Campine Region Research Articles

GIS-BASED location optimization of a biomass conversion plant on contaminated willow in the Campine region (Belgium)

The Campine region is diffusely contaminated with heavy metals like cadmium. Since traditional excavation techniques are too expensive, phytoremediation is preferred as a remediation technique. In a previous study, the biomass potential from phytoremediation of contaminated agricultural land in the Campine region in Belgium was assessed. Based on recently upgraded figures of willow potential from phytoremediation on agricultural land in the seven most contaminated municipalities of the Belgian Campine region, the current paper uses GIS-knowledge to investigate which of three previously identified locations is most suitable for a biomass plant, taking into account the spatial distribution of the contaminated willow supply and the total cost of willow transport.Biomass transport distance from the centroid of each contaminated agricultural parcel to each of the three potential biomass plant locations was determined following Euclidian distance calculations and distance calculations over the existing road network. A transport cost model consisting of distance fixed and distance dependent biomass transport costs was developed.Of the locations identified, the Overpelt Fabriek site results in the lowest biomass transport distance and costs. When willow allocation for each parcel occurs based on the nearest potential plant location, transport costs are on average 23% lower than when all biomass is transported to the single Overpelt Fabriek site location. Therefore, when only considering transport costs, installing a smaller plant at each of the three potential plant locations would be less expensive than when installing a single biomass plant at the Overpelt Fabriek site.

Final Palaeolithic of the Campine region (NE Belgium) in their environmental context: optical age constraints

Final Palaeolithic of the Campine region (NE Belgium) in their environmental context: optical age constraints

Distribution and ecology of the caddisflies (Trichoptera) of Flanders (Belgium)

Based on a literature survey and the identification of all available collection material, a checklist and distribution maps for the caddisflies occurring in Flanders were prepared. Of the 126 species that have been recorded, 16 are now extinct in Flanders, while the majority of the remaining species is rare and their populations are often vulnerable due to isolation. Caddisflies only occurred at high oxygen levels and relatively low conductivities and three species assemblages could be recognized. A first group of species lived in stagnant waters and those species tolerated slightly lower oxygen concentrations than species characteristic for running waters. In streams of the Campine region, which are characterized by a low pH and a low conductivity, a second group of species was found. The last group of species mainly occurred in the loamy region, where pH and conductivity are higher. Running waters in other ecoregions mainly contained ubiquist species and did not possess a characteristic species assemblage. Despite the fact that the ecological water quality in Flanders slightly increased during the last few decades, the ecological water quality of most waters is still too low for caddisflies. According to the European Union water framework directive, a good ecological water quality should be obtained in all surface waters. Additional measures to improve the water quality are necessary in order to obtain sustainable populations of the caddisfly species occurring in Flanders.

Screening the current soil drainage class map of Flanders (Belgium) for its predictive quality

AbstractThe predictive quality of the current drainage class map of Flanders was evaluated using data from two monitoring networks: one with good spatial coverage but poor temporal coverage and another with better temporal but poor spatial coverage. We combine both networks to obtain 1678 point predictions for mean highest water (MHW) and mean lowest water (MLW) tables by applying time series modelling and total least squares regression. The resulting MHW and MLW point data set was used to evaluate the currency of the existing map and to identify regional differences. The quality of the current map is moderate, and large differences occur between regions. Especially the Campine region shows large and systematic differences, whereas the southeastern hills and chalk–loam region is relatively accurate. If more weight is given to errors in the wetter drainage classes, about 50% of the area of Flanders would benefit from remapping. Copyright © 2011 John Wiley & Sons, Ltd.

Local habitat and landscape affect Ixodes ricinus tick abundances in forests on poor, sandy soils

A large fraction of the forests in northern Belgium consists of homogeneous pine stands on nutrient-poor and acid sandy soils. However, in common with many other parts of Europe, the current forest management aims at increasing the share of deciduous and mixed forests. This might create favourable habitats for the tick Ixodes ricinus, which is Europe’s main vector of Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis in humans. Considering the threat to human health, it is important to know which factors regulate tick abundance. The influence of local habitat and landscape variables on the abundance of I. ricinus ticks were studied by collecting questing larvae, nymphs, and adults at 176 locations in forests in the Campine region (northern Belgium). Both I. ricinus ticks and B. burgdorferi spirochetes occurred throughout the study area, which means that the entire region represents an area of risk for contracting Lyme borreliosis. At the forest stand level, the main tree species and the shrub cover significantly affected the abundance of all life stages of I. ricinus. The abundance was higher in oak stands compared to pine stands, and increased with increasing shrub cover. Additionally, at the landscape level, a positive effect was found for forest edge length but not for forest cover. These patterns may be explained by the habitat preferences of the tick’s main hosts. Our results indicate that forest conversion might indeed create suitable habitats for ticks, which highlights the need for intensive information campaigns and effective tick control measures.

Phytoremediation, a sustainable remediation technology? Conclusions from a case study. I: Energy production and carbon dioxide abatement

This study examines the renewable energy production of crops used for phytoremediation. Our analysis is based on a case study in the Campine region (Belgium and The Netherlands), where agricultural soils are diffusely contaminated with cadmium, lead, and zinc, with an enhanced risk for uptake of these metals in crops and leaching to the groundwater. However, the area has such a large extent (700 km2) that conventional remediation is not applicable. Cultivation of crops for energy purposes on such land offers the opportunity to come up with an approach that efficiently uses contaminated agricultural land and that can be beneficial for both farmer and society. Performing a Life Cycle Analysis (LCA), we examined the energy and CO2 abatement potential of willow (Salix spp.), silage maize (Zea mays L.), and rapeseed (Brassica napus L.) originating from contaminated land. Taking into account the marginal impact of the metals in the biomass on the energy conversion efficiency and on the potential use of the biomass and its rest products after conversion, digestion of silage maize with combustion of the contaminated digestate shows the best energetic and CO2 abating perspectives. The replacement of cokes based electricity by willow is more efficient in CO2 abatement than willow used in a Combined Heat and Power (CHP) unit, despite lower net energy production in the former option. Willow reaches the same energy production and same CO2 abatement per hectare per year as silage maize when its biomass yield is respectively 13 and 8.7 Mg dm ha−1 y−1.

GIS-based assessment of the biomass potential from phytoremediation of contaminated agricultural land in the Campine region in Belgium

Abstract Dedicated energy crop cultivation is expected to be the prevalent form of biomass production for reaching renewable energy targets set by the European Union. However, there are some concerns with regard to its sustainability. This study demonstrates how this problem can be evaded by applying phytoremediation, i.e. the use of plants to remove pollutants from moderately contaminated soils. By selecting the appropriate plants a considerable biomass flow is produced without taking in scarce agricultural land, while simultaneously remediating the soil to levels of contamination below threshold values. Since phytoremediation is only applicable within a limited range of soil pollutant concentrations, the outer values of this range have to be determined at first. Subsequently, a Geographic Information System (GIS) is needed to perform further analyses. The contamination in the region is predicted using GIS, after which the agricultural area is determined that can be committed to energy crop cultivation. This way, the biomass potential and the resulting bioenergy potential from phytoremediation can be assessed. In this paper the Campine region in Belgium, a region diffusely contaminated with heavy metals like cadmium (Cd), is examined. It is illustrated that more than 2000 ha of agricultural land hold Cd concentrations exceeding guide values set by the Flemish Government. However, a large majority of these soils can be remediated by phytoremediation within a reasonable time span of 42 years. Concurrently, a significant amount of biomass is supplied for renewable energy production.

Final Palaeolithic settlements of the Campine region (NE Belgium) in their environmental context: Optical age constraints

The sand sequences exposed at the archaeological sites of Arendonk-Korhaan and Lommel-Maatheide offer a unique means to study the possible relation between human occupation patterns and climatic and environmental changes during the Weichselian–Holocene transition in the Campine region (NE Belgium). Of particular importance is that, at these localities, the Final Palaeolithic and Early Mesolithic settlement phases are stratigraphically separated. Optically stimulated luminescence (OSL) dating established a chronology for the evolution of the physical landscape around these sites; such a framework is essential when trying to understand settlement dynamics in response to environmental forcing.Thirty samples in total were dated using quartz SAR-OSL. The luminescence ages range from 16.2 ± 1.4 ka to 10.6 ± 0.7 ka. They indicate that sand deposition at Arendonk and Lommel was already going on during the final phase of the Late Pleniglacial and/or the onset of the Late Glacial. At Arendonk, sediments and soils from the early Late Glacial until the Allerød are missing, whereas a single interruption in the aeolian activity during the Allerød interstadial is reported for Lommel. Landscape stabilisation during the Allerød is also suggested by stratigraphical evidence, i.e. the presence of a bleached horizon both at elevated and low-lying flat areas, and extensive peat growth in wet depressions. The Bølling interstadial, on the other hand, has not been recognised in the lithostratigraphic record; this corroborates earlier suggestions that the climatic amelioration during the Bølling was not accompanied by a general stabilisation of the land surface in the NW European lowlands.The continuation of sand transport and deposition across the Late Pleniglacial/Late Glacial boundary may explain why human societies did not occupy the Campine region until the Allerød. During this interstadial, environmental conditions improved sufficiently to attract Final Palaeolithic Federmessergruppen to settle on higher grounds in the area. The climate deteriorated at the onset of the Late Dryas and, as a consequence, aeolian activity intensified again at Arendonk and Lommel, with at least 0.5–1 m of sand being deposited in a period of ∼1 ka; this may have caused the Federmesser to leave the area. At both localities, no occupation has been attested for the Late Dryas period until the Early Holocene, when Early Mesolithic societies settled in the area. This study illustrates how luminescence dating can contribute to an improved understanding of the environmental context around archaeological sites in the Campine region.

Radiocarbon based assessment of soil organic matter contribution to soil respiration in a pine stand of the Campine region, Belgium

The contribution of decomposing soil organic carbon (SOC) to total annual soil respiration (SR) was evaluated by radiocarbon measurements at a Scots pine stand growing on a plaggen soil in the Belgian Campine region. Two approaches were used to estimate the contribution of different C pools to SR. In the first approach, the variations in 14C content of soil CO2 efflux were monitored during one year (2003) and compared to the atmospheric and SOC 14C signatures to determine the contribution of “fast” (root respiration and fast decomposing SOC) and “slow” cycling C pools to total SR. In the second approach an estimate of the total heterotrophic soil respiration (Rh), comprising the slow cycling C and the heterotrophic part of the fast-cycling C pools, was derived applying a box model based on the amount of the bulk SOC pool and its 14C-derived mean residence time (MRT). The quantification of the Rh and the decomposition rate of the slow-cycling SOC allows to indirectly determining the contribution of the heterotrophic C that decompose within a year. Measurements of total SR performed in the field allowed assessing the contribution of the different C pools to total soil C efflux. On an annual basis, the fast-cycling C was the main contributor to SR, about 85%, while the contribution of the slow-cycling C (with MRT >1 yr) to total SR was 15%. Total annual Rh was 36% of total SR, which is in the lower range reported for temperate coniferous forests. The comparison of Rh with other estimates for the same site (47–50% of total SR) suggest a possible underestimation of the C flux from the mineral soil. In fact, the “very old” C contained in the plaggen horizon strongly affects the signature of the mostly young C leaving the soil. In conclusion, our results indicate that the contribution of SOC decomposition to total soil CO2 flux in this forest is less than 40%, and at least half of it comes from organic compounds less than 1 year old.

Distribution and ecology of the mayflies (Ephemeroptera) of Flanders (Belgium)

A literature survey and the identification of all available collection material resulted in a checklist and distribution maps for the mayflies occurring in Flanders. In addition, the relationship between the occurrence of mayflies and water characteristics was analysed. Of the 32 species that have been recorded, six are now extinct in Flanders (three of which are potamal species), while the majority of the remaining species are rare and their populations are often strongly isolated and therefore extremely vulnerable. Waters with relatively low oxygen levels and high conductivities were characterized by the most tolerant mayfly species Cloeon dipterum and Caenis robusta. However, most other species only occurred at higher oxygen concentrations and lower conductivities and could be separated into two groups. The first group mainly occurred in waters with a high pH and were often restricted to the loamy region or to stagnant waters, while the second group occurred in waters with a lower pH and mainly occurred in the Campine region. For most mayfly species, sustainable populations can only be achieved when their current habitats are adequately protected and, in addition, measures should be taken to connect and enlarge the remaining populations.

Decadal water balance of a temperate Scots pine forest (<i>Pinus sylvestris</i> L.) based on measurements and modelling

Abstract. We examined the water balance components of an 80-year-old Scots pine (Pinus sylvestris L.) forest stand in the Campine region of Belgium over a ten year period using five very different approaches; our methods ranged from data intensive measurements to process model simulations. Specifically, we used the conservative ion method (CI), the Eddy Covariance technique (EC), an empirical model (WATBAL), and two process models that vary greatly in their temporal and spatial scaling, the ORCHIDEE global land-surface model and SECRETS a stand- to ecosystem-scale biogeochemical process model. Herein we used the EC technique as a standard for the evapotranspiration (ET) estimates. Using and evaluating process based models with data is extremely useful as models are the primary method for integration of small-scale, process level phenomena into comprehensive description of forest stand or ecosystem function. Results demonstrated that the two process models corresponded well to the seasonal patterns and yearly totals of ET from the EC approach. However, both WATBAL and CI approaches overestimated ET when compared to the EC estimates. We found significant relationships between several meteorological variables (i.e., vapour pressure deficit [VPD], mean air temperature [Tair], and global radiation [Rg]) and ET on monthly basis for all approaches. In contrast, few relationships were significant on annual basis. Independent of the method examined, ET exhibited low inter-annual variability. Consequently, drainage fluxes were highly correlated with annual precipitation for all approaches examined, except CI.

Short-Rotation Coppice of Willow for Phytoremediation of a Metal-Contaminated Agricultural Area: A Sustainability Assessment

Large areas of land contaminated with cadmium (Cd), lead (Pb), and zinc (Zn) are currently in agricultural production in the Campine region in Belgium. Cadmium contents in food and fodder crops frequently exceed legal threshold values, resulting in crop confiscation. This imposes a burden on agriculture and regional policy and, therefore, encourages proper soil management. One way to increase agricultural income and improve soil quality is by growing alternative nonfood crops such as willows in short-rotation coppice (SRC) systems that remediate the soil. This paper compares SRC of willow with rapeseed and energy maize regarding four attributes: metal accumulation capacity, gross agricultural income per hectare, CO2 emission avoidance potential, and agricultural acceptance. Based on multicriteria decision analysis, we conclude that, although SRC of willow has a high potential as an energy and remediating crop, it is unlikely to be implemented on the short term in Flanders unless the economic incentives for the farmers are improved.

Radiocarbon dating reveals different past managements of adjacent forest soils in the Campine region, Belgium

The soils of adjacent first generation monospecific stands of Scots pine ( Pinus sylvestris L.) and pedunculate oak ( Quercus robur L.) in the Campine region, Belgium, apparently developed under the same forming factors, were studied for carbon dynamics to disentangle eventual different past land uses. In fact, visual observations suggested that the soil under pine experienced substantial addition of organic matter and ploughing, such to be considered a plaggen, opposite to the soil under oak, which is inexplicably much poorer in C. In order to prove this hypothesis, the soil organic carbon was quantified by horizons and, both bulk soil organic matter (SOM) and the least mobile SOM fractions – the humic acid and the unextractable fractions – were radiocarbon dated. Surprising was the marked difference between the mean SOM age from the two stands. In fact, while under oak this age is a few years or decades, under pine it amounts to more than a millennium, so confirming the hypothesis of a confined C supply occurred mainly in the Middle Age, or later using partly humified matter. The mean residence time (MRT) of SOM in the organic layers matches almost perfectly with that estimated via a mass balance approach and, as expected, was much lower in the oaks than in the pines. The humic acid fraction, generally the most stable fraction of SOM, in terms of both mobility and degradability, reflects the behaviour of the bulk SOM, showing higher radiocarbon ages under pine. The findings of this work indicate that the large human-induced additions of organic material in the area now occupied by the pine stand, probably occurred in the Middle Age and it continues to strongly affect the present soil C pools and their dynamics. Any study dealing with budgets and dynamics of C in soil should avail itself of a careful reconstruction of the land uses and management history, in order to provide reliable conclusions about the real role of the current vegetation on soil carbon.

Modeling Human Exposure to Cadmium and Arsenic in the Northern Campine Region

20th Annual Conference of the International-Society-for-Environmental-Epidemiology, OCT 12-16, 2008 [Standaert, A. R.; Van Holderbeke, M.; Cornelis, C.; Torfs, R.; Berghmans, P.] Vlaamse Instelling Technol Onderzoek, Flemish Inst Technol Res, B-2400 Mol, Belgium. [Nelen, V] PIH Prov Inst Technol Res, Antwerp, Belgium. [Bruckers, L.] Univ Hasselt, Diepenbeek, Belgium. [Van Gestel, G.] OVAM Publ Waste Agcy Flanders, Mechelen, Belgium. [Claeys, N.] VMM Flemish Environm Agcy, Erembodegem, Belgium. [Van Campenhout, K.] LNE, Dept Environm Nat & Energy, Brussels, Belgium. [Wildemeersch, D.] VAZG Flemish Agcy Care & Hlth, Brussels, Belgium. [Verlaek, M.] MMK Reg Environm Hlth Workers, Brussels, Belgium.

Distribution and ecology of the stoneflies (Plecoptera) of Flanders (Belgium)

Based on a literature survey and the identifi cation of all available collection material from Flanders, a checklist is presented, distribution maps are plotted and the relationship between the occurrence of the different species and water characteristics is analysed. Of the sixteen stonefly species that have been recorded, three are now extinct in Flanders (Isogenus nubecula, Taeniopteryx nebulosa and T. schoenemundi), while the remaining species are rare. The occurrence of stoneflies is almost restricted to small brooks, while observations in larger watercourses are almost lacking. Although a few records may indicate that some larger watercourses have recently been recolonised, these observations consisted of single specimens and might be due to drift. Most stonefly population are strongly isolated and therefore extremely vulnerable. Small brooks in the Campine region (northeast Flanders), which are characterised by a lower pH and a lower conductivity, contained a different stonefly community than the small brooks in the rest of Flanders. Leuctra pseudosignifera, Nemoura marginata and Protonemura intricata are mainly found in small brooks in the loamy region, Amphinemura standfussi, Isoperla grammatica, Leuctra fusca, L. hippopus, N. avicularis and P. meyeri mainly occur in small Campine brooks, while L. nigra, N. cinerea and Nemurella pictetii can be found in both types. Nemoura dubitans can typically be found in stagnant water fed with freatic water. Sustainable populations of these stonefly species can only be achieved when their present habitats are adequately protected and in addition, measures should be taken to connect and enlarge the remaining populations.

Using the EM38DD Soil Sensor to Delineate Clay Lenses in a Sandy Forest Soil

The objective of this study was to locate clay lenses in a sandy forest soil. The study site was a Scots pine (Pinus sylvestris L.) plantation in the Campine region of Belgium, which has been selected as a European Union‐funded Level II Research Site for soil monitoring. Typically, the soils in the area have homogeneous sandy soil profiles, but clay lenses occur locally within a depth of 2 m of the soil surface. Locating these clay lenses is necessary because they can have a substantial impact on soil processes. Therefore, we used the EM38DD soil sensor to measure the soil apparent electrical conductivity (ECa) simultaneously in two orientations. Apparent electrical conductivity maps were generated and it was found that the variation in ECa was mainly driven by the spatial variability of soil texture across the study site. The ratio of the two orientations (profile ratio or PR) clearly revealed a circular pattern with decreased PR values (<1), which was identified as a clay lens. To delineate the extent of this lens, two numerical methods were used: (i) a fuzzy‐k‐means classification of the PR map focusing on the lowest centroid class, and (ii) a probability approach through indicator kriging. Using a validation image obtained from directed auguring, cell‐by‐cell comparisons were made for these two methods complemented with spatial accuracy measures. Although both methods tended to underestimate the spatial extent of the clay lens, the indicator kriging method was the most accurate, with an overall accuracy of 0.838, a proportion of error due to locational errors (κ‐loc) of 0.864, and an average similarity of 0.841.

Variation of specific leaf area and upscaling to leaf area index in mature Scots pine

Reliable and objective estimations of specific leaf area (SLA) and leaf area index (LAI) are essential for accurate estimates of the canopy carbon gain of trees. The variation in SLA with needle age and position in the crown was investigated for a 73-year-old Scots pine (Pinus sylvestris L.) stand in the Belgian Campine region. Allometric equations describing the projected needle area of the entire crown were developed, and used to estimate stand needle area. SLA (cm2 g−1) as significantly influenced by the position in the crown and by needle age (current-year versus 1-year-old needles). SLA increased significantly from the top to the bottom of the crown, and was significantly higher near the interior of the crown as compared to the crown edge. SLA of current-year needles was significantly higher than that of 1-year-old needles. Allometric relationships of projected needle area with different tree characteristics showed that stem diameter at breast height (DBH), tree height and crown depth were reliable predictors of projected needle area at the tree level. The allometric relationships between DBH and projected needle area at the tree level were used to predict stand-level needle area and estimate LAI. The LAI was 1.06 (m2 m−2) for current-year needles and 0.47 for 1-year-old needles, yielding a total stand LAI of 1.53.

Contrasting net primary productivity and carbon distribution between neighboring stands of Quercus robur and Pinus sylvestris

Standing biomass, net primary production (NPP) and soil carbon (C) pools were studied in a 67-year-old pedunculate oak (Quercus robur L.) stand and a neighboring 74-year- old Scots pine (Pinus sylvestris L.) stand in the Belgian Campine region. Despite a 14% lower tree density and a lower tree height in the oak stand, standing biomass was slightly higher than in the pine stand (177 and 169 Mg ha(-1) in oaks and pines, respectively), indicating that individual oak trees contained more biomass than pine trees of similar diameter. Moreover, NPP in the oak stand was more than double that in the pine stand (17.7 and 8.1 Mg ha(-1) year(-1), respectively). Several observations indicated that soil organic matter accumulated at higher rates under pines than under oaks. We therefore hypothesized that the pines were exhibiting an age-related decline in productivity due to nutrient limitation. The poor decomposability of pine litter resulted in the observed accumulation of organic matter. The subsequent immobilization of nutrients in the organic matter, combined with the already nutrient-poor soil conditions, resulted in a decrease in total NPP over time, as well as in a substantial shift in the allocation of NPP toward fine roots. In the oak stand, litter is less recalcitrant to decay and soil acidity is less severe; hence, organic matter does not accumulate and nutrients are recycled. This probably explains why NPP was much higher in the oaks than in the pines and why only a small proportion of NPP was allocated to oak fine roots.

Soil respiration in a mixed temperate forest and its contribution to total ecosystem respiration

Soil respiration (SR) was measured with an infrared gas analyzer in nine plots representative of the heterogeneous vegetation in a mixed coniferous-deciduous forest in the Belgian Campine region. Selected plots included the two most representative overstory species (Pinus sylvestris L. and Quercus robur L.) in combination with the most representative understory species of the forest. A model that includes temperature and water as the main controlling variables was fitted to the data. We found large spatial variability in SR among plots, with typically lower fluxes under the coniferous overstory than under the deciduous overstory (means of 4.8 +/- 0.4 and 8.8 +/- 0.5 Mg C ha(-1) year(-1), respectively). Total annual soil carbon (C) emissions were estimated by weighting fluxes from different types of vegetation according to their relative contribution to the footprint area of the eddy covariance flux measurement. The relative contribution of the two main tree species to the footprint-weighted total SR varied among seasons with the more abundant coniferous overstory contributing the most to total SR during most of the year. Nonetheless, during summer, the contribution of deciduous plots to total SR was disproportionally high because of the more pronounced seasonality of belowground metabolic activity. Net ecosystem carbon dioxide exchange was measured by eddy covariance, and we estimated total ecosystem respiration (TER) with footprint-constrained nighttime fluxes. Mean total annual SR and TER were 6.1 +/- 0.11 and 9.1 +/- 1.15 Mg C ha(-1) year(-1), respectively. The 95% confidence interval of the ratio of annual SR:TER ranged from 0.58 to 0.76, with a mean of 0.67. The contribution of SR to TER tended to vary seasonally, with minimum contributions during summer (less than 50% of TER) and maximum contributions during winter (about 94% of TER).

Calibration and validation of an empirical approach to model soil CO2 efflux in a deciduous forest

Soil respiration (Rs) was monitored periodically throughout 2001 and 2003 in a pedunculate oak (Quercus robur L.) stand located in the Belgian Campine region. An empirical model originally developed for a neighboring pine stand, that accounts for variation in tempera- ture, soil moisture, rewetting of the surface layers by rain during dry periods and seasonal fresh litter inputs, was fitted to the data. The model explained 92% and 94% of the temporal variability in Rs during 2001 and 2003 respectively. Monthly measurements of Rs can suffice to build a robust empirical model if temperature is the main controlling factor. However, during the driest period of the year a weekly sampling schedule was needed to capture the combined effect of temperature, soil water content (SWC) and the short-term effect of rewetting played. Although the model was developed for gap-filling purposes it also showed a remarkable predictive ability for this site and these conditions. Annual emissions of carbon (C) estimated with the model were significantly higher in 2001 than in 2003 (7.8 and 5.9 ton C ha � 1 year � 1 , respectively). The severe drought during most of the growing season in 2003 caused a high fine root mortality and a decrease in microbial activity, and was likely the main responsible factor of the almost 2 ton C ha � 1 year � 1 differences in Rs between both years. Pulses of Rs during drying/rewetting cycles accounted for a substantial fraction of the total flux, especially during the driest year. Finally, our results show that quality of the substrate may play an important role in both the intensity of the rewetting pulses of CO2 and the seasonality of Rs.