Abstract:
Quantifying land use sources and understanding the dynamics of organic carbon
(OC) in river catchments are essential to reduce both on-site and off-site impacts
of soil OC (SOC) erosion. The aim of this research is to improve determination of
the dominant terrestrial land-use sources of OC in freshwater sediment at a
catchment scale and to assess the likely processes driving spatial and temporal
changes in these sources. Four interlinked studies were conducted on two
catchments to investigate specific objectives.
First, OC fingerprinting and carbon loss modelling (a combination of “net” soil
erosion and OC spatial distribution modelling) were carried out using existing OC
and n-alkane biomarker data from Carminowe Creek, a mixed land use
catchment in Cornwall, UK. This unique combination of two sediment origin
techniques crucially identified that riparian woodland disconnected upslope
eroded SOC and, concomitantly, provided an input of woodland-derived OC to
the streams, giving an increased understanding of sediment and OC transport
processes.
Secondly, extensive new data from Loch Davan catchment, Aberdeenshire, was
used to find the effect of novel combinations of n-alkane concentration ratios, n-
alkane compound-specific stable isotopes (CSSI) and short-chain neutral lipid
fatty acid (SC-NLFA) biomarkers on land use source discrimination using a
Bayesian un-mixing model. In comparison to using only n-alkane ratios, a
combination of n-alkane ratios and CSSI improved discrimination between arable
and pasture land uses and using a combination of n-alkane ratios and SC-NLFA
reduced error when discriminating four land uses (arable, pasture, forest and
moorland).
Thirdly, in an innovative approach, OC source proportions were identified, in both
streambed and suspended sediment (SS), at a headwater sub-catchment and
catchment scale. Different drivers of OC dynamics were detectable at the two
different scales (sub-catchment and catchment scale), and different dominant
land use sources were found in streambed and SS OC leading to improved
identification of processes driving spatial and temporal OC dynamics.
And finally, soil erosion “hotspots” (i.e. where there is high risk of soil degradation)
can be identified by modelling catchment erosion using a variety of different
erosion models. The utility of these soil erosion models in identifying hotspots,
and guiding Best Management Practices (BMP), depends upon their accuracy
and there is a need to assess model usefulness. Thus, a new method was
developed and tested using streambed sediment land use -specific yields
estimated using OC fingerprinting as a benchmark to determine which erosion
model best identified the relative land use OC yields in streambed sediment.
The new methods and findings from their application will improve determination
of dominant terrestrial land-use sources of OC in freshwater sediment at a
catchment scale, and support development of BMP to reduce impacts on land
productivity and water quality due to changes in climate and human activity.
Description:
Meersmans, Jeroen. Associate supervisor University of Liege.
Glendell, Miriam. Associate supervisor James Hutton Institute