An integrated modelling and multicriteria analysis approach to managing nitrate diffuse pollution: 2. A case study for a chalk catchment in England

The site-specific land use optimisation methodology, suggested by the authors in the first part of this two-part paper, has been applied to the River Kennet catchment at Marlborough, Wiltshire, UK, for a case study. The Marlborough catchment (143 km(2)) is an agriculture-dominated rural area over a deep chalk aquifer that is vulnerable to nitrate pollution from agricultural diffuse sources. For evaluation purposes, the catchment was discretised into a network of 1 kmx1 km grid cells. For each of the arable-land grid cells, seven land use alternatives (four arable-land alternatives and three grassland alternatives) were evaluated for their environmental and economic potential. For environmental evaluation, nitrate leaching rates of land use alternatives were estimated using SHETRAN simulations and groundwater pollution potential was evaluated using the DRASTIC index. For economic evaluation, economic gross margins were estimated using a simple agronomic model based on nitrogen response functions and agricultural land classification grades. In order to see whether the site-specific optimisation is efficient at the catchment scale, land use optimisation was carried out for four optimisation schemes (i.e. using four sets of criterion weights). Consequently, four land use scenarios were generated and the site-specifically optimised land use scenario was evaluated as the best compromise solution between long term nitrate pollution and agronomy at the catchment scale.     

Integration for sustainable catchment management

Sustainable catchment management requires increased levels of integration between groups of natural and social scientists, land and water users, land and water managers, planners and policy makers across spatial scales. Multiple policy drivers, covering urban and rural communities and their relationships with land and water use, have resulted in the need for an integrated decision making framework that operates from the strategic national scale to the local catchment scale. Large gaps in integration between policies are resulting in uncertain outcomes of conflicting and competing policy measures. The need for further integration is illustrated by little or no reductions in nitrate and phosphate levels in surface and ground waters in England and Wales. There is a requirement for natural scientists to consider the socio-economic setting and implications of their research. Moreover, catchment system level science requires natural and social scientists to work more closely, to provide robust analysis of the state of the environment that fully considers the bio-physical, social, political and economic settings. The combined use of spatial technologies, scenarios, indicators and multicriteria analysis are increasingly being used to enable improved integration for sustainable catchment management.     

Managing Agricultural Pollution Using a Linked Geographical Information System and Non-Point Source Pollution Model

This study documents the development of a link between a geographical information system (GIS) and a non-point source pollution model. The GIS ARC/INFO was linked to the agricultural non-point source pollution model and ORACLE data sources. Application of the system is demonstrated using the Bedford-Ouse catchment as a suitable case study. Water quality impacts are predicted from source data describing topography, soils, land use and river network. The model results were in agreement with observed nitrate concentrations at the catchment outlet, and more appropriate data sources are considered to be the main priority for improving model predictive ability. Management scenarios were established to assess the impact of changing agricultural management practices on predicted water quality. The approach has significant potential for the management of agricultural pollution in the UK.     

Buffer zone versus whole catchment approaches to studying land use impact on river water quality

Secondary databases, GIS and multivariate analysis tools were used to determine whether there was a correlation between water quality and landscape characteristics within three local southern Ontario watersheds. Whole catchment and 100 m buffer zone influences on water quality over three seasons were compared. Chemical fluxes were also calculated and used to compare the loading of pollutants to downstream environments. Urban land use had the greatest influence on water quality. The influence of agricultural land use was variable and did not agree with the results of other studies. The only natural landscape variables that appeared to have an influence on water quality were slope and silt-clay surficial geology deposit. There was a clear trend of increased chemical fluxes with increasing urban land use intensity within a watershed. Forested land use appeared important in mitigating water quality degradation. The catchment landscape characteristics appeared to have slightly greater influence on water quality than the 100 m buffer. The results of this study may have been influenced by the scale and accuracy of databases used. The secondary data were useful in determining major trends in water quality and possible non-point origins of surface water pollution, and in identifying areas that are in need of further investigation.     

Spatialised fate factors for nitrate in catchments: modelling approach and implication for LCA results

The challenge for environmental assessment tools, such as Life Cycle Assessment (LCA) is to provide a holistic picture of the environmental impacts of a given system, while being relevant both at a global scale, i.e., for global impact categories such as climate change, and at a smaller scale, i.e., for regional impact categories such as aquatic eutrophication. To this end, the environmental mechanisms between emission and impact should be taken into account. For eutrophication in particular, which is one of the main impacts of farming systems, the fate factor of eutrophying pollutants in catchments, and particularly of nitrate, reflects one of these important and complex environmental mechanisms. We define this fate factor as: the ratio of the amount of nitrate at the outlet of the catchment over the nitrate emitted from the catchment's soils. In LCA, this fate factor is most often assumed equal to 1, while the observed fate factor is generally less than 1. A generic approach for estimating the range of variation of nitrate fate factors in a region of intensive agriculture was proposed. This approach was based on the analysis of different catchment scenarios combining different catchment types and different effective rainfalls. The evolution over time of the nitrate fate factor as well as the steady state fate factor for each catchment scenario was obtained using the INCA simulation model. In line with the general LCA model, the implications of the steady state fate factors for nitrate were investigated for the eutrophication impact result in the framework of an LCA of pig production. A sensitivity analysis to the fraction of nitrate lost as N(2)O was presented for the climate change impact category. This study highlighted the difference between the observed fate factor at a given time, which aggregates both storage and transformation processes and a "steady state fate factor", specific to the system considered. The range of steady state fate factors obtained for the study region was wide, from 0.44 to 0.86, depending primarily on the catchment type and secondarily on the effective rainfall. The sensitivity of the LCA of pig production to the fate factors was significant concerning eutrophication, but potentially much larger concerning climate change. The potential for producing improved eutrophication results by using spatially differentiated fate factors was demonstrated. Additionally, the urgent need for quantitative studies on the N(2)O/N(2) ratio in riparian zones denitrification was highlighted.     

A dynamic Mills heritage model with replaceable capital

A general equilibrium, linear programming model of urban land use formulated in the heritage of Edwin Mills is reformulated for dynamic solution. This multiperiod extension identifies discontinuous land use as an optimal market strategy under reasonably general conditions of economic change. Information about future economic conditions is assumed to be complete, and capital is assumed to be replaceable at finite cost. As a result, land uses and export mixes adjust over time in response to exogenous shifts in export prices. It is noted that discontinuous land uses can constitute long-run outcomes, and a distinction is drawn between the assumptions associated with static and long-run perspectives.     

Analysis of vulnerability factors that control nitrate occurrence in natural springs (Osona Region, NE Spain)

Nitrate pollution is one of the main concerns of groundwater management in most of the world's agricultural areas. In the Osona region of NE Spain, high concentrations of nitrates have been reported in wells. This study uses the occurrence of this pollutant in natural springs as an indicator of the sub-surface dynamics of the water cycle and shows how groundwater quality is affected by crop fertilization, as an approach to determine the aquifer vulnerability.Nitrate concentration and other hydrochemical parameters based on a biannual database are reported for approximately 80 springs for the period 2004-2009. The background concentration of nitrate is first determined to distinguish polluted areas from natural nitrate occurrence. A statistical treatment using logistic regression and ANOVA is then performed to identify the significance of the effect of vulnerability factors such as the geological setting of the springs, land use in recharge areas, sampling periods, and chemical parameters like pH and EC, on groundwater nitrate pollution.The results of the analysis identify a threshold value of 7-8 mg NO₃⁻/L for nitrate pollution in this area. Logistic regression and ANOVA results show that an increase in EC or a decrease in pH values is linked to the possibility of higher nitrate concentrations in springs. These analyses also show that nitrate pollution is more dependent on land use than the geological setting of springs or sampling periods. Indeed, the specific geological and soil features of the uppermost layers in their recharge areas do not contribute to the buffering of nitrate impacts on aquifers as measured in natural springs. Land use, and particularly fertilization practices, are major factors in groundwater vulnerability.     

Modelling nitrogen in the Yeşilirmak River catchment in Northern Turkey: impacts of future climate and environmental change and implications for nutrient management

Recent research in catchments of rapidly developing countries such as Brazil and China suggests that many catchments of the developing world are already showing signs of nitrogen pollution reminiscent of past experiences in developed countries. This paper looks at both the individual and combined effects of future climate change and other likely environmental changes on in-stream nitrate concentrations in a catchment in Northern Turkey. A model chain comprised of simulated future temperature and precipitation from a Regional Circulation Model (RCM), a conceptual hydrological model (HBV) and a widely tested integrated catchment nitrogen model (INCA-N) is used to model future changes in nitrate concentrations. Two future periods (2021-2050 and 2069-2098) are compared to the 1961-1990 baseline period in order to assess the effectiveness of several possible interventions available to catchment authorities. The simulations show that in the urbanised part of the catchment, the effects of climate change and other environmental changes act in the same direction, leading to peak nitrate concentrations of 7.5 mg N/l for the 2069-2098 period, which corresponds to a doubling of the baseline values. Testing different available policy options reveals that the installation of wastewater treatment works (WWTWs) in all major settlements of the catchment could ensure nitrate levels are kept at near their baseline values for the 2021-2050 period. Nevertheless, a combination of measures including WWTWs, meadow creation, international agreements to reduce atmospheric N concentrations and controls on agricultural practises will be required for 2069-2098. The approach presented in this article could be employed in order to anticipate future pollution problems and to test appropriate solutions, some of which will necessitate international co-operation, in other catchments around the world.     

Managing a complex river catchment: a case study on the River Almond

The River Almond catchment in the east central belt rates amongst Scotland's most polluted rivers. This paper describes how shifting forms of economic development in the catchment since the 1860s have affected river quality. A legacy of effects from past land uses has combined with the impacts associated with current land uses to present a substantial and complex management challenge. It is argued that there have been, and still are, scientific, legislative and socio-economic constraints on the abilities of managers to respond promptly to changing patterns of impacts on the river system. This response lag has tended to increase the costs of subsequent remediation, and has consequently supported a downward pressure on the quality standards that are considered 'realistic' by river managers. Conversely, advances in science, the expansion of regulatory powers and resources, and an increase in public interest in the environment has helped to clarify the extent of the management problems in the catchment, and allowed major advances in some areas of pollution management. In an attempt to overcome some of the remaining weaknesses of river management, river managers and interest groups have started to form inter-sectoral and multidisciplinary partnerships. The success of these new groupings is highly contingent, not so much on the competence of their scientific advice, but on the priority given to water protection by the land-use decision-makers involved, and the resources they are prepared to commit to funding rehabilitation.     

Predicting stream N and P concentrations from loads and catchment characteristics at regional scale: a concentration ratio method

We used a concentration ratio method to predict yearly and summer averages of stream total nitrogen, nitrate and total phosphorus concentrations at a regional scale. The ratio of the median daily concentration on the flow weighted annual concentration was used. This ratio characterizes the concentration dynamics of a catchment. We took advantage of the commonly used budget type models applied at a regional scale to relate concentrations to loads instead of directly to land uses, as has previously been done. The relationship was modeled with Boosted Regression Trees using catchment and stream characteristics along with loads and flows obtained from the SPARROW budget model. The ratio modeling approach was compared to a direct approach for concentration prediction, and also to a simple method where the mean ratio was used. The modeling performances of the ratio models were overall satisfying (r² of 49% to 78%), and a better choice than the two other methods tested. This ratio modeling approach is based on a steady state assumption and largely ignores temporal dynamics. As such, this modeling technique does not replace the more physically-based techniques, but allows for hybrid approaches for improved spatial interpolations. This method could be used to predict effectively the impact (at equilibrium) of land use change and management scenarios on water quality at a regional scale.     

Integrated Lake and Catchment Phosphorus Model– A Eutrophication Management Tool. I: Model Theory

The paper describes an integrated lake and catchment model which was developed and tested against data from the Rutland Water catchment (River Nene and Welland) in Eastern England. The model uses export coefficients to predict annual diffuse losses of phosphorus from catchment land use, which are temporally disaggregated using empirical relationships between phosphorus load and discharge in headwater streams. Dynamic inputs of phosphorus are incorporated into a hydrologically based, multi-reach distributed catchment model which also simulates sewage discharges, abstractions and reservoirs/ lakes. The model allows a comparison of simulated output with observed discharge and water-quality data from various points within the river system.     

Monitoring a flood event in a densely instrumented catchment, the Upper Eden, Cumbria, UK

Multi‐day rainfall events appear to be an important cause of recent flooding in the UK. Hydrological data from an extensive, nested hydrometric network in the unregulated, predominantly rural Upper Eden catchment in northern England are presented for one such flood event. These highlight antecedent catchment conditions and the propagation of the multi‐day flood event during February 2004. An assessment of flood response is provided over varying scales and land use between the upland Gais Gill catchment (1.1 km²) and the larger Upper Eden catchment (616 km²). Large spatial variations in rainfall totals are identified from a dense raingauge network during the flood event and are principally related to catchment elevation. High cumulative rainfall totals for the 6‐day event, particularly at upland sites appear to be the exceptional feature of the flood event with return periods in the order of 100 years at some upland gauges. Resultant patterns of flood attenuation and translation are quantified in different areas of the catchment, highlighting the flashy response of the headwater catchments and the attenuated downstream response in the lowland environment. The study forms part of the national Catchment Hydrology And Sustainable Management (CHASM) programme.     

Spatial variations of storm runoff pollution and their correlation with land-use in a rapidly urbanizing catchment in China

The composition of land use for a rapidly urbanizing catchment is usually heterogeneous, and this may result in significant spatial variations of storm runoff pollution and increase the difficulties of water quality management. The Shiyan Reservoir catchment, a typical rapidly urbanizing area in China, is chosen as a study area, and temporary monitoring sites were set at the downstream of its 6 sub-catchments to synchronously measure rainfall, runoff and water quality during 4 storm events in 2007 and 2009. Due to relatively low frequency monitoring, the IHACRES and exponential pollutant wash-off simulation models are used to interpolate the measured data to compensate for data insufficiency. Three indicators, event pollutant loads per unit area (EPL), event mean concentration (EMC) and pollutant loads transported by the first 50% of runoff volume (FF50), were used to describe the runoff pollution for different pollutants in each sub-catchment during the storm events, and the correlations between runoff pollution spatial variations and land-use patterns were tested by Spearman's rank correlation analysis. The results indicated that similar spatial variation trends were found for different pollutants (EPL or EMC) in light storm events, which strongly correlate with the proportion of residential land use; however, they have different trends in heavy storm events, which correlate with not only the residential land use, but also agricultural and bare land use. And some pairs of pollutants (such as COD/BOD, NH₃-N/TN) might have the similar source because they have strong or moderate positive spatial correlation. Moreover, the first flush intensity (FF50) varies with impervious land areas and different interception ratio of initial storm runoff volume should be adopted in different sub-catchments.     

Risk prioritisation of stormwater pollutant sources

This paper describes the development of a pollutant risk prioritisation methodology for the comparative assessment of stormwater pollutants discharged from differing land use types and activities. Guidelines are presented which evaluate available data with respect to ‘likelihood of occurrence’ and ‘severity of impact’. The use of the developed approach is demonstrated through its application to total suspended solids, biochemical oxygen demand, lead and cadmium. The proposed benchmarking scheme represents a transparent and auditable mechanism to support the synthesis of data from a variety of sources and is sufficiently flexible to incorporate the use of chemical, physical and/or ecological data sets. Practitioners involved in developing and implementing pollutant mitigation programmes are assisted in two key ways. Firstly through enabling the risks to receiving waters from diffuse pollution on a source-by-source and/or pollutant-by-pollutant basis at a catchment scale to be comparatively assessed and prioritised. Secondly, the methodology informs the selection of appropriate diffuse pollution control strategies.     

Assessing the effects of land use on temporal change in well water quality in a designated nitrate vulnerable zone

The nitrate concentration in discharge from the Balmalcolm borehole in Fife, Scotland, has steadily increased from 4.5 mg l(-1) NO3-N in the early 1970s to 11.0 mg l(-1) NO3-N in 1998. Consequently the catchment of the borehole, covering an area of 400 ha has recently been designated a Nitrate Vulnerable Zone under the EC Nitrate Directive [Commission of European Communities L375, (1991) 1]. The sandstone aquifer that supplies the borehole is recharged by water draining from land that is intensively cropped to green vegetables. There is, therefore, a need to identify appropriate land management techniques that will help to abate the nitrate losses from the land and to estimate the length of time that it is likely to take before the abatement is observed as a decrease in well-water concentrations. Estimates of nitrate leaching for the range of crops that have been grown in the catchment over the last 30 years have been made using a balance sheet approach, modified to allow for estimates of denitrification and in-field composting of vegetable crop residues. Integration over the whole catchment using a GIS approach, indicates a steady-state well water [NO3--N] of 23 mg l(-1)--a situation that has not yet been reached. Prediction of the time course of change in well water quality from 1970 (when intensification began) has been made by calculating the travel time from different parts of the catchment both in the saturated and unsaturated zones. The results show good agreement between the measurements and simulation. Well water [NO3-N] under potential future management scenarios have also been investigated using the same approach. The greatest reduction in steady-state concentration, to 9 mg l(-1), is achieved for the scenario of extensification to spring cereals with moderately fertilised grassland. However, the temporal simulations suggest that it would take approximately 100 years before 80% of this change is observed in the well-water, starting from a concentration of 23 mg l(-1) .     

Nitrogen leaching in a typical agricultural extensively cropped catchment,China: experiments and modelling

Protecting water resources from nitrogen (N) contamination is an important public-health concern and a major national environmental issue in China. Loss of N in soils due to leaching is not only one of the most important problems in agriculture farming, but is also the main factor causing N pollution in aquatic environments. The study area selected is in a typical agricultural extensively cropped land, Fuxianhu Lake catchment in Yunnan Province, China. Three sets of soil columns laboratory experiments were conducted to investigate the migration dynamics and leaching loss of N under different artificial rainfall intensities. One groundwater observation well in agricultural extensively cropped land was built to investigate the groundwater pollution caused by agriculture N loss. Based on the laboratory experiment and field monitoring results, the migration dynamics of ammonia-nitrogen (NH₄-N) and nitrate-nitrogen (NO₃-N) were analysed in detail. The LEACHMN model was used to test against the laboratory and field data to evaluate the drainage water and N leaching loss from the soil. The results indicate that the LEACHMN model is useful to carry out a numerical simulation of the water and N transport both in a laboratory experiment and in field monitoring. The findings of this paper help to demonstrate the distribution and migration of N in agricultural lands, as well as to explore the mechanism of groundwater contamination resulting from agricultural activities. The work presented in this paper is also believed to be useful in formulating management strategies for an extensively cropped catchment to reduce diffusive pollution from agricultural activities.     

Prediction of biological integrity based on environmental similarity--revealing the scale-dependent link between study area and top environmental predictors

Indices of Biological integrity (IBI) are considered valid indicators of the overall health of a water body because the biological community is an endpoint within natural systems. However, prediction of biological integrity using information from multi-parameter environmental observations is a challenging problem due to the hierarchical organization of the natural environment, the existence of nonlinear inter-dependencies among variables as well as natural stochasticity and measurement noise. We present a method for predicting the Fish Index of Biological Integrity (IBI) using multiple environmental observations at the state-scale in Ohio. Instream (chemical and physical quality) and offstream parameters (regional and local upstream land uses, stream fragmentation, and point source density and intensity) are used for this purpose. The IBI predictions are obtained using the environmental site-similarity concept and following a simple to implement leave-one-out cross validation approach. An IBI prediction for a sampling site is calculated by averaging the observed IBI scores of observations clustered in the most similar branch of a dendrogram -a hierarchical clustering tree of environmental observations- built using the rest of the observations. The standardized Euclidean distance is used to assess dissimilarity between observations.The constructed predictive model was able to explain 61% of the IBI variability statewide. Stream fragmentation and regional land use explained 60% of the variability; the remaining 1% was explained by instream habitat quality. Metrics related to local land use, water quality, and point source density and intensity did not improve the predictive model at the state-scale. The impact of local environmental conditions was evaluated by comparing local characteristics between well- and mispredicted sites. Significant differences in local land use patterns and upstream fragmentation density explained some of the model’s over-predictions. Local land use conditions explained some of the model’s IBI under-predictions at the state-scale since none of the variables within this group were included in the best final predictive model. Under-predicted sites also had higher levels of downstream fragmentation.The proposed variables ranking and predictive modeling methodology is very well suited for the analysis of hierarchical environments, such as natural fresh water systems, with many cross-correlated environmental variables. It is computationally efficient, can be fully automated, does not make any pre-conceived assumptions on the variables interdependency structure (such as linearity), and it is able to rank variables in a database and generate IBI predictions using only non-parametric easy to implement hierarchical clustering.     

Delineating cost‐effective wellhead protection zones in a rural area in Greece

The aim of this study is the protection of groundwater resources from nitrate pollution by regulating land use and by establishing guidelines for agricultural activities within specific wellhead protection areas. Wellhead protection zones are specifically designed in four wells in the municipality of Nea Moudania, an area of intensive agricultural activities in northern Greece. Recent water samples from these wells indicate high levels of nitrates concentrations. Wellhead protection areas are delineated through a geographic information systems (GIS) analysis in order to determine the boundaries of protection zones, as well as to identify the land use patterns and the specific crop types around the contaminated wells. Different land use management techniques for groundwater protection zoning are also examined with respect to their implementation cost. The purpose of this analysis is to identify the least expensive management strategy for wellhead protection. The results show that land use changes are always more expensive than implementing agro‐environmental measures.     

Agriculture-induced increase in nitrate concentrations in stream waters of a large Mediterranean catchment over 25 years (1981–2005)

Anthropogenic activities influence past and present nitrate levels recorded in European stream waters, posing a threat to aquatic biota and human beings. Scarce information on temporal trends of nitrate concentration and its causes is available for Mediterranean catchments. This study presents the evolution of nitrate concentrations over 25 years in stream waters of the Ebro River Basin (Spain), a large Mediterranean catchment involving 85,566 km². Nitrate concentration increased with time in 46% of the 65 sites involved in the study. Agricultural cover of 30 hydrologically independent sub-catchments was the main land use related to nitrate concentration (R² = 0.69). Throughout the 25 year-period, the sites showing increased nitrate concentrations with time (trend sites) also presented an enhanced influence of agricultural cover on nitrate concentrations along the time frame of the study. As a result of these temporal changes, at the end of the studied period nitrate concentrations in stream waters responded similarly to agricultural cover in both trend and non-trend sites, showing non significant differences in the slope of the resultant regression models. At this time, agricultural cover explained 82% of the variability found in nitrate levels. If these trends remain unchanged, in 2015 many of the water bodies considered in this study would not comply with the requirements of the European Union Water Framework Directive (WFD). Therefore management decisions, mainly associated to agricultural practices, should be implemented as soon as possible at the catchment level to meet WFD objectives.     

Land‐use planning in ‘one country,two systems’: Hong Kong,Guangzhou and Shenzhen

This paper studies the political economy of urban governance and land‐use planning mechanisms in the ‘one country, two systems’ of mainland China and the Hong Kong Special Administrative Region (SAR). It is argued that the market economy of Hong Kong had, over the years as a British colony, established an efficiently‐run regulatory system of land‐use planning. The current land‐use planning mechanisms are biased toward economic growth as a result of its executive‐government‐led and business‐interests‐dominated political structure. The challenge for Hong Kong as a relatively autonomous SAR, therefore, is to incorporate the social and environmental dimensions in planning for territorial development within a wider regional context as a result of economic and political integration with China. In mainland China, the reforming socialist planned economy has now embraced privately and foreign‐owned enterprises though the Communist Party and the government have retained strong political control. A ‘dual’ land‐use development system operates under an economic‐growth‐oriented development strategy. On one hand, government authorities who are land owners, land managers, and the largest land users as they own most of the economic enterprises, may not, for various reasons, follow the planning intentions when formally allocating land for development projects. On the other hand, illegal construction and land uses are widespread, suggesting that the formal land‐use planning system is ineffective, if not irrelevant, in controlling development. Part of the explanation lies in the absence of a genuine land market where legitimate persons with land‐use rights can buy and sell land within a planning framework generally agreed by the community. Unless Chinese cities strive to establish formal land‐use planning processes to prepare plans with the participation of various actors to reflect their needs, and establish urban planning mechanisms that have teeth in controlling development, urban planning will continue to be marginal in local governance.