Anthropocene Sediment flux in the Manawatu River Catchment, New Zealand — ASN Events

Anthropocene Sediment flux in the Manawatu River Catchment, New Zealand (17090)

Simon Vale 1 2 , Ian Fuller 1 , Jonathan Procter 1
  1. Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand
  2. Landcare Research, Palmerston North, New Zealand

Human interaction with the environment has had an emphatic influence on the Earths systems, driving environmental changes in hydrological cycles, sediment flux and ecosystems. These global processes, systems and resources have been treated as if so vast and resilient that they could indefinitely absorb relentless effects of human development. That perception has long been put to rest as a viable paradigm for continued development. Despite these advances in environmental understanding, prior human–environment interactions have left a legacy of global challenges that we have to collectively navigate. Anthropogenic degradation of the catchment environment and associated sediment flux is one of those challenges, leading to an increase in research, quantification and modelling of sediment movement through a wide range of Earth surface processes. 

The Manawatu River Catchment has experienced extensive modification over the last 160 years following European settlement in New Zealand.  Wholesale landuse conversion from indigenous forest to pastoral agriculture has led to reduced slope stability in much of the catchment resulting in widespread mass movements, soil erosion and an increase of sediment supply to the river. The suspended sediment component in a fluvial environment is one of the most important components of the sediment cascade. Fine sediment production in the form of erosion, transport and deposition processes directly influences the form and character of fluvial channels and surrounding environment, and includes a range of physical, chemical and ecological effects that are more often regarded as detrimental in nature. Small changes in the input of fine sediment due to modifications in landuse can have significant downstream implications, adversely affecting river health. Intensification of agricultural practices, associated runoff and the existence of industrial and municipal discharges into the river have contributed to extensive deterioration of the catchment environment. Fast-forward to present day and the Manawatu River Catchment is a shadow of its former glory making news headlines for many of the wrong reasons. Sediment, nutrient and pathogen levels are at degraded levels and significant river and flood control works have introduced new challenges to consider.

To address the issues of catchment wide degradation and increased understanding of critical sediment source areas is required, however, catchment scale identification of erosion processes and geomorphically active areas contributing to sediment yield have often been poorly understood and quantified.  Sediment fingerprinting provides an additional approach to quantifying sediment sources in relation to the legacy of anthropogenic influences.