Research interests

General Research Interests

My research interests lie with biogeochemistry in general and in particular the fate of natural and anthropogenic compounds in terrestrial ecosystems. How does the chemistry of soils and sediments regulate the transportation, transformation and preservation/degradation of compounds in those systems? How is this chemistry, and thereby the fate of compounds, altered by natural or human-induced change? How can we measure or monitor such changes? And, most importantly, what are the implications for the functioning of ecosystems?

Having a background in environmental chemistry and soil science, I use applied analytical chemistry as my primary tool to tackle the questions at hand. In this respect I have a special interest in applying new analytical chemical techniques to soil systems. However, I realize that analytical chemistry alone does not suffice to understand the intricacies of terrestrial ecosystems in their full complexity. Therefore, I am a strong proponent of a multidisciplinary approach and always perform my research in cooperation with specialists from other groups, such as computational scientists, vegetation experts and (paleo-) ecologists. I have noticed that such collaboration, including the application of methods and approaches from other disciplines to soil chemical problems, often leads to surprising solutions to puzzles that at first appeared unsolvable.

A recent example: the RUFLE Project

One of my most recent research projects is the Reconstruction of the Upper Forest Line in Ecuador or RUFLE Project, which ended with a final workshop in Loja, Ecuador in 2009.

Within the RUFLE Project I fulfilled the role of researcher as well as of scientific coordinator. Below I present a detailed description of what RUFLE entailed as an example of my recent work.

Recent keynote lecture about the RUFLE project

Another presentation

Background

The higher parts of the Ecuadorian Andes consist of fragile ecosystems of high biodiversity that are characterized by endemic páramo grasslands and montane cloud forests. Where nowadays cloud forests are mainly found in scattered patches, they are believed to have once covered much larger stretches of mountain to much higheraltitudes. The reason for the reduction of cloud forest coverage, including a depression of the upper forest line, is sought in a response to natural climatic change and human interference in the form of burning and clear-cutting. Whereas most researchers agree that the upper forest line in the Ecuadorian Andes used to be higher than it is today, there was no consensus on how much higher it would have been in the absence of human interference. This was hindering efforts/plans to reconstruct the upper forest line in a sustainable manner.

The RUFLE project resolved the question of to what altitude the cloud forest would have extended in the research area the Ecuadorian Andes in the absence of disturbance. Thereby, it provides a guideline for the reconstruction of the upper forest line in other Andean ecosystems. In addition, it gave answers to the more fundamental question what part of the dynamics of the upper forest line was caused by human interference and what part by natural changes in climate. As such, RUFLE has proven not only to be of interest to local Ecuadorian scientists and policy makers, but also provided valuable tools to predict the response of the upper forest line in general to climaticchange.

Research area

As a research area for the RUFLE project two locations in the province of Carchi in the northern Ecuadorian Andes were chosen. The first location is the National Reserve of Guandera located near San Gabriel on the Eastern Cordillera. It is one of the last remaining relatively pristine areas in the sense that it still contains large areas of what is believed to be relatively undisturbed cloud forest.

The second location is the Ecological Reserve of ElAngel located at approximately the same longitude on the Western Cordillera. This area is and has been burdened with extensive human influence to the pointwhere only a few isolated patches of forest remain.Both areasare located on the`dry' inner slopes of the inter andien valley as this is the area that has most heavily suffered from human influence and is of the greatest interest of local scientists and policy makers. The fact that both areas are in close proximity and subject to similar climate made a comparison of the results possible.

My research within the RUFLE project

An important reason why there was controversy about the position of the upper forest line in the Ecuadorian Andes is that no one ideal method existed to reconstruct it. Therefore, in this project a combination of several state-of-the-art research methods were combined, each providing a different piece of the puzzle. These approaches were:

• vegetation analysis;
  
• pollen analysis;
  
• 14 C and thermoluminescence dating;
  
• organic chemical biomarker analysis
  

The RUFLE program was subdivided into three projects. My project focused on the analysis of organic chemical biomarkers, in addition to combining the results from all approaches.

Organic chemical biomarkers consist of specific characteristic organic chemical plant components. Themain candidates for use in the current study are n-alkanes and n-alcohols from leaf wax lipids, which have an odd-over-even preference peaking in the C29-C31 region for the former and an even-over-odd preference peaking in the C24-C28 region for the latter. Reasons to select leaf wax lipids are the fact that they are relatively persistent against microbial alteration, especially in acidic soils. Also, in the case of the n-alkanes, the extent of degradation may be assessed by investigation of the presence of oxidation products. Furthermore, leaf wax lipids can be highly diagnostic, i.e. they may allow for distinction of plants at the species level and can easily be distinguished from microbial input. Other biomarkers that were investigated are lignin and terpentoids.

In addition to their potential of being highly specific, the advantage of using organic chemical biomarkers is that they are mainly deposited in-situ. This allows for a high spatial resolution. A disadvantage is the uncertainty about preservation and the fact that it is unique concentration patterns of otherwise ubiquitous compounds that constitute biomarkers instead of single plant-unique compounds. As a result, once in the soil the concentration patterns of biomarkers from various plants mix and disentangling the mixed signal into the individual past plant contributions is a major challenge. We were able to significantly advance science in this area by developing the VERHIB model capable of unraveling such mixed biomarker patterns from soils and sediments.

Future research directions

The new biomarker analysis technique I developed shows great potential to develop into a fully fledged, independent proxy for past vegetation dynamics. The implications are far reaching. Improved reconstructions of upper forest line dynamics will yield crucial information to calibrate and test models linking the effects of past and present climatechange to the altitudinal distribution of vegetation and vice versa. In addition, the new approach enables a much more detailed insight into impact of human interference on forest distribution, helping direct sustainable replanting efforts under the Kyoto protocol. It also greatly facilitates studies of the organic carbon cycle in terrestrial ecosystems by elucidatingthe fate of organic matter inputted via plant roots and leaves, thereby shedding light on the crucial question whether soils function as net source or sink of CO2 .

Therefore, I see it as an important future challenge is to further develop and apply the biomarker analysis technique. Main focus points will be  i) to establish the applicability of the technique in various other soil and sediment types, ii) to couple the technique to other proxies than fossil pollen analysis alone (e.g. stable carbon isotopes), and iii) to combine the technique with models that use vegetation dynamics to reconstruct past, present and future climate change.

I see elucidating the soils carbon cycle and the role of soils in the global carbon cycle, both of which are subject of fierce scientific debate, as another very exciting research opportunity. Again, in my view multi-disciplinarity is the only way forward here. It will be crucial to combine soil chemical investigations of carbon dynamics under climate change and increased occurrence of extreme meteorological events, with in-depth analysis of the role and response of belowground biodiversity and physical processes such as erosion.

However, my research interests do not lie exclusively with climate change. For instance, a very interesting application of biomarker analysis might be to unravel the fate of other component mixtures in soils or sediment. One could think of an application within forensic science, where it might be used to unravel mixtures of pollutants such as oils or flame retardants to manufacturer-specific sources of origin.

The combination of top rate earth scientific, environmental chemical, paleo-ecological, computational, microbial and forensic research groups within IBED, as well as the expertise with multi-disciplinary research and the combination of processes operating at various spatio-temporal scales, makes it the ideal environment for my research. At the same time through my research I hope to contribute to, and further strengthen the multi-disciplinarity of research within IBED. In this respect I feel stimulated by the fact that since August 2010 all groups of IBED are located at new Science Park Amsterdam.

The combination of top rate earth scientific, environmental chemical, paleo-ecological, computational, microbial and forensic research groups within IBED, as well as the expertise with multi-disciplinary research and the combination of processes operating at various spatio-temporal scales, makes it the ideal environment for my research. At the same time through my research I hope to contribute to, the multi-disciplinarity of research within IBED. I find it especially stimulating that since August 2010 all groups of IBED are located at the new Science Park Amsterdam.