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Inland waters play an active role in the global carbon cycle and emit large volumes of the greenhouse gases (GHGs), methane (CH4) and carbon dioxide (CO2). A considerable body of research has improved emissions estimates from lakes, reservoirs and rivers but recent attention has been drawn to the importance of small, artificial waterbodies as poorly quantified but potentially important emission hotspots. Of particular interest are emissions from drainage ditches and constructed ponds. These waterbody types are prevalent in many landscapes and their cumulative surface areas can be substantial. Furthermore, GHG emissions from constructed waterbodies are anthropogenic in origin and form part of national emissions reporting, whereas emissions from natural waterbodies do not (according to Intergovernmental Panel on Climate Change guidelines). Here, we present GHG data from two complementary studies covering a range of land uses. In the first, we measured emissions from nine ponds and seven ditches over a full year. Annual emissions varied considerably: 0.1-44.3 g CH4 m(-2) year(-1) and -36-4421 g CO2 m(-2) year(-1). In the second, we measured GHG concentrations in 96 ponds and 64 ditches across seven countries, covering subtropical, temperate and sub-arctic biomes. When CH4 emissions were converted to CO2 equivalents, 93% of waterbodies were GHG sources. In both studies, GHGs were positively related to nutrient status (C, N, P), and pond GHG concentrations were highest in smallest waterbodies. Ditch and pond emissions were larger per unit area when compared to equivalent natural systems (streams, natural ponds). We show that GHG emissions from natural systems should not be used as proxies for those from artificial waterbodies, and that artificial waterbodies have the potential to make a substantial but largely unquantified contribution to emissions from the Agriculture, Forestry and Other Land Use sector, and the global carbon cycle. Funding Agencies|European Research CouncilEuropean Research Council (ERC)European Commission [725546]; FORMASSwedish Research Council Formas [2018-01794, 2020-00950]; NERCUK Research & Innovation (UKRI)Natural Environment Research Council (NERC) [NE/N018087/1]

Mirim lagoon is the second largest lacustrine water body in Southern Brazil, providing water for local communities. However, algae growth and water quality in the lagoon and in tributaries rivers is influenced by nutrient’s increase. In this context, this study performs the empirical and semi-empirical chlorophyll-a (Chl-a) modeling using remote sensing and in situ data for water quality assessment. Water quality data were collected at 15 sample locations in the lagoon on the date of Sentinel-2 satellite overpass. Surface reflectance data were derived from the Sen2Cor atmospheric correction method and correlated with Chl-a concentration. The best model presented a Pearson’s correlation coefficient = 0.81 and Mean Absolute Error = 0.13µg.L-1. Low Chl-a concentration is observed at the Northern lagoon, possibly due to suspended solids presence. The same occurs in the left margin, being associated with the influence of land use for agriculture. High Chl-a concentrations are associated with shallower and lentic areas. The mean Chl-a concentration predicted by the model was 17.34μg.L-1, similar to the observed value in situ (16.32μg.L-1). Overall, the empirical model developed can be applied as a tool to reduce costs and efforts in fieldwork measures and to understand eutrophication in this river-lake transition ecosystem.

This is the report from the Northern Area Fisheries Advisory Committee meeting, which was held on the 12th October, 1981. It includes the information on the recommendations of the Area Fisheries Advisory Committees on the Review of Inland and Coastal Fisheries in England and Wales, and the restructuring of rod and line fishing licence duties. It also covers the report by the area fisheries officer on fisheries activities. This comments on river conditions and fishing, migratory fish movements from Yearl Weir fish counter and an update on Holmwrangle hatchery with the summary of the fly planting programme for salmon, sea trout and brown trout. Finally the report adds about stockings carried out by the Angling Associations, fish disease and management and survey work.The Fisheries Advisory Committee was part of the Regional Water Authorities, in this case the North West Water Authority. This preceded the Environment Agency which came into existence in 1996. Environment Agency Archives North West

This is the report from the Regional Fisheries Advisory Committee meeting, which was held on the 2nd February, 1987. The report contains sections on fishing licence duties, the abolition of coarse fish close season in enclosed waters, commercial salmon fishing in the River Lune and proposed fish counter validation studies. The Fisheries Advisory Committee was part of the Regional Water Authorities, in this case the North West Water Authority. This preceded the Environment Agency which came into existence in 1996. Environment Agency Archives North West

This is the Roy of the Rivers (cartoon) report produced by the National Rivers Authority (NRA) South West Region. This NRA document is a leaflet comic format which looks at the fishing and safe issues in rivers. This comic highlights the community policing to help guard the water environment. It gives a 24 hour emergency number and three steps to be followed in case of pollution, dead, distressed fish or suspects someone of illegally catching or selling fish. Environment Agency Archives North West

Inland waters receive a significant quantity of carbon (C) from land. The fate of this C during transit, whether it is emitted to the atmosphere, accumulated in sediments or transported to the ocean, can considerably reshape the landscape C balance. However, these different fates of terrestrial C are not independent but are instead linked via several catchment and aquatic processes. Thus, according to mass conservation, any environmental change inducing a shift in a particular C fate should come at the expense of at least one other fate. Nonetheless, studies that have investigated C emission, accumulation and transport concertedly are scarce, resulting in fragmented knowledge of the role of inland waters in the global C cycle. Here, we propose a framework to understand how different C fates in aquatic systems are interlinked and covary under environmental changes. First, to explore how C fates are currently distributed in streams, rivers, reservoirs and lakes, we compiled data from the literature and show that ‘C fate allocation’ varies widely both within and among inland water systems types. Secondly, we developed a framework that integrates C fates in any inland water system by identifying the key processes underlying their linkages. Our framework places the partitioning between the different C forms, and how this is controlled by export from land, internal transformations and hydrology, as central to understanding C fate allocation. We argue that, by focusing on a single fate, studies could risk drawing misleading conclusions regarding how environmental changes will alter the role of inland waters in the global C cycle. Our framework thus allows us to holistically assess the consequences of such changes on coupled C fluxes, setting a foundation for understanding the contemporary and future fate of land‐derived C in inland water systems., The different fates of terrestrial C in inland waters, whether it is emitted, stored or transported downstream, are linked via various catchment and aquatic processes. According to mass conservation, any environmental change inducing a shift in a particular C fate should come at the expense of at least one other fate, thus modifying the ‘C fate allocation’. Here we propose a framework that allows us to holistically assess the consequences of such changes on the coupled C fluxes of inland waters, setting a foundation for understanding the contemporary and future fate of land‐derived C in inland water systems.

Heat uptake is a key variable for understanding the Earth system response to greenhouse gas forcing. Despite the importance of this heat budget, heat uptake by inland waters has so far not been quantified. Here we use a unique combination of global‐scale lake models, global hydrological models and Earth system models to quantify global heat uptake by natural lakes, reservoirs, and rivers. The total net heat uptake by inland waters amounts to 2.6 ± 3.2 ×1020 J over the period 1900–2020, corresponding to 3.6% of the energy stored on land. The overall uptake is dominated by natural lakes (111.7%), followed by reservoir warming (2.3%). Rivers contribute negatively (‐14%) due to a decreasing water volume. The thermal energy of water stored in artificial reservoirs exceeds inland water heat uptake by a factor ∼10.4. This first quantification underlines that the heat uptake by inland waters is relatively small, but non‐negligible., Geophysical Research Letters, 47 (12), ISSN:0094-8276, ISSN:1944-8007

Carbon dioxide (CO2) uptake by phytoplankton can significantly reduce the partial pressure of CO2 (pCO2) in lakes and rivers, and thereby CO2 emissions. Presently, it is not known in which inland waters on Earth a significant pCO2 reduction by phytoplankton is likely. Since detailed, comparable carbon budgets are currently not available for most inland waters, we modified a proxy to assess the pCO2 reduction by phytoplankton, originally developed for boreal lakes, for application on a global scale. Using data from 61 rivers and 125 lakes distributed over five continents, we show that a significant pCO2 reduction by phytoplankton is widespread across the temperate and sub-/tropical region, but absent in the cold regions on Earth. More specifically, we found that a significant pCO2 reduction by phytoplankton might occur in 24% of the lakes in the temperate region, and 39% of the lakes in the sub-/tropical region. We also showed that such a reduction might occur in 21% of the rivers in the temperate region, and 5% of the rivers in the sub-/tropical region. Our results indicate that CO2 uptake by phytoplankton is a relevant flux in regional and global carbon budgets. This highlights the need for more accurate approaches to quantify CO2 uptake by primary producers in inland waters, particularly in the temperate and sub-/tropical region.

Remote sensing approaches to measuring inland water quality date back nearly 50 years to the beginning of the satellite era. Over this time span, hundreds of peer-reviewed publications have demonstrated promising remote sensing models to estimate biological, chemical, and physical properties of inland waterbodies. Until recently, most of these publications focused largely on algorithm development as opposed to implementation of those algorithms to address specific science questions. This slow evolution contrasts with terrestrial and oceanic remote sensing, where methods development in the 1970s led to publications focused on understanding spatially expansive, complex processes as early as the mid-1980s. This review explores the progression of inland water quality remote sensing from methodological development to scientific applications. We use bibliometric analysis to assess overall patterns in the field and subsequently examine 236 key papers to identify trends in research focus and scale. The results highlight an initial 30 year period where the majority of publications focused on model development and validation followed by a spike in publications, beginning in the early-2000s, applying remote sensing models to analyze spatiotemporal trends, drivers, and impacts of changing water quality on ecosystems and human populations. Recent and emerging resources, including improved data availability and enhanced processing platforms, are enabling researchers to address challenging science questions and model spatiotemporally explicit patterns in water quality. Examination of the literature shows that the past 10–15 years has brought about a focal shift within the field, where researchers are using improved computing resources, datasets, and operational remote sensing algorithms to better understand complex inland water systems. Future satellite missions promise to continue these improvements by providing observational continuity with spatial/spectral resolutions ideal for inland waters.

To evaluate and reflect the sustainability of services in the region, an overall sector sustainability assessment was done taking into account four main dimensions: access to services, quality of services, efficiency of services, and financing of services. Each of these dimensions is measured through three simple and objective indicators. For each indicator, best practice values are established by looking at the best performers in the region, and the countries closest to those best performers are deemed to have a more mature sector. A more complete description of the methodology to assess sector sustainability is included in the annex of the state of the sector regional report from the Danube Water Program. The outcomes of this assessment for the Croatia water sector are displayed in Figure 9, which also shows average and best practices in the Danube region. The Croatian sector sustainability score is 72, which is above the Danube average sustainability of 64. The assessment shows that on average, the country performs well in terms of access to piped water and flush toilets, continuity of service, nonrevenue water and customer satisfaction. The main deficiencies of the Croatia water sector identified through the sector sustainability assessment are the wastewater treatment coverage and the operating cost ratio. The main challenges are: financing compliance with the European environmental acquis; ensuring affordability of future tariffs; implementing successfully the aggregation reform; and strengthening regulation in the water sector.

Although only a small amount of the Earth's water exists as continental surface water bodies, this compartment plays an important role in the biogeochemical cycles connecting the land to the atmosphere. The territory of Brazil encompasses a dense river net and enormous number of shallow lakes. Human actions have been heavily influenced by the inland waters across the country. Both biodiversity and processes in the water are strongly driven by seasonal fluvial forces and/or precipitation. These macro drivers are sensitive to climate changes. In addition to their crucial importance to humans, inland waters are extremely rich ecosystems, harboring high biodiversity, promoting landscape equilibrium (connecting ecosystems, maintaining animal and plant flows in the landscape, and transferring mass, nutrients and inocula), and controlling regional climates through hydrological-cycle feedback. In this contribution, we describe the aquatic ecological responses to climate change in a conceptual perspective, and we then analyze the possible climate-change scenarios in different regions in Brazil. We also indentify some potential biogeochemical signals in running waters, natural lakes and man-made impoundments. The possible future changes in climate and aquatic ecosystems in Brazil are highly uncertain. Inland waters are pressured by local environmental changes because of land uses, landscape fragmentation, damming and diversion of water bodies, urbanization, wastewater load, and level of pollutants can alter biogeochemical patterns in inland waters over a shorter term than can climate changes. In fact, many intense environmental changes may enhance the effects of changes in climate. Therefore, the maintenance of key elements within the landscape and avoiding extreme perturbation in the systems are urgent to maintain the sustainability of Brazilian inland waters, in order to prevent more catastrophic future events.

The impact of agro-industrial activities on the water quality within River Nyando, Lake Victoria Basin (Kenya) was studied at different hierarchical levels between August 1997 and June 1999. Triplicate water samples were collected on a monthly basis from various stations ranging from the source to the mouth of the river and analyzed for selected physical and chemical water quality parameters using standard analytical methods. Statistical analysis was performed using MINITAB and STATISTICA computer packages. Agricultural land use was found to be the major factor contributing to changes in water quality. Salinity and pH varied at river basin scale, turbidity, TDS and conductivity at catchment scale, while DO, alkalinity and pH at subcatchment and river reach scale. The nutrient loads increased downstream. Anthropogenic sources contribute to high levels of nutrients within the basin. The changes recorded in water quality along the river were comparable to the modified Index of Biotic Integrity (IBI) and Nyando Habitat Evaluation Index (NHEI) derived for the river during the same period of study. Findings of this study can be used to design measures for mitigating and monitoring environmental impacts arising from agro-industrial activities within the Lake Victoria Basin. The study recommends a comprehensive Nyando River Basin Management Programme to address the multiple issues environmental within the basin. Published

This is the Visual survey ERS Dane, Weaver & Bollin Catchments produced by the Environment Agency in 2005. Visual surveys of the River Dane downstream of the confluence with the Swettenham Brook, the River Weaver, and the River Bollin catchment in the EA Northwest South area of England were undertaken between 3rd and 9th February 2005 with the aim of identifying the spatial distribution and relative quality of exposed Riverine sediments (ERS). The potential value of these ERS in terms of likely habitat quality for ERS invertebrate communities was determined by recording a suite of appropriate environmental variables. Following an initial cartographical analysis of reaches likely to contain ERS, tens of kilometres of riverbank were inspected and 67 areas of ERS were selected for detailed visual survey. Site characteristics ranged widely both between and within catchments, with habitat quality ranging from poor to very high. Environment Agency Archives North West

This is the Coleopteran Fauna of ERS on the river Dane, Cheshire: a survey report produced by the Environment Agency in 2003. A comprehensive survey of the Exposed Riverine Sediment (ERS) on the River Dane, Cheshire was undertaken between mid-April and mid-June 2003. 6 locations were selected and subsequently examined to determine the importance of the constituent invertebrate fauna. Appropriate sampling techniques (i.e. pitfall trapping, hand searching and excavations) were directed towards the target group (Coleoptera). All adults from the chosen taxa were identified to species level. The relative value of the fauna was assessed using species richness, conservation status, fidelity score and a site quality index. Environment Agency Archives North West + appendices

This is the Effect of water quality on coarse fish productivity and movement in the Lower River Irwell and Upper Manchester Ship Canal: a watercourse recovering from historical pollution report produced by the Environment Agency in 2003. The aim of this study was to investigate the impact of water quality upon coarse fish population dynamics in a lowland, urban watercourse. All of the research carried was undertaken in the lower River Irwell and upper Manchester Ship Canal, between February 1998 and December 2001. Of particular interest was the natural sustainability of the urban fishery given recent concern raised in the angling community over an apparent decline in coarse fish populations in lowland rivers. The research described in this report has concentrated upon the role of water quality in determining coarse fish population dynamics, and in particular: The impact of water quality upon fish growth and productivity; The impact of poor water quality and low dissolved oxygen concentrations upon fish distribution and movement; The impact of water quality upon the sexual development of fish. Environment Agency Archives North West

This is the 2001 annual report on fisheries in the North West produced by the Environment Agency North West in 2002. This report has four main aims: to inform the Agency’s customers of developments within the Agency, to inform the Agency’s customers of the work carried out by the Agency, to publish information on the performance of fisheries and the Fisheries Department, and to be a source of future reference. The fisheries service is funded in the main by a mixture of rod licence income and government grant-in-aid. The latter has declined substantially since the mid 1990’s and we are increasingly reliant on licence income to fund fisheries work. The environment agency had managed to use some of this money to fund their Urban Fisheries Development Programme, (UFDP). This is aimed at delivering new or improved fisheries in areas where demand for fishing is high, but where available fisheries are few in number or of poor quality. This work is dependent on good co-operation with local angling clubs, councils and other interests. Environment Agency Archives North West

This is the Mersey Estuary baseline survey: Analysis of macroinfaunal samples, literature review and database production report produced by the Environment Agency North West in 2002. This report presents an ecological review of the Mersey estuary along with an extensive bibliography of the available environmental literature for this system. The central objective of this programme has been to provide the information necessary to support the Environment Agency's review of existing and future consents (for discharges, abstractions etc) in the Mersey estuary. This review of consents was required because the Mersey had been designated as a Special Protection Area (SPA) under the EC Birds Directive. Therefore under Regulation 50 of the Conservation, the Environment Agency was responsible for reviewing any extant consent, or future applications, which may directly or indirectly, affected this SPA. Environment Agency Archives North West + appendices

This report presents a preliminary assessment of the state of salmon stocks and fisheries in England and Wales in 2001 to assist ICES in providing scientific advice to NASCO and to provide early feedback to fishery managers and anglers. The chief indicators of the state o f salmon stocks are normally the catches taken by rod and net fisheries. However, in 2001 angling was affected by the outbreak of foot and mouth disease (FMD), which restricted angling opportunities and access to rod fisheries in many parts of the country for lengthy periods. It is impossible to quantify the impact that FMD had on rod catches, although these were undoubtedly significantly reduced; net fisheries were unaffected by FMD. The declared salmon catch for 2001 (including those fish released alive by anglers) is provisionally estimated at 209 tonnes, representing some 57,000 fish, and comprising 153 tonnes (-43,000 fish) by nets and fixed engines and 56 tonnes (-14,000 fish) by rods. For direct comparison with previous years, it should be noted that the declared catch prior to the issue of a second reminder was about 49 tonnes (see below). An estimated 26 tonnes (43%) of the rod catch was released alive. These figures do not take account of catches of salmon which go unreported (including those taken illegally), and it is estimated that there may have been a total of 33 tonnes of additional fish caught in 2001; approximately 15% of all fish killed. Environment Agency Archives North West

This is the Water Quality Monitoring in the Mersey Estuary report produced by the Environment Agency in 2001. This report focuses on the Water Quality Monitoring Programme held in the Mersey Estuary. Since the mid-1960s water samples have been collected at approximately monthly intervals along the length of the estuary between Warrington and New Brighton and in later years further off-shore. This data-set provides an invaluable resource to determine how the very large capital spending of recent years has resulted in the dramatic improvements in water quality that we are now able to record. Initially, the interest was focused on parameters such as dissolved oxygen, BOD, nutrients and suspended solids. Over the last decades, as analytical methods have improved, toxic metals and persistent organic compounds have been included in the routine monitoring programme at a limited number of sites. Moreover, with the introduction of the European Water Framework Directive monitoring programmes it was an opportune time to review the Mersey monitoring strategy. This revised monitoring programme required data from several other components (water, sediments, flora, fauna, fish and birds. This report also contains information about Routine monthly surveys, Special surveys, Chloralkali Directive, UKNMP, British Geological Survey, EDMAR and NERC Environmental Diagnostics Thematic Programme. Environment Agency Archives North West + appendices

This is the River Eden RHS and geomorphology evaluation: Final report October 2001 produced by the Environment Agency North West in 2001. This report analysed the River Habitat Survey (RHS) and geomorphology data to evaluate the level of habitat quality and the geomorphological characteristics of the River Eden and sub-catchments. RHS data and geomorphological assessment data was collected within the study areas by CEH and Fluvial Environmental Services Ltd. The River Eden and its sub-catchments are being considered as a Special Area for Conservation (SAC) due to the presence of habitat types and species, which are rare or threatened within Europe. The purpose of the project is to provide an overview of the state of the catchment in terms of river habitats and geomorphological processes in order to aid the derivation of sound management for this proposed SAC.The aim of this report was to determine the state of the environment within the Eden and sub-catchments and identify the main pressures on the system in order to derive sound management options. Environment Agency Archives North West

This is the River Leven (at Newby Bridge) freeze coring report produced by Lancaster University in 2000. This study looks at fine materials in river Leven that may have to be considered detrimental to successful salmonid spawning. Following an observed decline in quality of salmonid fisheries at the site an investigation was initiated to assess the extent of ingress of fine sediments into the spawning gravels. A broader picture was sought by sampling both above and below the weir and close to both banks of the river. A comparison of the fine sediment from each sample site was undertaken. All the freeze cores used in this report contained distinct horizontal strata down through their length. The cores often penetrated into a highly compacted layer of light grey coloured material. The upper surface of this highly compacted layer is considered as a boundary between fine materials of different origin. Considerable variability was observed in the median grain size (D50) of the gravels from the cores. In addition variability was observed in the thickness of the upper less compacted layers. The role of regulated river flow across the weir in clearing fines from river gravels is briefly considered. Environment Agency Archives North West +appendices

This report is the fourth collation of salmon and migratory trout catch statistics for England and Wales produced by the Environment Agency. For the years 1989-94 these statistics were published by the National Rivers Authority (NRA) and for the years 1983-88 by the Ministry of Agriculture, Fisheries and Food, Directorate of Fisheries Research, in its Data Report series. This report is designed to be a reference document of declared salmonid catches in England and Wales. Salmon stock assessment data including provisional catches, counter run estimates and some juvenile data are now published in an annual assessment for the International Council for the Exploitation of the Seas (ICES). The second report in this series was published jointly by the Environment Agency and the Centre for Environment, Fisheries & Aquatic Science (CEFAS) in April 1998 (Anon 1999). Environment Agency Archives North West + tables and figures

This is the River Crake (at Bouthrey Bridge) freeze coring report produced by Lancaster University in 1999. This study looks at fine materials in river Crake at Bouthrey Bridge that may have to be considered detrimental to successful salmonid spawning. Following an observed decline in quality of salmonid fisheries at the site an investigation was initiated to assess the extent of ingress of fine sediments into the spawning gravels. Fine sediments from one potential source, upstream riverbanks, are also compared to those isolated from the spawning gravels. The percentage by weight of fine sediments for the six freeze cores, was found to be lower than first expected, given the visual appearance of the reach. However the fines were found to be distributed evenly down the cores with a marked absence of an upper, coarse gravel armour layer. In addition the median grain size (D50) of the six samples was generally low, falling to 6mm for core 5. The low median grain size and the absence of coarse grained upper strata are considered detrimental to the success rate of salmonid spawning. Environment Agency Archives North West +appendices

This is the River Leith fluvial audit: Final project report produced by Lancaster University in 1998. Freeze cores extracted from the upper and lower ends of River Leith illustrate that the bed is highly compacted in the downstream reach. Fine material is locally derived from bedrock at depths of only 32 cms into the bed and in one core fine material is 66% of the extracted core. Levels of fines that are believed to be detrimental to fish are put at 20 to 30%. Reduced flow and stream power from water abstraction may lead to a greater infiltration of fine material if gravels are not regularly flushed through with flood flows. Infiltration of fine material can lead to river bed compaction and concretion. A small abstraction may have no effect on the morphology of a river if the reduced discharge is within the normal range of flows experienced. However if the impact on flows is small it is still possible that fine sediment problems will develop progressively and the effects may not be noticed for several years. Environment Agency Archives North West

This report is the third collation of salmon and migratory trout catch statistics for England and Wales produced by the Environment Agency. For the years 1989-94, these statistics were published by the National Rivers Authority (NRA) and the years 1983-88 by the Ministry of Agriculture, Fisheries and Food, Directorate of Fisheries Research in its Data Report series. This report is designed to be a reference document of declared salmonid catches in England and Wales and is produced in the autumn following the season. Salmon stock assessment data including provisional catches, counter run estimates and some juvenile data are now published in an annual assessment for the International Council for the Exploitation of the Seas (ICES). The first report in this series was published jointly by the Environment Agency and the Centre for Environment, Fisheries & Aquatic Science (CEFAS) in April 1997 (Anon 1998). Environment Agency Archives North West

This is the history of contamination in sediments from the Mersey Estuary: Development of a chronology for the contamination of the Mersey Estuary by heavy metals and organochlorines Report produced by the Environment Agency in 1998. This report looks at the history of industrial contamination of the Mersey and Ribble Estuaries back to the early part of the last century, many decades before the start of monitoring programmes providing a remarkably detailed picture of very complex changes. There is a clear record in the sediment of the contamination by each heavy metal (including: Cu, Cr, Hg, Pb, Zn) and organochlorine chemical (including DDT isomers and PCB congeners) studied. The results of the study clearly show the increases in levels of contamination as industry expanded early last century followed by various improvements as this century progressed. Each pollutant has its own idiosyncratic pattern of change with some improvements predating modern environmental concerns whilst other changes seem to relate directly to recent improvements in legislative control. Overall, for the pollutants studied, the results clearly demonstrate the magnitude of improvement that has been achieved in what was a very polluted area. The only major reservation to this story is that despite the wide range of substances covered, many other potentially important pollutants remain to be studied in a similar manner. Environment Agency Archives North West

This is the River Ehen and Tributaries SSSI consultation Protocol for the Environment Agency with English Nature, produced in 1998. The Protocol is intended to provide for consistency of approach, to clarify responsibilities and help to streamline the statutory consultation and consenting procedures in which both organisations are involved. It provides guiding principles on the approach to management issues. Based on the operations likely to damage the special interest (OLDSI) which forms part of the SSSI notification, the protocol identified acceptable management activities which contribute to the special interest of the site and those which may adversely affect that interest. OLDSI includes activities such: land drainage consents, discharge consents, herbicides approvals, fish-stocking consents, fishing licences, abstraction and impoundment licences, consents to construct/test pump boreholes, integrated pollution Control Licences and Waste Management Licences, capital projects, flood defence maintenance works, water resources, fisheries, pollution control, ecology surveys and Recreation works. Environment Agency Archives North West

Aquatic sediments in sedimentation zones of major rivers are in general sinks for pollutants. The sedimentation zone Ketelmeer/IJsselmeer is an important sink for contaminants of the river Rhine (i.e. river IJssel). Recent and historical pollution interact here. Redistribution of suspended solids and erosion of deposited sediment in the shallow Dutch lakes (due to wave action) are likely to change contamination levels of sediments in these lakes, which is the subject of this thesis. The aim of this research was to study and explain the variability of contaminants in the sedimentation area Ketelmeer/IJsselmeer in order to predict the fate of the contaminants in the future. For this purpose a number of methodologies and models were developed and/or adapted.Chapter 2 describes the collection and analysis of sediment cores, top-layer sediments and geologically different layers in Lake Ketelmeer. Sediment cores were sectioned into thin slices and the year of deposition of each layer was determined using radio-chemical analyses. The contaminant concentrations were plotted versus the year of deposition of each sediment layer to (re-)construct the history of contamination. Similar vertical changes in contaminant concentrations were found as in a number of sediment cores sampled in sandpits in Lake Ketelmeer. Further, differences in concentration between the top-layer sediments and the degree of contamination in the entire recent IJsselmeer deposits (IJm-deposits) of Lake Ketelmeer were found. The older Zuiderzee deposits (Zu-deposits) underlying the IJm-deposits have low background values for heavy metals, PAHs and PCBs. This indicates that downward transport of these contaminants with infiltrating water is negligible in this lake. The concentrations of metals and PAHs in the sediment cores reflect, without any serious alterations, the historical input of the past five decades. The pollution history is characterized by, in the early 1940s, low concentrations of metals and already elevated levels of PAHs; a possible reduction of these contaminants during the Second World War and attaining, their highest levels between 1955 and 1970. Rather low levels occur in recently deposited sediments, some of which are the lowest ever observed over the last five decades (Pb, As, and all studied PAHs). Almost all chlorinated compounds showed a certain decline in concentration in anaerobic sediments as compared to samples of the top-layer collected in 1972 and stored in the laboratory, which still reflect the original pollution input. For several PCBs this decline proved to be significant; it may have been caused by microbial dechlorination reactions in the anaerobic sediment. Consequently, the concentration profiles of the chlorinated compounds do not reflect the original pollution history directly. Despite the attenuation of concentration, peaks in PCB concentration profiles were still observed. The following trends in concentrations of PCBs can be currently observed in Lake Ketelmeer sediment:- Almost all PCBs studied had rather low concentrations in the early 1940s.- The highest levels of PCBs occurred between 1960 and 1975.- Recently deposited sediments also have elevated levels of PCBs as compared to the levels in layers from the early 1940s.Overall, recently deposited material is far less-polluted than sediment deposited in the 1960s and 1970s. These findings prove that in this lake older, highly polluted sediments are buried under a younger, less- polluted layer. However, at some locations, such as in dredged parts or erosive zones, the highly polluted layers may remain uncovered, so aquatic organisms may still be exposed to highly polluted sediments from the 1960s and 1970s through the benthic food chain.In Chapter 3 attention is focused on the distribution and geochronology of the sediments of Lakes Ketelmeer and IJsselmeer The concentrations of metals, PCBs, PAHs and various sediment characteristics were determined in 77 samples of the surface sediments and one 3 in core of both lakes. Absolute concentrations of these pollutants were normalized for sediment composition (e.g. clay fraction and organic matter contents). In Lake IJsselmeer the youngest geological layer (IJm-deposit) is mainly found in deep sedimentation areas (25%). This deposit is severely polluted in Lake Ketelmeer (Chapter 2). Concentrations of all polluting compounds in the IJm-deposit of Lake Ketelmeer proved to be 1.6 - 9 times higher than in Lake IJsselmeer Concentrations in the same deposit in Lake IJsselmeer were 2 - 4 times higher than those in the older sandy sediments of the lake. Concentrations of heavy metals, As and PCBs initially increase with depth, but then decrease to lower or even background levels. This corresponds with the inputs of the river IJssel). during the past five decades. As the distance from the river mouth (i.e. Lake Ketelmeer) to Lake IJsselmeer increases, there is a decrease in the degree of pollution in this (IJm-deposit) The hypothesis is developed that primary production (with related calcite formation) and mixing with eroded sediment from elswhere in Lake IJsselmeer are together responsible for this dilution.Chapter 4 describes the core sampling and analysis for two similar sedimentation zones of two major river deltas. Uniformly soft anoxic sediments in the Volga and Danube deltas were collected, using satellite images, which reflect the concentration of suspended solids. Cesium-isotope dating and measurement of the concentration profiles of heavy metals and PAHs, which reflect (without serious alterations) the historic pollution input into these rivers, were used in the comparison. The contents of the 7 PCBs investigated and of cadmium were below the detection limits for all sediment samples in the Volga and Danube deltas. Low, more or less constant concentrations of arsenic, copper, zinc and all studied PAHs were observed in sediments of the last five decades in the Volga river. Nickel concentrations in Volga delta sediments were rather high, and recently deposited sediments seemed to show slightly increasing levels for zinc, chromium and arsenic. The pollution history of the Danube is characterized by low concentrations of metals but elevated PAH levels in the early 1940s; increasing levels of metals and PAHs between 1950 and 1987; and decreasing levels in more recently deposited sediments. When comparing the concentrations of heavy metals, PAHs and PCBs in the aquatic sediments of the rivers Rhine, Danube and Volga deltas for the past five decades it is evident that the Volga delta was, and still is, the cleanest of the three. A combination of natural (background) inputs, industrial inputs and man made technical changes in the river systems (like the building of storage lakes) can explain most differences in the historical contaminant profiles of the three deltas. Nowadays the concentrations of heavy metals (except copper and nickel), PAHs and PCBs in sediments of the river Rhine are still higher than in the other two rivers, but the sediment loading rate for heavy metals (except cadmium and zinc) of the Danube is higher than for the other two rivers.In Chapter 5 the geostatistical sampling approach chosen for Lake Ketelmeer is explained. When monitoring contaminants and related sediment characteristics in an aquatic environment, their spatial variability needs to be taken into account. The sampling strategy covered short-distance variability (65 m) and long-distance variability (500 m) of the investigated variables. In Lake Ketelmeer we chose three sub-areas. The distances between sampling points takes into account the size of each sub-area. With this approach the number of sampling points needed to monitor trends of contaminants in sediments can be minimized, taking into account the necessary accuracy. The choice of sampling strategy for monitoring sub-areas, characterised by either water depth, sedimentation/erosion behaviour or sediment type, will result in different sampling spacings. For example, in Lake Ketelmeer the optimal sampling distance for monitoring Benzo(A)pyrene (BAP) in the central part of the lake was larger than near the harbour and shore, where gradiënts in water depth are steeper. Thus, when designing a dredging programme to remove seriously contaminated sediments, the identification of sub-areas is essential to ensure the adequate dredging of the sediments. If spatial variability is not taken into account for dredging contaminated layers, seriously contaminated spots may be overlooked or rather clean sediments may be dredged needless. Thorough (although expensive) spatial investigations of the contaminated layer before dredging starts, identifying critical sub-areas, is therefore recommended. Practical, cost-effective, geostatistical methods allow an efficient use of limited financial resources for monitoring aquatic sediments.Another important process affecting sediment concentration profiles is consolidation. Chapter 6 deals with this physical process of settling of suspended solids and the loss of water after deposition. Consolidation in principle can be described by mathematical models, but because of local circumstances in the Lake IJsselmeer area an empirical approach seemed more reliable. Five representative cores of the (IJm- deposit) were taken from deep zones of the lakes. Periodic water depth surveys at these locations over the last sixty years provided information on the net sedimentation rate and total thickness of the (IJm-deposit) at known time intervals. To calculate a time-equivalent of the depth scale, correction factors for sediment consolidation were needed. These factors were based on a simplification of the various stages of compression (i.e. 0%, 30% and 45%). A factor n , which represents changes of water content of the sediment as a dependent variable of clay content, was derived for each layer, making it possible to determine the initial, uncompressed thickness of each layer by an inverse calculation procedure. Hence, a fairly reliable time-scale for depth could be reconstructed. This time-scale was compared with radio-isotope-dated layers and the results showed close consistency.Annual variability of contaminants in the IJsselmeer area is described in Chapter 7. Measurements of the concentrations of six heavy metals in suspended solids, discharged by the river IJssel). and settling solids at two locations in Lake IJsselmeer showed a typical spatial gradient. The heavy metals concentrations decreased with increasing distance from the river IJssel). inlet. This spatial gradient corresponds with gradients observed in the bottom sediment (Chapter 3). Measurements in sediment cores from Lake Ketelmeer, i.e. the river mouth, and the central part of Lake IJsselmeer showed that the heavy metals concentration in sediments, deposited during the same periods, is 2 to 3 times higher in Lake Ketelmeer than in Lake IJsselmeer The concentration gradient in the settling solids is still significant when changes in the clay and organic matter content are accounted for by using normalized metal concentrations. A rough sediment mass balance for heavy metals, based on river input data and observed sedimentation fluxes, indicates that the total internal sedimentation fluxes of heavy metals in Lake IJsselmeer far exceed the external aereal loading by the river. Due to the complexity of the relationships between the measured variables, the heavy metal concentrations and variables related to primary production and erosion, single correlation analysis did not reveal clear relations and processes that could explain this dilution. Principal component analysis and stepwise multiple regression however showed that the variation in the heavy metals concentration in settling solids is related to wind velocity and clay content, both of which are related to resuspension/erosion of sediments; or alternatively, to pH, chlorophyll and CaCO 3 , which are in turn related to algal growth in the lake. Resuspension/erosion-related variables are the dominant factors explaining the variation in heavy metals concentration in the southern part of Lake IJsselmeer whereas algal-growth-related variables explain most of the variation in the metal concentrations in settling solids in the central part of the lake. In this central part, where algal concentrations are high, the negative relation between the concentration of most of the heavy metals in settling solids and the chlorophyll and organic matter concentration in the water compartment justifies the conclusion that dilution of contaminated suspended solids by primary production is active there. In the southern part of the lake, the heavy metals concentration is positively related to wind velocity and clay content. This indicates that resuspension of recent deposits contributes to the metal concentrations of the water compartment. The gradual increase in theδ 13C value with distance from the river IJssel). mouth (passing from the southern to the central part of Lake IJsselmeer shows that the freshwater sediments are mixed with eroded Zu deposits from within the lake, which were originally saline. It can be concluded, therefore, that the decrease in the heavy metals concentrations in suspended and bottom sediments in Lake IJsselmeer is the result of dilution of contaminated sediments due to erosion of old sediments and of primary production related to algal growth.In Chapter 8 the specific knowledge reported in all previous chapters on sediment contamination, dilution, transport and processes like consolidation and primary production occurring in this area, is integrated in a modeling framework. The sediment distribution processes and the related contaminant dilution of previous decades has been reconstructed. This exercise was the basis for prediction of the future sediment composition and contamination resulting from the expected changes in the contaminant load of the river IJssel). The adapted model STRESS-2d gives a reconstruction of resuspension, erosion, sedimentation and horizontal sediment transport processes, resulting in a good simulation of total-suspended-solids concentration and of the sediment fluxes. This model was nested into the more aggregated model DIASPORA, which simulates changes in morphology (net sedimentation fluxes) quite well. It also accounted for the effects of biogenic calcite production and the consolidation of sediment layers. The decrease of the lead concentration in sedimentation areas in Lake IJsselmeer reflects the reduced suspended input from the river IJssel). but this is dominated by the effects of internal redistribution of sediments in the area. The modelling results support the above mentioned conclusion of Chapter 7. Simulation of sediment fluxes and future contamination by lead are simulated for a constant sediment input and a 50% reduction of lead input from the river IJssel). Modelling results show a steady decrease of the lead concentration in sedimentation zones of Lake IJsselmeer and a purification effect in these zones due to the dredging of sediments in Lake Ketelmeer.

This is the report on the River Ehen salmonid fishery - current status and a summary of fisheries work during the period 1993-1996, produced by the Environment Agency North West in 1997. This report draws together a number of investigations and surveys undertaken following the 1993 Strategic fisheries survey of the River Ehen. It specifically details the historic catch data available for this catchment for both salmon and sea trout and examines the current stock levels based on this data. Concerns over sea trout stock levels are raised and a detailed examination of the possible limiting factors involved is included. Information from surveys on the River Keekle is analysed with reference to its potential for sea trout production both currently and with the proposed clean up on Oatlands tip. Salmon production in the historically acidified River Liza sub catchment is examined along with ways of boosting production further following recent reductions in acidic episodes. Future and current issues and actions required in the catchment are listed along with the responsible party and estimated costs involved. Environment Agency Archives North West + maps

This is the Report on fisheries invertebrate survey of the Groove Beck, Thornsgill Beck and Troutbeck system produced by the Environment Agency North West in 1997. In 1996 the National Rivers Authority (NRA) report on the 1992 strategic stock assessment for the Upper Derwent catchment Jane Atkins recommended that should subsequent electrofishing show continued low densities, a survey of the invertebrate fauna should be undertaken to assess the food availability for salmonids, in order that lack of food could be ruled out as a contributory factor in their poor breeding success. Additionally the survey looked at the substrate to try to determine whether the bed type might actually be unsuitable for spawning, especially in view of the previously mentioned silt inputs. Environment Agency Archives North West + tables

This is the Salmonid & Freshwater Fisheries Statistics for England & Wales 1996 produced by the Environment Agency in 1997. The principal aim of the Environment Agency in respect of fisheries is to maintain improve and develop fish stocks, the basic fisheries resource, in order to optimise the social and economic benefits from their sustainable exploitation. This report is the second collation of salmon and migratory trout catch statistics for England and Wales produced by the Environment Agency. For the years 1989-94, these statistics were published by the National Rivers Authority (NRA) and the years 1983-88 by the Ministry of Agriculture, Fisheries and Food, Directorate of Fisheries Research in its Data Report series. The 1996 data, have been presented in a broadly similar format to those of 1995. This report makes a general review of different catches: Northumbria, Yorkshire, Anglian, Thames, Southern, Wessex, South West, Severn-Trent, Welsh and North West. Environment Agency Archives North West

Aquatic sediments in sedimentation zones of major rivers are in general sinks for pollutants. The sedimentation zone Ketelmeer/IJsselmeer is an important sink for contaminants of the river Rhine (i.e. river IJssel). Recent and historical pollution interact here. Redistribution of suspended solids and erosion of deposited sediment in the shallow Dutch lakes (due to wave action) are likely to change contamination levels of sediments in these lakes, which is the subject of this thesis. The aim of this research was to study and explain the variability of contaminants in the sedimentation area Ketelmeer/IJsselmeer in order to predict the fate of the contaminants in the future. For this purpose a number of methodologies and models were developed and/or adapted.Chapter 2 describes the collection and analysis of sediment cores, top-layer sediments and geologically different layers in Lake Ketelmeer. Sediment cores were sectioned into thin slices and the year of deposition of each layer was determined using radio-chemical analyses. The contaminant concentrations were plotted versus the year of deposition of each sediment layer to (re-)construct the history of contamination. Similar vertical changes in contaminant concentrations were found as in a number of sediment cores sampled in sandpits in Lake Ketelmeer. Further, differences in concentration between the top-layer sediments and the degree of contamination in the entire recent IJsselmeer deposits (IJm-deposits) of Lake Ketelmeer were found. The older Zuiderzee deposits (Zu-deposits) underlying the IJm-deposits have low background values for heavy metals, PAHs and PCBs. This indicates that downward transport of these contaminants with infiltrating water is negligible in this lake. The concentrations of metals and PAHs in the sediment cores reflect, without any serious alterations, the historical input of the past five decades. The pollution history is characterized by, in the early 1940s, low concentrations of metals and already elevated levels of PAHs; a possible reduction of these contaminants during the Second World War and attaining, their highest levels between 1955 and 1970. Rather low levels occur in recently deposited sediments, some of which are the lowest ever observed over the last five decades (Pb, As, and all studied PAHs). Almost all chlorinated compounds showed a certain decline in concentration in anaerobic sediments as compared to samples of the top-layer collected in 1972 and stored in the laboratory, which still reflect the original pollution input. For several PCBs this decline proved to be significant; it may have been caused by microbial dechlorination reactions in the anaerobic sediment. Consequently, the concentration profiles of the chlorinated compounds do not reflect the original pollution history directly. Despite the attenuation of concentration, peaks in PCB concentration profiles were still observed. The following trends in concentrations of PCBs can be currently observed in Lake Ketelmeer sediment:- Almost all PCBs studied had rather low concentrations in the early 1940s.- The highest levels of PCBs occurred between 1960 and 1975.- Recently deposited sediments also have elevated levels of PCBs as compared to the levels in layers from the early 1940s.Overall, recently deposited material is far less-polluted than sediment deposited in the 1960s and 1970s. These findings prove that in this lake older, highly polluted sediments are buried under a younger, less- polluted layer. However, at some locations, such as in dredged parts or erosive zones, the highly polluted layers may remain uncovered, so aquatic organisms may still be exposed to highly polluted sediments from the 1960s and 1970s through the benthic food chain.In Chapter 3 attention is focused on the distribution and geochronology of the sediments of Lakes Ketelmeer and IJsselmeer The concentrations of metals, PCBs, PAHs and various sediment characteristics were determined in 77 samples of the surface sediments and one 3 in core of both lakes. Absolute concentrations of these pollutants were normalized for sediment composition (e.g. clay fraction and organic matter contents). In Lake IJsselmeer the youngest geological layer (IJm-deposit) is mainly found in deep sedimentation areas (25%). This deposit is severely polluted in Lake Ketelmeer (Chapter 2). Concentrations of all polluting compounds in the IJm-deposit of Lake Ketelmeer proved to be 1.6 - 9 times higher than in Lake IJsselmeer Concentrations in the same deposit in Lake IJsselmeer were 2 - 4 times higher than those in the older sandy sediments of the lake. Concentrations of heavy metals, As and PCBs initially increase with depth, but then decrease to lower or even background levels. This corresponds with the inputs of the river IJssel). during the past five decades. As the distance from the river mouth (i.e. Lake Ketelmeer) to Lake IJsselmeer increases, there is a decrease in the degree of pollution in this (IJm-deposit) The hypothesis is developed that primary production (with related calcite formation) and mixing with eroded sediment from elswhere in Lake IJsselmeer are together responsible for this dilution.Chapter 4 describes the core sampling and analysis for two similar sedimentation zones of two major river deltas. Uniformly soft anoxic sediments in the Volga and Danube deltas were collected, using satellite images, which reflect the concentration of suspended solids. Cesium-isotope dating and measurement of the concentration profiles of heavy metals and PAHs, which reflect (without serious alterations) the historic pollution input into these rivers, were used in the comparison. The contents of the 7 PCBs investigated and of cadmium were below the detection limits for all sediment samples in the Volga and Danube deltas. Low, more or less constant concentrations of arsenic, copper, zinc and all studied PAHs were observed in sediments of the last five decades in the Volga river. Nickel concentrations in Volga delta sediments were rather high, and recently deposited sediments seemed to show slightly increasing levels for zinc, chromium and arsenic. The pollution history of the Danube is characterized by low concentrations of metals but elevated PAH levels in the early 1940s; increasing levels of metals and PAHs between 1950 and 1987; and decreasing levels in more recently deposited sediments. When comparing the concentrations of heavy metals, PAHs and PCBs in the aquatic sediments of the rivers Rhine, Danube and Volga deltas for the past five decades it is evident that the Volga delta was, and still is, the cleanest of the three. A combination of natural (background) inputs, industrial inputs and man made technical changes in the river systems (like the building of storage lakes) can explain most differences in the historical contaminant profiles of the three deltas. Nowadays the concentrations of heavy metals (except copper and nickel), PAHs and PCBs in sediments of the river Rhine are still higher than in the other two rivers, but the sediment loading rate for heavy metals (except cadmium and zinc) of the Danube is higher than for the other two rivers.In Chapter 5 the geostatistical sampling approach chosen for Lake Ketelmeer is explained. When monitoring contaminants and related sediment characteristics in an aquatic environment, their spatial variability needs to be taken into account. The sampling strategy covered short-distance variability (65 m) and long-distance variability (500 m) of the investigated variables. In Lake Ketelmeer we chose three sub-areas. The distances between sampling points takes into account the size of each sub-area. With this approach the number of sampling points needed to monitor trends of contaminants in sediments can be minimized, taking into account the necessary accuracy. The choice of sampling strategy for monitoring sub-areas, characterised by either water depth, sedimentation/erosion behaviour or sediment type, will result in different sampling spacings. For example, in Lake Ketelmeer the optimal sampling distance for monitoring Benzo(A)pyrene (BAP) in the central part of the lake was larger than near the harbour and shore, where gradiënts in water depth are steeper. Thus, when designing a dredging programme to remove seriously contaminated sediments, the identification of sub-areas is essential to ensure the adequate dredging of the sediments. If spatial variability is not taken into account for dredging contaminated layers, seriously contaminated spots may be overlooked or rather clean sediments may be dredged needless. Thorough (although expensive) spatial investigations of the contaminated layer before dredging starts, identifying critical sub-areas, is therefore recommended. Practical, cost-effective, geostatistical methods allow an efficient use of limited financial resources for monitoring aquatic sediments.Another important process affecting sediment concentration profiles is consolidation. Chapter 6 deals with this physical process of settling of suspended solids and the loss of water after deposition. Consolidation in principle can be described by mathematical models, but because of local circumstances in the Lake IJsselmeer area an empirical approach seemed more reliable. Five representative cores of the (IJm- deposit) were taken from deep zones of the lakes. Periodic water depth surveys at these locations over the last sixty years provided information on the net sedimentation rate and total thickness of the (IJm-deposit) at known time intervals. To calculate a time-equivalent of the depth scale, correction factors for sediment consolidation were needed. These factors were based on a simplification of the various stages of compression (i.e. 0%, 30% and 45%). A factor n , which represents changes of water content of the sediment as a dependent variable of clay content, was derived for each layer, making it possible to determine the initial, uncompressed thickness of each layer by an inverse calculation procedure. Hence, a fairly reliable time-scale for depth could be reconstructed. This time-scale was compared with radio-isotope-dated layers and the results showed close consistency.Annual variability of contaminants in the IJsselmeer area is described in Chapter 7. Measurements of the concentrations of six heavy metals in suspended solids, discharged by the river IJssel). and settling solids at two locations in Lake IJsselmeer showed a typical spatial gradient. The heavy metals concentrations decreased with increasing distance from the river IJssel). inlet. This spatial gradient corresponds with gradients observed in the bottom sediment (Chapter 3). Measurements in sediment cores from Lake Ketelmeer, i.e. the river mouth, and the central part of Lake IJsselmeer showed that the heavy metals concentration in sediments, deposited during the same periods, is 2 to 3 times higher in Lake Ketelmeer than in Lake IJsselmeer The concentration gradient in the settling solids is still significant when changes in the clay and organic matter content are accounted for by using normalized metal concentrations. A rough sediment mass balance for heavy metals, based on river input data and observed sedimentation fluxes, indicates that the total internal sedimentation fluxes of heavy metals in Lake IJsselmeer far exceed the external aereal loading by the river. Due to the complexity of the relationships between the measured variables, the heavy metal concentrations and variables related to primary production and erosion, single correlation analysis did not reveal clear relations and processes that could explain this dilution. Principal component analysis and stepwise multiple regression however showed that the variation in the heavy metals concentration in settling solids is related to wind velocity and clay content, both of which are related to resuspension/erosion of sediments; or alternatively, to pH, chlorophyll and CaCO 3 , which are in turn related to algal growth in the lake. Resuspension/erosion-related variables are the dominant factors explaining the variation in heavy metals concentration in the southern part of Lake IJsselmeer whereas algal-growth-related variables explain most of the variation in the metal concentrations in settling solids in the central part of the lake. In this central part, where algal concentrations are high, the negative relation between the concentration of most of the heavy metals in settling solids and the chlorophyll and organic matter concentration in the water compartment justifies the conclusion that dilution of contaminated suspended solids by primary production is active there. In the southern part of the lake, the heavy metals concentration is positively related to wind velocity and clay content. This indicates that resuspension of recent deposits contributes to the metal concentrations of the water compartment. The gradual increase in theδ 13C value with distance from the river IJssel). mouth (passing from the southern to the central part of Lake IJsselmeer shows that the freshwater sediments are mixed with eroded Zu deposits from within the lake, which were originally saline. It can be concluded, therefore, that the decrease in the heavy metals concentrations in suspended and bottom sediments in Lake IJsselmeer is the result of dilution of contaminated sediments due to erosion of old sediments and of primary production related to algal growth.In Chapter 8 the specific knowledge reported in all previous chapters on sediment contamination, dilution, transport and processes like consolidation and primary production occurring in this area, is integrated in a modeling framework. The sediment distribution processes and the related contaminant dilution of previous decades has been reconstructed. This exercise was the basis for prediction of the future sediment composition and contamination resulting from the expected changes in the contaminant load of the river IJssel). The adapted model STRESS-2d gives a reconstruction of resuspension, erosion, sedimentation and horizontal sediment transport processes, resulting in a good simulation of total-suspended-solids concentration and of the sediment fluxes. This model was nested into the more aggregated model DIASPORA, which simulates changes in morphology (net sedimentation fluxes) quite well. It also accounted for the effects of biogenic calcite production and the consolidation of sediment layers. The decrease of the lead concentration in sedimentation areas in Lake IJsselmeer reflects the reduced suspended input from the river IJssel). but this is dominated by the effects of internal redistribution of sediments in the area. The modelling results support the above mentioned conclusion of Chapter 7. Simulation of sediment fluxes and future contamination by lead are simulated for a constant sediment input and a 50% reduction of lead input from the river IJssel). Modelling results show a steady decrease of the lead concentration in sedimentation zones of Lake IJsselmeer and a purification effect in these zones due to the dredging of sediments in Lake Ketelmeer.