Fate of organic matter from land to ocean via rivers

Soils hold a large quantity of carbon. This carbon may leach into rivers and streams that can transport it to the estuary and eventually the sea. Changes in land use and climate change are expected to increase the soil carbon losses that can have a profound impact in the aquatic ecosystems. However, little is known about the fate of this carbon, what processes and controls the loss and transport from soils, through the freshwater system and out to coastal waters.

LOCATE (Land-Ocean Carbon Transfer) brought together soil biogeochemists, hydrologists, and oceanographers from four UK research institutions (National Oceanography Centre, British Geological Survey, UK Centre for Ecology & Hydrology, and Plymouth Marine Laboratory) to begin a multidisciplinary national-scaled project to quantify the transport of soil organic matter from the land to the ocean, through assessment of rivers, estuaries, and coastal waters.

Composite of three images of rivers and researchers gathering data

The vision of LOCATE is that in ten years the key processes relevant to decomposition of terrigenous carbon are well represented in models, particularly for carbon stored in boreal peatlands.

The challenge

The largest organic carbon reserves in Europe are in the peat soils of north and west of Great Britain. Every year increasing amounts of carbon is leached from these soils into rivers and streams, reaching coastal areas via estuaries. Once the organic carbon is released from the soil, it is open to undergo many different physical, chemical and biological changes. One such change might result in it being converted into inorganic carbon (carbon dioxide or methane), which can out-gas into the atmosphere, contributing atmospheric greenhouse gases and climate change. Or the carbon may be recaptured and stored in the sediments of rivers, estuaries or transported to the open ocean.

Despite its importance for the global carbon cycle, there are still many questions that remained unanswered, such as:

  • How much carbon is being transported from the soils to rivers and estuaries?
  • What processes affect the release and change of organic carbon?
  • What is the fate of this released organic matter?

A national-scale multidisciplinary approach

The LOCATE team are a collaboration of scientists from a range of research backgrounds aiming to provide robust evidence and modelling capability to begin to answer this challenge, through a range of sampling programmes, model development and technology innovation.

The team conducted a 1.5-year sampling programme in 2017–2018, sampling 40 rivers monthly (January 2017 – December 2017) and 13 estuaries quarterly (April 2017 – April 2018), selecting rivers and estuaries that represented the diverse land use and hydrological conditions (temperature, rainfall) present in Great Britain, these totalling a third of rivers that drain the UK.

Additionally, intensive sampling campaigns in three sites (Halladale, Conwy, Tamar) provided the detailed understanding of the processes and controls of organic carbon, with the data gathered being used in predictive models to make future projections of the fate of the UK organic carbon stocks.

Composite of three images of rivers and researchers gathering data

LOCATE is a project funded by NERC bringing together a multidisciplinary team from across the UK.