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We determined concentrations and fluxes of dissolved organic carbon (DOC) in precipitation, throughfall, forest floor and
mineral soil leachates from June 2004 to May 2006 across an age-sequence (2-, 15-, 30-, and 65-year-old) of white pine (Pinus strobus L.) forests in southern Ontario, Canada. Mean DOC concentration in precipitation, throughfall,...
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Context 1
... in this region are commonly well-to-imperfectly drained, with low-to-moderate water holding capacity (Presant and Acton 1984). A detailed description of soil and stand characteristics is given in Peichl and Arain (2006) and summarized here in Table 1. All four stands were planted on either cleared oak-savannah land (in case of two older stands) or former agricul- tural lands. ...
Context 2
... indicates that DOC concentrations in forest floor and organic soil solutions were indepen- dent of DOC input from precipitation and throughfall. Throughfall DOC concentrations were larger at the 15-year-old site than the two older sites, possible because the LAI is greatest at that site (see Table 1). The only age-related pattern was observed for forest floor leachates which showed increased DOC con- centrations with increasing stand age. ...
Citations
... Conifer trees are known to withstand extreme and harsh environmental conditions and are found in a wide range of habitats around the world [5]. Conifer forests extend across continents in the Northern hemisphere [6][7][8][9]. This makes the study of conifer fires a worldwide interest, as the ability to protect these natural landscapes is a matter of interest to many countries across the globe. ...
... This is the total energy that must accumulate in the needle's mass consisting of both dry and liquid for any moisture content value for ignition to take place. The specific formulation for Q acc,liveneedle is shown in Eq. (6). ...
... (1)-(3) and Eq. (6). Note that their heating source term corresponds to the microexplosion heating in our equation allowing us to predict the heating time to ignition using the law approach. ...
Live foliage for some tree and shrub species can support flaming fire spread at much higher moisture content than dead fuel materials. However, the role of live fuels in forest fires has been controversial in the past decades. Although ignition and spread statistical data for live and dead fuels exist in the literature, a clear understanding of the fundamental difference in the burning behavior is missing. To illuminate the role of live fuel on forest fire spreading, a laboratory ignition experiment was designed to examine the burning behavior of live Norway spruce needles. A Schlieren-Infrared combined measurement apparatus was developed with a spatial resolution of 0.75 mm and a time resolution of 0.0025 s, to visualize/measure the ignition behavior of live fuels. Schlieren and IR images revealed that the ejection of live fuel volatiles can alter the flame direction and induce previously un-accounted heating of the nearby fuel. Depending on the conditions, these interferences could heat and modify the heat flux received by the adjacent fuels. To analyze each of these outcomes, a scaling analysis using the law approach was performed. First, theoretical equations were developed and validated against a set of previously published experimental data. After the characteristic equations were verified, we used them to assess the volatile ejection phenomenon. We found that adjacent fuels were preheated by hot volatiles ejected from the heated live needle, and direct flame contact ignited the adjacent fuels. Our IR experiments confirmed the outcomes of the scaling analysis. The rapid ejection of volatiles was also found to propel burning needles far from the burning branch, resulting in micro-spotting.
... The DOC released from forest floor materials and upper, organic soil layers during decomposition can translocate into deeper, mineral soil horizons (Michalzik et al., 2001). The quantity of DOC found in the Ah horizon has been found to be largely due to amounts leaching from litter rather than in-situ production (Peichl et al., 2007). Our results broadly show this pattern (Fig. 5), with litter producing 2.3-2.5× ...
The forest floor is often considered the most important source of dissolved organic carbon (DOC) in forest soils, yet little is known about the relative contribution from different forest floor layers, understorey vegetation and deadwood. Here, we determine the carbon stocks and potential DOC production from forest materials: deadwood, ground vegetation, leaf litter, the fermentation layer and top mineral soil (Ah horizon), and further assess the impact of management. Our research is based on long-term monitoring plots in a temperate deciduous woodland, with one set of plots actively managed by thinning, understorey scrub and deadwood removal, and another set that were not managed in 23 years. We examined long-term data and a spatial survey of forest materials to estimate the relative carbon stocks and concentrations and fluxes of DOC released from these different pools. Long-term soil water monitoring revealed a large difference in median DOC concentrations between the unmanaged (43.8 mg L⁻¹) and managed (18.4 mg L⁻¹) sets of plots at 10 cm depth over six years, with the median DOC concentration over twice as high in the unmanaged plots. In our spatial survey, a significantly larger cumulative flux of DOC was released from the unmanaged than the managed site, with 295.5 and 230.3 g m⁻², respectively. Whilst deadwood and leaf litter released the greatest amount of DOC per unit mass, when volume of the material was considered, leaf litter contributed most to DOC flux, with deadwood contributing least. Likewise, there were significant differences in the carbon stocks held by different forest materials that were dependent on site. Vegetation and the fermentation layer held more carbon in the managed site than unmanaged, whilst the opposite occurred in deadwood and the Ah horizon. These findings indicate that management affects the allocation of carbon stored and DOC released between different forest materials.
... 10 Peatlands have been found to be hot spots for DOC export in permafrost region, 29 due to high DOC concentrations in the soil porewater. 30 Many studies show that water table play an important role of DOC production and export in peatlands. 10,28 But, our study dominated that temperature and thawing depth were more important to influence the DOC release in permafrost peatland. ...
Permafrost peatland plays an important role in the global carbon (C) cycle, and dissolved organic carbon (DOC) is one of the most important components to C budgets in this system. Through the Chinese–United States EcoPartnership program, Dr Xianwei Wang, Li Sun, and Prof Changchun Song et al. from the Northeast Institute of Geography and Agroecology of Chinese Academy of Sciences and Prof Aixin Hou from the Louisiana State University observed dynamics of DOC concentrations and specific ultraviolet absorbance at 254 nm (SUVA254) obtained from soil porewater of permafrost peatlands for two growing seasons in the Great Hing'an Mountains, Northeast China. Soil porewater DOC concentrations varied greatly with depths during the growing season, ranging between 22.08 and 65.02 mg L⁻¹. There was no significant relationship between DOC concentrations and SUVA254. DOC concentrations were higher in autumn and increased as the seasonal thaw depth increased. DOC concentrations of supra‐permafrost water at freeze–thaw boundary were also higher than those at the other soil depths. Temperature and thawing depth had been shown to affect DOC concentrations at different soil depths. Our finding suggests that warming and deepening of the active layer likely increase the DOC productions in the permafrost peatland, which may influence the C balance in these C‐enriched ecosystems.
... However, climate transect studies within the boreal forest zone revealed greater DOC fluxes at warmer (low-latitude) relative to cooler (highlatitude) sites, suggesting that this difference can be explained by higher N deposition (Kleja et al., 2008) or higher net primary productivity (Fröberg et al., 2006;Ziegler et al., 2017) in the lower-latitude sites. The DOC fluxes from O to mineral horizons in white pine stands were observed to be negatively correlated with stand age (Peichl et al., 2007), and a stand species comparison study demonstrated larger DOC fluxes from the thicker O horizons of Norway spruce stands relative to silver birch stands (Fröberg et al., 2011). It is likely that a combination of hydrological and biogeochemical factors regulate DOC production and mobilization through soil, but the relative importance of each of these factors is dependent on the scale of investigation, both spatially and temporally (Michalzik et al., 2001), and remains to be confirmed. ...
Boreal forests are subject to a wide range of temporally and
spatially variable environmental conditions driven by season, climate, and
disturbances such as forest harvesting and climate change. We captured
dissolved organic carbon (DOC) from surface organic (O) horizons in a boreal
forest hillslope using passive pan lysimeters in order to identify controls
and hot moments of DOC mobilization from this key C source. We specifically
addressed (1) how DOC fluxes from O horizons vary on a weekly to seasonal
basis in forest and paired harvested plots and (2) how soil temperature,
soil moisture, and water input relate to DOC flux trends in these plots over
time. The total annual DOC flux from O horizons contain contributions from
both vertical and lateral flow and was 30 % greater in the harvested plots
than in the forest plots (54 g C m−2 vs. 38 g C m−2, respectively;
p=0.008). This was despite smaller aboveground C inputs and smaller soil organic carbon stocks in the harvested plots but analogous to larger annual O horizon
water fluxes measured in the harvested plots. Water input, measured as rain, throughfall, and/or snowmelt depending on season and plot type, was
positively correlated to variations in O horizon water fluxes and DOC fluxes
within the study year. Soil temperature was positively correlated to
temporal variations of DOC concentration ([DOC]) of soil water and
negatively correlated with water fluxes, but no relationship existed between
soil temperature and DOC fluxes at the weekly to monthly scale.
The relationship between water input to soil and DOC fluxes was seasonally
dependent in both plot types. In summer, a water limitation on DOC flux
existed where weekly periods of no flux alternated with periods of large
fluxes at high DOC concentrations. This suggests that DOC fluxes were water-limited and that increased water fluxes over this period result in
proportional increases in DOC fluxes. In contrast, a flushing of DOC from O
horizons (observed as decreasing DOC concentrations) occurred during
increasing water input and decreasing soil temperature in autumn, prior to
snowpack development. Soils of both plot types remained snow-covered all
winter, which protected soils from frost and limited percolation. The
largest water input and soil water fluxes occurred during spring snowmelt
but did not result in the largest fluxes of DOC, suggesting a production
limitation on DOC fluxes over both the wet autumn and snowmelt periods.
While future increases in annual precipitation could lead to increased DOC
fluxes, the magnitude of this response will be dependent on the type and
intra-annual distribution of this increased precipitation.
... The amount of aquatic C exports in the forms of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC; i.e., H 2 CO 3 , HCO − 3 , and CO 2− 3 ), and dissolved CO 2 and CH 4 reflect furthermore the aquatic-terrestrial links between water bodies and the surrounding soil and plants within the landscape (Cole et al., 2007). DOC fluxes vary with different stand ages (Justine et al., 2017;Peichl, Arain, et al., 2014;Peichl et al., 2007) and may account for up to 20% of annual net CO 2 uptake in boreal forest stands (Öquist et al., 2014). DIC fluxes together with the supersaturated CO 2 and CH 4 in the stream discharge (i.e., dissolved CO 2 and CH 4 fluxes) represent a significant channel of C transformation and cycling at the landscape scale (Wallin et al., 2013). ...
The boreal biome exchanges large amounts of carbon (C) and greenhouse gases (GHGs) with the atmosphere and thus significantly affects the global climate. A managed boreal landscape consists of various sinks and sources of carbon dioxide (CO2), methane (CH4), and dissolved organic and inorganic carbon (DOC and DIC) across forests, mires, lakes, and streams. Due to the spatial heterogeneity, large uncertainties exist regarding the net landscape carbon balance (NLCB). In this study, we compiled terrestrial and aquatic fluxes of CO2, CH4, DOC, DIC, and harvested C obtained from tall‐tower eddy covariance measurements, stream monitoring, and remote sensing of biomass stocks for an entire boreal catchment (~68 km2) in Sweden to estimate the NLCB across the land‐water‐atmosphere continuum. Our results showed that this managed boreal forest landscape was a net C sink (NLCB = 39 g C m‐2 yr‐1) with the landscape‐atmosphere CO2 exchange being the dominant component, followed by the C export via harvest and streams. Accounting for the global warming potential of CH4, the landscape was a GHG sink (−237 g CO2‐eq/m2 yr‐1), thus providing a climate‐cooling effect. The CH4 flux contribution to the annual GHG budget increased from 0.6% during spring to 3.2% during winter. The aquatic C loss was most significant during spring contributing 8% to the annual NLCB. We further found that abiotic controls (e.g. air temperature and incoming radiation) regulated the temporal variability of the NLCB whereas land cover types (e.g. mire vs. forest) and management practices (e.g. clear‐cutting) determined their spatial variability. Our study advocates the need for integrating terrestrial and aquatic fluxes at the landscape scale based on tall‐tower eddy covariance measurements combined with biomass stock and stream monitoring to develop a holistic understanding of the NLCB of managed boreal forest landscapes and to better evaluate their potential for mitigating climate change.
... Previous research has examined the characteristics of dissolved organic matter release from either forests (e.g. Baldwin 1999;O'Connell et al. 2000;Peichl et al. 2007;Wilson et al. 2011;Whitworth et al. 2014;Huang et al. 2015), croplands (e.g. Lundquist et al. 1999;Chen et al. 2010;Xu et al. 2013) or pasturelands (e.g. ...
Overbank floods in modified lowland rivers often inundate a mosaic of different land uses (e.g. forests, crops and pastures) on the floodplain. We used a glasshouse experiment to investigate dissolved organic carbon (DOC) and nutrient (TP, NH4+, NOx) releases, chemical oxygen demand (COD) and dissolved oxygen (DO) depletion in water following inundation of soil and vegetation from a lowland river floodplain in southern Australia. Six replicate samples of six intact soil and groundcover treatments were collected during summer; three from a forest (bare soil, wallaby grass and leaf litter) and three from an adjacent paddock (bare soil, wheat and ryegrass). Samples were placed in pots, inundated with river water over 16 days, and their leachates were compared with a river-water control. All vegetated groundcover treatments had significantly higher DOC and COD and significantly less DO at both Day 1 and Day 16 than did the soil-only treatments or the control. Leachates from paddock treatments were less coloured than those from forest treatments, despite having similar concentrations of DOC. Our findings imply that the inundation of any vegetation during summer floods can be a major source of DOC and a major contributor to DO depletion.
... For example, precipitation was negatively correlated with the WEOC concentration (Appendix Fig. 1). Additionally, it has been suggested that the soil water content was positively (Kalbitz et al., 2000), negatively (Peichl et al., 2007) or not correlated (Fröberg et al., 2006) with the WEOC concentration in different studies. We found a strong positive correlation between the soil water content and WEOC concentration, which may indicate that the soil water content has a substantial effect on the WEOC concentration at our sites (Table 3, Table A. 2). ...
We investigated the differences among two types of forest (pine and oak forests) and a meadow in soil water extractable organic carbon (WEOC), ammonium (NH4⁺) and nitrate (NO3⁻) concentrations in the Qinling Mountains, China. Our results showed that soil WEOC, NH4⁺ and NO3⁻ concentrations were higher in the meadow than in the forests, and they were higher in the pine forest than in the oak forest. The soil surface temperature and soil water content were positively correlated with WEOC and inorganic nitrogen concentrations (P < 0.01). In addition, there was a significantly negative correlation between soil WEOC concentration and pH (P < 0.01). Moreover, soil WEOC concentration was positively correlated with the inorganic nitrogen concentration (P < 0.01). Generally, soil WEOC concentration decreased in the forests, and increased in the meadow under warming condition. The effects of warming on soil WEOC and dissolved inorganic nitrogen (DIN) concentrations varied with time. We elucidated that warming had a significant influence on soil WEOC concentration in the pine forest, whereas soil DIN concentration was affected significantly by warming only in the meadow. Our findings indicate that soil WEOC and DIN show different responses to warming in the mountain forest and meadow ecosystems. This study could provide useful insights for the prediction of soil carbon and nitrogen cycling and their responses to climate change in the complex mountain ecosystem.
... Multiple linear regression was conducted to evaluate the important factors (canopy coverage, tree species, tree BAs, tree height, slope, litter thickness, distance from the sampling plot to the top of the slope, litter C, and N content; these data are shown in Table S1) influencing DOM concentration in surficial water. Multiple linear regressions were conducted using the stats package in R Redundancy analysis (RDA) was conducted using the vegan package (Oksanen et al. 2017) to explore the relation between environmental variables and DOM characteristics (DOC, DON, DOC/ DON, and DON%TDN) of PW10. Environmental variables tested in the RDA analysis included soil parameters (SOC, TN, soil available phosphorus, pH, and clay %) and vegetation parameters (species richness, Shannon-Wiener Index, litter weight). ...
Dissolved organic matter is important in the vertical and lateral translocation of nutrients in forest ecosystems. However, little is known about the changes in dissolved organic matter concentration and chemical components in ecosystem sources in humid mountain forests. Here, we measured the concentration and chemical components of dissolved organic matter at throughfall, stemflow, litter leachate, runoff, and soil pore water (at depths of 10 cm, 30 cm, and 60 cm) in a subtropical humid mountain forest during two growing seasons. The concentration of dissolved organic carbon and dissolved nitrogen showed a clear monthly trend. The dissolved organic carbon concentration and the proportion of hydrophobic organic acid in the surficial water were higher than those in the soil pore water, and this difference was accompanied by a decrease in the hydrophobic organic acid concentration from the surficial water to the soil pore water. We also found that dissolved organic matter properties in surficial water were related to canopy cover, tree species, litter carbon content, and slope, whereas dissolved organic matter in soil pore water was associated with soil C, N, and P content and pH. In addition, the rainfall pattern is important to the dissolved organic matter concentration and partitioning within the seven sources. These findings showed that the dissolved organic carbon movement from surficial water into soil pore water is a significant component of carbon cycling in forest ecosystems, and this is important in estimating the carbon budget in forest ecosystems.
... For TF, DOC concentrations documented in the literature ranged from 2 to 35 mg L −1 (Michalzik et al., 2001;Moore, 2003;, for SF from 12 to 95 mg L −1 (Moore, 2003;Levia et al., 2012; and for LL from 14 to 90 mg L −1 (Michalzik et al., 2001;Ide et al., 2017;. Investigating soil solutions, others reported DOC concentrations of 7-40 mg L −1 for topsoil (Moore, 2003;Fellman et al., 2008b;Kindler et al., 2011;Ide et al., 2017) and 2-5 mg L −1 for subsoil solutions (Michalzik et al., 2001;Peichl et al., 2007;Kindler et al., 2011). This pattern indicates that water is enriched in DOM during aboveground ecosystem passage and depleted while passing through mineral soil horizons. ...
... If DOM was immobilized as insoluble metalorganic matter precipitate in B horizons, no limitation by available sorption sites of surfaces of pedogenic (hydr)oxides would apply, so that reductions of DOC concentrations with increasing depth in mineral soil would be independent of the soil OC/(Fe 0 + Al 0 ) saturation index. Consistent with findings in other studies, SUVA 254 values of our DOM samples ranged from 1.8 to 4.7 L mg −1 m −1 for TF (Peichl et al., 2007;, from 1.9 to 11.2 L mg −1 m −1 for SF and between 2.7 and 5.2 L mg −1 m −1 for LL (Peichl et al., 2007;. This indicates an increasing share of aromatic DOM compounds when passing through the aboveground forest ecosystem. ...
... If DOM was immobilized as insoluble metalorganic matter precipitate in B horizons, no limitation by available sorption sites of surfaces of pedogenic (hydr)oxides would apply, so that reductions of DOC concentrations with increasing depth in mineral soil would be independent of the soil OC/(Fe 0 + Al 0 ) saturation index. Consistent with findings in other studies, SUVA 254 values of our DOM samples ranged from 1.8 to 4.7 L mg −1 m −1 for TF (Peichl et al., 2007;, from 1.9 to 11.2 L mg −1 m −1 for SF and between 2.7 and 5.2 L mg −1 m −1 for LL (Peichl et al., 2007;. This indicates an increasing share of aromatic DOM compounds when passing through the aboveground forest ecosystem. ...
Dissolved organic matter (DOM) is part of the biogeochemical cycles of carbon
and nutrients, carries pollutants and drives soil formation. The DOM
concentration and properties along the water flow path through forest
ecosystems depend on its sampling location and transformation processes. To
improve our understanding of the effects of forest management, especially
tree species selection and management intensity, on DOM concentrations and
properties of samples from different ecosystem fluxes, we studied
throughfall, stemflow, litter leachate and mineral soil solution at 26 forest
sites in the three regions of the German Biodiversity Exploratories. We
covered forest stands with three management categories (coniferous, deciduous
age class and unmanaged beech forests). In water samples from these forests,
we monitored DOC concentrations over 4 years and characterized the quality
of DOM with UV-vis absorption, fluorescence spectroscopy combined with
parallel factor analysis (PARAFAC) and Fourier transform ion cyclotron
resonance mass spectrometry (FT-ICR-MS). Additionally, we performed
incubation-based biodegradation assays. Multivariate statistics revealed
strong significant effects of ecosystem fluxes and smaller effects of main
tree species on DOM quality. Coniferous forests differed from deciduous
forests by showing larger DOC concentrations, more lignin- and protein-like
molecules, and fewer tannin-like molecules in throughfall, stemflow, and
litter leachate. Cluster analysis of FT-ICR-MS data indicated that DOM
compositions, which varied in aboveground samples depending on tree species,
become aligned in mineral soil. This alignment of DOM composition along the
water flow path in mineral soil is likely caused by microbial production and
consumption of DOM in combination with its interaction with the solid phase,
producing a characteristic pattern of organic compounds in forest mineral
soils. We found similarly pronounced effects of ecosystem fluxes on the
biodegradability of DOM, but surprisingly no differences between deciduous
and coniferous forests. Forest management intensity, mainly determined by
biomass extraction, contribution of species, which are not site-adapted, and
deadwood mass, did not influence DOC concentrations, DOM composition and
properties significantly.
... LMW materials refer to carbohydrates, small proteins/peptides, organic acids (OA), amino acids, vitamins, hormones, etc (Rengel, 2002). HMW compounds mainly contain humics, mucilage polysaccharides, secretory proteins and ectoenzymes (Matthias et al., 2007). So, there are abundant organic functional groups (e.g., amide, carboxyl, phenol, and hydroxyl) with high active sites in DOM. ...
High concentration of Cu ²⁺ in swine wastewater raises concerns about its potential adverse effects on nutrient removal by aquatic plants like duckweed. In this work, the effects of copper ions on nutrient removal and release of dissolved organic matter (DOM)were investigated in duckweed systems. Results showed that the removal performance of ammonia nitrogen (NH 3 [sbnd]N)and total phosphorus (TP)increased at 0.1–1.0 mg/L of Cu ²⁺ , while dropped at 2.0–5.0 mg/L of Cu ²⁺ . A novel kinetic model in which Cu ²⁺ was taken into account was then developed which was used to optimize Cu ²⁺ concentration at 0.96 mg/L for nutrient removal in duckweed systems. NADH, detected in DOM by the parallel factor (PARAFAC)analysis, exhibited high capacities of binding copper ions, so it played an important role on the decrease of Cu ²⁺ concentrations in duckweed systems. The principle component analysis (PCA)showed that the dominant DOM were lower molecular weight compounds at 1.0 mg/L of Cu ²⁺ and higher molecular weight compounds at 2.0–5.0 mg/L of Cu ²⁺ . The bonds of C[sbnd]H (humic-like), N[dbnd]O (NO 3⁻ )and Ar[sbnd]H (tyrosine)in DOM were responsible for not only the fastest binding with Cu ²⁺ from the result of the two-dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR-CoS)but also the variations of DOM conformations at a critical concentration of 0.5 mg/L Cu ²⁺ from the perturbation correlation moving window two-dimensional (PCMW2D)analysis. These findings lead to a better understanding on the environmental behaviors and mechanisms of Cu ²⁺ in duckweed systems.
