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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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    Bioremediation of chlorinated ethenes in aquifer thermal energy storage
    Ni, Z. - \ 2015
    Wageningen University. Promotor(en): Huub Rijnaarts, co-promotor(en): Tim Grotenhuis; P.F.M. van Gaans. - Wageningen : Wageningen University - ISBN 9789462575752 - 216
    watervoerende lagen - thermische energie - verzwakking - grondwater - waterzuivering - duurzame energie - biogeochemie - aquifers - thermal energy - attenuation - groundwater - water treatment - sustainable energy - biogeochemistry

    Subjects: bioremediation; biodegradation; environmental biotechnology, subsurface and groundwater contamination; biological processes; geochemistry; microbiology

    The combination of enhanced natural attenuation (ENA) of chlorinated volatile organic compounds (CVOCs) and aquifer thermal energy storage (ATES) appears attractive because such integration provides a promising solution for redevelopment of urban areas in terms of improving the local environmental quality as well as achieving sustainable energy supply. It will reduce the current negative interference between groundwater contaminants and ATES systems that arises from the rapid increase of ATES system numbers and generally long duration of contaminated groundwater treatments. However, currently the implementation of the combined system is at an initial stage, and still requires comprehensive study before advancing to mature application. Studies should specifically focus on understanding of the basic biogeochemical processes in aquifer systems under conditions of ATES and enhanced bioremediation and their mutual impacts when combined in ATES-ENA. To this end, the research as reported in this thesis employed laboratory experiments and modeling approaches focused on finding the essential process factors involved in the combined system, revealing possible drawbacks, and providing a better understanding to design alternative options on better operation of the combined system.

    Chapter 2 assessed the limiting factor for reductive dechlorination of PCE in an Fe(III) reducing aquifer, being the typical type of subsurface in the Netherlands. A step-wise batch study was performed which consisted of redox conditioning by lactate and ascorbic acid, followed by reductive dechlorination in different scenarios. For the sediment material sampled from the Fe(III) reducing aquifer, conditioning of the redox potential could stimulate PCE dechlorination. It was concluded that 75 µmol electron equivalents per gram dry mass of aquifer material was the threshold to obtain a redox potential of -450 mV, which is theoretically suitable for PCE reductive dechlorination. However, dechlorinating bacteria required for fully reductive dechlorination are generally lacking in Fe(III) reducing aquifers. Without bioaugmentation of dechlorinating bacteria, PCE could only be reduced to TCE or cis-DCE. The step-wise approach and findings obtained from different scenarios tested in this study are relevant for improving the cost-effectiveness of the design and operation of in situ bioremediation. The redox potential of an aquifer can be used as a general indicator to evaluate the potential for CVOCs reductive dechlorination. For achieving specific goals of in situ bioremediation projects at different CVOCs contaminated sites with various environmental conditions, the balance between cost, benefit, and potential risks (e.g. bio‑chemical well clogging due to bacteria growth and precipitation of metal-oxides) should be estimated before the design and operation of the ATES-ENA systems. This chapter provides insights into the essential factors that determine the feasibility of ATES-ENA.

    In Chapter 3, the two most important impacts of ATES on enhanced bioremediation of CVOCs were investigated using batch experiments. Besides, another type of underground thermal energy storage system, the borehole thermal energy storage (BTES) was also studied as a comparison to ATES. Here cis-DCE was targeted as it is commonly found to accumulate in the subsurface due to incomplete dechlorination. Compared to a natural situation (NS) with sufficient electron donor and bioaugmentation at a constant temperature of 10 ˚C, we assessed the effect of ATES by exchanging liquid between bottles kept at 25 and 5 ˚C, and the effect of BTES by alternating temperature between 25 and 5 ˚C periodically. Under ATES warm condition, cis-DCE was dechlorinated to ethene and at an increasing rate with each liquid exchange, despite no biodegradation being observed under ATES cold condition. The overall removal rate under alternating ATES conditions reached 1.83 μmol cis‑DCE/day, which was over 1.5 and 13 times faster than those in BTES and NS conditions. Most probably growth of biomass occurred under ATES warm condition, leading to an autocatalytic increase in conversion rates due to higher biomass concentration. Comparison between batches with or without Dehalococcoides inoculum revealed that their initial presence is a determining factor for the dechlorination process. Temperature then became the dominant factor when Dehalococcoides concentration was sufficient. The results also indicated that Dehalococcoides was preferentially attached to the soil matrix. This chapter highlights the importance of the dynamic temperature regimes in ATES on the bioremediation of CVOCs and recommends to implement biostimulation actions in the ATES warm well.

    Further impacts of ATES related to change in redox condition on bioremediation of CVOCs, with focus on microbial responses of Dehalococcoides, were explored in Chapter 4. In this chapter, we adopted a recirculating column experiment with a flow rate of 10 mL/min (representing the flow velocity at a distance of 1.3 m from the center of a typical ATES well) to simulate the ATES system. To mimic potential periodic redox fluctuations that accompany ATES, serial additions of lactate and nitrate were performed. Firstly, also at the relatively high liquid velocity (compared to normal bioremediation conditions) complete reductive dechlorination from cis-DCE to ethene was achieved in the column system. However, dechlorination was immediately terminated by subsequent nitrate addition due to direct interruption of Dehalococcoides retention to the soil matrix. In our column system, which was much more homogeneous than subsurface in reality, repeated interruption of dechlorination via Dehalococcoides was extremely severe. Such repeated interruption by nitrate dosing eventually led to less easily reversible while requiring more efforts for recovering dechlorination. In addition, the hypothesis of the immobility of Dehalococcoides was further confirmed by the microbial analysis of microorganism in the liquid phase where only less than 0.1% of the Dehalococcoides inoculum could be found back. Although some field studies demonstrated easier regeneration of Dehalococcoides in the subsurface after suffering oxidant, results from this chapter emphasized the sensitive resilience of Dehalococcoides which needs careful consideration in biostimulated ATES condition, and a functional combined system requires dedicated ATES operation and monitoring on the aquifer geochemical conditions.

    The major concern on possible negative impact of enhanced bioremediation on ATES is biological clogging attributed to biomass growth. As chemical clogging due to Fe(III) precipitates is a common problem in the functioning of ATES, the clogging issues (both biological and chemical) should be addressed before practical application. The potential clogging issues in the combined system were then researched in Chapter 5 using the same recirculating column system as in the previous chapter. For this purpose, two flow rates, 10 and 50 mL/min, were implemented. In the two columns, enhanced biological activity and chemically promoted Fe-oxide precipitation were studied by addition of lactate and nitrate respectively. Pressure drop (∆P) between the influent and effluent of the columns was monitored to indicate clogging of the system. The results showed no increase in ∆P during the period of enhanced biological activity, with large amount of lactate and active inoculum being added, even when the concentration of total bacteria in the liquid phase increased by four orders of magnitude. Nitrate addition, however, caused significant increase of ∆P. Remarkably, in the column with higher flow rate (50 mL/min), an unforeseen blow-up occurred at the end of experiment, as the buildup of pressure in the system was higher than the strength of the glass column. However, in the column with flow rate of 10 mL/min, high pressure buildup caused by nitrate addition could be alleviated by lactate addition. Such finding indicates that the risk of biological clogging related to biostimulation is relatively small, because by maintaining a low redox condition biostimulation itself may counter chemical clogging in ATES. Nevertheless, acknowledging that a column system cannot fully mimic real ATES conditions, additional tests are necessary to further investigate the clogging issues in the combined system.

    In Chapter 6, we performed a simulation of ATES-ENA with a reactive transport model, using ATES as the engineering tool for lactate injection in a hypothetical TCE contaminated aquifer which is assumed to be homogeneous. Many relevant processes in the combined system were simulated, such as TCE, cis-DCE and VC dechlorination, sulphate and Fe(III) reduction, organic acid fermentation and oxidation and growth of different biomass. In total 15 scenarios are considered in the model, including variations in lactate dosage (three concentration levels: 3.8, 1.9 and 0.38 mmol/L), temperature (three pairs for the ATES cold/warm well: 5/15 ˚C, 10/10 ˚C, 5/25 ˚C), biomass mobility (purely mobile or immobile), and pH limitation on Fe(III) reduction (absence and presence of such an effect). In the five years’ simulation by the model, complete dechlorination to ethene was achieved within 1 year, in the influence zone of the ATES wells, for the reference scenario with 3.8 mmol/L lactate, 5/15 ˚C ATES well temperatures and mobile biomass. Scenarios with lower dosage of lactate gave results with less dechlorination progress. Growth of biomass, especially iron reducer and lactate fermenter, was significant also in the first year (for both mobile and immobile biomass scenarios). Biomass also spread throughout the influence volume of ATES for both warm and cold wells. However, scenarios with different well-temperature pairs did not noteworthy differ in dechlorination progress. This could probably be due to biomass concentration being the limiting factor in this model setup, while temperature was not. Such situation was quite different than that in Chapter 3, of which experiment with bioaugmentation in the beginning. Besides, the model here could not include the important autocatalytic process (Chapter 3) which generated much faster dechlorination than just could be realized by only temperature increase in this chapter. In general, the modeling in this chapter suggests that applying ATES as engineering tool for biostimulation (substrate injection and bioaugmentation) can be a cost-effective approach to support the combined system.

    Eventually in Chapter 7, overall discussions upon results gained from previous chapters were integrated and the research questions as presented in the introduction are reiterated. In addition, recommendation upon future study, and wider implications with future perspective for practical application are also discussed. We concluded that redox condition is the most essential factor in the ATES-ENA system. The mutual impacts of ATES and ENA were revealed to be quite positive. Elevated temperature in the ATES warm well synergizing with groundwater transport can provide “1 + 1 > 2” effect. Besides, ENA can probably reduce risk of chemical clogging in ATES, instead of causing biological clogging. The further investigation was recommended to perform with larger scale pilot tests. Finally, a brief review of possible applications was given for two countries, the Netherlands and China, which both have dense groundwater and subsurface contaminations around urban areas. The ATES technology is much more mature in the Netherlands, whereas in China, the advantage is the more flexible usage of subsurface. For both countries, ATES-ENA can provide cost‑effective outcomes on both energy production and groundwater management.

    Sensitivity of power functions to aggregation: bias and uncertainty in radar rainfall retrieval
    Sassi, M.G. ; Leijnse, H. ; Uijlenhoet, R. - \ 2014
    Water Resources Research 50 (2014)10. - ISSN 0043-1397 - p. 8050 - 8065.
    zero-rainfall - semi-variance - resolution - hydrology - time - multifractals - distributions - attenuation - variability - netherlands
    Rainfall retrieval using weather radar relies on power functions between radar reflectivity Z and rain rate R. The nonlinear nature of these relations complicates the comparison of rainfall estimates employing reflectivities measured at different scales. Transforming Z into R using relations that have been derived for other scales results in a bias and added uncertainty. We investigate the sensitivity of Z-R relations to spatial and temporal aggregation using high-resolution reflectivity fields for five rainfall events. Existing Z-R relations were employed to investigate the behavior of aggregated Z-R relations with scale, the aggregation bias, and the variability of the estimated rain rate. The prefactor and the exponent of aggregated Z-R relations systematically diverge with scale, showing a break that is event-dependent in the temporal domain and nearly constant in space. The systematic error associated with the aggregation bias at a given scale can become of the same order as the corresponding random error associated with intermittent sampling. The bias can be constrained by including information about the variability of Z within a certain scale of aggregation, and is largely captured by simple functions of the coefficient of variation of Z. Several descriptors of spatial and temporal variability of the reflectivity field are presented, to establish the links between variability descriptors and resulting aggregation bias. Prefactors in Z-R relations can be related to multifractal properties of the rainfall field. We find evidence of scaling breaks in the structural analysis of spatial rainfall with aggregation.
    Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment
    Peltola, O. ; Hensen, A. ; Helfter, C. ; Belelli Marchesini, L. ; Bosveld, F.C. ; Bulk, W.C.M. van de; Elbers, J.A. ; Haapanala, S. ; Holst, J. ; Laurila, T. ; Lindroth, A. ; Nemitz, E. ; Röckmann, T. ; Vermeulen, A.T. ; Mammarella, I. - \ 2014
    Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 3163 - 3186.
    water-vapor - atmospheric methane - mixing-ratio - wpl terms - path - ch4 - attenuation - accuracy - strategy - quality
    The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH4 fluxes observed at the location, of the order of 25 nmol m-2 s-1, provided a suitable signal for testing the instruments' performance. Generally, all analysers tested were able to quantify the concentration fluctuations at the frequency range relevant for turbulent exchange and were able to deliver high-quality data. The tested cavity ringdown spectrometer (CRDS) instruments from Picarro, models G2311-f and G1301-f, were superior to other CH4 analysers with respect to instrumental noise. As an open-path instrument susceptible to the effects of rain, the LI-COR LI-7700 achieved lower data coverage and also required larger density corrections; however, the system is especially useful for remote sites that are restricted in power availability. In this study the open-path LI-7700 results were compromised due to a data acquisition problem in our data-logging setup. Some of the older closed-path analysers tested do not measure H2O concentrations alongside CH4 (i.e. FMA1 and DLT-100 by Los Gatos Research) and this complicates data processing since the required corrections for dilution and spectroscopic interactions have to be based on external information. To overcome this issue, we used H2O mole fractions measured by other gas analysers, adjusted them with different methods and then applied them to correct the CH4 fluxes. Following this procedure we estimated a bias of the order of 0.1 g (CH4) m-2 (8% of the measured mean flux) in the processed and corrected CH4 fluxes on a monthly scale due to missing H2O concentration measurements. Finally, cumulative CH4 fluxes over 14 days from three closed-path gas analysers, G2311-f (Picarro Inc.), FGGA (Los Gatos Research) and FMA2 (Los Gatos Research), which were measuring H2O concentrations in addition to CH4, agreed within 3% (355–367 mg (CH4) m-2) and were not clearly different from each other, whereas the other instruments derived total fluxes which showed small but distinct differences (±10%, 330–399 mg (CH4) m-2).
    Comparative efficacy of two next-generation Rift Valley fever vaccines
    Kortekaas, J.A. ; Oreshkova, N. ; Keulen, L.J.M. van; Kant, J. ; Bosch, B.J. ; Bouloy, M. ; Moulin, V. ; Goovaerts, D. ; Moormann, R.J.M. - \ 2014
    Vaccine 32 (2014). - ISSN 0264-410X - p. 4901 - 4908.
    nss protein - down-regulation - mp-12 vaccine - virus-vaccine - safety - transcription - sheep - immunogenicity - attenuation - rna
    Rift Valley fever virus (RVFV) is a re-emerging zoonotic bunyavirus of the genus Phlebovirus. A natural isolate containing a large attenuating deletion in the small (S) genome segment previously yielded a highly effective vaccine virus, named Clone 13. The deletion in the S segment abrogates expression of the NSs protein, which is the major virulence factor of the virus. To develop a vaccine of even higher safety, a virus named R566 was created by natural laboratory reassortment. The R566 virus combines the S segment of the Clone 13 virus with additional attenuating mutations on the other two genome segments M and L, derived from the previously created MP-12 vaccine virus. To achieve the same objective, a nonspreading RVFV (NSR-Gn) was created by reverse-genetics, which not only lacks the NSs gene but also the complete M genome segment. We have now compared the vaccine efficacies of these two next-generation vaccines and included the Clone 13 vaccine as a control for optimal efficacy. Groups of eight lambs were vaccinated once and challenged three weeks later. All mock-vaccinated lambs developed high fever and viremia and three lambs did not survive the infection. As expected, lambs vaccinated with Clone 13 were protected from viremia and clinical signs. Two lambs vaccinated with R566 developed mild fever after challenge infection, which was associated with low levels of viral RNA in the blood, whereas vaccination with the NSR-Gn vaccine completely prevented viremia and clinical signs.
    Small-scale oxygen distribution determines the vinyl chloride biodegradation pathway in surficial sediments of riverbed hyporheic zones
    Atashgahi, S. ; Maphosa, F. ; Dogan, E. ; Smidt, H. ; Springael, D. ; Dejonghe, W. - \ 2013
    FEMS microbiology ecology 84 (2013)1. - ISSN 0168-6496 - p. 133 - 142.
    chlorinated aliphatic-hydrocarbons - dehalococcoides sp strain - contaminated groundwater - tidal flat - ethene - identification - attenuation - community - perchloroethene - bioremediation
    Surficial riverbed sediments are often characterized by sharp redox gradients between the aerobic benthic sediment and underlying anoxic sediment, potentially representing an ideal niche for aerobic and anaerobic vinyl chloride (VC) degraders. To test this, the fate of VC in aerobic and anaerobic microcosms containing surficial sediment of a riverbed hyporheic zone receiving VC-contaminated groundwater was explored. Quantitative PCR showed that Dehalococcoides 16S rRNA gene and VC reductive dehalogenase–encoding genes (vcrA, bvcA) were highly enriched in anaerobic microcosms, with stoichiometric conversion of VC to ethene. In aerobic microcosms, etnC and etnE involved in aerobic ethene/VC oxidation were enriched with concomitant low or no accumulation of ethene. However, Dehalococcoides 16S rRNA gene, vcrA and bvcA copy numbers were also enriched in oxygen-exposed microcosms containing sediment with high organic carbon and small grain size, whereas they were reduced in oxygen-exposed sediment with low organic carbon and larger grain size in line with extensive oxygen penetration into the sediment. These results suggest the coexistence and coactivity of anaerobic and aerobic VC degraders in the same small volume of surficial sediment and that oxygen distribution, as determined by sediment grain size and organic matter content, affects the local VC-degrading bacterial community and VC biodegradation pathway
    Trade-offs between biodiversity and flood protection services of coastal salt marshes
    Loon-Steensma, J.M. van; Vellinga, P. - \ 2013
    Current Opinion in Environmental Sustainability 5 (2013)3-4. - ISSN 1877-3435 - p. 320 - 326.
    zoutmoerassen - kustgebieden - herstelbeheer - ecosysteemdiensten - hoogwaterbeheersing - klimaatadaptatie - biodiversiteit - natuurbeheer - salt marshes - coastal areas - restoration management - ecosystem services - flood control - climate adaptation - biodiversity - nature management - sea-level rise - vegetation - ecosystems - wetlands - sedimentation - restoration - attenuation - management - dynamics - systems
    Coastal salt marshes provide a range of ecosystem services. However, their area is steadily diminishing as a result of human-made modifications to the coastal zone. The accelerated rise of sea level is another challenge to the self-generating capacity of coastal salt marshes. This is a subject of extensive research, leading to conservation and restoration strategies. The value of salt marshes as a natural sea defense is an area of growing interest as well. This article reviews salt-marsh restoration options described in the literature, including the idea of sediment nourishment on the scale of the estuary or lagoon as a whole. It then considers trade-offs between enhancement of salt marshes’ flood protection service and the ecological quality of the ecosystem
    Protoanemonin: a natural quorum sensing inhibitor that selectively activates iron starvation response
    Fazzini, R.A. ; Skindersoe, M. ; Bielecki, M. ; Puchalka, J. ; Givskov, M. ; Martins Dos Santos, V.A.P. - \ 2013
    Environmental Microbiology 15 (2013)1. - ISSN 1462-2912 - p. 111 - 120.
    pseudomonas-aeruginosa virulence - to-cell communication - polymorphonuclear leukocytes - genes - expression - infection - bacteria - identification - attenuation - pyocyanin
    Many Gram-negative bacteria employ cell-to-cell communication mediated by N-acyl homoserine lactones (quorum sensing) to control expression of a wide range of genes including, but not limited to, genes encoding virulence factors. Outside the laboratory, the bacteria live in complex communities where signals may be perceived across species. We here present a newly found natural quorum sensing inhibitor, produced by the pseudomonads Pseudomonas sp. B13 and Pseudomonas reinekei MT1 as a blind end in the biodegradation of organochloride xenobiotics, which inhibits quorum sensing in P. aeruginosa in naturally occurring concentrations. This catabolite, 4-methylenebut-2-en-4-olide, also known as protoanemonin, has been reported to possess antibacterial properties, but seems to have dual functions. Using transcriptomics and proteomics, we found that protoanemonin significantly reduced expression of genes and secretion of proteins known to be under control of quorum sensing in P. aeruginosa. Moreover, we found activation of genes and gene products involved in iron starvation response. It is thus likely that inhibition of quorum sensing, as the production of antibiotics, is a phenomenon found in complex bacterial communities
    Sorption of perfluorooctane sulfonate to carbon nanotubes in aquatic sediments
    Kwadijk, C.J.A.F. ; Velzeboer, I. ; Koelmans, A.A. - \ 2013
    Chemosphere 90 (2013)5. - ISSN 0045-6535 - p. 1631 - 1636.
    natural organic-matter - adsorption - nanomaterials - environment - attenuation - release - surface - acids - pfos
    To date, sorption of organic compounds to nanomaterials has mainly been studied for the nanomaterial in its pristine state. However, sorption may be different when nanomaterials are buried in sediments. Here, we studied sorption of Perfluorooctane sulfonate (PFOS) to sediment and to sediment with 4% multiwalled carbon nanotubes (MWCNTs), as a function of factors affecting PFOS sorption; aqueous concentration, pH and Ca2+ concentration. Sorption to MWCNT in the sediment–MWCNT mixtures was assessed by subtracting the contribution of PFOS sorption to sediment-only from PFOS sorption to the total sediment–MWCNT mixture. PFOS Log KD values ranged 0.52–1.62 L kg-1 for sediment and 1.91–2.90 L kg-1 for MWCNT present in the sediment. The latter values are relatively low, which is attributed to fouling of MWCNT by sediment organic matter. PFOS sorption was near-linear for sediment (Freundlich exponent of 0.92 ± 0.063) but non-linear for MWCNT (Freundlich exponent of 0.66 ± 0.03). Consequently, the impact of MWCNT on sorption in the mixture was larger at low PFOS aqueous concentration. Effects of pH and Ca2+ on PFOS sorption to MWCNT were statistically significant. We conclude that MWCNT fouling and PFOS concentration dependency are important factors affecting PFOS–MWCNT interactions in sediments.
    Microwave links for rainfall estimation in urban environment: insights from an experimental setup in Luxembourg city
    Fenicia, F. ; Pfister, L. ; Kavetski, D. ; Matgen, P. ; Iffly, J.F. ; Hoffman, L. ; Uijlenhoet, R. - \ 2012
    Journal of Hydrology 464-465 (2012). - ISSN 0022-1694 - p. 69 - 78.
    path-averaged rainfall - dual-frequency - attenuation - resolution - fields - gauges - radar
    Although the theoretical aspects of rainfall monitoring through microwave links are quite well established, only few practical applications have evaluated this technique in an operational setting. Microwave links are of particular interest in urban areas, where high frequency measurements are needed due to the fast hydrological response of the system, and link networks are usually already in-place. This study presents the first results of an on-going experiment in Luxembourg-City, which includes two dual-frequency links and several rain gauges at intermediate locations along the links. The experimental set-up allows comparing rain rate estimates based on the individual frequencies as well as estimates based on the difference between the two frequencies. We compared several models for expressing the relationship between attenuation and rain rate, including different baseline estimation methods such as the traditional constant-baseline model and a one-parameter model based on a first order low-pass filter. The models were evaluated using a Bayesian approach and subjected to posterior scrutiny based on several diagnostics. In contrast to previous research, our results indicated that estimates based on the attenuation difference appeared poorer than the estimates based on individual frequencies. The one-parameter baseline estimation method provided consistently better results than the traditional constant-baseline method, which justifies the increased model complexity. Uncertainty of model predictions was relatively large for low intensity rainfall, which highlights one of the limitations of this technique. Models were validated in different periods and on different links, in some cases demonstrating large bias. Model parameters were generally well-identifiable, though uncertainty in the rainfall predictions appeared under-estimated in some cases.
    Effectiveness of unfertilized buffer strips for reducing nitrogen loads from agricultural lowland to surface waters
    Noij, I.G.A.M. ; Heinen, M. ; Heesmans, H.I.M. ; Thissen, J.T.N.M. ; Groenendijk, P. - \ 2012
    Journal of Environmental Quality 41 (2012)2. - ISSN 0047-2425 - p. 322 - 333.
    vegetative filter strips - stream riparian zones - nitrate removal - groundwater-flow - field-scale - retention - landscape - transport - constituents - attenuation
    Unfertilized buffer strips (BS) are widely accepted to reduce nitrogen (N) loads from agricultural land to surface water. However, the relative reduction of N load or concentration (BS effectiveness, BSE), varies with management and local conditions, especially hydrogeology. We present novel experimental evidence on BSE for 5-m-wide grass BS on intensively drained and managed plain agricultural lowland with varying hydrogeology. We selected characteristic sites for five major hydrogeological classes of the Netherlands and installed paired 5-m-wide unfertilized grass (BS) and reference (REF) treatments along the ditch. The REF was managed like the adjacent field, and BS was only harvested. Treatments were equipped with reservoirs in the ditch to collect and measure discharge and flow proportional N concentration for 3 or 4 yr. In addition, N concentration in upper groundwater was measured. We found a statistically significant BSE of 10% on the peat site. At the other sites, BSE for N was low and statistically insignificant. Low BSE was explained by denitrification between adjacent field and ditch, as well as by the site-specific hydrologic factors including low proportion of shallow groundwater flow, downward seepage, low residence time in the BS, and surface runoff away from the ditch. We emphasize that a REF treatment is needed to evaluate BSE in agriculture and recommend reservoirs if drainage patterns are unknown. Introduction of a 5-m-wide BS is ineffective for mitigating N loads from lowland agriculture to surface waters. We expect more from BS specifically designed to abate surface runoff.
    Organische stof is lastig op peil te houden in duinzandgrond
    Pronk, A.A. ; Leeuwen, P.J. van; Berg, H. van den - \ 2011
    De Boomkwekerij 24 (2011)51/52. - ISSN 0923-2443 - p. 32 - 33.
    bodemkwaliteit - duingronden - organische stof - bemesting - verzwakking - toedieningshoeveelheden - soil quality - dune soils - organic matter - fertilizer application - attenuation - application rates
    Organische stof in duinzandgrond breekt snel af. Vooral bij grond die enige jaren in gebruik is en goed is verzien van organische bemesting, loopt het percentage organische stof snel terug. Dat bleek in een proef waarin de afbraak van organische stof in diverse duinzandgronden werd vergeleken met dekzandgrond.
    Path-average rainfall estimation from optical extinction measurements using a large-aperture scintillometer
    Uijlenhoet, R. ; Cohard, J.M. ; Gosset, M. - \ 2011
    Journal of Hydrometeorology 12 (2011)5. - ISSN 1525-755X - p. 955 - 972.
    multiple-scattering corrections - raindrop size distribution - sensible heat fluxes - heterogeneous land-surface - flevoland field experiment - beer-lambert law - area - attenuation - precipitation - scintillation
    The potential of a near-infrared large-aperture boundary layer scintillometer as path-average rain gauge is investigated. The instrument was installed over a 2.4-km path in Benin as part of the African Monsoon Multidisciplinary Analysis (AMMA) Enhanced Observation Period during 2006 and 2007. Measurements of the one-minute-average received signal intensity were collected for 6 rainfall events during the dry season and 16 events during the rainy season. Using estimates of the signal base level just before the onset of the rainfall events, the optical extinction coefficient is estimated from the path-integrated attenuation for each minute. The corresponding path-average rain rates are computed using a power-law relation between the optical extinction coefficient and rain rate obtained from measurements of raindrop size distributions with an optical spectropluviometer and a scaling-law formalism for describing raindrop size distribution variations. Comparisons of five-minute rainfall estimates with measurements from two nearby rain gauges show that the temporal dynamics are generally captured well by the scintillometer. However, the instrument has a tendency to underestimate rain rates and event total rain amounts with respect to the gauges. It is shown that this underestimation can be explained partly by systematic differences between the actual and the employed mean power-law relation between rain rate and specific attenuation, partly by unresolved spatial and temporal rainfall variations along the scintillometer path. Occasionally, the signal may even be lost completely. It is demonstrated that if these effects are properly accounted for by employing appropriate relations between rain rate and specific attenuation and by adapting the pathlength to the local rainfall climatology, scintillometer-based rainfall estimates can be within 20% of those estimated using rain gauges. These results demonstrate the potential of large-aperture scintillometers to estimate path-average rain rates at hydrologically relevant scales.
    Errors and uncertainties in microwave link rainfall estimation explored using drop size measurements and high-resolution radar data
    Leijnse, H. ; Uijlenhoet, R. ; Berne, A.D. - \ 2010
    Journal of Hydrometeorology 11 (2010). - ISSN 1525-755X - p. 1330 - 1344.
    path-averaged rainfall - x-band radar - dual-frequency - communication-networks - video disdrometer - weather radar - axis ratios - attenuation - matrix - distributions
    Microwave links can be used for the estimation of path-averaged rainfall by using either the path-integrated attenuation or the difference in attenuation of two signals with different frequencies and/or polarizations. Link signals have been simulated using measured time series of raindrop size distributions (DSDs) over a period of nearly 2 yr, in combination with wind velocity data and Taylor’s hypothesis. For this purpose, Taylor’s hypothesis has been tested using more than 1.5 yr of high-resolution radar data. In terms of correlation between spatial and temporal profiles of rainfall intensities, the validity of Taylor’s hypothesis quickly decreases with distance. However, in terms of error statistics, the hypothesis is seen to hold up to distances of at least 10 km. Errors and uncertainties (mean bias error and root-mean-square error, respectively) in microwave link rainfall estimates due to spatial DSD variation are at a minimum at frequencies (and frequency combinations) where the power-law relation for the conversion to rainfall intensity is close to linear. Errors generally increase with link length, whereas uncertainties decrease because of the decrease of scatter about the retrieval relations because of averaging of spatially variable DSDs for longer links. The exponent of power-law rainfall retrieval relations can explain a large part of the variation in both bias and uncertainty, which means that the order of magnitude of these error statistics can be predicted from the value of this exponent, regardless of the link length.
    The effect of reported high-velocity small raindrops on inferred drop size distributions and derived power laws
    Leijnse, H. ; Uijlenhoet, R. - \ 2010
    Atmospheric Chemistry and Physics 10 (2010)14. - ISSN 1680-7316 - p. 6807 - 6818.
    rainfall estimation - video disdrometer - doppler radar - attenuation - band
    It has recently been shown that at high rainfall intensities, small raindrops may fall with much larger velocities than would be expected from their diameters. These were argued to be fragments of recently broken-up larger drops. In this paper we quantify the effect of this phenomenon on raindrop size distribution measurements from a Joss-Waldvogel disdrometer, a 2-D Video Distrometer, and a vertically-pointing Doppler radar. Probability distributions of fall velocities have been parameterized, where the parameters are functions of both rainfall intensity and drop size. These parameterizations have been used to correct Joss-Waldvogel disdrometer measurements for this phenomenon. The effect of these corrections on fitted scaled drop size distributions are apparent but not major. Fitted gamma distributions for three different types of rainfall have been used to simulate drop size measurements. The effect of the high-velocity small drops is shown to be minor. Especially for the purpose of remote sensing of rainfall using radar, microwave links, or optical links, the errors caused by using the slightly different retrieval relations will be masked completely by other error sources
    PPO gaat leliegeur wetenschappelijk bekijken (interview met Hans Kok)
    Dwarswaard, A. ; Kok, B.J. - \ 2010
    BloembollenVisie 2010 (2010)190. - ISSN 1571-5558 - p. 68 - 68.
    lilium - lelies - rassen (planten) - cultivars - plantenveredeling - rassenproeven - welriekendheid - organoleptische kenmerken - geurstoffen - verzwakking - lilium - lilies - varieties - cultivars - plant breeding - variety trials - fragrance - organoleptic traits - odours - attenuation
    De geur van met name Oriëntale lelies en OT-hybriden is voor menigeen reden deze lelies niet te kopen. Japans onderzoek zette PPO-onderzoeker Hans Kok op het spoor van een stof die mogelijk kan helpen om de geursterkte substantieel te verminderen. Kok zou het fantastisch vinden als het werkt. "Dat zal de marktkansen flink vergroten."
    Performance of high-resolution X-band radar for rainfall measurement in the Netherlands
    Beek, C.Z. van de; Leijnsel, H. ; Stricker, J.N.M. ; Uijlenhoet, R. ; Russchenberg, H.W.J. - \ 2010
    Hydrology and Earth System Sciences 14 (2010)2. - ISSN 1027-5606 - p. 205 - 221.
    neerslag - regen - meteorologische waarnemingen - hydrologische gegevens - gegevensanalyse - precipitation - rain - meteorological observations - hydrological data - data analysis - weather radar - nonprecipitating echoes - size distribution - mountainous area - reflectivity - attenuation - hydrology - calibration - retrieval
    This study presents an analysis of 195 rainfall events gathered with the X-band weather radar SOLIDAR and a tipping bucket rain gauge network near Delft, The Netherlands, between May 1993 and April 1994. The aim of this paper is to present a thorough analysis of a climatological dataset using a high spatial (120 m) and temporal (16 s) resolution X-band radar. This makes it a study of the potential for high-resolution rainfall measurements with non-polarimetric X-band radar over flat terrain. An appropriate radar reflectivity – rain rate relation is derived from measurements of raindrop size distributions and compared with radar – rain gauge data. The radar calibration is assessed using a long-term comparison of rain gauge measurements with corresponding radar reflectivities as well as by analyzing the evolution of the stability of ground clutter areas over time. Three different methods for ground clutter correction as well as the effectiveness of forward and backward attenuation correction algorithms have been studied. Five individual rainfall events are discussed in detail to illustrate the strengths and weaknesses of high-resolution X-band radar and the effectiveness of the presented correction methods. X-band radar is found to be able to measure the space-time variation of rainfall at high resolution, far greater than what can be achieved by rain gauge networks or a typical operational C-band weather radar. On the other hand, SOLIDAR can suffer from receiver saturation, wet radome attenuation as well as signal loss along the path. During very strong convective situations the signal can even be lost completely. In combination with several rain gauges for quality control, high resolution X-band radar is considered to be suitable for rainfall monitoring over relatively small (urban) catchments. These results offer great prospects for the new high resolution polarimetric doppler X-band radar IDRA
    Weather radar and hydrology
    Delrieu, G. ; Braud, I. ; Berne, A. ; Borga, M. ; Boudevillain, B. ; Fabry, F. ; Freer, J. ; Gaume, E. ; Nakakita, E. ; Seed, A. ; Tabary, P. ; Uijlenhoet, R. - \ 2009
    Advances in Water Resources 32 (2009)7. - ISSN 0309-1708 - p. 969 - 974.
    raindrop size distributions - rainfall estimation - hydrometeor classification - dynamic topmodel - model - scale - catchment - methodology - variability - attenuation
    Do zooplankton contribute to an ultraviolet clear-water phase in lakes?
    Williamson, C.E. ; Lange, H.J. de; Leech, D.M. - \ 2007
    Limnology and Oceanography 52 (2007)2. - ISSN 0024-3590 - p. 662 - 667.
    dissolved organic-carbon - solar uv-radiation - attenuation - matter - ponds
    Seasonal increases in the ultraviolet (UV) transparency of the surface waters of an oligotrophic lake in Pennsylvania suggest that clear-water phase (CWP) events similar to those previously observed for visible light also exist for the potentially damaging UV wavelengths. Seasonal increases in zooplankton grazers indicate that they play a role in these changes in UV that is similar to the role that zooplankton play in CWP events involving longer-wavelength visible, or photosynthetically active radiation (PAR, 400¿700 nm). The potential role of zooplankton and incident UV in generating UV CWP events was investigated with a set of in situ microcosm experiments that manipulated UV and zooplankton, and followed changes in particulate and dissolved absorbance in the UV (320 nm) and PAR wavelength ranges over an 8-d period in April. Nutrients were also manipulated independently to examine the potential role of nutrient regeneration by zooplankton grazing in altering water transparency. Photobleaching by incident solar UV led to a strong and significant decrease in dissolved UV and PAR absorbance. The presence of zooplankton grazers also significantly decreased dissolved UV absorbance but increased dissolved PAR absorbance. Neither zooplankton nor UV had any significant effects on UV or PAR absorbance by particulates. In contrast, nutrient additions significantly increased dissolved absorbance in both the UV and PAR wavelength ranges, indicating that regeneration of nutrients by zooplankton offsets decreases in UV absorbance and enhances increases in PAR absorbance due to grazing. While photobleaching by UV radiation is likely to make a consistent strong contribution to UV CWP events in lakes, the net effects of zooplankton on UV transparency in a given lake will depend upon multiple factors including zooplankton density and a balance between the edibility and extent of nutrient limitation of the phytoplankton.
    Positive feedbacks in seagrass ecosystems - implications for success in conservation and restoration
    Heide, Tj. van; Nes, E.H. van; Geerling, G.W. ; Smolders, A.J.P. ; Bouma, T.J. ; Katwijk, M.M. van - \ 2007
    Ecosystems 10 (2007)8. - ISSN 1432-9840 - p. 1311 - 1322.
    dutch wadden-sea - eelgrass zostera-marina - catastrophic regime shifts - shallow lakes - dynamics - beds - attenuation - meadow - growth - wind
    Seagrasses are threatened by human activity in many locations around the world. Their decline is often characterized by sudden ecosystem collapse from a vegetated to a bare state. In the 1930s, such a dramatic event happened in the Dutch Wadden Sea. Before the shift, large seagrass beds (Zostera marina) were present in this area. After the construction of a large dam and an incidence of the ¿wasting disease¿ in the early 1930s, these meadows became virtually extinct and never recovered despite restoration attempts. We investigated whether this shift could be explained as a critical transition between alternative stable states, and whether the lack of recovery could be due to the high resilience of the new turbid state. We analyzed the depth distribution of the historical meadows, a long-term dataset of key factors determining turbidity and a minimal model based on these data. Results demonstrate that recovery was impossible because turbidity related to suspended sediment was too high, probably because turbidity was no longer reduced by seagrass itself. Model simulations on the positive feedback suggest indeed the robust occurrence of alternative stable states and a high resilience of the current turbid state. As positive feedbacks are common in seagrasses, our findings may explain both the worldwide observed collapses and the low success rate of restoration attempts of seagrass habitats. Therefore, appreciation of ecosystem resilience may be crucial in seagrass ecosystem management.
    Hydrometeorological application of a microwave link: 2. Precipitation
    Leijnse, H. ; Uijlenhoet, R. ; Stricker, J.N.M. - \ 2007
    Water Resources Research 43 (2007). - ISSN 0043-1397 - p. W04417 - W04417.
    path-averaged rainfall - dual-frequency - attenuation - radar - band - resolution - hydrology - gauges - size
    The suitability of a 27-GHz microwave link for measuring path-averaged precipitation is investigated. Theoretical analyses show that the specific attenuation of an electromagnetic signal at this frequency varies nearly linearly with the rainfall intensity, which is ideal for line-integrating instruments. The dependence of this relation on the drop size distribution and on the temperature is small, so that uncertainties in these variables do not play large roles in the estimation of rainfall intensity. Data from an experiment with a 4.89-km microwave link and a line configuration of seven tipping bucket rain gauges are used to test whether this instrument is indeed suitable for the estimation of path-averaged rainfall. Results from this experiment show that the attenuation due to wet antennas can have a significant effect on the retrieved rainfall intensity. However, when a two-parameter wet antenna correction function is applied to the link data, comparisons with the rain gauge data show that the instrument is indeed well suited for the measurement of path-averaged rainfall
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