Temporal Flooding Research Articles

Soil fauna groups respond differentially to changes in crop rotation cycles in rice production systems

Permanently flooded rice cropping is increasingly converted to rotation systems including upland crops, managed with adaptive nitrogen fertilizer application schemes for the sake of both saving water and optimizing nutrient application. Such changes alter the diversity and composition of the edaphic fauna, with a critical impact on soil functioning. We conducted a survey at 12 plots in Central Luzon (Philippines) over four cropping seasons to quantify the response of soil nematodes, enchytraeids, and microarthropods (collembolans and mites) to different crop rotations. We additionally assessed the impact of three different N-fertilizer input levels. A marked shift from enchytraeids to microarthropods (i.e. from semi-aquatic to terrestrial taxa) occurred in crop rotations involving upland crops. Microarthropod abundance increased faster in permanently non-flooded rotation system than in rotation schemes including temporal flooding. Mites and most springtail taxa proved to be very vulnerable to crop-associated flooding. Enchytraeids, in contrast, responded positively. Bacterivorous and fungivorous nematodes were affected to a much greater degree by the level of nitrogen input than by crop rotation. N fertilizer application thus significantly altered the trophic composition only of the soil micro-food web. According to our results we propose that the establishment of a genuine terrestrial soil food web after cropping scheme conversion in the conditions of volcanic soils in Central Luzon island may potentially be driven by two processes: The first is associated with the seasonally disrupted increase of microarthropod abundance driven by individuals invading from associated habitats through the top of the bunds, accompanied by an extinction of the semi-aquatic mesofauna, and second, the recovery of microarthropods that are able to survive submerged conditions in low numbers. The marked effect of N fertilizer application on the microfauna indicates that fertilizer management may significantly impact the conversion process by altering the microbial base of the soil food web.

Fast and Automatic Data-Driven Thresholding for Inundation Mapping with Sentinel-2 Data

Satellite data offer the opportunity for monitoring the temporal flooding dynamics of seasonal wetlands, a parameter that is essential for the ecosystem services these areas provide. This study introduces an unsupervised approach to estimate the extent of flooded areas in a satellite image relying on the physics of light interaction with water, vegetation and their combination. The approach detects automatically thresholds on the Short-Wave Infrared (SWIR) band and on a Modified-Normalized Difference Vegetation Index (MNDVI), derived from radiometrically-corrected Sentinel-2 data. Then, it combines them in a meaningful way based on a knowledge base coming out of an iterative trial and error process. Classes of interest concern water and non-water areas. The water class is comprised of the open-water and water-vegetation subclasses. In parallel, a supervised approach is implemented mainly for performance comparison reasons. The latter approach performs a random forest classification on a set of bands and indices extracted from Sentinel-2 data. The approaches are able to discriminate the water class in different types of wetlands (marshland, rice-paddies and temporary ponds) existing in the Doñana Biosphere Reserve study area, located in southwest Spain. Both unsupervised and supervised approaches are examined against validation data derived from Landsat satellite inundation time series maps, generated by the local administration and offered as an online service since 1983. Accuracy assessment metrics show that both approaches have similarly high classification performance (e.g., the combined kappa coefficient of the unsupervised and the supervised approach is 0.8827 and 0.9477, and the combined overall accuracy is 97.71% and 98.95, respectively). The unsupervised approach can be used by non-trained personnel with a potential for transferability to sites of, at least, similar characteristics.

Benefits of flooding-induced aquatic adventitious roots depend on the duration of submergence: linking plant performance to root functioning.

Temporal flooding is a common environmental stress for terrestrial plants. Aquatic adventitious roots (aquatic roots) are commonly formed in flooding-tolerant plant species and are generally assumed to be beneficial for plant growth by supporting water and nutrient uptake during partial flooding. However, the actual contribution of these roots to plant performance under flooding has hardly been quantified. As the investment into aquatic root development in terms of carbohydrates may be costly, these costs may - depending on the specific environmental conditions - offset the beneficial effects of aquatic roots. This study tested the hypothesis that the balance between potential costs and benefits depends on the duration of flooding, as the benefits are expected to outweigh the costs in long-term but not in short-term flooding. The contribution of aquatic roots to plant performance was tested in Solanum dulcamara during 1-4 weeks of partial submergence and by experimentally manipulating root production. Nutrient uptake by aquatic roots, transpiration and photosynthesis were measured in plants differing in aquatic root development to assess the specific function of these roots. As predicted, flooded plants benefited from the presence of aquatic roots. The results showed that this was probably due to the contribution of roots to resource uptake. However, these beneficial effects were only present in long-term but not in short-term flooding. This relationship could be explained by the correlation between nutrient uptake and the flooding duration-dependent size of the aquatic root system. The results indicate that aquatic root formation is likely to be selected for in habitats characterized by long-term flooding. This study also revealed only limited costs associated with adventitious root formation, which may explain the maintenance of the ability to produce aquatic roots in habitats characterized by very rare or short flooding events.

Lithological and land-use based assessment of heavy metal pollution in soils surrounding a cement plant in SW Europe

We study the influence of phasing out a cement plant on the heavy metal (Hg, Pb and Cr) content in the surrounding soils, taking into account factors often neglected, such as contributions due to local lithology or land use. The range of total Hg was 10–144µg kg−1, reaching up to 41 and 145mgkg−1 for total contents of Pb and Cr, respectively. Forest soils showed higher concentration of Hg than prairie soils, indicating the importance of land use on the accumulation of volatile heavy metals in soils. In forest soils, total Hg showed a trend to decrease with soil depth, whereas in prairie soils the vertical pattern of heavy metal concentrations was quite homogeneous. In most cases, the distance to the cement plant was not a factor of influence in the soils content of the analyzed heavy metals. Total Pb and Cr contents in soils nearby the cement plant were quite similar to those found in the local lithology, resulting in enrichment factor values (EF's) below 2. This suggests that soil parent material is the main source of these heavy metals in the studied soils, while the contribution of the cement plant to Pb and Cr soil pollution was almost negligible. On the contrary, the soils surrounding the cement plant accumulate a significant amount of Hg, compared to the underlying lithology. This was especially noticeable in forest soils, where Hg EF achieved values up to 36. These results are of relevance, bearing in mind that Hg accumulation in soils may be an issue of environmental concern, particularly in prairie soils, where temporal flooding can favor Hg transformation to highly toxic methyl-Hg. In addition, the concurrence of acid soils and total-Cr concentrations in the range of those considered phytotoxic should be also stressed.

Advantages of pre-harvest temporal flooding in a catch crop field in relation to soil moisture and nutrient salt removal by root uptake

Catch crop cultivation coupled with subsequent flood activity is an environmental friendly method of removing nutrient salts from soil in greenhouse. However, in comparison with the usual fallow period in greenhouse horticulture in Japan, a longer time is required for cultivation and soil drying after flooding. To minimize such time while retaining catch crop performance, temporal flooding was conducted in an experimental catch crop field of corn before harvest (i.e., pre-harvest temporal flooding), when crops were growing well and most nutrient salts within the soil had been taken up by the roots. Results showed that pre-harvest temporal flooding enhanced crop growth and stomatal opening; hence, evapotranspiration (mostly transpiration) was increased to a high value (3.5 times that of bare soil plot in greenhouse). Therefore, compared with the bare soil field, there was a remarkable pronounced decrease in the soil water content due to evapotranspirational water loss in the catch crop field after temporal flooding. Furthermore, the total nutrient (nitrogen) uptake by crops was also significantly accelerated in relation to pre-harvest flooding owing to the increase in crop growth. It was also found that electrical conductivity and nitrate nitrogen concentration of soil solution (at a soil-water ratio of 1:5) decreased with time owing to root uptake, and were at a fairly low level when pre-harvest flooding was conducted. These results suggest that pre-harvest temporal flooding shortens the implementation time by accelerating soil drying, and increases salt removal by root uptake; thus, this method delivers considerable advantages for practical use in catch crop cultivation.

Temporal flooding of regular islands by chaotic wave packets

We investigate the time evolution of wave packets in systems with a mixed phase space where regular islands and chaotic motion coexist. For wave packets started in the chaotic sea on average the weight on a quantized torus of the regular island increases due to dynamical tunneling. This flooding weight initially increases linearly and saturates to a value which varies from torus to torus. We demonstrate for the asymptotic flooding weight universal scaling with an effective tunneling coupling for quantum maps and the mushroom billiard. This universality is reproduced by a suitable random matrix model.

Characterizing floods in the poorly gauged wetlands of the Tana River Delta, Kenya, using a water balance model and satellite data

Abstract. Wetlands, such as those of the Tana River Delta in Kenya, are vital but threatened ecosystems. The flooding characteristics of wetlands largely determine their physical, chemical and biological properties, so their quantification is crucial for wetland management. This quantification can be achieved through hydrological modelling. In addition, the analysis of satellite imagery provides essential hydrological data to monitor floods in poorly gauged zones. The objective of this study was to quantify the main water fluxes and flooding characteristics (extent, duration and number of floods) in the poorly gauged Tana River Delta in East Africa during 2002–2011. To do so, we constructed a lumped hydrological model (the Tana Inundation Model, TIM) that was calibrated and validated with MODIS data. Further analysis of the MYD09A1 500 m composite product provided a map of the empirical probability of flooded state. In non-extreme years and for the current topology of the delta, the flood extent exceeded 300 km2. Floods over 200 km2 occurred on average once a year, with a mean duration of 18 days. River discharge from the upper basin counted for over 95% of the total water inflow. The results are discussed in the light of possible improvements of the models and wetland management issues. This study provides the first known quantification of spatial and temporal flooding characteristics in the Tana River Delta. As such, it is essential for the water and natural resource management of the Tana River basin. The water balance approach was pertinent to the study of this system, for which information on its internal properties and processes is limited. The methodology, a combination of hydrological modelling and flood mapping using MODIS products, should be applicable to other areas, including those for which data are scarce and cloud cover may be high, and where a medium spatial resolution is required.

Effects of summer flooding on floodplain biogeochemistry in Poland; implications for increased flooding frequency

The frequency of summer flood events has strongly increased in Eastern Europe during the last decades. The creation of water storage areas to avoid flooding is often combined with the re-creation of more natural and biodiverse riverine systems. This urges the need to understand the consequences of summer inundation, when microbial activity is significantly higher than during winter inundation, for floodplain biogeochemistry. In order to test the interacting effects of temporal flooding, water quality and agricultural use we used a mesocosm design with sods including vegetation from an area along a tributary of the Vistula River, where water storage compartments have been planned. Concentrations of nitrate and sulphate in the flood water, expected to interfere with soil redox processes, were varied at environmentally relevant concentrations. Inundation led to increased nutrient mobilization in all treatments, particularly for phosphate which reached very high concentrations in both soil water (200–300 μmol l−1) and overlaying surface water (25–35 μmol l−1) as a result of iron reduction. The response was clearly linked to different soil characteristics like the Olsen P concentration, probably caused by varying kind of land use. Unexpectedly, the flood water quality played a less important role in the response to short-term flooding. This could partly be explained by the relatively low infiltration rate into these waterlogged soils, indicating the importance of local hydrology. The findings of this study are important to understand and predict the effects of (more frequent) summer flooding of Eastern European rivers. It also indicates that it is necessary to take into account the soil quality in assessing the consequences of planned measures on biodiversity and ecosystem functioning.

Risk factors and characteristics of H5N1 Highly Pathogenic Avian Influenza (HPAI) post-vaccination outbreaks

Highly pathogenic avian influenza (HPAI) virus H5N1 is now endemic in South-East Asia but HPAI control methods differ between countries. A widespread HPAI vaccination campaign that started at the end of 2005 in Viet Nam resulted in the cessation of poultry and human cases, but in 2006/2007 severe HPAI outbreaks re-emerged. In this study we investigated the pattern of this first post-vaccination epidemic in southern Viet Nam identifying a spatio-temporal cluster of outbreak occurrence and estimating spatially smoothed incidence rates of HPAI. Spatial risk factors associated with HPAI occurrence were identified. Medium-level poultry density resulted in an increased outbreak risk (Odds ratio (OR) = 5.4, 95% confidence interval (CI): 1.6–18.9) but also climate-vegetation factors played an important role: medium-level normalised difference vegetation indices during the rainy season from May to October were associated with higher risk of HPAI outbreaks (OR = 3.7, 95% CI: 1.7–8.1), probably because temporal flooding might have provided suitable conditions for the re-emergence of HPAI by expanding the virus distribution in the environment and by enlarging areas of possible contacts between domestic waterfowl and wild birds. On the other hand, several agricultural production factors, such as sweet potatoes yield, increased buffalo density, as well as increased electricity supply were associated with decreased risk of HPAI outbreaks. This illustrates that preventive control measures for HPAI should include a promotion of low-risk agricultural management practices as well as improvement of the infrastructure in village households. Improved HPAI vaccination efforts and coverage should focus on medium poultry density areas and on the pre-monsoon time period.

Bottomland hardwood forest species responses to flooding regimes along an urbanization gradient

Urbanization alters stream hydrology, hence flooding frequency and duration in floodplain wetlands. Potential impacts include shifts in species composition and survival, making restoration and selection of wetland species difficult. Cephalanthus occidentalis, Fraxinus pennsylvanica, and Quercus shumardii seedlings were subjected to experimental flooding regimes typical of floodplain forests in rural and urban settings. Treatments included a rural flood regime with three 7-day floods, an Urban-short flood regime with six 4-day floods, and an Urban-long flood regime with six 10-day floods over a growing season. Specific responses, measured by stem length, leaf area, and leaf, stem, and root biomass, varied between species from different wetland indicator classes. C. occidentalis, a wetland obligate, was well adapted to both urban flooding regimes, whereas productivity of F. pennsylvanica, a facultative wetland species, and Q. shumardii, a facultative species, was significantly reduced by the Urban-long treatment. Growth rates also varied over time, indicating the importance of temporal flooding patterns on species productivity. Because urban flooding regimes directly and selectively alter species productivity, proper restoration methods in urbanizing environments should include species selection based on current and potential future hydrologic conditions and use of reference standards from reference sites subjected to similar urban hydrologic regimes.

Shoot Population Dynamics of Carex kobomugi on a Coastal Sand Dune in Relation to its Zonal Distribution

Shoot population dynamics of Carex kobomugi Ohwi, a rhizomatous perennial sedge with a guerilla-type growth form, dominating on Japanese coastal dunes, were examined to detect factors generating the zonal distribution pattern of the plant species. Relative growth rate of shoot (RGRS) and number of branching shoots formed by a mother shoot in a year (NBr) were measured in three populations occurring at three different distances from the shoreline. In 1992, Carex kobomugi shoots at the most inland site (90 m from the shoreline), where Imperata cylindrica var. koenigii dominated and soil-water salinity is always low, showed the lowest RGRS (0.0172 g g-1 day-1 from April to June and 0.00079 g g-1 day-1 in July) and the smallest NBr (1.3 shoots shoot-1 year–1 averaged for 3 years). Shoots of the species at the most seaward site (40 m from the shoreline), where the soil-water salinity is always higher than that of more inland sites, showed the highest RGRS (0.0228 g g-1 day-1 from April to June and 0.0093 g g-1 day-1 in July) and the largest NBr (2.5 shoots-1). However, Carex kobomugi population at the 40 m site had a high fraction of injured shoots (46% of total shoots sampled), which were recorded as shoots without any greenish above-ground part, and high mortality (0.34) due to temporal flooding of sea water caused by storms. In the intermediate site (70 m from the shoreline), Carex kobomugi had intermediateRGRS and NBr with low injury rate. The NBr value, however, showed a decreasing trend over the 3 years of observation, suggesting deteriorating effects of intraspecific competition on population dynamics. In the spring of the fourth year, shoots of Carex kobomugi at 70 m and 90 m from the shoreline produced 1.2 to 2.0 times higher number of buds per shoot than the 3-year-averaged NBrs. This suggests that some fractions of the buds were terminated or became dormant through intra- and/or inter-specific competition. The sparse distribution of Carex kobomugi at the 90 m site may be dictated by its competitive inferiority to Imperata cylindrica which has a denser root system and an aggressive growth form of a phalanx type.

Distribution pattem, genesis and classification of soils of an arid dune area in Northern Negev

AbstractA dune area of 2 km2 in the Negev (Israel) with an annual precipitation of 90 mm was mapped. The soils developed from eolic and fluviatile sediments were Arenosols, Calcisols. Solonchaks, Regosols and Fluvisols. The Arenosols of the dunes are more homogeneous in texture and salt content than the soils of the interdunal corridors: Besides the Fluvisols, also the Calcisols, Solonchaks and Regosols are stratified due to episodic flooding by a wadi, and are rich in salts and lime. The soils are of minor development. Aggregation and enrichment of lime, enrichment and movement of salts, and the enrichment of organic substances are indications of soil formation.The distribution of salts within the profiles was calculated by their solubility. High and low soluble salts appear together in thin layers of Calcisols, Solonchaks and Fluvisols, while the most‐soluble salts appear in deeper layers. The salts, therefore, must have accumulated by lateral movement, precipitation and temporal flooding. Influence of groundwater can therefore be excluded. The Arenosols also show the same sequence of salt types, indicating the accumulation due to precipitation and eolic mass movement. Abandoned arable land sites did not show any different soil characteristics from the unused soils.On the basis of the distribution of salts in the profiles and soil types genesis and classification of the soils is discussed.