Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Abundance, Activity and Community Structure of Denitrifiers in Drainage Ditches in Relation to Sediment Characteristics, Vegetation and Land-Use
    Veraart, Annelies J. ; Rocha Dimitrov, Mauricio ; Schrier-Uijl, Arina P. ; Smidt, Hauke ; Klein, Jeroen J.M. de - \ 2017
    Ecosystems 20 (2017)5. - ISSN 1432-9840 - p. 928 - 943.
    agroecosystem - denitrification - DGGE - ecosystem functioning - macrophytes - nitrogen - qPCR - wetlands
    Drainage ditches are ubiquitous yet understudied features of the agricultural landscape. Nitrogen pollution disrupts the nutrient balance of drainage ditch ecosystems, as well as the waterbodies in which they drain. Denitrification can help ameliorate the impact of N-fertilization by converting reactive nitrogen into dinitrogen gas. However, factors affecting denitrification in drainage ditches are still poorly understood. In this study, we tested how within-ditch and regional environmental conditions affect denitrifier activity, abundance, and community structure, to understand controls on denitrification at multiple scales. To this end, we quantified in situ denitrification rates and denitrifier abundance in 13 drainage ditches characterized by different types of sediment, vegetation and land-use. We determined how denitrification rates relate to denitrifier abundance and community structure, using the presence of nirS, nirK and nosZ genes as a proxy. Denitrification rates varied widely between the ditches, ranging from 0.006 to 24 mmol N m−2 h−1. Ditches covered by duckweed, which contained high nitrate concentrations and had fine, sandy sediments, were denitrification hotspots. We found highest rates in ditches next to arable land, followed by those in grasslands; lowest rates were observed in peatlands and nature reserves. Denitrification correlated to nitrate concentrations, but not to nirK, nirS and nosZ abundance, whereas denitrifier-gene abundance correlated to organic matter content of the sediment, but not to nitrate concentrations. Our results show a mismatch in denitrification regulators at its different organizational scales. Denitrifier abundance is mostly regulated at within-ditch scales, whereas N-loads, regulated by landscape factors, are most important determinants of instantaneous denitrification rates.
    Effects of diet composition and ultrasound treatment on particle size distribution and carbon bioavailability in feces of rainbow trout
    Meriac, A. ; Tilburg, T. van; Eding, E.H. ; Kamstra, A. ; Schrama, J.W. ; Verreth, J.A.J. - \ 2015
    Aquacultural Engineering 65 (2015). - ISSN 0144-8609 - p. 10 - 16.
    recirculating aquaculture systems - activated-sludge - anaerobic-digestion - waste-water - feed - fish - denitrification - digestibility - pretreatment - sonication
    The effect of a high and low non-starch polysaccharide diet (HNSP and LNSP diet) and ultrasound treatment on particle size distribution and carbon bioavailability in fecal waste of rainbow trout (Oncorynchus mykiss) was studied. Feces were collected from four flow-through fish tanks, two tanks fed the HNSP diet and two the LNSP diet. The collected feces were sonicated (disintegrated) in duplicate with high-intensity (0.6 W/ml), low-frequency (f = 20 Hz) ultrasound at five different energy levels (0.6 W/ml for 0, 0.25, 1, 4, and 16 min). The particle size distribution of the treated feces samples was measured by wet sieving (1000, 500, 200, 100, 63, 36, 1.2 µm screen size) and total suspended solids (TSS) measurement. Carbon bioavailability in sonicated fecal waste samples was determined with oxygen uptake rate (OUR) tests. The results showed that: (1) feces from the HNSP diet contained significant more particulate material and bigger particles; (2) carbon bioavailability was almost three times higher in untreated LNSP feces when compared with HNSP feces; (3) almost 50% of HNSP feces could have been recovered on a microscreen of 36 µm after wet sieving, whereas it was only 10% for LNSP feces; (4) the production of small particles (1.2–36 µm), which could pass a drum filter screen and potentially accumulate in RAS, was approximately 50 g/kg feed, showing no significant differences between diets; (5) sonication increased fecal dry matter below 36 µm (p = 0.015), but it had no significant effect on the median particle size; (6) sonication increased carbon bioavailability with 7–10% for the HNSP feces (p = 0.037); (7) fecal particles withstood up to 16 min sonication at an intensity of 0.6 W/ml and a frequency of 20 Hz corresponding to specific energy input of 20,000 kJ/kg DM without major changes in particle size distribution. The results of this study indicate that the applied ultrasound treatment of fecal waste is not an effective method to increase short-term carbon bioavailability.
    The molar H: Corg ratio of biochar is a key factor in mitigating N2O emissions from soil
    Cayuela, M.L. ; Jeffery, S.L. ; Zwieten, L. van - \ 2015
    Agriculture, Ecosystems and Environment 202 (2015). - ISSN 0167-8809 - p. 135 - 138.
    greenhouse-gas emissions - rice - impact - straw - co2 - carbon - china - paddy - plant - denitrification
    A previously published meta-analysis of biochar impacts on soil N2O emissions by Cayuela et al. (2014) found a “grand mean” reduction in N2O emissions of 54 ± 6% following biochar application to soil. Here we update this analysis to include 26 additional manuscripts bringing the total to 56 articles. The updated meta-analysis confirms that biochar reduces soil N2O emissions by 49 ± 5% (mean ± 95% confidence interval). Importantly, this meta-analysis has sufficient data to investigate the impact of biochar under field conditions, showing a statistically significant lower average reduction in the field (28 ± 16%) compared to controlled laboratory studies (54 ± 3%). A key finding is the importance of the molar H:Corg ratio of biochar in determining mitigation of N2O. Biochars with a molar H:Corg ratio 0.5 were less effective at 40 ± 16%. Together with previously published information, our new results suggest that a key mitigation mechanism is linked to the degree of polymerization and aromaticity of biochar.
    Effect of temperature on denitrifying methanotrophic activity of 'Candidatus Methylomirabilis oxyfera'
    Kampman, C. ; Piai, L. ; Hendrickx, T.L.G. ; Temmink, B.G. ; Zeeman, G. ; Buisman, C.J.N. - \ 2014
    Water Science and Technology 70 (2014)10. - ISSN 0273-1223 - p. 1683 - 1689.
    waterzuivering - denitrificatie - biologische behandeling - water treatment - denitrification - biological treatment - anaerobic methane oxidation - municipal waste-water - nitrogen removal - membrane bioreactor - sewage-treatment - uasb-digester - degrees-c - bacteria - enrichment - nitrite
    The activity of denitrifying methanotrophic bacteria at 11-30 degrees C was assessed in short-term experiments. The aim was to determine the feasibility of applying denitrifying methanotrophic bacteria in low-temperature anaerobic wastewater treatment. This study showed that biomass enriched at 21 degrees C had an optimum temperature of 20-25 degrees C and that activity dropped as temperature was increased to 30 degrees C. Biomass enriched at 30 degrees C had an optimum temperature of 25-30 degrees C. These results indicated that biomass from low-temperature inocula adjusted to the enrichment temperature and that low-temperature enrichment is suitable for applications in low-temperature wastewater treatment. Biomass growth at
    Determination of potential N2O-reductase activity in soil
    Qin, S.P. ; Yuan, H.J. ; Hu, C.S. ; Oenema, O. ; Zhang, Y.M. ; Li, X.X. - \ 2014
    Soil Biology and Biochemistry 70 (2014). - ISSN 0038-0717 - p. 205 - 210.
    nitrous-oxide reduction - acetylene inhibition technique - denitrifying bacteria - community composition - pseudomonas-mandelii - aquatic sediments - marine-sediments - enzyme-activity - n2o reduction - denitrification
    Determination of N2O-reductase activity in soil is important for understanding the microbial regulation of nitrous oxide (N2O) concentrations in soil. Unfortunately, there are no easily applicable and accurate methods for determining N2O-reductase activity, which frustrates the understanding of the mechanisms that control soil management effects on denitrification and N2O emissions. The objectives of the study reported here were (i) to define the optimal experimental conditions for the determination of potential N2O-reductase activity in soil, (ii) to compare the direct-N-2 method with the acetylene inhibition technique, and (iii) to investigate the effects of long-term nitrogen (N) fertilization on the potential N2O-reductase activity. Various substrate concentrations, water/soil ratios, incubation times, temperatures and pH values were tested to find the optimal conditions for the potential N2O-reductase activity in soils from two sites. Then, the potential N2O-reductase activity was determined under optimal conditions (10 g soil, 10 ml buffer solution, pH 9, 40 degrees C, 100 ppmv N2O) in soils from the long-term N fertilization experiment. There were significant differences between soils in potential N2O-reductase activity, but the optimal experimental conditions were similar. The acetylene inhibition technique underestimated N2O-reductase activity in soil relative to the direct-N-2 method, especially in the treatment where fertilizer N was withheld for 15 yrs. We recommend that the optimal experimental conditions for the determination of the potential N2O-reductase activity are established also for other soils. More studies are needed to fully understand the interactive effects of long-term N fertilization on nosZ gene expression and N2O-reductase activity in soils. (C) 2014 Elsevier Ltd. All rights reserved.
    Microbial community dynamics in a submerged fixed bed bioreactor during biological treatment of saline urban wastewater
    Cortés-Lorenzo, C. ; Sipkema, D. ; Rodríguez-Díaz, M. ; Fuentes, S. ; Juárez-Jiménez, B. ; Rodelas, B. ; Smidt, H. ; González-López, J. - \ 2014
    Ecological Engineering 71 (2014). - ISSN 0925-8574 - p. 126 - 132.
    activated-sludge - treatment plants - bacterial diversity - sewage-treatment - biofilm reactor - gradient - denitrification - sea
    The influence of salt (NaCl) on bacterial and archaeal communities in a submerged fixed bed bioreactor system for the treatment of urban wastewater was determined by DGGE and 454 pyrosequencing of PCR-amplified 16S ribosomal RNA gene fragments. Cluster analysis of DGGE fingerprints showed significant differences in the community structure dependent on the salt concentration in the influent. Proteobacteria was found to be the dominant bacterial phylum in all experiments, with a-Proteobacteria being the main order at low salinity and ¿-Proteobacteria the dominant order at high salinity. Euryarchaeota was the main archaeal phylum in all experiments, with all microorganisms corresponding to methanogenic archaea. Whereas bacterial a-diversity decreased as salinity increased, archaeal a-diversity increased with higher NaCl concentrations.
    Dietary carbohydrates and denitrification in recirculating aquaculture systems
    Meriac, A. - \ 2014
    Wageningen University. Promotor(en): Johan Verreth. - Wageningen : Wageningen University - ISBN 9789462570351 - 129
    dieren - vissen - aquacultuur - koolhydraten - denitrificatie - aquacultuur en milieu - feces - vezels - recirculatie aquacultuur systemen - animals - fishes - aquaculture - carbohydrates - denitrification - aquaculture and environment - faeces - fibres - recirculating aquaculture systems

    Due to overfishing of global fish stocks and increasing fish meal prices, plant ingredients are being increasingly used as an alternative source of protein in fish feeds. However, the inclusion of unpurified plant ingredients will also increase the content of fibers in feeds. Fibers are nearly indigestible and will therefore increase solid waste production in aquaculture. This solid waste can be used to as a carbon source for denitrification to control nitrate levels in recirculating aquaculture systems (RAS), thereby reducing both solid and dissolved waste production. Additionally, fibers can change the recovery characteristics and lower the degradability of fecal waste. Therefore, this study investigates how changes in the dietary carbohydrate composition can affect waste production, system performance and denitrification in RAS. Furthermore, ultrasound treatment (to decrease particle size in fecal waste) and enzymatic conditioning (to increase fiber degradability) were tested as possible means to increase the bioavailability of carbon in fecal waste for denitrification.

    Comparing a high fiber (HNSP) and low fiber (LNSP) diet in RAS stocked with rainbow trout confirmed that the fibers in the HNSP diet increase fecal waste production. Although the HNSP diet produced more fecal waste than the LNSP diet, both diets produced the same amount of biodegradable fecal carbon. Since feces removal was higher in RAS using the HNSP diet, the load of degradable organic matter on the biofilters was lower with the HNSP diet than with the LNSP diet. Furthermore, fecal waste produced with the HNSP diet contained larger particles than feces of the LNSP diet, which could also improve the recovery of fecal waste with microscreens. Feces produced with the HNSP diet were also less degradable than feces produced with the LNSP diet. By using fecal waste as an internal carbon source for denitrification, solid and dissolved waste emissions from RAS could be reduced by ~50% for the HNSP diet. However, only approximately half of the supplied cellulose and hemicellulose were degraded in the denitrification reactors, whereas lignin was not degraded at all. Thus, the overall degradability of organic carbon in fecal waste was limited by fibers as hemicellulose, cellulose and lignin. Ultrasound and enzymatic conditioning did not sufficiently increase the degradability of fecal waste. Nonetheless, fibers originating from unpurified plant ingredients may also have beneficial effects on RAS performance by increasing fecal recovery. A more selective choice of feed ingredients could be used to increase the recovery and degradability of fecal waste in RAS.

    Soil N mineralization in a dairy production system with grass and forage crops
    Verloop, J. ; Hilhorst, G.J. ; Oenema, J. ; Keulen, H. van; Sebek, L.B.J. ; Ittersum, M.K. van - \ 2014
    Nutrient Cycling in Agroecosystems 98 (2014)3. - ISSN 1385-1314 - p. 267 - 280.
    net nitrogen mineralization - in-situ methods - organic-matter - field measurement - incubation method - pasture soils - cover crops - rates - denitrification - netherlands
    This paper describes the dynamics of soil N mineralization in the experimental intensive dairy farming system ‘De Marke’ on a dry sandy soil in the Netherlands. We hypothesized that knowledge of the effects of crop rotation on soil N mineralization and of the spatial and temporal variability of soil N mineralization in a farming system can be used to better synchronize N application with crop N requirements, and hence to increase the recovery of applied N and to reduce N losses. Soil N mineralization was recorded continuously in the soil layer 0–0.30 m, from 1992 to 2005, using a sequential in situ coring technique on six observation plots, of which two were located in permanent grassland and four in crop rotations with a 3 year grassland phase and an arable phase of 3 or 5 years, dominated by maize. Average annual soil N mineralization was highest under permanent grassland: 381 kg ha-1 and lowest under =3rd years arable crops: 184 kg ha-1. In temporary grassland, soil N mineralization increased in the order: 1st year, 2nd year, 3rd year grassland and in arable crops after grassland mineralization decreased in the order: 1st year, 2nd year, =3rd years. Total mineral N input, i.e. the sum of N mineralization and mineral N supply to soil, exceeded crop N requirements in 1st year maize and was lower than the requirements in 1st year temporary grassland. N mineralization in winter, outside the growing season, was 77 kg ha-1 in maize and 60 kg ha-1 in grassland. This points at the importance of a suitable catch crop to reduce the susceptibility to N leaching. Temporal and spatial variability of soil N mineralization was high and could not be related to known field conditions. This limits the extent to which N fertilization can be adjusted to soil N mineralization. Variability increased with the magnitude of soil N mineralization. Hence, situations with high soil N mineralization may be associated with high risks for N losses and to reduce these risks a strong build-up of soil organic N should be avoided. This might be achieved, for instance, by fermenting slurry before application on farmland to enhance the fraction mineral N in slurry at the expense of organic N.
    Comparing the environmental impact of a nitrifiying biotrickling filter with or without denitrification for ammonia abatement at animal houses
    Vries, J.W. de; Melse, R.W. - \ 2014
    Lelystad : Wageningen UR Livestock Research (Report / Wageningen UR Livestock Research 717) - 14
    intensieve veehouderij - varkenshouderij - rundveehouderij - luchtreinigers - nitrificatie - denitrificatie - vergelijkend onderzoek - filters - ammoniakemissie - fijn stof - broeikasgassen - intensive livestock farming - pig farming - cattle husbandry - air cleaners - nitrification - denitrification - comparative research - filters - ammonia emission - particulate matter - greenhouse gases
    The aim was to assess the environmental impact of a biotrickling filter with nitrification only and with subsequent denitrification. Life cycle assessment was applied to assess greenhouse gases, nitrate, ammonia and fossil fuel depletion. The biotrickling filter with nitrification and denitrification had higher greenhouse gas emission, whereas nitrification only had higher nitrate leaching and ammonia emission from field application of discharge water
    Balancing the organic load and light supply in symbiotic microalgal–bacterial biofilm reactors treating synthetic municipal wastewater
    Boelee, N.C. ; Temmink, B.G. ; Janssen, M. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2014
    Ecological Engineering 64 (2014). - ISSN 0925-8574 - p. 213 - 221.
    afvalwaterbehandeling - biofilms - symbiose - algen - bacteriën - heterotrofe micro-organismen - fotosynthese - acetaten - stikstof - fosfor - nitrificatie - denitrificatie - biologische waterzuiveringsinstallaties - biobased economy - waste water treatment - biofilms - symbiosis - algae - bacteria - heterotrophic microorganisms - photosynthesis - acetates - nitrogen - phosphorus - nitrification - denitrification - biological water treatment plants - biobased economy - activated-sludge - nutrient removal - growth - phytoplankton - fluorescence - enhancement
    Symbiotic microalgal–bacterial biofilms can be very attractive for municipal wastewater treatment. Microalgae remove nitrogen and phosphorus and simultaneously produce the oxygen that is required for the aerobic, heterotrophic degradation of organic pollutants. For the application of these biofilms in new wastewater treatment systems, the engineering aspects need to be investigated to obtain a balanced system where no additional oxygen is required. In this study symbiotic microalgal–bacterial biofilms were grown in flow cells with ammonium and phosphate, and with acetate as biodegradable organic pollutant at a hydraulic retention time of 4.5 h. The symbiotic biofilms removed acetate from 323 mg/L to 39 mg/L without an external oxygen or carbon dioxide supply at a removal rate of 43 g COD/m2/d. Ammonium and phosphate could not be completely removed, but removal rates of 3.2 g/m2/d and 0.41 g/m2/d were obtained, respectively. Further nitrogen removal may be obtained by nitrification and denitrification as the biofilm obtained a considerable heterotrophic denitrification capacity. The symbiotic relationship between microalgae and aerobic heterotrophs was proven by subsequently removing light and acetate. In both cases this resulted in the cessation of the symbiosis and in increasing effluent concentrations of both acetate and the nutrients ammonium and phosphate. Future research should investigate the dimensioning of an up-scaled symbiotic biofilm reactor, and the possibilities to obtain additional nitrogen and phosphorus removal under day–night cycles utilizing real wastewater.
    Liebig's law of the minimum applied to a greenhouse gas: Alleviation of P-limitation reduces soil N2O emmission
    Baral, B.R. ; Kuyper, T.W. ; Groenigen, J.W. van - \ 2014
    Plant and Soil 374 (2014)1-2. - ISSN 0032-079X - p. 539 - 548.
    nitrous-oxide emission - agricultural soils - phosphorus - fertilizer - denitrification - mineralization - mycorrhizas - netherlands - grassland - release
    Emission of the greenhouse gas (GHG) nitrous oxide (N2O) are strongly affected by nitrogen (N) fertilizer application rates. However, the role of other nutrients through stoichiometric relations with N has hardly been studied. We tested whether phosphorus (P) availability affects N2O emission. We hypothesized that alleviation of plant P-limitation reduces N2O emission through lowering soil mineral N concentrations. We tested our hypothesis in a pot experiment with maize (Zea mays L.) growing on a P-limiting soil/sand mixture. Treatment factors included P and N fertilization and inoculation with Arbuscular Mycorrhizal Fungi (AMF; which can increase P uptake). Both N and P fertilization, as well as their interaction significantly (P <0.01) affected N2O emission. Highest N2O emissions (2.38 kg N2O-N ha(-1)) were measured at highest N application rates without P fertilization or AMF. At the highest N application rate, N2O fluxes were lowest (0.71 kg N2O-N ha(-1)) with both P fertilization and AMF. The N2O emission factors decreased with 50 % when P fertilization was applied. Our results illustrate the importance of the judicious use of all nutrients to minimize N2O emission, and thereby further underline the intimate link between sound agronomic practice and prudent soil GHG management.
    Transport and degradation of propylene glycol in the vadose zone: model development and sensitivity analysis
    Schotanus, D. ; Meeussen, J.C.L. ; Lissner, H. ; Ploeg, M.J. van der; Wehrer, M. ; Totsche, K.U. ; Zee, S.E.A.T.M. van der - \ 2014
    Environmental Science and Pollution Research 21 (2014)15. - ISSN 0944-1344 - p. 9054 - 9066.
    in-situ bioremediation - soil respiration - biodegradation - groundwater - diffusion - water - denitrification - contaminants - simulation - aggregate
    Transport and degradation of de-icing chemical (containing propylene glycol, PG) in the vadose zone were studied with a lysimeter experiment and a model, in which transient water flow, kinetic degradation of PG and soil chemistry were combined. The lysimeter experiment indicated that aerobic as well as anaerobic degradation occurs in the vadose zone. Therefore, the model included both types of degradation, which was made possible by assuming advection-controlled (mobile) and diffusion-controlled (immobile) zones. In the mobile zone, oxygen can be transported by diffusion in the gas phase. The immobile zone is always water-saturated, and oxygen only diffuses slowly in the water phase. Therefore, the model is designed in a way that the redox potential can decrease when PG is degraded, and thus, anaerobic degradation can occur. In our model, manganese oxide (MnO2, which is present in the soil) and NO 3 - - 3 (applied to enhance biodegradation) can be used as electron acceptors for anaerobic degradation. The application of NO 3 - - 3 does not result in a lower leaching of PG nor in a slower depletion of MnO2. The thickness of the snowcover influences the leached fraction of PG, as with a high infiltration rate, transport is fast, there is less time for degradation and thus more PG will leach. The model showed that, in this soil, the effect of the water flow dominates over the effect of the degradation parameters on the leaching at a 1-m depth.
    Balancing carbon sequestration and GHG emissions in a constructed wetland
    Klein, J.J.M. de; Werf, A.K. van der - \ 2014
    Ecological Engineering 66 (2014). - ISSN 0925-8574 - p. 36 - 42.
    waste-water treatment - phragmites-australis - methane emission - nitrous-oxide - emergent macrophytes - ecosystem services - restored wetlands - greenhouse gases - fresh-water - denitrification
    In many countries wetlands are constructed or restored for removing nutrients from surface water. At the same time vegetated wetlands can act as carbon sinks when CO2 is sequestered in biomass. However, it is well known that wetlands also produce substantial amounts of greenhouse gasses CH4 and N2O. Especially N2O, resulting from nitrification and denitrification, is a very potent GHG. To assess the environmental sustainability of constructed wetlands the benefit of carbon sink and the downside of GHG emissions have to be evaluated. Since nutrient and carbon cycles in wetlands are complex and variable among wetlands and in time such a balance always contains uncertainties. Several studies have addressed this issue and indicated that CW can be either a sink or a source of CO2 equivalents depending on the time scale of research and the environmental and management conditions involved. Here we balance carbon sequestration with CH4 and N2O emissions in a multi-functional constructed wetland, dominated by emergent Phragmites vegetation. Detailed measurements were combined with a nitrogen budget, and all fluxes were expressed as a range indicating the uncertainties in measurements and extrapolation techniques. Measured methane emissions were variable and showed clear relationship with temperature and density of the emergent vegetation. Average CH4 emissions in the vegetation were 7.8 at 15 °C and 24.5 mg m-2 h-1 at 24 °C. Estimated N2O emissions ranged from 0.5 to 1.9 g m-2 y-1. After converting the fluxes to CO2 equivalents we concluded that the Lankheet constructed wetland is most likely a sink of CO2 in the present conditions. Annual net sequestration of CO2 amounts 0.27–2.4 kg m-2 y-1 which represents 12–67% of the CO2 fixation in the biomass. N2O emissions represent a substantial part of the total effect of GHG emissions (12–29%) and should not be disregarded in budget studies. We acknowledge the limitations and uncertainties of our estimates, however, we are confident that our findings contribute to assessing the environmental sustainability of constructed wetlands.
    Role of maize stover incorporation on nitrogen oxide emissions in a non-irrigated Mediterranean barley field
    Abalos, D. ; Sanz-Cobena, A. ; Garcia-Torres, L. ; Groenigen, J.W. van; Vallejo, A. - \ 2013
    Plant and Soil 364 (2013)1-2. - ISSN 0032-079X - p. 357 - 371.
    treated pig slurries - nitric-oxide - inorganic fertilizer - microbial biomass - plant residues - crop residues - soil - n2o - fluxes - denitrification
    Agricultural soils in semiarid Mediterranean areas are characterized by low organic matter contents and low fertility levels. Application of crop residues and/or manures as amendments is a cost-effective and sustainable alternative to overcome this problem. However, these management practices may induce important changes in the nitrogen oxide emissions from these agroecosystems, with additional impacts on carbon dioxide emissions. In this context, a field experiment was carried out with a barley (Hordeum vulgare L.) crop under Mediterranean conditions to evaluate the effect of combining maize (Zea mays L.) residues and N fertilizer inputs (organic and/or mineral) on these emissions. Crop yield and N uptake, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification capacity, N2O, NO and CO2 fluxes were measured during the growing season. The incorporation of maize stover increased N2O emissions during the experimental period by c. 105 %. Conversely, NO emissions were significantly reduced in the plots amended with crop residues. The partial substitution of urea by pig slurry reduced net N2O emissions by 46 and 39 %, with and without the incorporation of crop residues respectively. Net emissions of NO were reduced 38 and 17 % for the same treatments. Molar DOC:NO (3) (-) ratio was found to be a robust predictor of N2O and NO fluxes. The main effect of the interaction between crop residue and N fertilizer application occurred in the medium term (4-6 month after application), enhancing N2O emissions and decreasing NO emissions as consequence of residue incorporation. The substitution of urea by pig slurry can be considered a good management strategy since N2O and NO emissions were reduced by the use of the organic residue.
    Different land use intensities in grassland ecosystems drive ecology of microbial communities involved in nitrogen turnover in soil
    Meyer, A. ; Focks, A. ; Radl, V. ; Keil, D. ; Welzl, G. ; Schoning, I. ; Boch, S. - \ 2013
    PLoS ONE 8 (2013)9. - ISSN 1932-6203
    ammonia-oxidizing archaea - denitrifying bacteria - management-practices - species composition - nosz genes - nitrification - abundance - nirk - diversity - denitrification
    Understanding factors driving the ecology of N cycling microbial communities is of central importance for sustainable land use. In this study we report changes of abundance of denitrifiers, nitrifiers and nitrogen-fixing microorganisms (based on qPCR data for selected functional genes) in response to different land use intensity levels and the consequences for potential turnover rates. We investigated selected grassland sites being comparable with respect to soil type and climatic conditions, which have been continuously treated for many years as intensely used meadows (IM), intensely used mown pastures (IP) and extensively used pastures (EP), respectively. The obtained data were linked to above ground biodiversity pattern as well as water extractable fractions of nitrogen and carbon in soil. Shifts in land use intensity changed plant community composition from systems dominated by s-strategists in extensive managed grasslands to c-strategist dominated communities in intensive managed grasslands. Along the different types of land use intensity, the availability of inorganic nitrogen regulated the abundance of bacterial and archaeal ammonia oxidizers. In contrast, the amount of dissolved organic nitrogen determined the abundance of denitrifiers (nirS and nirK). The high abundance of nifH carrying bacteria at intensive managed sites gave evidence that the amounts of substrates as energy source outcompete the high availability of inorganic nitrogen in these sites. Overall, we revealed that abundance and function of microorganisms involved in key processes of inorganic N cycling (nitrification, denitrification and N fixation) might be independently regulated by different abiotic and biotic factors in response to land use intensity.
    Spatial and temporal variability of nutrient retention in river basins: A global inventory
    Tysmans, D.J.J. ; Löhr, A.J. ; Kroeze, C. ; Ivens, W.P.M.F. ; Wijnen, T.K. van - \ 2013
    Ecological Indicators 34 (2013). - ISSN 1470-160X - p. 607 - 615.
    coastal zone - future-trends - export - nitrogen - phosphorus - explicit - denitrification - eutrophication - watersheds - pollution
    Nutrient export by rivers may cause coastal eutrophication. Some river basins, however, export more nutrients than others. We model the Basin-Wide Nutrient Export (BWNE) Index, defined as nutrient export by rivers as percentage of external nutrient inputs in the basins. We present results for rivers worldwide for the period 1970–2050. The results indicate that nutrient retentions differ largely among basins. They indicate that BWNE increases with nutrient inputs to the land, indicating that the percentage of, for instance, fertilizers exported to sea increases with fertilization rate. We argue that a better understanding of the BWNE Index might help to identify where measures and technologies to reduce nutrient inputs to coastal waters are most effective.
    Apparatus for the ammonium recovery from liquid animal manure
    Starmans, D.A.J. ; Timmerman, M. - \ 2013
    Applied Engineering in Agriculture 29 (2013)5. - ISSN 0883-8542 - p. 761 - 767.
    denitrification - nitrification - removal
    Nitrogen present in animal manure can be a limiting factor when considering manure application rates onto arable land. EU-regulations triggered the development of a new ammonia exchange apparatus for the recovery of ammonia. The described apparatus has a liquid to liquid ammonia mass transfer coefficient of 0.0058 m/s. The results were fitted using a simple first order ammonia exchange model with constant time step that additionally predicted that 80% of the ammonia could be recycled from the liquid fraction of animal manure within a residence time of 10 h with addition of 0.2 M NaOH to the manure, yielding a liquid artificial fertilizer with a calculated achievable maximum concentration of about 18 % nitrogen.
    Soil invertebrate fauna affect N2O emissions from soil
    Kuiper, I. ; Deyn, G.B. de; Thakur, M.P. ; Groenigen, J.W. van - \ 2013
    Global Change Biology 19 (2013)9. - ISSN 1354-1013 - p. 2814 - 2825.
    greenhouse-gas emissions - nitrous-oxide - nutrient mineralization - n mineralization - forest soil - carbon - ecosystems - denitrification - decomposition - enchytraeids
    Nitrous oxide (N2O) emissions from soils contribute significantly to global warming. Mitigation of N2O emissions is severely hampered by a lack of understanding of its main controls. Fluxes can only partly be predicted from soil abiotic factors and microbial analyses – a possible role for soil fauna has until now largely been overlooked. We studied the effect of six groups of soil invertebrate fauna and tested the hypothesis that all of them increase N2O emissions, although to different extents. We conducted three microcosm experiments with sandy soil and hay residue. Faunal groups included in our experiments were as follows: fungal-feeding nematodes, mites, springtails, potworms, earthworms and isopods. In experiment I, involving all six faunal groups, N2O emissions declined with earthworms and potworms from 78.4 (control) to 37.0 (earthworms) or 53.5 (potworms) mg N2O-N m-2. In experiment II, with a higher soil-to-hay ratio and mites, springtails and potworms as faunal treatments, N2O emissions increased with potworms from 51.9 (control) to 123.5 mg N2O-N m-2. Experiment III studied the effect of potworm density; we found that higher densities of potworms accelerated the peak of the N2O emissions by 5 days (P <0.001), but the cumulative N2O emissions remained unaffected. We propose that increased soil aeration by the soil fauna reduced N2O emissions in experiment I, whereas in experiment II N2O emissions were driven by increased nitrogen and carbon availability. In experiment III, higher densities of potworms accelerated nitrogen and carbon availability and N2O emissions, but did not increase them. Overall, our data show that soil fauna can suppress, increase, delay or accelerate N2O emissions from soil and should therefore be an integral part of future N2O studies.
    Mainstreaming ecosystem services into EU policy
    Maes, J. ; Hauck, J. ; Paracchini, M.L. ; Ratamäki, O. ; Hutchins, M. ; Termansen, M. ; Furman, E. ; Perez-Soba, M. ; Braat, L.C. ; Bidoglio, G. - \ 2013
    Current Opinion in Environmental Sustainability 5 (2013)1. - ISSN 1877-3435 - p. 128 - 134.
    pollination services - forest recreation - biodiversity loss - water-quality - conservation - landscapes - trends - denitrification - agriculture - indicators
    This paper presents a synthesis of the PRESS initiative (PEER7 Research on Ecosystem Services). In support of the EU Biodiversity Strategy to 2020, this initiative demonstrated a multi-scale mapping and assessment approach of ecosystem services using three case studies. The water purification case studied the impacts of agricultural and water policy scenarios on the capacity of ecosystems to purify water. The conclusion was that greening the subsidies to farmers in Europe would improve water quality and increase the benefits to society as measured via monetary valuation. Yet, scenario based nitrogen reduction levels differed among the different scales (EU and basin scale) suggesting that the assessment of policy measures is scale-dependent, which, in turn, justifies a multi-scale mapping and assessment approach. The recreation case presented evidence that millions of people visited forests several times per year and they expressed their willingness to pay to continue doing so. The visitor statistics that were used in this study suggested that the Recreation Opportunity Spectrum approach is a useful method to identify areas in terms of their accessibility and potential to provide recreation services. Finally, we demonstrated that the coverage and resolution of current datasets are already sufficient to map the potential of ecosystems to provide pollination services. Further research should contribute to better ecological observations of key pollinator species to include important drivers of pollinator abundance in modelling and mapping approaches.
    Potential of mechanical cleaning of membranes from a mebrane bioreactor
    Brink, P. van den; Vergeldt, F.J. ; As, H. van; Zwijnenburg, A. ; Temmink, H. - \ 2013
    Journal of Membrane Science 429 (2013). - ISSN 0376-7388 - p. 259 - 267.
    drinking-water - biofilm reactor - critical flux - waste-water - exopolysaccharides - denitrification - precipitation - communities - limitation - bacteria
    Several membrane fouling mechanisms have been identified in membrane bioreactors. While cake layers can be removed by physical cleaning, irreversible fouling such as a gel layer is difficult to remove by physical cleaning during filtration. Harsh mechanical cleaning was applied in this study to evaluate how much fouling could be maximally removed and distribution of remaining fouling was investigated. The fouling resistance of several membranes operated at different relatively low fluxes was followed during long term continuous flux operation. Remaining fouling was observed with scanning electron microscopy (SEM) and magnetic resonance imaging (MRI). Dead-end filtration tests with mechanically cleaned membranes showed a decreased permeability. To determine whether bacteria were present in the remaining fouling, oxygen consumption was quantified. Even after harsh mechanical cleaning, membrane samples showed considerable oxygen consumption. SEM did not show fouling inside the membrane. Of several membranes operated for at least 1 year, the permeate side was covered with bacteria and extracellular polymeric substances (EPS). These results show that fouling cannot be removed completely by harsh mechanical cleaning and that both feed and permeate side of the membrane contains biofouling. This fouling on the permeate side should not be neglected when designing membrane cleaning.
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