Throughfall In Forest Research Articles

Impact of seasonality and forest stand age on ion deposition inrehabilitated forests.

This study examines the critical interaction between seasonal precipitation variability and forest maturity in determining ion deposition patterns in rehabilitated forest ecosystems. This research was conducted in rehabilitated forest sites in Bintulu, Sarawak, Malaysia that had ecologically similar plant distribution, species, and age in each planting area. This facilitated the standardization of rainfall deposition in the different study plots which streamlined the study of these specific facets of ecosystem dynamics. The goal is to understand how seasonal changes and the age of the forest influence the chemical composition of the flux that relates to the movement and deposition of nutrients through the forest ecosystem. This flux is a key factor in the health of the forest ecosystem and nutrient cycling. Using ion exchange resin (IER) samplers, we accurately measured and compared the deposition of different ions (Ca2+, Na+, Fe2+, Cu2+, NO3 -, NH4 + and SO4 2-) across different seasons and forest ages. The deposition of Ca2+ and NH₄+ was significantly lower in the low-precipitation season than in the high-precipitation season in all forest stands, regardless of the year they were established (1996, 1999, 2002, 2005, and 2009). In contrast, ions such as Na+, Fe2+, Cu2+, NO3 - and SO4 2- showed no clear seasonal fluctuations. In addition, the study shows that through-fall in forest stands from 2002, 2005 and 2009 had higher concentrations of Ca2+ in both seasons than in 1996 and 1999. Interestingly, forest stands from 2009 and 2002 had elevated levels of Na+ and SO₄2- in seasons with low precipitation, while stands from 1996 had higher levels in seasons with high precipitation. Our results emphasize the crucial role of precipitation amount and canopy age in determining ion deposition in forest ecosystems. By demonstrating the significant influence of precipitation seasonality and forest maturity on the chemical composition of throughfall, this study contributes to a deeper understanding of nutrient dynamics in developing forest landscapes and provides valuable insights for ecological restoration measures.

Root water uptake patterns are controlled by tree species interactions and soil water variability

Abstract. Root water uptake depends on soil moisture which is primarily fed by throughfall in forests. Several biotic and abiotic elements shape the spatial distribution of throughfall. It is well documented that throughfall patterns result in reoccurring higher and lower water inputs at certain locations. However, how the spatial distribution of throughfall affects root water uptake patterns remains unresolved. Therefore, we investigate root water uptake patterns by considering spatial patterns of throughfall and soil water in addition to soil and neighboring tree characteristics. In a beech-dominated mixed deciduous forest in a temperate climate, we conducted intensive throughfall sampling at locations paired with soil moisture sensors during the 2019 growing season. We employed a linear mixed-effects model to understand controlling factors in root water uptake patterns. Our results show that soil water patterns and interactions among neighboring trees are the most significant factors regulating root water uptake patterns. Temporally stable throughfall patterns did not influence root water uptake patterns. Similarly, soil properties were unimportant for spatial patterns of root water uptake. We found that wetter locations (rarely associated with throughfall hotspots) promoted greater root water uptake. Root water uptake in monitored soil layers also increased with neighborhood species richness. Ultimately our findings suggest that complementarity mechanisms within the forest stand, in addition to soil water variability and availability, govern root water uptake patterns.

Atmosphere-Transported Emerging and Persistent Contaminants (EPCs) in Rainfall and Throughfall: Insights from a Rural Site in Northern Thailand

This study investigates the presence and concentrations of emerging and persistent contaminants (EPCs) in rainwater and throughfall water collected from urban areas and agricultural lands in northern Thailand. It focuses on one daily-use compound (caffeine), two industrial compounds (4-nitrophenol and tris(2-butoxyethyl) phosphate (TBEP)), and three agrichemicals (atrazine, fenobucarb, and 2,4-D). Additionally, information is provided regarding the presence of acetaminophen, fexofenadine, diphenhydramine, and gabapentin. Small differences in the chemical composition of the six main contaminants were observed between rainwater and forest throughfall water. However, significant variations were found in the concentration ranges of each EPC. In most cases, throughfall samples exhibited slightly higher concentrations, suggesting a limited contribution from dry deposition compared to rainfall. Limited reliable evidence was found concerning seasonal patterns in EPC concentrations in precipitation (rainfall and throughfall) and surface water samples in remote ponds and reservoirs. The transportation of EPCs via rainwater appears to vary among the compounds tested and is likely to vary from one rainfall event to another, rather than showing a strong and common seasonal response within the monsoon rainfall regime. These findings suggest that the transport of EPCs to remote areas via rainfall does occur for some EPCs. However, the dominance of this process over other transport mechanisms could not be determined with high confidence.

Seasonal dynamics of canopy interception loss within a deciduous and a coniferous forest

AbstractCanopy interception loss is a key process in forest hydrology and the role of interception loss in relation to the forest water budgets and future impact of afforestation on water resources is important to quantify. Based on high frequency in situ monitoring, the effect of species‐ and leaf‐cover‐specific canopy structure metrics for interception loss estimation is examined at the two most typical forest types in Denmark. First, interception loss is estimated from precipitation and throughfall data collected in two even‐aged (40–60 years) temperate oak (deciduous) and Norway spruce (coniferous) forests over 13 and 11 months, respectively. Second, based on these observations we estimated canopy structure parameters relevant for interception loss; direct throughfall (ρ), the precipitation necessary to saturate the canopy (P'), the canopy evaporation as a fraction of precipitation (EC/P) and canopy storage capacity (S). Third, we compare observation‐based interception loss with predictions obtained by the analytical Gash interception model using the derived canopy structure parameters. Lastly, the effect of species‐ and leaf‐cover on the interception loss is quantified by applying the canopy structure parameters of the deciduous and coniferous forest on the same daily precipitation data set of approximately 1 year in the Gash model. We found that the derived canopy structure parameters reflect the seasonal change in the leaf cover of the deciduous forest and different parameters are identified for the two forest types. In the deciduous forest, improved agreement between observation‐based and predicted interception loss is obtained using canopy structure parameters for the leafless and full‐foliage periods instead of annual average values. The share of throughfall and interception loss to precipitation (total sum of precipitation = 526 mm) is 65% (340 mm) and 35% (186 mm) for the deciduous forest, respectively, and 49% (260 mm) and 51% (266 mm) for the coniferous forest, respectively. A seasonal variation of interception loss is observed in the deciduous forest where the share of interception loss to precipitation is 40% during the period with leaves on the trees (June to November) and 22% for the leafless periods (December to May). Thus, species‐ and leaf‐cover‐specific canopy structure metrics enhance model performance of throughfall and interception loss dynamics in forests.

Quantifying throughfall, stemflow and interception loss in five vegetation communities in a maritime raised bog

Throughfall and stemflow observations were used to quantify interception loss from five vegetation communities with complex multi-layered vegetative structure over the course of a year in a maritime raised bog in southwestern British Columbia, Canada. Separate plot-averaged interception loss estimates for trees and shrubs were computed from randomly relocated throughfall collectors and stemflow observations of trees. Independent throughfall observations from individual trees stratified by distance from the trunk were scaled to the plot extent based on tree configuration and canopy structure derived from LiDAR. Estimates from tree-based sampling compared favorably with plot-averaged tree throughfall means; however, results were biased towards underestimating throughfall compared to estimates from random observations possibly due to evaporation from the tree-based throughfall samplers, an issue that could be remedied using a different design. Nevertheless, this approach shows potential as a tool for estimating throughfall in forests with heterogeneous vegetation characteristics, and should be further tested and developed. Annual tree interception loss from birch was 15% of gross precipitation and average throughfall ranged from 75% to 83% during the leafed and leafless seasons, respectively. Tree interception loss in three pine stands of varying height and density was 13, 15 and 9% of gross precipitation. Stemflow from trees contributed between 0.4 and 3% of net precipitation, and smaller trees generated stemflow more efficiently. Interception loss from shrub ranged from 20% to 36% of gross precipitation. Tree throughfall increased with distance from trunks whereas shrub throughfall showed an opposite trend, and the relationship varied between stands. This study demonstrates the importance of shrub vegetation when quantifying net precipitation in vegetation communities typical of peatlands.

Throughfall and stemflow nutrient flux in deodar and oak forests, Garhwal Himalaya, India

Abstract A study to understand the throughfall and stemflow chemistry under deodar and oak forests of Garhwal Himalaya was conducted during 2014–2015. Total rainfall during experimental period was 1473.8 mm and estimated interception loss was 34.018% for deodar forest, 24.85% for oak forest. Stemflow represented the minimum proportion of gross rainfall, i.e. 0.321% in deodar forest and 0.463% in oak forest. pH of throughfall and stemflow in both deodar (6.087 and 6.47 respectively) and oak forests (6.75 and 7.03 respectively) was significantly more acidic than the gross rainfall (7.15). Electrical conductivity was recorded higher in deodar stemflow (231.89 μs/cm) and throughfall (102.75 μs/cm) compared to oak forest (172.92 μs/cm and 83.83 μs/cm respectively). Net nutrient leaching and stemflow were considerably higher from oak forest than deodar forest. Oak forest has better water yield capacity than deodar forest as the interception loss was higher in deodar forest. The idea of sustainable agriculture may be possible surrounding such forests as the need for chemical fertilizer and water can be met by the nutrient-rich soil, available soil moisture and surface water.

Variations in the natural 13C and 15N abundance of plants and soils under long-term N addition and precipitation reduction: interpretation of C and N dynamics

BackgroundThe nitrogen isotope natural abundance (δ15N) provides integrated information on ecosystem N dynamics, and carbon isotope natural abundance (δ13C) has been used to infer how water-using processes of plants change in terrestrial ecosystems. However, how δ13C and δ15N abundances in plant life and soils respond to N addition and water availability change is still unclear. Thus, δ13C and δ15N abundances in plant life and soils were used to investigate the effects of long-time (10 years) N addition (+ 50 kg N·ha− 1·yr− 1) and precipitation reduction (− 30% of throughfall) in forest C and N cycling traits in a temperate forest in northern China.ResultsWe analyzed the δ13C and δ15N values of dominant plant foliage, litterfall, fungal sporophores, roots, and soils in the study. The results showed that δ15N values of foliage, litterfall, and surface soil layer’s (0–10 cm) total N were significantly increased by N addition, while δ15N values of fine roots and coarse roots were considerably decreased. Nitrogen addition also significantly increased the δ13C value of fine roots and total N concentration of the surface soil layer compared with the control. The C concentration, δ13C, and δ15N values of foliage and δ15N values of fine roots were significantly increased by precipitation reduction, while N concentration of foliage and litterfall significantly decreased. The combined effects of N addition and precipitation reduction significantly increased the δ13C and δ15N values of foliage as well as the δ15N values of fine roots and δ13C values of litterfall. Furthermore, foliar δ15N values were significantly correlated with foliage δ13C values, surface soil δ15N values, surface soil C concentration, and N concentrations. Nitrogen concentrations and δ13C values of foliage were significantly correlated with δ15N values and N concentrations of fine roots.ConclusionsThis indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15N under precipitation reduction, suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.

Advantages of rainfall partitioning by the global invader Ligustrum lucidum over the dominant native Lithraea molleoides in a dry forest

Vegetation canopy plays a key role in the local water balance by partitioning rainfall into interception, throughfall and stemflow in dry forests. Many invasive plants have the capacity to replace native species and alter the net amount and spatial distribution of rainfall reaching the soil. In this paper, we aimed to compare the rainfall partitioning for the invader Ligustrum lucidum and the dominant native Lithraea molleoides, to evaluate the influence of morphological characteristics on stemflow generation in both species, and to explore spatio-temporal patterns of throughfall at stand scale. Stemflow percentage for L. lucidum was hugely higher than for L. molleoides (18 and 1%, respectively), which overcompensated its lower throughfall percentage (58.1 and 68.6%, respectively). Interception losses were lower for L. lucidum than for L. molleoides (23.2 and 30.6%, respectively). The minimum rainfall amount needed to generate throughfall and stemflow was 1.8 and 0.5 mm for L. lucidum, while 2.2 and 7.2 mm for L. molleoides. The differences in morphological characteristics between species mainly explained the stemflow generation. The increment on tree basal area, projected canopy area, and number of branches favored stemflow in L. lucidum, but not in L. molleoides. The throughfall spatial patterns showed that the dripping from different canopy densities was homogenous in L. lucidum stands, whereas throughfall increase towards more opened-canopies in L. molleoides stands. Lateral inflows were registered from small-scale crown sections at both forest stands, but less frequent in L. lucidum stands. The time stability of throughfall pattern differed between forest stands. Based on our results, relatively higher stemflow and lower interception losses for L. lucidum than for L. Molleoides may represent a competitive advantage in terms of plant invasion in water-limited ecosystems. These findings highlight the need for further inquiries determining the underlying role of rainfall partitioning in the invasion process of woody species.

Comportamento físico da precipitação interna em um povoamento de <i>Eucalyptus</i>

A compreensão das características físicas da chuva e sua interação com a paisagem possibilita o desenvolvimento de modelos matemáticos mais condizentes com a realidade além de auxiliar no planejamento eficiente de obras e práticas agrícolas. O objetivo deste estudo foi caracterizar a precipitação interna de um povoamento de Eucalyptus no município de Lavras, Minas Gerais, associado a padrões hidrológicos e potencial erosivo. Para individualização dos eventos de precipitação interna foram adotados os intervalos de 3 e 6 horas entre chuvas. Para cada abordagem foi realizada a classificação do padrão hidrológico da precipitação, incidente e interna, e, associados a estes, as características das chuvas: lâmina precipitada, tempo de duração, energia cinética, intensidades média e máxima, e erosividade. A precipitação interna no povoamento de eucalipto representou 79,2% da precipitação externa. A precipitação interna mostrou-se 36,4% menos erosiva do que a precipitação externa, na qual o padrão avançado foi identificado como predominante na série analisada em ambas as metodologias de individualização dos eventos.

Estimates of exceedances of critical loads for acidifying deposition in Alberta and Saskatchewan

Abstract. Estimates of potential harmful effects on ecosystems in the Canadian provinces of Alberta and Saskatchewan due to acidifying deposition were calculated, using a 1-year simulation of a high-resolution implementation of the Global Environmental Multiscale-Modelling Air-quality and Chemistry (GEM-MACH) model, and estimates of aquatic and terrestrial ecosystem critical loads. The model simulation was evaluated against two different sources of deposition data: total deposition in precipitation and total deposition to snowpack in the vicinity of the Athabasca oil sands. The model captured much of the variability of observed ions in wet deposition in precipitation (observed versus model sulfur, nitrogen and base cation R2 values of 0.90, 0.76 and 0.72, respectively), while being biased high for sulfur deposition, and low for nitrogen and base cations (slopes 2.2, 0.89 and 0.40, respectively). Aircraft-based estimates of fugitive dust emissions, shown to be a factor of 10 higher than reported to national emissions inventories (Zhang et al., 2018), were used to estimate the impact of increased levels of fugitive dust on model results. Model comparisons to open snowpack observations were shown to be biased high, but in reasonable agreement for sulfur deposition when observations were corrected to account for throughfall in needleleaf forests. The model–observation relationships for precipitation deposition data, along with the expected effects of increased (unreported) base cation emissions, were used to provide a simple observation-based correction to model deposition fields. Base cation deposition was estimated using published observations of base cation fractions in surface-collected particles (Wang et al., 2015).Both original and observation-corrected model estimates of sulfur, nitrogen, and base cation deposition were used in conjunction with critical load data created using the NEG-ECP (2001) and CLRTAP (2017) methods for calculating critical loads, using variations on the Simple Mass Balance model for terrestrial ecosystems, and the Steady State Water Chemistry and First-order Acidity Balance models for aquatic ecosystems. Potential ecosystem damage was predicted within each of the regions represented by the ecosystem critical load datasets used here, using a combination of 2011 and 2013 emissions inventories. The spatial extent of the regions in exceedance of critical loads varied between 1 × 104 and 3.3 × 105 km2, for the more conservative observation-corrected estimates of deposition, with the variation dependent on the ecosystem and critical load calculation methodology. The larger estimates (for aquatic ecosystems) represent a substantial fraction of the area of the provinces examined.Base cation deposition was shown to be sufficiently high in the region to have a neutralizing effect on acidifying deposition, and the use of the aircraft and precipitation observation-based corrections to base cation deposition resulted in reasonable agreement with snowpack data collected in the oil sands area. However, critical load exceedances calculated using both observations and observation-corrected deposition suggest that the neutralization effect is limited in spatial extent, decreasing rapidly with distance from emissions sources, due to the rapid deposition of emitted primary dust particles as a function of their size. We strongly recommend the use of observation-based correction of model-simulated deposition in estimating critical load exceedances, in future work.

Correction of Canopy Interception Loss Measurements in Temperate Forests: A Comparison of Necessary Adjustments among Three Different Rain Gauges Based on a Dynamic Calibration Procedure

ABSTRACT Tipping-bucket rain gauges are used widely to measure the amount and intensity of gross rainfall and throughfall in forests, despite the fact that their systematic underestimations are well known. To the knowledge of the authors, no dynamic calibrations for the budget-conscious Davis gauge (Rain Collector II, Davis Instruments, California) have been published. Thus, five Davis gauges were dynamically calibrated under different constant intensities of inflow and a correction equation was derived. The derived correction equation for the Davis rain gauge is V = −0.2005Q2 + 0.702Q + 1 (R2 = 0.95, p < 0.001), where V is the actual volume of a single tip scaled by the static volume of single tip c (cm3 cm−3), and Q is actual inflow scaled by c (s−1). The Davis rain gauge was then compared to the Onset rain gauge and the Ota rain gauge, and the corrections were applied to field observation data of canopy interception loss from a temperate forest in Japan. It is necessary to apply corrections to gross rainfall and throughfall data by tipping-bucket gauges because the results reveal that such corrections change the actual interception loss computed by values from −20% to 40%, depending on the combination of gauges employed. This difference is not trivial. The systematic bias of the Davis gauge is larger than the Onset and Ota gauges. Thus, it is recommended that researchers using Davis rain gauges apply the dynamically calibrated correction equation presented here to ensure more reliable estimates of gross rainfall and canopy interception loss.

Acclimation of branch and leaf hydraulics in adult Fagus sylvatica and Picea abies in a forest through-fall exclusion experiment.

Decreasing water availability due to climate change poses the question of whether and to what extent tree species are able to hydraulically acclimate and how hydraulic traits of stems and leaves are coordinated under drought. In a through-fall exclusion experiment, hydraulic acclimation was analyzed in a mixed forest stand of Fagus sylvatica L. and Picea abies (L.) Karst. In drought-stressed (TE, through-fall exclusion over 2 years) and control (CO) trees, hydraulic vulnerability was studied in branches as well as in leaves (F. sylvatica) and end-twigs (P. abies, entirely formed during the drought period) sampled at the same height in sun-exposed portions of the tree crown. In addition, relevant xylem anatomical traits and leaf pressure-volume relations were analyzed. The TE trees reached pre-dawn water potentials down to -1.6 MPa. In both species, water potentials at 50% loss of xylem hydraulic conductivity were ~0.4 MPa more negative in TE than in CO branches. Foliage hydraulic vulnerability (expressed as water potential at 50% loss of leaf/end-twig hydraulic conductance) and water potential at turgor loss point were also, respectively, 0.4 and 0.5 MPa lower in TE trees. Minor differences were observed in conduit mean hydraulic diameter and cell wall reinforcement. Our findings indicate significant and fast hydraulic acclimation under relatively mild drought in both tree species. Acclimation was well coordinated between branches and foliage, which might be essential for survival and productivity of mature trees under future drought periods.

Effects of canopy interception on epikarst water chemistry and its response to precipitation in Southwest China

The effects of vegetation on epikarst water are unclear due to the lack of understanding of the effects of canopy interception on epikarst water properties. In this study, throughfall (T), stemflow (S), borehole (B) and epikarst (E) spring water (PTSBE profile) from two different vegetation canopies, forest and shrub, from July to October 2015 in Southwest China, were sampled to investigate the effects of canopy interception on epikarst water chemistry and its response to precipitation. Significant difference in pH, EC, and DO concentrations exists among precipitation, throughfall, stemflow and epikarst water. Stemflow is an acidic input and throughfall is a less acidic input to the epikarst zone. The mean δ18O value of precipitation is −7.45‰, and the mean δ18O values of throughfall in forest and shrub are −7.11 and −7.37‰, respectively. The results indicate that precipitation becomes acid and nutrient enrichment after canopy interception. The canopy also alters hydrologic cycle processes and enhances the precipitation solute input to the epikarst zone. Our study suggests that precise interpretation of the mechanisms of carbonate rock dissolution and deposition requires the use of throughfall and stemflow.

Dissolved Organic and Inorganic Carbon Flow Paths in an Amazonian Transitional Forest

As a raindrop falls from the atmosphere, over vegetation and forest canopies, and enters soils and streams it experiences a dynamic exchange of carbon constituents with the surrounding environment. Understanding the magnitude and dynamics of carbon export in above and below ground flow paths is critical for constraining the influence of terrestrial and aquatic ecosystems on global carbon cycling. Here we examine the concentration and flux of dissolved organic and inorganic carbon (DOC and DIC) in rainfall, throughfall, stemflow, overland flow, soil solution, groundwater, and stream water in an Amazonian transitional forest located near the arc of deforestation. Rainfall was enriched in DOC by interactions with atmospheric particles derived from both biogenic and anthropogenic emissions, resulting in a flux of 82.3 kg C ha-1 yr-1, which was the largest flux from each respective flow path. Forest throughfall, stemflow, and direct overland flow mobilized DOC from products of terrestrial primary production and decomposition. Net throughfall represented the second largest DOC flux (68.4 kg C ha-1 yr-1), whereas stemflow and overland flow only had a flux of 1.5 and 3.9 kg C ha-1 yr-1, respectively. Much of the DOC in above ground flow paths was removed from solution as the rain percolated through soil layers due to both biological decomposition and sorption/desorption to mineral surfaces, resulting in low concentrations in stream and groundwater (2.6 ± 2.4 mg L-1 and 1.45 ± 0.3 mg L-1, respectively) relative to throughfall (43.9 ± 5.2 mg L-1) and stemflow (30.6 ± 2.7 mg L-1). The flux of DIC in each respective flow path was generally lower than for DOC, and likely driven by atmospheric gas exchange and inputs from respiration and decomposition. DOC concentrations in above ground flow paths were highest during the first rainfall after a dry period, whereas DIC concentrations generally increased throughout the rainy season as soil moisture increased.

Role of natural organic matter on iodine and 239,240Pu distribution and mobility in environmental samples from the northwestern Fukushima Prefecture, Japan

In order to assess how environmental factors are affecting the distribution and migration of radioiodine and plutonium that were emitted from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, we quantified iodine and 239,240Pu concentration changes in soil samples with different land uses (urban, paddy, deciduous forest and coniferous forest), as well as iodine speciation in surface water and rainwater. Sampling locations were 53–63 km northwest of the FDNPP within a 75-km radius, in close proximity of each other. A ranking of the land uses by their surface soil (<4 cm) stable 127I concentrations was coniferous forest > deciduous forest > urban > paddy, and 239,240Pu concentrations ranked as deciduous forest > coniferous forest > paddy ≥ urban. Both were quite distinct from that of 134Cs and 137Cs: urban > coniferous forest > deciduous forest > paddy, indicating differences in their sources, deposition phases, and biogeochemical behavior in these soil systems. Although stable 127I might not have fully equilibrated with Fukushima-derived 129I, it likely still works as a proxy for the long-term fate of 129I. Surficial soil 127I content was well correlated to soil organic matter (SOM) content, regardless of land use type, suggesting that SOM might be an important factor affecting iodine biogeochemistry. Other soil chemical properties, such as Eh and pH, had strong correlations to soil 127I content, but only within a given land use (e.g., within urban soils). Organic carbon (OC) concentrations and Eh were positively, and pH was negatively correlated to 127I concentrations in surface water and rain samples. It is also noticeable that 127I in the wet deposition was concentrated in both the deciduous and coniferous forest throughfall and stemfall water, respectively, comparing to the bulk rainwater. Further, both forest throughfall and stemflow water consisted exclusively of organo-iodine, suggesting all inorganic iodine in the original bulk deposition (∼28.6% of total iodine) have been completely converted to organo-iodine. Fukushima-derived 239,240Pu was detectable at a distance ∼61 km away, NW of FDNPP. However, it is confined to the litter layer, even three years after the FDNPP accident-derived emissions. Plutonium-239,240 activities were significantly correlated with soil OC and nitrogen contents, indicating Pu may be associated with nitrogen-containing SOM, similar to what has been observed at other locations in the United States. Together, these finding suggest that natural organic matter (NOM) plays a key role in affecting the fate and transport of I and Pu and may warrant greater consideration for predicting long-term stewardship of contaminated areas and evaluating various remediation options in Japan.

Reactivity of dissolved organic matter in response to acid deposition

Fluvial export of organic matter from the terrestrial catchment to the aquatic system is a large and increasing carbon flux. The successful reduction in sulfuric acid deposition since the 1980s has been shown to enhance the mobility of organic matter in the soil, with more terrestrially derived dissolved organic matter (DOM) reaching aquatic systems. Changes in soil acidity also affect the quality of the DOM. In this study we explore the consequences this may have on the reactivity and turnover of the terrestrially derived DOM as it reaches the aquatic system. DOM of different quality (estimated by absorbance, fluorescence and size exclusion chromatography) was produced through extraction of boreal forest O-horizon soils from podzol at two sulfuric acid concentrations corresponding to natural throughfall in spruce forest in Southern Sweden around 1980 and today. Extraction was done using two different methods, i.e. field leaching and laboratory extraction. The DOM extracts were used to assess if differences in acidity generate DOM of different reactivity. Three reactivity experiments were performed: photodegradation by UV exposure, biodegradation by bacteria, and biodegradation after UV exposure. Reactivity was assessed by measuring loss of dissolved organic carbon and absorbance, change in fluorescence and molecular weight, and bacterial production. DOM extracted at lower sulfuric acid concentration was more susceptible to photooxidation, and less susceptible to bacterial degradation, than DOM extracted at a higher sulfuric acid concentration. Thus the relative importance of these two turnover processes may be altered with changes in acid deposition.

Spatial variability of throughfall in a Pinus tabulaeformis plantation forest in Loess Plateau, China

ABSTRACTThroughfall varies in space, which complicates measurements and makes it difficult to achieve accurate spatial representation. In the present research, we measured gross rainfall and throughfall from May 2011 to September 2012, leaf area index, and locations of trees within a Pinus tabulaeformis plantation forest in the Loess Plateau of northwestern China. The spatial heterogeneity of throughfall and related factors, as well as the minimum number and locations of collectors needed to measure throughfall accurately, were analyzed by statistical techniques. The results indicated that the throughfall was concentrated at the canopy edge, indicating that the edge of the canopy of P. tabulaeformis had a convergence effect on throughfall. The analysis of semivariance of throughfall demonstrated that canopy structure was a key factor influencing spatial variation of throughfall in low rainfall events, but measurement errors and other nonspatial variables were the primary factors affecting the variation of throughfall in high rainfall events. Based on the mean throughfall at different proportions of canopy radius centered on the individual tree stem, the minimum number and locations of collectors needed to accurately measure throughfall was estimated. In this study, four rain collectors (diameter 20 cm) at the 3/5 canopy radius could reasonably represent the average throughfall under the individual P. tabulaeformis canopy.

Erratum to: Long-term changes in acidity and DOC in throughfall and soil water in Finnish forests

Erratum to: Long-term changes in acidity and DOC in throughfall and soil water in Finnish forests

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.

Modeling of leachable 137Cs in throughfall and stemflow for Japanese forest canopies after Fukushima Daiichi Nuclear Power Plant accident

The Fukushima accident dispersed significant amounts of radioactive cesium (Cs) in the landscape. Our research investigated, from June 2011 to November 2013, the mobility of leachable Cs in forests canopies. In particular, 137Cs and 134Cs activity concentrations were measured in rainfall, throughfall, and stemflow in broad-leaf and cedar forests in an area located 40km from the power plant.Leachable 137Cs loss was modeled by a double exponential (DE) model. This model could not reproduce the variation in activity concentration observed. In order to refine the DE model, the main physical measurable parameters (rainfall intensity, wind velocity, and snowfall occurrence) were assessed, and rainfall was identified as the dominant factor controlling observed variation. A corrective factor was then developed to incorporate rainfall intensity in an improved DE model.With the original DE model, we estimated total 137Cs loss by leaching from canopies to be 72±4%, 67±4%, and 48±2% of the total plume deposition under mature cedar, young cedar, and broad-leaf forests, respectively. In contrast, with the improved DE model, the total 137Cs loss by leaching was estimated to be 34±2%, 34±2%, and 16±1% of the total plume deposition under mature cedar, young cedar, and broad-leaf forests, respectively. The improved DE model corresponds better to observed data in literature.Understanding 137Cs and 134Cs forest dynamics is important for forecasting future contamination of forest soils around the FDNPP. It also provides a basis for understanding forest transfers in future potential nuclear disasters.