Canopy Throughfall Research Articles

Effects of Douglas fir cultivation in German forests on soil seepage water quantity and quality

Norway spruce (Picea abies L.) has been a key tree species and timber source in European forests the last centuries and is increasingly suffering from drought and bark beetle infestations due to climate warming. Current management options include replacing of Norway spruce monocultures with pure and mixed stands of European beech (Fagus sylvatica) that is the naturally dominating tree species in Central Europe. Additionally, Douglas fir (Psudotsuga menziesii), a tree species with high water use efficiency and drought tolerance, is being increasingly cultivated to increase the resilience of European forests and meet the future demand of conifer timber in a warming climate. We studied the seepage water quantity and quality with a particular focus on the nitrate (NO3–) concentration and N leaching under pure and mixed stands of Douglas fir, Norway spruce, and European beech at seven sites in Germany. Additionally, we investigated seepage water concentrations of SO4-S, Ca, Mg, K, Al and hydrological variables (interception, canopy throughfall, transpiration). Looking at the seepage water quantity and quality, the best management option is the cultivation of pure beech stands. However, this is associated with the well-known risk of monocultures concerning ecosystem disturbance. Beech stands showed the highest seepage water quantities and the lowest seepage water concentrations of major cations and anions, including NO3–. Seepage water quantity was the smallest under pure Douglas fir compared to spruce and beech stands. The composition effects of stand tree species on seepage water quality and nutrient leaching were site-dependent. At N-rich sites, pure Douglas fir stands showed higher seepage water NO3– concentrations than spruce and beech stands, whereas the tree species effects were small at N-poor sites. With respect to seepage water quantity and quality, cultivation of mixed Douglas fir–beech stands is a promising option for producing conifer timber and at the same time avoiding increased disturbance risks of mono-species forests under a warmer climate. Our results support the recommendation of mixed Douglas fir–beech stands based on soil quality, ecosystem resilience, and forest economic studies.

Nitrogen forms and dissolved organic matter optical properties in bulk rainfall, canopy throughfall, and stormwater in a subtropical urban catchment

The study of nitrogen (N) transformation in urban ecosystems is crucial in the protection of coastal water bodies because excess N may fuel harmful algae blooms (HABs). The purpose of this investigation was to study and identify the forms and concentrations of N in rainfall, throughfall, and stormwater runoff for 4 storm events in a subtropical urban ecosystem and to use fluorescence spectroscopy to evaluate the optical properties and expected lability of dissolved organic matter (DOM) in the same samples. The rainfall contained both inorganic and organic N pools, and organic N as nearly 50 % of total dissolved N in the rainfall. As water moved through the urban water cycle, from rainfall to stormwater and from rainfall to throughfall, it was enriched in total dissolved N, with most of the enrichment coming from dissolved organic N. Throughfall fluxes of total dissolved N were as high as 0.67 kg ha−1, compared to 0.44 kg ha−1 from rainfall, suggesting that the urban tree canopy can facilitate anthropogenic subsidies of N to the urban water cycle. Through analysis of sample optical properties, we saw that the throughfall presented the highest humification index and the lowest biological index when compared to rainfall, suggesting throughfall likely consists of higher molecular weight compounds of greater recalcitrance. This study highlights the importance of the dissolved organic N fraction of urban rainfall, stormwater, and throughfall and shows how the chemical composition of dissolved organic nutrients can change as rainfall is transformed into throughfall in the urban tree canopy.

Steal the rain: Interception loses and rainfall partitioning by a broad-leaf and a fine-leaf woody encroaching species in a southern African semi-arid savanna.

Woody plant encroachment (WPE) has been found to alter ecosystem functioning and services in savannas. In rain-limited savannas, increasing woody cover can reduce streamflow and groundwater by altering evapotranspiration rates and rainfall partitioning, but the ecological relevance of this impact is not well known. This study quantified the altered partitioning of rainfall by two woody plant structural types (fine- and broad-leaved trees) across a gradient of encroachment in a semi-arid savanna in South Africa. Averaged across both plant functional types, loss of rainfall through canopy interception and subsequent evaporation roughly doubled (from 20.5% to 43.6% of total rainfall) with a roughly 13-fold increase in woody cover (from 2.4 to 31.4m2/ha tree basal cover). Spatial partitioning changes comprised fourfold increases in stemflow (from 0.8% to 3.9% of total rainfall) and a decline in throughfall proportion of about two-fifths (from 80.2% to 47.3% of total rainfall). Changes in partitioning were dependent on plant functional type; rainfall interception by the fine-leaved multi-stemmed shrub Dichrostachys cinerea was almost double that of the broad-leaved tree Terminalia sericea at the highest levels of woody encroachment (i.e., 49.7% vs. 29.1% of total rainfall intercepted at tree basal area of 31.4m2/ha). Partitioning was also dependent on rainfall characteristics, with the proportion of rainfall intercepted inversely related to rainfall event size and intensity. Therefore, increasing tree cover in African grassy ecosystems reduces the amount of canopy throughfall, especially beneath canopies of fine-leaved species in smaller rainfall events. Rainfall interception traits may thus confer a selective advantage, especially for fine-leaved woody plant species in semi-arid savannas.

Stable Isotopes Reveal the Effect of Canopy and Litter Layer Interception on Water Recharge in a Subtropical Manmade Forest of Southwest China

In areas completely covered by vegetation, the rainwater that passes through the canopy layer and litter layer is the source supplying surface runoff and seeping into the soil layer. To reveal the influence mechanisms of the canopy and litter layer on water supply in forest areas, this study conducted event-scale water sampling and hydrogen and oxygen isotopic comparison for the rainfall, canopy throughfall and litter layer throughfall in a manmade forest. The results show that canopy interception will lead to a more concentrated distribution and lower isotopic variability. The d-excess and the intercept and slope of the δD-δ18O regression line of the canopy throughfall are slightly higher than those of rainfall, reflecting that the evaporation fractionation caused by canopy interception is weak, and the selection process may play a leading role. Compared with the canopy throughfall, the distribution of the δ18O, δD and d-excess in the litter layer throughfall is more dispersed, and the slope and intercept of the δD-δ18O regression line are higher, indicating the strong influence of non-equilibrium fractionation on the water input caused by litter layer interception. The isotopic differences between the litter layer throughfall and canopy throughfall indicate that the water components of small-scale precipitation events (precipitation amount lower than 5 mm) and the early stage of large-scale precipitation events (precipitation amount higher than 25 mm) may be dissipated by litter layer interception, while that of the latter stage of large-size events is slightly affected. The findings of this study will be helpful to deeply understand the mechanisms of the water cycle in the forest ecosystem under the background of climate change and provide insights for the sustainable utilization of water resources.

Canopy throughfall links canopy epiphytes to terrestrial vegetation in pristine conifer forests

To what extent does epiphytic community composition in boreal forests reflect soil nutrient status? To answer this question, we investigated potential links between terrestrial plants and lichen-dominated communities in Picea glauca x engelmannii canopies in south-central British Columbia. We combined original data on vegetational composition in the ground and tree layers with published data on elemental uptake in standardized transplants of the lichen Lobaria pumonaria affixed to the lower branches of studied trees. Procrustean association metrics revealed a significant concordance between community composition among the epiphytic and terrestrial vegetation, which was stronger in Mn-enriched conifer canopy settings, and weaker within the cation-enriched dripzones of adjacent Populus trees. We also found that the NMDS1-gradient for each vegetation layer was strongly correlated with base cations (and inversely with Mn) in canopy throughfall, as well as with soil and bark pH. We conclude that elemental composition in canopy throughfall forms a functional link between terrestrial and epiphytic vegetation. • Epiphytes in the lower canopy and plants in the rooting zone of Picea were recorded • There was a concordance between community composition for epiphytes and plants • Across canopy settings, a throughfall gradient underlined both vegetation layers • The gradient ranked from Ca, Mg, K-rich Populus dripzones to Mn-rich conifer stands • Throughfall chemistry likely mediated the link between plants and epiphytes

Time‐series of δ26Mg values in a headwater catchment reveal decreasing magnesium isotope variability from precipitation to runoff

AbstractData on temporal variability in Mg isotope ratios of atmospheric deposition and runoff are critical for decreasing the uncertainty associated with construction of isotope mass balances in headwater catchments, and statistical evaluation of isotope differences among Mg pools and fluxes. Such evaluations, in turn, are needed to distinguish between biotic and abiotic contributions to Mg2+ in catchment runoff. We report the first annual time‐series of δ26Mg values simultaneously determined for rainfall, canopy throughfall, soil water and runoff. The studied 55‐ha catchment, situated in western Czech Republic, is underlain by Mg‐rich amphibolite and covered by mature spruce stands. Between 1970 and 1996, the site received extremely high amounts of acid deposition and fly ash form nearby coal‐burning power plants. The δ26Mg values of open‐area precipitation (median of −0.79‰) at our study site were statistically indistinguishable from the δ26Mg values of throughfall (−0.73‰), but significantly different from the δ26Mg values of soil water (−0.55‰) and runoff (−0.55‰). The range of δ26Mg values during the observation period decreased in the order: open‐area precipitation (0.57‰) > throughfall (0.27‰) > runoff (0.21‰) > soil water (0.16‰). The decreasing variability in δ26Mg values of Mg2+ from precipitation to soil water and runoff reflected an increasing homogenization of atmospheric Mg in the catchment and its mixing with geogenic Mg. In addition to atmospheric Mg, runoff also contained Mg mobilized from the three major solid Mg pools, bedrock (δ26Mg of −0.32‰), soil (−0.28‰), and vegetation (−0.31‰). The drought of summer 2019 did not affect the nearly constant δ26Mg value of runoff. Collectively, our data show that within‐catchment processes buffer the Mg isotope variability of the atmospheric input.

INTERSEPSI DAN ALIRAN BATANG TANAMAN KOPI DENGAN BERBAGAI NAUNGAN DI SUMBERMANJING WETAN, MALANG

The current climate change has an impact on crop production, especially coffee plants. Rainfall is one of the climate elements that influences the process of crop cultivation, because of its role in the availability of water crops. Raindrops that fall on the vegetated land cover does not directly reach to ground, but will temporarily be accommodated by a canopy, stems and plant branch. Once those places saturated with water, the raindrops will drop to the soil surface through the canopy, stem flow and partially evaporated back into the atmosphere that called interception. The study aims to determine the effect of the shade of coffee plants on the interception, and stemflow of plant canopy. As well as knowing the relationship between rainfall with throughfall, stemflow, and interception. This research was conducted at smallholder coffee plantation in Sumbermanjing Wetan District on the use of gamal shade coffee grown, sengon shade coffee grown, and sun-grown coffee. The results showed that the value of canopy throughfall in the three land uses was not statistically significantly different, but there was a tendency for monoculture coffee plants which has a greater yield that is 66,38% of the total rainfall of 15,32 mm. The highest stemflow value is in the sengon shade coffee grown of 3,07% of the total rainfall of 15,32 mm. Interception in the gamal shade coffee grown is the highest compared to other land uses that results obtained are 36,92% of the total rainfall of 17,1 mm. Rainfall has a relationship with the value of stemflow, throughfall and interception. Based on the correlation analysis test the results were significantly correlated with strong relationship.

Winter arsenic pollution in 10 forest ecosystems in the mountainous border regions of the Czech Republic.

Arsenic (As) concentrations and deposition fluxes were measured in snow and rime at 10 mountain-top sites near the borders between the Czech Republic and Austria, Germany, Poland, and Slovakia during three consecutive winter seasons (2009-2011). Our study was performed at a time following several decades of sharply decreasing regional atmospheric pollution and following the 2006 implementation of stricter air quality standards across Europe. Our objective was to compare vertical and horizontal depositions of soluble and insoluble As forms throughout the Czech Republic and define a recent Central European As pollution gradient. Arsenic soluble in weak nitric acid contributed 83 to 85% to the total As deposition, with the remaining 17-15% bound to stable particulate forms. The highest As deposition rates were recorded in the eastern Czech Republic near the borders with Poland and Slovakia. Complementary hydrochemical monitoring in four mountain-slope catchments situated near selected main study sites revealed a further decrease in open-area As deposition by the end of 2018 in the east of the country. In contrast, spruce canopy throughfall flux did not change significantly between 2009-2011 and 2016-2018. The site-specific relative roles of coal-burning-derived and ore-smelting-derived atmospheric As are discussed.

Magnesium and calcium isotope systematics in a headwater catchment underlain by amphibolite: Constraints on Mg–Ca biogeochemistry in an atmospherically polluted but well-buffered spruce ecosystem (Czech Republic, Central Europe)

Lithogenic and biologically-fractionated magnesium (Mg) and calcium (Ca) are viewed as alternative controls of the δ26Mg and δ44Ca isotope signatures of streams and rivers. Understanding of Mg–Ca isotope systematics and of runoff generation in headwater catchments is crucial for upscaling riverine variability in δ26Mg and δ44Ca values to Mg–Ca isotope inputs into the oceans, and for global climate change considerations. Here we report Mg–Ca–Sr isotope systematics in a small, spruce-forested, high-elevation catchment in western Czech Republic, which has received high Mg and Ca inputs from dissolution of base-rich bedrock amphibolite and from industrial emissions. Our study site NAZ (Slavkov Forest) experienced a relatively long period of acid rain (ca. 1950–1995), accompanied by deposition of partly soluble dust from coal-burning power plants. Bedrock contained as much as 11 and 10 wt% of MgO and CaO, respectively. Input–output monitoring revealed a large net export of Mg, Ca, but also S, from the catchment via surface runoff. The δ26Mg values increased in the order: open-area precipitation (−1.44‰) < soil water (−1.10‰) < spruce canopy throughfall (−1.00‰) < runoff (−0.96‰) < spruce bark (−0.59‰) < spruce needles (−0.46‰) < spruce xylem (−0.40‰) < bedrock (−0.32‰) < soil (−0.30‰) < spruce fine roots (−0.07‰). The δ44Ca values increased in the order: spruce bark (−1.91‰) < spruce xylem (−0.86‰) < spruce fine roots (−0.83‰) < spruce needles (−0.43‰) < spruce canopy throughfall (0.31‰) < soil water (0.44‰) < soil (0.46‰) < open-area precipitation (0.69‰) < plagioclase (0.83‰) < bulk bedrock (0.86‰) < runoff (0.92‰) < amphibole (1.10‰). Our data indicated a relatively small Mg isotope fractionation toward higher δ26Mg values in organic matter, and a large Ca isotope fractionation toward lower δ44Ca values in all studied organic compartments. In contrast to Mg, most Ca isotope variability at NAZ was driven by biological fractionations. While excess Mg and Ca in NAZ export fluxes via catchment runoff are most easily explained by lithological control of runoff Mg–Ca, the Mg–Ca–Sr isotope systematics were also consistent with measurable atmospheric contribution to Mg and Ca in runoff.

Canopy settings shape elemental composition of the epiphytic lichen Lobaria pulmonaria in unmanaged conifer forests

• Ecologically significant canopy leachates should be explored in undisturbed forests. • We used lichens to assess leachates from cottonwood/aspen and hybrid spruce canopy. • Standardized lichen transplants accumulated elements for 1 year in tree dripzones. • Base cations, soil pH and conifer bark pH was highest in cottonwood/aspen dripzones. • Lichen transplants are ecologically relevant indicators of throughfall chemistry. The importance of forest canopy settings for the elemental chemistry of epiphytic lichens in undisturbed forests is poorly understood despite its impact on epiphytes, understory vegetation and microbial soil communities. Here, we examine the elemental composition in standardized thalli of the cephalolichen Lobaria pulmonaria transplanted to the lower branches of Picea glauca x engelmannii in inland British Columbia. Transplants were attached to nets (avoiding direct contact with tree bark) exposed to natural canopy throughfall in three categories of natural forest stands: 1) within dripzones of Populus species in mixed stands always supporting L. pulmonaria ; 2) outside Populus dripzones, yet with L. pulmonaria and 3) outside Populus dripzones and without L. pulmonaria , which is the most common canopy setting. After one year, and with the exception of Fe and Al, the elemental content in lichen transplants changed within and between forest categories. Lichen transplants within Populus dripzones had more base cations (Ca, Mg, K) and less Mn than in the two categories outside dripzones. In Picea canopies outside Populus dripzones , lichen transplants had higher Ca, Na, Mo and lower C, S and Cu in trees with L. pulmonaria than without. The pH of Picea branches and soil within the rooting zone of trees with transplants were both approximately ten times more acidic outside Populus dripzones than within them. However, bark pH did not differ between the two categories of stands outside Populus dripzones. Based on our findings we conclude that canopy setting shapes the elemental composition of epiphytic lichen transplants, suggesting that such transplants might be used to monitor spatial variation in throughfall elements from forest canopies in unmanaged stands. We also conclude that elemental concentrations, Ca in particular, is a better predictor than bark pH for the occurrence of L. pulmonaria on Picea .

Calcium and strontium isotope dynamics in three polluted forest ecosystems of the Czech Republic, Central Europe

Calcium and strontium isotope ratios were used to identify Ca sources for bulk soil, soil solutions and runoff in the stressed forest ecosystems of Central Europe. All three study sites are underlain by Ca-poor crystalline bedrock (orthogneiss, leucogranite and serpentinite, respectively), but differ in historical rates of acid deposition. UDL, the spruce die-back affected site at the Czech–Polish border underlain by orthogneiss, received six times more acidifying compounds from the atmosphere than LYS and PLB, two paired catchments near the Czech–German border. The paired catchments near the Czech–German border, whose forests were only mildly damaged by industrial pollution, differ in their acid buffering capacity (extremely low for LYS leucogranite, extremely high for PLB serpentinite). At the spruce die-back affected catchment UDL, 19 years of monthly hydrochemical monitoring revealed six times higher atmospheric deposition and runoff fluxes of Ca, compared to the paired catchments LYS and PLB. Across the three sites, the mean δ44Ca values increased in the order: spruce bark (−0.84‰) < spruce xylem (−0.31‰) < spruce fine roots (0.0‰) < bedrock (0.08‰) < soil (0.11‰) < spruce needles (0.31‰) < open-area precipitation (0.68‰) < spruce throughfall (0.71‰) < runoff (0.74‰) < soil water (1.11‰). At all three sites, Ca from atmospheric deposition was isotopically similar to Ca in runoff, indicating export of recent atmospheric Ca. All three catchments had isotopically lighter Ca in silicate bedrock and exported isotopically heavier Ca via runoff. Trees mostly represented the isotopically lightest Ca pool, whereas soil water collected by lysimeters contained isotopically heavy Ca. The 87Sr/86Sr isotope ratios were nearly uniform at the serpentinite site PLB (0.710). The 87Sr/86Sr ratios across the two felsic sites (UDL and LYS) increased in the order: open-area precipitation (0.710) < spruce canopy throughfall (0.715) < spruce xylem (0.723) < spruce needles (0.725) < soil water (0.734) < runoff (0.740) < soil (0.862) < bedrock (0.881). Collectively, the δ44Ca and 87Sr/86Sr isotope systematics indicated that organic Ca cycling, along with atmospheric input of isotopically heavy Ca, largely contributed to the high-δ44Ca values of runoff. The studied silicate bedrock had significantly lower δ44Ca values than the reported world-wide average. While bulk soil Ca was likely affected by bedrock Ca even after the period of acid rain, the δ44Ca difference between soil and soil water indicated a major role of recycled organic Ca in supplying nutrition to the trees. Future Ca-Sr isotope research in headwater catchments should include isotope analysis of sequentially leached Ca fractions from weathered minerals in soil to better assess the geogenic Ca inputs to runoff. In catchments currently recovering from pollution, Ca-Sr isotope fingerprinting of dust emitted from coal-fired power plants will be needed. Isotope analysis of local coal can indicate to what extent Ca-Sr isotope composition of past deposition contributes to the isotope signatures of present-day runoff.

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.

Spatial and Temporal Variability of Throughfall among Oak and Co-Occurring Non-Oak Tree Species in an Upland Hardwood Forest

Canopy throughfall comprises the largest portion of net precipitation that is delivered to the forest floor. This water flux is highly variable across space and time and is influenced by species composition, canopy foliage, stand structure, and storm meteorological characteristics. In upland forests throughout the central hardwoods region of the Eastern United States, a compositional shift is occurring from oak-hickory to more mesic, shade-tolerant species such as red maple, sweetgum, and winged elm. To better understand the impacts of this shift on throughfall flux and the hydrologic budget, we monitored throughfall for one year in Northern Mississippi under the crowns of midstory and overstory oak (post oak and southern red oak) and non-oak species (hickory, red maple, and winged elm). In general, oak had more throughfall than co-occurring non-oak species in both canopy levels. In the overstory during the leaf-off canopy phase, white oak had relatively higher throughfall partitioning (standardized z-score = 0.54) compared to all other species (z-score = −0.02) (p = 0.004), while in the leaf-on canopy phase, red maple had relatively lower throughfall (z-score = −0.36) partitioning compared to all other species (z-score = 0.11). In the midstory, red maple was the only species to exhibit a difference in throughfall between canopy phases, with much lower throughfall in the leaf-off compared to the leaf-on canopy phase (z-score = −0.30 vs. 0.202, p = 0.039). Additionally, throughfall under oak crowns was less variable than under non-oak crowns. These results provide evidence that the spatial and temporal distribution of throughfall inputs under oak crowns are different than non-oak species, likely due to differences in crown architecture (i.e., depth and density). As oak dominance diminishes in these forests, it is possible that the portion of rainfall diverted to throughfall may decrease as well. The net impacts to watershed hydrology are still unknown, but these results provide one mechanism by which the distribution of water resources may be affected.

LEAF: Logger for ecological and atmospheric factors

Abstract The fields of meteorology, surface- and groundwater hydrology, and forestry are often decoupled despite the fact that they occur simultaneously at the intersection of living systems and the physical environment. In this work, we describe a system that allows concurrent measurement of canopy throughfall, transpiration, air temperature, pressure, and humidity at multiple heights, in addition to soil moisture and several surface water parameters. LEAF is designed to be generalizable to many other hydrology and meteorology applications, and is modular such that it is easily adaptable for use with additional, diverse environmental monitoring sensors. This low-cost, light-weight, solar-powered system is capable of simultaneous streaming telemetry as well as local data logging via SD card.

Seasonal and Topographic Variations in Ecohydrological Separation Within a Small, Temperate, Snow‐Influenced Catchment

AbstractThe hypothesis of ecohydrological separation (ES) proposes that the water contained in surface soils is not uniformly extracted by root water uptake nor uniformly displaced by infiltration. Rather vegetation selectively removes water held under tension, and water infiltrating wet soil will bypass much of the water‐filled pore space. Methodological differences across previous studies have contributed to disagreement concerning the prevalence of ES. We measured stable isotopes of O and H in precipitation, snowpack, canopy throughfall, and stream water over a period of 18 months in a temperate catchment. At six locations across a wetness gradient, we sampled bulk soil water isotopes weekly and xylem water of Eastern hemlock and American beech stems seasonally. We used these observations in a soil column model including StorAge Selection functions to estimate the isotopic composition and ages of groundwater recharge and ET. Our findings suggest ES may exist with spatial and temporal heterogeneity. Root water uptake ages possibly vary between Eastern hemlock and American beech, suggesting functional strategies for water uptake may control the presence of ES. Newly infiltrated water bypassing the shallow soil was the most likely explanation for bulk soil isotopic measurements made at upslope locations during the winter and summer seasons, whereas rapid displacement of stored soil water by infiltrated waters was the most likely during the spring and fall seasons. Future research incorporating high temporal frequency soil and plant xylem water isotopic measurements applied to StorAge Selection functions may provide a useful framework for understanding rooting zone isotope dynamics.

Nitrogen deposition sources and patterns in the Greater Yellowstone Ecosystem determined from ion exchange resin collectors, lichens, and isotopes

Over the past century, atmospheric nitrogen deposition (Ndep) has increased across the western United States due to agricultural and urban development, resulting in degraded ecosystem quality. Regional patterns of Ndep are often estimated by coupling direct measurements from large-scale monitoring networks and atmospheric chemistry models, but such efforts can be problematic in the western US because of complex terrain and sparse sampling. This study aimed not only to understand Ndep patterns in mountainous ecosystems but also to investigate whether isotope values of lichens and throughfall deposition can be used to determine Ndep sources, and serve as an additional tool in ecosystem health assessments. We measured Ndep amounts and δ15N in montane conifer forests of the Greater Yellowstone Ecosystem using canopy throughfall and bulk monitors and lichens. In addition, we examined patterns of C:N ratios in lichens as a possible indicator of lichen physiological condition. The isotopic signature of δ15N of Ndep helps to discern emission sources, because δ15N of NOx from combustion tends to be high (−5 to +25‰) while NHx from agricultural sources tends to be comparatively low (−40 to −10‰). Summertime Ndep increased with elevation and ranged from 0.26 to 1.66 kg ha−1. Ndep was higher than expected in remote areas. The δ15N values of lichens were typically −15.3 to −10‰ suggesting agriculture as a primary emission source of deposition. Lichen %N, δ15N and C:N ratios can provide important information about Ndep sources and patterns over small spatial scales in complex terrain.

Interception and Fog Drip Estimates in Fragmented Mountain Forests

Forest interception is a major loss of water balance in mountain catchments, reducing the recharge of water resources. Fog precipitation occurring at higher elevations can reduce this loss by saturating the vegetative surface and dripping down to the soil surface. In 2015–2017, detailed observations of canopy throughfall and fog drip were performed in the upper plain of the Jizera Mountains (North Bohemia, Czech Republic). In the warm season (May–October), the interception loss of 106 mm was found in investigated mature spruce stand at 975 m a.s.l., i.e., 16% of the gross precipitation (662 mm). In 51 days a year, the forest interception was affected by a canopy fog drip. Hypothetically, by a negligible fog drip, the mean seasonal interception calculated by the Gash analytical model (225 mm) was 34% of the ‘open field’ rainfall. The fog drip volume (119 mm) was confirmed by the Slinn model (128 mm, + 9%), while the relatively simple models of Gallagher and Vermeulen significantly underestimated results by −23 and − 38%. Therefore, the Slinn model was employed to calculate daily fog drip over an annual cycle in heavy fragmented forest stands over 1 km2 of an experimental catchment. We found only slightly increased fog drip (up to 10%) within 30 m of the forest edge, reflective of the relatively high forest fragmentation (an absence of large homogenous stands and sharp edges). Four basic canopy classes (from mature spruce stands to herbaceous cover) were distinguished. The mean annual fog drip was PF = 81 mm (i.e., 7% of the gross precipitation) and fog drip reached 7–8% of the mean annual gross precipitation, or 10–12% of the mean annual runoff. In addition, the winter fog drip of up to 60% confirmed previous findings from this area.

Deposition of Sulfur, Nitrogen and Mercury in Two Typical Forest Ecosystems in Southern China

Bulk precipitation collectors and canopy throughfall collectors were applied to measure the deposition of sulfur, nitrogen, and mercury at two forest ecology stations, Qianyanzhou (QYZ) in Jiangxi Province and Huitong (HT) in Hunan Province, from December 2013 to November 2014. During the observation period, the volume weighted average concentrations of SO42--S, NO3--N, NH4+-N, and Hg at QYZ station were 1.89 mg·L-1, 0.957 mg·L-1, 0.401 mg·L-1, and 12.5 ng·L-1 in the bulk precipitation, respectively, and 2.39 mg·L-1, 1.18 mg·L-1, 0.897 mg·L-1, and 22.2 ng·L-1 in the throughfall, respectively. The concentrations of these components increased by different proportions for the bulk precipitation compared to the throughfall. At HT station, the average concentrations of SO42--S, NO3--N, NH4+-N, and Hg in the throughfall were 2.93 mg·L-1, 1.60 mg·L-1, 0.502 mg·L-1, and 22.0 ng·L-1, respectively. In addition, atmospheric deposition fluxes based on the throughfall were 3.56 g·(m2·a)-1 for sulfur, 3.02 g·(m2·a)-1 for nitrogen, and 30.6 μg·(m2·a)-1 for mercury at QYZ station, while the corresponding fluxes were 6.18 g·(m2·a)-1, 4.48 g·(m2·a)-1, and 37.3 μg·(m2·a)-1 at HT station. The deposition rates of all three elements were the highest in summer. The contribution of dry deposition to the total deposition of mercury was similar to that of wet deposition, while wet deposition contributed more to the total deposition of sulfur and nitrogen than did dry deposition. Unlike sulfur and nitrogen depositions, which were mainly derived from anthropogenic sources, mercury deposition might have a greater contribution from natural sources, especially at HT station.

Evidence for the Activation of Shallow Preferential Flow Paths in a Tropical Panama Watershed Using Germanium and Silicon

AbstractIn humid tropical watersheds, the hydrologic flow paths taken by rain event waters and how they interact with groundwater and soil matrix water to form streamflow are poorly understood. Preferential flow paths (PFPs) confound storm infiltration processes, especially in the humid tropics where PFPs are common. This work applies germanium (Ge) and silicon (Si) as natural flow path tracers in conjunction with water stable isotopes and electrical conductivity to examine the rapid delivery of shallow soil water, the activation of PFPs, and event water partitioning in an experimental catchment in central Panama. We employed a three‐component mixing model for hydrograph separation using the following end‐member waters: (i) base flow (high [Si], low [Ge], and low Ge/Si ratio), (ii) dilute canopy throughfall (low [Si] and low [Ge]), and (iii) shallow (&lt;15 cm) soil matrix water (low [Si], high [Ge], and high Ge/Si ratio). These three end‐members bounded all observed Ge/Si streamflow ratios. During small rain events (&lt;∼24 mm), base flow and dilute canopy throughfall components dominated stormflow. During larger precipitation events (&gt;∼35 mm), we detected the third shallow soil water component with an elevated [Ge] and Ge/Si ratio. This component reached its maximum during the hydrograph's receding limb coincident with the maximum event fraction, and increased proportionally to the total storm rainfall exceeding ∼35 mm. Only shallow (&lt;15 cm) soil matrix water exhibited elevated Ge concentrations and high Ge/Si ratios. This third component represents rapidly delivered soil matrix water combined with shallow lateral PFP activation through which event waters interact with soil minerals.

Variability, drivers, and effects of atmospheric nitrogen inputs across an urban area: Emerging patterns among human activities, the atmosphere, and soils

Atmospheric deposition of nitrogen (N) is a major input of N to the biosphere and is elevated beyond preindustrial levels throughout many ecosystems. Deposition monitoring networks in the United States generally avoid urban areas in order to capture regional patterns of N deposition, and studies measuring N deposition in cities usually include only one or two urban sites in an urban-rural comparison or as an anchor along an urban-to-rural gradient. Describing patterns and drivers of atmospheric N inputs is crucial for understanding the effects of N deposition; however, little is known about the variability and drivers of atmospheric N inputs or their effects on soil biogeochemistry within urban ecosystems. We measured rates of canopy throughfall N as a measure of atmospheric N inputs, as well as soil net N mineralization and nitrification, soil solution N, and soil respiration at 15 sites across the greater Boston, Massachusetts area. Rates of throughfall N are 8.70±0.68kgNha−1yr−1, vary 3.5-fold across sites, and are positively correlated with rates of local vehicle N emissions. Ammonium (NH4+) composes 69.9±2.2% of inorganic throughfall N inputs and is highest in late spring, suggesting a contribution from local fertilizer inputs. Soil solution NO3− is positively correlated with throughfall NO3− inputs. In contrast, soil solution NH4+, net N mineralization, nitrification, and soil respiration are not correlated with rates of throughfall N inputs. Rather, these processes are correlated with soil properties such as soil organic matter. Our results demonstrate high variability in rates of urban throughfall N inputs, correlation of throughfall N inputs with local vehicle N emissions, and a decoupling of urban soil biogeochemistry and throughfall N inputs.