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Lakes in the long term

June 27, 2019
Lake monitoring Windermere
Lake monitoring on Windermere in the Lake District, UK. Image: Stephen Thackeray

A guest blog by Dr. Stephen Thackeray, a lake ecologist at the Centre for Ecology & Hydrology.

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A cold wind bites and stiffens fingers that deftly prepare the probe for its descent. Moments later the instrument slips through the surface and glides from well-lit to ever-darker waters, where it will gather important data on the living conditions experienced by the hidden life of the lake. This is a world unseen. A world of constant change, where warmth, light, nourishment and danger vary hugely in time and space. It is also a place of super-abundant life.

This event is the latest episode in a multi-decade scientific endeavour that has tracked the changing fortunes of some of England’s most iconic lakes in Cumbria; a landscape now endowed with UNESCO World Heritage Status. Data from this ongoing year-round research, initiated by the Freshwater Biological Association in the 1940s and continued by the Centre for Ecology & Hydrology since 1989, tells a story of long-term change in the physical, chemical and biological conditions of the lakes. In Windermere, it is a story of decades of nutrient enrichment caused by sewage inputs and agricultural run-off and, increasingly, a story of climate change.

The lake supports a bewilderingly complex web of life. Microscopic plants and animals, organisms that challenge our perceptions of what distinguishes these groups, along with larger invertebrates and fish coexist there. Competitors, predators, prey, cannibals, parasites. Environmental change affects them all.

Mesocyclops
Mesocyclops: a plankton species used to understand long-term changes in Lake District lakes. Image: Stephen Thackeray

Our long-term records allow us to trace these effects. Our lake monitoring has shown increases in algal growth in response to rising phosphorus concentrations, including increases in the prevalence of blue-green algae. Sediments accumulated in the darkest recesses of the lake interior provide us with an even longer-term view of these changes. Deposited ‘mud’, although opaque and turbid, provides a window into the distant past. Such records have clearly shown how changing wastewater treatment has affected the algae of the lake.

Though the fossil record suggests that blue-green algae have existed for billions of years, excessive growth can affect water taste and odour, raise treatment costs, and result in unsightly scums. Research at this iconic lake prompted sewage treatment improvements in the early 1990s, in order to address these issues.

Closterium plankton
Closterium plankton. Image: Stephen Thackeray

Over the same time period that the lake has been enriched with nutrients, it has also warmed. Even winter temperatures have been rising. With warming has come a shift in the underwater seasons, with spring plankton blooms shifting earlier in the year, as well as spawning times for perch. However, perch spawning times have not kept pace with changes in the seasonal timing of plankton food resources, meaning that larval perch may emerge out of sync with their main food resource.

This change in nature’s calendar might already be affecting the survival of the young fish. The fortunes of other fish species have been changing too. Over the same long time scales we have seen that catches of the cold-water Arctic charr, a fish similar to trout and salmon, have greatly declined, while numbers of warm-water roach and bream have increased.

Water flea
Bosmina, or ‘water flea’. Image: Stephen Thackeray

We have these exceptional records, objectively documenting ecological change more accurately than the shifting baselines of generational memories, thanks to the ongoing efforts and dedication of skilled field researchers. The Cumbrian lakes are sentinels, helping us understand the consequences of climate change, and other emerging environmental issues.

However, their relevance is not restricted only to northern England. Just as the species within these lakes are interconnected, so too are researchers across the world. Data and ideas flow through this network, as energy flows through a food web, creating opportunities to collaborate, learn, and build a global picture of how life beneath the water surface is changing.

As such, records from the Cumbrian Lakes are increasingly being used in large-scale scientific investigations into pressing environmental issues that will have global implications. Continuation of this vital work is more important than ever.

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Dr. Stephen Thackeray’s research webpage.

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