Variability Of Throughfall Research Articles

Measurements and modeling of throughfall variability for five forest communities in the southeastern US

The temporal variability of interception losses was measured for contrasting forest communities in the southeastern United States. Throughfall was measured simultaneously at Fort Benning in western Georgia for the five forest communities that are characteristic of the region. The measured interception losses over the study period were 22.3, 18.6, 17.7, 17.6, and 17.4% of the total precipitation in the pine, mixed forest, lowland hardwood, pine plantation, and upland hardwood forests, respectively. The Gash model with a wet canopy Penman–Monteith evaporation, using annual average canopy cover values, predicted interception losses with an agreement of −8.1–10.5% on an annual basis. The model improved accuracy for all forest communities when seasonal changes in canopy cover were included. The Gash model's assumption of a constant canopy storage capacity was examined for pine and lowland hardwood plots with varying densities and found to have good agreement for mature pine forests having 64, 44, and 29% canopy cover. However, riparian wetland forest predictions required corrections for species composition and understory vegetation.

Determination of Sulfate, Nitrate, and Chloride in Throughfall using Ion-Exchange Resins

Throughfall, the solution that falls from the forest canopy, is an important and commonly measured flux in forest ecosystem studies. Throughfall water and chemistry are highly variable spatially, requiring large numbers of collectors to quantify it. This and the fact that the solution can be chemically unstable make throughfall sampling very labor intensive, thus we have developed a method to reduce the field labor portion of this effort. Our throughfall collection method uses com- pact ion exchange resin columns that need only be collected every 1-2 months. The resin columns are subsequently extracted with 1.0 M potassium iodide (KI), releasing anions back into solution, with extraction efficiencies > 94% for sulfate, nitrate, and chloride. The extracts are analyzed by ion-chromatography (IC) to determine the total microequivalents of anions per unit area of collector surface collected over the period of resin column exposure. This ion exchange resin method was originally developed for a project in which we needed to deploy over 300 throughfall collectors to quantify throughfall variability across mountainous terrain with heterogeneous vegetation.

マレーシア-サラワク-ランビル国立公園における林内降水量研究

マレーシア-サラワク-ランビル国立公園における林内降水量研究

Trace metal fluxes in bulk deposition, throughfall and stemflow at two evergreen oak stands in NE Spain subject to different exposure to the industrial environment

We compare here the bulk deposition, throughfall and stemflow fluxes of dissolved trace metals in two holm oak ( Quercus ilex L.) forests in the Montseny Mountains (NE Spain) with the aim of: (1) applying different methods to distinguish between dry deposition and canopy leaching and (2) to add to the almost non-existing deposition measurements for dissolved Cu, Pb, Mn, V, Zn, Ni and Cd in two Spanish forests differentially exposed to the urban and industrial environment. No significant differences in mean bulk deposition concentrations or fluxes were found between sites, indicating little differential effect of the urban/industrial environment on bulk precipitation chemistry . At both sites, throughfall and stemflow fluxes increased relative to bulk deposition for all elements, except for Zn and Cd. The relative contribution of leaching and dry deposition was evaluated through: (1) the seasonal variability of throughfall, (2) regressions of element fluxes on water flux in net throughfall, (3) washing branches and metacrylate plates, and (4) the sequential washing of branches. Results indicated that leaching was the main enrichment process for Mn. For Ni, except the sequential washings, all other evidences also pointed to leaching. For Cu, Pb, Zn, Cd and V there was ample evidence for dry deposition. The fact that Zn and Cd had negative net throughfall fluxes indicated that canopy uptake was greater than deposition (wet plus dry). Net throughfall fluxes pointed to higher dry deposition onto the canopies in the more exposed site, but the occurrence of uptake impeached quantification. Therefore, dry deposition was estimated from the recovered quantities from experimental washings of foliage, taken to represent the impaction of small particles onto the canopy. The foliage-wash fluxes were, for Zn, Cu and Pb, respectively, 407, 25 and 16 g ha −1 yr −1 at the sheltered site and 423, 38 and 26 g ha −1 yr −1 at the exposed site. Deposition in bulk precipitation (wet deposition+an unknown fraction of dry deposition mostly accounted by coarse particles settling gravitationally) was lower: 222, 6.3 and 6.5 g ha −1 yr −1 for Zn, Cu and Pb, respectively, averaged for the two sites.

Measurement of snow interception and canopy effects on snow accumulation and melt in a mountainous maritime climate, Oregon, United States

The results of a 3 year field study to observe the processes controlling snow interception by forest canopies and under canopy snow accumulation and ablation in mountain maritime climates are reported. The field study was further intended to provide data to develop and test models of forest canopy effects on beneath‐canopy snowpack accumulation and melt and the plot and stand scales. Weighing lysimeters, cut‐tree experiments, and manual snow surveys were deployed at a site in the Umpqua National Forest, Oregon (elevation 1200 m). A unique design for a weighing lysimeter was employed that allowed continuous measurements of snowpack evolution beneath a forest canopy to be taken at a scale unaffected by variability in canopy throughfall. Continuous observations of snowpack evolution in large clearings were made coincidentally with the canopy measurements. Large differences in snow accumulation and ablation were observed at sites beneath the forest canopy and in large clearings. These differences were not well described by simple relationships between the sites. Over the study period, approximately 60% of snowfall was intercepted by the canopy (up to a maximum of about 40 mm water equivalent). Instantaneous sublimation rates exceeded 0.5 mm per hour for short periods. However, apparent average sublimation from the intercepted snow was less than 1 mm per day and totaled approximately 100 mm per winter season. Approximately 72 and 28% of the remaining intercepted snow was removed as meltwater drip and large snow masses, respectively. Observed differences in snow interception rate and maximum snow interception capacity between Douglas fir (Pseudotsuga menziesii), white fir (Abies concolor), ponderosa pine (Pinus ponderosa), and lodgepole pine (Pinus contorta) were minimal.

Spatial variation of throughfall volume in an old-growth tropical wet forest, Costa Rica

Throughfall volume and interception of bulk precipitation events were measured during individual rain events of differing magnitudes in a primary wet tropical forest at La Selva Biological Station, Costa Rica. The relationship between canopy structure and throughfall were examined to identify key sources of spatial variation. Geostatistical analyses were also used to examine the spatial variation in throughfall, spatial autocorrelation and to determine minimum distances for independence of collectors. Throughfall volume was collected from 56 ground-based (funnel-style) collectors. Throughfall was collected for 26 separate precipitation events during July and August 1998. Per cent cover, distance to nearest tree, distance to nearest leaf were also estimated for each collection point. A weak relationship was found with per cent cover (r2 = 0.11). No relationship was found between throughfall and distance to the nearest leaf above the collector. Estimated interception was 1.88 mm (r2 = 0.94) with increased variance as bulk precipitation increased. A range distance of 45 m was estimated from variograms, strongly suggesting that large tree canopies and gaps are the source of much of the spatial variance in throughfall volume. Interception was reduced by 19% if only spatially independent collectors were used.

A six-year study of sapling and large-tree growth and mortality responses to natural and induced variability in precipitation and throughfall.

Global climatic change may cause changes in regional precipitation that have important implications for forest growth in the southern United States. In 1993, a stand-level experiment was initiated on Walker Branch Watershed, Tennessee, to study the sensitivity of forest saplings and large trees to changes in soil water content. Soil water content was manipulated by gravity-driven transfer of precipitation throughfall from a dry treatment plot (-33%) to a wet treatment plot (+33%). A control plot was included. Each plot was 6400 m2. Measurements of stem diameter and observations of mortality were made on large trees and saplings of Acer rubrum L., Cornus florida L., Liriodendron tulipifera L., Nyssa sylvatica Marsh, Quercus alba L. and Quercus prinus L. every 2 weeks during six growing seasons. Saplings of C. florida and A. rubrum grew faster and mortality was less on the wet plot compared with the dry and control plots, through 6 years of soil water manipulation. Conversely, diameter growth of large trees was unaffected by the treatments. However, tree diameter growth averaged across treatments was affected by year-to- year changes in soil water status. Growth in wet years was as much as 2-3 times greater than in dry years. Relationships between tree growth, phenology and soil water potential were consistent among species and quantitative expressions were developed for application in models. These field growth data indicate that differences in seasonal patterns of rainfall within and between years have greater impacts on growth than percentage changes in rainfall applied to all rainfall events.

Nutrient content of incident rainfall, throughfall and stemflow in a Nigerian secondary lowland rainforest

Abstract. Nutrient content of rainfall, throughfall and stemflow was studied over one year in the open and under the crowns of three tree species in a secondary rain forest at Ile‐Ife, Nigeria. Throughfall and stemflow comprised 78.8 % and 5.2 % respectively; 16.0 % of the incident rainfall was intercepted by the forest canopy. The concentrations of various nutrient elements in throughfall and stemflow were higher than those of incident rainfall. In throughfall and stemflow potassium concentration was highest and that of ammonium nitrogen was the lowest. Only calcium and sodium concentrations showed significant monthly variation in incident rainfall. Ca, Mg, K. Cu and P showed significant monthly variation in throughfall and stemflow. The concentrations of the elements were highest during the heavy‐rain months (May‐September). High concentrations of some of the elements were recorded also in November, the last rain month and the beginning of the dry season.The concentration of these elements in stemflow and throughfall was affected by tree species. The highest quantity of each element was deposited in the forest via throughfall followed by incident precipitation and the lowest via stemflow. The tree species affected the quantities of these elements by the volume of their stemflow and throughfall and the concentration of the various elements herein. Total nutrient concentration was much higher than available (dissolved) nutrient concentration. This was very pronounced with micronutrients.

Spatial Variability of Throughfall in a Subtropical Rain Forest in Taiwan

AbstractEight rainfalls were intensively sampled in a subtropical rain forest in northeastern Taiwan. This study, carried out at Fu‐shan Experimental Forest was designed to examine variability of throughfall characteristics. The volume and chemistry of the throughfall associated with individual rains have a high degree of spatial variability, with throughfall chemistry more variable than volume. When data from all of the storms were combined, there was lower variability than that seen with individual storms, largely as a result of a lack of consistent storm to storm spatial variation. Thus, individual storms cannot be used to represent the seasonal or annual pattern of spatial variation in throughfall chemistry or volume of the study forest. Twenty samples were required to estimate throughfall volume within 10% of the population mean with 95% confidence for individual storms. Yet, more than 100 samples were required to estimate the throughfall chemistry of some ions (e.g., H+). When the data from all eight storms were combined, 7, 20, and 25 samples were necessary to estimate throughfall volume, ion concentrations, and ion fluxes (except for Mg2+ and H+) within 10% of the population mean with 95% confidence. In the absence of estimates of spatial variation, differences in sampling protocols among throughfall studies make comparisons of throughfall characteristics difficult. In this study three funnels were used in tandem to capture small scale variability at each sample location, thus reducing spatial variability of throughfall chemistry.

Spatial variability of throughfall fluxes in a spruce forest

The spatial variability of throughfall deposition of H +, Ca 2+, Mg 2+, Na +, K +, Cl −, NO 3 −, NH 4 +, O 4 2− to a Norway spruce ( Picea abies (L.) Karst.) forest was intensively examined during the period October 1986 to October 1987. Large systematic spatial variability of the atmospheric deposition within the forest was observed. The flux of throughfall water was higher away from the trunk compared to the flux close to the trunk. In contrast to this, the deposition of all substances was considerably higher close to the trunk compared to the deposition at the periphery of the canopy. A linear decrease in deposition as a function of the distance from the nearest tree trunk was found. Further, the deposition varied quite dramatically between trees according to their size. The observed spatial variability in throughfall may be due to variabilities in the processes taking part in altering the distribution and composition of the precipitated water as it moves through the canopy. The influence of these processes of precipitation, wash-off, dry deposition and canopy exchange is discussed, and it is found that both increased dry deposition and canopy exchange in the tree tops contribute to the higher solute fluxes found close to the tree trunk.

Interception loss, throughfall and stemflow in a maritime pine stand. I. Variability of throughfall and stemflow beneath the pine canopy

Patterns of spatial variability of throughfall and stemflow were determined in a maritime pine ( Pinus pinaster Ait.) stand for two consecutive years. Data were obtained from 52 fixed rain gauges and 12 stemflow measuring devices located in a 50m × 50m plot at the centre of an 18-year-old stand. The pine trees had been sown in rows 4m apart and had reached an average height of 12.6m. The spatial distribution of stems had a negligible effect on the throughfall partitioning beneath the canopy. Variograms of throughfall computed for a sample of storms did not reveal any spatial autocorrelation of throughfall for the sampling design used. Differences in throughfall, in relation to the distance from the rows, were not consistently significant. In addition, the distance from the tree stem did not influence the amount of throughfall. The confidence interval on the amount of throughfall per storm was between 3 and 8%. The stemflow was highly variable between trees. The effect of individual trees on stemflow was significant but the amount of stemflow per tree was not related to tree size (i.e. height, trunk diameter, etc.). The cumulative sampling errors on stemflow and throughfall for a single storm created a confidence interval of between ±7 and ±51% on interception. This resulted mainly from the low interception rate and sampling error on throughfall.

Rainfall interception and boundary layer conductance in relation to tree spacing

The effect of tree spacing on rainfall interception loss has been investigated in stands of Sitka spruce ( Picea sitchensis (Bong.) Carr) spaced at intervals of 2, 4, 6 and 8 m. The traditional volume balance method was used to measure throughfall, stemflow and interception loss. The variation of throughfall, stemflow and interception loss between the four spacing treatments is analysed. The results obtained showed that, on average, annual intercepton loss as a percentage of gross rainfall was 33, 24, 15 and 9% in the 2, 4, 6 and 8 m spacing treatments, respectively. An estimate of average boundary layer conductance was made by equating interception loss with evaporation rate and inverting a truncated form of the Penman equation. The boundary layer conductance per tree increased with spacing from 0.58 m 3 s −1 in the 2 m spacing treatment to 4.24 m 3 s −1 in the 8 m spacing treatment, whereas boundary layer conductance per unit area declined from 0.17 to 0.07 m s −1 as the density of trees decreased. The difference in interception loss between the spacing treatments was attributed to the difference in the boundary layer conductance.

The interception, throughfall and stemflow in a forest in Highland Scotland and the comparison with other upland forests in the U.K.

Interception loss from a 50-year-old Sitka spruce forest at Balquhidder in Highland Scotland has been determined by measuring precipitation, throughfall and stemflow. Annual mean precipitation at the site was 2130mm and for the period October 1983 to June 1986, the average interception was 28% with throughfall and stemflow comprising 69 and 3%, respectively of the precipitation. This interception loss is similar to results from other upland forests in the U.K. While large variations were found throughout the year, interception was greatest in the summer months, reaching 79% in May 1985, and least in the winter, 0% in January 1985. Snow interception can be large, 37% in January 1984 when storage on the canopy was estimated to have reached 22mm water equivalent. The spatial variability of throughfall was dependent on distance away from the tree stem and on the density of the canopy cover. Tree age does not appear to determine interception values but comparison of the relative amounts of throughfall and stemflow with those from other sites shows that there is an increase in throughfall with the age of the tree. This has important consequences for water quality in young forests.

Spatial variability of throughfall and stemflow measurements in Amazonian rainforest

The spatial variability of throughfall and stemflow in Amazonian tropical rainforest is analysed. Statistical tests are used to assess the minimum sampling size and number of gauges required. Random relocation of throughfall gauges is shown to be better than fixed position gauges and random relocation of gauges on a transect line is better than over an area. During the study period, throughfall and stemflow, calculated as percentages of gross rainfall, were 91(± 2) and 1.8(± 1)%, respectively. No attempt was made in this study to investigate storm size dependency of these figures.

Interception of rainfall in a hedgerow apple orchard

Measurements of incident rainfall for an orchard, and throughfall and stemflow under the crowns of apple trees are presented for a 3-month period. The variability of throughfall under a single tree and between trees is assessed and equations to estimate interception loss, throughfall and stemflow from incident rainfall are given. During the period of assessment, the overall interception loss in the rows was about 15% of the incident rainfall.

THROUGHFALL IN A FOREST

Abstract For a period, 1958–60, a record was kept of 24 wedge-shaped gages randomly placed under a secondary hardwood forest canopy to determine the amount and variation in throughfall and drip from the rain. An average of the 24 gages under the canopy for each rain was then compared with the catch in a standard 8-inch rain gage maintained in the open. The comparisons were made by linear and curvilinear regression equations for summer and winter rains, over one inch and under one inch. The size of storm had the most pronounced effect on the throughfall regardless of the seasons. The data showed that the throughfall as a percent of total rainfall varied as the size of the storm. This was represented best by the equations y = 0.834 x 1.045.