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Gerard Govers

KU Leuven, Department of Earth and Environmental Sciences, Department Member

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Address: Leuven, Vlaams-Brabant, Belgium

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Papers by Gerard Govers

Spatial variability in crop response under contour hedgerow systems in the Andes region of Ecuador

by Raul Vanegas and Gerard Govers

Soil and Tillage …, Jan 1, 2006

Land management practices on tropical soils have been studied extensively during the past decades... more Land management practices on tropical soils have been studied extensively during the past decades. However, assessments of their impact on field-scale spatial variability in crop performance are rare. A case of practices affecting spatial crop response at field level in a systematic way is the contour hedgerow system, a widespread soil conservation technique on steep lands in the tropics. The objectives of this study were to assess: (i) spatial variability in crop response under contour hedgerow systems in the Andes and (ii) implications for management of steep land alley farming. In order to measure spatial variability in crop response, Triticum aestivum was sown in rows following the contours, placed every 25 cm along the slope direction. Grain yield was monitored on eight alleys, having slopes from 15 to 30%, a length of 4-8 m and soils ranging from Dystri-Vertic Cambisols to Haplic Phaeozem, in the Andes region of Ecuador. In order to relate crop response with soil fertility, soil sampling was carried out in bands following the contour. Top soil properties, such as organic carbon, N Total , NO 3 À , P, exchangeable Aluminium, P fixation, exchangeable bases, CEC and texture, were analysed. The barrier strips of the contour hedgerow systems were composed of: (i) Pennisetum clandestinum and Lolium multiflorum or (ii) Phalaris tuberosa. Spatial variability in crop response was described by fourth-order polynomial equations, where position in the alley was the independent variable and plant characteristics were the dependent variables. Grain yield ranged from 0.8 to 4.0 t ha À1 (net area). Clear and significant patterns of spatial variability in crop response were found in all alleys, with R 2 varying from 0.55 to 0.90. Crop response was strongly and positively correlated with NO 3

Modelling estuarine variations in tidal marsh sedimentation: response to changing sea level and suspended sediment concentrations

by Stanislas Wartel and Gerard Govers

Marine Geology, 2004

This study presents the validation of a zero-dimensional time-stepping physically based model (MA... more This study presents the validation of a zero-dimensional time-stepping physically based model (MARSED) to simulate the varying rates of long-term (10-100 years) tidal marsh accumulation within an estuary. First, field data on long-term tidal marsh accumulation were collected for 25 marsh sites scattered along the Scheldt estuary (NW Europe), based on old topographic data and radiometric and paleoenvironmental dating of sediment cores. The field data showed that estuarine marshes accumulate at highly varying rates depending on (1) the age of the marsh, (2) estuarine variations in mean high water-level (MHWL) rise, and (3) variations in suspended sediment concentrations (SSCs). As a general mechanism, young low marsh surfaces accumulate quickly and asymptotically up to an equilibrium level around MHWL. After this, high old marshes accumulate much slower at rates that are comparable to local MHWL rise. Furthermore, marsh accumulation rates are higher in the inner part than in the outer part of the estuary. This difference can be attributed to the faster MHWL rise and higher SSC values in the inner estuary. Second, the MARSED model was validated against the field data. The model was able to simulate the observed variations in marsh accumulation rates with good accuracy. Furthermore, the model allows to quantify the combined effect of sea-level change and SSC on variations in accumulation rates: they showed that tidal marshes can maintain their equilibrium elevation around MHWL, only if incoming SSC is high enough. Finally, the model allows to predict marsh accumulation rates in response to changing environmental conditions. Simulations for the next 100 years suggest that the tidal marshes in the Scheldt estuary will be able to keep up with the rising MHWL, unless MHWL rise would increase and SSC would decrease importantly. D

Modelling long-term tidal marsh growth under changing tidal conditions and suspended sediment concentrations, Scheldt estuary, Belgium

by Gerard Govers and Stanislas Wartel

Marine Geology, 2003

Existing numerical models simulating the vertical growth of tidal marshes have only, to a very li... more Existing numerical models simulating the vertical growth of tidal marshes have only, to a very limited degree, been validated using observed data. In this study, we describe a refined zero-dimensional time-stepping model, which is based on the mass balance approach of Krone [in: Coastal Sediments '87, 1987, pp. 316^323], Allen [Mar. Geol. 95 (1990) 77^96] and French [Earth Surf. Process. Landforms 18 (1993) 63^81]. The model is applied and evaluated, using field data on suspended sediment and tidal regime as input and the historical growth of a specific minerogenic tidal marsh in the Scheldt estuary (Belgium) as independent data for model testing. First, the historical rise of the marsh surface during the past 55 years is reconstructed based on land use and vegetation cover changes, which are dated using aerial photographs and which are recognised in sediment cores. After marsh formation, the marsh surface builds up very quickly and asymptotically to an equilibrium level relative to the tidal frame. Second, temporal variations in suspended sediment concentration (SSC) were measured above the actual marsh surface during a 1-year period. These measurements show that the SSC, in the water that floods the marsh surface at the beginning of an inundation, increases linearly with maximum inundation height. The application of existing models, which assume a constant incoming SSC, leads to an underestimation of the observed historical growth and to biased predictions under scenarios of future sea-level rise. However, after incorporation of the relationship between SSC and inundation height, the observed vertical growth is successfully simulated. This leads to the conclusion that not only the decrease in tidal inundation, but also the decrease in SSC with decreasing marsh inundation height, is of great importance to fully explain and successfully simulate the long-term vertical morphodynamics of tidal marshes. ß

Small-scale sediment transport and deposition patterns within a salt-marsh basin, Paulinaschor, Western Scheldt

by Gerard Govers and Stanislas Wartel

During inundation of tidal marshes, fine-grained suspended matter is transported to and partly de... more During inundation of tidal marshes, fine-grained suspended matter is transported to and partly deposited on the marsh surface. In this research the complex spatial patterns of sediment transport and deposition are studied at the temporal scale of individual inundations and spatial scale of a small tidal creek basin (ca. 6 ha) within the salt Paulina marsh, Western Scheldt. Field measurements are used for the implementation and validation of 2-dimensional numerical models for tidal marsh sedimentation. Near the ...

Human impact on late-Holocene sediment transfers: typology, controlling factors and scaling issues

by Gerard Govers, etienne paulissen, and Gert Verstraeten

… 2009, held 19-24 …, Apr 1, 2009

During the course of the Holocene, humans have impacted the sediment dynamics of hillslopes, rive... more During the course of the Holocene, humans have impacted the sediment dynamics of hillslopes, river channels and even global river systems, mostly with ever-increasing intensity. However, there is no clear one on one relation between the intensity of human presence (population density) and the magnitude of impact on sediment transfers. Several thresholds have to be crossed for coupling between the various landscape elements in a river catchment to occur, ensuring that anthropogenic landscape disturbances impact ...

Soil loss due to crop harvesting: significance and determining factors

by Gerard Govers and Gert Verstraeten

Progress in Physical Geography, 2004

Water, wind and tillage erosion are well-studied soil erosion processes. However, there is anothe... more Water, wind and tillage erosion are well-studied soil erosion processes. However, there is another process of soil erosion that is rarely considered in the field of earth sciences but one that should not be neglected when calculating soil denudation rates and sediment budgets, i.e., soil loss due to crop harvesting (SLCH). Loose soil and soil adhering to the crop and rock fragments are harvested and exported from the field along with crops such as sugar beet (Beta vulgaris L.), potato (Solanum tuberosum L.) and chicory (Cichorium intybus L.). In this paper several assessments of SLCH found in the literature are listed, revealing that soil loss due to crop harvesting may range from a few Mg up to a few tens of Mg per hectare per harvest. As most literature discussing this soil loss does not originate from the field of earth sciences, and terms used to describe this phenomenon are not standardized, a terminology is proposed to describe soil losses due to crop harvesting compatible with terms used in the field of soil erosion. Furthermore, the parameters determining SLCH are reviewed based on a detailed literature study that focuses mainly on sugar beet. These parameters may be grouped into four factors, i.e. soil, crop, agronomic practices and harvest technique. Variations in soil moisture and soil texture cause the largest variations in SLCH, although other factors, such as harvest technique, also play an important role. Given the importance of SLCH in terms of on-site and off-site effects, more research is needed to quantify SLCH under different environmental conditions.

Pan‐European Soil Erosion Assessment and Maps

by Anne Gobin and Gerard Govers

Soil Erosion in Europe, Oct 19, 2006

Soil erosion is a natural process, occurring over geological time, and most concerns about erosio... more Soil erosion is a natural process, occurring over geological time, and most concerns about erosion are related to accelerated erosion, where the natural rate has been significantly increased by human activity. Soil erosion poses severe limitations to sustainable agricultural land use, as it reduces on-farm soil productivity and causes the accumulation of sediments and agro-chemicals in waterways. In Europe, soil erosion is caused mainly by water and, to a lesser extent, by wind. Rill and inter-rill erosion affects the largest area, but evidence of ...

Erosie en natuur: vrienden of vijanden?

by Anton Van Rompaey and Gerard Govers

status: published, 2006

Associatie KULeuven. ...

Soil erosion and sediment deposition in the Belgian loess belt during the Holocene: establishing a sediment budget for a small agricultural catchment

by Anton Van Rompaey and Gerard Govers

Holocene, 2005

A method to establish a Holocene sediment budget for a 103 ha agricultural catchment representati... more A method to establish a Holocene sediment budget for a 103 ha agricultural catchment representative for the Belgian loess belt is presented. Soil erosion and sediment deposition were determined based on 185 coring locations and a large excavation in the valley bottom. Results were integrated in a GIS and interpolation techniques applied to derive spatial patterns of erosion and sedimentation. Total soil erosion, sediment deposition and sediment export were calculated and the results show that volumes are highly dependent on the interpolation technique used. Sediment delivery ratios between 20% and 42% are derived and are consistent with data reported in previous studies. This clearly shows that the majority of the sediments produced during the Holocene have been stored near their source area and have not been delivered to the downstream rivers. The spatial distribution of soil erosion and sediment deposition within the catchment is strongly dependent on slope gradient and position within the catchment, which suggests that, since human impact began, topography has been the main factor determining long-term soil erosion and sedimentation.

Modelling mean annual sediment yield using a distributed approach

by Anton Van Rompaey and Gerard Govers

Earth Surface Processes and Landforms, 2001

In this paper a spatially distributed model for the calculation of sediment delivery to river cha... more In this paper a spatially distributed model for the calculation of sediment delivery to river channels is presented (SEDEM: SEdiment DElivery Model). The model consists of two components: (1) the calculation of a spatial pattern of mean annual soil erosion rates in the catchment using a RUSLE (Revised Soil Erosion Equation) approach; and (2) the routing of the eroded sediment to the river channel network taking into account the transport capacity of each spatial unit. If the amount of routed sediment exceeds the local transport capacity, sediment deposition occurs. An existing dataset on sediment yield for 24 catchments in central Belgium was used to calibrate the transport capacity parameters of the model. A validation of the model results shows that the sediment yield for small and medium sized catchments (10-5000 ha) can be predicted with an average accuracy of 41 per cent. The predicted sediment yield values with SEDEM are significantly more accurate than the predictions using a lumped regression model. Moreover a spatially distributed approach allows simulation of the effect of different land use scenarios and soil conservation techniques.

Indicators for pan-European assessment and monitoring of soil erosion by water

by Anne Gobin and Gerard Govers

Soil erosion forms a major threat to European soil resources. Although soil is a vital and largel... more Soil erosion forms a major threat to European soil resources. Although soil is a vital and largely non-renewable resource, it has not been the subject of comprehensive EU action so far. A thematic strategy for soil protection, which recognises soil erosion as one of the major threats, has currently been placed high on Europe's political Agenda. Assessing and monitoring soil erosion is needed to evaluate the impact of, inter alia, agricultural and land use policies in Europe.

Biodiversity: Basic Commodity or Luxury Item?

by Kurt Deketelaere, Maurice Proft, Gerard Govers, Olivier Honnay, and Sandra Rousseau

status: published, Nov 4, 2010

Taakbalk. taskbar; subnavigation; contents. Contact; Who's who; Organisational chart; Librar... more Taakbalk. taskbar; subnavigation; contents. Contact; Who's who; Organisational chart; Libraries; Toledo; Intranet; KU Leuven Nederlands. logo zoekterm: Navigation. Education: International programmes; Faculties; ECTS; Vision and policy. Research: Research at KU Leuven; Support and funding; Industry and society; PhD; Postdoc researchers; Output and impact; Networking; Vision and policy. Admissions: How to apply; Scholarships; Degree-seeking students; ...

Biodiversiteit: basisproduct of luxegoed?

by Sandra Rousseau, Maurice Proft, Gerard Govers, Bart Muys, and Rony Swennen

Metaforum visietekst 2, Nov 4, 2010

De huidige biodiversiteit op aarde is het resultaat van meer dan drie miljard jaar evolutie. De a... more De huidige biodiversiteit op aarde is het resultaat van meer dan drie miljard jaar evolutie. De alsmaar toenemende impact van menselijke activiteiten heeft echter geleid tot een nooit geziene afname van de diversiteit aan genen, soorten en ecosystemen. Soorten verdwijnen vandaag meer dan duizend keer sneller dan de afgelopen miljoenen jaren. De oorzaken zijn habitatverlies en-fragmentatie, vervuiling, de invasie van exotische soorten, overbejaging en-bevissing, en, eerder recent, klimaatsverandering. De dramatische ...

Establishing a Holocene sediment budget for the river Dijle

by Bart Vanmontfort, Gerard Govers, Jean Poesen, and Gert Verstraeten

Catena, 2009

A Holocene sediment budget was constructed for the 758 km 2 Dijle catchment in the Belgian loess ... more A Holocene sediment budget was constructed for the 758 km 2 Dijle catchment in the Belgian loess belt, in order to understand long-term sediment dynamics. Hillslope sediment redistribution was calculated using soil profile information from 809 soil augerings, which was extrapolated to the entire catchment using morphometric classes. As large parts of the forests within the catchment prove to have undergone little or no erosion since medieval times, a correction was applied for the presence of forests. Total Holocene erosion amounts 817 ± 66 Mt for the catchment, of which 327 ± 34 Mt was deposited as colluvium. This corresponds with a net Holocene soil erosion rate of 10.8 ± 0.8 × 10 3 Mg ha − 1 for the entire Dijle catchment. Alluvial deposits were studied through 187 augerings spread over 17 cross-valley transects. The total alluvial sediment deposition equals 352 ± 11 Mt or 42% of total eroded sediment mass. Results indicate that at the scale of a medium-sized catchment the colluvial sediment sink is as important as the alluvial sediment sink and should not be neglected. As a result the estimation of erosion through alluvial storage and sediment export would yield large errors. Dating of sediment units show an important increase in alluvial deposition from medieval times onwards, indicating the important influence of agricultural activities that developed from that period. Mean sediment export rates from the catchment for the last 1000-1200 years range between 0.8 and 1.3 Mg ha − 1 a − 1 and are consistent with present suspended sediment measurements in the Dijle. Erosion for agricultural land for this period is 9.2 ± 2.2 Mg ha − 1 a − 1 . Sediment budgets for the various tributary catchments provide an insight in the sources and sinks of sediment at different scales within the catchment.

Pan-European soil erosion risk assessment for Europe: the PESERA Map

by Gerard Govers and Mathias Boer

JRC, Ispra, Italy. Available online at http://eusoils. jrc. it/ESDB_Archive/pesera/pesera_cd/pdf/ThePeseraMap. pdf [verified 25 October 2006]. Quinton JN (1997). Reducing predictive uncertainty in model simulations: a comparison of two methods using the European Soil Erosion Model. Catena, 2003

Erosion by running water has been identified as the most severe hazard threatening the protection... more Erosion by running water has been identified as the most severe hazard threatening the protection of soil in Europe. By removing the most fertile topsoil, erosion reduces soil productivity and can, where soils are shallow, lead to an irreversible loss of natural farmland. Severe erosion is commonly associated with the development of temporary or permanently eroded channels or gullies that can fragment farmland. The soil removed by runoff from the land, during a large storm, accumulates below the eroded areas, in severe cases blocking ...

Evaluation of runoff, peak flow and sediment yield for events simulated by the AnnAGNPS model in a belgian agricultural watershed

Land Degradation & Development, 2012

Abstract The AnnAGNPS model, widely utilized as a practical tool for addressing erosion problems ... more Abstract The AnnAGNPS model, widely utilized as a practical tool for addressing erosion problems and land use planning, was implemented in a small agricultural watershed located in central Belgium, to assess its prediction capacity of runoff, peak flow and sediment yield in humid temperate conditions. Model performance was evaluated at the event scale by using a database reporting hydrological, geomorphologic and land use data collected during a 2-year period. Seventeen events were modelled and compared with the corresponding ...

ASSESSING THE PERFORMANCE OF A SPATIALLY DISTRIBUTED SOIL EROSION AND SEDIMENT DELIVERY MODEL (WATEM/SEDEM) IN NORTHERN ETHIOPIA

Land Degradation & Development, 2013

Most regional-scale soil erosion models are spatially lumped and hence have limited application t... more Most regional-scale soil erosion models are spatially lumped and hence have limited application to practical problems such as the evaluation of the spatial variability of soil erosion and sediment delivery within a catchment. Therefore, the objectives of this study were as follows: (i) to calibrate and assess the performance of a spatially distributed WATEM/SEDEM model in predicting absolute sediment yield and specific sediment yield from 12 catchments in Tigray (Ethiopia) by using two different sediment transport capacity equations (original and modified) and (ii) to assess the performance of WATEM/SEDEM for the identification of critical sediment source areas needed for targeting catchment management.

How long should we measure? An exploration of factors controlling the inter-annual variation of catchment sediment yield

Journal of Soils and Sediments, 2012

Abstract Purpose Although it is well-known that catchment suspended sediment yields (SY; tons per... more Abstract Purpose Although it is well-known that catchment suspended sediment yields (SY; tons per square kilometre per year) can vary significantly from year to year, little information exists on the magnitude and factors controlling this variability. This is crucial to assess the reliability of average SY values for a given measuring period (MP) and is of great geomorphic significance. This paper aims to bridge this research gap. Materials and methods A worldwide database was compiled with time series of measured SY values. ...

Changing hillslope and fluvial Holocene sediment dynamics in a Belgian loess catchment

Journal of Quaternary Science, 2011

Abstract Floodplain deposition is an essential part of the Holocene sediment dynamics of many cat... more Abstract Floodplain deposition is an essential part of the Holocene sediment dynamics of many catchments and a thorough dating control of these floodplain deposits is therefore essential to understand the driving forces of these sediment dynamics. In this paper we date floodplain and colluvial deposition in the Belgian Dijle catchment using accelerator mass spectrometric radiocarbon and optical stimulated luminescence dating. Relative mass accumulation curves for the Holocene were constructed for three colluvial sites and 12 ...

The prediction of runoff flow directions on tilled fields

Journal of Hydrology, 2001

On tilled ®elds runoff directions may be affected by tillage induced oriented roughness, causing ... more On tilled ®elds runoff directions may be affected by tillage induced oriented roughness, causing runoff to¯ow along tillage lines instead of topographic direction. That this has an important effect on runoff and erosion patterns was already reported [Ludwig et al., Catena 25 (1995); Desmet and Govers, Catena 29 (1997); Souche Áre et al., J. Hydrol. 206 (1998); Takken et al., Catena 37 (1999)]. However, limited research has been carried out to develop models that can be used to predict whether¯ow will be in tillage or topographic direction. In this study a wide range of data was collected on runoff patterns observed in an agricultural catchment in the Belgian loess belt. The data show that for more than 75% of the mapped areas on hillslopes thē ow was in direction of tillage. The data were analysed to develop two logistic regression models to predict runoff direction. The ®rst model uses topographic slope, the angle between the tillage orientation and aspect direction and the degree of oriented roughness as input. In the second model, the effect of discharge on the¯ow direction is also considered using unit contributing area as a substitute variable. However, the application of the second model is complicated and error-prone. Furthermore, application of both models to a validation dataset showed only a minor increase in model performance when upslope area is included (95 vs. 93% of correct predictions). Therefore, it may be better to predict¯ow directions without taking discharge into account. The model without unit contributing area predicted very well the spatial variation of¯ow directions within a ®eld surveyed by [Desmet and Govers, Catena 29 (1997)]. Including this logistic model in runoff and erosion models will result in much better predictions of runoff and erosion patterns than can be obtained by using the traditional approach of calculating a runoff pattern based on topography only. q