Flooded Sites Research Articles

Changes of methane and nitrous oxide emissions in a transition bog in central Germany (German National Park Harz Mountains) after rewetting

During the last decades, various renaturation programmes have been initialized to recover nutrient sink and ecological functions of peatlands by rewetting. Rewetting, however, often results in the formation of hotspots for methane (CH4) emissions and in temporal dieback of local vegetation. The present study aimed at quantifying changes of CH4 and nitrous oxide (N2O) emissions in a peatland currently under continuous rewetting conditions. Emissions where studied at a permanently flooded site and a non-flooded peat site with fluctuating water tables by using common closed chamber method. The permanently flooded site revealed extremely high CH4 emissions (up to 1195 mg C m−2 d−1) which were positively correlated with temperature, nutrient content, dissolved organic carbon and nitrogen concentration of the peat soil water. In contrast, the non-flooded peat site, with lower and fluctuating water tables (WT), showed significantly lower CH4 emissions and an increasing trend of CH4 release associated with a generally increasing WT caused by the progressing rewetting process. Lower N2O emissions (<24 µg N m−2 d−1) were observed at the flooded site. By contrast, the non-flooded peat site with fluctuating WT showed significantly higher N2O emissions (up to 4178 µg N m−2 d−1), in particular at high temperatures during summer time. The present results indicate that permanently flooded conditions during rewetting processes might cause higher CH4 emissions compared to fluctuating WT which in contrast might enhance N2O emissions. In total, however, no decreasing trend for CH4 emissions throughout the five-year renaturation period could be found. At least for N2O we observed a decreasing trend during rewetting.

Flooding-related increases in CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O emissions from a temperate coastal grassland ecosystem

Abstract. Given their increasing trend in Europe, an understanding of the role that flooding events play in carbon (C) and nitrogen (N) cycling and greenhouse gas (GHG) emissions will be important for improved assessments of local and regional GHG budgets. This study presents the results of an analysis of the CO2 and N2O fluxes from a coastal grassland ecosystem affected by episodic flooding that was of either a relatively short (SFS) or long (LFS) duration. Compared to the SFS, the annual CO2 and N2O emissions were 1.4 and 1.3 times higher at the LFS, respectively. Mean CO2 emissions during the period of standing water were 144 ± 18.18 and 111 ± 9.51 mg CO2–C m−2 h−1, respectively, for the LFS and SFS sites. During the growing season, when there was no standing water, the CO2 emissions were significantly larger from the LFS (244 ± 24.88 mg CO2–C m−2 h−1) than the SFS (183 ± 14.90 mg CO2–C m−2 h−1). Fluxes of N2O ranged from −0.37 to 0.65 mg N2O–N m−2 h−1 at the LFS and from −0.50 to 0.55 mg N2O–N m−2 h−1 at the SFS, with the larger emissions associated with the presence of standing water at the LFS but during the growing season at the SFS. Overall, soil temperature and moisture were identified as the main drivers of the seasonal changes in CO2 fluxes, but neither adequately explained the variations in N2O fluxes. Analysis of total C, N, microbial biomass and Q10 values indicated that the higher CO2 emissions from the LFS were linked to the flooding-associated influx of nutrients and alterations in soil microbial populations. These results demonstrate that annual CO2 and N2O emissions can be higher in longer-term flooded sites that receive significant amounts of nutrients, although this may depend on the restriction of diffusional limitations due to the presence of standing water to periods of the year when the potential for gaseous emissions are low.

Multifaceted Solution of Analytical Challenges in Complex Oilfield Materials With Synchrotron Techniques

Summary The versatility of synchrotron techniques for the solution of oilfield questions is illustrated by the application of powder X-ray diffraction (PXRD) and X-ray absorption near-edge structure (XANES) spectroscopy to a toluene-insoluble oilfield-residue sample from an alkaline/surfactant/polymer (ASP) -flood site in Taber, Alberta, Canada. The primary questions regarding the sample were the sources of the barium and nitrogen (both at levels of approximately 0.8 wt%). Synchrotron PXRD provided better signal–noise and detection limits than previously obtained laboratory PXRD data, enabling the identification of four additional crystalline minerals including heulandite, (Ba, Ca, Sr, K, Na)5 Al9 Si27 O72 (H2O)22, a tecto-silicate zeolite known for accommodation of a wide variety of cations. Heulandite provides a plausible location for barium (and strontium) observed with chemical analysis. Synchrotron XANES spectra at the nitrogen K-edge suggested that the source of the nitrogen content was a corrosion inhibitor, rather than a polyacrylamide (PAM) -based compound, as originally assumed.

Decay resistance of four fast-growing Eucalypts wood exposed to three types of fields

The evaluation of wood durability enables the definition of reliable parameters to predict the servicelife of wood-based products. This study aimed to evaluate the wood deterioration of four fast-growing eucalypts species (Eucalyptus botryoides, Corymbia citriodora, Eucalyptus paniculata e Eucalyptustereticornis) exposed to three field tests (outdoor, flooded site and forest canopy) during 540 days. The physical properties measured were: mass loss, density and moisture content. Furthermore, we determined changes in wood color by CIEL*a*b* method and performed a visual analysis by CENgrades. Among the four wood eucalypts, Eucalyptus tereticornis presented the highest decay resistance. The flooded site presented the best conditions for the proliferation of xylophagous agents. Mature wood was least susceptible to deterioration than juvenile wood.

The Role of Psychosocial Resource Loss in Psychological Health after a Flood Disaster: A Retrospective Study of Adjustment in Flood Victims in Southwest Nigeria

The Role of Psychosocial Resource Loss in Psychological Health after a Flood Disaster: A Retrospective Study of Adjustment in Flood Victims in Southwest Nigeria Natural disaster such as flood brings heavy toll on the emotional and mental strength of its victims. Unfortunately, the emergency preparedness and responsiveness of the authority is not often adequate and even sometimes unavailable to the survivors and consequently leading to a mental health of the survivors. Therefore, this study is interested in the role of psychosocial resource loss in psychological health of flood victims in Nigeria. The study used a retrospective survey design and a total of 52 respondents were used in two flood sites. The participants were measured on sociodemographics, resource loss, and psychological distress. The study found out that there was no significant difference between low resource loss and high resource loss on psychological distress among flood victim t (41)=-0.451, p>0.05. That there was no significant interaction between sex and resource loss on psychological distress F (1,16)=1.408, p>0.05. There was significant moderate negative relationship between sex and psychological distress r=-0.521, p 0.05); between educational level and psychological distress (r=-0.241, p>0.05); between resource loss and psychological distress (r=0.198, p>0.05). There was significant interaction between survivors who are older with lower educational status having significantly higher psychological distress than flood survivors who are younger with higher educational status F (2,12)=6.168, p<0.05. There was significant joint influence of age, sex, and educational level on psychological distress, R2=0.430, F (3,16)=4.016, p<0.05. In most disasters, the focus is often on women and children however the focus should be on the younger population with higher educational qualification and screening for mental health issues after a disaster.

Beaver-created deadwood dynamics in the boreal forest

Deadwood is a markedly important ecosystem element, and increasingly rare in managed landscapes. Beavers (Castor sp.) are ecosystem engineers of the boreal forest, where they modify riparian forests and wetlands through damming. The subsequent inundation causes extensive die-off of trees in the flood zone. We measured the deadwood volumes and types for six beaver-created flood sites, and compared these to control sites with no beaver influence. Our results show beavers create abundant volumes of deadwood in areas rarely experiencing other disturbance types. Significant amounts of beaver-created deadwood consist of rare types, e.g. snags and deciduous wood. Both coarse and fine woody debris are created. These varying substrates increase deadwood heterogeneity and create differing saproxylic community diversity compared to other disturbances. The roaming lifestyle of beavers cause repeated flooding in boreal landscapes. This upholds deadwood continuity in areas where deadwood levels are very low due to intensive forest management. The reoccurring pulses of deadwood created by beavers may facilitate a wide scope of deadwood-dependent species. The beaver can be used as a deadwood facilitator and engine of restoration in boreal wetlands and riparian forests. This is an economic option compared to costly and time-consuming man-made restoration.

New insights into the 21 November 2000 tsunami in West Greenland from analyses of the tree−ring structure of Salix glauca

Abstract We test the application of dendrochronological methods for dating and assessing the environmental impacts of tsunamis in polar regions, using an example of the 21 Novem− ber 2000 landslide−generated tsunami in Vaigat Strait (Sullorsuaq Strait), West Greenland. The studied tsunami inundated a c. 130 m−wide coastal plain with seawater, caused erosion of beaches and top soil and covered the area with an up to 35 cm−thick layer of tsunami de− posits composed of sand and gravel. Samples of living shrub, Salix glauca (greyleaf wil− low) were collected in 2012 from tsunami−flooded and non−flooded sites. The tree−ring analyses reveal unambiguously that the tsunami−impacted area was immediately colonized during the following summer by rapidly growing shrubs, whilst one of our control site spec− imens records evidence for damage that dates to the time of the tsunami. This demonstrates the potential for dendrochronological methods to act as a precise tool for the dating of Arc− tic paleotsunamis, as well as rapid post−tsunami ecosystem recovery. The reference site shrubs were likely damaged by solifluction in the autumn 2000 AD that was triggered by high seasonal rainfall, which was itself a probable contributory factor to the tsunami−gener− ating landslide.

Short‐term resilience of arthropod assemblages after spring flood, with focus on spiders (Arachnida: Araneae) and carabids (Coleoptera: Carabidae)

AbstractDespite the expected increase in extreme flood frequency, the manner in which terrestrial arthropods cope with regular submersion of their habitat remains poorly understood in meadows, especially in temperate floodplains. Here, we studied the recolonization dynamics of arthropods after a severe spring flood in the Loire Valley (France). We carried out analyses at the community (order or family identification level) and species scales, focusing on the assemblages of two dominant and diverse groups: carabids and spiders. Our objectives were the following: (i) to describe the temporal changes in community structure after flooding and (ii) to assess the influence of landscape configuration on recolonization patterns of species and their functional traits. Fieldwork was performed along three sampling transects, by using 75 pitfall traps, in 2012. A total of 14 767 arthropods belonging to 87 families were trapped, including 5538 spiders (55 species) and 3396 carabids (66 species). Multivariate analyses discriminated assemblages from flooded and non‐flooded habitats and revealed changes over time in arthropod families and species after flood withdrawal. In particular, wolf spiders (Lycosidae) were the first to recolonize, whereas other groups clearly avoided flooded sites. Our results also revealed that short distances to hedgerows, and to a lesser extent, distance to woodlands, favoured the recolonization of large and ground‐running spiders. In conclusion, our study shows the short‐term resilience of certain groups or stenotopic species to flooding and also the relevance of multi‐taxon‐based studies. The presence of hedgerows has to be considered carefully in management plans because of their role of refuge during flooding. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Local Hydrological Conditions Explain Floristic Composition in Lowland Amazonian Forests

AbstractAmazonian forests harbor a large variety of understory herbs adapted to areas with different hydrological conditions, ranging from well‐drained to seasonally flooded forests. The presence versus absence of flooding forms the extremes of a hydrological gradient, with various intermediate conditions, such as seasonal soil waterlogged areas, in between. We investigated the relationship between understory herbs and hydrological conditions in Central Amazonian forests using eighty‐eight 250 × 2 m plots distributed along a 600‐km transect. Hydrological conditions were determined regionally by precipitation and locally by topographic conditions based on drainage potential, flooding height and soil permeability (sand content). Soil cation concentration was used as a proxy for soil fertility. The floristic dissimilarities among plots were visualized by Nonmetric Multidimensional Scaling, and simple and multiple regressions were used to identify the best predictor of herb species composition. Local drainage potential was more important in determining herb species composition than soil fertility or precipitation at non‐flooded and flooded sites. Flooded sites comprised a very distinctive herb species composition even when the flood height was low (0.3 m). We conclude that hydrological conditions are the primary constraint of herb distribution within this flat regional landscape with moderate amounts of soil fertility variation (0.09–2.280 cmol(+)/kg). Hydrological models that consider local water conditions explained the largest part of herb species composition. Therefore, predictions of species distribution based on large‐scale climatic variables may underestimate the favorable area for understory herbs if the variation on local hydrological conditions is not considered.

Spatial and Seasonal CH4 Flux in the Littoral Zone of Miyun Reservoir near Beijing: The Effects of Water Level and Its Fluctuation

Wetlands, and especially their littoral zones, are considered to be CH4 emissions hotspots. The recent creation of reservoirs has caused a rapid increase in the area of the world’s littoral zones. To investigate the effects of water depth and water level fluctuation on CH4 fluxes, and how these are coupled with vegetation and nutrients, we used static closed chamber and gas chromatography techniques to measure CH4 fluxes in the littoral zone of a large reservoir near Beijing, China, from November 2011 to October 2012. We found that CH4 flux decreased significantly along a transect from open water to dry land, from 3.1 mg m−2 h−1 at the deep water site to approximately 1.3 mg m−2 h−1 at the shallow water site, and less than 0.01 mg m−2 h−1 in the non-flooded area. Water level influenced CH4 flux by affecting soil properties including soil redox potential, soil carbon and nitrogen, and bulk density. The largest emission of all was from the seasonally flooded site after a flooding event (up to 21.1 mg m−2 h−1), which may have been caused by vegetation decomposition. Submerged sites had greater emissions, while the driest site had lower emissions. Immediately after the monthly measurements had been made, we removed the aboveground vegetation to enable an assessment of the gas transportation per unit of biomass. Removal of biomass decreased emissions by up to 53%. These results indicated the dominant effect of water depth on CH4 flux through effects of soil conditions, plant species composition and distribution. This study suggests that temporally flooded wetlands, including littoral zones, contribute significantly to the global CH4 burden. However, the current challenge is to capture their spatial extent and temporal variation in the fluxes.

Concerning the Measures for Stabilization of Epidemiological Situation in the Territory of the Amur Region under Conditions of Emergency

A large-scale rainfall flooding in the territory of the Amur Region formed the foundation for dramatic aggravation of epidemiological situation, in that which concerns outbreaks of diarrheal disease, activation of epidemic processes associated with enteroviral infection and a number of natural-focal infectious diseases, as well as emergence of anthrax cases both among animals and humans. Basic anti-epidemic and preventive activities under emergency situation included: epidemiological monitoring over infectious and non-infectious morbidity among the population; microbiological and virusological laboratory surveillance of the ambient environment objects and water supply sources; sanitary-hygienic monitoring of the habitant living environment; immunization of the population depending on epidemiological indications; planning and implementation of disinfection, deratization, and disinsection procedures in the flood-stricken areas. Successful cooperation between the Rospotrebnadzor local agencies, Irkutsk Research Anti-Plague Institute SAET, regional health institutions and other organizations involved, in a challenging situation at the flooding site, made it possible to avoid serious epidemic complications among the population of the Amur Region.

Integrated Evaluation of Soil Erosion Hazard and Risk Management in the Oued Beht Watershed Using Remote Sensing and GIS Techniques: Impacts on El Kansra Dam Siltation (Morocco)

The initial state of the Oued Beht watershed (430,728 ha) is characterized by a socio-ecological vulnerability associated to the water erosion risk. Especially, the consequences are chained and the soil loss alters its hydrological behavior and its ability to protect functional and structural challenges (good land, El Kansra dam, agricultural activities). In this perspective, this study suggests a methodology, reproducible and generalizable, to assess the natural water erosion risk (R). The approach used is based on spatial processing technology of information to develop a spatial database and geographic information system (GIS) concerning biophysical and topoclimatic parameters in the Oued Beht watershed. Thus, the risk analysis is obtained by combining thematic maps of Susceptibility (S) and potential Consequences (C). Although, the spatial analysis of maps obtained reveals the extent of susceptibility involving land degradation, with the potential risks, which generated a decrease in the storage capacity of El Kansra dam (?3.03 Mm3/year). The results show that erosion is active on more than three quarters (3/4) of the watershed, and a considerable loss of land with 8.36 Million tonnes per year. In this way, flood analysis and study of hydrometeorological events identified the vulnerability of flood sites (hot-spot) contributing at 77% of El Kansra siltation dam. Therefore, the consequence assessment is obtained by identifying risk elements and estimating potential damage coefficient, which represents the financial gap flow affecting the socio-economic context due to the erosion impacts.

The Effect of Different Flooding Duration on Soil Organic Carbon and its Labile Fraction in the Riparian Zone of Three Gorges Reservoir Area

The labile fractions of organic carbon (OC) in soil can respond rapidly to changes in C supply and have been suggested as a sensitive indicator of soil quality. The object is to determine soil organic C and its labile fractions at the duration of different flooding. Three elevation gradient sites were chose: below 145m (permanently flooding site), 145-175m (seasonal flooding site), and above 175m (never flooding site) in the riparian zone of Three Gorges reservoir Area. The results showed that soil OC, dissolved organic C (DOC) and water-soluble carbohydrate (WSCh) were lower under seasonal flooding sites than those of never flooding upland and permanently flooding sites, whereas microbial biomass C (MBC) decreased with the flooding duration. Correlation analysis showed that soil OC and MBC had significantly positive relationship with DOC. The results suggested that seasonal flooding significantly affected soil OC and its labile fractions in the riparian zone of Three Gorges reservoir Area.

Type II Aerobic Methane Oxidizing Bacteria (AMOB) Drive Methane Oxidation in Pulsed Wetlands as Indicated by 13C-Phospholipid Fatty Acid Composition

AbstractMethane (CH4) is a potent greenhouse gas and management strategies have been proposed to limit CH4 emissions from freshwater wetlands. The methanotrophic bacteria can intercept much of the CH4 produced by methanogenic archaea and thus management protocols for wetlands could conceivably include manipulations not only to limit the production of CH4 by methanogens, but also to enhance the consumption of CH4 by benthic or planktonic methanotrophs. The hydrological characteristic of a wetland is a major determinant of the CH4 emission rates. A major consideration for CH4 production is whether a wetland is static or flowing (wetlands connected to rivers and streams). Very little is known about the effects of hydrologic pulsing on wetland carbon dynamics and especially CH4 oxidation. Furthermore, although it has been established that methanotrophs are very active at the oxic sediment water interface of wetlands, little is known about the ecology of methanotrophs in the “pulsing fringe”. Stable isotope probing (SIP) of biomarker Phospholipid Fatty Acids provide a means to connect CH4 oxidation to specific methanotrophs and track the shifts in community structure. Three landscape treatments were: 1) upland aerobic soil, 2) the intermediately flooded zone, and 3) the permanently flooded site with two landscape level replicates in a freshwater pulsing experimental wetlands at the Olentangy River Wetland (ORW) Research Park, The Ohio State University, Columbus. Two soil depths (organic horizon, 0-8 cm that includes the oxidized layer in flooded sites and 8-16 cm depth of surface mineral layer) were sampled at each site four times/year over a two-year period (early spring, mid summer, early fall and mid winter). Immediately after sampling the samples are stored at -20° C and transported under dry ice to the Soil Microbial Ecology Lab, SENR, the Ohio State University, Columbus for analysis. Samples were taken back to the lab to determine potential CH4 oxidation and 13C-PLFA analyses after extraction and analysis on GC-C-IRMS.The PF sites had significantly higher (p&lt;0.05) Potential Methane Oxidation (PMO) than the IF sites. PMO rates at 0-8 cm depth of soil were significantly higher than those at depth of 8-16 cm (p&lt;0.05). PMO in Winter was also significantly higher than in Summer (p&lt; 0.01). PLFA profiling of methanotrophs showed that the Type type II methanotrophs and I methanotrophs were more pronounced in winter that was highly correlated by the seasonal dynamics of PMO. Concentrations of the Type II methanotroph PLFA biomarker (18:ω8c, 18:ω9c and 18:ω7c) were significantly higher (p&lt;0.05) than the Type I PLFA biomarkers (16:ω5c).The highest potential to oxidize the substrate-available methane in the Permanently Flooded site is entirely attributed to the methanotrophic population (as reflected by the relative abundance of the signature PLFAs). Even if with very low 13C incorporation, the PLFA profile in the Intermittently Flooded site is dominated by the Type II methanotrophs.

High Prevalence of Bacterial Spore-Formers Active Against Mosquito Larvae in Temporary Monsoon Flooded Sites in Orissa, India

Different ecosystems were probed in the vicinity of the city of Bhubaneswar in the Indian state of Orissa for the presence of bacterial spore-formers with activity against mosquito larvae. The most productive sites were places that were flooded during the monsoon season, including roadside ditches and shorelines of ponds. Among 630 isolates screened, 44 (7%) showed larvicidal activity against larvae of Aedes aegypti. The specific activity of the bacterial spore-formers varied greatly. Isolates were found with specific activities superior to the Bacillus thuringiensis israelensis reference strain of the Pasteur Institute. All mosquitocidal strains produced crystal proteins, and based on the biochemical analyses could be classified into the species B. thuringiensis. Such strains possess the potential for the development of new microbial products for mosquito control in India.

Nesting Ecology of the Grey-Headed Fish-Eagle At Prek Toal, Tonle Sap Lake, Cambodia

Little is known about the ecology of the Grey-headed Fish-Eagle (GHFE; Ichthyophaga ichthyaetus) despite it being a globally near-threatened species in apparent decline. We here present the first quantitative information on nesting ecology of this species, in a regionally significant population at Prek Toal, part of the seasonally flooded swamp forest surrounding the Tonle Sap Lake, Cambodia. We found that GHFE selected trees as nest sites that had an open crown structure and were relatively tall. Grey-headed Fish-Eagles preferred nesting closer to permanent water than expected, but the timing of breeding did not differ according to distance to permanent water: we suggest that their preference for nests near water may reflect an advantage based on prey availability. Water snakes, known prey of GHFE, were significantly more abundant at a site in permanent water than at a temporarily flooded site, in December. We also found that human habitation was negatively correlated to GHFE nest-site occupancy rates. This may reflect indirect effects of human exploitation of GHFE food supplies, which may be exacerbated in the future by changes to the Tonle Sap ecosystem resulting from upstream dam construction.

Subglacial hydraulic scouring and deposition during surge-related outburst floods, Bering Glacier, Alaska

Fed by a persistent conduit system, three outburst floods released pressurized water from subglacial conduits midway through the 1993–95 surge of Bering Glacier, Alaska. The foreland substrate was mobilized and streamlined by overriding ice, but the effects of hydraulic erosion and deposition were far more effective in altering overridden terrain. Two sub-kilometer basins were scoured decameters into foreland terrain immediately up-glacier from outburst flood sites. These emerged fully formed from beneath the retreating glacier. Flood deposits in scoured subglacial channels consist of meter-size lag boulders beneath meters of well-sorted, graded gravel couplets. Eskers consisting of flood deposits formed within subglacial conduits during outburst flood events were exposed during retreat. Knowledge of pre-surge topography combined with foreland stratigraphy provides a basis for the recognition of subglacial, paleo-flood landforms and deposits.

Effects of waterlogging stress on morphology and physiology of Camptotheca acuminata.

Aims Camptotheca acuminate is a common tree species in southern and eastern China. It is planted widely as a virescence species and is cultivated as an officinal species, because its seed, leaf and stem can be used to distill camptothecin, which is used to treat cancer. Our objective was to examine C. acuminate’s resistance to waterlogging. Methods One-year seedlings of C. acuminata were grown in pots in a greenhouse in January, and we implemented four treatments in May: CK (common soil water content), A (water level 10 cm under soil surface), B (water level equal with soil surface) and C (water level 4 cm above soil surface). Treatments lasted 21 days, and indexes of lenticels, root growth, root vigor, POD, SOD, MDA and LDH were determined at different times after treatment. Important findings Root growth was better in A and CK treatments, and roots gradually died in B and C treatments. Comparatively, root vigor was higher in A and decreased gradually under B and C with treatment time. Many lenticels were observed on the stem under B and C, but not under CK and A. The POD and SOD activity of leaves of A treatment were higher during treatment, but increased and then decreased under B and C treatments. The production rate of O2–·, H2O2 content and MDA content of leaves of A, B and C treatments increased gradually with treatment time, but was higher under C and B treatments. The LDH activity of roots in A, B and C treatments was lower early in treatment, but increased significantly late in treatment. We conclude that C. acuminata grows well in lightly waterlogged sites, but not in waterlogged and flooded sites.

Flooding forested groundwater recharge areas modifies microbial communities from top soil to groundwater table

Subsurface microorganisms are crucial for contaminant degradation and maintenance of groundwater quality. This study investigates the microbial biomass and community composition [by phospholipid fatty acids (PLFAs)], as well as physical and chemical soil characteristics at woodland flooding sites of an artificial groundwater recharge system used for drinking water production. Vertical soil profiles to c. 4 m at two watered and one nonwatered site were analyzed. The microbial biomass was equal in watered and nonwatered sites, and considerable fractions (25-42%) were located in 40-340 cm depth. The microbial community structure differed significantly between watered and nonwatered sites, predominantly below 100 cm depth. Proportions of the bacterial PLFAs 16:1omega5, 16:1omega7, cy17:0 and 18:1omega9t, and the long-chained PLFAs 22:1omega9 and 24:1omega9 were more prominent at the watered sites, whereas branched, saturated PLFAs (iso/anteiso) dominated at the nonwatered site. PLFA community indices indicated stress response (trans/cis ratio), higher nutrient availability (unsaturation index) and changes in membrane fluidity (iso/anteiso ratio) due to flooding. In conclusion, water recharge processes led to nutrient input and altered environmental conditions, which resulted in a highly active and adapted microbial community residing in the vadose zone that effectively degraded organic compounds.

Unstructured mesh generation and landcover-based resistance for hydrodynamic modeling of urban flooding

Urban flood inundation modeling with a hydrodynamic flow solver is addressed in this paper, focusing on strategies to effectively integrate geospatial data for unstructured mesh generation, building representation and flow resistance parameterization. Data considered include Light Detection and Ranging (LiDAR) terrain height surveys, aerial imagery and vector datasets such as building footprint polygons. First, a unstructured mesh-generation technique we term the building-hole method (BH) is developed whereby building footprint data define interior domain boundaries or mesh holes. A wall boundary condition depicts the impact of buildings on flood hydrodynamics. BH provides an alternative to the more commonly used method of raising terrain heights where buildings coincide with the mesh. We term this the building-block method (BB). Application of BH and BB to a flooding site in Glasgow, Scotland identifies a number of tradeoffs to consider at resolutions ranging from 1 to 5 m. At fine resolution, BH is shown to be similarly accurate but execute faster than BB. And at coarse resolution, BH is shown to preserve the geometry of buildings and maintain better accuracy than BB, but requires a longer run time. Meshes that ignore buildings completely ( no-building method or NB) also support surprisingly good flood inundation predictions at coarse resolution compared to BH and BB. NB also supports faster execution times than BH at coarse resolution because the latter uses localized refinements that mandate a greater number of computational cells. However, with mesh refinement, NB converges to a different (and presumably less-accurate) solution compared to BH and BB. Using the same test conditions, Hunter et al. [Hunter NM, Bates PD, Neelz S, Pender G, Villanueva I, Wright NG, Liang D, et al. Benchmarking 2D hydraulic models for urban flood simulations. ICE J Water Manage 2008;161(1):13–30] compared the performance of dynamic-wave and diffusive-wave models and reported that diffusive-wave models under-predicted the longitudinal penetration of the flood zone due to important inertial effects. Here, we find that a relatively coarse-mesh implementation of a dynamic-wave model suffers from the same drawback because of numerical diffusion. This shows that whether diffusion is achieved through the mathematics or numerics, the effect on flood extent is similar. Finally, several methods of distributing resistance parameters (e.g., Manning n) across the Glasgow site were evaluated including methods that utilize aerial imagery-based landcover classification data, MasterMap ® landcover classification data and LiDAR-based feature height data (e.g., height of shrubs or hedges). Results show that landcover data is more important than feature height data in this urban site, that shadows in aerial imagery can cause errors in landcover classification which degrade flood predictions, and that aerial imagery offers a more detailed mapping of trees and bushes than MasterMap ® which can locally impact depth predictions but has little impact on flood extent.