Incident Precipitation Research Articles

Measuring and modeling soil moisture and runoff at solar farms using a disconnected impervious surface approach

AbstractGround‐mounted photovoltaic sites are often treated as impervious surfaces in stormwater permits. This ignores the pervious soils beneath and between solar arrays and leads to an overestimation of runoff. Our objective was to improve solar farm stormwater hydrology models by explicitly considering the disconnected impervious nature of solar design and site characteristics. Experimental sites established on utility scale solar farms in Colorado, Georgia, Minnesota, New York, and Oregon had perennial vegetative plantings with mean precipitation ranging from 40.6 to 124.5 cm, and soil texture ranging from loamy sand to clay. Soil moisture measurements were collected beneath arrays, under drip edges, and in the vegetated area between arrays at each site. Hydrus‐3D models for soil moisture and stormwater hydrology were developed that accounted for precipitation falling on solar panels, drip edge redistribution of rainfall, infiltration, and runoff in the pervious areas between solar arrays and beneath panels. Drip edge runoff averaged 3‐ to 10‐times incident precipitation at the New York and Minnesota sites, respectively. Root mean square error values between measured sub‐hourly soil moisture and predicted moisture for large measured single storm events averaged 0.029 across all five sites. Predicted runoff depths were strongly affected by precipitation depth, soil texture, soil profile depth, and soil bulk density. Runoff depths across the five experimental sites averaged 13%, 25%, and 45% of the 2‐, 10‐, and 100‐year design storm depths, clearly showing that these solar farms do not behave like impervious surfaces, but rather as disconnected impervious surfaces with substantial infiltration of runoff in the vegetated areas between and beneath solar arrays.

Response of water yield to silvicultural treatments in a temperate forest in northern Mexico

Forest management modifies tree cover, directly influencing various ecosystem services, such as water regulation. Evapotranspiration, water interception, surface runoff, stemflow, and throughfall are among those processes that depend on tree cover. The objective of this study was to evaluate the changes in water yield, defined as the difference between precipitation and evapotranspiration, after the application of silvicultural treatments in a temperate forest ecosystem in northern Mexico. Fifteen experimental plots were established in which the following treatments were applied: intensive management (clearcutting), semi-intensive management (selection, tree cutting of 59–61% of basal area), conservative management (selection, tree cutting of 29–31% of basal area), and no treatment (control group). Incident precipitation, throughfall, stemflow, net precipitation, interception, and surface runoff were analyzed. Results show that conservative management treatments increase water yield between 2 to 3.6 mm per m-2 ha-1 of tree basal area removed. Water flow distribution, in relation to the incident precipitation, ranged from 72.3 to 91.8% for throughfall, 0.2 to 0.4% for stemflow, 72.7 to 91.8% for net precipitation, 8.19 to 27.42% for interception or evaporation, and 0.54 to 1.93% for surface runoff. The conservative management treatment was the most viable alternative for increasing water yield without compromising timber harvesting and loss of soil due to hydric erosion.

UV radiation and drought interact differently in grass and forb species of a mountain grassland

Among abiotic stressors, drought and enhanced ultraviolet radiation (UV) received a lot of attention, because of their potential to impair plant growth. Since drought and UV induce partially similar protective mechanisms, we tested the hypothesis that UV ameliorates the effect of reduced water availability (WA) in selected grass (Holcus mollis and Agrostis capillaris) and forb species (Hypericum maculatum and Rumex acetosa). During 2011–2014, an outdoor manipulation experiment was conducted on a mountain grassland ecosystem (Beskydy Mts; Czech Republic). Lamellar shelters were used to pass (WAamb) or exclude (WA–) incident precipitation in order to simulate reduced water availability (WA). In addition, the lamellas were made from acrylics either transmitting (UVamb) or blocking (UV–) incident UV. Generally, both UV exposure and reduced WA enhanced epidermal UV-screening, while exposure to both factors resulted in less than additive interactions. Although UV radiation increased epidermal UV-screening rather in the grass (up to 29 % in A. capillaris) than forb (up to 12 % in H. maculatum) species and rather in well-watered than reduced WA plants, such acclimation response did not result in significant alleviation of reduced WA effects on gas exchange and morphological parameters. The study contributes to a better understanding of plant responses to complex environmental conditions and will help for successful modelling forecasts of future climate change impacts.

Incident Precipitation, Throughfall and Stemflow chemistry in <i>Pinus wallichiana</i> A.B. Jack. stand in Dal Lake catchment, Srinagar, J & K, India

The paper presents the results of chemical analysis of stem flow, throughfall and incident precipitation under Pinus wallichiana stand located in Dal Lake catchment in Kashmir Himalayas. The maximum values of Na (10.6 mg l -1), Cl (7.0 mg l -1) and K (2.3 mg l -1) were found in throughfall followed by stemflow (Na = 7.2 mg l -1; Cl = 4.6 mg l -1; K = 1.4 mg l - 1) and incident rainfall (Na = 4.8 mg l -1; Cl = 3.0 mg l -1; K = 1.0 mg l -1). In case of phosphorus however, the maximum values (1.5 mg l -1) were found in incident rainfall and minimum (0.8 mg l -1) in throughfall. The values of all four nutrients varied significantly (P < 0.05) during the course of the study. General trend of increase in nutrients in stemflow, throughfall and incident rainfall was in the order of Na > Cl > K > P. All four nutrients of the stemflow were significantly (P < 0.05) and positively correlated with the diameter at breast height (DBH), and inversely correlated with tree height, however this relationship was not significant. In case of throughfall, Na (r = 0.46), Cl (r = 0.60), K (r = 0.57) and P (r = 0.59) were significantly (P < 0.01) correlated with the crown area.

Net precipitation, infiltration and overland flow production in three types of community-managed forest in the Mid-hills of East Central Nepal

It is widely believed that community forest management concurrently improves the social, ecological and economic conditions of local populations. Accordingly, large areas of Nepal's Mid-hills’ forests are used and managed by local Community Forest User Groups (CFUGs). The CFUGs plant seedlings as well as thin and prune forest trees at varying intensities as determined by local forest conditions and the need for forest products (mainly timber, firewood, livestock fodder and compostable litter). However, the hydrological effects of these activities are uncertain. We present results of throughfall (Tf), stemflow (Sf) and overland flow (OF) measurements made between June 2015 and December 2016 (including two consecutive rainy seasons) in three types of community-managed forests subject to different levels of community usage in the Kavre district (East Central Nepal): (i) regenerating natural broad-leaved (BF), (ii) predominantly-planted pine (PF), and (iii) mixed pine-broad-leaved (MF). The BF and MF were used more intensively than the PF. Overall Tf fractions were 72.0%, 73.7% and 77.5% of incident precipitation (P) for the BF, MF and PF, respectively, with corresponding Sf fractions of 1.6%, 1.3% and 0.6%. Overall rainfall interception fractions were 26.4%, 25.1% and 21.9% for the BF, MF and PF, respectively, and reflected the trend in leaf area index. Total amounts of OF constituted 11.4%. 9.8% and 4.7% of net precipitation (Tf+Sf) inputs to the forest floor in the BF, MF and PF, respectively and broadly followed the relative intensity of forest usage. Observed amounts of OF in the study forests represent ca. 50–115 mm of foregone infiltration opportunity per year under average rainfall, implying reductions in the recharge of soil and groundwater reserves of ∼6% in the PF to 12–14% in the MF and BF. Our results thus show that regular harvesting of litter, fodder and firewood combined with surface compaction by human traffic constitute important determinants of hillslope hydrological functioning, particularly regarding amounts of foregone infiltration and runoff as OF in the more intensively used community-managed forests of Nepal's Mid-hills.

Precipitation interception in Pinus engelmannii Carr. and Quercus rugosa Née inthe Ejido Adolfo Ruiz Cortines, Pueblo Nuevo, Durango

Whith the purpose to determine the percentage of the incident precipitation, direct precipitation, stem runoff, interceptation lossesand physiochemical properties of rainfall in Pinus engelmannii Carr. and Quercus rugosa Née, 30 rain events were analyzed withinfragment of the Adolfo Ruiz Cortines Ejido, in the municipality of Pueblo Nuevo, Durango. Where a plot of 2500 mwasestablished to measure the hydrological properties during the period from May 05, 2018 to December 07, 2018. The results showedan incident precipitation of 856.24 mm. The direct precipitation in P. engelmannii Carr. and Q. rugosa Née represented the 72.11 %and 79.40 %, respectively. With an average of 75.76 % of the total precipitation. The stem runoff represented the 0.46 % and 0.11 %while the canopy interception showed 27.42 % and 20.27 % in P. engelmannii and Q. rugosa, respectively. The analysis ofthroughfall indicated that the maximum value of pH in the incident precipitation was 6.78 in direct precipitation in P. engelmannii,5.78 and in Q. rugosa 6.78. The stem runoff in P. engelmannii showed a pH of 6.08 and in Q. rugosa of 7.51. The electricconductivity of the stem runoff was 84.63 μS cmin P. engelmannii and of 170 μS cmin Q. rugosa; higher values compared toincident precipitation and to the direct precipitation in both species. The structure of the vegetation cover, the conformation of thetrees and the type of precipitation influence the amount of precipitation that reaches the soil ground.

Stemflow Infiltration Hotspots Create Soil Microsites Near Tree Stems in an Unmanaged Mixed Beech Forest

In stemflow, rainfall is collected and channeled to a concentrated soil water input. It can constitute up to 30% of incident precipitation in some ecosystems. However, the size of the zone influenced by stemflow is unclear, and statistically representative measurement of stemflow (on and in between sites) is scarce. Therefore, whether stemflow creates hotspots of infiltration and potential impacts on forest soils remain subject to controversy. In this study, we investigated the areal dimension of infiltrating stemflow fluxes as well as effects on near-stem soils. We measured throughfall, stemflow and soil properties in high-resolution statistical designs on a mixed forest plot in Germany receiving moderate stemflow. From this data, we modeled the spatial distribution of net precipitation infiltration depth on the plot. Furthermore, we examined soil chemical and physical properties around tree stems to test for and assess a stemflow impact. Results show that stemflow infiltration areas are much smaller than typically assumed and constitute strong infiltration hotspots compared to throughfall. This is also mirrored in soil properties, which are significantly altered near stems. Here, accelerated soil formation and enhanced translocation processes indicate increased soil water fluxes due to high inputs. Additionally, altered soil hydraulic properties enable quicker soil water fluxes near stems. Our findings attest that even comparatively low stemflow fractions (of gross precipitation) can generate strong hotspots of water and matter inputs, which are impactful to subsequent hydrological and biogeochemical processes and properties. Trees shape their direct soil environment, thereby establishing pathways of preferential water flow connecting the canopy and the deeper subsurface.

Global quantitative synthesis of effects of biotic and abiotic factors on stemflow production in woody ecosystems

AbstractAimStemflow has been increasingly recognized as an indispensable component in water and nutrient budgets within vegetated ecosystems. Here we aim to quantify the stemflow percentage (St, %) of incident precipitation (i.e. stemflow production) at a global scale, and to provide a systematic evaluation on how biotic and abiotic factors affect St.LocationGlobal.Time period1970–2019.Major taxa studiedWoody plants (trees and shrubs).MethodsWe compiled a global stemflow dataset from 234 peer‐reviewed papers, which included 488 observations of St and the related biotic (stand characteristics) and abiotic factors (climate variables) at 283 sites within terrestrial woody plant ecosystems. We explored the global pattern of St and performed a machine learning method (boosted regression trees) to model the effects of biotic and abiotic variables on St.ResultsGlobally, the median (interquartile range, IQR) St was 2.7% (1.0–6.3%). We found that St in arid zones (type B in the Köppen‐Geiger climate classification) was significantly higher (p < .01) than in other climate types, and we also detected a significant difference (p < .01) in St between trees (median: 2.4%; IQR: 1.0–5.3%) and shrubs (median: 7.2%; IQR: 5.2–11.9%). Predictor variables that substantially accounted for the explained deviance of the final model included vegetation height (27.0%), mean annual precipitation (16.1%), mean annual temperature (14.4%), stand density (10.8%), stand age (8.9%) and bark type (5.5%). In contrast, leaf area index, diameter at breast height, basal area, phenology type, life‐form and leaf type were classified as low importance.Main conclusionsOur synthesis provides a cross‐site comparison of St, and gives a holistic view on how climate variables and stand characteristics contribute to and affect global stemflow production.

In situ monitoring of an inclined cover made with mine waste materials to control water infiltration on a reactive waste rock dyke

The development of a cover for inclined acid-generating areas, such as the external face of dykes and the slope of waste rock piles, is undoubtedly one of the biggest technical reclamation challenges at several mine sites. The LaRonde mine site, owned and operated by Agnico Eagle Mines (Quebec, Canada) is currently engaged to identify an optimal reclamation scenario for the Dyke 1 of its acid-generating tailings storage facilities. One of the promising reclamation options for controlling water infiltration in the acid-generating waste rock on the Dyke 1 is the use of an inclined cover built with available mine waste materials. An instrumented inclined cell with an inclination angle of 18.3 degrees was built on a slope of this dyke to validate if low sulfide tailings and non potentially acid-generating waste rock can be used as cover material to reclaim the Dyke 1. The instrumented inclined cell was monitored for 3 years (2017 to 2019) using volumetric lysimeters, suction sensors, and volumetric water content sensors. The monitoring was done under natural climatic conditions and artificial wetting events. Under natural conditions, less than 1% (5 mm) of incident rainfall percolated in the volumetric lysimeters installed along the slope of the inclined cell. Under controlled conditions associated with artificial wetting events of 6.4 mm/h over a period of 12 h, net percolation values between 1 and 9% (4 to 60 mm) of the sum of incident precipitation were measured. The distance between the top of the cell and the Down Dip Limit (DDL) point was greater than the slope length of the cover under natural conditions and the DDL point moved from the bottom toward the top to reach values between 12 and 20 m from the top of the slope when the wetting events were applied on the cover. These results confirmed the suitability of mining materials as an inclined cover material to control water infiltration in reactive mine waste rocks.

Balance hídrico en plantaciones de Pinus radiata en el NO de la Patagonia argentina

In the Patagonia Andean Region, silvopastoral system success depends on forestry management, which seeks to guarantee highest water input into the soil to forage production. The aim of this study was to quantify and compare different components of the water balance in a Pinus radiata forest under two different management practices: silvopastoral and forest treatment (325 and 622 trees/ha, respectively). In order to explain incident precipitation distribution within the forest, different variables were measured: direct precipitation, stemflow, interception, soil moisture content, percolation and evapotranspiration. Additionally, canopy cover, leaf area index (LAI) and forage production was determined. Silvopastoral system, with respect to forest system, presented higher direct precipitation (84±1 vs. 75±2%), lower stemflow (2±0.3 vs. 3±0.27%), lower interception (14±1 vs. 22±2%), higher soil moisture content (24.2±2.5 vs. 20.9±2.1%) and lower canopy cover (70.9±0.05 vs. 74.89±0.34%). In turn, percolation (0.33±0.12 vs. 0.11±0.08%), evapotranspiration (78.2 vs. 73.3%), pasture production (230.76±97.57 vs. 66.60±60.02 kg MS.ha-1.year-1) and LAI (1.28±0.04 vs. 1.31±0.02) were similar in both systems. These results show that management density modified only some components of water balance. However, adding more water the silvopastoral system was not reflected in an increase in pasture production. Density management is key, mainly in silvopastoral system, where different system components must be raised up for a more efficient water usage. https://doi.org/10.25260/EA.19.29.2.0.776

Incident Precipitation Partitioning: The Canopy Interactions Enrich Water Solution With Nutrients in Throughfall and Stemflow

Atmospheric deposition is responsible for the ions input, which may be due to dust and aerosols and rainfall. During rainfall a portion is intercepted by the tree canopy and returned to the atmosphere by evapotranspiration, another part crosses the forest canopy called throughfall and stemflow. The objective of the present work was to quantify the nutrient input of the incident rainfall, throughfall, stemflow and canopy enrichment in an Eucalyptus dunnii plantation, established in soil with low natural fertility. Four plots of 20 m × 21 m were demarcated. The rainfall consists 3 rain collectors in an open área. The throughfall consisted 3 collectors per plot in the line, interlining and diagonal positions of the trees. The stemflow consisted in the installation of three systems per plot formed by a hose in the trunk of the tree that leads the solution to a reservoir. Through rainfall, 29.5 kg ha-1 of nutrients were supplied. When we consider the sum of the throughfall and stemflow, the amount of nutrients was 77.6 kg ha-1. After interaction with the tree canopy 48.2 kg ha-1 of nutrients were incorporated. Potassium showed the highest enrichment: 607%. The average nutrient enrichment was 163%. The input of N and K via incident rainfall was 1.8 and 3.1 kg ha-1. Considering the fertilization described in the methodology, this contributed amount represents 6.1 and 2.6% of the total. If we consider the rotation of 7 years for Eucalyptus dunnii, the contribution at the end of rotation represents 42.4 and 18% of N and K2O. The interaction with the canopy of Eucalyptus dunnii enriches the rainwater with nutrients making the solution with a more basic character.

Incident Precipitation Partitioning: Throughfall, Stemflow and Canopy Interception in Eucalyptus dunnii Stand

Atmospheric deposition is responsible for the ions input, which may be due to dust and aerosols and rainfall. During rainfall a portion is intercepted by the tree canopy and returned to the atmosphere by evapotranspiration, another part crosses the forest canopy called throughfall and stemflow. The objective of the study was to quantify incident rainfall partitioning into throughfall, stemflow and canopy interception in a Eucalyptus dunnii stand in southern Brazil. Four plots of 20 m × 21 m were demarcated. The rainfall consists 3 rain collectors in an open area. The throughfall consisted 3 collectors per plot in the line, interlining and diagonal positions of the trees. The stemflow consisted in the installation of three systems per plot formed by a hose in the trunk of the tree that leads the solution to a reservoir. The adjustment of the throughfall, stemflow and canopy interception in function of the incident precipitation was of 99%, 90% and 52%. As the volume of rainfall increases, the coefficient of variation decreases. The annual rainfall was 1903 mm, with a canopy interception average of 8.9%.

Capacidade de retenção de água do dossel vegetativo: comparação entre Mata Atlântica e plantação florestal de eucalipto

A Mata Atlântica, um dos ecossistemas mais ameaçados do planeta, reduzida atualmente a menos de 8% de sua cobertura original, necessita de atenção especial para sua melhor conservação. O objetivo do estudo foi comparar a capacidade de retenção de água do dossel vegetativo em uma microbacia coberta por Floresta Ombrófila Densa (Mata Atlântica), situada no Parque Estadual da Serra do Mar e outra com cobertura de Eucalyptus urophylla x Eucalyptus grandis em área próxima ao Parque. O monitoramento foi realizado nos anos de 2008 e 2009 através de pluviômetros e a retenção de água do dossel florestal foi avaliada a partir de regressões lineares entre a precipitação (PR) e a precipitação interna (TR). Os resultados mostraram que com exceção da interceptação na época “seca” que apresentou os menores coeficientes de determinação (R2), sendo de 77% no eucalipto e 82% na Mata Atlântica, as variáveis apresentaram bom ajuste com a precipitação incidente com coeficientes maiores de 90%. A microbacia de Mata Atlântica obteve maior capacidade de retenção de água das copas em relação ao eucalipto, em todo o período de estudo foi observado que precipitações inferiores a 5 mm na Mata Atlântica e 0,78 mm no Eucalipto são totalmente interceptadas pelo dossel florestal e o período úmido apresentou a maior capacidade de retenção de água, provavelmente pela maior regeneração vegetal nesta época, já que no período seco a queda das folhas pode diminuir a retenção.

Linear Regression of Incident Precipitation Explains the Throughfall, Stemflow and Interception by the Eucalyptus Canopy under Different Fertilization Management

The present work aims to quantify the precipitation partition after interaction with the Eucalyptus urophylla canopy under two fertilization treatments. The experimental design was completely causalized with two fertilization treatments. Each plot had a dimension of 30 m x 60 m, and the spacing of the seedlings was 3 m x 2 m. The study was developed in a arenizaded area located in the municipality of Maçambará, state of Rio Grande do Sul, Brazil. The duration of the study was one year (from April 2017 to March 2018). Biweekly over twelve months the volume of precipitation was quantified. The experiment consists of two fertilization treatments in a Eucalyptus urophylla stand: T1 with smaller and T2 greater fertilization. In each treatment 3 throughfall collectors were installed at one meter of the soil level and three stemflow collectors. In the open area 3 collectors of the incident precipitation were installed 1.5 meters from the ground level. The percentages of the throughfall, stemflow and canopy interception in relation to the incident precipitation were 95.3; 1.3 and 4.3% for treatment 1 and 91.7; 3.2 and 6.2% for treatment 2. The coefficients of determination for throughfall, stemflow and canopy interception were 0.99; 0.96 and 0.85 for treatment 1 and 0.99; 0.97 and 0.89 for treatment 2. The graphical analysis of the regression residues shows independence of the errors. The fertilization management described for treatment 2 results in a greater interception of rainfall due to the greater amount of biomass of the canopy.

Mapped Hydroclimatology of Evapotranspiration and Drainage Runoff Using SMAP Brightness Temperature Observations and Precipitation Information

AbstractThe partitioning of incident precipitation into evapotranspiration, runoff, drainage, storage change, and hydrologic fluxes depends on the soil moisture state. With the availability of global remotely sensed soil moisture fields, the functional dependence of each flux on soil moisture may be identifiable. In this study we develop an observation‐driven approach to map key hydroclimatology fields using remotely sensed soil moisture and gauge‐based precipitation data only. National Aeronautics and Space Administration's Soil Moisture Active Passive (SMAP) low‐frequency microwave brightness temperature observations and precipitation fields, from the National Centers for Environmental Prediction, are the sole inputs into an adjoint‐state variational estimation framework. Furthermore, the proposed methodology does not rely on micrometeorological information, or land surface models. The approach is flexible by design so that almost any partitioning pattern can result from estimation and corresponding evapotranspiration and drainage fields can be quantified. Three‐year averaged summer season evapotranspiration estimates are compared with available vapor flux at in situ AmeriFlux eddy‐covariance sites. Basin‐averaged drainage over major U.S. hydrologic units is also compared with U.S. Geological Survey streamgages measurements. The remote sensing‐based estimated hydroclimate fields explain about 70% of the variance in the in situ measurements. This exploratory study adds to the body of evidence emerging in literature that a significant amount of hydrologic information is encoded in the dynamic fields of remotely sensed soil moisture. Observation‐driven hydroclimate data fields that are independent of land surface models can provide valuable insights into the state of the water cycle and guide future development of land surface models.

Rainfall partitioning through a mixed cedar swamp and associated C and N fluxes in Southern Ontario, Canada

AbstractPartitioning of rainfall through a forest canopy into throughfall, stemflow, and canopy interception is a critical process in the water cycle, and the contact of precipitation with vegetated surfaces leads to increased delivery of solutes to the forest floor. This study investigates the rainfall partitioning over a growing season through a temperate, riparian, mixed coniferous‐deciduous cedar swamp, an ecosystem not well studied with respect to this process. Seasonal throughfall, stemflow, and interception were 69.2%, 1.5%, and 29.3% of recorded above‐canopy precipitation, respectively. Event throughfall ranged from a low of 31.5 ± 6.8% for a small 0.8‐mm event to a high of 82.9 ± 2.4% for a large 42.7‐mm event. Rain fluxes of at least 8 mm were needed to generate stemflow from all instrumented trees. Most trees had funnelling ratios <1.0, with an exponential decrease in funnelling ratio with increasing tree size. Despite this, stand‐scale funnelling ratios averaged 2.81 ± 1.73, indicating equivalent depth of water delivered across the swamp floor by stemflow was greater than incident precipitation. Throughfall dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) averaged 26.60 ± 2.96 and 2.02 ± 0.16 mg L−1, respectively, which were ~11 and three times above‐canopy rain levels. Stemflow DOC averaged 73.33 ± 7.43 mg L−1, 35 times higher than precipitation, and TDN was 4.45 ± 0.56 mg L−1, 7.5 times higher than rain. Stemflow DOC concentration was highest from Populus balsamifera and TDN greatest from Thuja occidentalis trees. Although total below‐canopy flux of TDN increased with increasing event size, DOC flux was greatest for events 20–30 mm, suggesting a canopy storage threshold of DOC was readily diluted. In addition to documenting rainfall partitioning in a novel ecosystem, this study demonstrates the excess carbon and nitrogen delivered to riparian swamps, suggesting the assimilative capacity of these zones may be underestimated.

Comparisons of stemflow and its bio-/abiotic influential factors between two xerophytic shrub species

Abstract. Stemflow transports nutrient-enriched precipitation to the rhizosphere and functions as an efficient terrestrial flux in water-stressed ecosystems. However, its ecological significance has generally been underestimated because it is relatively limited in amount, and the biotic mechanisms that affect it have not been thoroughly studied at the leaf scale. This study was conducted during the 2014 and 2015 rainy seasons at the northern Loess Plateau of China. We measured the branch stemflow volume (SFb), shrub stemflow equivalent water depth (SFd), stemflow percentage of incident precipitation (SF %), stemflow productivity (SFP), funnelling ratio (FR), the meteorological characteristics and the plant traits of branches and leaves of C. korshinskii and S. psammophila. This study evaluated stemflow efficiency for the first time with the combined results of SFP and FR, and sought to determine the inter- and intra-specific differences of stemflow yield and efficiency between the two species, as well as the specific bio-/abiotic mechanisms that affected stemflow. The results indicated that C. korshinskii had a greater stemflow yield and efficiency at all precipitation levels than that of S. psammophila. The largest inter-specific difference generally occurred at the 5–10 mm branches during rains of ≤ 2 mm. Precipitation amount was the most influential meteorological characteristic that affected stemflow yield and efficiency in these two endemic shrub species. Branch angle was the most influential plant trait on FR. For SFb, stem biomass and leaf biomass were the most influential plant traits for C. korshinskii and S. psammophila, respectively. For SFP of these two shrub species, leaf traits (the individual leaf area) and branch traits (branch size and biomass allocation pattern) had a great influence during lighter rains ≤ 10 mm and heavier rains > 15 mm, respectively. The lower precipitation threshold to start stemflow allowed C. korshinskii (0.9 mm vs. 2.1 mm for S. psammophila) to employ more rains to harvest water via stemflow. The beneficial leaf traits (e.g., leaf shape, arrangement, area, amount) might partly explain the greater stemflow production of C. korshinskii. Comparison of SFb between the foliated and manually defoliated shrubs during the 2015 rainy season indicated that the newly exposed branch surface at the defoliated period and the resulting rainfall intercepting effects might be an important mechanism affecting stemflow in the dormant season.

Modelling interception loss using the revised Gash model: a case study in a mixed evergreen and deciduous broadleaved forest in China

AbstractInterception loss accounts for a substantial portion of incident precipitation and evapotranspiration in forest ecosystems. Hence, identifying its magnitude is crucial for our understanding of biogeochemical cycling and related hydrological processes. In this study, gross rainfall partitioning into interception loss, throughfall and stemflow were measured and modelled using the revised Gash model for a mixed evergreen and deciduous broadleaved forest over the 2014 growing season. Field survey results revealed that interception loss accounted for 14.3% of gross rainfall, while understory rainfall was 84.8% throughfall and 0.9% stemflow. The revised Gash model produced a fairly good agreement between observed and estimated rainfall partitioning. The model underestimated interception loss by only 6.6%, while throughfall and stemflow were also slightly misestimated. Hence the interception loss predictions from the model were robust and reliable for this mixed evergreen and deciduous broadleaved forest. As quantified by the model, the vast majority of interception loss occurred as evaporation from the canopy under saturated conditions: 54.9% evaporated during rainfall events, and 38.3% after rainfall ceased. The sensitivity analysis indicated that predictions from the revised Gash model were most affected by changes in canopy storage capacity (S), followed by the mean evaporation rate (Ē) during rainfall events, the mean rainfall rate ( ) and last canopy cover (c). Model predictions were least sensitive to trunk parameters (St and pt). Copyright © 2016 John Wiley & Sons, Ltd.

Photosynthetic response of mountain grassland species to drought stress is affected by UV-induced accumulation of epidermal flavonols

Interactive effects of drought and ultraviolet (UV) radiation on CO2 assimilation rate and accumulation of epidermal flavonols were studied in two herbs (Hypericum maculatum and Rumex obtusifolius) and two grasses (Agrostis capillaris and Holcus mollis) under field conditions of Beskydy Mts. The main objective of this study was to evaluate a protective role of epidermal flavonols against drought stress. Experimental shelters were used to manipulate amount of incident precipitation and UV radiation intensity for 12 weeks (May–July). The light-saturated CO2 assimilation rate (Amax) and the content of epidermal flavonols were regularly measured at intervals of 2–3 weeks during the entire period. Drought-induced reduction of Amax was enhanced by high UV intensity in R. obtusifolius, whereas in other species UV radiation reduced a negative effect of drought. Generally, drought increased flavonol content in leaves as compared to non-stressed plants. Similarly, high UV intensities increased the flavonol content in control plants, but not in drought-stressed ones. Regression analysis between the flavonol content and Amax revealed a positive correlation especially for A. capillaris and R. obtusifolius. In both species, a separation of these relationships was observed as the result of water availability. Thus lower Amax were observed at the same flavonol content in drought-stressed plants when compared to control, well-watered counterparts. We conclude that UV-induced accumulation of epidermal flavonols can alleviate negative impacts of summer drought on photosynthesis, particularly in species with slower ontogeny like H. maculatum and A. capillaris.

Evaluation of drought and UV radiation impacts on above-ground biomass of mountain grassland by spectral reflectance and thermal imaging techniques

Drought represents one of the major factors limiting productivity of managed and natural ecosystems. Under natural field conditions drought is often associated with other stress factors such as high temperature and UV radiation, which may result in enhancement or vice versa alleviation of drought impact. Remote sensing methods have a large potential to evaluate impacts of drought on plant production at regional scale. The main objective of this study was to analyse the potential of ground-based measurement of spectral reflectance and thermal imaging for monitoring the impacts of drought and UV radiation on above-ground biomass production of mountain grassland ecosystem. Experimental rain-out shelters were used to manipulate incident precipitation and UV radiation for 7 weeks (May–July). A canopy spectral reflectance, thermal images, and total above-ground biomass were determined at the end of drought and UV treatment. Results show that drought led to a significant reduction of above-ground biomass, particularly under ambient UV radiation. In contrary, UV had only negligible effect on biomass production. Canopy temperature as well as selected spectral reflectance indices showed significant response to drought stress and also significant relationships to above-ground biomass. However, the relationship between canopy temperature and above-ground biomass is modified by UV radiation. Best prediction of changes in biomass caused by drought stress was provided by vegetation index NDVI.