Restronguet Creek Revisited - Dr Charlotte Braungardt


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Restronguet Creek Revisited - Dr Charlotte Braungardt

My first close encounter with pollution emanating from the abandoned mines in England’s Southwest occurred in the mid 1990s, when research for my undergraduate dissertation brought me to Restronguet Creek in the Fal Estuary. A former tin mine had come to fame for all the wrong reasons…

Wheal Jane was a successful tin mine that also yielded some arsenic, copper, silver and zinc. It was worked from the mid-18th to the late 19th century, with some sporadic operations until 1991.

Throughout the working life of such a mine, vast quantities of waste rock and ores are deposited at the surface, a contamination legacy that lasts for centuries and has the potential to cause air, land and water pollution, with toxic effects on biological systems [1][2][3].

Post-closure mine management is important, but no legally binding provisions were in place at the time, so when the de-watering pumps of the Wheal Jane mine were switched off in early 1992, trouble was brewing fast: groundwater rebounded and flooded the underground workings, leached tin, copper, iron, arsenic and acid from the rocks and eventually rose to the surface. This caused a large spill of acid mine drainage into the Carnon River, Restronguet Creek and Falmouth Bay. Along the contamination plume, waters turned visibly reddish brown, killed fish and affected the bird population [4][5].

There was one positive outcome from this disaster: the first (and so far only) full-scale acid mine drainage (AMD) treatment plant in the Southwest was constructed by 1994 [6]. However, this partial treatment only reduced the amount of pollution added into the Carnon Valley going forward and the pollution legacy in the estuary remained [7].

Wheal Jane mine water treatment. Photo (c) C Braungardt 2011.

When metals (e.g. copper, zinc, iron, cadmium) and metalloids (e.g. arsenic, antimony) that are dissolved in river water mix with the the saltwater in the estuary, their solubility decreases and much of them finish up deposited in the sediment. As a result of a couple of hundred years of metal/loid inputs, Restronguet Creek is silted up with highly contaminated sediment. Healthy estuarine sediment is inhabited by a great diversity of fauna, including invertebrates important for wading birds, but in Restronguet Creek the infauna is limited to the most resilient worms [8 and references therein]. 

Although much of the pollution entering the Creek ends up in the sediment, some of it remains in the water or is remobilised from the sediment over time. This means that concentrations of metal/loids, may still be high enough to be toxic to marine life, such as microscopic algae, zooplankton and bivalves.

In the first decade of this millennium, international colleagues and PhD students at the University of Plymouth collected clear evidence of the toxic effects of water at Restronguet Point during several studies of metal concentrations and oyster embryo bioassays [9][10]. These studies revealed the high variability of biologically relevant copper (5-180 nmol/L Cu) cadmium (0.2-3.1 nmol/L Cd) and lead (0.1-1.0 nmol/L) levels in the Fal Estuary [9]. Bioavailable copper concentrations at Restronguet Point exceeded the concentration at which 50 percent of oyster larvae are killed in laboratory experiments [10] during all six surveys.

Biologically available copper concentrations (Cudyn) at Restronguet Point, as measured in situ over the time of a tidal cycle in different seasons. The concentration at which 50% of oyster larvae are damaged is marked as a purple line and labelled “EC50 Cu OEL”. The horizontal axis gives time relative to the time of low water, which was shifted to 12 noon, in hours. The copper concentration units are in nanomole per litre on the vertical axis. (c) C Braungardt.

In September 2023, the opportunity arose to return to the Fal Estuary on board Pelican of London with a crew of sail trainees who signed up for an ocean science voyage, Scientist in Residence Jeremy Woolfe and I quickly devised a plan that would indicate the current impact of metal/loid pollution on rocky shore biodiversity.

On the eve of the fieldwork we were moored up off Falmouth and I gave a briefing that outlined previous findings of my pollution studies in this estuary. I also introduced the cycle of research, that starts with questions and aims, progresses through experimental design, data collection, analysis, interpretation and reporting to conclusions and, typically, to more questions.

Research cycle for the biodiversity surveys in the Fal estuarine system in September 2023.
Research cycle for the biodiversity surveys in the Fal estuarine system in September 2023.

In practice, it looked like this for the youngsters on board:

  • Question: does pollution from legacy mines in Restronguet Creek affect biodiversity on rocky shores today?
  • Method development with the aim to assess the biodiversity with respect to the number of species present at a polluted and a control site within the Fal Estuary.
  • In dense drizzle, a RIB run to Restronguet Point and a Ferry ride to St Mawes for team Charly and team Jeremy, respectively.
  • Synoptic surveys of rocky shores of similar exposure and aspect at Restronguet Point and near St Mawes, the unpolluted control site, using seven trainees with no experience in the field to record all the different organisms that can be found on site within 2 hours.
  • Detailed analysis of specimen and photographs to identify different seaweeds, mollusks, sponges, anemones, crustaceans, seasquirts, fish and other organisms visible without microscopy, where possible to species level.
  • Calculation of a biodiversity index, specifically developed by Jeremy to suit the limitations of the study (time, level of experience, area surveyed, lack of systematic counting).
  • Comparison of results, discussion, conclusions.
  • Question: what’s next?
Simplified map of the Fal estuary in southwest England with areas impacted by legacy mining indicated at the head of Restronguet Creek. The test site at Restronguet Point and control site at St Mawes are marked in red and green, respectively.

So, what’s the story at Restronguet Point today?

Leading the team at Restronguet Point, I was positively surprised to see that the colour of the exposed mud in the Creek had lost the unnatural ochre-red hue it featured on my first visit in 1996. Perhaps the reddish-brown of today indicates an improvement of sediment quality? But this was not something we were here to assess directly.

The next surprise was finding a much greater number of brown seaweeds than I remember from before, as well as various sponges, crabs, anemones, sea squirts, tube worms, an eel and small fish fry.

Meanwhile at the control site near St Mawes, Jeremy’s team discovered a wider range of green and red seaweeds and rockpool dwellers that were largely absent at the polluted creek. Even though the number of animal species were similar at the two sites, the species present differed, something that can be explored in more detail elsewhere…

Jeremy devised the Woolfe’s Biodiversity Index Dw, which takes into account of the different area sizes surveyed at the two sites. Dw enables direct comparison of the results and shows that pollution entering the Fal Estuary from abandoned mines still supresses biodiversity today (Dw = 1.9 at Restronguet Point), when compared to the control site (Dw = 3.4 at St Mawes), even though a proportion of the mine waters from Wheal Jane have been treated for years.

Number of species of animals and seaweeds identified during a survey in September 2023 at Restronguet Point, a site influenced by legacy mining pollution and the control site at St Mawes, where no mining took place. The Woolfe Diversity index makes the results comparable.

Seawater flooding and ebbing dilutes and disperses pollution and its effects diminish with distance. How far it reaches is a question for a different study, as is the apparent greater diversity of brown seaweeds at Restronguet Point, compared to St Mawes.

What we found could be food for thought for university students seeking topics for their dissertations… just as what others found here was raising my curiosity for my undergraduate research all those years ago.

Acknowledgments: many thanks to the professional crew of Pelican of London (Ben, Ali, Tamsin, George, Janice, Saul, Franklin, Shell) and volunteers for supporting our science work, to Jeremy for his good humour and biological expertise and to all trainees for their enthusiasm and hard work in spite of adverse weather.

Featured Image: Beadlet anemone of around 3 mm diameter found at Restronguet Point during our 2023 survey. This and all other photos and illustrations (c) C Braungardt.

[1] Mighanetara K, Braungardt CB, Rieuwerts JS, Azizi F. 2008. Contaminant fluxes of point and diffuse sources from abandoned mines in the River Tamar catchment, UK. Journal of Geochemical Exploration 100, 116-124.

[2] Rieuwerts JS, Mighanetara K, Braungardt CB, Rollinson GK, Pirrie D. 2014. Geochemistry and mineralogy of arsenic in mine wastes and stream sediments in a historic metal mining area in the UK. The Science of the Total Environment 472, 226-234.

[3] Rainbow PS. 2020. Mining-contaminated estuaries of Cornwall – field research laboratories for trace metal ecotoxicology. Journal of the Marine Biological Association of the UK 100 (2), 195-210. DOI link

[4] Exeter University. The Wheal Jane incident and water quality. Wheal Jane Project Website. online [accessed 18/09/2023]

[5] Whitehead PG, Jefrey H, Neal M. 2005. The water quality of the River Carnon, west Cornwall, November 1992 to March 1994: the impacts of Wheal Jane discharges. The Science of the Total Environment 338 (1-2), 23-39.

[6] Whitehead PG, Prior H. 2005. Bioremediation of acid mine drainage: an introduction to the Wheal Jane wetlands project. The Science of the Total Environment 338 (1-2), 15-21.

[7] Braungardt CB, Howell KA, Tappin AD, Achterberg EP. 2011. Temporal variability in dynamic and colloidal metal fractions determined by high resolution in situ measurements in a UK estuary. Chemosphere 84 (4), 432-431.

[8] Rainbow PS et al. 2004. Enhanced food-chain transfer of copper from a diet of copper-tolerant estuarine worms. Marine Ecology Progress Series 371, 183-191.

[9] Braungardt CB et al. 2011. Temporal variability in dynamic and colloidal metal fractions determined by high resolution in situ measurements in a UK estuary. Chemosphere 84, 423-431.

[10] Money C. 2008. Trace metal chemical speciation and acute toxicity to Pacific oyster larva. PhD Thesis. University of Plymouth.

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