Riverine carbon and alkalinity flows

Rivers are an important source of dissolved carbon, nutrients and other ions to the ocean. The river water picks up some of these components through the process of weathering - dissolving minerals out of rocks on the land. Different minerals impart different chemical properties to the water. From a CO2 perspective, dissolving calcium carbonate (CaCO3) increases the water’s alkalinity, which enhances its capacity to take up CO2 from the air. Rivers with catchments through limestone bedrock therefore provide significant fluxes of alkalinity to the surrounding ocean, stabilising additional dissolved CO2 in the seawater, and elevating its pH.

UK river chemistry monitoring

LOCATE is a multidisciplinary project undertaking the first ever coordinated chemical sampling of Great Britain's major rivers. Many of these rivers, especially towards the south, include limestone in their catchments, making them of particular interest for understanding the marine carbonate system in the surrounding northwest European shelf sea.

PhD student Ruth Matthews is measuring the dissolved CO2 and alkalinity in LOCATE samples at the University of East Anglia (UEA). I am supervising Ruth's PhD studies along with lead supervisor Dr Dorothee Bakker (also at UEA), Dr Naomi Greenwood and Dr Silke Kröger (Cefas), and Prof Richard Sanders (NOC Southampton). The results will allow us to better quantify the flows of alkalinity and dissolved inorganic carbon from rivers into the shelf sea from the whole island of Great Britain, and study their consequences for oceanic CO2 uptake from the atmosphere and ocean acidification.

Right: map of river catchments sampled within the LOCATE programme (source).

Map of UK river catchments investigated by the LOCATE research programme.

Alkalinity method development

Measuring the LOCATE samples has required pushing the analytical instruments at UEA beyond their normal operating bounds. These instruments (i.e. VINDTAs) were primarily designed for measuring salty seawater samples from the open ocean, not fresh and brackish river and estuary water. Ruth has been modifying the UEA VINDTAs' hardware and software to more reliably determine the LOCATE samples' alkalinity over a wider range of salinity. We are also further developing my Calkulate software to ensure that meaningful alkalinity values can be extracted from these unusual titration data.

Left: titration cell constructed in-house for small-volume samples, set up for total alkalinity analysis with a VINDTA at UEA (photo by Ruth Matthews).

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