Throughfall Samples Research Articles

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.

Canopy Leaching Rather than Desorption of PM2.5 From Leaves Is the Dominant Source of Throughfall Dissolved Organic Carbon in Forest

AbstractDissolved organic carbon (DOC) in throughfall plays a vital role in providing carbon and energy to organisms in forests. We utilized carbon isotope analysis to allocate the sources of throughfall DOC, including leaching from plant tissues, PM2.5 deposition on plant foliage, and precipitation. Rainwater, PM2.5, and throughfall samples were collected from pine and oak forests between March and November 2021. The mean concentration of throughfall DOC was 7.9 mg L−1, approximately six times higher than that of rainfall. The mean Δ14C of throughfall DOC was −38.2‰, ∼200‰ higher than that of rainwater or PM2.5. Mass balance estimates revealed that canopy leaching contributed to ∼83% of throughfall DOC, while desorption of PM2.5 and rainwater accounted for only ∼3% and ∼14% of throughfall DOC, respectively. These results clearly highlight canopy leaching as the primary source of carbon input to the forest floor, with a relatively minor contribution from PM2.5 desorption on leaves.

Spatio‐temporal variability and intra‐event variation of throughfall ammonium and nitrate in a pine plantation

AbstractForest canopies are the functional interface between ecosystem and the atmospheric nitrogen (N) deposition. However, the sources of spatio‐temporal variability and intra‐event variation of N deposition via throughfall (TF) remain ambiguous. Here, we analysed TF samples for concentrations and fluxes of ammonium (NH4+) and nitrate (NO3−) using an array of 20 fixed‐position collectors on an event and within event basis throughout the 2019 growing season in a Chinese pine plantation, Northern China. Results showed that the volume weighted mean concentrations of NH4+ and NO3− in TF were significantly higher than those in bulk precipitation (BP) during the study period. A canopy budget model indicated that canopy uptake was more dominant than dry deposition for NH4+, while the reverse was true for NO3−. This caused a comparable TF NH4+ flux but an enhanced TF NO3− fluxes compared to BP. The intra‐event trend and magnitude of TF NH4+ and NO3− concentrations were influenced by the antecedent dry period and rainfall intensity, and indicated that biological nitrification may occur in the canopies. In addition, due to the larger of canopy NH4+ uptake that counteracted the amplifying effect of dry deposition, the spatial variability of TF NH4+ concentration was significantly lower than that of TF NO3− concentration, and exhibited more temporal persistence. No relationship was found between the spatial distribution of TF NH4+ concentration and the TF amount, the distance to the nearest trunk, nor the canopy cover, whereas the TF NO3− concentration was significantly related to the TF amount and the canopy cover. These findings can enhance our understanding of N processes within canopies, and have important implications for evaluating the impacts of N deposition in forest ecosystems.

A Method Proposal for Throughfall Measurement in Grassland at Plot Scale in Temperate Climate: ‘Interception Tubes’

While net precipitation entering the soil is commonly measured in woody ecosystems, there is a lack of field measurements for herbaceous vegetation. Small canopy heights and fragile stem structures are the primary challenges for net precipitation sampling in grasslands under field conditions. We designed a new in situ device, “interception tubes”, for throughfall sampling in temperate grasslands. The instrument allows a natural development of grass canopy and sampling at multiple locations. Although it does not strictly separate throughfall and stemflow, the dominant part of the collected water is throughfall. We tested the interception tubes for splash loss with a drip experiment. Next, we evaluated the tubes’ measurements in a field installation at 25 locations both with and without vegetation cover. Also, we used measurements of gross precipitation, canopy height and soil water content to check the plausibility of the measurements. The experiment showed splash loss for the tubes is small ( < 3%) for the typical rain drop size for the growing season in the region, as well as for throughfall drops of lower falling velocity. In the uncovered period, splash loss corrected tubes’ measurements were generally smaller than classical funnel measurements. But the statistical model revealed that the slope of their relationship is close to unity (0.92) when accounting for topography and was probably related to wind effects. During the covered period, grass height systematically reduced below canopy precipitation measured by the tubes, indicating that they can capture spatial canopy drip patterns under denser grass foliage. The canopy height also altered the wind effect on the tube measurements. As in forest ecosystems, below canopy precipitation patterns were temporally stable and smaller events increased the spatial heterogeneity. The measured below canopy precipitation was between 95% and 22% that above, and grass height amplified the loss. The soil water balance showed the tubes underestimated soil water input at peak grass height, which suggests enhanced occurrence of stemflow in tall grass. Despite the underestimation of stemflow, the interception tubes are a suitable method for estimating the canopy effect on throughfall patterns in temperate grasslands, and stemflow can be quantified by additional soil moisture measurements.

Nitrogen Deposition in Different Mediterranean Forest Types along the Eastern Adriatic Coast

Mediterranean forests along the eastern Adriatic coast have an important ecological role. However, few studies have been conducted on nitrogen deposition so far. To improve this knowledge, the main aims of our study were: (i) to estimate nitrogen inputs and determine differences among the four Mediterranean forests, (ii) to determine the seasonal behaviour of N deposition compounds, and (iii) to discuss the results in relation to forest type and precipitation. Measurements were carried out over a two-year period on four plots in two regions: holm oak and pubescent oak in Istria, Aleppo pine and black pine in Dalmatia. Bulk open field and throughfall deposition were sampled with continuously exposed collectors. Measurements, analyses and data validation of precipitation and N compounds were carried out. The results showed that the highest average monthly precipitation was recorded in the black pine plot and the lowest in the Aleppo pine plot. Nitrate and ammonia in conifer plots in throughfall samples were lower than in bulk open field samples, indicating possible retention by the tree canopy. The results revealed a higher amount of N deposition collected in broadleaved forests than in conifer forests indicating the washing out of N compounds previously deposited and accumulated in forest canopy. The chemistry of N deposition was strongly influenced by local and anthropogenic sources as well as neighbouring countries. Our results may fill the knowledge gap in understanding the influence of precipitation and seasonality of N compounds in different Mediterranean forest types along the eastern Adriatic coast.

Ratios of phosphatase activity to activities of carbon and nitrogen-acquiring enzymes in throughfall were larger in tropical forests than a temperate forest

Tropical forests are considered as phosphorus (P)-poor ecosystems, where microorganisms are suggested to allocate more resources to P acquisition compared to carbon (C) and/or nitrogen (N) acquisition. Therefore, ratios of activities of acid/alkaline phosphomonoesterase (AP) to C-acquiring enzymes such as β-1,4-glucosidase (BG) and C and/or N-acquiring enzymes such as β-1,4-N-acetyl-glucosaminidase (NAG) and leucine amino peptidase (LAP) are generally larger in tropical forest soils (i.e., BG: AP and (NAG+LAP): AP are smaller). However, those ratios were never reported for enzymes in throughfall. In this short note, we reported that both BG: AP and (NAG+LAP): AP of throughfall samples were smaller in five tropical forests than those in a temperate forest, which was consistent with generally-observed patterns in soils. This implies that phyllosphere microorganisms may allocate more resources to obtain P in P-poor tropical forest canopy, which should be considered in future P cycling quantifications in forest ecosystems.

Difference between rainfall and throughfall chemistry for different forest stands in the Qinling Mountains, China

Abstract This study compared the effects of four forest canopies on throughfall chemistry in the Qinling Mountains, China. Rainfall and throughfall samples were collected in stands of Quercus aliena (Qa) var. Acuteserrata, Pinus tabulaeformis (Pt), P. armandii (Pa), and mixed broad-leaved (Mb) trees from 2009 to 2011. The results indicated that the pH of the rainfall, which was mildly acidic, increased as it passed through the forest canopy. The pH increased more within the broad-leaved forest canopy than the coniferous forest. Concentrations of decreased as rainfall passed through the Qa canopy but increased after passing through the other species. The concentrations of and Zn, Cd and Pb decreased as rainfall passed through the four canopies. The coniferous forest canopy was more effective than the broad-leaved forest in reducing in rainwater. The decreases in Cd concentrations were similar among the four canopies. The Pb concentration decreased the most among the heavy metals, and the order of the decrease was Qa > Pt > Pa > Mb. The results may provide a basis for the selection of tree species for afforestation in water sources in the Qinling Mountains and similar areas.

Assessing the efficacy of eDNA metabarcoding for measuring microbial biodiversity within forest ecosystems

We investigated the nascent application and efficacy of sampling and sequencing environmental DNA (eDNA) in terrestrial environments using rainwater that filters through the forest canopy and understory vegetation (i.e., throughfall). We demonstrate the utility and potential of this method for measuring microbial communities and forest biodiversity. We collected pure rainwater (open sky) and throughfall, successfully extracted DNA, and generated over 5000 unique amplicon sequence variants. We found that several taxa including Mycoplasma sp., Spirosoma sp., Roseomonas sp., and Lactococcus sp. were present only in throughfall samples. Spiroplasma sp., Methylobacterium sp., Massilia sp., Pantoea sp., and Sphingomonas sp. were found in both types of samples, but more abundantly in throughfall than in rainwater. Throughfall samples contained Gammaproteobacteria that have been previously found to be plant-associated, and may contribute to important functional roles. We illustrate how this novel method can be used for measuring microbial biodiversity in forest ecosystems, foreshadowing the utility for quantifying both prokaryotic and eukaryotic lifeforms. Leveraging these methods will enhance our ability to detect extant species, describe new species, and improve our overall understanding of ecological community dynamics in forest ecosystems.

Decreases in inorganic nitrogen inputs and effects on nitrogen saturation and soil acidification

ABSTRACT We aimed to elucidate the effects of decreases in nitrogen (N) inputs on N budgets and soil acidity in N saturated forests in Tokyo, Japan using new analysis and comparison to sampling data collected in the 1990s. Canopy throughfall and soil-percolated water samples were collected from stands of Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa), where allophanic Andisols have developed. Stream water was sampled at the outlet of the catchment (2.15 ha). The total inorganic N input due to throughfall in the Japanese cypress stand was 104–184 mmolc m−2 year−1, which is a marked decrease from sampling results from the 1990s (1991–1992 and 1995). This decrease can be ascribed to a reduction in NOx emission from automobiles. Consequently, nitrate (NO3 −) outputs from the catchment decreased when compared with the previous study, although outputs were comparable to N inputs. Based on i) N budgets for the catchment and ii) episodic acidification of stream water, the study site remains N saturated. The degree of decrease in ammonium (NH4 +) inputs was larger than NO3 − inputs, which resulted in a decrease in acid production due to nitrification or plant uptake and contributed to reduced soil acidification. As a result, the pH values of soil-percolated water in the Japanese cypress stand increased slightly, compared to levels in the 1990s. On the other hand, soil pH values in the Japanese cypress stand were comparable to those in the 1990s due to the large acid-neutralizing capacity of allophanic Andisols.

Root‐zone moisture replenishment in a native vegetated catchment under Mediterranean climate

AbstractThe root‐zone moisture replenishment mechanisms are key unknowns required to understand soil hydrological processes and water sources used by plants. Temporal patterns of root‐zone moisture replenishment reflect wetting events that contribute to plant growth and survival and to catchment water yield. In this study, stable oxygen and hydrogen isotopes of twigs and throughfall were continuously monitored to characterize the seasonal variations of the root‐zone moisture replenishment in a native vegetated catchment under Mediterranean climate in South Australia. The two studied hillslopes (the north‐facing slope [NFS] and the south‐facing slope [SFS]) had different environmental conditions with opposite aspects. The twig and throughfall samples were collected every ~20 days over 1 year on both hillslopes. The root‐zone moisture replenishment, defined as percentage of newly replenished root‐zone moisture as a complement to antecedent moisture for plant use, calculated by an isotope balance model, was about zero (±25% for the NFS and ± 15% for the SFS) at the end of the wet season (October), increased to almost 100% (±26% for the NFS and ± 29% for the SFS) after the dry season (April and May), then decreased close to zero (±24% for the NFS and ± 28% for the SFS) in the middle of the following wet season (August). This seasonal pattern of root‐zone moisture replenishment suggests that the very first rainfall events of the wet season were significant for soil moisture replenishment and supported the plants over wet and subsequent dry seasons, and that NFS completed replenishment over a longer time than SFS in the wet season and depleted the root zone moisture quicker in the dry season. The stable oxygen isotope composition of the intraevent samples and twigs further confirms that rain water in the late wet season contributed little to root‐zone moisture. This study highlights the significant role of the very first rain events in the early wet season for ecosystem and provides insights to understanding ecohydrological separation, catchment water yield, and vegetation response to climate changes.

Particulate Matter Fluxes in a Mediterranean Mountain Forest: Interspecific Differences Between Throughfall and Stemflow in Oak and Pine Stands

AbstractIn forested areas, canopies play an important role in the partitioning of rainfall. During this process there is also a redistribution of particulate matter (PM) that is deposited from the atmosphere on vegetative surfaces and transported to soil layers by throughfall and stemflow. We collected samples of rainfall, throughfall, and stemflow from two different forest plots (pine and oak) in a Mediterranean mountainous area and analyzed the amount and size distributions of PM (0.45 μm < PM < 500 μm). The exploration of backward trajectories revealed that PM content varied significantly. This depended on the origin of the air mass, with Atlantic fronts transporting less PM in the atmosphere than North African dust intrusions, which added disproportionate inputs of PM. Overall, throughfall provided the largest proportion of incoming PM under trees, but, at the base of each tree, stemflow led to a localized input of water that was more PM enriched than water through open precipitation or throughfall. Interspecific differences in PM fluxes were noted with pines retaining more PM in their crowns than oaks. Furthermore, the presence of leaves on oak increased the size and the amount of particulates released by throughfall. The PM in stemflow was smaller and rounder than in throughfall. This study adds to our understanding knowledge of the processes that control the deposition and distribution of PM delivered to forest soils, a fraction that is often ignored in studies of nutrient and energy fluxes in ecosystems.

A potential source of soil ecoenzymes: From the phyllosphere to soil via throughfall

Soil ecoenzymes play an important role in the decomposition and formation of soil organic matter, and are often considered to be derived from soil microbial and plant root activities. This study found another potentially-important source, transfer of ecoenzymes in phyllosphere to soil via throughfall. Throughfall samples were collected in five subtropical forests, and six ecoenzymes were determined therein. Data from this study showed that the ecoenzyme activity in throughfall was significantly higher than that in rainfall. Although this study has the limitation of a single measurement, it is the first report of the potential importance of ecoenzymes in throughfall in forest ecosystems.

Spatio‐temporal variability of the isotopic input signal in a partly forested catchment: Implications for hydrograph separation

AbstractThe isotopic composition of precipitation (D and 18O) has been widely used as an input signal in water tracer studies. Whereas much recent effort has been put into developing methodologies to improve our understanding and modelling of hydrological processes (e.g., transit‐time distributions or young water fractions), less attention has been paid to the spatio‐temporal variability of the isotopic composition of precipitation, used as input signal in these studies. Here, we investigated the uncertainty in isotope‐based hydrograph separation due to the spatio‐temporal variability of the isotopic composition of precipitation. The study was carried out in a Mediterranean headwater catchment (0.56 km2). Rainfall and throughfall samples were collected at three locations across this relatively small catchment, and stream water samples were collected at the outlet. Results showed that throughout an event, the spatial variability of the input signal had a higher impact on hydrograph separation results than its temporal variability. However, differences in isotope‐based hydrograph separation determined preevent water due to the spatio‐temporal variability were different between events and ranged between 1 and 14%. Based on catchment‐scale isoscapes, the most representative sampling location could also be identified. This study confirms that even in small headwater catchments, spatio‐temporal variability can be significant. Therefore, it is important to characterize this variability and identify the best sampling strategy to reduce the uncertainty in our understanding of catchment hydrological processes.

Six-year monitoring study of radiocesium transfer in forest environments following the Fukushima nuclear power plant accident

The study investigated temporal changes in the 137Cs concentrations in vegetal and hydrological samples collected from various forests in Yamakiya District, Kawamata Town of Fukushima prefecture over six years following the Fukushima Dai-ichi nuclear power plant accident. Cesium-137 was detected in all forest environmental samples. However, the concentration in most samples decreased exponentially with time. The 137Cs concentrations in throughfall samples exhibited a double-exponential decreasing trend with time. Temporal changes in the 137Cs concentration in vegetal samples and stemflow were approximated by using a single-exponential equation. A comparison of the decline coefficient for the latter observation period (>2 y since the accident) revealed that the declining trend of 137Cs concentrations varied between foliage and the outer barks of the Japanese cedar and Japanese konara oak trees. The 137Cs concentration in cedar needles decreased exponentially while that in konara oak leaves was constant over the last six years. Conversely, the declining trend of 137Cs concentration in the outer bark of konara oak exceeded that of cedar. The results suggested that self-decontamination processes and internal recycling of 137Cs varied among tree species and different tree parts. The results indicated that the leaching of 137Cs in the throughfall in Japanese cedar was dependent on the 137Cs concentration in needles. However, a comparison of 137Cs concentrations in vegetal and hydrological samples from each sampling year showed that the leaching rate decreased with time. Conversely, the 137Cs concentrations in the stemflow were independent of the concentrations in the outer bark. The declining trend of 137Cs concentrations in litterfall (λ: 0.31–0.33 y−1) was similar to that of the mean of new/old needles (λ: 0.26–0.33 y−1) for cedar stands. With respect to the hydrological components, the 137Cs concentration in the stemflow (λ: 0.32–0.33 y−1) decreased at a slightly slower rate than that in the throughfall (λ: 0.36–0.54 y−1) for the cedar forest. The decline coefficients of 137Cs concentration in the aforementioned types of hydrological components slightly exceeded that for the vegetal samples. The results suggest that monitoring of 137Cs concentrations in hydrological components and vegetal samples can aid in further understanding the leaching mechanisms of 137Cs from trees to rainwater.

The role of fog, orography, and seasonality on precipitation in a semiarid, tropical island

AbstractIsotopes of water (2H/1H and 18O/16O) are commonly used to trace hydrological processes such as moisture recycling, evaporation loss, and moisture source region and often vary temporally in a given region. This study provides a first‐ever characterization of temporally variable precipitation mechanisms of San Cristóbal Island, Galápagos. We collected fog, rain, and throughfall samples over three field seasons to understand the mechanisms driving seasonal‐ and event‐based variability in the isotopic composition of precipitation in Galápagos. We establish that fog is a common phenomenon in San Cristóbal, especially during the dry season, and we found that fog, compared with cocollected rainfall, is consistently enriched. We further suggest that the relative contribution of fog formed via different mechanisms (orographic, advective, radiation) varied seasonally. We found that the source region is the most dominant control of the isotopic composition of rainfall in the Galápagos at both the seasonal and event scales, but subcloud evaporative processes (the nontraditional manifestation of the amount effect) became a dominant control on the isotopic composition of rainfall during the dry season. Overall, our findings suggest that understanding seasonally variable water‐generating mechanisms is required for effective water resource management in San Cristóbal Island and other semiarid island ecosystems under current and future regimes of climate change.

Analysis of pesticides in surface water, stemflow, and throughfall in an agricultural area in South Georgia, USA

To study spray drift contributions to non-targeted habitats, pesticide concentrations in stemflow (water flowing down the trunk of a tree during a rain event), throughfall (water from tree canopy only), and surface water in an agriculturally impacted wetland area near Tifton, Georgia, USA were measured (2015–2016). Agricultural fields and sampling locations were on the University of Georgia's Gibbs Research Farm, Tifton, GA. Samples were screened for more than 160 pesticides, and cumulatively, 32 different pesticides were detected across matrices. Data indicate that herbicides and fungicides were present in all types of environmental samples analyzed while insecticides were only detected in surface water samples. The highest pesticide concentration observed was 10.50 μg/L of metolachlor in an August 2015 surface water sample. Metolachlor, tebuconazole, and fipronil were the most frequently detected herbicide, fungicide, and insecticide, respectively, regardless of sample origin. The most frequently detected pesticide in surface water and stemflow samples was metolachlor (0.09–10.5 μg/L), however, the most commonly detected pesticide in throughfall samples was biphenyl (0.02–0.07 μg/L). These data help determine the importance of indirect chemical exposures to non-targeted habitats by assessing inputs from stemflow and throughfall into surface waters.

Oxygen and hydrogen isotopic characterization of rainfall and throughfall in four South Korean cool temperate forests

ABSTRACTUnderstanding the isotopic composition of precipitation in a forested catchment is critical for ecohydrological studies. Changes in the water isotopes of rainfall were assessed during its passage through the canopy in throughfall, and the effect of different forest stands on the isotope composition of throughfall. In a cool temperate forest in Korea, rainfall and throughfall samples collected under Pinus densiflora (red pine), Castanea crenata (chestnut), Robinia pseudoacacia (black locust) and mixed stands (mix of these three species) were analysed for oxygen and hydrogen isotopes. Throughfall δ18O and δD were enriched compared to rainfall. A difference of δ18O and δD among throughfall may be related to the difference in interception–storage capacity of different species due to dissimilar canopy characteristics. Since isotopic composition of throughfall and rainfall are different due to canopy isotopic effects, use of rainfall isotopic signatures for ecohydrological studies in forested ecosystem can lead to biases.

Detection and characterization of Cu-bearing particles in throughfall samples from vine leaves by DLS, AF4-MALLS (-ICP-MS) and SP-ICP-MS

Some evidence shows that Cu-based fungicides used on vines increase the levels of copper in soil and sediments. The rainfall induced foliar wash-off is the most complex pathway of contaminants in the environment. Since the Cu wash-off occurs during rain episodes, Cu can be transported in streams along considerable distances as particulate forms. The colloidal properties of Cu suspended in runoff are related to its mobility in the environment. Asymmetrical-flow field-flow fractionation (AF4) performs colloid separation based on hydrodynamic properties and can contribute as a useful tool to understand the environmental fate of colloidal contaminants. In this work, we studied the Cu-bearing micro- and nanoparticles (NPs) in throughfall samples containing fungicide residues of vines previously sprayed with copper oxychloride. Suspended particles in the throughfall were characterized by Dynamic light scattering (DLS) and AF4 coupled to multi-angle laser light scattering and inductively coupled plasma mass spectrometry (AF4-MALLS-ICP-MS). Then, single-particle ICP-MS analysis (SP-ICP-MS) was performed to evaluate the presence of Cu NPs. AF4 allowed particle fractionation and detection in throughfall waters coupled AF4-MALLS-ICP-MS demonstrating that Cu was bound to a well-defined fraction of small particles clearly separated from a broad size distribution of organic colloids that did not contain Cu. SP-ICP-MS supported the evidence that throughfall contained Cu bound to organo-mineral particles of much smaller size than the powder formulation sprayed on vines, which favors their mobility in natural waters.

The Genesis and Exodus of Vascular Plant DOM from an Oak Woodland Landscape

Evaluating the collective impact of small source inputs to larger rivers is a constant challenge in riverine biogeochemistry. In this study, we investigated the generation of dissolved organic matter (DOM) in a small oak woodland catchment in the foothills of northern California, the subsequent transformation in lignin biomarkers and chromophoric DOM (CDOM) parameters during transport through the landscape to an exporting stream, and finally the overall compositional impact on the larger receiving stream and river. Our study included a natural leaching experiment in which precipitation passing through oak, pine, and grass litter and duff samples was collected after each of a series of storms. Also included were soil trench samples to capture subsurface flow, stream samples along with point-source reservoir inputs, and samples of canopy throughfall, stemflow, and gopher hole (bypass) flow. The litter/duff leaching study demonstrated changing DOM fractionation patterns throughout the season, as evidenced by changing lignin compositions in the leachates with each successive storm. This adds a necessary seasonal component to interpreting lignin compositions in streams, as the source signatures are constantly changing. Released DOM from leaching was modified extensively during transit through the subsurface to the stream, with preferential increases in aromaticity as evidenced by increases in carbon-normalized absorbance at 254 nm, yet preferential decreases in lignin phenols, as evidence by carbon-normalized lignin yields in the headwater stream that was less than half that of the litter/duff leachates. Our extensive number of lignin measurements for source materials reveals a much more complex perspective on using lignin as a source indicator, as many riverine values for syringyl:vanillyl and cinnamyl:vanillyl ratios that have previously been interpreted as degraded lignin signatures are also possible as unmodified source signatures. Finally, this study demonstrated that the impact of numerous small headwater streams can significantly overprint the DOM signatures of much larger rivers over relatively short distances spanning several to tens of kilometers. This finding in particular challenges the assumption that river studies can be adequately conducted by focusing only on the main tributaries.