Freshwater physical habitat
What is measured
This indicator measures the physical habitat condition of New Zealand waterways. We report on 369 sites across six North Island regions and 90 sites in one South Island region (Southland), identifying the overall state of stream habitat at each site based on at least three years of data between 2013/14 and 2018/19. Ten physical habitat components are measured during the assessment, including bank erosion and the diversity and abundance of fish cover (Clapcott et al, 2019).
Why it is important
The physical habitat of a river or stream provides the living space for species (Maddock, 1999). Its condition affects the diversity, abundance, and distribution of freshwater biological communities, providing species with refuge from predation, protection against floods and droughts, and areas for nurseries and spawning (Harding et al, 2009). Degraded physical habitat can also affect the amenity and aesthetic value of rivers and streams, or their suitability for recreation or cultural uses.
Physical habitat assessments provide information that support appropriate river and stream management and restoration. Assessment data is also used to provide a mechanism through which to investigate patterns in diversity, abundance, and distribution of freshwater biological communities (Harding et al, 2009).
Key findings
Based on the Habitat Quality Scores (HQS) calculated from data collected using the Rapid Habitat Assessment (RHA) method applied at 459 monitoring sites between 2013/14 and 2018/19 (Clapcott et al, 2019):
- 22.2 percent had excellent habitat condition
- 57.1 percent had good condition
- 20.7 percent had fair condition.
HQS were excellent or good at:
- 97.4 percent of 115 sites dominated by native land cover
- 75.4 percent of 301 sites dominated by pastoral land cover
- 65.0 percent of 20 sites dominated by exotic forest land cover
- 52.2 percent of 23 sites dominated by urban land cover.
Where this data comes from
Cawthron Institute, via regional councils and unitary authorities
View data tables
Related indicators
- Deposited sediment in rivers
- Streambed sedimentation
- River water quality: clarity and turbidity
- Estimated long-term soil erosion
- Highly erodible land
- Cultural health index for freshwater bodies
Related content
About the data
The Rapid Habitat Assessment (RHA) is a field survey protocol for assessing the physical habitat condition of New Zealand’s waterways (Clapcott, 2015). RHA identifies the overall state of stream habitat at each assessed site based on the qualitative scoring of ten component measures at each assessed site which are then summed to calculate a Habitat Quality Score (HQS). This indicator reports on 369 sites across six North Island regions and 90 sites across one South Island region that collected data over three or more years, at least once per year between 2013/14 and 2018/19 (Clapcott et al, 2019). The HQS for a site was calculated as the median score obtained during the measurement period.
The area of a site is 20 times the mean wetted width at base flow (with a minimum of 50 meters and a maximum of 500 meters); the wetted width is defined as the distance across the stream that is submerged by water on the day of sampling (Harding et al, 2009). This does not allow for a catchment-wide approach where adjacent sites to the measured site are captured; some measures, such as fish abundance due to movement of fish between habitats, may be affected by this.
Sites span six regions in the North Island:
- Wellington
- Hawke’s Bay
- Waikato
- Gisborne
- Northland
- Taranaki
Sites span one region in the South Island:
- Southland
All sites have been classified by dominant land cover. We used the Land Cover Database version 4.1 detailed classes grouped according to Land, Air, Water Aotearoa’s (LAWA) medium land cover classes. We aggregated these medium classes into the following five dominant land cover categories:
- Urban area
- Pastoral
- Exotic forest
- Native
- Other (includes ‘Gorse and/or Broom’, ‘Surface mines and dumps’, ‘Mixed exotic shrubland’, and ‘Transport infrastructure’).
We excluded the LAWA medium land cover class ‘Water bodies’ from our calculations.
Dominant land cover in the upstream catchment is assigned by the following series of rules (Snelder et al 2010):
- Urban area – if urban cover exceeds 15 percent of catchment area.
- Pastoral – if pastoral exceeds 25 percent of catchment area and not already assigned urban.
- Exotic forest, Native, or Other – according to the largest land cover type by area, if not already assigned urban or pastoral.
See the New Zealand River Environment Classification User Guide for more information.
The HQS is the sum of ten parameters measured:
- deposited sediment – the percentage of the stream bed covered by fine sediment, measured using a bankside visual estimate; note that this component is not comparable to the Deposited sediment in rivers indicator as this component includes data gathering via both SAM1 (bankside visual assessment) and SAM2 (in-stream visual assessment) methods, whereas the ‘Deposited sediment in rivers’ indicator only reports on those sites measured using the SAM2 method
- invertebrate habitat diversity – the number of different substrate types such as boulders, cobbles, gravel, sand, wood, leaves, root mats, macrophytes, periphyton
- invertebrate habitat abundance – the percentage of substrate favourable for colonisation by Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies)
- fish cover abundance – the percentage of fish cover available
- fish cover diversity – the number of fish taxa, including percent of exotic fish taxa
- hydraulic heterogeneity – the number of different hydraulic environments, such as pools (deep water that is slow flowing, often on the outside bend of a river), riffles (where stones break the surface water, and the water moving over them is shallow and fast moving), and runs (unbroken, smooth area of flowing water between pools and riffles)
- bank erosion – the percentage of the stream bank recently/actively eroding due to scouring at the water line, slumping of the bank, or stock pugging (when the soil body breaks down and soil pores are reduced due to intensive trampling by stock)
- bank vegetation – measures how mature, diverse, and natural the bank vegetation is
- riparian width – the width of the riparian buffer defined by a change in vegetation, fence, or other structures
- riparian shade – percentage cover of shade on the stream bed due to vegetation, bands, or other structures.
Each parameter is given a score between 1 and 10. The lowest scores indicate the greatest deviation from the condition expected with no, or minimal, human influence or impact (reference state). These individual parameter scores are then summed to determine an overall Habitat Quality Score: Excellent (>75), Good (51–75), Fair (26–50) or Poor (< 26).
Data quality
The accuracy of the data source is of medium quality.
Freshwater physical habitat is a direct measure of the ‘Freshwater ecosystems and habitats’ topic.
Stats NZ and the Ministry for the Environment must report on topics related to the five environmental domains: air, atmosphere and climate, fresh water, land, and marine. These topics identify key issues within each domain.
Topics for environmental reporting describes the topics for each domain.
Data quality information has more information about the criteria we use to assess data quality.
References
Clapcott, J, Casanovas, P, Doehring, K (2019). Indicators of freshwater quality based on deposited sediment and rapid habitat assessment. Prepared for the Ministry for the Environment. Cawthron Report No. 3402.
Clapcott, J (2015). National rapid habitat assessment protocol development for streams and rivers. Prepared for Northland Regional Council. Cawthron Report No. 2649.
Clapcott, JE, Young, RG, Harding, JS, Matthaei, CD, Quinn, JM, Death, RG (2011). Sediment Assessment Methods: Protocols and guidelines for assessing the effects of deposited fine sediment on in-stream values. Nelson, New Zealand, Cawthron Institute.
Maddock, I (1999). The importance of physical habitat assessment for evaluating river health. Freshwater Biology (1999) 41, 373–391.
Harding, J, Clapcott, J, Quinn, J, Hayes, J, Joy, MK, Storey, RG, Greig, HS, Hay, J, James, T, Beech, MA, Ozane, R, Meredith, AS, Boothroyd, IKG (2009). Stream Habitat Assessment Protocols for wadeable rivers and streams of New Zealand. School of Biological Sciences, Christchurch.
Snelder, T, Biggs, B, & Weatherhead, M. (2010) New Zealand River Environment Classification User Guide. March 2004 (Updated June 2010) Retrieved from www.mfe.govt.nz.
Snelder, TH, & Biggs, BJF (2002). Multiscale river environment classification for water resources management. Journal of the American Water Resources Association, 38(5), 1225–1239. https://doi.org/10.1111/j.1752-1688.2002.tb04344.x
