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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Biodiversity-ecosystem functioning relationships in a long-term non-weeded field experiment
Veen, G.F. ; Putten, Wim H. van der; Bezemer, T.M. - \ 2018
Ecology 99 (2018)8. - ISSN 0012-9658 - p. 1836 - 1846.
diversity–productivity - diversity–stability - ecosystem functioning - functional divergence - functional richness - grassland - long-term - species diversity

Many grassland biodiversity experiments show a positive relationship between biodiversity and ecosystem functioning, however, in most of these experiments plant communities are established by sowing and natural colonization is prevented by selective weeding of non-sown species. During ecosystem restoration, for example on abandoned fields, plant communities start on bare soil, and diversity is often manipulated in a single sowing event. How such initial plant diversity manipulations influence plant biodiversity development and ecosystem functioning is not well understood. We examined how relationships between taxonomic and functional diversity, biomass production and stability develop over 16 yr in non-weeded plots sown with 15 species, four species, or that were not sown. We found that sown plant communities become functionally similar to unsown, naturally colonized plant communities. However, initial sowing treatments had long-lasting effects on species composition and taxonomic diversity. We found only few relationships between biomass production, or stability in biomass production, and functional or taxonomic diversity, and the ones we observed were negative. In addition, the cover of dominant plant species was positively related to biomass production and stability. We conclude that effects of introducing plant species at the start of secondary succession can persist for a long time, and that in secondary succession communities with natural plant species dynamics diversity–functioning relationships can be weak or negative. Moreover, our findings indicate that in systems where natural colonization of species is allowed effects of plant dominance may underlie diversity–functioning relationships.

Tolerability and safety of souvenaid in patients with mild Alzheimer's disease : Results of multi-center, 24-week, open-label extension study
Olde Rikkert, Marcel G.M. ; Verhey, Frans R. ; Blesa, Rafael ; Arnim, Christine A.F. Von; Bongers, Anke ; Harrison, John ; Sijben, John ; Scarpini, Elio ; Vandewoude, Maurits F.J. ; Vellas, Bruno ; Witkamp, Renger ; Kamphuis, Patrick J.G.H. ; Scheltens, Philip - \ 2015
Journal of Alzheimers Disease 44 (2015)2. - ISSN 1387-2877 - p. 471 - 480.
Alzheimer's disease - clinical trial - dietary management - intervention studies - long-term - medical nutrition therapy - memory - patient adherence - safety

Background: The medical food Souvenaid, containing the specific nutrient combination Fortasyn Connect, is designed to improve synapse formation and function in patients with Alzheimer's disease (AD). Two double-blind randomized controlled trials (RCT) with Souvenaid of 12 and 24 week duration (Souvenir I and Souvenir II) showed that memory performance was improved in drug-naïve mild AD patients, whereas no effects on cognition were observed in a 24-week RCT (S-Connect) in mild to moderate AD patients using AD medication. Souvenaid was well-tolerated in all RCTs. Objective: In this 24-week open-label extension (OLE) study to the 24-week Souvenir II RCT, long-term safety and intake adherence of the medical food Souvenaid was evaluated. Methods: Patients with mild AD (n = 201) received Souvenaid once-daily during the OLE. Main outcome parameters were safety and product intake adherence. The memory domain z-score from a revised neuropsychological test battery was continued as exploratory parameter. Results: Compared to the RCT, a similar (low) incidence and type of adverse events was observed, being mainly (68.3%) of mild intensity. Pooled data (RCT and OLE) showed that 48-week use of Souvenaid was well tolerated with high intake adherence (96.1%). Furthermore, a significant increase in the exploratory memory outcome was observed in both the active-active and control-active groups during Souvenaid intervention. Conclusion: Souvenaid use for up to 48-weeks was well tolerated with a favorable safety profile and high intake adherence. The findings in this OLE study warrant further investigation toward the long-term safety and efficacy of Souvenaid in a well-controlled, double-blind RCT.

Effects of large herbivores on grassland arthropod diversity
Klink, R. van; Plas, F. van der; Noordwijk, C.G.E. ; Wallis de Vries, M.F. ; Olff, H. - \ 2015
Biological reviews 90 (2015)2. - ISSN 1464-7931 - p. 347 - 366.
ungrazed chalk grassland - ground beetle coleoptera - plant-species richness - grazing management - phytophagous insects - seminatural grasslands - community structure - tallgrass prairie - long-term - butterfly communities
Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity.
Conservation tillage of rainfed maize in semi-arid Zimbabwe: A review
Nyakudya, I.W. ; Stroosnijder, L. - \ 2015
Soil & Tillage Research 145 (2015). - ISSN 0167-1987 - p. 184 - 197.
zea-mays l. - sandy soils - sustainable agriculture - water conservation - rural livelihoods - smallholder farms - southern africa - use efficiency - rainwater use - long-term
Food security in Sub-Saharan Africa, particularly in semi-arid tropics (41% of the region; 6 months of dry season) is threatened by droughts, dry spells and infertile soils. In Zimbabwe, 74% of smallholder farming areas are located in semi-arid areas mostly in areas with soils of low fertility and water holding capacity. The dominant crop in these areas, maize (Zea mays L.), is susceptible to drought. Under smallholder farming in Zimbabwe, conventional tillage entails cutting and turning the soil with a mouldboard plough thereby burying weeds and crop residues. Seed is planted by hand into a furrow made by the plough, ensuring that crops germinate in relatively weed free seedbeds. Inter-row weed control is performed using the plough or ox-drawn cultivators and hand hoes. Conventional tillage has been criticised for failure to alleviate negative effects of long dry spells on crops and to combat soil loss caused by water erosion estimated at 50 to 80 t ha-1 yr-1. Therefore, conservation tillage has been explored for improving soil and water conservation and crop yields. Our objective was to determine the maize yield advantage of the introduced technology (conservation tillage) over conventional tillage (farmers’ practice) based on a review of experiments in semi-arid Zimbabwe. We use a broad definition of conservation tillage instead of the common definition of =30% cover after planting. Eight tillage experiments conducted between 1984 and 2008 were evaluated. Conventional tillage included ploughing using the mouldboard plough and digging using a hand hoe. Conservation tillage included tied ridging (furrow diking), mulch ripping, clean ripping and planting pits. Field-edge methods included bench terraces (fanya juus) and infiltration pits. Results showed small yield advantages of conservation tillage methods below 500 mm rainfall. For grain yields =2.5 t ha-1 and rainfall =500 mm, 1.0 m tied ridging produced 144 kg ha-1 and mulch ripping 344 kg ha-1 more than conventional tillage. Above 2.5 t ha-1 and for rainfall >500 mm, conventional tillage had =640 kg ha-1 yield advantage. Planting pits had similar performance to ripping and conventional tillage but faced digging labour constraints. Experiments and modelling are required to test conservation tillage seasonal rainfall thresholds. Constraints to adoption of conservation tillage by smallholder farmers necessitate best agronomic practices under conventional tillage while work on adoption of alternative tillage methods continues.
Food quality dominates the impact of food quantity on Daphnia life history: possible implications for re-oligotrophication
Sarpe, D. ; Senerpont Domis, L.N. de; Declerck, S.A.J. ; Donk, E. van; Ibelings, B.W. - \ 2014
Inland Waters : Journal of the International Society of Limnology 4 (2014)4. - ISSN 2044-2041 - p. 363 - 368.
phosphorus limitation - nutrient limitation - long-term - lakes - carbon - eutrophication - growth
The elemental composition of phytoplankton is highly variable compared to the relatively narrow stoichiometry of zooplankton grazers. Using a full factorial design, we tested the effects of alterations in algal elemental composition (i.e., food quality) combined with food quantity on the life history of a Daphnia galeata clone from Lake IJsselmeer. Lower food quality reduced survival, growth, and reproduction. Food quantity became important at high food quality only. The strong effect of food quality indicates the potential for a stoichiometric bottleneck in Lake IJsselmeer, resulting in less high quality food for higher trophic levels as a result of re-oligotrophication.
A novel Bass-type model for product life cycle quantification using aggregate market data
Guo, X. - \ 2014
International Journal of Production Economics 158 (2014). - ISSN 0925-5273 - p. 208 - 216.
word-of-mouth - novelty seeking - consumer durables - personality-trait - diffusion-models - packaged goods - repeat model - long-term - behavior - growth
Product LifeCycle(PLC)isawidelyacceptedconceptthathasbeengivensignificant attentionin operations managementandmarketingliterature.However,itsquantification remainsamajor challenge. ThisstudyaimstodevelopauniqueandoriginalanalyticalmodelforquantifyingPLCsusing aggregatemarketdata.TheBassdiffusionmodelisusedtoforecastconsumers' first purchasesofthe product. Next,theNovelty–LoyaltyBasedConsumerUtility(NLBCU)theory,whichhasaconfirmed neuropsychologicalbasis,isusedtomodelrepeat(orreplacement)purchases.Theuniquecontribution of thisworkisthatitsynthesizestheprevailinginnovationdiffusiontheoryandtheNLBCUtheoryto provideadistinct,dynamicandendogenousperspectiveonconsumerpurchasingbehavioracrossthe entire PLC.Themodel'sadvantagesincludeitssimplemathematicalformulation,itsminimaluseofdata and itsharmonywiththepredominatingideasoftheinnovationdiffusionliterature.Throughsimulation studies andempiricalinvestigations,thedescriptivepoweranddata-fitting performanceofthemodel are demonstrated.
Diversity-stability relationships in plant communities of contrasting habitats
Kuiters, A.T. - \ 2013
Journal of Vegetation Science 24 (2013)2. - ISSN 1100-9233 - p. 453 - 462.
species turnover - statistical inevitability - temporal variability - current knowledge - long-term - biodiversity - grassland - ecology - time - productivity
Questions To what extent are small-scale (
A comparative review of recovery processes in rivers, lakes, estuarine and coastal waters
Verdonschot, P.F.M. ; Spears, B.M. ; Feld, C.K. ; Brucet, S. ; Keizer-Vlek, H.E. ; Borja, A. ; Elliot, M. ; Kernan, M. ; Johnson, R.K. - \ 2013
Hydrobiologia 704 (2013)1. - ISSN 0018-8158 - p. 453 - 474.
large woody debris - long-term - stream restoration - climate-change - fresh-water - fish communities - marine systems - dam removal - ecological relationships - anthropogenic pressures
The European Water Framework Directive aims to improve ecological status within river basins. This requires knowledge of responses of aquatic assemblages to recovery processes that occur after measures have been taken to reduce major stressors. A systematic literature review comparatively assesses recovery measures across the four major water categories. The main drivers of degradation stem primarily from human population growth and increases in land use and water use changes. These drivers and pressures are the same in all four water categories: rivers, lakes, transitional and coastal waters. Few studies provide evidence of how ecological knowledge might enhance restoration success. Other major bottlenecks are the lack of data, effects mostly occur only in short-term and at local scale, the organism group(s) selected to assess recovery does not always provide the most appropriate response, the time lags of recovery are highly variable, and most restoration projects incorporate restoration of abiotic conditions and do not include abiotic extremes and biological processes. Restoration ecology is just emerging as a field in aquatic ecology and is a site, time and organism group-specific activity. It is therefore difficult to generalise. Despite the many studies only few provide evidence of how ecological knowledge might enhance restoration success.
New EU Legislation for risk assessment of GM food: no scientific justification for mandatory animal feeding trails
Kuiper, H.A. ; Kok, E.J. ; Davies, H.V. - \ 2013
Plant Biotechnology Journal 11 (2013)7. - ISSN 1467-7644 - p. 781 - 784.
long-term - varieties - maize
This commentary focuses on the potential added value of and need for (sub)-chronic testing of whole genetically modified (GM) foods in rodents to assess their safety. Such routine testing should not be required since, due to apparent weaknesses in the approach, it does not add to current risk assessment of GM foods. Moreover, the demand for routine testing using animals is in conflict with the European Union (EU) Commission's efforts to reduce animal experimentation. Regulating agencies in the EU are invited to respect the sound scientific principles applied to the risk assessment of foods derived from GM plants and not to interfere in the risk assessment by introducing extra requirements based on pseudo-scientific or political considerations
Multiwalled Carbon Nanotubes at Environmentally Relevant Concentrations Affect the Composition of Benthic Communities
Velzeboer, I. ; Peeters, E.T.H.M. ; Koelmans, A.A. - \ 2013
Environmental Science and Technology 47 (2013)13. - ISSN 0013-936X - p. 7475 - 7482.
macroinvertebrate community - manufactured nanoparticles - engineered nanomaterials - contaminated sediments - aquatic sediments - black carbon - long-term - toxicity - bioavailability - ecotoxicology
To date, chronic effect studies with manufactured nanomaterials under field conditions are scarce. Here, we report in situ effects of 0, 0.002, 0.02, 0.2, and 2 g/kg multiwalled carbon nanotubes (MWCNTs) in sediment on the benthic community composition after 15 months of exposure. Effects observed after 15 months were compared to those observed after 3 months and to community effects of another carbonaceous material (activated carbon; AC), which was simultaneously tested in a parallel study. Redundancy analysis with variance partitioning revealed a total explained variance of 51.7% of the variation in community composition after 15 months, of which MWCNT dose explained a statistically significant 9.9%. By stepwise excluding the highest MWCNT concentrations in the statistical analyses, MWCNT effects were shown to be statistically significant already at the lowest dose investigated, which can be considered environmentally relevant. We conclude that despite prolonged aging, encapsulation, and burial, MWCNTs can affect the structure of natural benthic communities in the field. This effect was similar to that of AC observed in a parallel experiment, which however was applied at a 50 times higher maximum dose. This suggests that the benthic community was more sensitive to MWCNTs than to the bulk carbon material AC.
Within-patch habitat quality determines the resilience of specialist species in fragmented landscapes
Ye, X. ; Skidmore, A.K. ; Wang, T. - \ 2013
Landscape Ecology 28 (2013)1. - ISSN 0921-2973 - p. 135 - 147.
metapopulation dynamics - population-dynamics - environmental variation - relative importance - isolation paradigm - extinction risk - effect size - long-term - heterogeneity - persistence
Patch geometry and habitat quality among patches are widely recognized as important factors affecting population dynamics in fragmented landscapes. Little is known, however, about the influence of within-patch habitat quality on population dynamics. In this paper, we investigate the relative importance of patch geometry and within-patch habitat quality in determining population dynamics using a spatially explicit, agent-based model. We simulate two mobile species that differ in their species traits: one resembles a habitat specialist and the other a habitat generalist. Habitat quality varies continuously within habitat patches in space (and time). The results show that spatial variation in within-patch quality, together with patch area, controls population abundance of the habitat specialist. In contrast, the population size of the generalist species depends on patch area and isolation. Temporal variation in within-patch quality is, however, less influential in driving the population resilience of both species. We conclude that specialist species are more sensitive than generalist species to within-patch variation in habitat quality. The patch area-isolation paradigm, developed in metapopulation theory, should incorporate variation in within-patch habitat quality, particularly for habitat specialists.
Spatio-temporal dynamics of the invasive plant species Elytrigia atherica on natural salt marshes
Veeneklaas, R.M. ; Dijkema, K.S. ; Hecker, N. ; Bakker, J.P. - \ 2013
Applied Vegetation Science 16 (2013)2. - ISSN 1402-2001 - p. 205 - 216.
sea-level rise - long-term - vegetation changes - elymus-athericus - tidal marshes - wadden sea - deposition - gradient - impact - opportunities
Question In the past decades, the tall native invasive grass, Elytrigia atherica, has been increasing in frequency and dominance on salt marshes along the Wadden Sea coast. Is this rapid expansion an outcome of natural succession or is it driven by anthropogenic eutrophication resulting from atmospheric deposition? Location Salt marshes on four back-barrier islands, Wadden Sea on the coast of the Netherlands and Germany. Methods We used a combination of time series of vegetation maps and chronosequence data of four naturally developed salt marshes to address our questions. These salt marshes have not been grazed by livestock or subject to other management regimes. By comparing development within and between four different salt marshes, we were able to study the spatial and temporal dynamics of the community dominated by E. atherica on natural salt marshes. Results The expansion rate of the E. atherica community was highest on young salt marshes (up to 30yr old) with vertical accretion rates of 0.35cm center dot yr1. The rate of expansion decreased on older marshes and the direction reversed, becoming negative, on the oldest marshes (around 90yr old), which have no vertical accretion and are under waterlogged conditions. Conclusions The expansion of E. atherica on natural, back-barrier islands along the Wadden Sea coast is more influenced by the age of the salt marsh and patterns in vertical accretion of soil than by uniformly spread atmospheric deposition.
Beyond the Plankton Ecology Group (PEG) Model: Mechanisms Driving Plankton Succession
Sommer, U. ; Adrian, R. ; Domis, L.D. ; Elser, J.J. ; Gaedke, U. ; Ibelings, B. ; Jeppesen, E. ; Lürling, M.F.L.L.W. ; Molinero, J.C. ; Mooij, W.M. ; Donk, E. van; Winder, M. - \ 2012
Annual Review of Ecology, Evolution, and Systematics 43 (2012)7. - ISSN 1543-592X - p. 429 - 448.
phytoplankton spring bloom - fresh-water phytoplankton - critical depth hypothesis - clear-water - long-term - lake constance - climate-change - population-dynamics - food quality - deep lake
UV/H2O2 treatment can be part of the process converting surface water to drinking water, but would pose a potential problem when resulting in genotoxicity. This study investigates the genotoxicity of samples collected from the water treatment plant Andijk, applying UV/H2O2 treatment with an electrical energy dose of 0.54 kWh/m(3) and a H2O2 dose of 6 mg/l. Genotoxicity was tested in vitro using the Ames and Comet assay. All samples showed negative results. Samples were also tested in in vivo genotoxicity tests in Eastern mudminnow fish (Umbra pygmaea) by a sister chromatid exchange (SCE) and a Comet assay. No significant increases in SCEs were observed, but gill cells isolated from fish exposed to water obtained immediately after UV/H2O2 treatment and to Lake IJsselmeer water showed significantly increased DNA damage in the Comet assay. All other samples tested negative in this Comet assay. This indicates that DNA damaging compounds may result from the UV/H2O2 treatment, but also that these can be efficiently eliminated upon granular activated carbon (GAC) treatment of the water. It is concluded that when combined with this subsequent GAC treatment, UV/H2O2 treatment for the production of drinking water from surface water is not of concern with respect to genotoxicity.
Rarity in large data sets: Singletons, model values and the location of the species abundance distribution
Straatsma, G. ; Egli, S. - \ 2012
Basic and Applied Ecology 13 (2012)4. - ISSN 1439-1791 - p. 380 - 389.
null hypothesis - long-term - richness - communities - dynamics - area
Species abundance data in 12 large data sets, holding 10 × 103 to 125 × 106 individuals in 350 to 10 × 103 samples, were studied. Samples and subsets, for instance the summarized data of samples over years, and whole sets were analysed. Two methods of the binning of data, assigning abundance values to classes for histograms, have been applied in the past: bins of equal size and bins of exponentially increasing size (‘octaves’). A hump in a histogram with exponential bins does not represent a mode of primary, non-transformed abundance values, but of log transformed abundance values. A proper interpretation of the hump is given. Moreover, the extrapolation to the left of a histogram with exponential bins, below an abundance of unity, lifting a ‘veil’, hiding species present in the community but absent from the sample, is rejected. The literature is confusing at these points and, as a result, prevents a proper view on the species abundance distribution. Applying bins of equal size, modal values equalled or approached unity. The number of singletons increased with sample size in some data sets but decreased in others. However, singletons remain present in large samples, subsets or sets, in agreement with the results on modal values. The relatively high number of singletons in small samples is no artefact of undersampling. The mode at unity, that is at the left end of the species abundance distribution, independent of scale (sample, subset or set), is an important statistical property of the species abundance distribution. Our results may have implications for theory development in community ecology: the selection and/or development of an accurate species abundance model, and, connected to this, the formulation of improved assembly rules, and the selection and/or development of more precise species richness estimators.
Declines amongst breeding Eider Somateria mollissima numbers in the Baltic/Wadden Sea flyway
Ekroos, J. ; Fox, A.D. ; Christensen, T.K. ; Cervencl, A. - \ 2012
Ornis Fennica 89 (2012). - ISSN 0030-5685 - p. 81 - 90.
population-dynamics - spring migration - wadden sea - long-term - age
We report on the status of theBaltic/Wadden Sea flyway Eider population based on trends in breeding and wintering numbers throughout the region, supplemented by changes in the sex ratio and proportion of young Eiders as monitored in the Danish hunting bag. At the flyway scale, total numbers of breeding pairs decreased by 48% during 2000–2009, after relatively stable breeding numbers in 1991–2000. The majority of the population nest in Finland and Sweden,where the number of breeding pairs has halved over the same period. After initial declines in winter numbers between 1991 and 2000, during 2000–2009, national wintering numbers increased in the Baltic Sea, but decreased in the Wadden Sea. The annual proportion of adult females in the Danish hunting bag data de creased from ca.45%(1982) to ca.25%(2009) and simultaneously the proportion of firstwinter birds fell from ca. 70% to ca. 30%, indicating dramatic structural changes in the Danish wintering numbers. These results suggest that the total flyway populationwill experience further declines, unless productivity increases and the factors responsible for decreasing adult female survival are identified and ameliorated.We discuss potential population drivers and present some recommendations for improved flyway-levelmonitoring and management of Eiders.
Did tillage erosion play a role in millennial scale landscape development?
Baartman, J.E.M. ; Temme, A.J.A.M. ; Schoorl, J.M. ; Braakhekke, M.H.A. ; Veldkamp, A. - \ 2012
Earth Surface Processes and Landforms 37 (2012)15. - ISSN 0197-9337 - p. 1615 - 1626.
land-use change - river drainage-basin - coon creek basin - soil-erosion - agricultural land - sediment yield - long-term - mediterranean region - rainfall variability - climatic variability
Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to the ~250¿km2 Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale.
Evapotranspiration of deforested areas in central and southwestern Amazonia
Randow, R.C.S. von; Randow, C. ; Hutjes, R.W.A. ; Tomasella, J. ; Kruijt, B. - \ 2012
Theoretical and Applied Climatology 109 (2012)1-2. - ISSN 0177-798X - p. 205 - 220.
large-aperture scintillometer - net ecosystem exchange - tropical deforestation - surface conductance - sensible heat - water-vapor - rain-forest - long-term - pasture - fluxes
Considering the high rates of evapotranspiration of Amazonian forests, understanding the impacts of deforestation on water loss rates is important for assessing those impacts on a regional and global scale. This paper quantifies evapotranspiration rates in two different pasture sites in Amazonia and evaluates the differences between the sites. In both places, measured evapotranspiration varies seasonally, decreasing during the dry season. The decrease is higher at the southwestern Amazonia site, while at the central Amazonia site, the decrease is less pronounced. During the dry season, average values of evapotranspiration are around 2.2¿±¿0.6 mm day-1 in central Amazonia and 2.4¿±¿0.6 mm day-1 in southwestern Amazonia, while during the wet season, those values are 2.1¿±¿0.6 mm day-1 in central Amazonia and 3.5¿±¿0.8 mm day-1 in southwestern Amazonia. On an annual basis, the pasture in southwestern Amazonia has higher evapotranspiration than in central Amazonia. We conclude that the main reason for this difference is the lower available energy in the wet season at the central Amazonian site, combined with a lower leaf area index at this site during the whole year. Still, the evapotranspiration is significantly controlled by the vegetation, which is well coupled with the local moisture conditions in the dry season
Is there a decline in marine phytoplankton?
McQuatters-Gollop, A. ; Reid, P.C. ; Edwards, M. ; Burkill, P.H. ; Castellani, C. ; Batten, S. ; Gieskes, W. ; Beare, D.J. ; Bidigare, R.R. ; Head, E. ; Johnson, R. ; Kahru, M. ; Koslow, J.A. ; Pena, A. - \ 2011
Nature 472 (2011)7342. - ISSN 0028-0836 - p. E6 - E7.
long-term - northeast atlantic - ocean - chlorophyll - plankton - biomass - variability - trends - sea
Chapter Three - From Natural to Degraded Rivers and Back Again: A Test of Restoration Ecology Theory and Practice
Feld, C.K. ; Birk, S. ; Bradley, D.C. ; Hering, D. ; Kail, J. ; Marzin, A. ; Melcher, A. ; Nemitz, D. ; Pedersen, M.L. ; Pletterbauer, F. ; Pont, D. ; Verdonschot, P.F.M. ; Friberg, N. - \ 2011
Advances in Ecological Research 44 (2011). - ISSN 0065-2504 - p. 119 - 209.
large woody debris - small dam removal - low-head dam - regulated california river - stream habitat restoration - fish community structure - south-eastern australia - fresh-water ecosystems - sand-bed stream - long-term
Extensive degradation of ecosystems, combined with the increasing demands placed on the goods and services they provide, is a major driver of biodiversity loss on a global scale. In particular, the severe degradation of large rivers, their catchments, floodplains and lower estuarine reaches has been ongoing for many centuries, and the consequences are evident across Europe. River restoration is a relatively recent tool that has been brought to bear in attempts to reverse the effects of habitat simplification and ecosystem degradation, with a surge of projects undertaken in the 1990s in Europe and elsewhere, mainly North America. Here, we focus on restoration of the physical properties (e.g. substrate composition, bank and bed structure) of river ecosystems to ascertain what has, and what has not, been learned over the last 20 years. First, we focus on three common types of restoration measures—riparian buffer management, instream mesohabitat enhancement and the removal of weirs and small dams—to provide a structured overview of the literature. We distinguish between abiotic effects of restoration (e.g. increasing habitat diversity) and biological recovery (e.g. responses of algae, macrophytes, macroinvertebrates and fishes). We then addressed four major questions: (i) Which organisms show clear recovery after restoration? (ii) Is there evidence for qualitative linkages between restoration and recovery? (iii) What is the timescale of recovery? and (iv) What are the reasons, if restoration fails? Overall, riparian buffer zones reduced fine sediment entry, and nutrient and pesticide inflows, and positive effects on stream organisms were evident. Buffer width and length were key: 5–30 m width and > 1 km length were most effective. The introduction of large woody debris, boulders and gravel were the most commonly used restoration measures, but the potential positive effects of such local habitat enhancement schemes were often likely to be swamped by larger-scale geomorphological and physico-chemical effects. Studies demonstrating long-term biological recovery due to habitat enhancement were notable by their absence. In contrast, weir removal can have clear beneficial effects, although biological recovery might lag behind for several years, as huge amounts of fine sediment may have accumulated upstream of the former barrier. Three Danish restoration schemes are provided as focal case studies to supplement the literature review and largely supported our findings. While the large-scale re-meandering and re-establishment of water levels at River Skjern resulted in significant recovery of riverine biota, habitat enhancement schemes at smaller-scales in other rivers were largely ineffective and failed to show long-term recovery. The general lack of knowledge derived from integrated, well-designed and long-term restoration schemes is striking, and we present a conceptual framework to help address this problem. The framework was applied to the three restoration types included in our study and highlights recurrent cause–effect chains, that is, commonly observed relationships of restoration measures (cause) and their effects on abiotic and biotic conditions (effect). Such conceptual models can provide useful new tools for devising more effective river restoration, and for identifying avenues for future research in restoration ecology in general.
Comparing demersal fish assemblage between periods of contrasting climate and fishing pressure
Hofstede, R. ter; Rijnsdorp, A.D. - \ 2011
ICES Journal of Marine Science 68 (2011)6. - ISSN 1054-3139 - p. 1189 - 1198.
north-sea - species-richness - community structure - atlantic-ocean - marine fishes - long-term - diversity - trends - temperature - populations
Fish communities are dynamic and their structure is known to change over time. Traditionally, these changes were considered to be fisheries-induced, but recent analyses also suggest that global warming could affect the distribution, abundance, and assemblage composition of marine fish. However, disentangling the effects of fisheries and those resulting from climate change is difficult, because both potential drivers act simultaneously. In our study, we distinguished between the effects of fisheries and climate change on the fish assemblage of the southern North Sea by comparing survey catch data for that region during four unique periods throughout the past century, characterized by (i) low fishing pressure during a cold period (1902–1908), (ii) low fishing pressure during a warm period (1950–1956), (iii) high fishing pressure during a cold period (1978–1984), and (iv) high fishing pressure during a warm period (2002–2008). Our analysis indicates that the demersal fish community in the southern North Sea has changed in response to changes in both climate and fishing pressure. Our results suggest both a relatively higher richness of Lusitanian (warm-favouring) species compared with boreal (cool-favouring) species, and a lower mean body size of the fish community during times of warming, independent of fishing pressure
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