Riparian management: investigating public perception and the effect of land-use, groundcover and rainfall on sediment retention.

Abstract

The physical and biological characteristics of a stream are strongly influenced by its surrounding catchment. The riparian zone acts as a buffer between land and water ecosystems and can play an essential role to retain contaminants (e.g. sediment) from entering and affecting the receiving waterway. When the riparian zone is not managed, the consequence can be high amounts of sediment entering the waterway that negatively affects in-stream communities with a decline in native invertebrate and fish populations. I investigated three aspects of riparian management in the Canterbury region, South Island, New Zealand, by investigating the public perception using a questionnaire to determine what the public knows about riparian management and what practices are being done in the farming community. Results showed that riparian management varied across farm types, and there was some confusion about the roles of riparian management. Crop farmers were the least likely to do riparian management, in contrast to dairy farmers who were the most likely to do riparian management. A main concern is that the majority of respondents highlighted that filtering nutrients was the main goal for riparian management, and only 5% thought it was due to sediment, and 10% to decrease erosion. I then conducted a field survey to investigate riparian zone sediment retention in different land-uses (dairy farming, production forestry and urbanisation) compared to native forest. Surprisingly, dairy farms produced the least amount of sediment, and urban areas produced the most, and there was a marginal effect of season. However, generally there was no difference between the amounts of sediment passing through the riparian zone. Therefore, I was unable to distinguish if there were any vegetation effects occurring within the riparian zone. To complement the field survey, I tested sediment overflow by conducting multiple experiments using a rain simulator. The simulator controlled the intensity and amount of rainfall over differing percentages of riparian groundcover. My results were consistent with other studies showing that as groundcover increases, sediment runoff decreases. However, there was no relationship between rainfall intensity and the amount of sediment in runoff. My thesis indicated that riparian planting to reduce sediment flow into streams needs to focus on high amounts of groundcover (such as rank grass).