Flooded Fields Research Articles

Water Flooding Timing Research and Field Practice in Light Oil Reservoir

Water flooding timing is the research focus in the process of reservoir development, especially for offshore reservoir, reasonable water flooding timing can ensure better development effect, at the same time, it can save the investment cost in the process of reservoir development, so as to achieve sustainable and efficient development of offshore oilfield. At present, there are many researches on the flooding timing of conventional heavy oil reservoir, but few on the flooding timing of light oil reservoir. In order to clarify the development effect of light oil reservoir under different water flooding timing, taking offshore oilfield A as an example, combining with numerical simulation technology and reservoir engineering analysis method, the development effect under different water flooding timing is analyzed. The results show that when the reservoir pressure drops to half of the saturation pressure, the development effect of water flooding for light oil reservoir is the best. Therefore, the water flooding time can be postponed for the light oil reservoir with high porosity and permeability. The research results are applied to the actual development case of oilfield A. The practice shows that water flooding in the late development stage of light oil reservoir can effectively prolong the water-free oil production period, improve the initial oil recovery rate, reduce the initial development investment, thus effectively shorten the investment recovery period and improve the development effect of the reservoir in the whole life production cycle.

Loss levels regarding flood affected areas in the upper Citarum Watershed

The Upper Citarum Watershed is an area that replaces the annual flood. The annual flooding experienced by the Upper Citarum watershed is influenced by several factors, such as changes in land use. From these annual flood events, there will be a level of loss experienced by communities affected by floods. Floods that occur in the Upper Citarum watershed can be seen from the results of the visual model of the upstream Citarum watershed, so that the information can be obtained on the areas affected by flooding and large floods from each affected areas. The purpose of this study is to determine losses due to flooding obtained from flood risk level data, which is the result of an overlay of the level of flood hazard and flood vulnerability. The level of flood hazard can be obtained from the processing of the digitized flood model and field survey. While the rate of flood returns is obtained from the processing of land use data which is the economic value of each land use. This research resulted in a level of flood risk which is dominated by a moderate level of flood risk of 44.15%, then the high-risk level is 42.25%, and the low flood risk level is 13.6%. The extent of the flood risk level is then converted to the economic value of each land use, to get the value of the loss rate. Determination the level of loss, in addition to taking into account the level of the parameters of flood risk, the extent of each region level of risk also influences the determination of the level of flood losses in the Upper Citarum Watershed. This research is carried out as an effort to develop disaster mitigation in the annual flood prone area tobe used as a reference in the development planning process.

Induction of resistance to Meloidogyne graminicola in rice

Root-knot nematodes are responsible for substantial losses in rice production. These parasites are difficult to control, particularly in flooded fields, which require carefully designed strategies to avoid contamination of water bodies. This study investigated whether biotic and abiotic elicitors can induce resistance to the root-knot nematode Meloidogyne graminicola in rice plants. An initial screening test was performed to determine the elicitors with the greatest potential to control nematodes. Then, a second experiment was conducted under net house conditions to assess the effects of a mannanoligosaccharide-based fertilizer (MOS), acibenzolar-S-methyl (ASM), and silicate clay on nematode reproduction, penetration, and activation of plant defence-related enzymes. Elicitor treatment reduced nematode reproduction by 57.4 to 75.6% at 60 days after inoculation (DAI). Two factors that may have contributed to this result include reduced nematode penetration and delayed development, as observed in the screening test. All elicitors increased phenylalanine ammonia-lyase activity at 10 DAI. MOS and silicate clay also increased catalase, peroxidase, and glucanase activity at 8 DAI. Elicitor treatment activates defence responses in rice plants and may be an environmentally friendly strategy for controlling M. graminicola in an integrated management system.

Evaluation of dynamic characteristics of silt in Yellow River Flood Field after freeze-thaw cycles

Frothing is a main disease of highways in Yellow River Flood Field, due to the loss of dynamic strength of roadbed soils under the couple effects of temperature, salt, and vehicle traffic load. This is strongly linked to the dynamic characteristics of silt in this region. To analyze these couple effects on the dynamic characteristics of silt, a series of tests (i.e., freeze-thaw cycling tests, vibration triaxial tests and ultrasonic wave velocity tests) were conducted and two kinds of silt (i.e., salt-free and 3%-salt silt) were designed. The results indicate that the dynamic shear strength and dynamic modulus decrease with increasing freeze-thaw cycles, while the damping ratio simultaneously increases. Furthermore, compared to salt-free silt, the decrement of dynamic shear strength and dynamic modulus of silt with 3% salt is more significant, but the damping ratio of 3%-salt silt is larger. In ultrasonic wave velocity tests, ultrasonic wave velocity of frozen soil specimens decreases as the number of freeze-thaw cycles increases. Based on the results of ultrasonic wave velocity tests, a preliminary model is proposed to evaluate damage of silt through field measurement ultrasonic data. The study could provide a theoretical basis for the treatment of silty soil highway.

Effect of Root Colonization by Arbuscular Mycorrhizal Fungi on Growth, Productivity and Blast Resistance in Rice

BackgroundArbuscular mycorrhizal (AM) fungi form symbiotic associations with roots in most land plants. AM symbiosis provides benefits to host plants by improving nutrition and fitness. AM symbiosis has also been associated with increased resistance to pathogen infection in several plant species. In rice, the effects of AM symbiosis is less studied, probably because rice is mostly cultivated in wetland areas, and plants in such ecosystems have traditionally been considered as non-mycorrhizal. In this study, we investigated the effect of AM inoculation on performance of elite rice cultivars (Oryza sativa, japonica subspecies) under greenhouse and field conditions, focusing on growth, resistance to the rice blast fungus Magnaporthe oryzae and productivity.ResultsThe response to inoculation with either Funneliformis mosseae or Rhizophagus irregularis was evaluated in a panel of 12 rice cultivars. Root colonization was confirmed in all rice varieties. Under controlled greenhouse conditions, R. irregularis showed higher levels of root colonization than F. mosseae. Compared to non-inoculated plants, the AM-inoculated plants had higher Pi content in leaves. Varietal differences were observed in the growth response of rice cultivars to inoculation with an AM fungus, which were also dependent on the identity of the fungus. Thus, positive, negligible, and negative responses to AM inoculation were observed among rice varieties. Inoculation with F. mosseae or R. irregularis also conferred protection to the rice blast fungus, but the level of mycorrhiza-induced blast resistance varied among host genotypes. Rice seedlings (Loto and Gines varieties) were pre-inoculated with R. irregularis, transplanted into flooded fields, and grown until maturity. A significant increase in grain yield was observed in mycorrhizal plants compared with non-mycorrhizal plants, which was related to an increase in the number of panicles.ConclusionResults here presented support that rice plants benefit from the AM symbiosis while illustrating the potential of using AM fungi to improve productivity and blast resistance in cultivated rice. Differences observed in the mycorrhizal responsiveness among the different rice cultivars in terms of growth promotion and blast resistance indicate that evaluation of benefits received by the AM symbiosis needs to be carefully evaluated on a case-by-case basis for efficient exploitation of AM fungi in rice cultivation.

Laboratory Evaluation of Polymer Retention in a Heavy Oil Sand for a Polymer Flooding Application on Alaska's North Slope

SummaryFor a polymer flooding field trial in a heavy oil reservoir on Alaska's North Slope, polymer retention is a key parameter. Because of the economic impact of retention, this parameter was extensively studied using field core material and conditions. In this paper, multiple types of laboratory measurements were used to assess hydrolyzed polyacrylamides (HPAM) polymer retention, including a brine tracer, effluent viscosity, total effluent organic carbon, and effluent chemiluminescent nitrogen. Retention tests were conducted in different Milne Point Schrader Bluff sands, with extensive permeability, grain size distribution, X-ray-diffraction (XRD), and X-ray fluorescence (XRF) characterizations. Several important findings were noted. Polymer retention based on effluent viscosity measurements can be overestimated unless the correct (nonlinear) relation between polymer concentration and viscosity is used. Polymer degradation (either mechanical or oxidative) can also lead viscosity-based measurements to overestimate retention. Inaccessible pore volume (PV) (IAPV) can be overestimated if insufficient brine is flushed through the sand between polymer banks. Around 100 PVs of brine may be needed to displace mobile polymer to approach a true residual resistance factor and properly measure IAPV. Even for a sandpack with kwsor = 20 md, IAPV was zero for HPAM with a molecular weight (Mw) of 18 MM g/mol. Fine-grained particles (<20 µm) strongly impacted polymer retention values. Native NB#1 sand with a significant component of particles <20 µm exhibited 290 µg/g, while the same sand exhibited 28 µg/g after these small particles were removed. Polymer retention did not necessarily correlate with mineral composition. The NB#1, NB#3, and OA sands had similar elemental and clay compositions, but the NB#1 sand exhibited ∼10 times higher retention than the NB#3 sand. Polymer retention did not necessarily correlate with permeability. NB#1 sand exhibited much higher retention than OA sand, even though NB#1 sand was twice as permeable as OA sand. No evidence of chromatographic separation of HPAM molecular weights was found in our experiments. Although retention tended to be greater without a residual oil saturation (than at Sor), the effect was not strong. Aging a core (with high oil saturation) at 60°C reduced HPAM retention by a factor of two. Under similar conditions, polymer retention was greater for a higher Mw HPAM (18 MM g/mol) than for a lower Mw HPAM (10 to 12 MM g/mol). In many cases with high polymer retention values (e.g., 240 µg/g), polymer arrival at the end of the core was relatively quick, but achieving the injected concentration occurred gradually over many PVs. This effect was not caused by chromatographic separation of polymer molecular weights. Results from modeling of this behavior were consistent with concentration-dependent polymer retention. The form assumed for the retention function in a simulator can have an important impact on the timing and magnitude of the oil response from a polymer flood. Field-based observations can underestimate polymer retention, depending on when the tracer and polymer concentrations were measured and the assumptions made about reservoir heterogeneity.

Usage of SIMWE model to model urban overland flood: a case study in Oslo

Abstract There has been a surge of interest in the field of urban flooding in recent years. However, current stormwater management models are often too complex to apply on a large scale. To fill this gap, we use a physically based and spatially distributed overland flow model, SIMulated Water Erosion (SIMWE). The SIMWE model requires only rainfall intensity, terrain, infiltration, and surface roughness as input. The SIMWE model has great potential for application in real-time flood forecasting. In this study, we use the SIMWE model at two resolutions (20 m and 500 m) for Oslo, and at a high resolution (1 m) at the Grefsen area, which is approximately 1.5 km2 in Oslo. The results show that the SIMWE model can generate water depth maps at both coarse and high resolutions. The spatial resolution has strong impacts on the absolute values of water depth and subsequently on the classification of flood risks. The SIMWE model at a higher spatial resolution produces more overland flow and higher estimation of flood risk with low rainfall input, but larger areas of risk with high rainfall input. The Grefsen case study shows that roads act as floodways, where overland flow accumulates and moves fast.

Impacts of fertilization optimization on N loss from paddy fields: Observations and DNDC modeling case study in Shanghai, China

Nitrogen (N) loss from paddy fields is an important source of agricultural nonpoint source pollution and leads to widely existing water contamination issues. The current fertilization rate in paddy fields of Shanghai exceeds the actual demand of rice and leads to substantial N loss. The objective of this study is to optimize the current fertilization scheme in paddy fields of Shanghai with the combination of field observations and modeling approach. In this study, N loss from a typical flooded paddy field in a Shanghai suburb was observed with an embedded lysimeter system from 2009 to 2013 rice seasons. The denitrification-decomposition (DNDC) model was adopted to assist with the integration and upgrading of the observed data. During the experimental period, the observed paddy field generated a seasonal average N loss of 14.9 kg N·ha−1 through runoff and leaching, which accounted for 5.0 % of the total fertilizer N. Surface runoff events that occurred shortly after fertilization largely contributed to the total N loss from the experimental paddy field. According to the validation test against observational data, the DNDC model simulated N loss from the experimental paddy field well both in terms of runoff and leaching. Sensitivity analysis and scenario simulations conducted with the DNDC model demonstrated that the current fertilization rate of 300 kg N·ha−1 exceeded the actual crop demand at the experimental site. An application rate of 240 kg N·ha−1 with the optimized fertilization time was the best fertilization scheme for the experimental paddy field, which significantly reduced total N loss by 31.6 % while maintaining the optimal rice yields. The mitigating efficiencies varied from 23.8%–37.2 % under different precipitation and clay content in Shanghai suburb. A combination of field experiments with the DNDC model is an efficient approach to optimize field management practices and transfer the field results to other regions, thereby achieving a balance between agricultural production and the surrounding environment.

Ammonia- and Methane-Oxidizing Bacteria: The Abundance, Niches and Compositional Differences for Diverse Soil Layers in Three Flooded Paddy Fields

Ammonia oxidizing bacteria (AOB), Ammonia oxidizing archaea (AOA) and methane oxidizing bacteria (MOB) play cogent roles in oxidation and nitrification processes, and hence have important ecological functions in several ecosystems. However, their distribution and compositional differences in different long-term flooded paddy fields (FPFs) management at different soil depths remains under-investigated. Using qPCR and phylogenetic analysis, this study investigated the abundance, niches, and compositional differences of AOA, AOB, and MOB along with their potential nitrification and oxidation rate in three soil layers from three FPFs (ShaPingBa (SPB), HeChuan (HC), and JiDi (JD)) in Chongqing, China. In all the FPFs, CH4 oxidation occurred mainly in the surface (0–3 cm) and subsurface layers (3–5 cm). A significant difference in potential methane oxidation and nitrification rates was observed among the three FPFs, in which SPB had the highest. The higher amoA genes are the marker for abundance of AOA compared to AOB while pmoA genes, which is the marker for MOB abundance and diversity, indicated their significant role in the nitrification process across the three FPFs. The phylogenetic analysis revealed that AOA were mainly composed of Nitrososphaera, Nitrosospumilus, and Nitrosotalea, while the genus Nitrosomonas accounted for the greatest proportion of AOB in the three soil layers. MOB were mainly composed of Methylocaldum and Methylocystis genera. Overall, this finding pointed to niche differences as well as suitability of the surface and subsurface soil environments for the co-occurrence of ammonia oxidation and methane oxidation in FPFs.

Reducing yield-scaled global warming potential and water use by rice plastic film mulching in a winter flooded paddy field

Winter flooded paddy fields emit considerable amounts of CH4 and N2O that add to global warming potential (GWP). However, mitigating the GWP and water use without compromising crop yield in the fields is poorly documented. A 3 year-round field experiment was conducted with the use of PM (plastic film mulching cultivation with water-saving irrigation in rice season while drainage in winter season) in comparison of two traditional paddies that were flooded in the winter season but either rain-fed (TC1) or continuously flooded (TC2) in the rice season. Shifting TC1 into PM significantly promoted rice tiller and increased grain yields by 23 %, showing a significant increase in effective number of panicles per m2 (40 %), total filled grains per m2 (55 %) and filled grains percentage (4.2 %). Changing TC2 into PM, however, had little effect on these variables. Compared with TC1 and TC2, the PM reduced annual water use by 20–69 %. Meanwhile, it decreased annual cumulative CH4 emissions by 23–64 % and increased N2O emissions by 56–4.2 %. This change was probably related to the significant decreases in both dissolved organic carbon content (DOC) and CH4 production potential (MPP) for CH4, and much higher NH4+-N concentration at the beginning of the rice season and a more favorable soil water content (SWC) for N2O. Because mean CH4 emission was positively correlated with mean DOC and MPP, and mean N2O emission was negatively related to mean SWC, respectively. Overall, the PM reduced annual GWP by 18–60 % and yield-scaled GWP by 34–60 % relative to TC1 and TC2. The findings suggest that the application of PM in the winter flooded paddy fields substantially mitigates GWP and has a great potential to reduce water use while maintaining high yields.

Greenhouse gases from early flooded organic paddy field

Greenhouse gases from early flooded organic paddy field

Thermodynamic modeling of aqueous migration of chemical elements in irrigation water

Research of migration forms in irrigation water of flooded fields contributes to understanding geochemical barrier formation and functioning. It can improve pollution and nutrification control in the soil-water-plant system since geochemical barriers promote concentrating chemical elements at different depths of a soil cross-section. The research aimed to simulate the aqueous migration of chemical elements and their precipitation in the flooded rice fields’ irrigation water to determine the potential of removing them from the solution at the sorption geochemical barrier. The samples of irrigation water were taken after harvesting in the Poyang Lake basin (China) and analyzed with a standard set of methods for natural water, including ICP-MS and ICP-AES. To assess the migration forms, the HCh software package was used. The thermodynamic values database was supplemented with free energies of formation of metal complexes with fulvic and humic acids for standard conditions. Modeling has shown that most of the considered chemical elements migrate in positively charging simple ions. The main agents of complexation with humic substances are Fe, Ca, and U. Kaolinite potentially precipitates from the irrigation water. Results show that sorption of positively charged simple ions and MoO42−on clay minerals should be under special attention.

Genetic diversity in Calibrachoa pygmaea (Solanaceae): A hawkmoth-pollinated nightshade from the Pampas

ABSTRACT Calibrachoa pygmaea is a unique species of Calibrachoa, especially concerning its flower morphology and the environment where it occurs. The species is self-incompatible and is narrowly distributed in wet and flooded fields of the Pampas region. We characterize the genetic diversity of the species based on traditional plastid markers and newly developed nuclear microsatellites to identify drivers that guide its evolution. Our results identified markers that are informative and useful for studying the population structure of C. pygmaea, as well as that of other species of Calibrachoa. Both marker sets were congruent in developing conclusions regarding the evolutionary scenario of C. pygmaea, and revealed that the genetic variability and population structure of the species could be explained by common allele fixation or shared ancestral polymorphism, while its diversification can be attributed mainly to the species’ dispersal ability and certain ecological features.

TRACE ELEMENTS DISTRIBUTION IN HEIRLOOM PADDY PANDASAN CULTIVATED UNDER FIELD CONDITIONS OF DRY AND WET SOIL

Trace elements phytoavailability depends on the physical and chemical propertiesof soil. At the Crocker range of West Coast Sabah, Malaysia, the Pandasan paddyvariety can be cultivated as flooded rice paddies or upland rice on acidic soil.Pandasan paddy samples were collected in Kiulu subdistrict from traditionalfarmer at two different locations. Available sources of trace elements were fromweathering, fertilizers and pesticides. Soil and plant samples were collected aftertwo months of seed sowing and during harvest season which was five months oldfor heavy metal analysis by inductively coupled plasma optical emissionspectrometry (ICP-OES). Translocation factor of arsenic from root to grainindicated this trace element was very mobile in Pandasan paddy cultivated at drysoil compared to wet soil followed by zinc. Although, cadmium was not detected inpaddy cultivated at flooded field for both, soil and plant, cadmium was detected insoil and plant roots cultivated in dry condition. Enrichment factor results suggestedthat Pandasan plant cultivated on dry soil was only a good bioindicator for leadand zinc. Pandasan grain was rich with iron followed by zinc. Selected heavymetals accumulation in Pandasan grain cultivated in flooded field did not exceededthe permissible limit of Malaysia Food Regulation 1985. However arsenic andplumbum concentration in Pandasan grain harvested from dry soil exceeded thepermissible limit of Malaysia Food Regulation 1985. Health risk of heavy metalstoxicity can be reduced if Pandasan paddy is cultivated in flooded field comparedto dry soil.

Diversity of endophytic bacterial community inhabiting in tropical aerobic rice under aerobic and flooded condition.

The role and activity of bacterial endophytes remains largely unexplored and detail insight into Indian rice agro ecosystem is still little explored. In this study, we examined the diversity of endophytic bacteria in aerobic rice (variety ARB6) under aerobic and flooded field conditions. Based on 16S rRNA gene RFLP cloning sequencing, 900 clones with 144 representatives (72 aerobic and 72 flooded) revealed majority of clones affiliated toGammaproteobacteria (64.58%),Betaproteobacteria (9.72%),Alphaproteobacteria (17.36), Firmicutes (6.26%) and Bacteroidetes (2.08). The study suggests that the aerobic rice variety harbours plant growth promoting (PGP) genera (viz. Pantoea, Enterobacter, Paenibacillus, etc). Investigations on aerobic rice under aerobic and flooded conditions revealed high richness and diversity of endophytic bacteria under aerobic condition inferring that the endophytic bacteria are beneficial for rice growth and productivity, and hence, would be helpful in designing better strategies for rice cultivation under drought or water scarce conditions.

Day and night use of habitats by northern pintails during winter in a primary rice-growing region of Iberia.

Loss of natural wetlands is a global phenomenon that has severe consequences for waterbird populations and their associated ecosystem services. Although agroecosystems can reduce the impact of natural habitat loss, drivers of use of such artificial habitats by waterbirds remain poorly understood. Using the cosmopolitan northern pintail Anas acuta as a model species, we monitored home-range and fine-scale resource selection across the agricultural landscape. Individuals were tracked using GPS-GSM transmitters, and a suite of environmental and landscape features were measured throughout the winter seasons. Spatial patterns of habitat use were analysed using generalized linear mixed effect models by integrating field-observations with GPS telemetry. All birds used rice fields as foraging grounds at night and commuted to an adjacent reservoir to roost during daylight. Home-ranges and maximum foraging distances of nocturnally foraging birds increased with decreasing availability of flooded fields, and were positively correlated with moonlight levels. Birds selected flooded rice paddies (water depth range: 9–21 cm) with standing stubble and substrate with pebbles smaller than 0.5 cm in diameter. Density of rice seeds, rice paddy size, and other environmental and landscape features did not emerge as significant predictors. Our findings indicate that nocturnal foraging of northern pintails within rice fields is driven primarily by straw manipulation, water level and substrate pebble size. Thus, the presence of standing stubble in flooded paddies with soft bottoms should be prioritized to improve foraging areas for dabbling ducks. These management procedures in themselves would not increase economic costs or affect rice production and could be applied for dabbling-duck conservation throughout the world.

Mechanisms of soil macrofauna community sustainability in temperate rice-growing systems

Rice growing requires highly destructive and highly invasive field management negatively affecting soil biota and its functions. We aimed to compare taxonomic and functional trait compositions of soil macrofauna at different stages of rice cropping cycles in the three temperate rice-growing regions in Russia. Samples were collected in 2016 at four different biotopes in each region: flooded rice paddies; upland crops planted one year after flooded rice; rice paddy bunds; and relatively undisturbed seminatural control grasslands. Collected soil macrofauna were allocated to different traits according to their feeding preferences, vertical distribution, mobility and flood tolerance. The lowest macrofaunal abundance across all regions was observed in rice paddies. Cultivation of upland crops after paddy flooding consistently decreased the abundance of resident macrofauna, but not that of mobile soil macrofauna. In the upland crops, the abundance of belowground and mobile belowground macrofauna was significantly higher than that in control grasslands. The abundance of aboveground phytophages was significantly lower in the upland crops than in control sites. Flood-associated taxa showed low colonization ability after the paddies were drained. In contrast, representatives of other traits recorded in flooded fields increased their abundance at the next stage of crop rotation, demonstrating high resilience within an entire rice-growing system, including bunds. This finding indicates a high potential of seminatural grasslands and especially bunds as sources of rapid restoration of soil macrofauna functional diversity in rice-growing agroecosystems, thus maintaining the sustainability of soil food webs in the rice paddies.

The magnitude and variability of lateral seepage in California rice fields

Lateral seepage can be an important water loss pathway at the field level and a conduit for the discharge of pesticides and nutrients from rice fields. However, few studies have directly measured lateral seepage rates in flooded rice fields. This study sought to characterize the magnitude and variability of lateral seepage in California rice fields, and to explore the relationship between lateral seepage and soil properties or hydrologic conditions. Lateral seepage was measured during the growing season at 50 locations spread across six rice fields using a methodology that operates analogously to a double-ring infiltrometer. Lateral seepage rates varied over four orders of magnitude (0.05–33.11 cm2 h−1 or 0.0011–1.05 cm h−1), though even the highest rate measured was small compared to typical water inputs in California rice fields, and lateral seepage corresponded to only 1.0%–1.9% of water inputs at sites where irrigation inputs were measured. Lateral seepage was negatively correlated with levee width (p = 0.025) and the relative water height in the adjacent field, supply canal, or drainage ditch (p = 0.045), though this relationship explained little of the variation in lateral seepage rates (marginal r2 = 0.129). Contrary to expectations, not all supply canals or higher flooded fields were a source for lateral seepage into fields, as unsaturated zones present in most levees served as a sink for lateral seepage from both sides of the levee. Future research should examine the prevalence of preferential flow pathways in rice field levees and the potential for transport of nutrients or agrochemicals through these flow pathways.

Floating dynamics of Beckmannia syzigachne Seed Dispersal via Irrigation Water in a Rice Field

Water is one of the main dispersal agents of plant seeds and influences plant population dynamics and community structure. Although a large proportion of paddy fields are subjected to irrigation, limited research has addressed weed seed dispersal via water in rice-based systems. In this study, safranin T-dyed Beckmannia syzigachne seeds were released and their movement was tracked to characterize their dispersal dynamics via water in an irrigation canal and in a rice field. B. syzigachne seeds, floating on the water surface, moved from their release point at the canal entrance via irrigation water along the irrigation canal. A well-simulated Gaussian plume model indicated that the seed dispersal of B. syzigachne conformed to a leptokurtic distribution, and the peak dispersal kernel showed that seeds moved along the irrigation water flow to approximately 800–1000 m away from the release point 36 h after release into the canal. When seeds were released in the center of a flooded field, a total of 60% of the released seeds were water-dispersed to the northwest corner by the southeast prevailing monsoon wind within 72 h. The well-fitted Gauss 2D-model illustrated the widening of the seed distribution range with time and dispersal pattern with an accumulation center in the field. Our study is the first to show that buoyant weed seeds are mainly dispersed by irrigation water in both the canal and field and that the water dispersal of seeds influences the spatial deposition and distribution of the weed seed bank and strongly affects weed occurrence patterns in irrigated fields.

Methane and nitrous oxide emissions in rice-crab culture systems of northeast China

Rice-crab integrated ecosystem has been confirmed to improve the ecological environment and brought greater economic benefits. In order to know greenhouse gases methane (CH4) and nitrous oxide (N2O) emissions in rice-crab system, they were quantified from a flooding rice field in northeast China, as affected by integrated rice-crab cultivation. Three treatments with three replications each were given: (1) RC1- rice with crab (megalopa), (2) RC2 - rice with crab (juvenile), (3) RM - rice only. Seasonal CH4 and N2O fluxes were measured by closed chamber method. Compared with RM treatment, RC1 and RC2 treatments greatly enhanced the cumulative seasonal CH4 emissions (by 36.8% and 29.2%, respectively), and reduced the cumulative seasonal N2O emissions (by 28.2% and 19.7%, respectively). Across treatments, CH4 represented over 97% of total global warming potential (GWP) and as a result, RC1 and RC2 treatments significantly increased the GWP than RM treatment. Although the GWP was highest in RC1 treatment, it provided highest rice yield (8780 kg/ha) and net ecosystem economic budget (NEEB, 23,159 Yuan/ha) over RM (7668 kg/ha, 15,130 Yuan/ha) and RC2 (8042 kg/ha, 18,713 Yuan/ha) treatments. To summarize, cultivation of megalopa in rice field is a better strategy to optimize the economic and environmental benefits in northeast China.