EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Nitrate retention and subsidy in oligotrophic mountain stream-lake networks

Imke Grefe1, Peter Wynn1, Eleanor Mackay2, Philip Barker1, Helen Grant2, Gloria Pereira2, Stephen Maberly2, and Benjamin Surridge1
Imke Grefe et al.
  • 1Lancaster Environment Centre, Lancaster University, United Kingdom (
  • 2UK Centre for Ecology & Hydrology, United Kingdom

With human activity rapidly accelerating the global nitrogen cycle, aquatic environments are facing increasing eutrophication and ecosystem damage. Oligotrophic headwater streams are particularly susceptible to nutrient pollution, which is affecting biodiversity, ecosystem services and water quality. However, not much in known about biogeochemical nitrogen cycling in these remote environments. This research presents seasonal data for nitrate concentrations and stable isotope signatures from oligotrophic mountain stream-lake networks in the English Lake District, UK. While phosphate concentrations were frequently below detection limit, nitrate was present throughout the year with concentrations ranging from 0.01 to 0.49 mg N L-1. Dual isotope analysis of δ15N-NO3 and δ18O-NO3 identified atmospheric deposition as an important nutrient source to the ecosystem and provided information on the fate of nitrate moving through hydrologically connected stream-lake networks. Some mountain lakes removed up to 69% of nitrate delivered by the inflow stream, while others were substantial sources compared to upstream concentrations. This contrasting lake response was consistent throughout the year, with in-lake nitrate subsidy being observed in systems where concentrations in the inflow stream dropped below 0.25 mg N L-1. These findings suggest that dominant biogeochemical processes may be controlled by nutrient load, and ecosystem response could potentially change with increasing nutrient pollution.

How to cite: Grefe, I., Wynn, P., Mackay, E., Barker, P., Grant, H., Pereira, G., Maberly, S., and Surridge, B.: Nitrate retention and subsidy in oligotrophic mountain stream-lake networks, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5463,, 2023.