Recovery of an urbanised estuary: Clean-up, de-industrialisation and restoration of redundant dock-basins in the Mersey

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Abstract

For much of the 20th century, the Mersey in North West England was one of the worst polluted estuaries in Europe. Water from a range of polluting industries plus domestic sewage was discharged into the Mersey Catchment and Estuary. Recovery came through a concerted clean-up campaign and tightening environmental regulations, partly driven by European Commission Directives, coupled with de-industrialisation from the 1970s onward. Recovery of oxygen levels in the Estuary led to the return of a productive ecosystem. This led to conservation designations, but also concerns about transfer of pollutants to higher trophic levels in fish, birds and humans. As part of urban renewal, ecosystems in disused dock basins were restored using mussel biofiltration and artificial de-stratification, facilitating commercial redevelopment and creation of a tourist destination. The degradation and recovery of the Mersey from peak-pollution in the mid-20th century is put in the context of wider environmental change and briefly compared to other systems to develop a hysteresis model of degradation and recovery, often to novel ecosystems.

Introduction

From the 1930s to 1980s, the Mersey Estuary had the reputation of being one of the most polluted estuaries in the United Kingdom and Europe (Clark, 1989; NRA, 1995; Jones, 2000). Its catchment drained the industrial heartlands of Lancashire and Cheshire, especially the urban conglomerations of Manchester and Liverpool (Fig. 1), which grew rapidly throughout the 18th, 19th and early 20th centuries, peaking before the Second World War (Fig. 2). Thus the estuary was fed by highly polluted rivers, canalised rivers and canals including the Manchester Ship Canal (Porter, 1973). All of these waterways were used as open sewers and as conduits for much industrial waste with little treatment and regulation (Porter, 1973). The freshwater stretches were particularly foul. A report made in 1874 on a survey of the River Mersey in 1869 under the direction of three Commissioners appointed by Queen Victoria reported:

When taking samples at Throstlenest Weir below Manchester at 5 a.m. on 21 July 1869, we saw the whole water of the River Irwell, there 46 yards wide, caked over with a thick scum of dirty froth, looking like a solid sooty crusted surface. Through this scum here and there, at intervals of 6 to 8 yards, heavy bursts of bubbles were continually breaking, evidently rising from the bottom and, where every yard or two of the scum was cleared away, the whole surface was seen shimmering and sparkling with a continuing effervescence of smaller bubbles rising from various depths in the midst of the water, showing that the whole river was fermenting and generating gas. The air was filled with the stench of this gaseous emanation many yards away. The temperature of the water was 76 °F (24 °C) and that of the air 54 °F (12 °C).” (report quoted in NRA, 1995).

Textiles, coal mining, soap and detergent manufacturing, ship-building, glass-making, the chemical industry, petro-chemicals, car factories, tanneries, food-processing, sugar refining and much else were on the banks of the rivers in the catchment, the canalised lower reaches (Manchester Ship Canal) and the Estuary and its associated docks (Ritchie-Noakes, 1984). Much of the UK's growing chemical industry was located on the interface of the Cheshire salt-fields and Lancashire coal-fields on the banks of the Mersey Estuary (Allison, 1949; Ritchie-Noakes, 1984). There was also much domestic sewage, both partially-treated and raw, discharged to the rivers and Estuary (Porter, 1973; Jones, 2000). Recovery of the highly polluted waterway eventually came through a concerted clean-up campaign, on top of a century of tightening environmental regulations, in part latterly spurred-on by Directives from the European Commission (NRA, 1995). De-industrialisation also made a major contribution as some heavy industries were privatised (i.e., coal, power generation, ports, car-making, shipbuilding), and along with those already in the private sector, down-sized or shut down as they became increasingly redundant, uncompetitive or environmentally undesirable (e.g., putting lead in petrol/gasoline; Needleman and Gee, 2013).

We describe the recovery of the Mersey from peak-pollution in the mid-20th century by summarising unpublished data and published work, much of which is in the grey literature, often from now-defunct government agencies. This is prefaced by a brief history of the development of the Mersey catchment in terms of industry and population, describing how this led to pollution of the Estuary. We illustrate how metal pollutants have peaked historically and how levels have subsequently declined in response to stricter environmental standards and de-industrialisation. We then provide a similar description of persistent organic compounds. Domestic sewage pollution rose in parallel with industrialisation and is considered alongside nutrient enrichment. Many of the industries of the Mersey also supplied organic waste to the river, contributing to Biological Oxygen Demand (BOD), and hence, very low oxygen levels. Recovery from hypoxic and occasionally anoxic conditions, following sewage treatment, was critical to the recovery of the Estuary, eventually leading to conservation designations, especially for birds. We then consider how, with the Estuary recovering, pollutants began to pass from the productive benthos to higher trophic levels leading to bird mortalities and concerns about contamination of angler-caught fish.

In parallel to clean-up and recovery of the Mersey Estuary, pioneering work using biofiltration and artificial de-stratification helped restore ecosystems of redundant Liverpool dock basins as part of urban renewal programmes. This work is topical because of the recent resurgence in interest in using biofiltration in restoring degraded areas (e.g., the Billion Oyster Project in New York; Billion Oyster Project, 2019). Finally, the recovery of the Mersey and restoration of docks is put in the broader context of global environmental change, emphasising that local and regional pollution needs to be managed in relation to other local, regional and global drivers (see also Hawkins et al., 2017).

Section snippets

Development and decline in the Mersey Catchment in North West England

The North West of England was a key area of industrial development in the 18th and 19th centuries (Fig. 1, Fig. 2; Allison, 1949; Ritchie-Noakes, 1984). The juxtaposition of Lancashire's coal with Cheshire's salt provided the core ingredients for power and chemical industries, as well as being exported themselves as commodities (Allison, 1949; Ritchie-Noakes, 1984). The development of the first commercial enclosed dock basin in the modern world in Liverpool in the early 1700s (Porter, 1973;

Background inputs and data sources

Since the advent of the Industrial Revolution in the early 18th century, the Mersey Estuary and its catchment has been subjected to chemical wastes from cotton and silk production, port activities, metal ore refining, slag dumping, bleaching, dying and printing of textiles, soap and margarine manufacture, and various chemical processes, including caustic soda production and petrochemical refining (Porter, 1973; Langston et al., 2006). The increase in both industrial and urban development

Sewage pollution, biological oxygen demand (BOD) and dissolved oxygen levels

The whole of the sewage is still thrown into the river, much of it indeed, into the basins and all of it at such points as to act very prejudicially on the health of the town” - The Borough Engineer of Liverpool, 1848 (cited in NRA, 1995; Jones, 2006).

In response to the cholera epidemic in the rapidly growing and crowded town of Liverpool in the 1840s and 1850s, sewers were installed which then discharged raw sewage into the Estuary and also into the dock basins themselves (Porter, 1973;

Nutrients in the Mersey

Inadequate sewage treatment and discharges from sewer overflows all contributed to excess nutrients in the Mersey as well as oxygen demand (NRA, 1995). It is widely recognised, however, that diffuse urban and agricultural runoff are additional nutrient sources leading to further impacts on river catchments, not least the Mersey (e.g., Rothwell et al., 2010), possibly leading to eutrophication.

Earlier research placed the nutrient loading in the Mersey – and influence outward into Liverpool Bay –

Recovery of benthos, fish and birds plus pollutants at higher trophic levels

Invertebrate communities in intertidal sediment in the Mersey were frequently studied during the late 19th and early 20th centuries (Herdman, 1895; Herdman, 1920; Fraser, 1932; Bassindale, 1938); yet no extensive ecological studies were made again until the early 1970s (Mills, 1998). Although there have been many studies, it is difficult to compare results because survey methods, taxonomic expertise, site locations, sediment type (e.g., mud, sand, stone) and analyses differed among studies. For

Restoring disused docks

The growth of the global shipping trade in the 16 - 17th centuries resulted in development of major commercial maritime docks in harbour cities worldwide, and the associated modification and destruction of natural shoreline habitats (Hawkins et al., 1999a, Hawkins et al., 1999b; Chou, 2006). Here we use the example of the Liverpool, UK docks – the world's first mercantile dock system from the early 18th century (Ritchie-Noakes, 1984; Hawkins et al., 1999b) – to describe ecological

Overview and synthesis

Recovery of the Mersey has been influenced by wider contextual changes and far field impacts (Fig. 12a). Atmospheric inputs of nitrogen and nutrient enrichment of the catchment due to agricultural intensification can both lead to eutrophication (Bennett et al., 2001; Ulén et al., 2007; Oberholster et al., 2019) in addition to the nutrient loading from sewage treatment (Lapointe and Clark, 1992; Braga et al., 2000). There were also impacts in Liverpool Bay such as dumping of sewage sludge,

Funding

Work was supported in the 1970s and 1980s by Mersey Dock and Harbour Company, as well as the Merseyside Development Corporation, and the UK Nature Conservancy Council in the 1980s and 1990s. Work by W J Langston was supported by the National Rivers Authority and the Environment Agency. Write up was supported by a bursary from the MBA to KAO. LBF and SJH have been supported by the THESEUS (EU FP7, contract number 244104: Innovative technologies for safer European coasts in a changing climate)

CRediT authorship contribution statement

S.J. Hawkins: Conceptualization, Methodology, Validation, Investigation, Resources, Data curation, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition. K.A. O'Shaughnessy: Data Curation, Supervision, Writing - original draft, Writing - review & editing, Visualization. L.A. Adams: Data curation, Writing - review & editing, Visualization.W.J. Langston: Funding Acquisition, Methodology, Validation, Investigation, Formal

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Much of the early work on Sandon Dock was started by Dr. Ken O'Hara of the University of Liverpool. Hugh Jones, Keith White and George Russell also played a key role in the work on Sandon and in the South Docks. The late Dr. Rick Leah of Liverpool University led much of the work on pollution in the Estuary.

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