A putative mechanism for bog patterning

The surface of bogs commonly shows various spatial vegetation patterning. Typical are ¿string patterns¿ consisting of regular densely vegetated bands oriented perpendicular to the slope. Here, we report on regular ¿maze patterns¿ on flat ground, consisting of bands densely vegetated by vascular plants in a more sparsely vegetated matrix of nonvascular plant communities. We present a model reproducing these maze and string patterns, describing how nutrient-limited vascular plants are controlled by, and in turn control, both hydrology and solute transport. We propose that the patterns are self-organized and originate from a nutrient accumulation mechanism. In the model, this is caused by the convective transport of nutrients in the groundwater toward areas with higher vascular plant biomass, driven by differences in transpiration rate. In a numerical bifurcation analysis we show how the maze patterns originate from the spatially homogeneous equilibrium and how this is affected by changes in rainfall, nutrient input, and plant properties. Our results confirm earlier model results, showing that redistribution of a limiting resource may lead to fine-scale facilitative and coarse-scale competitive plant interactions in different ecosystems. Self-organization in ecosystems may be a more general phenomenon than previously thought, which can be mechanistically linked to scale-dependent facilitation and competition

Simulatie van de regionale hydrologie in het stroomgebied van de Dommel

The Dommel-life project aims to develop sustainable management plans for the catchment area of the river Dommel. One of the problems within the catchment area is the possible hydrological impact of socio-economic activities. To be able to assess the impact of these socio-economic activities, a regional hydrological model is developed. The model consists of two parts: a topmodel and a groundwatermodel. The topmodel is a waterbalance model, developed for the Life-Dommel project (Pieterse et al., 1998). This report gives a short summary of the construction and results of the topmodel because it is closely connected to the groundwater model. The topmodel calculates the net groundwater supply from precipitation and the spatial distributed dynamic stream discharge. Precipitation is discharged directly to the stream, to the sewer system in urban areas or percolates to the groundwater. The topmodel calculates a and phreatic groundwater dynamics for each timestep of 10-days. Discharge of effluent and transfer of stream discharge to other streams or to canals is accounted for. Because accurate discharge were available, an accurate calibration of the topmodel could be performed. Stream discharge is calculated adequately for the period 1990- 1996 with a Nashcoëfficient of 0.78 and a deviance between observed and simulated average discharge of 0.04 m3 sec-1 day-1. The groundwatermodel, implemented with the program MODFLOW, is linked with the topmodel. MODFLOW calculates the amount of seepage to- and from deep groundwater. This data is used as imput for the topmodel. The model parameters and (geo) hydrological data are identical for both models. The geohydrological schematisation of the groundwater model is based upon geological information from the REGIS database of TNO-NITG. The hydrological basis is defined as the basis of the Mioceen, consisting of the ‘Boomse klei’ and ‘Klei van Veldhoven’. The ‘Boomse klei’ is the first impermeable layer in the Belgian part of the modelarea. The schematisation method distributes the geological layers over regular rectangles. The thickness of each modellayer is applied with fining upward to the surface. The results of the waterbalance model represent very well the hydrology of the catchment. The deviation of calculated pheatic groundwater levels, compared with measurements from 1991, are in average 12 cm too high with a standard deviation of 67 cm

Habitat and vegetation response prediction for meadows and fens. Application of SMART-MOVE on a regional scale

To assess the impact of integrated management plans on brook valley ecosystems in the catchment area of the river Dommel, an integrated landscape ecological model is developed. Within this integrated model the Nature Planner (developed at the national institute of the public health and the environment (RIVM)) is used to predict effects for meadow and fen vegetation. Because the Nature Planner was developed for use at the National scale, it could not directly be applied for the regional scale of the Dommel catchment. Therefore the fundament of the nature planner, the models SMART2 developed at the DLO-Staring Centre) and MOVE (developed at the RIVM), were rewritten for application within the GIS ArcInfo to implement the flexibility of a GIS. Vegetation response prediction is carried out with the model MOVE, using three environmental variables: acidity, nutrient availability and wetness of a site. All three variables are based upon Ellenberg indication values, which have to be calibrated to measurable environmental habitat conditions. Calibration of Ellenberg indication values for acidity and wetness was already carried out. Calibration of Ellenberg-N indication values to measured nutrient availability of the soil was still necessary. Therefore a comprehensive field experiment in the catchment areas of the Dommel and the Zwarte Beek (B) was carried out. This experiment resulted in a significant relationship between Ellenberg-N indication values and net annual N-mineralization. The variables N-mineralization and acidity are simulated with the model SMART2. The variable wetness is implemented as the mean spring groundwater level, simulated with a hydrological model of the catchment area by Pieterse et al (1998a, 1998b). SMART2 simulations are compared with measurements in the Dommel catchment. Simulations of acidity are comparable with measured acidity. N-mineralization simulations do not match with field observations. Moreover, these simulations do not differentiate between various sites, although these sites have different soil properties and different hydrological regimes. The MOVE variable Ellenberg-N is therefore excluded from the MOVE equations. Because the multiple regression equations of MOVE cannot be altered, the optimum N for each plant species is used instead. MOVE simulations were carried out for the catchment area of the river Dommel. Simulations are in agreement with expectations of potentials for nature development, based upon fieldwork. The simulations show that in the larger part of the catchment, the probability of occurrence of species-rich grasslands and fens is very low for the current hydrological situation. At some locations however, a relative high probability of occurrence for Calthion palustris and Junco-Molinion is simulated. Because habitat conditions in the Dommel catchment are more likely to be eutrophic than oligothropic, the probability of occurrence of oligothrophic and mesothrophic vegetation types (Junco-Molinion, Caricion nigrae and Calthion palustris) is overestimated. From inventories of the occurrence of grasslands and fens in this catchment, it is concluded that hardly any of these vegetation types, and especially the species-rich types, are left. Therefore a validation of model simulations is not carried out

Streamflow, a GIS-based Environmental Assessment Tool for Lowland Streams

Human activities, such as stream management, drainage, urbanization and agriculture, heavily influence the aquatic ecosystems in small lowland streams. For the assessment of the impact of human activities of aquatic ecosystems, a modeling tool is created. This modeling tool is part of the EU-life Dommel project. The modeling tool consists of two parts: a model for the assessment of response of aquatic ecosystems ‘ECOSTREAM’ and, described in this report, an aquatic habitat condition model ‘STREAMFLOW’. The necessary aquatic habitat conditions are flow velocity, saprobic state, stream dimensions and subdivision between continuous and intermittent streams. To comply with these habitat conditions, an environmental assessment tool was needed. This tool had to be capable of performing hydrological operations, calculate transport of water and solutes and perform compex GIS operations. The dynamic GIS program PCRASTER, designed by the university Utrecht, complies with this functionality. STREAMFLOW is build with cells of 500 by 500 meter wide. Direction of transport is based upon height differences. A waterbalance model is made, calculating stream discharge for every location in the catchment (distributed), for time steps of 10 days over the period 1990 - 1996. The model is based upon the conceptual waterbalance model for the river Rhine. Several discharge observations within the catchment indicate that discharge simulations are reliable for most areas. In the direct neighborhood of transfer of water between sub catchments or to canals, the hydrograph could not be estimated appropriately. Results from the waterbalance are used for further calculations. Flow velocity calculations are based upon Manning's equation, needing stream dimensions, the specific contributing discharge of every cell, the slope and a roughness coefficient. The simulations yield for almost every cell into a flow velocity above 0.10 m.sec-1; a distinct limit for aquatic ecosystems in flowing water. The effect of weirs is implemented in the assessment model; a decrease of the flow velocity just before the weir is simulated (often below 0.1 m.sec-1). The calculated stream discharge and flow velocity are subsequently used for assessment of the saprobic state. One way to define saprobic state is by means of the concentration organic-N in streams. In STREAMFLOW, organic-N is approximated by Kjeldahl-N. The major sources for Kjeldahl-N are households and industry, disposal of effluent to wastewater plants, to untreated sewers and direct to the stream. Degradation of Kjeldahl-N is accounted for as function of the Kjeldahl-N load and residence time in a cell. After comparison with observations at several locations in the Netherlands can be concluded that distributed pattern of saprobic state is adequately simulated. The results of STREAMFLOW are applied in the model ECOSTREAM (Olde Venterink et al., 1998)

Is nutrient contamination of groundwater causing eutrophication of groundwater-fed meadows?

There is an ongoing debate as to whether nutrient contamination of groundwater under agricultural fields may cause nutrient-enrichment and subsequent eutrophication in discharge areas. Often, there is only circumstantial evidence to support this supposition (proximity of agricultural fields, direction of water flow, highly productive vegetation). Research on solute transport along a flow path is necessary to evaluate the risk for eutrophication. In this paper we present results of such a study. Two transects were established in a discharge meadow, a few meters downstream from fertilized cornfields. Highly productive vegetation in parts of the meadow suggested nutrient-enrichment caused by inflowof contaminated groundwater. This supposition was supported by an analysis of groundwater flow paths, residence times and chloride as tracer for pollution. However, the fate of nutrients along the flow path indicated otherwise.While we found high concentrations of DIN (dissolved inorganic nitrogen), P and K under the cornfields, DIN and P concentrations drop below detection limit when groundwater enters the meadow. Only K progressed into the meadow but did not enter the root zone. We conclude that (1) polluted groundwater from the cornfields did not cause the nutrientenrichment, as indicated by the highly productive vegetation. Restoration projects in discharge areas should not focus upon measures in upstreamareas if only circumstantial evidence is available. Solute transport should be considered as well. (2) BecauseKclearly showed to be the mostmobile nutrient, its importance for nutrientenrichment in discharge wetlands merits more attention in future research

Ecohydrological modelling and integrated management planning in the catchment of the river Dommel

The EU-LIFE Dommel project aims at the development of methods for the combined use of landscape ecological models and socio-economic knowledge in the drawing up of integrated management plans for catchment areas of small trans-border rivers. These methods were developed and tested in the catchment area of the river Dommel. The river Dommel is one of the important tributaries of the river Meuse. It crosses the border between Belgium and the Netherlands. Because there exist strong conflicts between the ecology and socio-economic developments within the catchment, many ecosystems have deteriorated during the last decades and the remains are threatened by future socio-economic developments. The short-term objective of the project was to lay the foundation for an integrated management plan to abate these problems in the study area. The project was executed in collaboration between scientists and regional policy actors. The project consisted of three phases. In the first phase an analysis was made of interrelated socio-economic and environmental developments. In the second phase a number of landscape-ecological models were developed to be able to predict environmental effects of different land use and water management scenarios. In the third phase a number of these scenarios were drawn up and compared with regard to ecological gains, societal acceptability and costs. This led to a final scenario which offered good perspectives for nature restoration and which was considered feasible by the relevant authorities in the catchment area. To comply with the long-term objective of the project, methods were developed which are applicable in other catchment areas. These methods concern organizational aspects (project phasing, co-operation in the project) and aspects with respect to scientific content (landscape-ecological models, determination of ecological gains)

A decision support system for restoration planning of stream valley ecosystems

Despite efforts that have been put into conservation, there is a continuing loss of species and ecosystems in Western Europe. There is a growing awareness that restoration is an essential step to stop this tide. Unfortunately, there is lack of understanding about the multitude of functions and the complexity of spatial interactions in a landscape. The focus of this paper is to demonstrate that an integrated decision support system (IDSS) is indispensable to offer insight into this complexity and to design efficient restoration programmes. The IDSS is applied in a lowland catchment on the border between the Netherlands and Belgium and leads to the following recommendations: the site conditions on the location where restoration is planned must be close to the range that is required for the target ecosystem; the manager has to decide for the most attainable targetecosystem, and accept the inevitable loss of other ecosystems as a result from this choice; restoration planning involves that the optimal measure for each catchment, subcatchment or region is assessed, being ecological, urban or agricultural; for each ecosystem an optimal set of measures must be selected. An analysis of the restoration efficiency (ecological gain divided by economic costs) is crucial for this selection

Curva crítica de diluição do nitrogênio para a cultura do melão Nitrogen critical dilution curve for the muskmelon crop

O objetivo do trabalho foi ajustar a curva crítica de diluição do nitrogênio da cultura do melão. O experimento foi conduzido em ambiente protegido na Universidade Federal de Santa Maria (UFSM), entre agosto de 2004 e janeiro de 2005. As mudas do híbrido Magellan foram plantadas em sacolas de polietileno contendo 4,5dm-3 de substrato comercial (Plantmax PXT®), na densidade de 3,3 plantas m-2 e fertirrigadas com solução nutritiva completa. As plantas foram conduzidas verticalmente com uma haste, deixando-se no máximo dois frutos por planta e foram podadas ao atingir a altura de 2m. Os tratamentos foram constituídos por concentrações de nitrogênio na solução nutritiva de 8; 11, 14; 17 e 20mmol L-1. O delineamento experimental utilizado foi o inteiramente casualizado com quatro repetições. Quatro plantas de cada tratamento foram coletadas semanalmente entre os 33 e 99 dias após o plantio para determinar o acúmulo de matéria seca (MS) e o teor de N nas folhas, haste e frutos. Foi constatada a diluição da concentração de N na matéria seca em todos os tratamentos e os dados ajustaram-se ao modelo potencial %N = aMS-b descrito na literatura. A curva crítica de diluição do N foi ajustada, com coeficientes a e b iguais a 5,16 e 0,63, respectivamente. Esse modelo poderá ser usado para estimar a quantidade de N extraída no decorrer do ciclo de crescimento e desenvolvimento dessa cultura, com base na análise do teor desse nutriente nas folhas.<br>The research was carried out to adjust the nitrogen critical dilution curve for the muskmelon crop, to be used in fertilization practices for this crop. The experiment was conducted in a greenhouse at Universidade Federal de Santa Maria, from August to January, 2005. Plantlets of the hybrid Magellan was grown in polyethylene bags with 4.5dm3 of the commercial substrate Plantmax PXT®, in a plant density of 3.3plants m-2, and fertigated with a complete nutrient solution. Plants were vertically trained with one stem and no more than two fruits per plant, and the main stem was cut at 2m height. Treatments were N concentrations in the nutrient solution of 8, 11, 14, 17, and 20mmol L-1, in a randomized experimental design with four replications. Four plants of each treatment were harvested at weekly intervals between 33 and 99 days after planting to determine dry mass (DM) accumulation and N concentration in leaves, stem and fruits. The N dilution in plant dry mass was confirmed in all treatments and data fitted the potential model %N = aMS-b described in the literature. The N dilution curve was adjusted, with values of 5.16 and 0.63 for a and b coefficients, respectively. This model could be used to estimate the N quantity absorbed during growth and development of this crop, based on the analysis of this element on leaf tissues