Natural Precipitation Events Research Articles

The effect of nitrogen input on N2O emission depends on precipitation in a temperate desert steppe

Nitrous oxide (N2O) is the third most important greenhouse gas, and can damage the atmospheric ozone layer, with associated threats to terrestrial ecosystems. However, to date it is unclear how extreme precipitation and nitrogen (N) input will affect N2O emissions in temperate desert steppe ecosystems. Therefore, we conducted an in-situ in a temperate desert steppe in the northwest of Inner Mongolia, China between 2018 and 2021, in which N inputs were combined with natural extreme precipitation events, with the aim of better understanding the mechanism of any interactive effects on N2O emission. The study result showed that N2O emission in this desert steppe was relatively small and did not show significant seasonal change. The annual N2O emission increased in a non-linear trend with increasing N input, with a much greater effect of N input in a wet year (2019) than in a dry year (2021). This was mainly due to the fact that the boost effect of high N input (on June 17th 2019) on N2O emission was greatly amplified by nearly 17–46 times by an extreme precipitation event on June 24th 2019. In contrast, this greatly promoting effect of high N input on N2O emission was not observed on September 26th 2019 by a similar extreme precipitation event. Further analysis showed that soil NH4+-N content and the abundance of ammonia oxidizing bacteria (amoA (AOB)) were the most critical factors affecting N2O emission. Soil moisture played an important indirect role in regulating N2O emission, mainly by influencing the abundance of amoA (AOB) and de-nitrification functional microorganisms (nosZ gene). In conclusion, the effect of extreme precipitation events on N2O emission was greatly increased by high N input. Furthermore, in this desert steppe, annual N2O flux is co-managed through soil nitrification substrate concentration (NH4+-N), the abundance of soil N transformation functional microorganisms and soil moisture. Overall, it was worth noting that an increase in extreme precipitation coupled with increasing N input may significantly increase future N2O emissions from desert steppes.

Higher concentrations of microplastics in runoff from biosolid-amended croplands than manure-amended croplands

Land-applied municipal biosolids, produced from municipal wastewater treatment sludge, contributes to microplastics contamination in agroecosystems. The impacts of biosolids on microplastic concentrations in agricultural soil have been previously investigated, however, the potential for microplastics transport from biosolid-amended croplands has not been previously quantified. In this study, manure and biosolids were applied to field plots, runoff was collected following natural precipitation events and the potential of bacterial biofilm to grow on different microplastic morphologies was investigated. Higher concentrations of microplastics were detected in runoff from plots with land-applied biosolid in comparison with manure-amended and control plots. Fibers and fragments were the most frequently detected plastic morphologies in runoff, correlated with their decreased surface roughness. The potential of biosolids to contribute to microplastic contamination to U.S. surface waters was quantified which is among the first to quantify the potential for nonpoint source microplastic contamination of surface waters adjacent to agricultural production areas.

Evaluation of a Runoff Monitoring Methodology for Rangelands: UBeTubes

Rangeland degradation is a global concern that is exacerbated by soil loss through water erosion. A deeper understanding of rainfall and runoff dynamics can assist in the development of sustainable management strategies. Current methods to measure surface runoff (e.g., natural runoff plots, rainfall simulation and overland flow experiments, modeling approaches) have many advantages but can be prohibitively expensive, may require considerable maintenance, and/or result in significant disturbance during installation. To address these limitations, we assessed a relatively new and underused method for monitoring runoff, the Upwelling Bernoulli Tube (UBeTube). The UBeTube is a low-cost, passive runoff monitoring method that estimates runoff from the height of water flowing out of a slot machined in the side of a vertical tube. In this study, we evaluated the UBeTube across a range of flow rates with three specific objectives: 1) calibrate the UBeTube measurements using clean water, 2) assess the impacts from varying sediment loads on UBeTube measurement accuracy, and 3) evaluate accuracy under conditions similar to those on undisturbed and disturbed rangelands. We found that properly calibrated UBeTubes could be a relatively accurate runoff monitoring method on rangelands (mean percent error = 7.7% clean water calibration, 34.1% sediment loading, 35.2% undisturbed overland flow, 17.7% disturbed overland flow). UBeTubes provide an alternative method to monitor runoff on rangelands that can augment current methods by providing near real-time measurements of runoff generated during natural precipitation events. Easily and rapidly deployed across the landscape, UBeTubes could allow for the relative measurement of spatially variable hydrologic dynamics and serve as another source of information for management decision-making processes and the creation of sustainable strategies for rangeland development.

Effects of warming and rainfall pulses on soil respiration in a biological soil crust-dominated desert ecosystem

Biological soil crusts (BSCs) across desert ecosystems play an important role in modulating terrestrial carbon cycles. Global warming and changes in precipitation patterns are expected to be important triggers for biological activity in BSC-dominated desert ecosystems. Therefore, it is crucial to study the effects of warming and rainfall pulses on soil respiration dynamics at BSC-dominated microsites to predict terrestrial carbon cycling under climate change. In this study, soil respiration rates were monitored continuously during three types of natural precipitation events in lichen-dominated and moss-dominated crusts in both control and warming treatments. Our results revealed that soil respiration was inhibited in BSC-dominated microsites in the warming treatment because of reduced soil water content induced by the warmer conditions, and that the extent of inhibition was lower in the lichen-dominated crusts than in the moss-dominated crusts. During all the precipitation events, soil respiration rates were significantly increased by rainfall pulses and gradually declined thereafter. Over the daily cycle, the clockwise diel hysteresis loop between soil respiration and soil temperature was modified by soil water availability, which was affected by the magnitude of rainfall pulses. Moreover, the effect of photosynthetically active radiation and the mismatch between the depth of carbon dioxide (CO2) production and soil temperature measurement may have contributed to the diel hysteresis pattern. Our results indicated that warming and different types of precipitation events in BSC-dominated desert ecosystems impact soil carbon release through changes in the magnitude of soil respiration.

Carbon availability affects soil respiration response to drying-rewetting cycles in semiarid grasslands of China under nitrogen deposition

Soil carbon (C) availability is an important limiting factor affecting the magnitude of soil respiration with increasing the drying-rewetting cycle number. Previous studies have reported that because of a deficiency in available C, improved nitrogen (N) availability has no effects on soil respiration in semiarid grasslands. However, it is not well understood whether the effects of N availability on soil respiration in response to drying-rewetting cycles is regulated by C availability in semiarid grasslands under N deposition scenarios. A field experiment was conducted in a semiarid grassland of northern China to investigate the response of soil CO2 efflux to drying-rewetting cycles (natural precipitation events) with the addition of labile C (glucose, 48 g C m−2 a−1) and N (NH4NO3, 10 g N m−2 a−1) in August 2014. The drying-rewetting cycle significantly increased soil respiration rate in the treatments with both C and N additions, whereas it did not significantly increase soil respiration rate in the treatments with added N alone. After the first drying-rewetting cycle, a significant increase in soil microbial biomass C (MBC) content was observed in the treatments with both C and N additions but was not observed in the treatment with added N alone. After a series of drying-rewetting cycles, the cumulative CO2 efflux over the observed period was significantly higher in the treatments with both C and N additions than that in the treatment with added N alone. These findings imply that improved N availability during the period of 20 days has no effects on soil respiration in response to the drying-rewetting cycle due to microbial C limitation under N deposition scenarios in a semiarid grassland.

Microbial diversity of individual raindrops collected from simulated and natural precipitation events

Precipitation samples collected at or near the surface of the earth are composite samples of many different raindrops. Little is known about the abiotic and biotic components found within individual raindrops. To help fill this knowledge gap, we designed a system for collecting individual raindrops called the Liquid Nitrogen Apparatus for Isolating Raindrops (LNAIR). The LNAIR was used in a series of laboratory experiments to determine (1) determine the recovery volume of drops with known sizes and to (2) measure the viability of seeded-microbes from drops of different sizes. The LNAIR recovered an average of 73% of the initial drop volume for drops ranging from 5 μl to 50 μl, and the original and recovered mean volumes were significantly correlated (R2 = 0.96). The viability of seeded ice-nucleating strains of Pseudomonas syringae and Fusarium avenaceum decreased after passage through the LNAIR, but the ice nucleation activity (INA) did not change. Moreover, the size (volume) of the droplet did not appear to have an effect on the viability of microbes after passage through the LNAIR, at least for the two strains of P. syringae tested. The LNAIR was then used in a series of field experiments to collect raindrops from simulated and natural precipitation events. The mean drop volume observed from six simulated rain events (SREs) was 9.4 μl ± 0.5, while the mean drop volume observed from four natural rain events (NREs) was 7.6 μl ± 0.4. Flow cytometer analysis showed that there was an average of 395 ± 103 DNA-containing particles per 10 μl of NRE drops (n = 6) and an average of 892 ± 171 DNA-containing particles per 10 μl of SRE drops (n = 4). NRE drops contained a similar range of particle sizes compared to SRE drops. Twenty seven percent (9/34) of the SRE drops and 28% (40/143) of the NRE drops collected with the LNAIR contained culturable microorganisms, but none of these displayed INA at −8 °C. Microbes cultured from individual NRE drops were identified to the level of genus using sequences. The genera Cladosporium (fungi) and Bacillus (bacteria) represented 22% (15/68) and 20% (19/68) of the microbes identified, respectively. One natural raindrop contained four different genera (Bacillus, Trichoderma, Penicillium, and Cladosporium). The LNAIR has the potential to increase our understanding of causal agents of precipitation processes.

Potential Efficiency of Grassy or Shrub Willow Buffer Strips against Nutrient Runoff from Soybean and Corn Fields in Southern Quebec, Canada.

Riparian buffer strips (RBS) are encouraged to control agricultural diffuse pollution. In Quebec Province, Canada, a policy promotes 3-m-wide RBS. Abiding farmers minimally maintain herbaceous vegetation, but nutrient retention efficiency could be improved with woody biomass. This work aimed to assess if fast-growing willows ( Seemen 'SX64') could reduce nutrient loads to a stream, in addition to yielding biomass. Triplicate treatments of two stem densities and a herbaceous control plot were monitored from 2011 to 2013 in a randomized block design on agricultural fields of the St. Lawrence Lowlands with sandy loam (Saint-Roch-de-l'Achigan [SR]) and organic-rich (Boisbriand [BB]) soils. Runoff, interstitial water, and water from the saturated zone were sampled 16 (SR) and 14 (BB) times to quantify nutrient buffering (NO, NH, P, and K). Sampling campaigns followed (i) snowmelt or ≥15-mm natural precipitation events after (ii) fertilization and (iii) glyphosate-based herbicide applications. Concentration reduction before and after the RBS was highest for nitrates (77-81% in runoff at BB, 92-98% at 35- to 70-cm depth at SR) just after fertilization, when edge-of-field concentrations peaked. Total P removal was observed in runoff after fertilization at SR, and K removal was punctually witnessed at BB. Riparian buffer strips were inefficient for NH and dissolved P removal, and RBS effluents exceeded aquatic life protection standards. plantations, irrespective of stem density, were not more efficient than herbaceous RBS. This shows that without fertilizer input reductions, narrow RBS are insufficient to protect streams from excess nutrients in corn ( L.) and soybean [ (L.) Merr.] crops.

Characteristics of Nitrogen Loss through Surface-Subsurface Flow on Red Soil Slopes of Southeast China

Soil nitrogen (N) loss related to surface flow and subsurface flow (including interflow and groundwater flow) from slope lands is a global issue. A lysimetric experiment with three types of land cover (grass cover, GC; litter cover, LC; and bare land, BL) were carried out on a red soil slope land in southeast China. Total Nitrogen (TN) loss through surface flow, interflow and groundwater flow was observed under 28 natural precipitation events from 2015 to 2016. TN concentrations from subsurface flow on BL and LC plots were, on average, 2.7–8.2 and 1.5–4.4 times greater than TN concentrations from surface flow, respectively; the average concentration of TN from subsurface flow on GC was about 36–56% of that recorded from surface flow. Surface flow, interflow and groundwater flow contributed 0–15, 2–9 and 76–96%, respectively, of loss load of TN. Compared with BL, GC and LC intercepted 83–86% of TN loss through surface runoff; GC intercepted 95% of TN loss through subsurface flow while TN loss through subsurface flow on LC is 2.3 times larger than that on BL. In conclusion, subsurface flow especially groundwater flow is the dominant hydrological rout for N loss that is usually underestimated. Grass cover has the high retention of N runoff loss while litter mulch will increase N leaching loss. These findings provide scientific support to control N runoff loss from the red soil slope lands by using suitable vegetation cover and mulching techniques.

Microbial ice nucleators scavenged from the atmosphere during simulated rain events

Rain and snow collected at ground level have been found to contain biological ice nucleators. These ice nucleators have been proposed to have originated in clouds, where they may have participated in the formation of precipitation via ice phase nucleation. We conducted a series of field experiments to test the hypothesis that at least some of the microbial ice nucleators (prokaryotes and eukaryotes) present in rain may not originate in clouds but instead be scavenged from the lower atmosphere by rainfall. Thirty-three simulated rain events were conducted over four months off the side of the Smart Road Bridge in Blacksburg, VA, USA. In each event, sterile water was dispensed over the side of the bridge and recovered in sterile containers in an open fallow agricultural field below (a distance of ∼55 m). Microbes scavenged from the simulated rain events were cultured and their ice nucleation activity was examined. Putative microbial ice nucleators were cultured from 94% (31/33) of the simulated rain events, and represented 1.5% (121/8331) of the total colonies assayed. Putative ice nucleators were subjected to additional droplet freezing assays, and those confirmed through these repeated assays represented 0.4% (34/8331) of the total. Mean CFUs scavenged by simulated rain ranged from 2 to 267 CFUs/mL. Scavenged ice nucleators belong to a number of taxa including the bacterial genera Pseudomonas, Pantoea, and Xanthomonas, and the fungal genera Fusarium, Humicola, and Mortierella. An ice-nucleating strain of the fungal genus Penicillium was also recovered from a volumetric air sampler at the study site. This work expands our knowledge of the scavenging properties of rainfall, and suggests that at least some ice nucleators in natural precipitation events may have been scrubbed from the atmosphere during rainfall, and thus are not likely to be involved in precipitation.

A savanna response to precipitation intensity.

As the atmosphere warms, precipitation events are becoming less frequent but more intense. A three-year experiment in Kruger National Park, South Africa, found that fewer, more intense precipitation events encouraged woody plant encroachment. To test whether or not these treatment responses persisted over time, here, we report results from all five years of that experiment. Grass growth, woody plant growth, total fine root number and area and hydrologic tracer uptake by grasses and woody plants were measured in six treated plots (8 m by 8 m) and six control plots. Treatment effects on soil moisture were measured continuously in one treated and one control plot. During the fourth year, increased precipitation intensity treatments continued to decrease water flux in surface soils (0–10 cm), increase water flux in deeper soils (20+ cm), decrease grass growth and increase woody plant growth. Greater root numbers at 20–40 cm and greater woody plant uptake of a hydrological tracer from 45–60 cm suggested that woody plants increased growth by increasing root number and activity (but not root area) in deeper soils. During the fifth year, natural precipitation events were large and intense so treatments had little effect on precipitation intensity or plant available water. Consistent with this effective treatment removal, there was no difference in grass or woody growth rates between control and treated plots, although woody plant biomass remained higher in treated than control plots due to treatment effects in the previous four years. Across the five years of this experiment, we found that 1) small increases in precipitation intensity can result in large increases in deep (20–130 cm) soil water availability, 2) plant growth responses to precipitation intensity are rapid and disappear quickly, and 3) because woody plants accumulate biomass, occasional increases in precipitation intensity can result in long-term increases in woody plant biomass (i.e., shrub encroachment). While results are likely to be site-specific, they provide experimental evidence of large ecohydrological responses to small changes in precipitation intensity.

Characterization of water content dynamics and tracer breakthrough by 3-D electrical resistivity tomography (ERT) under transient unsaturated conditions

Characterization of preferential flow and transport is still a major challenge but may be improved employing noninvasive, tomographic methods. In this study, 3-D time lapse electrical resistivity tomography (ERT) was employed during infiltration on an undisturbed, unsaturated soil core in a laboratory lysimeter. A tracer breakthrough was conducted during transient conditions by applying a series of short-term infiltrations, simulating natural precipitation events. The electrical response was quantitatively validated using data from a multicompartment suction sampler. Water content probes were also installed for ground-truthing of ERT responses. Water content variations associated with an infiltration front dominated the electrical response observed during individual short-term infiltration events, permitting analysis of water content dynamics from ERT data. We found that, instead of the application of an uncertain petrophysical function, shape measures of the electrical conductivity response might be used for constraining hydrological models. Considering tracer breakthroughs, the ERT observed voxel responses from time lapse tomograms at constant water contents in between infiltration events were used to quantitatively characterize the breakthrough curve. Shape parameters of the breakthrough derived from ERT, such as average velocity, were highly correlated with the shape parameters derived from local tracer breakthrough curves observed in the compartments of the suction plate. The study demonstrates that ERT can provide reliable quantitative information on both, tracer breakthroughs and water content variations under the challenging conditions of variable background electrical conductivity of the pore solution and non steady-state infiltration.

Phosphorus Reduction in Turfgrass Runoff Using a Steel Slag Trench Filter System

ABSTRACTExcessive concentrations of P can lead to the deterioration of surface waters through eutrophication. This study was conducted to test the effectiveness of a trench filter system for P removal from runoff and to determine the effect of P fertilizer on P losses in runoff from bermudagrass [Cynodon dactylon L. (Pers.)]. A total of 12 plots on a uniform 5% slope covered with ‘Astro’ bermudagrass mowed at 38 mm were used to collect pre‐ and postfiltered runoff from 14 natural or simulated precipitation events that occurred from March through September 2012. Runoff filtered by steel slag contained from 14.2 to 49.2% lower dissolved P concentrations than runoff filtered through an inert gravel control. The P concentrations in runoff from fertilized plots were always greater than unfertilized plots. The difference between P concentrations from the fertilized and unfertilized treatments tended to decline with each runoff event from 13.1 mg L–1 in an initial event after fertilization to 1.6 mg L–1, 133 d and nine runoff events later. Trench filter systems could be used to remove a portion of the P in runoff from turfgrass areas.

Improvement to the prediction of the USLE K factor

In the Universal Soil Loss Equation (USLE), the soil erodibility factor (K) corresponds to the collective effects of the detachment susceptibility of soil and the sediment transportability as well as the amount and rate of runoff under a given rainfall erosivity. Based on the USLE equation, K is sensitive to the particle size distribution (M), the percentage of organic matter (%OM), soil structure (Z), and soil permeability (perm). This study evaluated the sensitivity of K to lime content (%lime) in the soil and slope (%slope) of the site. Although the effects of the slope factor (S) on the amount of soil loss (A) have been independently taken into account in the USLE, our results and other studies showed that K is highly sensitive to other factors including %lime and %slope. To evaluate the appropriateness of the USLE nomograph and other methods for estimating K and to develop a K estimation method for limy soils, a set of K values were measured in northern Iran using standard plots and natural precipitation events, for four different land uses (forest, rangeland, irrigated farming, and dry farming) and three slope categories (3–8%, 8–18% and 18–40%). Results indicated that there was considerable association between K and soil properties including the contents of sand, silt, very fine sand, organic matter and particularly lime, as well as slope inclination. A strong linear relationship was observed between the K values estimated from our model and the measured K was observed (adjusted R2=0.89), indicating that considering lime and slope gives a better estimate of K.

Pesticide fate in sodded kentucky bluegrass lawns in response to irrigation

Fertilizers and pesticides applied to home lawns can contaminate surface and groundwater making them unfit for aquatic organisms and human consumption. Application of fertilizers and pesticides can improve the aesthetics of a home lawn, improve turfgrass shoot and root density, water use, organic matter accumulation, and other factors known to be influential in urban hydrology. A field study determined the impact of applying home landscape pesticides with or without supplemental irrigation of leaching into groundwater or runoff to surface water. Free-draining lysimeters having a sandy loam soil (coarse-loamy, mixed, active, mesic Lamellic Hapludalf) were used to monitor total volume and nutrients and pesticides losses. Samples from natural precipitation events were analysed for pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2, 6-dinitrobenzenamine] applied in spring, mecoprop [2-(4-Chloro-2-methylphenoxy) propionic acid]+2, 4-D (2,4-dichlorophenoxyacetic acid) applied both in late spring and early fall, and bifenthrin [(2-methyl-1,1-biphenyl-3-y1)-methyl-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethyl cyclopropanecarboxylate] applied in late summer. Pesticide concentrations fluctuated over time, but no differences in concentrations were observed from irrigated or non-irrigated turfgrass for any pesticide. Mecoprop and 2,4-D were the most mobile and values found in runoff during establishment were above maximum contaminant levels (MCL) for U.S. standards. Surface runoff of lawn pesticides were observed at concentrations several magnitudes higher than leachate. The total extent of pesticide runoff was 0.71%, 1.3%, 6.0%, and 0.003% of the amount applied for 2,4-D, mecoprop, pendimethalin and bifenthrin, respectively. With the exception of one sampling period, pendimethalin concentrations in runoff and leachate were low; however, when applied during a period of minimal turf growth and high precipitation, pendimethalin could contribute significantly to surface water pollution.

Soil Temperature Regulates Nitrogen Loss from Lysimeters following Fall and Winter Manure Application

Many producers practice fall and winter manure spreading for economic and practical reasons. In order to minimize the risk of nitrogen (N) loss between application and crop uptake in the spring, university extension publications and industry professionals often make recommendations based on soil temperature. The objective of this research, therefore, was to determine how soil temperature affects N losses in runoff and leachate, and assess overwinter N losses based on application date and soil temperature. Phosphorus losses are discussed in a separate article. Dairy manure was surface-applied to a channery silt loam soil contained in lysimeters at soil temperatures of 15.7°C, 4.8°C, and -1.1°C, which corresponded to early fall (Oct. 22), late fall (Nov. 17), and winter (Dec. 15) applications, respectively. Nitrogen losses were determined during a series of rainfall simulations and natural precipitation events from October 2009 through March 2010. The soil temperature between manure application and the first rainfall-runoff event three days after application was held constant and significantly influenced N loss. As the soil temperature decreased, losses of NH4-N, organic N, and total N exponentially increased. The form of N losses was also significantly impacted by application date and overwinter soil temperature. Early fall application of manure resulted in significant overwinter NO3-N losses, while the winter-applied manure had significantly more overwinter NH4-N losses. Results of this research show that there are trade-off risks associated with manure application in the fall and winter and that these trade-offs need to be considered in manure management planning in order to enhance N retention and help reduce the risk of overwinter N losses.

Soil Temperature Regulates Phosphorus Loss from Lysimeters Following Fall and Winter Manure Application

Applying manure in the fall and winter increases the potential for nutrient loss prior to crop uptake in the spring. In order to minimize the risk of nutrient loss, recommendations are often based on soil temperature, since biological activity has been shown to decrease substantially at temperatures less than 10°C. These recommendations are often targeted toward reducing nitrogen (N) losses; thus, a smaller body of information is available on the fate of phosphorus (P) from fall and winter applied manure. The objective of this research was to determine how soil temperature affects P loss in runoff and leachate, and assess overwinter P losses based on application date and soil temperature. Nitrogen losses are discussed in a separate article. Dairy manure was surface applied to a channery silt loam soil contained in lysimeters at soil temperatures of 15.7°C, 4.8°C, and -1.1°C, which represented early fall, late fall, and winter applications, respectively. Phosphorus losses were determined during a series of rainfall simulations and natural precipitation events from October 2009 through March 2010. Phosphorus losses were significantly influenced by the soil temperature at the time of manure application and first rainfall-runoff event. As the soil temperature decreased, losses of DRP, TDP, and total P increased. Overwinter losses were also significantly impacted by soil temperature. The winter treatment had two times higher total P losses compared to the manure applied during the early fall. Results of this research show that soil temperature is important for determining P losses and that incorporating quantitative tools, such as soil temperature, into manure management plans could enhance P retention and help reduce the risk of overwinter P losses.

Field experiments constraining the probability distribution of particle travel distances during natural rainstorms on different slope gradients

ABSTRACTRain splash erosion is an important soil transport mechanism on steep hillslopes. The rain splash process is highly stochastic; here we seek to constrain the probability distribution of splash transport distances on natural hillslopes as a function of hillslope gradient and total precipitation depth. Field experiments were conducted under natural precipitation events to observe splash travel on varying slope gradients. The downslope fraction of splash transport on 15°, 25° and 33° gradients were 85%, 96% and 96%, respectively. Maximum splash transport (Lmax) was related to the rain splash detachment of soil particles and slope gradient. An empirical relationship of Lmax to the precipitation depth and gradient was obtained; it is linearly proportional to hillslope gradient and logarithmically related to precipitation depth. Measured splash distances were calibrated to the fully two‐dimensional (2D) model of splash transport of Furbish et al. (Journal of Geophysical Research 112: F01001, 2007) that is based on the assumption that radial splash distances are exponentially distributed; calibrated values of mean splash transport distances are an order of magnitude greater than those previously determined in a controlled laboratory setting. We also compared measured data with several one‐dimensional (1D) probability distributions to asses if splash transport distances could be better explained by a heavy‐tailed probability distribution rather than an exponential probability distribution. We find that for hillslopes of 15° and 25°, although a log‐normal probability distribution best describes the data, we find its likelihood is nearly indistinguishable from an exponential distribution based on computing maximum likelihood estimators for all 1D distributions (exponential, log‐normal and Weibull). At 33°, however, we find stronger evidence that measured travel distances are heavy‐tailed. Copyright © 2011 John Wiley & Sons, Ltd.

Evaluation of a peat moss plus soybean oil (PMSO) technology for reducing explosive residue transport to groundwater at military training ranges under field conditions

An evaluation of peat moss plus crude soybean oil (PMSO) for mitigation of explosive contamination of soil at military facilities was performed using large soil lysimeters under field conditions. Actual range soils were used, and two PMSO preparations with different ratios of peat moss:soybean oil (1:1, PO1; 1:2, PO2) were compared to a control lysimeter that received no PMSO. PMSO was applied as a 10 cm layer on top of the soil, and Composition B detonation residues from a 55-mm mortar round were applied at the surface of each of the lysimeters. Dissolution of the residues occurred during natural precipitation events over the course of 18 months. Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) emanating from the Composition B residues were significantly reduced by the PO2 PMSO material compared to the untreated control. Soil pore water RDX concentrations and RDX fluxes were reduced over 100-fold compared to the control plots at comparable depths. Residual RDX in the soil profile was also significantly lower in the PMSO treated plots. PO1 PMSO resulted in lower reductions in RDX transport than the PO2 PMSO. The transport of the RDX breakdown product hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) was also greatly reduced by the PMSO materials. Results were in general agreement with a previously developed fate and transport model describing PMSO effectiveness. These results demonstrate the potential effectiveness of the inexpensive and environmentally benign PMSO technology for reducing the subsurface loading of explosives at training ranges and other military facilities.

Summer rain pulse size and rainwater uptake by three dominant desert plants in a desertified grassland ecosystem in northwestern China

To examine the different effects of rain pulse size on uptake of summer rains by three dominant desert plants in field conditions of desertified grasslands on the Ordos Plateau of northwestern China, we studied relationships between precipitation event size and rainwater uptake using stable isotopes of hydrogen in plant and soil water. Four natural precipitation events that represented precipitation sizes of 5.3, 8.3, 13.3, and 65.3 mm in the summer were chosen for the experiment. The perennial grass Stipa bungeana, the shrub Artemisia ordosia, and the herb Cynanchum komarovii – the dominant species in the communities – were compared for their use of summer rains with different pulse sizes based on the changes in the hydrogen isotope ratios (dD) of their stem water 7 days following each natural rain event. We found that S. bungeana and C. komarovii took advantage of shallow water sources derived from small ( 65 mm) rain events, and C. komarovii relied primarily on rain events of intermediate (10 –20 mm) size. These different responses to rain pulses among species suggested that more frequent small rain events will promote the dominance of S. bungeana and C. komarovii, medium-sized events will facilitate development of C. komarovii, and large events will advance A. ordosia in this community. The rainwater utilization patterns of the three species would allow the coexistence of S. bungeana and A. ordosia or the coexistence of A. ordosia and C. komorovii in various successional serals following the disturbances. With an increase in variability of summer rain pulse size as predicted by climate change models, we expect that the structure of this community will undergo significant change in the future. Altered precipitation regimes, especially in combination with anthropogenic-related disturbances such as over-grazing, are likely to accelerate rates of degradation in northwestern China.

Nutrient Attenuation in Agricultural Surface Runoff by Riparian Buffer Zones in Southern Illinois, USA

Nutrients in overland flow from agricultural areas are a common cause of stream and lake water quality impairment. One method of reducing excess nutrient runoff from non-point sources is to restore or enhance existing riparian areas as vegetative buffers. A field scale study was conducted to assess the ability of remnant giant cane (Arundinaria gigantea (Walt.) Muhl.) and forest riparian buffer zones to attenuate nutrients in agricultural surface runoff from natural precipitation events. Two adjacent, 10.0 m wide riparian buffers were instrumented with 16 overland flow collectors to monitor surface runoff for nitrate, ammonium, and orthophosphate. Measurements were taken at 3.3 m increments within each buffer. The forest buffer significantly reduced incoming dissolved nitrate-N, dissolved ammonium-N, total ammonium-N, and total orthophosphate masses in surface runoff by 97, 74, 68, and 78 , respectively within the 10.0 m riparian buffer. Nutrient reductions within the cane buffer were 100 for all three nutrients due to relatively high infiltration rates. Significant reductions of total ammonium- N and total orthophosphate were detected by 3.3 m in the cane buffer and at 6.6 m in the forest buffer. Results suggest that both giant cane and forest vegetation are good candidates to incorporate into riparian buffer restoration designs for southern Illinois as well as in other regions within their native range with similar climatic and physiographic conditions.