Land Management Scenarios Research Articles

Soil Landscapes of Canada: Building a National Framework for Environmental Information

The Soil Landscapes of Canada (SLC) is a national soil map and accompanying database of environmental information for all of Canada, produced and maintained by the Canadian Soil Information Service (CanSIS) which is a part of Agriculture and Agri-Food Canada. The SLC maps were originally published as a set of paper products for individual provinces and regions. The maps were digitized in CanSIS, using one of the first geographic information systems in the world, and linked to soil and landscape attribute tables to serve an evolving variety of spatial modelling applications. The SLCs form the lowest level of the National Ecological Framework for Canada. The latest public release of the SLC is version 3.2, which provides updated soil and landscape information for the agricultural areas of Canada. The SLC v3.2 digital coverage includes an extensive set of relational data tables. The component table lists the soil components in each agricultural polygon along with their predicted dominant slope, class, and extent. The soil component codes are also linked to soil attribute tables which define fundamental soil properties, such as classification and parent material, as well as a description of the soil horizons and key soil attributes to a depth of 100 cm. SLC v3.2 adds a new set of landform tables which identify the major landform type in each polygon and indicates the most likely soil components in the upper, mid slope, lower slope, and depressional positions. These soil and landform attributes are designed to support a wide variety of national and international environmental modelling applications, such as the prediction of soil quality change, soil carbon sequestration, and land productivity for different agricultural crops in response to agricultural policy, land management, and climate change scenarios. Future versions of the SLC are under development that will have improved spatial resolution and include soils data for areas beyond the present agricultural zone of Canada.

Risk of erosion in peat soils – an investigation using Bayesian belief networks

AbstractPeat is an important carbon sink in the context of climate change. However, well‐documented examples suggest that risk of peat erosion is widespread and significant. Our understanding of peat vulnerability to erosion is commonly constrained by the complexity of drivers, and their interactions, in this process. However, the key constraints are: limited, consistent and comprehensive quantitative data relating to this process and, more significantly, the explicit relationships between the occurrence of peat erosion and its causes and drivers. Bayesian belief networks (BBNs) provide a methodology for integrating qualitative and quantitative knowledge. BBNs can capture and structure available knowledge and rationalize complex interactions, where empirical data are limited or poorly compatible and processes are complex or uncertain. In this article we explore the BBN potential to advance our understanding and to identify gaps in current knowledge. BBN has been demonstrated to be a useful tool in structuring and utilizing currently available knowledge, often with limited evidence, of peat’s actual exposure to erosive forces. Despite considerable research into peat erosion processes and understanding the inherent vulnerability of peat, results presented indicate clear gaps in knowledge regarding the role of land management, spatially explicit data related to land management as well as limited evidence of the relevant relationships between many of the variables. The attention of further research will focus on these gaps. The BBN approach provides a framework in which different scenarios of biophysical, climatic and land management (social and economic) conditions can examine and assess the probability of erosion.

Co-constructing an agent-based model to mediate land use conflict between herders and foresters in northern Thailand

In conservation areas, land use conflicts frequently occur due to the increasing number of land resource managers and users who usually have different interests, objectives and perceptions. Sharing all these a priori legitimate differences is a prerequisite for better collective management of the land. The companion modelling approach is used to build a shared representation of interactions between vegetation dynamics, reforestation efforts and livestock grazing in a forest conservation area of northern Thailand. This article focuses on the participatory modelling process that led to the co-construction of an agent-based model. Sensitizing exercises on vegetation dynamics and an agent-based simulator associated with a role-playing game were the main tools used. The social interactions and decision-making processes observed during the gaming and simulation sessions were used to construct a set of rules implemented in a subsequent autonomous agent-based model. It will be used to simulate future land management scenarios with local stakeholders.

Nitrate transport modeling to evaluate source water protection scenarios for a municipal well in an agricultural area

Fertilizers that are spread on agricultural fields can leach into aquifers and contaminate groundwater sources for drinking water particularly with nitrate. Modeling this phenomenon can help in evaluating the impact of current or future agricultural practices on nitrate content within an aquifer. The three-dimensional Water flow and Nitrate transport Global Model ( WNGM), that was previously developed and applied to a well-capture zone, is actually used to simulate future land management scenarios over the same zone. The studied area is located in a region with intensive agricultural practice in Southern Québec (Canada). The sandy unconfined aquifer underlying the agricultural fields is highly vulnerable to nitrate contamination from ground surface and nitrate concentrations around critical threshold of 45 mg NO 3 - /L were observed in the municipal well. Using the calibrated WNGM, a number of land management scenarios were simulated in order to predict future trends of nitrate concentrations in the pumping well from 2008 through 2040 that could be induced by changes in land management practices over this well-capture zone. More specifically, these scenarios simulate implementation of improved or ideal agricultural practices within the agricultural portion of the well-capture zone, and modification of the pumping rate at the municipal well. The results show how a decrease and stabilization of nitrate concentration should occur at the municipal well after a period varying from 5 to 30 years depending on the implemented agricultural modifications. It is also shown that, in this particular case, an increase of the pumping rate at the municipal well from 700 to 2800 m 3/d would lead to an increase of the well-capture zone from 0.8 to 2.5 km 2 and to a decrease of nitrate concentrations at the municipal well from 43 to 34 mg NO 3 - /L. Furthermore, it is predicted that application of improved agricultural practices in the vicinity of this municipal well could lead to a reduction of nitrate concentrations at the well of about 8 mg NO 3 - /L.

Uncertainty propagation in soil greenhouse gas emission models: An experiment using the DNDC model and at the Oensingen cropland site

The increase of green house gas (GHG) concentrations in the atmosphere is predominantly caused by the anthropogenic activities of fossil fuel burning and land use change. The flux of GHGs from soils and ecosystems to the atmosphere is large, and any errors in estimating these fluxes have a significant impact on our quantification of the relative importance of land use in contributing to global warming. Numerical models have been developed to estimate the net flux of the biogenic GHGs: CO 2, N 2O and CH 4, for various agricultural management practices. These models have been developed using data from many different experimental sites around the world, encompassing different crops, farm management systems, soil and climatic conditions. Crop experiments and GHG flux measurements are expensive and last several years if not decades so these models are often used to test hypothesis about the effect of future conditions, land use scenarios and also to predict the effect of novel land management scenarios to reduce emissions. However, uncertainties in the input soil parameters and meteorological data that drive these models propagates through them, resulting in uncertainties in the predictions of biogenic GHG emissions. This paper describes an experiment that investigates how well the commonly used de-nitrification de-composition (DNDC) soil model performs when used to predict the eddy-covariance CO 2 fluxes and crop yields measured in the first full year of the Oensingen cropland site in Switzerland. DNDC N 2O predictions are compared to the IPCC emissions factors for arable land. This study includes an estimation of the uncertainty of soil input parameters, a sensitivity study as to their effect on predicted GHG emissions and the propagation of their uncertainty through the model. This study considers uncertainty in meteorological measurements and the impact of using subsets of this data in the model. In particular the effect of using monthly meteorological parameters to generate daily time series for input into the model is investigated and the error propagation quantified. The overall impact of uncertainty in input parameters on predicted biogenic GHG emissions is relatively small with the PDF of the uncertainties indicating that the NEE is over estimated by 3.6% and has a SD of 3.6% of the actual NEE. Nitrous oxide emissions are not biased but have a larger SD of 23% of emissions, which when the global warming impact is considered is only 3% of net flux. DNDC can therefore be used with confidence to predict emissions, with the caveat that the biomass production needs to be match to local conditions.

Carbon and Nitrogen Isotopic Measurements from Southern Appalachian Soils: Assessing Soil Carbon Sequestration under Climate and Land-Use Variation

Measurements of the distribution of carbon and nitrogen isotopes in soils are needed due to their potential to improve our understanding of soil CO 2 emissions and sequestration under varying climatic conditions and land management technologies. Organic carbon and nitrogen isotopic and elemental composition was measured in baseline forest soils as well as in anthropogenically and intermittently flooded soils in the southern Appalachian Mountains. For the undisturbed forest soils, the consistent relationship between elemental and isotopic composition in the soil column, across soil organic matter pools, was supportive of the hypothesis that isotopic signature is reflective of microbial induced carbon turnover and nitrogen decomposition. A climatologic analysis suggested that isotopic indicators of soil organic matter turnover were influenced by mean annual temperature at our study sites, as well as in 10 other regional and global soil carbon and nitrogen isotopic studies. Intermittently flooded soils showed carbon and nitrogen distributions that reflected successive high magnitude events where sediments were deposited upon a developing forest floor. Measurements from soils disturbed by mining, agriculture, and recreation suggest the potential for using carbon and nitrogen isotopes to indicate the degree of soil organic matter turnover induced by different land management scenarios.

Modelling the effect of land use and climate change on the water balance and nitrate leaching in eastern Denmark

This article examines the effect of land use and climate change on the water balance and nitrate leaching in the eastern part of Denmark. The evaluation and scenario analysis is carried out using the dynamic agroecosystem model ‘Daisy’ set up for a number of representative soil types and land management scenarios providing the basis for an average regional assessment of nitrate leaching. It is found that evapotranspiration will increase while changes in percolation and drainage depend on soil type and land management. Average weighted nitrate leaching rates are increased by 24% if management practices are kept constant, whereas a status quo is expected when management options are changed. However, Daisy is sensitive to inputs in the soil organic N pool and a better understanding of how this pool develops in a climate change situation is required if reliable predictions should be obtained together with an assessment of the effect of land management changes.

Towards the implementation of the European Water Framework Directive?: Lessons learned from water quality simulations in an agricultural watershed

The main objective of the European Water Framework Directive (WFD) is the achievement of a good ecological and chemical status of the water environment (water bodies). This status corresponds to the limit value of Germany's Working Group of the Federal States on Water Problems Issues (LAWA) for water quality class II (3 mg/l total nitrogen). The rivers in the intensively cropped Upper Ems River basin (northwestern Germany) show total nitrogen concentrations in excess of 5–10 mg/l. Hence, the objective of our study was to find a land use and land management scenario that would reduce the total nitrogen concentration to meet the WFD requirements for good ecological and chemical status. We developed consecutive land use and management scenarios on the basis of policy instruments such as the support of agro-environmental measures by Common Agricultural Policy and regional landscape development programs. The model simulations were done by using the Soil and Water Assessment Tool (SWAT). Results of SWAT scenario calculations showed that drastic measures, which are unrealistic from a socio-economic point of view, would be needed to achieve the water quality target in the basin (reduction of arable land from 77.2% to 46% [13% organic farming], increase of pasture from 4% to 15%, afforestation from 10% to 21%, increase of protected wetlands from 0% to 9%, etc.). The example shows additionally that the achievement of the WFD targets is only possible with a consideration of regional landscape and land use distinctions. A related problem yet to be addressed is the general lack of measured water quality data with which to calibrate and validate water quality models such as SWAT. This adds considerable uncertainty to already complicated and uncertainty situations. Thus, improved strategies for water quality monitoring, and data accessibility must be established.

Phosphorus export from agricultural land: a simple approach

In the last few decades, increased inputs of nutrients (mostly nitrogen and phosphorus) to agricultural land have led to runoff transporting an ever growing portion of these nutrients from non-point (diffuse) pollution sources into rivers and lakes, thus threatening freshwater quality. Phosphorus (P), the focus of the present paper, is principally transported from agricultural land bound to sediments and can accelerate freshwater eutrophication. Two fundamental problems face land managers when dealing with the problem of non-point P pollution. The first is posed by the quantitative evaluation of P loads at basin scale, which is essential in assessing areas of higher export risk and transport pathways. The second is finding a satisfactory compromise between two opposing needs: simplicity, to satisfy management, and complexity, to interpret real processes and their related uncertainty. Uncertainty is not merely the uncertainty that is intrinsic to model simulations, but also that deriving from the inherent stochastic variability of real systems. In the present study, an attempt to maximise the advantages of both approaches was made. The Lake Vico basin, Central Italy, was selected as a suitable site, since the P concentration of the lake increased dramatically at the beginning of the 1990s, due to P non-point pollution source loads. The simulation model (Groundwater Leaching Effects of Agricultural Management Systems, GLEAMS) was used to evaluate field scale P losses in two different scenarios: conventional and conservative agricultural practices. A regression model for each of these two scenarios was then fitted, to find the best relation between slope, on the one hand, and P losses. This regression allowed the GLEAMS results to be extended to basin scale, by a digital terrain model and a geographic information system (GIS), making it possible to evaluate P export into the lake, thus meeting management needs. The accuracy of this type of approach was evaluated by comparing model predictions with monitored results of P concentration in water. The suggested approach offers solutions to several problems regarding land management sustainability, including: (i) a quantitative evaluation of different land management scenarios; (ii) the possibility of zoning landscape according to risk level, comparing different scenarios and related environmental efficiency; (iii) an integrated evaluation of land cover, in terms of its impact on freshwater ecological status and the long-term water body condition, as a consequence of land use.

Regional carbon stocks and dynamics in native woody shrub communities of Senegal's Peanut Basin

Estimating regional carbon (C) stocks and understanding their dynamics is crucial, both from the perspective of sustainable landscape management and global change feedback. This study combines remote sensing techniques and a coupled GIS-CENTURY model to estimate regional biomass C stocks and SOC dynamics for Guiera senegalensis shrub communities in Senegal's Peanut Basin. A statistical model relating field-measured shrub aboveground biomass C at training plots to satellite image-derived shrub abundances was developed and used to estimate regional biomass C across a major part of the Basin. Regional SOC dynamics were modeled by coupling the CENTURY model and GIS databases. Significant correlation ( r = 0.73; p = 0.05) was observed between aboveground biomass C and satellite image-derived shrub abundance at the training plots. Aboveground biomass C stocks ranged from 0.01 to 0.45 Mg ha −1 with an approximate total of 247,000 Mg C for the 3060 km 2 study area. CENTURY model predictions indicate that C sequestration in these systems is contingent on long-term effectiveness of non-thermal management of shrub residue and that the actual rates depend strongly on soil type and scenarios of future land management. Compared with the traditional “pruning-burned” management practice, returning prunings for 50 years would increase soil C sequestration by 200–350% without fertilization, and increase soil C sequestration by 270–483% under a low (35 kg ha −1 N yr −1; 20 kg ha −1 P yr −1) fertilization regime, depending on soil type and climate conditions. These results indicate that altered land management could contribute to transforming these degraded semiarid agroecosystems from a source to a sink for atmospheric CO 2.

Erosion and Nutrient Loss on Sloping Land under Intense Cultivation in Southern Vietnam

AbstractTo help improve the well‐being of the local people, a joint Vietnamese‐UK team set out to establish a way of estimating soil and nutrient losses under different land management scenarios, using field data extrapolated through remote sensing and GIS, to obtain catchment‐wide estimates of the impact of land cover change. Immigration from remote provinces to the Dong Phu District of Binh Phuóc Province, about 120 km north of Ho Chi Minh City, has led to disruption of soil surface stability on easily eroded clayey sandstones, creating rapid nutrient depletion that affects crop yields and siltation in the channel of the Rach Rat river downstream. The poor farmers of the areas see crop yields drop dramatically after two or three years of cultivation due to the fertility decline. Soil loss varies dramatically between wet season and dry season and with ground cover. Erosion bridge measurements showed a mean loss of 85.2 t ha−1 y−1 under cassava saplings with cashew nuts, 43.3 t ha−1 y−1 on uncultivated land and 41.7 t ha−1 y−1 under mature cassava. The rates of erosion were higher than those reported in many other parts of Vietnam, reflecting the high erodibility of the friable sandy soils on the steep side‐slopes of the Rach Rat catchment. However, although the actual measurements provide better soil loss data than estimates based on the parameters of soil loss equations, a large number of measurement sites is needed to provide adequate coverage of the crop and slope combinations in this dissected terrain for good prediction using GIS and remote sensing.

Drip irrigation water and salt flow model for table grapes in Coachella Valley, California

Unlike annual crops where reclamation leaching of salts can be readily conducted between cropping, leaching of salts in permanent crops that are drip irrigated pose challenges. A need exists to formulate and test a management-type of salinity model for drip irrigation of table grapes. The model reported herein predicts the distribution of salts along the vine row and between the rows during the growing season, as affected by reactivity of salts of the applied irrigation water as well as rate and duration of drip application. The calibrated model reproduced the initial field salinity profiles after repeated irrigation cycles by adjusting only the routing factor α which is the ratio of horizontal to vertical water flow. After eight cycles the profiles stabilized and the calibrated horizontal to vertical flow routing ratio was 0.6. There is remarkable agreement between measured and simulated salinity. Corresponding soil moisture profiles show the expected high water content with depth at the emitter, the decrease in surface water content with radial distance and the increase with depth, at the distal end of the wedge. Although the model is location specific it can be applied knowing soil, initial and boundary conditions, as well as irrigation application quantity and quality and as such can be applied location by location in order to assess flow and quality of deep percolation recharging the groundwater system. With this capacity the model can predict soil water quantity and quality outcomes for possible land and water management scenarios.

A Modelling Framework for Addressing the Synergies Between Global Conventions Through Land Use Changes: Carbon Sequestration, Biodiversity Conservation, Prevention of Land Degradation and Food Security in Agricultural and Forested Lands in Developing Countries

This paper proposed a methodological framework for the assessment of carbon stocks and the development and identification of land use, land use change and land management scenarios, whereby enhancing carbon sequestration synergistically increases biodiversity, the prevention of land degradation and food security through the increases in crop yields. The framework integrates satellite image interpretation, computer modelling tools (i.e. software customization of off-the-shelf soil organic matter turnover simulation models) and Geographical Information Systems (GIS). The framework addresses directly and indirectly the cross-cutting ecological concerns foci of major global conventions: climate change, biodiversity, the combat of desertification and food security. Their synergies are targeted by providing procedures for assessing and identifying simultaneously carbon sinks, potential increases in plant diversity, measures to prevent land degradation and enhancements in food security through crop yields, implicit in each land use change and land management scenario. The scenarios aim at providing “win-win” options to decision makers through the framework’s decision support tools. Issues concerning complex model parameterization and spatial representation were tackled through tight coupling soil carbon models to GIS via software customization. Results of applying the framework in the field in two developing countries indicate that reasonably accurate estimates of carbon sequestration can be obtained through modeling; and that alternative best soil organic matter management practices that arrest shifting “slash-and-burn” cultivation and prevent burning and emissions, can be identified. Such options also result in increased crop yields and food security for an average family size in the area, while enhancing biodiversity and preventing land degradation. These options demonstrate that the judicious management of organic matter is central to greenhouse gas mitigation and the attainment of synergistic ecological benefits, which is the concern of global conventions. The framework is to be further developed through successive approximations and refinement in future, extending its applicability to other landscapes.

The role of land management practices in soil erosion hazard in eucalypt stands in north-central Portugal following forest wildfires

The EROSFIRE project (POCI/AGR/60354/2004), funded by Portugal’s Foundation for Science and Technology (FCT), has as overall aim the development of a software tool that allows to assess and map, at the scale of individual hill slopes, soil erosion hazard in recently burned forest areas for different scenarios of post-fire land management. At the origin of the EROSFIRE project was the “Soil losses after the forest fires of the summer of 2003”-map elaborated by Portugal’s Water Institute (INAG) using some modified version of the Universal Soil Loss Equation (USLE), and the idea to test the applicability of erosion models with a more up-to-date scientific basis than USLE. The EROSFIRE project envisages intensive field campaigns of rainfall simulation experiments (RSE’s) as a possible way-around the data constraints easily encountered in model parameterisation, calibration and assessment in environments that are highly variable through time and in space. In the aftermath of a wildfire, vegetation and soil conditions can be expected to change quite rapidly. Land management practices can add to the spatial variability in post-fire conditions as well, especially also when they are still in course. Notwithstanding the prevalent role of RSE’s in the EROSFIRE project, runoff plots are employed as well. Small-scale plots having exactly the same dimension as the plots of the RSE’s are used to address the representativeness of the RSE-data and, in particular, the corresponding modelling results for natural rainfall conditions. Slope-scale plots, in turn, are used to evaluate the upscaling of the modelling results at the RSE-plot scale. Thus, besides RSE’s, soil erosion modelling is at the heart of the approach that the EROSFIRE project has set out to develop and test. Various existing erosion models, including the above-mentioned USLE version used by the INAG, are to be compared, and the best model eventually adapted to the Portuguese situation is to map qualitative or quantitative erosion hazard of recently burned forested slopes. In the first project year, having as principal aim model parameterization and calibration, fieldwork is being carried out in an area in the Albergaria-a-Velha and Agueda minicipalities that was affected by a wildfire during early July 2005. In this area, which is largely covered by commercial eucalypt plantations, four slope sections were selected in eucalypt stands for the installation of the runoff plots and for RSE’s. The four slope sections were chosen for representing distinct land management practices.

Simulation of soil thickness evolution in a complex agricultural landscape at fine spatial and temporal scales

Hedgerow networks in the landscape are adapted objects that can be used to study soil redistribution processes within the landscape. In hedged landscapes, water erosion redistributes soil, but hedges act as barriers to the physical transfers of soil particles. The most systematic effect is the increase in the thickness of A-horizons uphill from the hedges. A field experiment was carried out within an old agricultural area with a high density of hedges. A high resolution digital elevation model and a soil thickness map were created to investigate the effect of hedges on soil reorganization. The aims of this paper are to use this pedological knowledge for a better understanding of process dynamics, to simulate quantitatively the effect of hedgerow network on soil organization and redistribution, and to test different scenarios of land management on soil redistribution dynamics. The simulation uses a mechanistic model where the change in soil thickness over time depends on the transport of soil through a diffusive transport and a water erosion process. We tested the suitability of the model to operate on a DEM with grid size of 1 m and a simulation time of less than 1200 years. We performed the simulations on theoretical and actual DEMs with and without the hedgerow network. The effect of different land use and management scenarios on soil redistribution was tested. Those scenarios were applied on a DEM of real landscape, with the addition and removal of hedge on the DEM. The results suggest that the combination of diffusive transport and water erosion could significantly modify the topography and soil redistribution over a few centuries. The simulations show that hedges modify soil distribution and landforms by favouring deposition in the uphill position and soil erosion in the downhill position in agreement with field observations.

River pollution from non-point sources: a new simplified method of assessment

Assessment of the pollution of water bodies from non-point sources is a complex data- and time-consuming task. The potential non-point pollution index (PNPI), is a new tool designed to assess the global pressure exerted on rivers and other surface water bodies by different land uses. The main feature of PNPI is the wide availability of its input data. Very detailed input maps, often lacking over many areas, are not needed for PNPI calculation. As a consequence of the input data used, the modelling of physical reality and of processes is heavily simplified. The authors counterbalanced such a simplification using an ‘expert system’ approach. The system bypasses the accurate representation of the physical reality to assess globally the pollution potential of different land uses according to the judgement of scientists. The scientific community proposes many models for depicting the dynamics of pollutants coming from diffuse sources. Most of them can be grouped into two broad categories: statistical models and physically based models. PNPI belongs to neither of the above-mentioned groups. PNPI is a GIS-based, watershed-scale tool designed to inform decision makers and public opinion about the potential environmental impacts of different land management scenarios. PNPI applies the multicriteria technique to pollutant dynamics and water quality. The pressure exerted on water bodies by diffuse pollution coming from land units is expressed as a function of three indicators: land use, run-off and distance from the river network. They are calculated from land use data, geological maps and a digital elevation model (DEM). The weights given to different land uses and to the three indicators were set according to experts' evaluations and allow calculation of the value of the PNPI for each node of a grid representing the watershed; the higher the PNPI of the cell, the greater the potential impact on the river network. The output of the calculation is presented in the form of maps that highlight areas that are more likely to produce pollution. Last, possibilities, strategies and results of the validation of the PNPI are described. In the authors' view, the explicit link between land use and potential pollution on which PNPI is based, together with its high communication potential, make it particularly interesting for a participatory and integrated approach to land management and environmental protection.

An Integrated Modeling Approach to Total Watershed Management: Water Quality and Watershed Assessment of Cheney Reservoir, Kansas, USA

Degradation of water quality is the major health concern for lakes and reservoirs in the central regions of the United States as a result of heavily devoted agricultural production. A vital key to the development of a reservoir management strategy is to identify nutrient loading that describes associated water quality conditions in reservoirs. This study integrated AnnAGNPS watershed and BATHTUB lake models to simulate actual lake water quality conditions of Cheney Reservoir, KS, and demonstrated the use of the coupled model for simulating lake response to changes in different watershed land use and management scenarios. The calibrated current-conditions model simulated in-lake reductions as much as 52% for TN, 48% for TP, and 70% for chlorophyll a due to conversion to native grass, and increases as much as 4% for TN, 9% for TP and 6% for chlorophyll a due to conversion of land from the Conservation Reserve Program (CRP) to cropland (15.5% of watershed). This model also demonstrated an increase in chlorophyll a (19%) as the lake sediment capacity was reached over the next century.

Application of the SWAT model on the Medjerda river basin (Tunisia)

The Medjerda river basin (Northern Tunisia) is experiencing an intensification of agriculture and the irrigated area is increasing rapidly. The SWAT (Soil and Water Assessment Tool) model, a soil, water, sediment, and nutrient transformation and fate simulator for agricultural watersheds, was applied to this catchment to study the potential impact of land management scenarios. The model was able to represent the hydrological cycle even though some discrepancies were observed, probably due to a lack of sufficient rainfall data, and due to the lack of representation of reservoirs. It was predicted that converting all agricultural land to irrigated crop introduced significant changes on nitrate concentration in surface water. However, the concentration was still below the limit of potability. It was also predicted that drastic reduction in the load of ammonium and phosphorus could be achieved by collecting and treating wastewater from major urban areas.

Modelling and managing critical source areas of diffuse pollution from agricultural land using flow connectivity simulation

A combined critical source area and flow accumulation model is described that predicts the spatial distribution in the risk of diffuse nutrient losses from agricultural fields reaching surface waters. The model is applied to a number of agricultural fields under a range of different land management scenarios. The model output highlights the importance of land management features such as tramlines, tracks and field drains in concentrating flow towards receiving waters and in increasing the risk of the delivery of pollutants derived from diffuse agricultural sources to watercourses. The model allows scenario analysis of the likely impact of flow path mitigation on diffuse nutrient loads.

Reconstruction of the total N and P inputs from the IJsselmeer into the western Wadden Sea between 1935–1998

In this paper we reconstruct the Total Nitrogen (TN) and Total Phosphorus (TP) inputs into the western Wadden Sea from its major freshwater source the lake IJsselmeer between 1935–1998. The reconstruction is based on the TN and TP loads of the river Rhine at the German/Dutch border and follows the aquatic continuum approach to calculate loads further downstream in (1) the river IJssel feeding the IJsselmeer, and (2) the discharge of this lake into the western Wadden Sea. Our objectives are to determine (1) how the signal of changing nutrient loads of the Rhine is transferred downstream, and (2) how hydrological changes in the rivers-and-lake system affected the TN and TP discharges into the western Wadden Sea. Observational data from which TN and TP loads of the river Rhine could be calculated date back to the 1960s and we used background loads for European rivers for the period before World War II. The period in between was interpolated using the historic scenarios of watershed land use and management tested for the hypothetical Phison river (Billen and Garnier, 1997, Aquat. Microb. Ecol. 13, 3–17), adapted for the hydrology of the Rhine. The interpolations were constrained by loads of dissolved inorganic N and P compounds, for which data go back to the 1930s. Using the reconstructed loads of the river Rhine, TN and TP loads of the river IJssel and the lake IJsselmeer were calculated with simple mass balance models that were calibrated against data available from 1972–1993 onwards. Results show a gradual 12-fold increase of the TN discharge of the IJsselmeer into the Wadden Sea from 1935 to 1988, after which it decreased to levels still ∼5 fold those in 1935. The discharge of TP increased more abruptly in the early 1960s to values in 1983 ∼10 fold those before 1965, followed by a sharp decrease to values still ∼2.5 fold those before 1965. These patterns resemble those in the river Rhine, but are modified due to (1) variability of other sources to the lake, and (2) reduction of the retention capacity of the lake due to enormous land reclamation. TN:TP atomic ratios in the freshwater input to the Wadden Sea as high as 100 in 1995 were caused by successful P reduction programmes, less successful N reduction and N-rich inputs from smaller rivers and land runoff into the lake IJsselmeer. Land reclamation caused the lake's retention of TN to decrease step-wise from ∼70% to ∼45–50% and that of TP from 85% to 55–60% between 1950 and 1980.