Sufficient Water Supply Research Articles

Analysis on water requirement and water-saving amount of wheat and corn in typical regions of the North China Plain

This paper studied the variation characters on wheat and corn water consumption and irrigation watersaving amount under different water conditions (ample irrigation level, farmers conventional irrigation level and optimizing irrigation level). The water use efficiency and water saving potential of optimizing treatment and farmers’ conventional irrigation treatment were analyzed respectively. The objective of this study was to provide theoretical supporting for popularization and application of optimizing irrigation measures. Crop water requirement under sufficient water supply was calculated by Penman equation. We obtained crop water consumption under conventional treatment and optimizing treatment by field experiment. The main results showed that the irrigation amount of wheat and corn was too much under farmers’ conventional irrigation level and basically satisfied their water requirement, therefore, the water-saving amount was smaller while water-saving potential was bigger compared with the optimizing irrigation treatment. The grain yield under optimizing irrigation treatment was improved or appreciably reduced compared with that under conventional irrigation treatment, while the water consumption and irrigation amount of optimizing irrigation treatment was lower, with a higher water use efficiency. Therefore, the optimizing irrigation treatment could achieve a stable yield and high water efficiency at the same time. Moreover, when the optimizing irrigation measure was adopted, the grain yield reached 5940 kg/hm2, water-saving amount reached 91mm for winter wheat, and the grain yield reached 7743 kg/hm2, with water-saving amount of 49mm for summer corn in the piedmont region of Taihang Mount. The grain yield got 7710 kg/hm2, with water-saving amount of 20mm for winter wheat in Heilonggang Plain. Therefore, the water-saving amount in the piedmont region of Taihang Mountain was obviously higher than that in Heilonggang Plain. Thus, the piedmont region of Taihang Mountain in the North China Plain is viewed as the key district for water-saving.

Model Development of Rainwater Management for Agriculture Decision Support System in Semi Arid Area

Land cultivation for agricultural purposes in semiarid area is usually carried out only once a year specifically during the rainy season. The condition is even worse since it is not without the risk of failure because of dry-spell or water-logging. To cope with this situation, the researchers developed a model of Rainwater Management for Agriculture Decision Supporting System (RMA-DSS). The objective of this RMA-DSS is to facilitate the decision making to build water infrastructure. Using this program it is hoped that sufficient water supply for specific crops with correct planting time can be guaranteed, which in turn will optimize harvest. The model consists of three parts, namely, rainfall-runoff-infiltration model, crop water requirement-irrigation-drainage model and rainwater management for agriculture model. The Models are designed using Microsoft Excel’s Macro Visual Basic and finalized with Visual Basic language program for operating spatial database of map object and non spatial database.

Size-dependent responses to summer drought in Scots pine, Norway spruce and common oak

In this study, we provide a detailed analysis of tree growth and water status in relation to climate of three major species of forest trees in lower regions of Bavaria, Southern Germany: Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and common oak (Quercus robur). Tree-ring chronologies and latewood δ13C were used to derive measures for drought reaction across trees of different dimensions: growth reduction associated with drought years, long-term growth/climate relations and stomatal control on photosynthesis. For Scots pine, growth/climate relations indicated a stronger limitation of radial growth by high summer temperatures and low summer precipitation in smaller trees in contrast to larger trees. This is corroborated by a stronger stomatal control on photosynthesis for smaller pine trees under average conditions. In dry years, however, larger pine trees exhibited stronger growth reductions. For Norway spruce, a significantly stronger correlation of tree-ring width with summer temperatures and summer precipitation was found for larger trees. Additionally, for Norway spruce there is evidence for a change in competition mode from size-asymmetric competition under conditions with sufficient soil water supply to a more size-symmetric competition under dry conditions. Smaller oak trees showed a weaker stomatal control on photosynthesis under both dry and average conditions, which is also reflected by a significantly faster recovery of tree-ring growth after extreme drought events in smaller oak trees. The observed patterns are discussed in the context of the limitation-caused matter partitioning hypothesis and possible species-specific ontogenetic modifications.

Land cover effects on groundwater recharge in the tropics: ecohydrologic mechanisms

ABSTRACTManaging groundwater recharge to ensure sufficient water supply is a growing concern for many communities. We explore land cover effects on recharge processes and rate in Hawai'i, where precipitation on the mountain slopes of leeward Hawai'i Island recharges the aquifer that is the sole source of water for coastal communities. Applying a water balance, we quantify the influences of native forest and cattle pasture on recharge using measurements of precipitation and the drivers of evapotranspiration taken over 18 months. Surface runoff is negligible in these highly permeable basalt watersheds, simplifying fluxes into and out of the recharge area. On the basis of our analysis of measured fluxes, groundwater recharge is 96% of rainfall in pasture, 87% of above‐canopy rainfall in open forest, and 106% of above‐canopy rainfall in dense forest. Differences in recharge among vegetation types result largely from direct interception of cloud water by native Hawaiian forest. The majority of rainfall occurs in infrequent, large storms, so water moves quickly beyond plant rooting depth, limiting its availability for evapotranspiration. Potential evapotranspiration is low, as its drivers are modest and constant throughout the year. Existing estimates of submarine groundwater discharge support our conclusion that the rainfall‐to‐recharge ratio is close to one for all sites. Identifying primary influences on the recharge‐to‐rainfall ratio is key to predicting the types of changes that will have substantial effects on recharge. In any tropical setting with young, porous substrates, precipitation is likely to play a dominant role in the magnitude and variability of groundwater recharge; here, land‐use changes that affect local precipitation, such as an increase in fog interception, will play a larger role than vegetation shifts that affect evapotranspiration. Copyright © 2011 John Wiley & Sons, Ltd.

Sustainable strategies on water supply management in Hong Kong

AbstractThe growth in population and of the economy of Hong Kong has caused a significant increase in the demand for fresh water. To secure sufficient water supply and to reduce reliance on imported water from Dongjiang (East River) in Mainland China, the Hong Kong Special Administration Region (HKSAR) government has implemented a wide range of water conservation measures which include the use of seawater for toilet flushing, metering and a tiered water tariff, large‐scale replacement and rehabilitation of ageing pipelines to reduce leakage, valve‐type toilet flushing apparatus and education and publicity programmes. To ensure sustainable and safe water supply, the HKSAR government is actively exploring alternative water resources including the treated effluent from sewage treatment plant, desalination of seawater and the extension of water‐gathering grounds in the territory.

Influence of biochar on drought tolerance of Chenopodium quinoa Willd and on soil–plant relations

The application of pyrogenic carbon, biochar, to agricultural soils is currently discussed as a win-win strategy to sequester carbon in soil, thus improving soil fertility and mitigate global warming. Our aim was to investigate if biochar may improve plant eco-physiological responses under sufficient water supply as well as moderate drought stress. A fully randomized greenhouse study was conducted with the pseudo-cereal Chenopodium quinoa Willd, using three levels of biochar addition (0, 100 and 200 t ha−1) to a sandy soil and two water treatments (60% and 20% of the water holding capacity of the control), investigating growth, water use efficiency, eco-physiological parameters and greenhouse gas (GHG) fluxes. Biochar application increased growth, drought tolerance and leaf-N- and water-use efficiency of quinoa despite larger plant–leaf areas. The plants growing in biochar-amended soil accumulated exactly the same amount of nitrogen in their larger leaf biomass than the control plants, causing significantly decreased leaf N-, proline- and chlorophyll-concentrations. In this regard, plant responses to biochar closely resembled those to elevated CO2. However, neither soil- nor plant–soil-respiration was higher in the larger plants, indicating less respiratory C losses per unit of biomass produced. Soil-N2O emissions were significantly reduced with biochar. The large application rate of 200 t ha−1 biochar did not improve plant growth compared to 100 t ha−1; hence an upper beneficial level exists. For quinoa grown in a sandy soil, biochar application might hence provide a win-win strategy for increased crop production, GHG emission mitigation and soil C sequestration.

Prediction of spatial patterns of collapsed pipes in loess-derived soils in a temperate humid climate using logistic regression

Soil piping (tunnel erosion) has been recognised as an important erosion process in collapsible loess-derived soils of temperate humid climates, which can cause collapse of the topsoil and formation of discontinuous gullies. Information about the spatial patterns of collapsed pipes and regional models describing these patterns is still limited. Therefore, this study aims at better understanding the factors controlling the spatial distribution and predicting pipe collapse. A dataset with parcels suffering from collapsed pipes (n=560) and parcels without collapsed pipes was obtained through a regional survey in a 236km² study area in the Flemish Ardennes (Belgium). Logistic regression was applied to find the best model describing the relationship between the presence/absence of a collapsed pipe and a set of independent explanatory variables (i.e. slope gradient, drainage area, distance-to-thalweg, curvature, aspect, soil type and lithology). Special attention was paid to the selection procedure of the grid cells without collapsed pipes. Apart from the first piping susceptibility map created by logistic regression modelling, a second map was made based on topographical thresholds of slope gradient and upslope drainage area. The logistic regression model allowed identification of the most important factors controlling pipe collapse. Pipes are much more likely to occur when a topographical threshold depending on both slope gradient and upslope area is exceeded in zones with a sufficient water supply (due to topographical convergence and/or the presence of a clay-rich lithology). On the other hand, the use of slope-area thresholds only results in reasonable predictions of piping susceptibility, with minimum information.

Improvement of Volume Stability in Core Concrete of Concrete-Filled Steel Tube

Due to the concrete self-shrinkage, frequent load application and temperature fluctuation, and so on，the gap formed between the inner tube wall and the core concrete surfaces would decrease the performance of concrete-filled steel tube (CFST). To prevent this cavity problem, various types of expansive agents and aggregates were used in this study to improve the volume stability of core concrete. Comparative experiments with mortars and concrete were carried out respectively under standard curing condition and under enclosed curing condition which simulated the environment in steel tube. The results could be summarized as follows: ● Two types of expansive agents, ZY type expansive agent mainly containing sulfates and aluminates and M type expansive agent mainly containing magnesium oxide, presented different expansive behaviors with curing ages in mortar and concrete. Two types of expansive agents combined with each other could produce complementary and superimposition effects to improve continuously the volume stability of mortar and concrete. ● Sufficient water supply is the key factor for the formation and maintenance of expansion. The volume change caused by the self-shrinkage effect of core concrete could not be effectively off-set with whether two types expansive agents or their compounds under enclosed environment in which water was scarce and could not be supplied from outside. ● When some water-saturated ceramsite were used to partially replace aggregates in core concrete,the volume expansion performance of core concrete improved dramatically with the water storage and supply effects of water-saturated ceramsite.

Biomass allocation, relative competitive ability and water use efficiency of two dominant species in semiarid Loess Plateau under water stress

A better understanding of the growth and interspecific competition of native dominant species under water stress should aid in prediction of succession in plant communities. In addition, such research would guide the selection of appropriate conservation and agricultural utilization of plants in semiarid environments that have not been very well characterized. Biomass production and allocation, relative competitive ability and water use efficiency of one C 4 herbaceous grass ( Bothriochloa ischaemum) and one C 3 leguminous subshrub ( Lespedeza davurica), both important species from the semiarid Loess Plateau of China, were investigated in a pot-cultivation experiment. The experiment was conducted using a replacement series design in which B. ischaemum and L. davurica were grown with twelve plants per pot, in seven combinations of the two species (12:0, 10:2, 8:4, 6:6, 4:8, 2:10, and 0:12). Three levels of water treatments included sufficient water supply (HW), moderate water stress (MW) and severe water stress (LW). These treatments were applied after seedling establishment and remained until the end of the experiment. Biomass production and its partitioning, and transpiration water use efficiency (TWUE) were determined at the end of the experiment. Interspecific competitive indices (competitive ratio (CR), aggressiveness (A) and relative yield total (RYT)) were calculated from the dry weight for shoots, roots and total biomass. Water stress decreased biomass production of both species in monoculture and mixture. The growth of L. davurica was restrained in their mixtures for each water treatment. L. davurica had significantly ( P < 0.05) greater root:shoot allocation than B. ischaemum for each water treatment and proportion within the replacement series. Aggressiveness (A) values for B. ischaemum with respect to L. davurica were negative only at the proportions of B. ischaemum to L. davurica being 8:4 and 10:2 in LW treatment. B. ischaemum had a significantly ( P < 0.05) higher CR value under each water treatment, and water stress considerably reduced its relative CR while increased that of L. davurica. RYT values of the two species indicated some degree of resource complimentarity under both water sufficient and deficit conditions. The results suggest that it is advantageous for growing the two species together to maximize biomass production, and the suggested ratio was 10:2 of B. ischaemum to L. davurica because of significantly higher ( P < 0.05) RYT and TWUE under low water availability condition.

Strength Mechanism of Cement-Asphalt Mortar

The strength mechanisms of two kinds of cement-asphalt (CA) mortar, which vary principally in their strength and elastic modulus, were investigated by environmental scanning electron microscopy, calorimetry, and strength tests. The results showed that the asphalt emulsion delayed the early hydration of the cement and the asphalt membrane had a negative effect on the further hydration of the cement, to some extent. The cement products could impale the asphalt membrane, and the cement could hydrate adequately because of the sufficient water supply in the CA mortar. The framework formed by the hardened cement paste was the primary structure skeleton in the CA mortar with a high elastic modulus and the asphalt phase, exhibiting as a filling phase, increased the weak phase of the structure system. For CA mortar with a low elastic modulus, the asphalt phase exhibited as a dominant phase. Two weak structure skeletons, formed by the asphalt membrane and the hardened cement paste, respectively, were responsible for the strength together.

Processing Tomato Nitrogen Utilization and Soil Residual Nitrogen as Influenced by Nitrogen and Phosphorus Additions with Drip‐Fertigation

Timely sufficient water supply through drip irrigation or fertigation may increase nutrient demand of processing tomato (Lycopersicon esculentum Mill.) due to increases in yield production. However, excessive nutrient application could result in crop luxury uptake and enrichment in soil profile, especially mineral N, with the latter potentially causing environmental concerns. A study was conducted to determine the responses of crop N utilization and post‐harvest soil profile mineral N to fertilizer N and P additions under drip fertigated processing tomato in sandy loam soils from 2003 to 2005. Across the 3 yr, both fruit N removal and plant total N uptake were either linearly or quadratically related to fertilizer N rate, with 187 kg N ha−1 of fruit removal and 268 kg N ha−1 of plant total N uptake obtained at the maximum yield. Nitrogen uptake efficiency and apparent N recovery decreased linearly with increases in N rate. At the maximum fruit yield, N uptake efficiency was 0.71, and apparent N recovery was 51.7%. Post‐harvest soil profile (0–100 cm) mineral N increased with increases in fertilizer N rate, and at greater rates with fertilizer N applied at rates above those required for maximum fruit yield production. Of the soil residual N, 62% remained in the top 40‐cm soil layer. Addition of fertilizer P had no effects on plant N uptake, N uptake efficiency and post‐harvest mineral N in soil profile, presumably due to the high levels of soil test P. Beneficial management practices need to be developed to prevent soil N losses during the non‐growing season following production of processing tomato with drip fertigation.

Critical appraisal of an irrigation command and water productivity based on satellite remote sensing

Irrigation policy makers and managers need information on the irrigation performance and productivity of water at various scales to devise appropriate water management strategies, considering dwindling water availability, further threats due to continually rising population and food demand. It is often difficult to access sufficient water supply and use data to determine crop water consumption and irrigation performance. Energy balance techniques using remote sensing data have been developed by various researchers, and can be used as a tool to directly estimate actual evapotranspiration that is, water consumption. Study demonstrates how remote sensing-based estimates of water consumption and water stress combined with secondary agricultural production data, which provide better estimates of irrigation performance, water productivity. A principle benefit of the approach is that it allows identification of areas where agricultural performance is less than potential, there by providing insights into how irrigation systems can be managed to improve overall performance and increase water productivity in a sustainable manner. To demonstrate the advantages, the approach is planned to be applied in North Gujarat, India based Dharoi Irrigation Scheme. Remote sensing-based indicators reflecting equity, adequacy, reliability and water productivity can be estimated. This paper is purely the extensive research review and conceptualized concept to be used for future research in above said region. Key words: Actual evapotranspiration, equity, adequacy, reliability, water productivity, surface energy balance, SEBAL.

Recent and Historic Drivers of Landscape Change in the Everglades Ridge, Slough, and Tree Island Mosaic

More than half of the original Everglades extent formed a patterned peat mosaic of elevated ridges, lower and more open sloughs, and tree islands aligned parallel to the dominant flow direction. This ecologically important landscape structure remained in a dynamic equilibrium for millennia prior to rapid degradation over the past century in response to human manipulation of the hydrologic system. Restoration of the patterned landscape structure is one of the primary objectives of the Everglades restoration effort. Recent research has revealed that three main drivers regulated feedbacks that initiated and maintained landscape structure: the spatial and temporal distribution of surface water depths, surface and subsurface flow, and phosphorus supply. Causes of recent degradation include but are not limited to perturbations to these historically important controls; shifts in mineral and sulfate supply may have also contributed to degradation. Restoring predrainage hydrologic conditions will likely preserve remaining landscape pattern structure, provided a sufficient supply of surface water with low nutrient and low total dissolved solids content exists to maintain a rainfall-driven water chemistry. However, because of hysteresis in landscape evolution trajectories, restoration of areas with a fully degraded landscape could require additional human intervention.

Importancia de la hidrogeología urbana; ciencia clave para el desarrollo urbano sostenible

Urban expansion as a result of continuous population growth as well as the creation of a large variety of industries and the parallel high human population density require a sufficient supply of clean water. In many cities around the world groundwater is the main source of potable water. In turn, anthropogenic activities discharge large volumes of waste water and industrial effluents. The use of a variety of chemicals and hydrocarbons causes pollution of groundwater supplies and soils. The complex interaction between groundwater flow systems and cities (infrastructure, city process, activities and discharge) requires increasingly complex studies, which is why a new branch of science has emerged under the name of “urban hydrogeology”, considered to be a specialization within the hydrogeological sciences. This paper provides a general vision of urban hydrogeology that allows understanding its conceptual aspects, its scope of application and management. The information presented refers to the interdependence of cities and groundwater use. The paper details the processes and mechanisms studied through this new branch of knowledge as well as their effects in relation to the physical and chemical properties of water quality (pollution processes). Case studies are discussed in order to have a variety of viewpoints on environmental impacts, theoretical development and technological advances developed in order to seek efficient solutions. We highlight guidelines and models for sustainable groundwater management in urban settings that have been developed with the aim

Nitrogen, phosphorus and potassium nutritional status of semiarid steppe grassland in Inner Mongolia

In grazed semiarid steppe ecosystems, much attention has been paid to aspects of growth limitation by water. So far, potential limitation of primary production by plant nutrients was rarely considered. This knowledge is essential for identification of sustainable land-use practices in these large and important ecosystems on the background of over-exploitation and climate change. In the present study plant nutrient concentrations and ratios were investigated with factorial additions of water and N fertilizer at two sites with contrasting soil nutrient availability. Combined analysis of nutrient concentrations, contents, biomass production, and plant N:P ratios consistently confirmed primary growth limitation by water and a strong N limitation when sufficient amounts of water were supplied. P limitation only occurred at the site with low P availability when in addition to the natural supply, water and N fertilizer were given. According to reported thresholds of N:K and K:P ratios, K was not limiting in any plot. The observed nutritional patterns in the plant community were related to the dynamics of species composition and their specific nutrient status. Stipa grandis had the highest N:P ratio whereas Artemisia frigida showed lowest N:P. These nutrient characteristics were related to growth strategies of dominant species. Accordingly, the relative biomass contribution of S. grandis and A. frigida strongly affected the nutrient status of the plant community. Plant N:P ratios indicate the relative limitation by N or P in the semiarid grasslands under sufficient water supply, but other methods of nutritional diagnosis should be used when plant N:P ratios remain below critical values.

DROUGHT STRESS: Soil Water Availability Alters the Inter‐ and Intra‐Cultivar Competition of Three Spring Wheat Cultivars Bred in Different Eras

AbstractCompetition for water generates a classic aspect of the tragedy of the commons, the ‘race for fish’, where crops must allocate more resource to acquisition of the limiting resource than is optimal for crop yield allocation. A pot experiment using a simple additive (target–neighbour) design was conducted to examine the above‐ground and below‐ground growth of three spring wheat (Triticum aestivum L.) cultivars when grown alone and in mixtures at three levels of water availability. The effects of competition and water availability were compared by observing patterns of growth, biomass allocation and below‐ground outcomes. Competitive interactions were investigated among cultivars ‘HST’, ‘GY602’ and ‘LC8275’, target plant of each cultivar grown without neighbouring plants are referred to herein as control plant and one target plant of each cultivar sown surrounded either by same or another cultivar as intra‐ or inter‐cultivar competition. Competitive ability was assessed as the response ratio (lnRR) between the target plant surrounded by six other plants and the target plant in isolation. Our results showed that the cultivar ‘HST’, released over a century ago, produced a higher biomass and grain yield than the more recently released cultivars ‘LC8275’ and ‘GY602’ when grown as isolated plants with sufficient water supply. However, competition for resources from neighbours led to target plant biomass and grain yield being significantly reduced relative to controls in all three cultivars, particularly in ‘HST’. When subjected to intra‐cultivar competition, the two recently released cultivars ‘LC8275’ and ‘GY602’ had higher grain yields and water use efficiency for grain than ‘HST’ in all three water regimes. The landrace ‘HST’ had better and significantly linear relationships between biomass and biomass allocation, root length and specific root length, whereas the recent and modern cultivars had much more water‐related species‐specific changes in root morphology and allocation patterns. These results suggest that crop traits that influence competitive ability, such as biomass allocation to roots and root plasticity in response to drought have changed in modern wheat cultivars because of breeding and selection.

Quality Assessment of Stored Rainwater and Its Utilization in Dhaka City, Bangladesh

Monsoons provide Bangladesh with ample rainwater. However, many regions, both rural and urban, suffer from shortage of safe drinking water. While arsenic contamination of ground water affects many rural areas, some urban areas, including Dhaka City, also lack of sufficient potable water supply due to shortage of surface water. This research explored the quality of stored rainwater as well as the feasibility of harvesting monsoon rainwater as a source of drinking water. Rainwater had been experimentally harvested at Bangladesh University of Engineering and Technology in Dhaka using a simple traditional technology. The rainwater was collected using a small catchment area (4.57 m × 4.57 m) made of water-proof cloth and a 3.2 m3 capacity ferro-cement storage tank, attached with an automatic initial flushing device, for a family having five members for four months. Initial test results indicated that the stored rainwater had a slightly higher pH value (8.1 to 8.3) and presence of total coliform after three months of storage. The traditional filtering system removed contaminants completely and the total coliforms up to 60%. This research supports the viability of traditional filtering of harvested rainwater as a promising solution to potable water shortage in Bangladesh.

Seedling Biomass Partition and Water Use Efficiency of Switchgrass and Milkvetch in Monocultures and Mixtures in Response to Various Water Availabilities

Seedling biomass and allocation, transpiration water use efficiency (TWUE), and species competition between switchgrass (Panicum virgatum L.) and milkvetch (Astragalus adsurgens Pall.) were investigated in a pot-cultivated experiment under different levels of water availability. The experiment was conducted using a simple replacement design in which switchgrass and milkvetch were grown in growth chamber with ten seedlings per pot, in three combinations of the two species (0:10, 5:5 and 10:0). Five water treatments included sufficient water supply (HW), gradual soil drying from HW (DHW), moderate water stress (LW), gradual soil drying from LW (DLW), and re-establishment of LW conditions after 12 days of drying from LW (RLW). Water treatments were applied over a 15-day period. Biomass production and its partitioning, and TWUE were determined at the end of the experiment. Species competitive indices (competitive ratio (CR), aggressivity (A) and relative yield total (RYT)) were calculated from the biomass dry weight data for shoots, roots and total biomass. Water stress significantly reduced seedling biomass production but increased root:shoot ratios in both monocultures and mixtures. In the RLW treatment, only switchgrass monocultures displayed compensatory biomass production and TWUE, while both species demonstrated compensatory growth in the mixture. Switchgrass was the dominant species and much more aggressive than milkvetch in the LW treatment, while in the other four treatments milkvetch was the dominant species as measured by the positive value of aggressivity and higher values of CR. The total biomass RYT values of the two species were higher than 1.0, indicating some degree of resource complimentarity. In the two-species mixture, although the biomass production was lower than that of milkvetch in the monoculture, there was better TWUE, especially under low and fluctuating water availability.

Bank filtration in the sandy littoral zone of Lake Tegel (Berlin): Structure and dynamics of the biological active filter zone and clogging processes

This study focused on clogging processes and on the benthic microalgal and meiofaunal assemblage in the sandy littoral zone of Lake Tegel, which are significantly involved in bank filtration, in a long-term. Our approach combined field studies and “in situ” experiments to highlight the structure of the biological active filter zone as well as the mechanisms and effects of clogging in the interstices that influence the infiltration process. Campaigns to measure “in situ” infiltration rates and hydraulic potential were conducted monthly from March 2004 to April 2005. Meiofaunal abundances and fine particulate organic matter (FPOM) were determined every 6 weeks in freeze cores down to depths of 50 cm. In parallel, concentrations of carbon, nitrogen and chlorophyll a were measured in samples of unfrozen sediment cores, that were divided in 1-cm steps down to depths of ≥10 cm. Similar sediment profiles were generated for analysis of colloidal carbohydrates, extracellular polymeric substances (EPS) and proteins between December 2005 and June 2006. Electron microscopy was used to visualize biofilm structure. Long-term experiments with natural FPOM and melamine resin particles as fluorescent tracers were performed to study “in situ” particle retention and transport, respectively. Additionally seston input was quantified during a 1-week period in April 2005. Infiltration rates showed a high temporal and spatial variability, but were not correlated with hydraulic conductivities as hydraulic gradients changed a lot. Likewise a correlation between infiltration rates and hydraulic potentials was not observed, indicating clogging processes. These are triggered to a high extend by biological compounds. In addition, seston input and intermittent gas intrusion are considered to reduce the hydraulic conductivity considerably. No significant “in situ” transport of inert natural fluorescent tracers was observed. However, a complete and permanent clogging of the sandy sediment does not occur, and daily infiltration rates of 0.7–27 L m−2 h−1 (mean 9 L m−2 h−1) guarantee a sufficient water supply by bank filtration for decades.

Plant growth and root morphology of Phaseolus vulgaris L. grown in a split-root system is affected by heterogeneity of crude oil pollution and mycorrhizal colonization

Response of plant performance and root properties to heterogeneous distribution of crude oil pollutants and mycorrhizal colonization is poorly understood even though (high) heterogeneity represents the normal case rather than exception in re-vegetation and phytoremediation of polluted soils. We investigated the effects of heterogeneous versus homogeneous distribution of hydrocarbon pollution (crude oil, type OMV® A) and mycorrhizal colonization on shoot and root properties of Phaseolus vulgaris L. using a split-root compartment approach in a factorial design with the main factors pollution and mycorrhiza realized in either one or both root compartments. Apart from plant responses to homogeneous pollution (e.g., decreased shoot and root biomass) or mycorrhization (e.g., larger P contents in leaves) we identified systemic interactions between split roots of heterogeneous treatments. In the absence of mycorrhiza, pollution in one root compartment resulted in locally increased root biomass and root length, and decreased root average diameter (RAD), possibly to overcome (water-)stress by better exploration of the soil volume whereas opposite effects on root biomass and length were observed in the unpolluted conjugated compartment. This systemic impact may be explained by preferential allocation of carbon by the plant to the root system in the polluted compartment on expense of the roots in the conjugated compartment. Stress indicated by decreased shoot/root biomass ratios and smaller foliar P content was not reflected in overall root and shoot biomass, likely due to sufficient supply of water and nutrient resources from the unpolluted compartment. The observed responses were not significant in the presence of mycorrhiza, indicating that mycorrhized plants were less susceptible to the observed impacts of pollutant heterogeneity. Mycorrhization in one of the conjugated compartments systemically induced shorter roots in the non-mycorrhized compartment. The resulting decrease in nutrient supply from the non-colonized roots along with increased carbon allocation to the mycorrhizal association in the conjugated compartment are likely to explain the observed overall decreases of shoot and root biomass. We conclude that heterogeneity of mycorrhizal colonization and pollutant distribution in soil can substantially change the plant response as compared to homogeneous situations studied in most pot experiments. Further studies are required to improve our understanding of mechanisms involved and to evaluate the relevance for heterogeneous field situations.