Gully erosion reduces carbon and nitrogen storage and mineralization fluxes in catchments

This is my first PhD published paper:

Garzon-Garcia A, Olley JM, Bunn SE, Moody P. 2013. Gully erosion reduces carbon and nitrogen storage and mineralization fluxes in a headwater catchment of south-eastern Queensland, Australia. Hydrological processes. DOI: 10.1002/hyp.9974.

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Abstract

Increased erosion associated with land use change often alters the flux of sediments and nutrients but few studies have looked at the interaction between these disrupted cycles.  We studied the effects of gully erosion on carbon (C) and nitrogen (N) storage in surface soil/sediment and herbaceous vegetation, and on C and N mineralization in a headwater catchment used for cattle grazing. We found significantly lower C and N stored in an incising gully compared with an intact valley. This storage was significantly higher in an adjacent stabilizing gully though not to the levels found in the intact valley.  The intact valley had 2-4 times higher soil/sediment concentrations of TOC, TN and Colwell-P than the incising gully.  Lower storage was not explained by differences in vegetation biomass density or silt and clay content.  Vegetation accounted for only 8% of C and 2% of N storage, respectively. While not a significant store in itself vegetation has an important indirect role in restoring and maintaining soil/sediment C and N stocks in eroding areas.  We found significant linear relationships between C and N mineralization rates and soil/sediment C and N content, with lower rates occurring in the eroded sediment.  These findings support our initial hypothesis that gully erosion reduces C and N storage and mineralization rates in eroding catchments.  The implications of this study include a change to the quality of eroded sediments in headwater catchments, causing C- and N-poorer sediments to be exported but overall loads to increase.

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Gully erosion

Gully erosion is the formation of channels on valleys that previously didn't have distinct concentrated water flows by the action of erosion.  Gully erosion is a severe environmental problem in certain areas of Australia including South East Queensland.  It contributes massive amounts of sediment to stream ecosystems in the region being one the major causes of their degradation.

These are some pictures of gullies in South East Queensland.

                

  

    

                

 Gully restoration is of major importance to achieve river restoration in an affected catchment.  It takes place naturally as the gully evolves towards stabilization but can be accelerated by human intervention.   A stabilized gully achieves a new equilibrium between the settling and transport of sediments as rivers do and also becomes habitat for several species of plants and animals.  Gullies in the dry upper catchments of Australia tend to behave as intermittent streams having flows only associated with rain events and drying out soon after.