Nitrogen cycling in the glacier-fed rivers of the Cordillera Blanca, Peru
: seasonal and within-catchment dynamics, and the impacts of Acid Rock Drainage

  • Jessica Hammond

Student thesis: Master's ThesisMaster of Science by Research (MScR)

Abstract

The role of glaciated environments in regional and global biogeochemical cycles via the production, cycling, and export of nutrients, has recently come to the forefront of research, owing to the discovery of diverse communities of microorganisms which are capable of mediating and modulating these processes. This research is centred around the large ice sheets of Greenland and Antarctica and northern hemisphere mountain ranges, while the significance of tropical glaciers has, to date, been neglected. Constraining the nutrient dynamics of these tropical glaciers is important due to their extreme vulnerability in a warming climate, and the reliance placed on them by local communities as a water supply. Moreover, tropical glaciers within the Cordillera Blanca (CB), Peru, have recently been identified as being impacted by Acid Rock Drainage (ARD), severely impacting water quality, to the extent that it can be compared to regions which have been extensively mined (Acid Mine Drainage, AMD). While the impacts of AMD are widely understood, the consequences of ARD from glacial catchments remain relatively unknown, especially in the context of nitrogen production, cycling and export.

This study aims to constrain the spatial and temporal dynamics of nitrogen cycling within Peruvian glaciated catchments and gain a better understanding of how ARD may impact these processes. Samples were collected during two field seasons in the 2019 dry season and 2020 wet season from glacier-fed streams in two contrasting catchments, one impacted by ARD and the other not. Hydrochemical variables (water temperature, pressure, specific conductivity (SPC), pH, dissolved trace element concentration) and nitrogen concentrations (nitrate as NO3--N, ammonium as NH4+-N, and dissolved organic nitrogen (DON)) were analysed in the laboratory to identify any spatial and temporal trends within and between the catchments, and any impacts of ARD. Very few spatial and temporal differences were identified, likely owing to additional inputs of nitrogen from locally produced pollution, the limited evolution of the subglacial drainage system limiting variability in meltwater hydrochemistry, and the limited temporal coverage of each field season. On a local, site-specific scale, ARD did not appear to have large impacts on nitrogen production and cycling as there were very few significant differences between the ARD and non-ARD catchment. Differences between the two catchments became more apparent once extrapolated to estimate glacial fluxes; the fluxes of DON from the Shallap glacier stood out, estimated to be one order of magnitude greater than those from the Cojup glacier. The nitrogen fluxes from the glaciers in this study were found to be comparable to those from other glaciers around the world. This study can be used as the basis for future work investigating ARD in other glaciated environments and will be important to consider due to the projected glacial retreat under future climate change.
Date of Award27 Sept 2022
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorRory J Bingham (Supervisor), Jemma L Wadham (Supervisor) & Christopher Yates (Supervisor)

Cite this

'