BGS blogs

Esthwaite Water: applying novel approaches to understand lake-water nutrient pollution

Andi Smith (BGS) and Savannah Worne (Loughborough University) embarked on fieldwork in the Lake District, applying a novel stable isotope method for tracing phosphorus sources.

19/09/2025

Esthwaite Water looking beautiful in early summer sunshine. UKCEH and its partners have been sampling and monitoring many of the lakes in the English Lake District, including Esthwaite Water, for several decades. BGS © UKRI.

Phosphorus (P) is a key limiting nutrient for many lake systems. However, a rise in the level of phosphorus in lake waters can stimulate the growth of excess plants and algae. The increase in phosphorus facilitates rapid increases in lake productivity, causing events as such as algal blooms, which can lead to reductions in water quality. Phosphorus has been one of the major nutrients responsible for algal blooms over the last several decades.

Most sources of excess phosphorus in lakes are external to their catchments and are mainly due to human activities, such as agricultural runoff, sewage discharge and industrial pollution. These external sources of phosphorus have been well defined over the years and, in many of the UK’s most important lakes, they are regulated and strictly limited.

Lakes such as Esthwaite Water in the Lake District have seen significant reductions in external phosphorus inputs over recent decades, through conscious management to combat previous nutrient pollution problems. However, many lakes, including Esthwaite Water, are still experiencing issues with major algal blooms, despite stringent regulation and monitoring.

Our research aims to quantify why levels of phosphorus in these lakes are still so high, by assessing how much is still coming in from external sources and how much is being sourced from the nutrient-rich sediments historically deposited within the lake.

The team out on the lake getting stuck into the often muddy experience of collecting lake sediment cores. These cores cover the period of human interaction with the lake. This means the team can identify periods of minimum and maximum human-derived phosphorus input into the lake. Photo credit: Penny Reeve. — The team out on the lake getting stuck into the often muddy experience of collecting lake sediment cores. These cores cover the period of human interaction with the lake. This means the team can identify periods of minimum and maximum human-derived phosphorus input into the lake. Photo credit: BGS © UKRI.

This round of fieldwork saw the team collecting three lake sediment cores (for isotope and geochemical analyses) as well as numerous water samples from the lake itself and its input streams. All these samples will be analysed at the Loughborough University or BGS laboratories.

It is hoped that the stable phosphate oxygen isotope analysis of the lake sediments in particular will offer novel insights into the past and current phosphorus dynamics at Esthwaite Water. The team will then be able to identify if the lake sediments are contributing a large enough legacy source of phosphorus to the lake waters to maintain the algal blooms that the lake suffers from.

This work is ongoing and experimental but, if successful, it could be applied to a large range of polluted lake systems in the UK and worldwide, to help identify and fingerprint phosphorus sources.

Funding

This work was facilitated and supported by established Esthwaite scientists Gareth McShane and Ellie Mackay from the UK Centre for Ecology & Hydrology.