Hydrological research
My main research focus is on the interaction of the hydrological cycle with nutrient cycles, and later carbon cycles, in undisturbed and disturbed tropical and temperate environments.
Brazilian Amazon studies
In Brazil, research is carried out within the framework of the "Large Scale Biosphere Atmosphere Experiment in Amazonia (LBA)". This international research programme aims to study the functioning of natural Amazonian ecosystems in view of changing land use. Together with collegues from Alterra in Wageningen and the Instituto Nacional de Pesquisas da Amazônia (INPA) and the Centro de Previsão de Tempo e Estudos Climáticos (CPTEC-INPE) in Brazil, the carbon export in runoff from a small rainforest catchment near Manaus, Central Amazonia is being measured. The latest numbers converge to an annual carbon export of 10 - 25 g m-2, depending on the annual amount of discharge (835-1455 mm) from the catchment. As this is a blackwater area, most of the carbon leaves the catchment in dissolved organic form.
Two PhD students are presently involved in hydrological and biogeochemical research in the Asu catchment. Alessandro C. de Araujo is measuring spatial variation of nighttime storage of CO2 within and above the canopy in relation to differences in topography and therefore soil water status. Mr. Martin G. Hodnett is studying the soil moisture behaviour in the catchment in relation to the topographic position and the generation of surface runoff. He also compares the findings from the present study with those of earlier studies in the rainforest and pasture areas (ABRACOS project).
Within the framework of an intergrated reserach programme from the Foundation for the Advancement of Tropical Research (WOTRO) new studies will begin in November 2004 to assess the vulnerability of Amazonian rainforest to changes in climate (e.g. rainfall, temperature). We aim to study changes in plant physiology along topographic transects and implement a drought experiment in a valley to assess the impact of drought on the soil carbon and nitrogen cycles. In addition, we will study evaporation and plant physiology from nearby campina forests as these grow on similar soils as those found in the valleys, but with a different water regime.
Hydrological studies in the Dragonja catchment, Slovenia
In Slovenia, I am supervising a PhD student (Christiaan van der Tol)
who has been measuring changes in sap flow rates, soil moisture,
leaf area index and photosynthesis response curves of forests on
north and south slopes to determine if cahnges in forest productivity
can be related to differences in radiation and water status.
Hydrological studies in the rainforest of South Cameroon
In 1996 and 1997 studies were made within the Tropenbos Cameroon Project on rainforest hydrology and effects of logging. There are now plans to continue hydrological research on the rainforest in Cameroon in collaboration with Dr. Jean Claude Ntonga from the Institut de Geologie et Minières (IRGM) in Yaoundé.
Hydrology and carbon emissions in a Dutch Alder carr forest
In the Netherlands, I am involved in research into the hydrology and
CO2 and CH4
emissions in an Alder Carr forest in East Netherlands. This work
is carrioed out in collaboration with my collegue Ko van Huissteden,
the Dutch forestry service (Staatsbosbeheer), Bachelors students of the
Faculty of Earth and Life Sciences and several Erasmus exchange
students (Maria Raga and Ignacio) who carry out 6-month research
projects on this subject. Two years of data are now available showing
changes in soil chemistry and carbon emissions as a result of a
lowering of the groundwater level in part of the area.
Past research: Fiji water and nutrient study
Urban water supplies in Viti Levu, Fiji, depend mainly on surface water derived from catchments in the interior of the island. In the late 1960s and early 1970s several of the grassland water supply catchments (Nawetavuni, Varaciva catchments) for the Ba Province were converted to pine plantation forest. Several years later water shortages developped during the dry season, which were attributed to differences in water use between the pine forests and the grassland vegetation (Kammer and Raj, 1979). Planting activities of the Fiji Pine Commission are restricted to the dry western parts of Viti Levu and Vanua Levu and widespread reforestation of these dry grassland areas could therefore result in serious local water supply problems. Large-scale planting of trees has only begun recently in tropical countries (Evans, 1992) and information on the water use of either tropical grasslands or Pinus caribaea plantation forests, and therefore on effects of afforestation on water yield, was not available elsewhere. As such there was a need to quantify the water use of both vegetation types to enable the calculation of the economic implications of reforestation in Viti Levu, relative to the increased costs of water supply. The emphasis of such a study should be on dry season water use, as water yield during the rainy season was sufficient to meet demands (Drysdale and Rawaqa, 1987).
In addition to the question of increased water use by plantation forests and the negative effects of harvesting on water quality, concern has been expressed that the establishment of fast-growing trees on degraded soils may deplete soil nutrient reserves. This might result in low wood production during subsequent rotations. In Fiji, the production of second rotation forests fell below that of the first-rotation forests. It was not clear at the time whether this decline in productivity was related to water shortage during the dry season, to nutrient deficiencies, or frequent disturbance of the stands by cyclones. Indeed, at some locations signs of nutrient deficiencies (e.g. shoots without needles) were observed in second rotation forests (Dr. J.H.R. Heuch, pers. comm.). Although these deficiencies could possibly be overcome by fertilizing, the application of fertilizers to extensive forest areas would increase the costs of plantation development considerably. As such the sustainability of the current management practice needed to be evaluated to provide quantitative data on which predictions of the future costs of reforestation could be based.
A project was initiated in 1989 to address the pressing issues formulated above. The project was a collaboration of the Netherlands Foundation for the Advancement of Tropical Research (WOTRO, grant no. W84-295), the Faculty of Earth Sciences from the Vrije Universiteit of Amsterdam (FES-VUA) and the then Fiji Pine Commission (FPC, now Fiji Pine Ltd.). The work was undertaken by the author in partial fulfillment of the requirements of a doctoral degree from VUA, by his counterpart Mr.\ T.T.\ Rawaqa from Fiji Pine Ltd. and by seven VUA students in fulfillment of the requirements for their MSc degree. Field research was carried out over a two year period with the following objectives:
- To quantify the dry season water use of grassland, and that of a chronosequence of Pinus caribaea plantation forests planted on comparable soils
- To quantify the various components of the water and nutrient cycles over the period of a rotation (typically 15--20 years in the area)
- To study the effect of mechanized harvesting of merchantable timber, and subsequent burning of the slash on water yield and quality, as well as on soil properties
- To test various techniques that have become widely used in temperate zone forest hydrological research under humid tropical conditions
- To integrate the results in a descriptive mathematical model capable of making extrapolations in time
As it was not feasible to monitor a single forest over the length of a rotation the `false time series' approach (Hase and Foelster, 1982; Bruijnzeel, 1983) was used.The underlying assumption is that changes in water use and nutrient cycling following the planting of pines on grasslands, and those occurring over a rotation period, can be simulated by studying a forest age sequence provided that the environmental conditions (e.g. climate, topography, soil physical and chemical properties) in the study areas are similar.
This study was carried out between 1989 and 1991 in Viti Levu, Fiji and studied the water and nutrient cycling of Pinus caribaea plantation forests in comparison to Pennisetum polystachyon grassland. The thesis resulting from this study and published in 1994 can be downloaded from the Downloads page.
In 1995 soil and biomass samples were collected from a second rotation forest to see how the nutrient status may have changed after logging, burning and replanting of the Oleolega research catchment. Results of this study will soon be available.
Dr. M.J. Waterloo
VU University
De Boelelaan 1085
1081HV Amsterdam
The Netherlands
Phone: +31 20 5987319
e-mail: m.j.waterloo@vu.nl
Last modified: Fri Sep 21 12:19:53 CEST 2012
