High Precipitation Conditions Research Articles

Do Cover Crops Increase Subsequent Crop Yield in Temperate Climates? A Meta-Analysis

Cover crops (CCs) are a promising strategy for maintaining and enhancing agroecosystem sustainability, yet CCs’ effects on the subsequent crop yield are highly variable. To quantitatively synthesize the effects of CCs on subsequent crop yield, a meta-analysis of 672 observations collected from 63 recent studies (2015 to 2021) in temperate climates was conducted. Legume CC species increased subsequent crop yield significantly more than grass (by 14%), nonlegume broadleaves (by 7%), and mixtures (by 2%). Incorporation of CC residue into soil increased crop yield by approx. 15% compared to leaving the CC residue on the soil surface. Relative to the no-CC control, the adoption of grass and legume CC species in non-organic vegetable cropping systems enhanced crop yield by 14% and 19%, respectively. Likewise, crop yield with legume CCs in coarse and medium textured soil, and under high precipitation conditions (>700 mm), was significantly greater than the no-CC control by 18%, 4%, and 11%, respectively. Cover crops significantly increased vegetable crop yields and decreased the silage corn yield; however, grain corn, soybean, and winter wheat yield did not decrease with CC. Adoption of CC in no-tillage and plow tillage systems contributed to an increase in crop yield compared to the no-CC control. Our meta-analysis highlights that crop yield response to CC might become more robust when pedo-climatic conditions and agronomic factors are considered.

Impact of climate change on the elevational and latitudinal distributions of populations of Tipulidae (Diptera) in Wales, United Kingdom

Abstract As dominant features of most ecosystems, insects are responsive to changes in climate, both over short temporal scales (e.g. seasonal fluctuations in abundance) and over longer evolutionary scales (e.g. decade-scale changes in patterns of biodiversity). One such taxonomic group that is sensitive to changing climate are the craneflies (Diptera: Tipulidae). Here, we used aggregated biodiversity data to examine elevational and latitudinal distributions of adult Tipulidae between 1976 and 2019 in Wales, UK, and we related these distributions to climatic patterns. Our analyses showed that species with earlier-emerging adults were most affected by weather conditions in the year before observation. Specifically, as temperature increased, observed elevation increased in high-precipitation conditions, remained stable in average-precipitation conditions and decreased in low-precipitation conditions. For species with later-emerging adults, associations were seen between elevation and weather conditions in the year of observation. Observed latitude generally exhibited a negative association with maximum temperature in the year before observation, with observations of Tipulidae trending southwards during the 43-year study period. Our results support consideration of emergence phenology, weather and habitat data when predicting species distributional changes attributable to climate change, which is vital in understanding the selection pressures that species face in a changing environment.

Effect of precision planting and seeding rates on canola plant density and seed yield in southern Alberta

Precision planters are recently being adopted for seeding canola to improve crop establishment and seed yield. This study determined the effect of seeding canola using precision planters (30.5 and 50.8 cm seeding row width) and conventional air drill seeders at different rates (20, 40, 60, 80, and 160 seeds m−2) on plant density and seed yield. The study was conducted for 4 yr (2016 to 2019) at three locations in southern Alberta. Plant density increased with higher seeding rates following the negative exponential function distribution. The yield-density relationship was non-linear asymptotic in nature and weak-to-moderate in strength at most site-years. The parameters of yield-density relationship did not show statistically significant differences among the air drill and precision planters. When averaged among seeding rates, canola yield was higher for the narrow row precision planter at 5 site-years and for the air drill at 2 site-years out of a total of 12 site-years. Under irrigated and high-precipitation conditions, seed yield in narrow-row precision planted canola was higher than air drill seeded canola. There was an average increase of 463 kg ha−1 (10%) in the seed yield in narrow-row precision planted canola compared with the air drill seeded canola among irrigated systems; however, under water-limited conditions, seed yield in air drill seeded canola was comparable or higher than the precision planted canola. Wide-row planter led to poor crop establishment and seed yield under both irrigated and dryland conditions, attributed to higher in-row plant density due to wider row spacing.

Human impact, climate and dispersal strategies determine plant invasion on islands

AbstractAimBiological invasions are likely determined by species dispersal strategies as well as environmental characteristics of a recipient region, especially climate and human impact. However, the contribution of climatic factors, human impact, and dispersal strategies in driving invasion processes is still controversial and not well embedded in the existing theoretical considerations. Here, we study how climate, species dispersal strategies, and human impact determine plant invasion processes on islands distributed in all major oceans in the context of directional ecological filtering.LocationSix mountainous, tropical, and subtropical islands in three major oceans: Island of Hawai'i and Maui (Pacific), Tenerife and La Palma (Atlantic), and La Réunion and Socotra (Indian Ocean).TaxonVascular Plants.MethodsWe recorded 360 non‐native species in 218 plots along roadside elevational transects covering the major temperature, precipitation and human impact (i.e., road density) gradients of the islands. We collected dispersal strategies for a majority of the recorded species and calculated the environmental niche per species using a hypervolume approach.ResultsNon‐native species’ generalism (i.e., mean community niche width) increased with precipitation, elevation and human impact but showed no relationship with temperature. Increasing precipitation led to environmental filtering of non‐native species resulting in more generalist species under high precipitation conditions. We found no directional filtering for temperature but an optimum range of most species between 10 and 20°C. Niche widths of non‐native species increased with the prevalence of certain dispersal strategies, particularly anemochory and anthropochory.Main conclusionsPlant invasion on tropical and subtropical islands seems to be mainly driven by precipitation and human impact, while temperature seems to be of little importance. Furthermore, anemochory and anthropochory are dispersal strategies associated with large niche widths of non‐native species. Our study allows a more detailed look at the mechanisms behind directional ecological filtering of non‐native plant species in non‐temperature‐limited ecosystems.

Temperature and pH define the realised niche space of arbuscular mycorrhizal fungi.

The arbuscular mycorrhizal (AM) fungi are a globally distributed group of soil organisms that play critical roles in ecosystem function. However, the ecological niches of individual AM fungal taxa are poorly understood. We collected>300 soil samples from natural ecosystems worldwide and modelled the realised niches of AM fungal virtual taxa (VT; approximately species-level phylogroups). We found that environmental and spatial variables jointly explained VT distribution worldwide, with temperature and pH being the most important abiotic drivers, and spatial effects generally occurring at local to regional scales. While dispersal limitation could explain some variation in VT distribution, VT relative abundance was almost exclusively driven by environmental variables. Several environmental and spatial effects on VT distribution and relative abundance were correlated with phylogeny, indicating that closely related VT exhibit similar niche optima and widths. Major clades within the Glomeraceae exhibited distinct niche optima, Acaulosporaceae generally had niche optima in low pH and low temperature conditions, and Gigasporaceae generally had niche optima in high precipitation conditions. Identification of the realised niche space occupied by individual and phylogenetic groups of soil microbial taxa provides a basis for building detailed hypotheses about how soil communities respond to gradients and manipulation in ecosystems worldwide.

Temporal variability of parasites, bacterial indicators, and wastewater micropollutants in a water resource recovery facility under various weather conditions

Wastewater discharges lead to the deterioration of receiving waters through treated effluents and by-passes, combined and sanitary sewer overflows, and cross-connections to storm sewers. The influence of weather conditions on fecal indicator bacteria, pathogens and wastewater micropollutants on raw and treated sewage concentrations has not been extensively characterized. However, such data are needed to understand the effects of by-pass discharges and incomplete treatment on receiving waters. A water resource recovery facility was monitored for pathogenic parasites (Cryptosporidium oocysts, Giardia cysts), fecal indicator bacteria (Escherichia coli, Clostridium perfringens), and wastewater micropollutants (caffeine, carbamazepine, 2-hydroxycarbamazepine, acesulfame, sucralose, and aspartame) during 6 events under different weather conditions (snowmelt and trace to 32 mm 2-day cumulative precipitation). Greater intra- and inter-event variability was observed for Giardia, E. coli and C. perfringens than for studied WWMPs. Even with the addition of inflow and infiltration, daily variations dominated concentration trends. Thus, afternoon and early evening were identified as critical times with regards to high concentrations and flows for potential by-pass discharges. Peak concentrations of Giardia were observed during the June wet weather event (1010 cysts/L), with the highest flowrates relative to the mean monthly flowrate. Overall, Giardia, E. coli and C. perfringens concentrations were positively correlated with flowrate (R > 0.32, p < 0.05). In raw sewage samples collected under high precipitation conditions, caffeine, carbamazepine and its metabolite 2-OH-carbamazepine were significantly correlated (p < 0.05) with Giardia, E. coli, and C. perfringens demonstrating that they are useful markers for untreated sewage discharges. Data from the study are needed for estimating peak concentrations discharged from wastewater sources in relation to precipitation or snowmelt events.

Evaluation of 3B42V7 and IMERG daily-precipitation products for a very high-precipitation region in northwestern South America

The availability of water is critical in determining the distribution of species by favoring or limiting their development, and leading to the formation of different ecosystems. Thus, analyzing the trends and fluctuations of the precipitation is a key factor to understanding our planet's biodiversity. Different physical conditions exist in northwestern South America that cause extreme climate conditions, especially on the west coast of the continent. This region, known as Biogeographic Chocó, has high annual precipitation caused by interactions between the humid currents of the Pacific Ocean and the Andes Mountains. A limited network of hydro-meteorological stations are available in the region to monitor precipitation. Satellite precipitation products can provide valuable information in the absence of field stations, complementing the network of field stations in remote areas, and completing time series for stations that have stopped working. However, remote sensing data must be validated before being used. The goal of this study is thus to evaluate the accuracy of the products of the Tropical Rainfall Measuring Mission 3B42V7 and the Integrated Multi-satellite Retrievals for Global Precipitation Measurement (IMERG), under very high precipitation conditions, and evaluate their strengths and shortcomings. These programs provide daily-precipitation information with a spatial resolution of 0.25° for the former and 0.1° for the latter. The validation was done by using a time series of daily-precipitation data obtained from 185 hydro-meteorological stations distributed over the Biogeographic Chocó. Different statistic metrics were used in the evaluation and comparison: error metrics (mean difference MD, relative mean difference RMD, and root mean square error RMSE), a correlation metric (Pearson correlation CP), contingency metrics (probability of detection POD, false-alarm ratio FAR, and critical success index CSI). We also evaluate the grid and areal scale. The results show that (i) the 3B42V7 and IMERG daily-precipitation products represent well the spatial and temporal distribution of mean daily precipitation over the Biographic Chocó, and both products are accurate for detecting precipitation events. (ii) Mean daily precipitation tends to be overestimated in areas with relative low precipitation and medium-to-high altitude whereas, on the contrary, mean daily precipitation tends to be underestimated in areas with very high precipitation and medium-to-low altitude. (iii) Finally, copious precipitation (i.e., an annual accumulated precipitation over 5000 mm, which is common for over 55% of the study area) strongly affects the accuracy of the satellite products, leading to significant errors in estimates of daily precipitation for some regions. This study constitutes one of the first exhaustive validation of the IMERG daily precipitation product over the Biogeographic Chocó, and the results provide important information about the potential for using this product in the study area and over regions with high precipitation.

Biomass and essential oil of Tagetes minuta influenced by pinching and harvesting stage under high precipitation conditions in the western Himalayas

ABSTRACTA field experiment was conducted to study the effect of pinching and harvesting stages on duration of phenophases, aerial biomass partitioning, and essential oil productivity. It comprised of two pinching (pinching and without pinching) and four harvesting stages (bud initiation, flower initiation, 50% flowering and 100% flowering). All the phenological stages were delayed by pinching and the crop took 93–103 days, respectively, under control and pinching from transplanting to 100% flowering. Biomass accumulation in to leaf, flower and stem was enhanced by pinching. Pinching and 100% flowering stage recorded significantly higher fresh biomass and essential oil content than other treatments. Delay in harvesting stage from bud initiation to 100% flowering also caused variation in oil content and composition. Major constituents of essential oil (Z)-β-ocimene and (E)-ocimenone increases, while dihydrotagetone and (E)-tagetone decreases with delay in harvesting from bud initiation to 100% flowering stage.

Spatial and temporal limnological changes of an aquaculture area in a neotropical reservoir

This study evaluated the spatial and temporal limnological characteristics of an aquaculture area in the Itaipu reservoir, Brazil. During a one-year period, water quality parameters were evaluated in seven collection sites using a fish culture system as the reference point. A regression analysis was performed on water transparency versus chlorophyll a and total phosphorus versus chlorophyll a. The trophic state index (TSI) was calculated using data from water transparency, chlorophyll a, and total phosphorus. In addition, a study of the carrying capacity was conducted in situations of high and low flow and rainfall based on 725 m3 s−1 and 298 mm and 34.5 m3 s−1 and 11 mm, respectively. No difference was observed in the parameters of water quality and the TSI in relation to the collection sites; these parameters only varied significantly throughout the seasons. The regression analysis showed that increased total phosphorus in the environment leads to increase in chlorophyll a concentrations and consequently decreased water transparency. Evaluation of the carrying capacity demonstrated that under conditions of high precipitation and flow it is possible to produce 623.7 tons of fish per year, which is above the total cultivated in fish farms at the study site.

Estimation of lakes water storage and their changes on the northwestern Tibetan Plateau based on bathymetric and Landsat data and driving force analyses

Lake water storage changes in four lakes were analyzed based on in situ bathymetric survey data and Landsat images in the extremely dry and cold northwestern Tibetan Plateau region. The results indicated that Bangdag Co and Aksai Chin Lake, which are glacier-fed and closed lakes, showed decreasing trends from 1976 to 1996, then increasing trend from 1996 to 2015, during which period water storage increased by 1.24 km3 and 1.37 km3, respectively, and 65% of the water storage increase in Aksai Chin Lake during this period occurring in 2006 and 2013. Longmu Co, which is a non-glacier-fed lake, exhibited little variation from 1976 to 1996 and a slight increase of 0.1 km3 from 1996 to 2015. The precipitation, temperature and potential evaporation (Ep) trends indicated that lake shrinkage from 1976 to 1996 was attributed to less precipitation and less meltwater at lower surface air temperatures. Decreased Ep (15.5 mm/y) contributed approximately 2% and 4% to the lake expansion of Aksai Chin Lake and Bangdag Co from 2000 to 2009. Based on the assumption of equal precipitation-evaporation for the study area, glacial meltwater contributed 76.6% to the lake expansion of Bangdag Co from 2000 to 2015. Because change in lakes' water storage showed a large difference between glacier-fed lakes and non-glacier-fed lakes from 1996 to 2015 under relatively high precipitation conditions, it is suggested that glacial meltwater exerted more influence on increasing lake water storage associated with rising temperatures.

降雨格局变化对白刺幼苗根系形态特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 降雨格局变化对白刺幼苗根系形态特征的影响 DOI: 10.5846/stxb201608161679 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41361100，31560135，31360205，41461044）；甘肃省科技支撑项目（1604FKCA088）；中国博士后科学基金（2014M552514）；甘肃省高等学校科研项目（2015A-067，2015A-069） Response of the root morphology of Nitraria tangutorum seedlings to precipitation pattern changes Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探讨荒漠植物白刺幼苗根系形态对降雨格局变化的响应特征，设置3个降雨量梯度（W-、W、W+）和2个降雨间隔时间梯度（T、T+）进行人工模拟试验，结果表明，1）降雨量和降雨间隔时间对白刺幼苗根系形态有不同程度的影响，且降雨量的作用效应更大。2）降雨量相同时，延长降雨间隔时间均使白刺幼苗主根长、根系平均直径、根体积和根表面积减小，但总根长和根系生物量和总生物量却增加，在高降雨量条件下（W+）延长降雨间隔时间白刺幼苗比根长和比表面积分别增加了45.09%和20.20%，但差异均不显著。3）降雨间隔时间相同时，降雨量减少30%仅使主根长平均增加12.06%，总根长、根平均直径、根体积和根表面积等根系形态指标均显著减少，比根长和比表面积变化不大；降雨量增加30%仅使比表面积显著增加，其余各形态指标差异均不显著，低降雨量条件下（W-）主根长与根冠比达到最大，其他指标均在高降雨量条件下（W+）达到最大。4）对8个根系形态参数进行主成分分析，根系生物量、总根长、总根表面积、比根长、比表面积和根体积6个根系生态参数受降雨格局影响显著。 Abstract:A global climate model has predicted changes in precipitation patterns, with extended periods of time between precipitation events; larger individual precipitation events are expected to increase. Furthermore, with global climate change, local area rainfall patterns have also changed. Over 80 years, the annual precipitation in arid areas of central Asia has generally shown an increasing trend. Such an altered precipitation regime will significantly alter the temporal supply of water to desert ecosystems, and thus have important effects on ecological processes, which could ultimately affect species composition and biological diversity. Root growth of seedlings is the most important stage in plant regeneration and the most sensitive in the plant life cycle to environmental conditions. The responses of root morphology to changes in precipitation and the ability of seedlings to adapt can directly affect the success of subsequent seedling establishment, and may affect regeneration dynamics. Nitraria tangutorum, a super-xerophytic shrub, exhibits a strong tolerance for drought, cold, and saline-alkali soil. The shrub vegetation type in which N. tangutorum is the dominant species is an important vegetation type in the deserts of northwestern China. As a result, N. tangutorum is the key species for the revegetation of these arid and semiarid areas. Most research has examined the impacts of the amount of precipitation on this species rather than the effects of both the amount and interval of precipitation. To understand how climate-driven changes in precipitation can affect desert plants, especially the response of the root morphology to precipitation patterns change, we conducted a controlled experiment with two factors: precipitation quantity (natural precipitation as a control, reduction of 30% and increase of 30%) and interval (time elapsed between two precipitation events; 5 or 10 days). The results showed that root morphological characteristics were influenced by total precipitation and precipitation interval, the former playing a more significant role than the latter. Under the same precipitation condition, the main root length, root diameter, root volume, and root surface area were decreased, total root length, root biomass, and total biomass were increased by extended precipitation intervals, and specific root length (SRL) and specific root area (SRA) were considerably increased by 45.09% and 20.20% in high precipitation, respectively, but the difference was not significant. For the same precipitation condition interval, the main root length was increased by 12.06%, total length, diameter, volume and surface area were significantly decreased, and SRL and SRA were basically unchanged in precipitation reduced by 30% conditions. The SRA increased significantly, but the other index differences were not significant. The main root length and root-shoot ratio were largest in low precipitation, but others (total root length, root surface area, average root diameter, root volume, root biomass, SRL and SRA) were larger in high precipitation conditions. Eight characteristics of root morphology were analyzed using principle component analysis. The characteristics of root biomass, total root length, total root surface area, SRL, SRA and root volume were significantly affected by precipitation pattern changes. We suggested that the root morphology of N. tangutorum seedlings was mainly affected by the amount of precipitation. However, the precipitation interval could be as important as the amount of precipitation for the root morphology of N. tangutorum seedlings. Increasing the precipitation amount and extending the precipitation interval (less frequent but higher volume precipitation events) enhanced root growth and population regeneration. 参考文献 相似文献 引证文献

Effects of Climate and Sewer Condition on Virus Transport to Groundwater.

Pathogen contamination from leaky sanitary sewers poses a threat to groundwater quality in urban areas, yet the spatial and temporal dimensions of this contamination are not well understood. In this study, 16 monitoring wells and six municipal wells were repeatedly sampled for human enteric viruses. Viruses were detected infrequently, in 17 of 455 samples, compared to previous sampling at these wells. Thirteen of the 22 wells sampled were virus-positive at least once. While the highest virus concentrations occurred in shallower wells, shallow and deep wells were virus-positive at similar rates. Virus presence in groundwater was temporally coincident, with 16 of 17 virus-positive samples collected in a six-month period. Detections were associated with precipitation and occurred infrequently during a prolonged drought. The study purposely included sites with sewers of differing age and material. The rates of virus detections in groundwater were similar at all study sites during this study. However, a relationship between sewer age and virus detections emerged when compared to data from an earlier study, conducted during high precipitation conditions. Taken together, these data indicate that sewer condition and climate affect urban groundwater contamination by human enteric viruses.

Evaluation of evapotranspiration models over semi‐arid and semi‐humid areas of China

AbstractEvapotranspiration (ET) is a critical component in the hydrological cycle. However, its actual values appear to be difficult to obtain, especially in areas in which precipitation has high inter‐annual variability. Here, we evaluated eight commonly used ET models in semi‐arid and semi‐humid areas of China. The order of overall performance from best to worst is as follows: the revised Priestley–Taylor model (PT‐JPL, 0.71, 1.65 [18.37%], 4.72 [49.19%]), the modified PT‐JPL model (M1‐PT‐JPL, 0.67, −0.68 [7.56%], 3.87 [40.31%]), the Community Land Model (CLM, 0.68, −2.52 [28.01%], 5.10 [53.17%]), the modified PT‐JPL model (M2‐PT‐JPL, 0.63, 0.57 [6.27%], 5.04 [52.52%]), the revised Penman–Monteith model (RS‐PM, 0.62, 3.56 [37.40%], 6.11 [63.68%]), an empirical model (Wang, 0.59, −1.04 [11.57%], 5.61 [58.43%]), the advection‐aridity model (AA, 0.55, 5.56 [61.78%], 7.45 [77.60%]), and the energy balance model (SEBS, 0.35, 5.11 [56.72%], 9.43 [98.18%]). The performance of all of the models is comparably poor in winter and summer, except for the PT‐JPL model, and relatively good in spring and autumn. Because of the vegetation control on ET, the Wang, RS‐PM, PT‐JPL, M1‐PT‐JPL, and M2‐PT‐JPL models perform better for cropland, whereas the AA model, SEBS model and CLM perform better for grassland. The CLM, PT‐JPL, and Wang models perform better in semi‐arid region than in semi‐humid region, whereas the opposite is true for SEBS and RS‐PM. The AA, M1‐PT‐JPL, and M2‐PT‐JPL models perform similarly in semi‐arid and semi‐humid regions. When considering the inter‐annual variability in precipitation, the Wang model has relatively good performance under only some annual precipitation conditions; the performance of the PT‐JPL and AA models is reduced under conditions of high precipitation; the two modified PT‐JPL models inherited the steady performance of the PT‐JPL model and improved the performance under conditions of high annual precipitation by the modification of the soil moisture constraint. RS‐PM is more appropriate for humid conditions. CLM and PT‐JPL models could be effectively applied to all precipitation conditions because of their good performance across a wide annual precipitation range. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Fecal Indicator Bacteria Dynamics in a Surface Flow Constructed Wetland in Southwestern Illinois, USA

Constructed wetlands have been used to treat wastewater because of their efficiency at removing fecal indicator bacteria (FIB), their low cost, and their ease of maintenance. This study investigates the ability of a surface-flow wetland (0.03 ha in size), constructed in the rural village of Elsah, Illinois, to treat FIB pollution. The objectives of this study were to: 1) compare mean FIB concentrations (specifically thermotolerant coliforms [TTC] and enterococci [ENT]) in the wetland during low versus high precipitation conditions; 2) compare mean FIB levels among different sampling locations along the wetland’s treatment gradient; and 3) determine whether FIB and other environmental variables were significantly correlated. Both TTC and ENT levels increased during storm events, likely due to increased mobilization of sediment. Both TTC and ENT were significantly lower in zones located further from the inflow point. The strongest correlation was observed between TTC and ENT, and both parameters were strongly correlated with precipitation.

Characterizing of a capillary barrier evapotranspirative cover under high precipitation conditions

Capillary barrier covers are a type of evapotranspirative (ET) cover in which the water storage capacity of an overlying finer textured soil layer is enhanced by the presence of an underlying coarser textured soil layer. The capillary barrier will fail when the overlying finer textured layer becomes sufficiently saturated, so capillary barriers generally are considered for use in arid or semi-arid areas. As a result, there have been few tests or practical applications of capillary barrier covers in humid regions. In this study, a column test was conducted at a humid site where 2361 mm precipitation occurred during a 541-day monitoring period. Water content, percolation, surface runoff and meteorological data were recorded. The water balance of the column and a breakthrough characterization of the capillary barrier were investigated. Numerical predictions using the Hydrologic Evaluation of Landfill Performance (HELP) model and the VADOSE/W model were performed. Test results showed that surface runoff during the monitoring period was 88 mm, which corresponded to 3.7 % of precipitation. Percolation was 67 mm, which equated to 2.8 % of precipitation. The majority of the precipitation (93.5 %) was evaporated back to the atmosphere. Failure of the capillary barrier occurred only when the critical volumetric water content of the overlying clay layer was exceeded. The breakthrough was caused by consecutive intense rainfall events. VADOSE/W predicted the behavior more accurately than HELP, because VADOSE/W can model the unsaturated flow behavior associated with the capillary barrier covers.

Evaluating percolation of the herbicide S-metolachlor with bioindicator plants

Leaching can be infl uenced by the physical characteristics of soil and precipitation when the herbicide S-metolachlor is used intensively in sugarcane areas. The objective of this study was to use bioindicator plants to evaluate the percolation potential of S-metolachlor when submitted to natural pluviometric precipitation in two soils of contrasting textures: clayish (Entisols) and medium sandy (Oxisols). Samples were collected using PVC columns that were introduced in both soil types after the herbicide had been applied at the doses of 1,960 and 1,440 g ha–1 a.i of S-metolachlor, recommended for the clayish and sandy soils, respectively. The columns were carefully extracted from the soil by excavating around them, thus keeping soil physical integrity. The samples were taken after the soils had been submitted to 30 – 40, 60 – 80, and 100 – 120 mm of rainfall. The columns were divided by a longitudinal cut to permit the sowing of seeds of the bioindicator plants, allowing suffi cient space for 25 plants per species in the columns (cucumber and lettuce). The bioindicator plants were evaluated with respect to their degree of toxicity by a degree scale ranging from 0 to 100%; these evaluations occurred at 5, 7, 10, and 12 days after sowing. We verifi ed that herbicide percolation depended on soil texture and accumulated rain. Under high precipitation conditions, the herbicide percolates to deeper depths in sandy soils. Cucumber was the most appropriate bioindicator plant in soils of clayish texture. In sandy soils, both cucumber and lettuce showed suitability as bioindicator plants.

Effects of additional N on herbaceous species of desertified steppe in arid regions of China: a four‐year field study

AbstractHuman‐induced nitrogen (N) enrichment is impacting the structure and function of grassland ecosystems, although few studies have been conducted in arid and semi‐arid ecosystems under field conditions. Here, a 4‐year multi‐level N addition experiment under ambient precipitation in a typical temperate desert steppe in arid regions of China was designed to evaluate the impact of N enrichment on the herbaceous vegetation community in desert ecosystems. The results showed that species richness declined in response to N addition during all 4 years, while aboveground biomass increased in the relatively wet year (2007) and decreased in the relatively dry years (2008–2010) according to N addition level, as compared to the control. Plant community composition differed among plant functional groups (PFGs) based on added N. Perennial grasses (PG) benefited more compared with annuals and perennial forbs (PF) from N enrichment in terms of biomass production under conditions of high precipitation in 2007. In relatively dry years, biomass production of all PFGs was strictly dependent on inter‐ and intra‐annual precipitation, which led PG to dominate in 2008 (with a dry spring) and PF to dominate in 2009 and 2010. Our results demonstrate that the impact of N enrichment on the herbaceous vegetation community in desert steppes may be strongly dependent on natural precipitation patterns characterized by shifts in plant community composition, particularly in terms of biomass production.

Analysis of parameter uncertainty in hydrological and sediment modeling using GLUE method: a case study of SWAT model applied to Three Gorges Reservoir Region, China

Abstract. The calibration of hydrologic models is a worldwide challenge due to the uncertainty involved in the large number of parameters. The difficulty even increases in a region with high seasonal variation of precipitation, where the results exhibit high heteroscedasticity and autocorrelation. In this study, the Generalized Likelihood Uncertainty Estimation (GLUE) method was combined with the Soil and Water Assessment Tool (SWAT) to quantify the parameter uncertainty of the stream flow and sediment simulation in the Daning River Watershed of the Three Gorges Reservoir Region (TGRA), China. Based on this study, only a few parameters affected the final simulation output significantly. The results showed that sediment simulation presented greater uncertainty than stream flow, and uncertainty was even greater in high precipitation conditions (from May to September) than during the dry season. The main uncertainty sources of stream flow came from the catchment process while a channel process impacts the sediment simulation greatly. It should be noted that identifiable parameters such as CANMX, ALPHA_BNK, SOL_K could be obtained with an optimal parameter range using calibration method. However, equifinality was also observed in hydrologic modeling in TGRA. This study demonstrated that care must be taken when calibrating the SWAT model with non-identifiable parameters because these may lead to equifinality of the parameter values. It was anticipated this study would provide useful information for hydrology modeling related to policy development in the Three Gorges Reservoir Region (TGRA) and other similar areas.

High precipitation causes large fluxes of dissolved organic carbon and nitrogen in a subtropical montane Chamaecyparis forest in Taiwan

Fluxes of dissolved organic carbon (DOC) and nitrogen (DON) may play an important role for losses of C and N from the soils of forest ecosystems, especially under conditions of high precipitation. We studied DOC and DON fluxes and concentrations in relation to precipitation intensity in a subtropical montane Chamaecyparisobtusa var. formosana forest in Taiwan. Our objective was, to quantify DOC and DON fluxes and to understand the role of high precipitation for DOC and DON export in this ecosystem. From 2005 to 2008 we sampled bulk precipitation, throughfall, forest floor percolates and seepage (60 cm) and analyzed DOC, DON and mineral N concentrations. Average DOC fluxes in the soil were extremely high (962 and 478 kg C ha−1 year−1 in forest floor percolates and seepage, respectively) while DON fluxes were similar to other (sub)tropical ecosystems (16 and 8 kg N ha−1 year−1, respectively). Total N fluxes in the soil were dominated by DON. Dissolved organic C and N concentrations in forest floor percolates were independent of the water flux. No dilution effect was visible. Instead, the pool size of potentially soluble DOC and DON was variable as indicated by different DOC and DON concentrations in forest floor percolates at similar precipitation amounts. Therefore, we hypothesized, that these pools are not likely to be depleted in the long term. The relationship between water fluxes in bulk precipitation and DOC and DON fluxes in forest floor percolates was positive (DOC r = 0.908, DON r = 0.842, respectively, Spearman rank correlation). We concluded, that precipitation is an important driver for DOC and DON losses from this subtropical montane forest and that these DOC losses play an important role in the soil C cycle of this ecosystem. Moreover, we found that the linear relationship between bulk precipitation and DOC and DON fluxes in forest floor percolates of temperate ecosystems does not hold when incorporating additional data on these fluxes from (subtropical) ecosystems.

Long tails in deep columns of natural and anthropogenic tropospheric tracers

Simple prototypes for forced advection‐diffusion problems are known to produce passive tracer distributions that exhibit approximately exponential or stretched exponential tails. Having previously found an approximately exponential tail for the column integrated water vapor (CWV) distribution under high precipitation conditions, we conjectured that if such prototypes are relevant to more complex tropospheric tracer problems, we should find such tails for a wide set of tracers. Here it is shown that such tails are indeed ubiquitous in observed, model, and reanalysis data sets for a variety of tracers, either column integrated or averaged through a deep layer, including CO and CO2. The long tails in CWV are associated with vertical transport and can occur independent of a local precipitation sink. These non‐Gaussian distributions can have consequences for source attribution studies of anthropogenic tracers, and for mechanisms of precipitation extremes; the properties of the tails may help constrain model tracer simulations.