Reduced Soil Conditions Research Articles

Assessing New Developments in IRIS Technology

Reducing soil conditions may impact more static properties like soil morphology, as well as more dynamic soil chemical properties and microbial ecology. Identifying reducing conditions is especially important when evaluating wetland soil systems. Indicator of Reduction in Soils (IRIS) tubes have been approved by the National Technical Committee for Hydric Soils (NTCHS) as a method to identify reducing soil conditions. Recently, a new development in IRIS technology utilizing flexible films has emerged. IRIS films are strips of vinyl sheeting painted with iron- or manganeseoxide paint. The films are intended to simplify field work and facilitate acquisition and computer analysis of IRIS images. This mesocosm study demonstrates that IRIS films perform comparably to IRIS tubes and accurately document reducing soil conditions.

A System for Making and Deploying Oxide‐Coated Plastic Films for Environmental Assessment of Soils

Core Ideas IRIS films document reducing soil conditions. IRIS films perform the same as IRIS tubes. IRIS films permit easy acquisition of two‐dimensional images. The IRIS film deployment system protects IRIS from abrasion or scratching. IRIS films require 5% of the storage volume of traditional IRIS tubes. The documentation of reducing conditions in soils is important in the study, monitoring, and delineation of hydric soils and wetlands. Over the last decade, IRIS (Indicator of Reduction In Soils) technology has moved from the periphery into common use in hydric soils studies. Their appeal has been their ease of use and their conceptual simplicity, and IRIS technology has been approved by the US National Technical Committee for Hydric Soils (NTCHS). Recent developments in IRIS applications have also utilized Mn oxide paint, in addition to Fe oxide paint. While IRIS technology has encompassed a variety of forms, polyvinyl chloride (PVC) tubes are used most commonly. There are, however, challenges when using traditional PVC IRIS tubes. These include: (1) difficulty in acquiring a two‐dimensional image from a three‐dimensional cylindrical structure; (2) abrasion or scratching of the tubes during transport and on insertion (especially in sandy or dense soil conditions); (3) expense of shipping due to their weight and size; (4) long term storage issues; (5) general environmental and/or sustainability concerns with using non‐reusable plastic tubing. This paper describes a system for the delivery and installation of oxide‐coated plastic films in soils. Field testing of both Fe‐coated and Mn‐coated devices demonstrates that data provided by films does not differ significantly from data provided by tubes. However, many of the problems and issues that have plagued the use of IRIS tubes are eliminated by use of IRIS films.

Dissolved organic carbon cycling, methane emissions and related microbial populations in temperate rice paddies with contrasting straw and water management

Rice cultivation is recognised as a pivotal source of atmospheric methane (CH4), accounting for 11% of global emissions. The main drivers of CH4 production are redox conditions of soil, substrate availability, and abundance of methanogenic archaea, all potentially governed by management practices for straw and water management. In the present study, we combined crop residue and water management practices aimed at limiting substrate availability and reducing soil conditions required for methanogenesis, and tested their efficiency for mitigating CH4 emission in a field trial conducted on a long-term experimental platform. Combined straw and water management practices (i.e. the early crop residue incorporation, AUT, the adoption of dry with respect to water seeding, DRY, and the straw removal, REM) were effective in reducing dissolved organic carbon (DOC) concentrations, methanogenic abundances and overall CH4 fluxes, with respect to the typical technique adopted in the Italian rice district that involves spring incorporation of straw and water seeding (SPR). The latter treatment enhanced substrate availability as well as favoured methanogenic archaea abundances and resulted in the highest CH4 fluxes and cumulative emissions. Treatments AUT and REM showed similar behaviours, reducing emissions of SPR by 48% and 46%, respectively. The highest mitigation efficiency was obtained by DRY that reduced emissions by 69% as a result of the oxic soil conditions during the early vegetative stage, the decreased substrate availability with the onset of field flooding, and the lower abundance of methanogenic communities.

The MIS 3/2 transition in a new loess profile at Krems-Wachtberg East – A multi-methodological approach

Local to regional paleoenvironmental reactions to past climate changes are preserved in loess-paleosol sequences (LPS). In order to extract this information we used a multi-methodological approach in the Upper Paleolithic site of Krems-Wachtberg East in Lower Austria. Detailed field studies and high-resolution geochemical, colorimetric, and granulometric analyses help to understand the interplay between soil formation, loess accumulation, and surface processes. In comparison to the main profile/excavation of Krems-Wachtberg 2005–2015 it can be stated that OSL- and 14C-ages as well as the (archeological) stratigraphy of both profiles are comparable. However, pedogenic features are more evident at Krems-Wachtberg East. The new investigations show that well-established weathering indices do not clearly trace interstadial soil formation in the studied profile. Apart from this fact, single specific elements like Fe and Mg react more sensitive to initial pedogenic processes. Weak pedogenesis can further be evidenced by quantitative spectrophotometric results. The latter is also capable of refining and supporting the stratigraphy/pedology based on field analyses. As a general rule, next to loess also initial soil horizons of the MIS 3 are remarkably rich in primary carbonates indicating that soil formation took place in an alkaline environment. Due to the fact that hydrolysis of feldspars could not clearly be detected by the application of pedochemical indices, soil formation was probably limited to the oxidation of iron bearing minerals and weak carbonate leaching. These phases of favorable climatic conditions in terms of pedogenesis were terminated by increasing dust input towards the onset of MIS 2. The eolian deposits are overprinted during reducing conditions in soils and/or modified by colluvial processes. Altogether, weak pedogenesis can be reliably detected using a multi-methodological approach which leads to enhanced paleoenvironmental interpretations. The OSL-ages put the profile in a range of ∼41 to 30 ka. We present a tentative correlation of the studied loess profile to the record of the North Greenland Ice Core Project (NGRIP) for the part of the profile where OSL and 14C complement each other.

Reducing conditions in soil of Gallocanta Lake, northeast Spain

Saline wetlands have received limited attention from researchers and this neglect has often resulted in their degradation and limited conservation, and insufficient information to design conservation and management plans. Gallocanta Lake is a nature reserve of international importance for winter birds. The importance of the soil here, which supports niches and protected habitats for certain species of birds, has been recognized more recently. The soil of Gallocanta Lake undergoes strong oscillations of saturation and drainage followed by drying because of irregular rain and variable flooding conditions associated with fluctuations in the level of the lake. This study examined reducing conditions and morphological indicators of reduction in the soil around the lake with indicators of reduction in soils (IRIS) tubes, which are coated with iron oxides. We surveyed five sites for between 22 and 34 weeks. The average amount of iron removed from the IRIS tubes during the period studied ranged between 4 and 96%. The intensity of reduction in the soil differs according to subtle topographic differences between sites; it increases with the decrease in elevation. The large soil salinity (electrical conductivity saturated soil extract, ECe, from 18.1 to 182 dS m–1), carbonate‐rich composition (from 18.4 to 69.7% calcium carbonate equivalent, CCE) and overall small organic matter content (from 0.4 to 6.2% organic matter) do not seem to constrain iron mobilization because of the reducing conditions. Differences in iron depletion and patterns on the IRIS tubes show the heterogeneity of soil conditions and the complexity of factors involved in redox processes. Further research is needed to gain knowledge of the redox processes in the context of pedogenesis in semiarid lacustrine environments.HighlightsHow soil intermittently exposed to waterlogging expresses redox conditions. Current reducing conditions are evident in a fluctuating saline lake by IRIS tubes. Soil reduction occurs in alkaline soil with intermittent waterlogging. IRIS tubes are suitable field indicators of the heterogeneity of soil reducing conditions in saline lakes.

A Synthesized Manganese Oxide for Easily Making Durable Manganese‐Coated IRIS Tubes

Core Ideas We developed a new synthesis of well‐crystalline birnessite for making Mn‐coated IRIS tubes. The Mn coating can be easily and quickly applied using a foam brush and lathe. The Mn coating on PVC tubes has strong adhesion and good durability. Up to 30 (50‐cm) Mn‐coated IRIS tubes can be manufactured per hour. The speed and ease of manufacturing permits broader use of Mn‐coated IRIS tubes. During the last decade, Indicator of Reduction in Soils (IRIS) technology has been developed whereby polyvinyl chloride (PVC) devices coated with an Fe‐oxide paint are inserted into the soil to document strongly reducing conditions. The IRIS devices are easy to use and interpret, are less prone to difficulties associated with other methods of assessing reducing soil conditions, and have been endorsed by the National Technical Committee for Hydric Soils. There has been longstanding interest in Mn‐oxide‐coated tubes, but until lately there have been insurmountable problems associated with poor adhesion and durability of the Mn‐oxide coating. Recently, workers have suggested an easily synthesized, poorly crystalline birnessite to make Mn‐coated PVC IRIS devices, but their manufacturing procedure for tubes with a durable Mn coating is cumbersome and time consuming. We have developed an easily synthesized crystalline birnessite paint that can be used to quickly make IRIS tubes with a strongly adhering and durable Mn‐oxide coating. The procedure requires a large excess of sodium lactate to reduce KMnO4 quickly, followed by centrifuge washing and 3 d of dialysis. Once adjusted to the proper consistency, the birnessite can be painted onto PVC tubing using a foam brush and a lathe‐type device, such that approximately 30 tubes can be prepared in as little as 1 h. Preliminary testing conformed with other investigations suggesting that Mn‐oxide coatings become solubilized and stripped from tubes more rapidly, and under less strongly reducing conditions, than the Fe‐oxide‐coated tubes.

Anaerobic soil disinfestation reduces survival and infectivity of Phytophthora nicotianae chlamydospores in pepper

Phytophthora nicotianae is the principal causal agent of root and crown rot disease of pepper plants in Extremadura (western Spain), a spring-summer crop in this region. Preplant soil treatment by anaerobic soil disinfestation (ASD) may effectively control plant pathogens in many crop production systems, but field conditions and availability of C sources can limit its practical application. A laboratory experiment was conducted to study P. nicotianae control by ASD with low temperatures and several carbon (C) sources: rice bran, rapeseed cake, grape pomace and brewer’s spent grain. Survival and infectivity of pepper by P. nicotianae chlamydospores were reduced with all C sources assayed and redox potential in all ASD treatments indicated that reductive soil conditions were achieved. Rice bran (20tonsha−1); rapeseed cake (20tonsha−1), and grape pomace (40tonsha−1) were also assayed in a field experiment in early spring. Survival and infectivity of P. nicotianae were also reduced with all C sources. An increase of dehydrogenase and urease activities and a strong pH decline were observed with rice bran and rapeseed cake, probably related to an increase of anaerobic bacterial populations in soil. Application of ASD with high C source rates may be effective in control of P. nicotianae under low temperature conditions.

Effects of Riparian Buffer Vegetation and Width: A 12-Year Longitudinal Study.

Agricultural contributions of nitrogen are a serious concern for many water resources and have spurred the implementation of riparian buffer zones to reduce groundwater nitrate (NO). The optimum design for buffers is subject to debate, and there are few long-term studies. The objective of this project was to determine the effectiveness over time (12 yr) of buffer types (trees, switchgrass, fescue, native, and a control) and buffer widths (8 and 15 m) by measuring groundwater NO-N and dissolved organic carbon (DOC) trends. At the intermediate groundwater depth (1.5-2.1 m), NO-N reduction effectiveness was 2.5 times greater (46 vs. 16%) for the wider buffer, and, regardless of width, buffer effectiveness increased 0.62% yr. Buffer vegetative type was never statistically significant. In the deep-groundwater depth (2.1-3.5 m), there was no change in NO-N removal over time, although the statistical interaction of width and vegetative type indicated a wide range of removal rates (19-82%). The DOC concentrations were analyzed at the field/buffer and buffer/stream sampling locations. Depending on location position and groundwater sampling depth, DOC concentrations ranged from 1.6 to 2.8 mg L at Year 0 and increased at a rate of 0.13 to 0.18 mg L yr but always remained low (≤5.0 mg L). Greater DOC concentrations in the intermediate-depth groundwater did not increase NO-N removal; redox measurements indicated intermittent reduced soil conditions may have been limiting. This study suggests that riparian buffer width, not vegetation, is more important for NO-N removal in the middle coastal plain of North Carolina for a newly established buffer.

Fate of Phosphorus in a Grass Buffer Zone Under Concentrated Flow Condition

The grass buffer zone (GBZ) is commonly used a best management practice for the control of agricultural pollutants. However, the sorption and removal mechanisms of pollutants within GBZ have not been clearly identified. We studied changes in soluble reactive phosphorus (SRP) from dairy house wastewater in the GBZ, after the wastewater application to the field was stopped. The results showed that Morgan soil test P levels in the saturated area were low compared to the soils in the relatively drier area. High SRP concentrations >4 mg/L were observed in monitoring wells near the discharge points and in the downslope area. The SRP concentration as high as 9.4 mg/L near the discharge point in the saturated area was caused by the highly reduced soil conditions, while the SRP concentration in the downslope area was likely due to the topographic convergence. The SRP concentrations for the wells in the GBZ decreased <10% of the influent dairy house wastewater concentration once the soil was dry after an application has been intentionally shut down. Therefore, we concluded that the GBZ may play a significant role to remove P from wastewater under the condition that the soil stays aerobic.

Comparison of Manganese and Iron Oxide-Coated Redox Bars for Characterization of the Redox Status in Wetland Soils

Characterization of the soil redox status is important for pedogenesis but simple field methods for monitoring are limited. Recently, we introduced manganese (MnIII,IV) oxide-coated redox bars as an indicator for reducing conditions in soils. In this study, we compared these redox bars with well-established iron (FeIII) oxide-coated bars. For a 5-month monitoring period, we quantified the monthly oxide removal along three wetland plots with different variations in water table. Preferential dissolution of the Mn oxide coating exceeded the Fe oxide removal by two to five times that is coherent with the thermodynamic stability of the minerals. Enhanced removal of Mn oxide coatings in the capillary fringe compared to minor depletion of Fe oxides enables to differentiate weakly (300 to 100 mV, range of MnIII,IV reduction) and moderately (100 to −100 mV, range of FeIII reduction) reducing conditions. Processes that occur under weakly reducing soil conditions, e.g. denitrification and trace metal mobilization associated with the reductive dissolution of Mn oxides, can be identified when Mn oxide removal along redox bars occurs but the Fe oxide coating remains stable. Simultaneous use of Mn and Fe redox bars results in a better temporal and spatial characterization of the soil redox status.

Linking dissolved organic carbon cycling to organic carbon fluxes in rice paddies under different water management practices

Although paddy soils are generally characterized by relatively high dissolved organic carbon (DOC) concentrations and fluxes, little is yet known on how water management influences the cycling of this important organic C pool. This work aims at providing insights into the link between DOC cycling during rice cropping and organic C input to the subsoils and export with surface waters, as well as methane (CH4) emissions in a temperate paddy soil as a function of different water management practices. DOC quantity, quality and fluxes, as well as CH4 emissions were evaluated at field-scale over two cropping seasons for three water management systems including continuous flooding, dry seeding with delayed flooding, and intermittent irrigation. DOC cycling in the different water management systems were strongly linked to the reducing soil conditions resulting from field flooding. In contrast to dry seeding or intermittent irrigation, adoption of continuous flooding not only favoured the accumulation of DOC in the topsoil (>10–20 mg C l−1), but also enhanced C inputs to the subsoil (33–51 g C m−2), and exports with surface waters (18–44 g C m−2). Moreover, changes in DOC quality in paddy soils were linked to a positive feedback on the abiotic release of soil-derived DOC, and substrate availability for CH4 production. Water management practices in rice paddies strongly affect the temporal trends in DOC quantity and quality over the cropping season, with important implications on organic C fluxes.

Effect of the number of tillages in fallow season and fertilizer type on greenhouse gas emission from a rice (Oryza sativa L.) paddy field in Ehime, southwestern Japan

ABSTRACTAgricultural fields, including rice (Oryza sativa L.) paddy fields, constitute one of the major sources of atmospheric methane (CH4) and nitrous oxide (N2O). Organic matter application, such as straw and organic fertilizer, enhances CH4 emission from paddy fields. In addition, rice straw management after harvest regulates CH4 emissions in the growing season. The interaction of tillage times and organic fertilizer application on CH4 and N2O emissions is largely unknown. Therefore, we studied the effects of fallow-season tillage times and fertilizer types on CH4 and N2O emissions in paddy fields in Ehime, southwestern Japan. From November 2011 to October 2013, four treatments, two (autumn and spring) or one (spring) in the first year, or two (autumn and spring) or three (autumn, winter, and spring) in the second year times of tillage with chemical or organic fertilizer application, were established. Gas fluxes were measured by the closed-chamber method. Increasing the number of tillage times from one to two decreased succeeding CH4 emission and the emission factor for CH4 (EFCH4) in the rice-growing season, suggesting that the substrate for CH4 production was reduced by autumn and spring tillage in the fallow season. Higher EFCH4 [1.8–2.0 kg carbon (C) ha−1 d−1] was observed when more straw was applied (6.9–7.2 Mg ha−1) in the second year. Organic fertilizer application induced higher CH4 emission just after the application as basal and supplemental fertilizers, especially at a lower straw application rate. This indicated that EFCH4 in the organically managed fields should be determined individually. Organic fertilizer application with two tillage times induced N2O efflux during the rice-growing season in the second year, but N2O emissions were not affected by winter tillage. Although paddy fields can act as an N2O sink because of reduced soil conditions when straw application was high, application of organic C and nitrogen as fertilizer can enhance N2O production by the denitrification process during the growing season, especially in the ripening stage when soil anaerobic conditions became moderate. These results suggest that negative emission factors for N2O (EFN2O) can be applied, and EFN2O of organic fertilizer should be considered during the estimation of N2O emission in the paddy field.

Response of Schoenoplectus acutus and Schoenoplectus californicus at Different Life-History Stages to Hydrologic Regime

For wetland restoration success to be maximized, restoration managers need better information regarding how the frequency, depth, and duration of flooding affect soil chemistry and the survival, growth, and morphology of targeted plant species. In a greenhouse study we investigated the impact of four different flooding durations (0 %, 40 %, 60 %, and 100 %) on soil physicochemistry and the responses of seedlings and adults of two species of emergent wetland macrophytes commonly used in restoration efforts (Schoenoplectus acutus and Schoenoplectus californicus). The longest flooding duration, which created more reducing soil conditions, resulted in significantly reduced survival of S. acutus adults (34 ± 21 % survival) and complete mortality of seedlings of both species. Schoenoplectus californicus adults exhibited higher flooding tolerance, showing little impact of flooding on morphology and physiology. A companion field study indicated that S. californicus maintained stem strength regardless of flooding duration or depth, supporting the greenhouse study results. This information serves to improve our understanding of the ecological differences between these species as well as provide restoration managers with better guidelines for targeted elevation and hydrologic regimes for these species in order to enhance the success of restoration plantings and better predict restoration site development.

Nitrous oxide emissions during biological soil disinfestation with different organic matter and plastic mulch films in laboratory-scale tests

Nitrous oxide (N2O), which is a greenhouse gas, may be more emitted as an intermediate product of denitrification during biological soil disinfestation. The biological soil disinfestation is a method to suppress soil-borne pathogens under reductive soil conditions produced by the application of organic matter and water irrigation with plastic film. The objective of the study was to determine the effects of different organic matter and mulch films on N2O emissions during biological soil disinfestation. Grey lowland soil amended with cattle compost plus rice bran (0.2%), rice husk (0.2%) or dent corn (0.1%, 0.2% and 0.4%) was incubated at 100% water-holding capacity with or without plastic films made of polyvinyl chloride (PVC) and triple-layer polyolefin (3PO) for 72 h at 50°C. Permeation of the two films was also measured at 25°C and 50°C. Results showed that incorporation of organic matter increased N2O emissions compared with no organic matter addition at 50°C. Incorporation of rice bran and dent corn with easily decomposable C and low C:N ratios increased N2O emissions for the first 12 h, but thereafter, available C supply from these amendments suppressed N2O emissions. Permeability of mulch films increased at a higher temperature and was larger for PVC than for 3PO. Our study indicated that rice husk should not be used for soil disinfestation and that application rates of organic matter must be determined based on their decomposability. Moreover, mulch film covering would not suppress N2O emission in biological soil disinfestation because of high temperature.

Flooding tolerance in maize (Zea mays subsp. mays) F1 hybrids containing a QTL introgressed from teosinte (Zea nicaraguensis)

Worldwide climate change has increased the risk of crop yield losses caused by flooding. Here, we report the development of maize F1 hybrids containing a teosinte QTL for flooding tolerance on chromosome 4 and the evaluation of flooding tolerance under reducing soil conditions. We used F1 hybrid Mi29 × Mi47 (cultivar Yumechikara) and two versions of Yumechikara into which the QTL has been introgressed, Mi47 × IL#18 (heterozygous for the QTL) and IL#18 × BC3#90 (homozygous for the QTL). Flooding tolerance was evaluated at three treatment levels (i.e., soluble starch at 1, 0.5 or 0 g L−1) and the non-flooded control at an early growth stage (2.6- to 3.0-leaf stage) and at the 5.5-leaf stage. Tolerance was assessed by measuring leaf injury, leaf SPAD values, and shoot and root dry weight ratios (treatment/control). The F1 hybrids containing the QTL were significantly more tolerant (as evaluated by leaf injury and SPAD values) than the original F1 cultivar (Mi29 × Mi47) at both growth stages. When flooding tolerance was evaluated by shoot dry weight ratio at an early growth stage, IL#18 × BC3#90 was significantly more tolerant than Mi29 × Mi47 at the 1 and 0 g L−1 treatment levels. At the 5.5-leaf stage, there were no significant differences among the three F1 hybrids under the three treatment levels. Although plants at an early growth stage are generally more sensitive to flooding than at later stages, IL#18 × BC3#90 should overcome flooding stress at the sensitive early stage of growth.

Manganese-oxide-coated redox bars as an indicator of reducing conditions in soils.

Identification of reducing conditions in soils is of concern not only for pedogenesis but also for nutrient and pollutant dynamics. We manufactured manganese (Mn)-oxide-coated polyvinyl chloride bars and proved their suitability for the identification of reducing soil conditions. Birnessite was synthesized and coated onto white polyvinyl chloride bars. The dark brown coatings were homogenous and durable. As revealed by microcosm devices with adjusted redox potentials (E), under oxidizing conditions (E ∼450 mV at pH 7) there was no Mn-oxide removal. Reductive dissolution of Mn-oxides, which is expressed by the removal of the coatings, started under weakly reducing conditions (E ∼175 mV) and was more intensive under moderately reducing conditions (∼80 mV). According to thermodynamics, the removal of Mn-oxide coatings (225 mm d) exceeded the removal of iron (Fe)-oxide coatings (118 mm d) in soil column experiments. This was confirmed in a soil with a shallow and strongly fluctuating water table where both types of redox bars were inserted. Consequently, it was possible to identify reducing conditions in soils using Mn-oxide-coated bars. We recommend this methodology for short-term monitoring because tri- and tetravalent Mn is the preferred electron acceptor compared with trivalent Fe, and this additionally offers the possibility of distinguishing between weakly and moderately reducing conditions. If dissolved Fe is abundant in soils, the possibility of nonenzymatic reduction of Mn has to be taken into account.

Trace Element Solubility in a Multimetal-Contaminated Soil as Affected by Redox Conditions

Redox conditions play an outstanding role in controlling the behaviour of trace elements in soil environments. They are not only sensitive to water saturation but also to soil temperature because many redox reactions are mediated by microorganisms. In this study, we investigated the influence of oxidising (oxygen predominant), weakly reducing (MnIII,IV reduction) and moderately reducing (FeIII reduction) conditions at three temperature regimes (7, 15 and 25 °C) on the solubility of ten trace elements. Multimetal-contaminated topsoil (pH 5.8) from a floodplain in Germany was investigated with the following aqua regia-soluble concentrations: Zn 903, Cu 551, Cr 488, Pb 354, Ni 93.5, As 35.7, Co 22.4, Sb 20.5, Cd 8.3 and Mo 6.5 mg kg−1. Soil suspensions were held at fixed redox potential in microcosm experiments, sampled at every third day and analysed for trace elements. Time to achieve weakly and particularly moderately reducing conditions was temperature dependent and increased in the order 25 °C < 15 °C < 7 °C. Under oxidising conditions, the solubility of the trace elements was low. Reductive dissolution of Mn oxides under weakly reducing conditions was accompanied by a release of Co and Mo. Reductive dissolution of Fe oxides (and of remaining Mn oxides) under moderately reducing conditions additionally led to a release of As, Cd, Cr, Ni and Pb, whereas Cu and Zn were hardly affected. Antimony revealed a different behaviour because, after a first increase, a continuous decrease in its concentration was observed soon after the onset of weakly reducing conditions. We conclude that soil temperature should be considered as a master variable, to distinguish between weakly and moderately reducing soil conditions, and that it is necessary to keep element-specific behaviour in mind when dealing with the effects of redox conditions in soils on trace element solubility.

Reduction of metal leaching by poplars during soil treatment of wastewaters: Small-scale proof of concept studies

Land application of food processing wastewaters, a common practice, can create continuously saturated and reducing soil conditions that potentially mobilize native soil metals such as arsenic, manganese, and iron, contributing to contamination of groundwater. Small-scale column studies were used to evaluate the potential of poplar trees to decrease groundwater contamination from land application of wastewaters. Research assessed growth of poplar trees during land application of food processing wastewater, the evapotranspiration by poplar trees under such conditions, and treatment of chemical oxygen demand (COD), nitrate, iron, and manganese in columns with and without poplar trees for four months. In addition, plant tissues and soil were analyzed for metals, macronutrients, and micronutrients at the conclusion of the experiment. Poplar growth, as measured by shoot height, shoot mass, number of leaves, number of shoots, mass of leaves, and root length, was not affected by application of fruit and vegetable processing wastewater at the rate of 1–2 times the highest reported application rate in Michigan. However, significantly less root mass and fewer root branches were observed in columns receiving wastewater at the end of the experiment. Poplar trees withstood continuous saturation of soils and evapotranspired significantly more water than no plant controls, with an average evapotranspiration coefficient of 3.25. Mass removal rate of chemical oxygen demand (COD) was significantly higher in columns with poplar trees than in soil-only columns. Additionally, leaching of nitrate and iron was lower in columns with poplar trees than in soil only columns. Poplars accumulated arsenic, manganese and iron, and translocated these metals into above-ground tissues. Therefore, poplar trees demonstrated the ability to decrease saturation, potentially modify redox conditions, and uptake metals—resulting in decreased leaching of COD, nitrate, iron, and manganese during land application of food processing wastewaters.

Readily available phosphorous and nitrogen counteract for arsenic uptake and distribution in wheat (Triticum aestivum L.).

Elevated arsenic content in food crops pose a serious human health risk. Apart from rice wheat being another main food crop is possibly cultivated on contaminated sites. But for wheat uptake mechanisms are not entirely understood especially with regard to nutrient fertilization and different moisture regimes taking into account heavy rainfall events due to climate change. Here we show that especially higher P-fertilization under changing redox conditions may enhance arsenic uptake. This counteracts with higher N-fertilization reducing arsenic transfer and translocation into aboveground plant parts for both higher P-fertilization and reducing soil conditions. Arsenic speciation did not change in grain but for leaves P-fertilization together with reducing conditions increased the As(V) content compared to other arsenic species. Our results indicate important dependencies of nutrient fertilization, moisture conditions and substrate type on As accumulation of wheat as one of the most important crop plants worldwide with implications for agricultural practices.

Flooding Effect on the Distribution of Native Austral Cordgrass Spartina densiflora in Patagonian Salt Marshes

Idaszkin, Y.L.; Bortolus, A., and Bouza, P.J., 2014. Flooding effect on the distribution of native austral cordgrass Spartina densiflora in Patagonian salt marshes. Plant zonation is one of the most conspicuous ecological features of salt marshes worldwide. In Patagonian salt marshes the cordgrass Spartina alterniflora forms dense monospecific stands along the lowest marsh level, while the higher levels are dominated by Spartina densiflora or Sarcocornia perennis. In this study, we coupled field transplants combined with neighbor exclusion treatments and greenhouse experiments to evaluate the effect of submersion and waterlogged anoxic soil in the determination of the lower distribution limit of S. densiflora in Central Patagonian salt marshes within its native range. In the field experiment, no S. densiflora survived the frequent tidal submersion by approximately 2 m of seawater in the low marsh, independent of the S. alterniflora neighbor's presence, while in the greenhouse experiment, all plants were able to tolerate strongly reducing soil conditions. Our results suggest that the absence of S. densiflora in the low marsh level is a consequence of the effect of the submersion, independent of the presence of S. alterniflora neighbors and of the strong soil anoxia. Our results contribute to optimize the efforts addressed to control or eradicate this exotic species in salt marshes where it is invading.