Autumn migration of the migrant hawker (Aeshna mixta) at the Baltic coast.

BACKGROUND: Migratory insects are important for the provision of ecosystem services both at the origin and destination sites but - apart from some iconic species - the migration routes of many insect species have not been assessed. Coastlines serve as a funnel where migrating animals including insects accumulate. Migratory behaviour and captures of dragonflies in bird traps suggest autumn migration of dragonflies along coastlines while the origin and regularity of this migration remain unclear. METHODS: Dragonfly species were caught at the bird observatory Kabli at the Baltic coast in Estonia in 2009, 2010 and 2015. For the 2015 data set, we used a stable hydrogen (H) approach to trace the potential natal origin of the migrant hawker (Aeshna mixta). RESULTS: 1079 (2009), 701 (2010) and 88 (2015) A. mixta individuals were caught during the study periods (35, 37 and 11 days in 2009, 2010 and 2015, respectively). The migration period lasted from end of August to end of September. Based on the results from our stable isotope analysis, we identified two populations of A. mixta: One (range of isotope signatures of non-exchangeable H [δ2Hn wing]: -78‰ to -112‰) had a local likely origin while the other (δ2Hn wing: -113‰ to -147‰) migrated from northerly directions even in headwind from the South. The former showed an even sex ratio whereas the actively migrating population was dominated by males. CONCLUSIONS: Our results suggest a regular southbound autumn migration of A. mixta along the Baltic coast. However, nearly half of the sampled individuals originated from the surroundings suggesting either no, partial or "leap-frog" migration. Contrary to our expectation, A. mixta did not select favourable wind conditions but continued the southbound autumn migration in the flight boundary layer even in case of headwinds. The dominance of males might indicate migration as a result of competition for resources. Further repeated, large-scale studies along the Baltic coast are necessary to pinpoint the migratory pattern and the reason for migration of A. mixta. Such studies should also comprise locations north of the known species range of A. mixta because of the rapid climate-change induced range expansion.

Impact of abiotic and biogeochemical processes on halogen concentrations (Cl, Br, F, I) in mineral soil along a climatic gradient.

In contrast to earlier ideas that halogens behave inertly in soil, extensive biogeochemical cycling of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) has been shown for temperate forests. To further advance our understanding of halogen behaviour in soil beyond humid temperate forests, we sampled soil profiles in protected areas along the Chilean Coastal Cordillera, representing a pronounced climatic gradient spanning from arid to humid. Halogen concentrations in soil were analysed by combustion ion chromatography. Highest average total halogen concentrations occurred at the arid site (Cl, F: 4270 and 897 mg kg-1) as well as the humid end of the climatic gradient (Br, I: 42.6 and 9.8 mg kg-1). Vertical distribution patterns of halogens were most pronounced at the humid end of the gradient and became less distinct under drier climate. The climatic gradient demonstrates the important role of biotic processes (e.g. the halogenation of organic matter) on the retention of halogens in the soil. However, this climate-specific role may be overridden by mainly abiotic processes within a given climate zone (e.g. weathering, leaching, sorption to secondary soil minerals, evaporative enrichment), resulting in vertical relocation of halogens in the soil. Since some of these processes oppose each other, complex interactions and depth distributions of F, Cl, Br and I occur in the soil. In summary, our findings provide new insights into the fate of halogens in mineral soil of different climatic zones, which is important, for example, when radiohalogens are deposited on a large scale after nuclear accidents.

Phosphate addition enhances alkaline extraction of glyphosate from highly sorptive soils and aquatic sediments.

BACKGROUND: Analytical constraints complicate environmental monitoring campaigns of the herbicide glyphosate and its major degradation product aminomethylphosphonic acid (AMPA): their strong sorption to soil minerals requires harsh extraction conditions. Coextracted matrix compounds impair downstream analysis and must be removed before analysis. RESULTS: A new extraction method combined with subsequent capillary electrophoresis-mass spectrometry for derivatization-free analysis of glyphosate and AMPA in soil and sediment was developed and applied to a suite of environmental samples. It was compared to three extraction methods from literature. We show that no extraction medium reaches 100% recovery. The new phosphate-supported alkaline extraction method revealed (1) high recoveries of 70-90% for soils and aquatic sediments, (2) limits of detections below 20 µg kg-1 , and (3) a high robustness, because impairing matrix components (trivalent cations and humic acids) were precipitated prior to the analysis. Soil and sediment samples collected around Tübingen, Germany, revealed maximum glyphosate and AMPA residues of 80 and 2100 µg kg-1 , respectively, with residues observed along a core of lake sediments. Glyphosate and/or AMPA were found in 40% of arable soils and 57% of aquatic sediment samples. CONCLUSION: In this work, we discuss soil parameters that influence (de)sorption and thus extraction. From our results we conclude that residues of glyphosate in environmental samples are easily underestimated. With its possible high throughput, the method presented here can resolve current limitations in monitoring campaigns of glyphosate by addressing soil and aquatic sediment samples with critical sorption characteristics.

Spatial variation in dissolved phosphorus and interactions with arsenic in response to changing redox conditions in floodplain aquifers of the Hetao Basin, Inner Mongolia.

Increasing numbers of studies have reported groundwater with naturally high phosphorous (P) and arsenic (As) concentrations, which can potentially threaten the environment and human health. However, the cycling of P and its interactions with As in groundwater under changing redox conditions remain largely unknown. In this study, 83 groundwater samples and 14 sediment samples were collected from the Hetao Basin, Inner Mongolia, for systematic hydrogeochemical investigation and complementary geochemical evaluation. The results showed that P cycling in floodplain aquifers was tightly constrained by redox conditions. Under oxic/suboxic conditions, mineralization of organic matter and weathering of P-bearing minerals were the two dominant processes that mobilized considerable amounts of P in groundwater. When redox conditions became reducing, Fe(III)-oxide reduction dominated, resulting in enrichment of both P and As in groundwater. In Fe(III)-reducing conditions, secondary Ca/Fe(II)-minerals might serve as an important sink for P. When redox conditions became SO42--reducing, preferential adsorption and incorporation of P over As on Fe(II)-sulfides might constrain the As immobilization pathway, resulting in immediate retardation of P and hysteretic immobilization of As. This P-immobilization pathway in natural aquifers has not been described before. This study provides novel insights into P cycling and As enrichment in groundwater systems. Understanding the roles of Fe(II)- and S(-II)-minerals in the immobilization of and interaction between P and As in response to SO42- reduction may help to inspire effective in-situ remediation of contaminated groundwater, in which P and As coexist and remain mobile for decades or longer.

Metagenomic Sequencing of Multiple Soil Horizons and Sites in Close Vicinity Revealed Novel Secondary Metabolite Diversity.

Discovery of novel antibiotics is crucial for combating rapidly spreading antimicrobial resistance and new infectious diseases. Most of the clinically used antibiotics are natural products-secondary metabolites produced by soil microbes that can be cultured in the lab. Rediscovery of these secondary metabolites during discovery expeditions costs both time and resources. Metagenomics approaches can overcome this challenge by capturing both culturable and unculturable hidden microbial diversity. To be effective, such an approach should address questions like the following. Which sequencing method is better at capturing the microbial diversity and biosynthesis potential? What part of the soil should be sampled? Can patterns and correlations from such big-data explorations guide future novel natural product discovery surveys? Here, we address these questions by a paired amplicon and shotgun metagenomic sequencing survey of samples from soil horizons of multiple forest sites very close to each other. Metagenome mining identified numerous novel biosynthetic gene clusters (BGCs) and enzymatic domain sequences. Hybrid assembly of both long reads and short reads improved the metagenomic assembly and resulted in better BGC annotations. A higher percentage of novel domains was recovered from shotgun metagenome data sets than from amplicon data sets. Overall, in addition to revealing the biosynthetic potential of soil microbes, our results suggest the importance of sampling not only different soils but also their horizons to capture microbial and biosynthetic diversity and highlight the merits of metagenome sequencing methods. IMPORTANCE This study helped uncover the biosynthesis potential of forest soils via exploration of shotgun metagenome and amplicon sequencing methods and showed that both methods are needed to expose the full microbial diversity in soil. Based on our metagenome mining results, we suggest revising the historical strategy of sampling soils from far-flung places, as we found a significant number of novel and diverse BGCs and domains even in different soils that are very close to each other. Furthermore, sampling of different soil horizons can reveal the additional diversity that often remains hidden and is mainly caused by differences in environmental key parameters such as soil pH and nutrient content. This paired metagenomic survey identified diversity patterns and correlations, a step toward developing a rational approach for future natural product discovery surveys.

Phosphate immobilisation dynamics and interaction with arsenic sorption at redox transition zones in floodplain aquifers: Insights from the Red River Delta, Vietnam.

Although phosphate (PO43-) may play a decisive role in enriching toxic arsenic (As) in the groundwater of many Asian deltas, knowledge gaps exist regarding its interactions with As. This study investigates the simultaneous immobilisation of PO43- and As in aquifer sediments at a redox transition zone in the Red River Delta of Vietnam. The majority of PO43- and As was found to be structurally bound in layers of Fe(III)-(oxyhydr)oxide precipitates, indicating that their formation represents a dominant immobilisation mechanism. This immobilisation was also closely linked to sorption. In the surface sorbed sediment pools, the molar ratios of total P to As were one order of magnitude higher than found in groundwater, reflecting a preferential sorption of PO43- over As. However, this competitive sorption was largely dependent on the presence of Fe(III)-(oxyhydr)oxides. Ongoing contact of the aquifer sediments with iron-reducing groundwater resulted in the reductive dissolution of weakly crystalline Fe(III)-(oxyhydr)oxides, which was accompanied by decreased competition for sorption sites between PO43- and As. Our results emphasise that, to be successful in the medium and long term, remediation approaches and management strategies need to consider competitive sorption between PO43- and As and dynamics of the biogeochemical Fe-cycle.

Vegetation canopy effects on total and dissolved Cl, Br, F and I concentrations in soil and their fate along the hydrological flow path.

Although halogens are omnipresent in the environment, detailed understanding of processes involving chlorine (Cl), bromine (Br), fluorine (F) and iodine (I) in the terrestrial halogen cycle is still sparse. Our objectives were to (i) assess vertical depth profiles of total and water-extractable inorganic halogen concentrations (Cltot, Brtot, Ftot, Itot) in solid soil, (ii) test the effect of a tree canopy, and (iii) follow the fate of dissolved inorganic halogens along the hydrological flow path. More than 200 soil samples and ecosystem solutions (rainwater, soil solution, adit and creek water) collected in the Schwarzwald, SW Germany, were analyzed by combustion ion chromatography and ion chromatography for total and inorganic halogen concentrations. We found decreasing Cltot concentrations with increasing soil depth which were indicative of biological chlorination of organic matter and nutrient uplift, both associated with Cl accumulation in upper soil horizons. Vertical patterns of total Br, F and I were contrary to Cltot concentrations and were related significantly (positively) to pedogenic oxides, revealing their dependence on abiotic processes. The presence of a canopy at our study site resulted in significantly higher halogen concentrations in throughfall compared to rainfall and higher Brtot concentrations in the organic layer. We attribute this difference to leaching from leaves and needles and wash-off of dry deposition. There were hardly any differences in halogen concentrations along the hydrological flow path except for significantly higher inorganic I concentrations in soil solution compared to rainfall due to equilibrium reactions between the soil solution and the solid soil phase. Highest inorganic F concentrations of up to 0.2 mg L-1 were detected in creek water samples and may originate from the weathering of fluorite-bearing veins. Our study indicates halogen-specific processes underlying Cl, Br, I and F cycling in ecosystems.

Phosphorus Pool Composition in Soils and Sediments of Transitional Ecotones under the Influence of Agriculture.

Transitional ecotones such as vegetated buffer strips, stream banks, and streambeds retain phosphorus (P) in the immediate surroundings of farmland. Yet the fate of P in these ecotones remains unclear. Our objectives were to (i) test the difference in the P pool composition of soil and sediment between sites surrounded by agriculture and forestry and (ii) test whether specific P pools differ among transitional ecotones. Phosphorus pools (by a modified Hedley fractionation scheme) and the degree of P saturation (DPS) were determined in 33 soil and sediment samples from eight farmland and three forest sites. At farmland sites, total P in soil and sediment was more than twofold higher as compared to forestry sites. The proportion of labile inorganic P (Pi) and the DPS were significantly larger in transitional ecotones close to farmland. We further used normalized values for comparing the respective ecotones at the sites. The deviation of each transitional ecotone relative to the respective site average revealed that the normalized total P concentration and proportions of labile and moderately labile Pi were significantly smaller in bed sediment adjacent to farmland as compared to respective stream bank and buffer strip soil, whereas the stable Ca-Pi proportion was larger. The results reflected a decreased Pi sorption capacity in combination with Pi desorption and transfer of Pi into secondary Ca-Pi minerals in bed sediment. In summary, the influence of agriculture increases labile P pools in soil and sediment, which are then subject to a succession of dynamic processes resulting in a partial loss of Pi to the aqueous phase as well as fixation of Pi in the Ca-Pi pool.

Insights into arsenic retention dynamics of Pleistocene aquifer sediments by in situ sorption experiments.

The migration of arsenic (As) enriched groundwater into Pleistocene aquifers as a consequence of extensive groundwater abstraction represents an increasing threat to the precious water resources in Asian delta regions. Pleistocene aquifer sediments are typically rich in FeIII-(hydr)oxides and are capable to adsorb high amounts of As. This results in a pronounced accumulation of As in Pleistocene aquifers, where high As groundwater infiltrates from adjacent Holocene aquifers. However, As retention by Pleistocene aquifers over long-term time scales remains largely unknown. We studied As sorption in situ by placing natural Pleistocene sediments and pure mineral phases directly inside groundwater monitoring wells at a study site near Hanoi (Vietnam). This in situ exposure allows for constant flushing of the samples with unaltered groundwater and the establishment of undisturbed sorption equilibria similar to those in local aquifer sediments, which is not readily attainable in traditional laboratory sorption experiments. The groundwaters in our experimental wells were characterized by different As concentrations (0.01-6.63 µmol/L) and redox states, reaching from suboxic to anoxic conditions (Eh of +159 to -4 mV). Results show that adsorption is the dominant As retention mechanism, independent from the respective groundwater chemistry (i.e. concentrations of dissolved P, HCO3- and Si). Whilst most of the As sorbed within the first week, sorption further increased slowly but consistently by 6-189%, respectively, within six months. Hence, the As sorption behavior of Pleistocene aquifer sediments should be determined over longer periods to avoid an underestimation of the As sorption capacity. Accompanying desorption experiments revealed that about 51% of the sorbed As was remobilized within six months when exposed to low As groundwater. We therefore conclude that a considerable proportion of the As accumulated in the aquifer sediments is prone to remobilization once the As concentrations in migrating groundwater decline. Remobilization of As should be considered in local water management plans to avoid contamination of precious groundwater resources with this As legacy.

Biogeochemical phosphorus cycling in groundwater ecosystems - Insights from South and Southeast Asian floodplain and delta aquifers.

The biogeochemical cycling of phosphorus (P) in South and Southeast Asian floodplain and delta aquifers has received insufficient attention in research studies, even though dissolved orthophosphate (PO43-) in this region is closely linked with the widespread contamination of groundwater with toxic arsenic (As). The overarching aim of this study was to characterize the enrichment of P in anoxic groundwater and to provide insight into the biogeochemical mechanisms underlying its mobilization, subsurface transport, and microbial cycling. Detailed groundwater analyses and in situ experiments were conducted that focused on three representative field sites located in the Red River Delta (RRD) of Vietnam and the Bengal Delta Plain (BDP) in West Bengal, India. The results showed that the total concentrations of dissolved P (TDP) ranged from 0.03 to 1.50 mg L-1 in groundwater, with PO43- being the dominant P species. The highest concentrations occurred in anoxic sandy Holocene aquifers where PO43- was released into groundwater through the microbial degradation of organic carbon and the concomitant reductive dissolution of Fe(III)-(hydr)oxides. The mobilization of PO43- may still constitute an active process within shallow Holocene sediments. Furthermore, a sudden supply of organic carbon may rapidly decrease the redox potential, which causes an increase in TDP concentrations in groundwater, as demonstrated by a field experiment. Considering the subsurface transport of PO43-, Pleistocene aquifer sediments represented effective sinks; however, the enduring contact between oxic Pleistocene sediments and anoxic groundwater also changed the sediments PO43--sorption capacity over time. A stable isotope analysis of PO43--bound oxygen indicated the influences of intracellular microbial cycling as well as a specific PO43- source with a distinct isotopically heavy signal. Consequently, porous aquifers in Asian floodplain and delta regions proved to be ideal natural laboratories to study the biogeochemical cycling of P and its behavior in groundwater environments.

Quantifying Reactive Transport Processes Governing Arsenic Mobility after Injection of Reactive Organic Carbon into a Bengal Delta Aquifer.

Over the last few decades, significant progress has been made to characterize the extent, severity, and underlying geochemical processes of groundwater arsenic (As) pollution in S/SE Asia. However, comparably little effort has been made to merge the findings into frameworks that allow for a process-based quantitative analysis of observed As behavior and for predictions of its long-term fate. This study developed field-scale numerical modeling approaches to represent the hydrochemical processes associated with an in situ field injection of reactive organic carbon, including the reductive dissolution and transformation of ferric iron (Fe) oxides and the concomitant release of sorbed As. We employed data from a sucrose injection experiment in the Bengal Delta Plain to guide our model development and to constrain the model parametrization. Our modeling results illustrate that the temporary pH decrease associated with the sucrose transformation and mineralization caused pronounced, temporary shifts in the As partitioning between aqueous and sorbed phases. The results also suggest that while the reductive dissolution of Fe(III) oxides reduced the number of sorption sites, a significant fraction of the released As was rapidly scavenged through coprecipitation with neo-formed magnetite. These secondary reactions can explain the disparity between the observed Fe and As behavior.

Role of competing ions in the mobilization of arsenic in groundwater of Bengal Basin: insight from surface complexation modeling.

This study assesses the role of competing ions in the mobilization of arsenic (As) by surface complexation modeling of the temporal variability of As in groundwater. The potential use of two different surface complexation models (SCMs), developed for ferrihydrite and goethite, has been explored to account for the temporal variation of As(III) and As(V) concentration, monitored in shallow groundwater of Bengal Basin over a period of 20 months. The SCM for ferrihydrite appears as the better predictor of the observed variation in both As(III) and As(V) concentrations in the study sites. It is estimated that among the competing ions, PO4(3-) is the major competitor of As(III) and As(V) adsorption onto Fe oxyhydroxide, and the competition ability decreases in the order PO4(3-) â‰« Fe(II) > H4SiO4 = HCO3(-). It is further revealed that a small change in pH can also have a significant effect on the mobility of As(III) and As(V) in the aquifers. A decrease in pH increases the concentration of As(III), whereas it decreases the As(V) concentration and vice versa. The present study suggests that the reductive dissolution of Fe oxyhydroxide alone cannot explain the observed high As concentration in groundwater of the Bengal Basin. This study supports the view that the reductive dissolution of Fe oxyhydroxide followed by competitive sorption reactions with the aquifer sediment is the processes responsible for As enrichment in groundwater.

Effect of carbon sources and of sulfate on microbial arsenic mobilization in sediments of West Bengal, India.

Arsenic (As) dissolution from sediments into groundwater in the Bengal Delta/West India was investigated. Two experimental sites were choosen with contrasting As concentrations in shallow groundwater. Apparently patches of high-As and low-As sediments occured in close neigbourhood. A fast As mobilization with lactate or ethanol as carbon sources and sulfate as an electron acceptor and a possible influence of indigenous flora because of higher As amounts and an increasing total cell count was observed over a peroid of 110 days. Sucrose was a less suitable carbon source. Inoculation of an arsenate-reducing Pseudomonas putida WB, that was isolated from the sediments did not improve arsenic mobilization. Maximal arsenic concentrations up to 160µg/l were leached out from sediment columns with lactate or ethanol+sulfate in the water at natural groundwater flow, but the majority of the As remained in the sandy sediments. Some correlation of arsenic with Fe, but not with Mn dissolution seems to exist.

Influences of groundwater extraction on the distribution of dissolved As in shallow aquifers of West Bengal, India.

Here we report temporal changes of As concentrations in shallow groundwater of the Bengal Delta Plain (BDP). Observed fluctuations are primarily induced by seasonally occurring groundwater movement, but can also be connected to anthropogenic groundwater extraction. Between December 2009 and July 2010, pronounced variations in the groundwater hydrochemistry were recorded in groundwater samples of a shallow monitoring well tapping the aquifer in 22-25 m depth, where Astot concentrations increased within weeks from 100 to 315 µg L(-1). These trends are attributed to a vertically shift of the hydrochemically stratified water column at the beginning of the monsoon season. This naturally occurring effect can be additionally superimposed by groundwater extraction, as demonstrated on a local scale by an in situ experiment simulating extensive groundwater withdrawal during the dry post-monsoon season. Results of this experiment suggest that groundwater extraction promoted an enduring change within the distribution of dissolved As in the local aquifer. Presented outcomes contribute to the discussion of anthropogenic pumping influences that endanger the limited and yet arsenic-free groundwater resources of the BDP.