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Riparian Characteristics of Pastoral Streams in the Waikato Region, 2002 and 2007

Report: TR 2010/07
Author: R Storey (NIWA)

Abstract

Fencing and planting of riparian zones are effective ways of improving the health of waterways. Fencing to exclude stock reduces stream bank erosion and removes direct input of dung (Parkyn and Wilcock, 2004). It also allows dense grass growth in the riparian zone, which increases filtration of particulates and uptake of nutrients from pasture runoff (Smith, 1989). Planting of woody vegetation in the riparian zone further benefits streams by increasing stream shading (which reduces algal growth and lowers water temperatures) and providing input of wood and leaves to the stream ecosystem (Quinn et al. 2009). Implementing these management measures has been shown to result in improved water quality (Williamson et al. 1996), a more diverse and balanced community of aquatic plants and animals (Quinn et al. 2009), as well as greater terrestrial biodiversity (Suren et al. 2004).

Since 2002, Environment Waikato has been actively promoting riparian fencing and planting through its Clean Streams programme (Campbell et al. 2002). In addition, in 2003, the Dairying and Clean Streams Accord set voluntary targets for dairy farmers to exclude dairy cattle from 50% of streams, rivers and lakes by 2007, and from 90% of these waterbodies by 2012 (Cowie et al. 2006). Fonterra reports annually on progress towards the Accord targets through its On-farm Environmental and Animal Welfare Assessment, using self-reported data from dairy farms. These figures are quoted in the annual Dairying and Clean Streams Accord Snapshots of Progress (e.g., MAF 2009). In 2002 and 2007 Environment Waikato conducted its own surveys of riparian characteristics in rural streams throughout the region to gauge the success of its investments (Campbell et al. 2002) in riparian management. The aim of these surveys was to provide a repeatable and quantitative assessment of fencing, vegetation and erosion in riparian margins through pastoral land in the Waikato Region (Grant et al. 2009). The survey covered 8 management zones (i.e., Coromandel, Waihou-Piako, Lower Waikato, West Coast, Waipa, Central Waikato, Lake Taupo and Upper Waikato) and two main land use types (i.e., dairy farming and drystock farming).

This report summarises the results of the 2002 and 2007 surveys. The aims were to:

  • compare the amount and type of fencing and riparian vegetation across management zones and land use types;
  • compare results of the Waikato Regional Council survey to self-reported data from the Dairying and Clean Streams Accord snapshots of progress;
  • assess changes in fencing and planting over the five years between 2002 and 2007;
  • determine the factors most strongly driving stream bank erosion; and
  • assess the statistical power of the current survey design and recommend changes to sample sizes.

Riparian Characteristics of Pastoral Streams in the Waikato Region, 2002 and 2007
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Table of contents

  Executive summary iv
1 Introduction 1
2 Methods 3
2.1 Site selection 3
2.2 Data capture 3
2.3 Data analyses 6
2.3.1 Different measures of riparian fencing, vegetation and erosion 7
2.3.2 Effective and ineffective fencing 8
3 Results and discussion 9
3.1 Summary statistics for fencing 9
3.2 Fencing on dairy vs. drystock farms 10
3.3 Fencing in different management zones 12
3.4 Comparison with dairying and clean streams accord data 14
3.4.1 Changes between 2002 and 2007 15
3.5 Riparian vegetation 17
3.5.1 Riparian vegetation change 2002-2007 19
3.5.2 Riparian vegetation on dairy vs. drystock farms 19
3.5.3 Riparian vegetation across management zoones 20
3.5.4 Riparian vegetation and stream order 20
3.5.5 Association between riparian fencing and riparian vegetation type 21
3.6 Stream bank erosion 22
3.7 Factors associated with erosion 23
3.7.1 Land use type and erosion 23
3.7.2 Land use capability and erosion 24
3.7.3 Soil and erosion 25
3.7.4 Valley gradient and erosion 25
3.7.5 Underlying geology and erosion 27
3.7.6 Stream order and erosion 28
3.7.7 Fencing and erosion 29
3.7.8 Riparian vegetation and erosion 30
3.7.9 Instream obstructions and erosion 31
3.7.10 Effect of accessways on erosion 32
3.7.11 Strongest drivers of erosion 33
3.8 Power analysis 35
3.8.1 Power of tests  between years 36
3.8.2 Power of tests for land use type 37
3.8.3 Power of tests for management zone and stream order 37
3.9 Recommendations for future sampling 46
3.10 Sample sizes 46
3.11 Parameters in future surveys 47
4 References 50
5 Appendix 52