the subsurface soil horizons. It was quantitatively shown that DOC leaching is important to the translocation of organic matter, Al and Fe in the acidic Ultisols in tropical forests, as well as the soils under boreal and temperate forests that undergo podzolization.

Dissolved Organic Carbon Concentrations in Throughfall and Soil Waters at Level II Monitoring Plots in Norway: Short- and Long-Term Variations

We investigated concentrations of dissolved organic carbon (DOC) in throughfall and soil solutions at 5, 15 and 40-cm depth in 16 Norway spruce and two Scots pine plots throughout Norway between 1996 and 2006. Average DOC concentrations ranged from 2.3 to 23.1 mg/l and from 1.1 to 53.5 mg/l in throughfall water and soil solutions, respectively. Concentrations of DOC in throughfall and soil waters varied seasonally at most plots with peaks in the growing season. By contrast to recently reported positive long-term trends in DOC concentrations in surface waters between 1986 and 2003, soil water data from 1996 to 2006 showed largely negative trends in DOC concentrations and no significant trends in throughfall. However, regression analysis for individual sites, particularly at 5- and 15-cm soil depths, showed that DOC concentrations in soil water were significantly and negatively related to non-marine sulphate (SO4) and chloride (Cl−). The lack of a long-term increase in DOC in soil water in the period May 1996–December 2006 may be due to the relatively small changes in the deposition of SO4 and Cl− in this period.

The contribution of fresh litter to dissolved organic carbon leached from a coniferous forest floor

SummaryThe relative contributions of litter and humified organic matter as the source of dissolved organic carbon (DOC) leached from organic layers of forest soils are poorly understood. In the present investigation, 13C labelled spruce litter was used to study the role of recent litter in the leaching of DOC from a coniferous forest floor in southern Sweden, while litterbags were used to quantify the total loss of C from the labelled litter. The labelled litter applied on bare lysimeters released considerable amounts of DOC during the first weeks, but the concentration of DOC originating from labelled litter decreased gradually from 176 mg litre−1 during the first sampling period in May to 5 mg litre−1 in the last sampling period in October. Only a moderate flush of DOC from the labelled litter occurred under the Oe and Oa horizons, with concentrations of 20 and 6 mg litre−1 from labelled litter, equal to 19 and 9% of the total DOC flux, respectively, during the first sampling period. Total flux of DOC from labelled litter from May to September was 16 g m−2, whereas only 2.2 and 0.9 g m−2 were captured under the Oe and Oa horizons, respectively. The almost complete loss of new DOC implies that DOC leached from the Oe and Oa horizons consists not of recent litter‐derived carbon, but of DOC produced in these two horizons themselves. Water‐extractable organic carbon from labelled litter left in litterbags in the field for 4 months consisted of about one‐third native carbon from external sources at the experimental site and two‐thirds of the labelled litter. In contrast, the 13C content of the bulk litter from the litterbags was not changed by the incubation in the field. We suggest that the soluble native carbon in water extracts originated from throughfall DOC that had been assimilated by microorganisms in the litterbags.

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.

Aphid infested Norway spruce are "hot spots" in throughfall carbon chemistry in coniferous forests

Throughfall chemistry in deciduous and coniferous forests is characterized by a high spatial and temporal variability, the sources of which are largely unknown. Aphids on Norway spruce (Picea abies (L.) Karst.) produce large quantities of honeydew, which is rich in sugars. We investigated the effect of changes in aphid abundance on throughfall carbon chemistry of Norway spruce using a rainfall simulation experiment. Aphid numbers in the experiment paralleled field infestations. Infested trees showed significantly higher concentrations of dissolved organic carbon (DOC) and hexose-C in throughfall solutions compared with uninfested trees. There was also a pronounced seasonal trend in the concentrations of these carbon compounds with highest concentrations recorded at the time of peak aphid abundance at the end of June - beginning of July. The throughfall from a spruce tree showed no spatial (center vs. periphery) differences in DOC and hexose-C concentrations. The number of aphids on a tree was the best predictor of the carbohydrate concentration of throughfall, explaining more than 60% of the variability. During the period of aphid infestation (May-September) average estimated field fluxes of DOC in throughfall collected under heavily infested trees ("hot spots") were 11.6 and 240 times higher than those recorded under moderately and uninfested trees, respectively. The results implicate herbivores as a major potential source of the spatiotemporal heterogeneity in flows of nutrients in forests.

Dissolved Organic Carbon In Northern Hardwood Stands With Differing Acidic Inputs and Temperature Regimes

AbstractWe monitored concentrations and fluxes of dissolved organic carbon (DOC) in throughfall and forest floor solutions in two northern hardwood stands located at the northern and southern end of a latitudinal acidic deposition and air temperature gradient in the Great Lakes Region to determine if DOC levels are altered by regional and temporal variation in acidic inputs and temperature. Amounts of precipitation received at the two sites were similar, but precipitation pH and air temperature, respectively, averaged 4.83 and 13.9°C at the northern gradient site and 4.29 and 15.1°C at the southern gradient site. Volume weighted DOC concentrations in throughfall were significantly greater at the northern (20.5 mg L−1) than the southern (15.9 mg L−1) site, but these differences in DOC levels were caused by the differing amounts of throughfall passing through the canopy of the two sites rather than levels of precipitation acidity or air temperature. Temporal variation in the levels of DOC in throughfall was not related to the variation in either precipitation acidity or air temperature. Like throughfall, levels of DOC in forest floor solutions were not found to be altered by acidic inputs. However, DOC in these solutions increased with seasonal increases in soil temperature. A regression equation relating seasonal variation in soil temperature and forest floor concentrations of DOC estimated that an observed 2.1°C difference in soil temperature at the two sites during the growing season could represent as much as 3.7 mg L−1 difference in forest floor solution concentrations of DOC.