Water Quality Dynamics of the Irwell Catchment

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“Water is essential for life and for all human activities but also for preserving the environment and its resources” (Benedini & Tsakiris, 2013). In many countries around the world water scarcity is a growing issue, with factors such as urbanisation, population increase, intensification of agriculture, and climate change putting increasing stress upon existing supply’s of fresh water. For much of human history, the focus of water management has been heavily upon issues regarding water quantity rather than water quality. It is only since the 1960s that concern for and understanding in water quality dynamics has began to play a bigger more important role in the assessment of fluvial systems (Abbasi & Tareen, 2012). In the present day, it can be said that water quality has acquired as much importance as water quantity. However, access to safe water for consumption and other uses is still not available to billions of people globally, with the United Nations estimating that 3,800 children die everyday as a result of unsafe water and lack of sanitation (Benedini & Tsakiris, 2013). This shows that much work is still needed on a global scale to address issues of water quality. The scientific field of water resources management is key to attaining the sustainability of water resources and the environment. This can be achieved through guided and efficient management of water resources development, usage and treatment (Benedini & Tsakiris, 2013). Despite the efforts in recent decades to publicise the vital importance of water quality, many fluvial systems in developed countries such as the UK are still subject to issues regarding water quality.

The Irwell catchment covers an area of 793km2 and is located in the south east of the North West River Basin District. It extends from the moors above Bacup to the Manchester Ship Canal. Predominantly rural areas are found to the north and west of the catchment, with the former industrial towns of Bolton, Bury, Oldham, Rochdale, Salford, and Manchester found in the southern and eastern reaches of the catchment. These urban areas make up roughly 30% of the total catchment area. Rapid industrial development, mainly in the late 19th century, resulted in many of the watercourses located in the Irwell catchment being heavily modified. A large proportion of the catchment is modified with walled banks, weirs, and culverts as a result (Environment Agency, 2009). Climate in the catchment area is wetter than the UK average, with 1,456 millimeters of rainfall per annum.

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The River Irwell travels a distance of 63km from its source in Deerplay Moor, near Bacup at an altitude of 400 meters, to where it feeds into the Manchester Ship Canal. Downstream of its source the rivers Roch and Croal merge with the Irwell before it is further fed by the rivers Irk and Medlock once in Salford. This stretch of river forms the boundary between Manchester and Salford. From here it feeds into the Manchester Ship Canal, which is then joined by the discharge from the River Mersey as it travels towards the sea.

The river is split into the Upper Irwell and the Lower Irwell, with each area comprising of different topography as well as land use. In the Upper Irwell Pennine moorland, pasture, and steep sided valleys dominate, with improved pastures, rough grazing, and small settlements a little further south. The Lower Irwell flows through a landscape of low lying flatter land, much of which has been developed into heavily urbanized areas over the past few centuries. This high level of urbanization has resulted in the catchment being one of the least naturally wooded areas in the north west (Environment Agency, 2009). Despite this, there still remain multiple nature conservation sites of both national and international importance. These include 14 Sites of Special Scientific Interest (SSSIs) such as Nob End, Longworth Clough, Oak Field, and the Tonge River Section (Environment Agency, 2009).

The Irwell catchment is predominantly comprised of rocks dating from the Late Carboniferous period, during which deposits of mud and sand were laid down from the shallow sea that covered much of south-east Lancashire. A high proportion of the catchment is relatively impermeable, creating short lag times from rainfall to discharge, as only a small proportion filters into groundwater stores (Environment Agency, 2009). Glaciation during the Pleistocene period eroded much of the landscape, leading to the deposition of pebbles, boulder clay, and sand once the glaciers had retreated. Evidence of this glaciation can be seen in the Lower Irwell where fluvioglacial ridges were formed (Hindle, 2003). Well-developed peat bodies also occur in much of the Upper Irwell area.

Today the Irwell catchment is populated by over 2 million people, a mixture of recreational activities and industrial use occurs along much of its watercourses. Sewage and urban runoff arguably are responsible for the largest concern to river pollution, with outdated Victorian sewage systems still present in some of the catchment. Public water supply is sourced mainly from the Upper Irwell area, where multiple tributaries are extensively reservoired. While the Lower Irwell area is used predominantly for industrial usage.

“The Manchester urban area evolved rapidly in the early 19th century from a series of small towns to a major industrial conurbation with huge material flows and worldwide trade connections.” (Douglas et al., 2002). Rodgers (1987) describes Manchester as an urban prototype, being the first of a new generation of big industrial cities developed in the Western world. In order to understand and discuss present day water quality dynamics of the River Irwell, it is first key to note the expansive changes that have occurred in the Irwell catchment over the last few centuries.

The River Irwell was historically one of the main transport links in the North West of England, and in addition provided the main source of drinking water for Manchester and Lancashire until just over a century ago. This made it an invaluable resource both before, but especially during the onset of the Industrial Revolution in the 18th and 19th centuries. In Manchester and the surrounding areas this period saw rapid, and mainly unregulated expansion in both industries, and urban extent, as well as drastic increases in population. Factories and mills became common on the banks of the river, making use of the water not only as a resource, but also as a supply of both energy and transportation. Cotton mills made up a large proportion of this new industrial development, with Manchester becoming a global hub for cotton production. By 1835, 90% of the British cotton industry was concentrated in Manchester and surrounding areas (Douglas et al., 2002), peaking in 1853 when 108 cotton mills were active in the city. Lack of regulation and knowledge of water quality issues meant that large quantities of pollutants were discharged directly into the River Irwell and its tributaries. As a result of this the river became severely polluted, leading to negative implications not only upon the human population of the surrounding areas, but also upon plant and animal life depended upon the water source.

Appreciation and understanding of the importance of water quality has come a long way since the industrial revolution, as has the condition of the Irwell catchment. However the legacy of pollutants left behind from the industrial revolution still impacts upon the system today, along with new modern day pollution inputs that threaten to further degrade water quality in the Irwell Catchment.

Water is a vital part of the natural environment, as well as providing a multitude of goods and services to people and industries. Agriculture, manufacturing, ecosystem health, and leisure activities are but a few examples of why water is such an important commodity. The estimated value, provided by The Office for National Statistics, of freshwater services in the whole of the UK was £39.5 billion. The scientific field of water resources management has come a long way in recent decades. The importance of sustainability and the incorporation of it to management and policy decisions has played a key role in the development of the field. Sustainability, also referred to as sustainable development, has become a common term across the world, mainly since the release of the Bruntland Commission report in 1987 (World Commission on Environment and Development: Our common future, 1987). This report stated that “Sustainable Development aims at ensuring that humanity meets its present needs without compromising the ability of future generations to meet their own needs” (Bruntland, 1987). This report helped to lay the foundations for much needed reform in the fields of environmental management and policy making.

It was until only a few decades ago that that governments and countries based their development upon an approach of single-purpose planning (Benedini & Tsakiris, 2013). This narrow-minded approach often meant that consequences in other sectors were seen resulting from decisions made in another. In the 1980s the definition of water resources management referred to all activities aiming to fulfil the present and future water requirements with water of sufficient quantity and appropriate quality (Benedini & Tsakiris, 2013). While this definition does consider the needs of the future helping to make decisions sustainable. It did not take into account the need for environmental protection. Instead its focus is upon meeting demands for water resources. It was in the late 1980s that individuals and governing bodies involved in the water sector (e.g. NGOs, scientists, policy makers, and stakeholders) began to incorporate a new approach of “integrated or comprehensive water resources management (IWRM) (Benedini & Tsakiris, 2013). This was an important step in the evolution of water resources management, and one that lead to the development of multi-objective management systems that incorporated economic, environmental, and social objectives. More importantly however, this change saw the inclusion of water quality in the management models for the first time (Quentin Grafton & Hussey, 2011). At first efforts to improve water quality were focused primarily on addressing the point sources of pollution to water courses (e.g. sewage treatments works or industrial discharge). However this approach has since developed into catchment-based approaches, where issues are researched and addressed in correlation with the catchment as a whole (Priestly & Barton, 2018). These developments have been integral to the evolution of water resources management, and in the present day it is now widely understood that activities and processes in the watershed are inherently linked together in a interconnected system of pressures and impacts (Benedini & Tsakiris, 2013). The modelling of these connections and how each variable reacts is therefore key to achieving a stable relationship between them.

In the UK, recent decades have seen the further development of many river corridors, both for commercial and residential usage. In addition to this the popularity of freshwater-based recreational activities has been increasing. The need for effective and sustainable multi-objective catchment management is therefore greater than ever. For the general public frequently exposed to freshwater sources, the implications of poor water quality can result in multiple negative health impacts. Humans in contact with polluted water are at risk of contracting bacterial, viral, or parasitic diseases. Diseases such as respiratory disease, cancer, diarrheal disease, neurological disorder and cardiovascular disease have all been linked to sources of polluted water (Ullah et al., 2014).

In 2000 the European Parliament and Councils Conciliation Committee came to an agreement setting out guidelines for the improvement of European water bodies. This provided a common international framework for water resources management and protection in Europe. From what had previously been a fragmented and inefficient policy area, this new integrated approach established river basin management systems tasked with the protection/ improvement of all aspects of the water environment (Priestly & Barton, 2018). This includes all rivers, lakes, estuaries, and coastal waters, as well as groundwater stores.

The classification of surface water status under the WFD is measured both by ecological and chemical status. The status is then categorised against a scale of high, good, moderate, poor, and bad. Ecological status is assessed using three criteria, biological quality (composition and abundance of freshwater species), hydromorphological quality (river continuity, channel patterns, dynamics of flow or substrate of the river bed), and physico-chemical quality (temperature, oxygenation, pH, nutrient conditions and the concentrations of specific pollutants). Chemical status is assessed by reference to environmental quality standards for chemical substances at European level. This comprises of specific or priority pollutants set out by the EU, along with maximum annual average concentrations for each pollutant. The WFD works so that if just a single section of a water body fails on any of these criteria, the water body will fail to achieve/ lose good status.

River Basin Management Plans (RBMPs) are another aspect of the WFD. RBMPs must be created for each river basin district, where objectives are then set for the water bodies contained within, as well as a plan set out for the measures needed to achieve them. The UK contains 16 river basin districts, with these all subject to corresponding RBMPs. The RBMPs must be updated every 6 years, with the first cycle occurring between 2009-2014, and the current cycle occurring between 2015-2021.

The initial aim of the WFD required all member states to achieve ‘good’ status in all water bodies by 2015. However this deadline was not met by the UK, as well as many other member states, with the WFD realising that due to a multitude of specific and limiting circumstances it was unrealistic that the targets would be met. Instead waivers to the deadline were allowed in the form of either extensions, or the adaption of objectives to meet lesser targets. The extension of these deadlines comes with the application of new planned objectives for the achievement of ‘good’ status. Only a further two cycles of RBMPs are allowed from the initial deadline of 2015 to achieve the required status, given that there are no exceptional conditions that prohibit the achievement of these goals within the time limit. Therefore, 2027 is now the new proposed deadline for the achievement of ‘good’ water status in all UK water bodies.

A report by the Joint Nature Conservation Committee (JNCC) in 2018 reported that in 2017, UK surface water bodies had achieved statuses of 5% high, 30% good, 47% moderate, 14% poor, and 3% bad (JNCC, 2018). While improvements in this classification have been notable since the beginning of the WFD, a small decrease was seen between 2012 and 2017 in the total number of water bodies in the UK achieving high or good status. 36% achieved this in 2012, compared to the 35% seen in 2017 (JNCC, 2018). The issue for the UK, as well as other member states enrolled in the WFD, is attempting to balance the achievement of water quality objectives, while accepting that for some of the water bodies within the country, the achievement of the same aims are unattainable within time limits set. The Defra Secretary of State voiced this issue in 2018, stating that due to high pressure from industry, human population, and agriculture, as well as the legacy of watercourse modification, around one quarter of England’s water bodies would not be able to achieve good status by 2027 (Environmental Audit Committee, 2018). Due to this, lower objectives have been set for these water bodies where technical feasibility or disproportionate costs limit their ability to achieve good status. It was also stated that due to the ambitious aims of the WFD, and the heavily modified state of may water courses within the EU, there will be pressure upon the EU Commission to revise or extend the current deadline and subsequent objectives that are set to be achieved by 2027 (Environmental Audit Committee, 2018). A more realistic estimate of what can be achieved by 2027, is the achievement of good status for 75% of UK waters, taking into account the factors discussed above.

It is also important to note that in the context of Brexit, the government has stated that it will not weaken any environmental protection guidelines currently in place within the EU framework. Any EU environmental requirements will be transferred to domestic UK law following exit from the EU. In 2018, the Department for Environment, Food and Rural Affairs (Defra) published the 25 Year Environment Plan, which proposes the government’s long-term plans for the improvement of the environment. Within this, similar to what is currently deemed achievable within the WFD, is the aim for England to have achieved the restoration of at least 75% of waters to as close to their natural state as possible (Defra, 2018). This plan sets out how the government plans to continue achieving the commitments currently made within the WFD. It plans to achieve this through: reducing damaging abstractions of water from rivers and groundwater, achieving or surpassing objectives for rivers, lakes, coastal and groundwater’s that are protected for biodiversity or drinking water, supporting OFWAT’s targets for the reduction of leakage in the water industry, and reducing as much as possible by 2030 the concentrations of harmful bacteria in designated bathing waters (Defra, 2018).

Pollution is defined as the contamination of water, land, or air by substances that can adversely impact the environment and human health (American Heritage Dictionary, 1982). Or as Holdgate (1979) more simplistically describes it as “something in the wrong place at the wrong time in the wrong quantity”. Pollutants can be introduced into river systems through a highly diverse range of sources. These include domestic sewage, urban runoff, industrial effluent, and agricultural runoff/ waste. Two different categories of sources can be defined when studying pollution, diffuse sources, and point sources. Diffuse sources are where no specific point of discharge can be determined, and are often active over large geographical areas making them difficult to manage. While point sources, under the definition of Hill (1997), are “any single identifiable source of pollution from which pollutants are discharged, such as a pipe, ditch, ship or factory smokestack”. Both point and diffuse sources of pollution are responsible for the contamination of surface water bodies in the UK. The most common sources of point source pollution are discharge from factories and sewage treatment plants. Some examples of factories often responsible for discharging polluting effluents include textile factories, oil refineries, car manufacturers, and paper mills. While some factories treat waste products before they are discharged, others discharge effluents directly into river systems, resulting in high concentrations of contaminants. Sewage treatment plants are responsible for the treatment of human waste. Although treatment means the resulting effluent is markedly better than raw sewage, unnaturally high levels of contaminants still results from the eventual discharge into watercourses. Both factories and sewage treatment plants in some instances also dispose of their waste by mixing it with urban runoff in a combined sewer system (National Ocean Service, 2017). Urban runoff is storm water trapped on the surface due to impermeable surfaces. This runoff in turn is responsible for the transportation of pollutants from road surfaces, construction sites etc. into sewer systems. During periods of excessive rainfall, combined sewer systems can become overburdened with the volume of water. Once they surpass capacity, a mixture of the urban runoff and raw sewage overflows from the system, getting transported directly into the closest water body before it is treated (National Ocean Service, 2017). These instances, while much of the pollutant load is from a diffuse area, are defined as point source pollution due to the nature of the input into watercourses.

A report by the Environment Agency in 2018 (‘The state of the environment: water quality’) assessed which current pressures upon water quality are the largest contributors to poor water quality in the UK. They concluded the three main sources as being: diffuse pollution from towns, cities, transport, and rural areas; pollution from waste water; and runoff from abandoned mines (Environment Agency, 2018). They also concluded that the main activities currently preventing UK water bodies from reaching good status were:

  • “Agriculture and rural land management (31% of reasons for water bodies not achieving good status)
  • The water industry (28%)
  • Urban and transport (13%)” (p. 9)

Agricultural Diffuse Pollution and Nutrients:

Diffuse sources of pollution are far harder to monitor and manage than point source pollution. Globally, agriculture is one of the main sources of diffuse water pollution, contributing a diverse range of pollutants to surface water bodies (Priestly & Barton, 2018). Among the most common of these pollutants is nutrients (e.g. nitrogen and phosphorus), pesticides, and sediment. Implications to the environment from agricultural diffuse pollution are often slow to appear, meaning that issues can develop in the long term (Baldock, 1992). Significant pollution incidents reported by the Environment Agency in 2018 suggest that agriculture is the greatest contributor responsible. The effects of this pollution can be highly damaging, however the overall number of water pollution incidents has been reducing in recent years, falling two-thirds between 2001 and 2016 (Environment Agency, 2018). The mobilisation of pollutants from agricultural land is linked to numerous factors, such as land use, soil texture/ composition, fertilisation, crop rotation, and effluent disposal (Vinten & Smith, 1993). It is possible that agricultural intensification as a result of increasing population growth in the UK could reverse the trends seen in recent years. Increasing inputs of nutrients, along with other agricultural effluents into water bodies poses a serious threat to the health of UK water bodies. In order to combat this, The Reduction and Prevention of Agricultural Diffuse Pollution (England) Regulations 2018 has been set out, and came into effect in April 2018. This new set of guidelines aims to encourage good farming practices, such as steps to prevent manure and fertiliser from entering water bodies (Environment Agency, 2018). In addition to this, Defra does provide a level of financial assistance to farmers, to help them reduces levels of pollution on their land.

Nutrient pollution can have serious implications upon water bodies and their ability to provide their services, both in terms of human use as well as for the surrounding ecosystems. Braga et al. (2000) states that the main contributors to nutrient pollution are derived from domestic and industrial waste, agricultural practices, and nitrogen deposited from the atmosphere. Infiltration of nutrients into surface water bodies can come from both diffuse and point sources, which makes the monitoring and management of nutrient pollution difficult. The main problem arising from excess nutrients in water bodies is the onset of a process called eutrophication. Nixon (1995) defined eutrophication as “the processes of increased organic enrichment of an ecosystem, generally through increased nutrient input”. This process results in the excessive growth of algae (algal blooms), and plants, which in turn uses up large amounts of oxygen creating dangerously low levels for other organisms present in the water body. While eutrophication does occur naturally, its occurrence and severity has been greatly increased through anthropogenic activities. High levels of nutrient inputs into water bodies can lead to the negative impacts such as the depletion of drinking water supplies, the onset of eutrophication, and subsequent damage to water ecology as a result of the algal blooms created. The highest levels of nutrient inputs into surface water bodies often comes from lowland environments, where high population densities and intensive agricultural practices are found (Neal et al., 2008).

In the UK, the main nutrients that affect water quality are phosphorus and nitrates. Monitoring published in the 2018 report by the Environment Agency, found that phosphorus was the most common reason for rivers failing to achieve good status in 2016. They found that out of the assessed freshwater bodies in England, 55% were at less than good status in terms of concentrations of phosphorus. The potential implications of this pollution was also found, with 56% of the same water bodies deemed to be at less than good status for plants and algae (Environment Agency, 2018). Phosphorus is the main cause of eutrophication in English rivers and lakes, with sewage effluent and runoff from agricultural land being the main sources contributing to pollution. UK concentrations of phosphorus in rivers has been falling since the mid 1990s, with the decrease closely attributed to improvements made to sewage treatment works (Environment Agency, 2018). The primary source of nitrates in the UK comes from agricultural land. Runoff processes transport nitrates to watercourses after they are applied to agricultural land for the enhancement of crop yields. Since 2000 slight declines in nitrate levels in UK rivers has been seen (Environment Agency, 2018). The Nitrates Directive 1991, was set out in order to attempt to reduce the input of nitrates into water bodies from diffuse agricultural sources. This directive, implemented by the Nitrate Pollution Prevention Regulations, required member states to identify nitrate vulnerable zones (NVZs), being areas of land that drain into water bodies currently polluted by nitrates (Priestly & Barton, 2018). These zones at present incorporate 58% of England. Objectives and plans for their achievement are to be devised for each of these NVZs, with good agricultural practises key to achieving any aims set.

Potential hydrogen (pH) is a measure of the concentration of hydrogen ions in water. Put more simply, it is a measure of acidity and alkalinity of water. The logarithmic scale varies from 14 (highly alkaline), to 0 (highly acidic), with a change in one unit representing a ten-fold change H+ ion concentration (Ward & Robinson, 2000).

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