Dr. ir. M.M. (Mariet) Hefting

Dr. ir. M.M. (Mariet) Hefting

Ecology and Biodiversity
030 253 7441


TEA BAG INDEX (TBI) Decomposition proxies to generate a global soil functioning map

Together with Joost Keuskamp, Bas Dingemans, Judith Sarneel and Taru Lethinen we developed a decomposition proxy, using commercially available tea bags. This proxy enables us to study decomposition rates in a large number of contrasting ecosystems and biomes across the world. Uniquely, this research will be done with the explicit participation of volunteers worldwide, putting this project potentially among the largest research networks of scientists and non- scientists ever.

The newly developed tea bag proxy will provide us with conceptually new integrative parameters describing this "decomposition matrix" or more generally "soil functioning" as indicators of soil functioning are classically provided by soil respiration measurements or enzyme activities strongly related to decomposition. The tea bag proxy has much potential as an integrative measure for soil functioning as this "functioning" cannot be measured directly, but is inferred by measuring soil attributes or properties that serve as indicators. Changes in these indicators can be used to determine whether soil functioning or soil quality is improving, stable, or declining with changes in environmental conditions or soil management.

Reading tea leaves for soil carbon sequestration


Two contrasting tree cemeteries (on nutrient poor sand and nutrient rich clay soil) were setup to study coarse wood decomposition of different tree species. This huge common garden approach in forest plots, initiated by Prof. Hans Cornelissen, together with an interdisciplinary team of researchers including myself. Other people joining this project are microbiologist (Dr. Annemieke van der Wal and Wietse de Boer), wood anatomy and forest ecologists (Dr. Ute Sass- Klaassen, Dr. Rene Klaassen, Frank Sterck and Dr. Lourens Poorter) and entomologists (Dr. Matty Berg). In the first months of 2012 we started the incubation of 120 big (dead) trees cut up into 600 logs of 25 cm diameter and 1 m length. Over the course of 15 years we will harvest and sample logs for decay dynamics, chemical changes, colonization by microbes, mosses and invertebrates. I will study the chemical changes (e.g. shifts in lignin types) of different tree species over time; perform multiple organ comparison and study the development of soil organic matter profiles below decomposing logs.

Photo: Gregoire Freschet

Cornelissen JHC., Sass-Klaassen U., Poorter L.,van Geffen K., van Logtestijn RSP.,van Hal J., Goudzwaard L.,Sterck F.J.,Klaassen RKWM., Freschet GT., van der Wal A, Eshuis H., Zuo J., de Boer W.,Lamers T.,Weemstra M., Cretin V.,Martin R.,den Ouden J., Berg MP., Aerts R., Mohren GMJ., Hefting MM. (2012) AMBIO 41: 231-3245

BNI Project

Study on the biological nitrification inhibition by characteristic plant species from Matgras sward vegetation in collaboration with Dr. Nina Smits (Alterra) and Prof. Riks Laanbroek (NIOO).


To study the interaction effect between warming and N deposition on soil organic carbon dynamics we run a long term field manipulation study, fertilising naturally ambient and wetland patches in a geothermal area in Iceland.


Identification of hot spots and hot moments of nitrous oxide emission in riverine ecosystems as a basis for reliable estimates of emissions at the landscape level

Recent changes in flood protection strategies, allowing a more natural situation by the creation of water retention zones and riparian wetlands may have positive effects on stream water quality. High nitrate concentrations in the groundwater and floodwater may however create hot spots and hot moments of nitrous oxide N2O emission in these wetlands. Until now the number of studies on N2O emission from (semi) aquatic systems is very limited and it is generally agreed that our current knowledge on N2O emissions from riparian zones is still not sufficient to evaluate the existing IPCC (Intergovernmental Panel on Climate Change) emission factor for indirect emissions. In this research we study N2O emission rates from wetlands at different stream orders, addressing landscape scale N2O emissions from N–loaded semi-natural riverine systems. We expect that N transformation by N-loaded riparian zones may result in a significant increase of greenhouse gas emission. Until now, only the beneficial function of wetlands on water quality improvement has received a lot of attention. To perform a full assessment, however, we have to evaluate the precise consequences of water pollution and N2O emission to determine the environmental risks. Results from this proposed research will contribute to the knowledge base for this future risk assessment.

LOSS Living on Soft Soils 12-06-2019 tot 31-12-2025
Algemene projectbeschrijving

Bodemdaling in Nederland is een actueel en complex probleem in stad en poldergebieden, waarvoor toenemend aandacht bestaat. Oude oplossingen werken niet meer goed. Er wordt geïnvesteerd in het vlakdekkend meten en modelleren van de bodemdaling, en nieuwe omgangsvormen zullen worden ontwikkeld, zodat beslissingen over maatregelscenario’s zijn gebaseerd op feitelijke kennis.

2e geldstroom - NWO NWA consortia 2018
Overige projectleden
  • Gilles Erkens (Deltares)
  • Bernardien Tiehatten (LOSS)
  • Prof. Ramon Hanssen (TU Delft)
  • J.G. Rots (TU Delft)
  • K.G. Gavin (TU Delft)
  • Prof. Ekko van Ierland (WUR)
  • Prof. Hans-Peter Weikard (WUR)
  • Jan Willem van Groenigen (WUR)
  • Jan JH van den Akker (WUR)
  • Dr. Mandy Korff (TUD
  • Deltares)
  • Dr. Peter Fokker (TNO Geological Survey of the Netherlands)
UU BioCliVE 01-06-2017 tot 12-12-2030
Algemene projectbeschrijving

The Utrecht University Biodiversity and Climate Variability Experiment, UU BioCliVE, is an experiment manipulating plant diversity and future precipitation scenarios to examine how biological diversity can provide us with natural insurance against climate change.


1e geldstroom
Overige projectleden
  • Open for collaborations
Drought Experiment 01-04-2015 tot 30-10-2026
Algemene projectbeschrijving

We established a new climate change experiment manipulating a major driver of change within grassland - drought. We exclude rainfall with rainout shelters such that precipitation is reduced by a constant percentage. This experiment contributes to the Drought-Net International Drought Experiment and to the NPKD Network.


1e geldstroom
Afgesloten projecten
Water, Klimaat en Delta's van de toekomst 01-02-2018 tot 31-12-2021
Algemene projectbeschrijving

Delta areas, as unique ecosystems, are among the most densely populated areas in the world. Deltas are under increasing human and natural pressure. Future global change, with intensifying human activity, increasing weather extremes, changing river flow regimes and accelerated sea-level rise, will put deltas and their societies at increasing risk.

We therefore need deltas that are resilient to natural hazards, make sustainable use of natural resources, have healthy environmental conditions, and are able to cope with future climate change and sea-level rise. It is now the moment for science and society to find sustainable pathways into such future. This requires addressing the wide variety of processes - physical, chemical, biological, institutional and socio-economic – that interact in deltas in an integrated approach.

In the hub Water, Climate and Future Deltas researchers from varying disciplines at Utrecht University cooperate with external partners to design and evaluate pathways to sustainable delta development. The hub will provide policy makers and delta managers with the essential scientific basis for informed decision-making on pathways towards sustainable deltas.


1e geldstroom Faculteit Geowetenschappen, Universiteit Utrecht
Overige projectleden
  • Dr. Marjolijn Haasnoot - Deltares
  • Dr. Gilles Erkens - Deltares
  • Drs. Henk van Hardeveld - HDSR
Living on subsiding peat soils in coastal zones 01-02-2015 tot 04-10-2016
Algemene projectbeschrijving

This is a pilot project of the UU research focus area Future Deltas. We study subsidence due to peat compaction and oxidation in built-up areas in three villages in the central part of the Rhine-Meuse delta, The Netherlands. Built-up areas are typically avoided because sealed surfaces and restricted property access hamper investigation the subsurface. These areas are however heavily impacted by land subsidence, and therefore, with an increasing number of people living on peaty soils, understanding processes leading to subsidence is critical. 

We made cross sections based on logged borehole data to reveal the lithological composition of the Holocene sequence underlying the villages. At selected sites, representing different land uses and subsurface composition, cores were extracted to determine current compaction conditions of peat layers, based on high-resolution bulk density measurements. Oxidation conditions of selected peat samples were determined based on respiration measurements. Derived information on compaction and oxidation conditions, along with data from previous studies, allowed to assess the relative contribution of both processes under different settings regarding loading and groundwater level. In addition, we assessed the potential for future land subsidence at our study sites under different development scenarios. Ultimately, insights derived from this study can be used for developing sustainable management strategies for inhabited organo-clastic coastal zones worldwide.

1e geldstroom Funded by Future Deltas

PhD-PROJECTS (of which I am the co-promotor)

  • Drs. Bas van de Riet. Rewetting peat meadows: possibilities and constraints for new nature Research in the framework of the ICES-KIS project 'Waarheen met het Veen? (2006-2012)
  • Drs. Joost Keuskamp. Mangrove wastewater loading and carbon sequestration (2008-2012)
  • Drs. Bas Dingemans. The effects of global warming and nitrogen enrichment on the decomposition of recalcitrant organic matter; consequences for long-term carbon storage (2009-2013)
  • Drs. Karlijn Brouns Climate effects on decomposition in drained peat meadows: implications for peat subsidence and water quality (2009-2013)
  • Drs. Suzanne Rotthier (WUR/OBN) Effects of sand deposition on the development of riverine levee grasslands (2010-2014)
  • Anne Daebler MSc (NIOO) NICE Archeal and bacterial nitrification as response to nitrogen fertilization and warming on Iceland. (2009-2013)
  • Juan Zuo MSc. linking invertebrate and bryophyte diversity and composition to wood decay rates and chemistry of different tree species (2011-2016)

PhD students supervised till doctorate

  • Smits N.A.C. Restoration of nutrient –poor grasslands in Southern Limburg (2010).
  • Heuvel, van den R.N. Nitrous oxide emission hotspots and acidic soil denitrification in a riparian buffer zone (2010).


Prof. dr. Hans Cornelissen (VU) LOGLIFE project

Taru Lethinen (Tea Bag Index )Devision of Science and Research, University of Iceland

Dr. Paul Bodelier (NIOO) collaboration on methane emission and consumption measurements in Dutch floodplain areas.

Dr. Judith Sarneel (NIOO) Tea bag index collaboration

Prof. dr Lex Bouwman (NMP/ GEO-UU) and Prof dr. Jasper Griffioen (DELTARES/GEO-UU) collaboration on world wide nitrous oxide emission estimates from riparian zones

In the Flevopolder, Prof. K. Kalbitz and Dr. C. Cerli will study biomarkers in soil profiles under different tree species to determine the origin of the sequestered carbon. We will perform our soil organic matter and decomposition measurements in the same plots and profiles. Data integration will strengthen the overall picture of carbon dynamics and will help to validate our functional plant trait approach.

Dr. Gilles Pinay, University of Rennes I, ECOBIO Rennes Cedex, France.

Prof Dennis Whigham, Smithonian Institute, Smithonian Environmental Research Centre. Edgewater, Maryland, USA

Dr. T. Thordarson, University of Iceland, Iceland (on global warming effects on wetland carbon sequestration, field work and meetings in Hengill Mountains, Hveragerdi, Iceland)