De rol van de berk bij herstel en beheer van hoogveen : gecombineerde resultaten van "Vervolg OBN hoogveenonderzoek & effecten van berkenopslag en dichtheid op de hoogveenvegetaties behorende tot het natte zandlandschap

Op veel plaatsen in Nederland wordt gepoogd hoogvenen te herstellen. Van oudsher waren die hoogvenen voor een groot deel vrijwel boomloos. Tegenwoordig echter is in bijna alle hoogveengebieden, zowel met levend hoogveen als met afgetakeld hoogveen, sprake van veel berkenopslag als gevolg van verdroging en stikstofdepositie. Inmiddels worden grote inspanningen gepleegd om deze oorzaken van de ‘verberking’ te verminderen. Daarmee alléén zijn de berken zelfs nog lang niet altijd verdwenen. De vraag die daarbij steeds opdoemt is: hoe zinvol is het om berken te verwijderen om hoogveenregeneratie te bevorderen en levend hoogveen te behouden? Het voorliggend rapport levert een belangrijke bijdrage aan een genuanceerd antwoord op deze vraag; bestrijding van berken blijkt veelal zinvol, maar niet altijd

Peatlands and the carbon cycle: from local processes to global implications - a synthesis

Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15-30% of the world's soil carbon ( C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change. The main drivers controlling most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange ( NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors. Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO2 and CH4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales

Hoogveenherstel in Nederland: meer dan een droom

Vernatten, de belangrijkste herstelmaatregel in hoogveenrestanten, heeft niet altijd het gewenste effect. Waarom dat zo is, is grotendeels nog onbekend. De auteurs beargumenteren dat recente inzichten uit empirische en experimentele studies in hoogveenherstelprojecten moeten worden gebruikt om de bestaande theoretische modellen uit te breiden, om deze vervolgens te kunnen gebruiken in het ontwikkelen van effectieve, gebiedspecifieke herstelplannen. Hierdoor kan de droom van zelfregulerende hoogvenen in Nederland wellicht op niet al te lange termijn werkelijkheid worden

Plant functional type affects composition and degradation of peat along a temperature gradient

Peatlands, storing significant amounts of carbon (C), are extremely vulnerable to climate change. Indirect effects of climate change are projected to lead to a growing dominance of vascular plants in moss dominated peatlands with unknown effects on peat decomposition. In this study we investigated the influence of different plant functional types (moss, graminoid, shrub) on peat composition and decomposition. Peat cores (20 cm depth) and plant material (Sphagnum sp., Calluna vulgaris, Eriophorum vaginatum) of two ombrotrophic moss dominated peatlands on a temperature gradient in the Italian Alps were analyzed. Peat cores were taken under shrub and graminoid coverage at the low temperature site (Low-T-Site) and the high temperature site (High-T-Site). We used carbon to nitrogen ratios, C-13 and N-15 and pyrolysis gas chromatography/mass spectrometry (py-GC/MS) to assess the influence of vascular plants on peat composition and degradation. In these moss dominated peatlands, methoxyphenols from lignin indicated highest contribution of vascular plant material at 2-5 cm under shrub coverage and 5-12 cm depth under graminoid coverage. Increasing C-13 ratios with depth could be related to increasing peat decomposition. This increase was higher for peat cores under graminoid coverage than under shrub coverage. Furthermore, the enrichment in C-13 with depth was higher at the High-T-Site than at the Low-T-Site. More detailed effects of plant functional type on peat degradation were established using species specific pyrolysis products as e.g. methoxyphenols from lignin (marker compounds for vascular plants) and 4-isopropenylphenol reflecting degradation of the sphagnum peat matrix. Comparing depth records of these molecular parameters indicated higher peat degradation in the presence of graminoids compared to shrubs and at the High-T-Site compared to the Low-T-Site confirming conclusions from C-13 data. Consequently, plant functional types are very likely to influence peat composition and degradation especially at elevated temperatures, while the projected vegetation shifts from graminoids to shrubs should counteract increasing peat degradation with increasing temperature. Therefore, vegetation shifts in response to climate change may play a crucial role in determining peat composition and degradation

Hoogveen en klimaatverandering in Nederland

Voor de instandhouding en ontwikkeling van hoogveen zijn het neerslagoverschot, de temperatuur en de positie in het landschap belangrijk. Gunstige ontwikkelingen doen zich voor in gebieden waar het (actieve) hoogveen water uit zijn omgeving ontvangt. De landelijke instandhoudingsdoelen voor Natura 2000-habitattype Actieve hoogvenen kunnen waarschijnlijk ook onder het klimaatscenario W+ worden gerealiseerd: behoud van kwaliteit en oppervlakte zijn kansrijk en verbetering van kwaliteit en uitbreiding van oppervlakte zijn mogelijk. Voorwaarden hierbij zijn een optimale waterhuishouding. Dat wil zeggen voldoende hoge grondwaterstanden in de zandondergrond en de veenbasis in combinatie met een waterondoorlatende (veen)laag en/of de toevoer van lokaal grondwater. Om hoogvenen op de lange termijn in Nederland te behouden onder het W+- scenario zijn waterhuishoudkundige maatregelen nodig, zoals de aanleg en inrichting van bufferzones en compartimenten en/of door het bevorderen van kwel

Dissolved organic matter indicates changes in temperature and plant communities in peatlands

Though northern peatlands cover only 3 % of the land surface they count as one of the largest terrestrial organic C pools. This huge C pool is threatened by increasing temperatures, related microbial degradation and indirect effects of climate change leading to vascular plant dominance over sphagnum mosses and a shift from graminoids to shrubs. Effects of these changes in vegetation on peat degradation are unknown. Dissolved organic matter (DOM) as an important component of the C cycle in peatlands might be used as a sensitive indicator of enhanced peat degradation. Furthermore, peatlands are the major source of DOM in many surface waters and understanding the mechanisms of peat degradation will help to elucidate the reasons for the ongoing trends of increasing concentrations of dissolved organic carbon (DOC) in surface waters. In this study we aimed to determine effects of temperature and plant functional types (PFT: graminoids, shrubs) on amounts and composition of DOM allowing conclusions about ongoing changes in peat degradation. We selected two ombrotrophic peatlands in the Italian Alps, reflecting a temperature gradient where we manipulated the vascular plant cover by selective clipping. On the established plant functional type plots we collected DOM directly after plant removal and during the following seasons over a period of one year. Besides DOC concentrations we determined DOM composition by C-13 of DOC and UV and fluorescence spectroscopy. The short term response (2-24h) of DOM to the plant clipping enabled us to estimate the C input of vascular plants via roots. The medium to long term data showed a clear relation of DOM to the temperature gradient and the PFT. All in all our results indicated a substantial contribution of the roots from vascular plants to DOM in peatlands. The release of DOM from peat clearly increased with temperature and vascular plant biomass. The difference between graminoids and shrubs seems to be marginal. We conclude that higher temperatures and greater vascular plant biomass result in increasing peat degradation as one likely reason for increasing DOC concentrations in many surface waters across Europe and North America

Stikstofdepositie, eutrofiëring en nutriëntenkringloop

Venen bestaan bij de gratie van een positieve balans tussen productie en afbraak van organisch materiaal. In hoogveen zijn veenmossen cruciaal in dit verband. Hogere planten komen echter in het gedrang. Binnen het hoogveen-onderzoek zijn de effecten van stikstof op de verschillende plantenniveau's onderzoch

On the Frontier of Assyria: Excavations at Tell Sabi Abyad, 1991

Wetensch. publicatieFaculty of Archeolog

The 2011 Philip C. Jessup International Law

The State of Rigalia and the State of Ardenia submit the present dispute concerning the Zetian Provinces to the International Court of Justice by Special Agreement, dated 5 May 2010, pursuant to article 40(1) of the Statute of the International Court ofJustice