Catherine Hirst

Lena River 1 Lena River 2

 

Background

My name is Catherine Hirst, a MetTrans Fellow and PhD student at Stockholm University and the Natural History Museum, Stockholm.  I completed an Undergraduate and Master’s degree in Earth Sciences at Oxford University. My Master’s project focused on the chromium isotope system, bulk elemental abundance and total organic carbon in Proterozoic Banded Iron Formations. I used the Inductively Coupled –Mass Spectrometry and Thermal Ionisation Mass Spectrometry to complete this project.

Overview

This PhD project is part of a larger research project, entitled “Climate warming in Siberian Permafrost Regions; tracing the delivery of carbon and trace metals to the Arctic Ocean”. As a team, we aim to investigate the riverine fluxes of carbon, nutrients, and trace metals from the Siberian watersheds. We seek to further understand how terrestrial changes due to climate warming will affect the marine environment.

Vast areas of the Northern Hemisphere in Europe, Asia and North America are covered by Taiga and Tundra biomes and hold a huge stock of carbon in soil and litter. Permafrost, (soil that remains at or below 0 oC for two or more years), constitutes 24% of this northern hemisphere land (Zhang et al 1999) – preserving these vast reserves of organic matter. Siberia contains both extensive permafrost and contributes 50% of the entire river runoff to the Arctic Ocean (Kuzmin et al 2009) via the Ob, Yenisei, Kolyma, and Lena Rivers. Consequently, these Siberian Rivers transport large quantities of organic carbon, nutrients, and inorganic material. Increasing global temperature threatens to thaw the permafrost and change climate patterns, changing the river fluxes of these constituents, and so altering the biogeochemistry of the Arctic Ocean.

This study will focus on the Lena River watershed, the largest in the Arctic hydrological cycle at 2.43 x 106 km2, with an average river discharge of 16650 m3s-1 (Martin et al 1993). We will observe the geochemical signature of the Lena River basin; provide a much needed data set which can be used to evaluate the future impact of these changes on the Arctic Ocean. Limited datasets are available, but long-term data indicates that significant hydrologic changes have already been occurring over the last 75 years (Yang et al., 2002).

My Focus

My project is concerned with the interaction between organic matter and trace metals at the rock, soil, water interface – in the Lena River watershed. Organic material derived from peat has strong chelating ligands that enhance the weathering rates of iron-silicate minerals and greatly increase the solubility and transport of metals, such as iron, in river water. I will analyse unfiltered, filtered, ultrafiltered waters and particles collected during the filtering process. I will categorize the particles into various size fractions (suspended phases, colloids, and dissolved phases) and apply background data of bedrock geology, active layer thickness, soil type, photoreduction processes and bacterial degradation, to decipher the importance of organic phases for iron and trace metal transport.

Field Work

We (Per Andersson, Don Porcelli, Liselott Kutcher and Catherine Hirst) have returned safely from a month of field work on the Lena River and its tributaries. The expedition was a great success – we sampled at 41 localities, returning to Sweden with 68 Kg of water, ready for processing and analysis.

The expedition team was accompanied by a three person crew, a cook and biologist. We ventured north of Yakutsk, on board a Russian vessel – aiming to build on the successful sampling of the central and southern Lena River and Aldan tributary, in 2012 (60oN to 63oN). Samples were collected along the main river channel, (dropping a bucket from the main boat) and in major tributaries, using a smaller motor boat (grab sampling or wading along the river bank). The collected water was filtered on board using a peristaltic pump, sond measurements (temperature, pH and conductivity) were measured insitu and alkalinity was determined directly onboard the vessel. Overall we sampled between 63oN to 68oN,  and also ventured 350km up the Vilyuy River – a major tributary with little previous sampling. These samples will be analysed alongside samples collected in July 2012 (60oN to 63oN) to produce a comprehensive and novel dataset of the Lena River watershed.

The expedition provided invaluable insight into the taiga biome and boreal forest ecosystem, valuable for the interpretation of the geochemical results. Further, it was fascinating to “witness “ permafrost at first hand and better understand it’s consequences, both for the watershed and the people and infrastructure within it.