Biological Survey of the Hutt River in the vicinity of the Kaitoke Water Abstraction Weir

Transcription

1 Biological Survey of the Hutt River in the vicinity of the Kaitoke Water Abstraction Weir Prepared for Greater Wellington Regional Council MAY 2009

2 This document has been prepared for the benefit of Greater Wellington Regional Council. No liability is accepted by this company or any employee or sub-consultant of this company with respect to its use by any other person. This disclaimer shall apply notwithstanding that the report may be made available to other persons for an application for permission or approval to fulfil a legal requirement. QUALITY ASSURANCE STATEMENT PROJECT MANAGER David Cameron REVIEWED BY Adam Forbes PREPARED BY David Cameron APPROVED FOR ISSUE BY David Cameron WELLINGTON Level 1, 123 Taranaki Street, Te Aro, PO Box 9624, Wellington 6141, New Zealand P , F Project number: Z17921 Our ref: Appendix 4 Macros 2009.docx

3 CONTENTS 1 Response to stakeholder comments Background Effect of low flows on invertebrate community composition Effect of low flows and high flows on invertebrate biomass Further monitoring Comment on proposed low flow management plan...4 References...6 Appendix A: NRWQN Invertebrate data Kaitoke (WN2) Table A1: Summary results for selected invertebrate species and metrics from annual surveys in Hutt River at Kaitoke (7 replicate 0.1m 2 Surber samples composited into a single sample for analysis). Data from NRWQN courtesy of NIWA. Table A2: Correlations of densities of selected taxa, metrics and flow measurements at the Kaitoke site (WN2) on the Hutt River (annual surveys from 1990 to 2006, data courtesy of NIWA). Project number: Z17921 Our ref: Appendix 4 Macros 2009.docx

4 Project number: Z17921 Our ref: Appendix 4 Macros 2009.docx

5 1 Response to stakeholder comments 1.1 Background The draft report Biological Survey of the Hutt River in the Vicinity of the Kaitoke Water Abstraction Weir was reviewed by Dr Dean Olsen at Cawthron Institute in a letter dated 31 October A revised version of the report was reviewed by Dr Olsen in a letter dated 2 May Stakeholder comments on the final report (MWH 2008) were received from the Wellington Fish and Game (F &G) on November 2008, Greater Wellington Regional Council (GWRC) on 5 December 2008, and Department of Conservation (DoC) on 16 December It is important to note that the original invertebrate survey methodology, as discussed with stakeholders at a meeting at Te Marua on 15 February 2006, included measurement of a range of invertebrate metrics, including invertebrate density, across a range of habitat types. These measurements, in combination with the output of the proposed IFIM investigations, were to provide the basis for an assessment of likely impacts of reducing the minimum flow on invertebrate populations, including productivity. The assessment was to have included multivariate analyses of the distribution of invertebrate taxa in relation to habitat characteristics. However, as a result of later discussions between the applicant and stakeholders, it was agreed that there would be no need for a detailed in-stream flow investigation, provided a residual flow of 90% of naturalised MALF was maintained at Birchville. As a result, the target of 90% of MALF was identified and the investigation scaled back accordingly. The IFIM study in the upper reaches was replaced by the fish passage study. This meant that the original concept for the invertebrate study, which relied on output from the IFIM study, was no longer possible. It was replaced instead by a simplified survey of macroinvertebrate communities at low flows which could be compared with the results of the1999 low flow survey. It was our understanding at that time that the stakeholder groups were comfortable with that approach. Comments now received from GWRC, F&G and DOC indicate that either this position has changed or that the officers providing comment were not involved in the early discussions. The comments focus on the absence of productivity measurements and on the differences in flow regime preceding the two surveys, which limit the extent to which the study results can be used to assess the potential effects of reducing the minimum flow at Kaitoke from 600 L/s to 400 L/s. The following response draws on the output of investigations undertaken as part of this project and references the wider New Zealand literature on benthic community dynamics, some of which is directly relevant to this project. 1.2 Effect of low flows on invertebrate community composition The biological survey report (MWH 2008) indicates that periods of low river-flow in the Hutt River at Kaitoke result in no more than minor changes in the composition of the invertebrate community. During the severe low flow event of 1999 where the flow over the weir is estimated at 50 L/s, the benthic fauna continued to be dominated by the sensitive EPT taxa, both upstream and downstream of the water abstraction weir. Some downstream changes were observed, such as reduced abundance of the caddisfies Helicopsyche, Olinga, Pycnocentrodes and Pycnocentria, but nevertheless downstream of the Pakuratahi confluence the composition of both periphyton and invertebrate communities remained indicative of a healthy river. These results are consistent with the findings of Suren, Biggs, Duncan and Bergey (2003) from their investigation of the effect of summer low-flow on invertebrate communities in two New Zealand rivers of contrasting enrichment. The authors found that the invertebrate community in the low enrichment river (Okuku River) was dominated by high numbers of clean-water insect taxa, and this community changed Project number: Z17921 Page 1 Our ref: Appendix 4 Macros 2009.docx

6 little over time. Mayflies and caddisflies in the Okuku River were not adversely affected by even extreme low flows, and the invertebrate community did not become dominated by aquatic worms, snails or chironomids, despite the low water velocities. Periphyton biomass remained low during the period of summer low flow and the algal community, composed of diatoms, changed little. This contrasts with the results for the high enrichment river (Waipara River) over the summer, where the relative abundance of dominant invertebrate taxa changed from insects and snails to ostracods. Periphyton biomass was high in this river, which was originally dominated by diatoms and cyanobacteria but which became dominated by filamentous green algae. Suren et al concluded that changes in the invertebrate community were linked to the increase in filamentous green algae and would not be predictable based on changes in hydraulic habitat alone. The Hutt River at Kaitoke, like the Okuku, is a low enrichment river, in which the composition of periphyton and invertebrate communities is not greatly affected by even extreme low flows. Although the hydraulic habitat changes as flows reduce, changes to invertebrate community composition are modest, presumably because of the lack of significant filamentous algae development. Other factors such as reduction in water velocity or increase in water temperature are evidently not sufficient to cause a large change in community composition. The absence of significant periphyton biomass in this part of the Hutt River is confirmed by annual benthic ecology surveys of the river at Te Marua, immediately downstream of the Hutt Gorge, which are normally undertaken during summer (January to March) when the river is close to its annual low flow. Periphyton has not been observed to develop beyond a fine diatom film on the upper surfaces of cobbles and boulders in any year from 1995 to 2009, and invertebrate metrics invariably indicate excellent in-stream conditions at this location (MWH 2009). NIWA collect quantitative invertebrate samples from the Hutt River at Kaitoke and Boulcott as part of the National Rivers Water Quality Network (NRWQN) programme. We obtained from NIWA the results for Kaitoke for the years 1990 to 2006 inclusive. Although this site is located upstream of the water abstraction weir, the data gives some insight into the response of invertebrate communities to sustained periods of low river flow. For instance samples taken during the summers of 1999, 2001 and 2003 were collected at a time when the river flow had receded to below the MALF, and when 24 to 37 days had elapsed since the last flushing flow (>3 x median). Correlations of densities of key taxa, total density, number of taxa, number of EPT taxa, percent EPT taxa and QMCI scores against river flow at the time of sampling and days since the last flushing flow (Qdays) were examined (refer Appendix A). Densities of Deleatium and Olinga, and total density, were found to be negatively correlated with river flow. In other words densities tended to be higher at lower river flows. This effect was weaker for other taxa, including the more tolerant Chironomidae, Aoteapsche, Orthocladiniinae and Elmidae. Aoteapsche density was however positively correlated with Qdays (i.e., density tended to be higher as the period between flushing flows lengthened). Neither taxa richness, EPT taxa, %EPT taxa nor QMCI was significantly correlated with flow at the time of sampling or days since the last flushing event. The results of the 17 annual surveys are indicative of a high quality benthic fauna which is remarkably stable during periods of low river flow (number to taxa: 17-24; total density: ; %EPT taxa: and QMCI: ). No significant shift in community composition occurred in response to low river flows in the range 3,263 to 1,225L/s (MALF is 1,341L/s). Downstream of the water abstraction weir where the proposed regime would allow flows to occasionally recede to 400L/s, the benthic fauna is likely to come under more stress than at the upstream site, with a potentially greater effect on densities of some taxa, Dewson et al (2007) and Death et al (2009) investigated invertebrate responses to water abstractions in a controlled experiment in three small Wairarapa streams, where flow was reduced by 89-98%, wetted width by 22-38% and water velocity by 52-89% compared with control sites. The authors concluded that responses to water abstraction varied depending on the initial compositions of the invertebrate fauna. The abstraction did not affect the invertebrate community at Booth Creek which contained relatively few sensitive taxa but the more sensitive EPT dominated fauna of Reef Creek was affected. At Reef Creek EPT(%), SQMCI and densities of the mayfly Deleatidium sp., stonefly Zealandobius sp., and caddisfly Orthopsyche sp. decreased (relative to a control site) in response to flow reductions. Although these Project number: Z17921 Page 2 Our ref: Appendix 4 Macros 2009.docx

7 changes were statistically significant the fauna continued to be dominated by sensitive EPT taxa after 12 months of flow reduction. These results indicate that a sustained period of low flow in the Hutt River at Kaitoke may have some effect on invertebrate community composition but that the fauna will continue to be dominated by mayflies stoneflies and caddisflies. It is anticipated that any adverse effects that occur would be temporary, with recovery likely to be initiated by downstream drift of invertebrates from upstream of the weir. Recolonisation of the affected reach would begin immediately after the low flow period ends. Transition to a more tolerant taxa dominated by aquatic worms, snails or chironomids is not likely to occur in this part of the river, even in an extreme event. The proposed change in minimum residual flow from 600 to 400L/s would not cause the river to recede to the level that occurred when the 1999 survey was undertaken (when almost no residual flow was provided) and is unlikely to have more than a minor effect on community composition. 1.3 Effect of low flows and high flows on invertebrate biomass The proposed reduction in the minimum residual flow at Kaitoke weir would reduce streamflow during low flow and high demand periods from 600 to 400 L/s in the reach from the weir to the Pakuratahi confluence (~900m). The available information indicates that this is unlikely to have any more than a minor effect on invertebrate community composition, but that some reduction in usable invertebrate habitat and therefore invertebrate biomass, may occur downstream. The difference in area of usable invertebrate habitat for flows of 600 versus 400 L/s has not been modelled as part of this project for the reasons discussed above. Nevertheless the hydraulic geometry for present and proposed minimum flow in downstream reaches has been described in the Hutt Gorge Fish Passage report (Hudson and Harkness 2008). The results for 6 transects within this Kaitoke to Pakuratahi reach (K1, K2, K3, S1, S2 & S3), 3 transects downstream of the Pakuratahi confluence (P1, P3 and P3) and 2 transects below the gorge at Te Marua (T1, T2) are summarised in Table 1.1. Table 1.1: Summary of hydraulic geometry for present and proposed minimum flows (from Hudson and Harkness 2008) Kaitoke to Pakuratahi Pakuratahi to Gorge Transect Width (m) Average depth (m) Average velocity (m/s) present proposed % reduction present proposed % reduction present proposed % reduction K K K S S S P1 P2 P Te Marua T1 T Highest invertebrate densities typically occur in rapids or riffles (transects K1, K2, S1, S2, P1, P2, T1, T2) with lower densities in pools (K3, S3, P3). Table 1.1 shows that for rapids in the 900m reach between the Kaitoke weir and the Pakuratahi confluence, wetted width is predicted to reduce between 2 and 21%, with up to 29% reduction in average water velocities. In the reach downstream of the Pakuratahi River wetted width is predicted reduce by between 2 and 8%, while velocities may reduce by up to 11%. These data suggest that the proposed reduction in minimum flow would cause a modest reduction in invertebrate Project number: Z17921 Page 3 Our ref: Appendix 4 Macros 2009.docx

8 abundance and biomass within the reach from the weir to Pakuratahi confluence and a lesser reduction downstream of the Pakuratahi during a low flow event. For most of the year invertebrate density and biomass in not controlled by low flows but rather by high flows. Suren and Jowett (2006) investigated the relative importance of floods and low flows in structuring invertebrate communities on the gravel-bed Waipara River. They found that invertebrate densities decreased after flood events and the degree of change was proportional to flood magnitude. Conversely, most invertebrates either remained unchanged or increased after low flow events. They concluded that invertebrate communities in the Waipara River were controlled by both floods and low flows, but that the relative effects of floods were greater than even extended periods of extreme low flow. The authors emphasise the highly resilient nature of New Zealand benthic communities that have adapted to living under highly variable flow regimes. The Hutt River is known to be disturbed frequently by freshets and flood flows. Goldsmith and Ryder (2008) used long term monitoring data to calculate the FRE 3 for the Hutt River at Birchville 1. The average FRE 3 at Birchville was 23.7yr -1. By comparison, Clausen and Biggs (1997) calculated the FRE 3 values for 83 New Zealand rivers and found the median FRE 3 to be 10yr -1. These results indicate the Hutt River is disturbed by flood flows more frequently than most. They also point to the importance of flood events in regulating invertebrate biomass in the Hutt River and suggest that the relative effects of the proposed reduction in minimum flow at Kaitoke would be minor by comparison. 1.4 Further monitoring Comments from GWRC include the following: Ideally assessment of the effect of flow reduction on invertebrate communities would have involved repeat invertebrate surveys at the three sites over the duration of an extended period of low flow. In addition, assessment of the invertebrate community composition should be accompanied by assessment of flow, temperature and periphyton cover over the low flow period. All of the components listed by GWRC are included in the Hutt Low Flow Management Plan, as discussed in the next section. 2 Comment on proposed low flow management plan. The Hutt River Low Flow Management Plan provides the framework for implementing demand management actions, system management actions and monitoring actions. With respect to the latter, it would require repeat monitoring of invertebrate and periphyton communities as well as key water quality parameters (temperature, dissolved oxygen and ph) as the river flow at Birchville recedes below a series of trigger points. For a sustained low flow event this would cause up to 5 repeat water quality and periphyton cover surveys and up to 4 repeat invertebrate surveys at approximately 15 day intervals. As currently proposed, these investigations would take place in the Hutt River at Birchville more than 2km downstream of the Mangaroa River confluence. In this reach river flow rates are typically 3 times higher 1 The FRE3 is the number of floods and freshets per year that are larger than three times the median flow and more than 1 day apart (Clausen and Biggs 1997). The FRE3 has been found to be useful for classifying rivers in relation to be periphyton habitat. In New Zealand rivers, invertebrate invertebrate abundance is generally highest, diversity high and periphyton biomass moderately low (but still sufficient as an invertebrate food source) where FRE3 is in the range 10 to 15 per year (Clausen and Biggs 1997). Project number: Z17921 Page 4 Our ref: Appendix 4 Macros 2009.docx

9 than at Kaitoke but the river has shifted from low enrichment to moderate enrichment status. It therefore presents a different set of issues in respect of the benthic ecology compared with Kaitoke. It would seem logical therefore to expand the scope of the survey to include both the Kaitoke and Birchville reaches, possibly with 3 sampling stations in each reach. In light of the concern expressed by stakeholders about invertebrate productivity, it is recommended also that quantitative invertebrate sampling be undertaken (with a surber sampler rather than kicknet) and that the following biotic metrics be measured: total abundance, taxonomic richness, the number of EPT taxa, the % abundance of EPT taxa and QMCI. Other factors that should be recorded for each survey include the river flow rate on sampling day and the number of days since the last high flow (>3 times median). Project number: Z17921 Page 5 Our ref: Appendix 4 Macros 2009.docx

10 References Clausen, B., and Biggs, B., Relationships between benthic biota and hydrological indices in New Zealand streams. Freshwater Biology 38: Death R. G., Dewson Z. S., and James A. B. W., Is structure or function a better measure of the effects of water abstraction on ecosystem intergrity? Freshwater Biology (2009) Dewson, Z. S., James, A. B. W., and Death R. G., Invertebrate community responses to experimentally reduced discharge in small streams of different water quality. J. N. Am. Benthol. Soc., 2007, 26(4): Goldsmith, R., and Ryder, G., 2008: Hutt River: Flushing flows and algae growths. Ryder Consulting, Dunedin. Hudson, H. R. and Harkness, M., 2008: Hutt River instream flow assessment: fish passage in the Hutt River gorge. Environmental Management Associates, Christchurch. Report p. Hudson, H. R., 2008: Hutt River instream flow assessment: instream habitat flow requirements. Environmental Management Associates, Chriustchurch. Report p. MWH 2008: Biological survey of the Hutt River in the vicinity of the Kaitoke water abstraction weir. Report prepared by David Cameron for Greater Wellington Regional Council. MWH 2009: Biological Survey of the Hutt River at Te Marua Water Treatment Plant. Report prepared by David Cameron for Greater Wellington Regional Council. Suren, A. M., Biggs B.J.F., Duncan M.J., Bergey L., 2003: Benthic community dynamics during summer low-flows in rivers of contrasting enrichment. 1. Periphyton. New Zealand Journal of Freshwater Research, 2003, Vol 37: Suren, A. M., and Jowett, I. 2006: Effects of floods versus low flows on invertebrates in a New Zealand gravel-bed river. Freshwater Biology 51(12), Project number: Z17921 Page 6 Our ref: Appendix 4 Macros 2009.docx

11 Appendix A: NRWQN Invertebrate data Kaitoke (WN2) : Project number: Z17921 Page 1 Our ref: Appendix 4 Macros 2009.docx

12 ADDENDUM to Biological Survey of the Hutt River in the vicinity of the Kaitoke Water Abstraction Weir Table A1: Summary results for selected invertebrate species and metrics from annual surveys in Hutt River at Kaitoke (7 replicate 0.1m 2 Surber s amples compos ited into a s ingle s ample for analys is ). Data from NRWQN courtesy of NIWA. Date N individuals N taxa Chironomidae Aoteapsyche Orthocladiinae Elmidae Olinga Deleatidium Zelandoperla EPT Taxa %EPT QMCI Qsample* Ndays** 6/03/ /02/ /03/ /02/ /02/ /04/ /03/ /01/ /03/ /02/ /02/ /03/ /04/ /02/ /04/ /09/ /03/ *Qsample = river flow (m 3 /s) at the time of sample collection **Ndays = days since last flushing flow (>3xmedian) Status: Draft April 2009 Project number: Z17921 Page 1 Our ref: Appendix 4 Macros 2009.docx

13 ADDENDUM to Biological Survey of the Hutt River in the vicinity of the Kaitoke Water Abstraction Weir Table A2: Correlations of densities of selected taxa, metrics and flow measurements at the Kaitoke site (WN2) on the Hutt River (annual surveys from 1990 to 2006, data courtes y of NIWA). Variable N individuals N taxa Chironomidae Aoteapsyche Orthocladiinae Elmidae Olinga Deleatidium Zelandoperla EPT Taxa %EPT QMCI Qsample Ndays Correlations (Hutt R WN1WN DC(2)) Marked correlations are significant at p < N=17 (Casewise deletion of missing data) N N individuals taxa ChironomidaeAoteapsyche Orthocladiinae Elmidae Olinga Deleatidium Zelandoperla EPT Taxa %EPT QMCI Qsample Ndays Notes: Qsample = river flow (m 3 /s) at the time of sample collection Ndays = days since last flushing flow (>3xmedian) Status: Draft April 2009 Project number: Z17921 Page 2 Our ref: Appendix 4 Macros 2009.docx