Ecological Survey of the Wairau River Estuary 1983
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AN ECOLOGICAL SURVEY OF THE WAIRAU RIVER ESTUARY l George A. Knox Estuarine Research Group Department of Zoology University of Canterbury Christchurch, New Zealand ~-- Estuarine Research Group Report No. 27 May, 1983 1 I I - J i i An aerial view of the Wairau River estuary and the Vernon Lagoons. i I r r Tl l l ~ J l l ~,. l ll i I I L r I rr I. I I • I i J i i ! : c • I c " .. I l " c., '~ c ' I . 1. ' 1 CONTENTS 1. INTRODUCTION ..... 5 2. PHYSICAL DESCRIPTION 9 2.1. Geomorphology 9 2.2. Climate 10 3. HUMAN IMPACT 15 3.1. Pre-European 15 3.2. European 16 4. OBJECTIVES 17 5. METHODS 19 5.1. Physical 19 l 5.1.1. Hydrology 19 5.1.2. Nutrients 21 l 5.1.3. Sediments 21 5.2. Biological .... 21 ~ 5.2.1. Intertidal 21 I 5.2.2. Subtidal 23 l 5.2.3. Fish 23 5.2.4. Birds 23 5.2.5. Vegetation 23 6. BATHYMETRY 25 7. HYDROLOGY 27 7.1. Tidal cycle 27 7.2. Tidal compartment 27 7.3. Currents and flows 29 7.3.1. Velocity profile 29 7. 3. 2. Flow data . 29 7.4. Salinity distributions 33 7.5. Temperature distributions 41 7.6. Oxygen concentrations 42 7.7. The hydrological regime 42 2 lJ 8. SEDIMENTS .. 45 ! I 8.1. General composition and distribution .. 45 . I 8.2. Sediment nutrients 48 l J 8.3. Sediment organic content 49 9. NUTRIENTS .• 53 10. VEGETATION 57 10.1. Species present '57 10.2. Transects .•.. 57 10.3. Vegetation distribution 57 [J 11. BENTHIC MACROFAUNA ..•..... 65 I I 11.1. Intertidal transects and stations 65 Ic.J ' 11.1.1. Species present 65 11.1.2. Species distribution 65 l i ll. 2. Subtidal species ...• 65 11.2.1. Species present 65 11.2.2. Species distribution 74 u 11.3. Distribution of the individual species 74 11.3.1. Mollusca 74 11.3.2. Crustacea 78 11.3.3. Polychaeta 78 11.4. Factors affecting the distribution of the species . • 78 II 11.4.1. Salinity 79 ll. 4. 2. Sediment 79 11.4.3. Tidal height and exposure . 80 12. FISH 83 I ' 12.1. Species occurrence 83 J 12.2. Distribution of the individual species 84 I i 12.3. Feeding habits • • . • • . 85 1... •...: 12.4. Commercial and recreational fisheries .. 89 13. BIRDS 91 13 .l. Species present 91 . i 13.2. Bird habitats and adaptations 100 13.3. Seasonal abundance 100 ; i 13.4. Food habits 101 13.5. Human impact 103 I i ' ~J l 3 l 14. THE ESTUARINE ECOSYSTEM .... 105 14.1. The estuarine community 105 14.2. Comparisons with other New Zealand estuarine ecosystems 105 ~ I 15. TROPHIC STATUS • . 111 15.1. Food webs in estuarine ecosystems 111 l 15.2. A model of the Wairau River Estuary and Vernon Lagoons •..... 113 15.3. Eutrophication potential .• 115 l 15.3.1. Nutrient inputs into the system . .. · 115 15.3.2. The problem of eutrophication 116 15.3.3. Present nutrient status 117 l I . 15.3.4. Establishment of nutrient criteria . • • . • • . " . 119 15.3.5. Current trophic status and ' I factors limiting primary production in the system . 119 15.3.6. Possible impact of the discharge 123 16. COLIFORM BACTERIA 125 16.1. Present coliform bacterial levels 125 16.1.1. Current coliform levels in shellfish from the Wairau River Estuary • • . • . • • . 12 5 16.1.2. Faecal coliform levels in shellfish from the Wairau River Estuary . • • . • • 125 16.2. Effects of microorganisms •.•• 128 16.3. Probable impact of the meatwork's effluent on coliform bacterial levels 129 17. RECOMMENDATIONS FOR FUTURE MANAGEMENT 131 17.1. Location of outfall .. 131 17.2. Monitoring programmes 131 17.3. Erosion problems 132 17.4. Wetlands 132 18. ACKNOWLEDGMENTS 133 19. REFERENCES 135 u 4 I I I L.l u CLOUDY BAY lJ I : N ll iruu Bur '~ 1 i • '-' ' . I ' I ' L j L,r I l1 ' i L __; Fig. 1.1. Location map and major physiographic features of the area. ·'L .J i I : 5 1. INTRODUCTION This study arose from the Tribunal Hearing of the Water Right Application by Waitaki (N.Z.) Refrigerating Ltd to discharge treated meatworks process liquors to the Wairau River estuary. The wastes to be discharged comprise the normal wash water and process liquors from a freezing works which will pass through a "Save all" to remove grease and coarse solids before being discharged to an anaerobic pond. If fellmongery is carried out, the resultant effluent would be dealt with by a special treatment plant which will remove heavy metals and produce an effluent of neutral pH. Domestic waste from the employees amenities will also be discharged to the anaerobic pond with the meat waste. The biochemical oxygen demand (BOD) of the combined waste leaving the works is expected to be up to 1500 mg/1 with a peak daily 3 l discharge of 4,500 m • These peak flows will occur from November to April (TSE Group Consultants Ltd, 1979). Experience with installations similar to the proposed l anaerobic pond indicate that a 10 day retention time would reduce the BOD by 75% from 1500 mg/1 down to 375 mg/1. The wastes from the primary treatment anaerobic pond will undergo secondary treat l ment in an aeration pond. From the performance of aerobic ponds similar to that proposed it is calculated that the BOD will be further reduced from 375 mg/1 to 50 mg/1. It was originally l proposed that the treated effluent from the aerobic pond would be taken via a pipeline to a holding pond near the mouth of the Wairau River (Fig. 1.2). Subsequently it was decided that the holding pond would not be req.uired. The effluent quality standards set by the Marlborough Regional Water Board following the Tribunal Hearing were: 1. The effluent standard to be maintained shall be that of a spot sample taken at any time during any four hour discharge l period, or a composite sample taken during the entire discharge period. 2. The effluent standard shall be maintained at all times when the plant is in operation, day or night, and no allowance shall be made for shock loading, starting up or any emergen cies. Any discharge due to stormwater etc., when the plant is not in normal operation shall also comply to the standard. 3. The effluent colour shall be that of normal healthy oxidation pond effluent. There shall be no coloration of blood. 4. The effluent shall not cause the receiving water to emit objectionable odours. 5 • There shall be no constituent of the effluent which emanates from the preparation of hides, other than from fellmongery. Any process using heavy metals, which would alter the effluent constituency from that indicated in the application, shall not contribute effluent to the treatment system. 6 I ! i' i l J Cloudy - [_I /I i Iu I L ' ' I ·--·~ Fig. l. 2. Plan showing the freezing works site, the proposed sites of the aerobic and anaerobic ponds, the proposed route of the pipeline and alternative discharge points. ' ! .u ' I . l: 7 6. The following limits shall not be exceeded in final effluent analysis. i) BODs 150 g/m3 ii) Suspended solids 100 g/m3 iii) Sulphides 1 g/m 3 iv) Ammoniacal nitrogen 100 g/m 3 N.B. After mixing with the receiving water, un-ionized 3 ammonia shall not exceed .0225 g/m • The final discharge point (Fig. 1.2) was to be determined after dye tests designed to determine the most efficient means of mixing. It was to be fitted with an effluent diffuser and situated in the deep water channel of the main Wairau River between a line drawn at right angles to the main channel and pas sing through the wharf, and a line at right angles to the channel, at a distance of 400 m upstream of a line through the wharf. The effluent is to be discharged on the outgoing tide, during a period of four hours being one hour after high tide and one hour before low tide, the tide measurement being related to the point of discharge. During the Tribunal Hearing the applicant company offered to support a baseline ecological survey of the estuarine complex likely to be affected by the discharge. Professor G.A. Knox of the Estuarine Research Group, Zoology Department, University of Canterbury, was invited to submit proposals for such a study in conjunction with the applicant, and the Regional Water Board. This report represents the results of the study which was proposed and accepted by the applicant and the Regional Water Board. 8 I i ''' CLOUDY BAY IJ I I I . Upper Lagoon 1. __ ; a~ Islands ~ Chandlers""'4- Lagoon Big Lagoon ! I Kidney Ponds ~' Fig. 2.1. Map of the Wairau River Estuary and the Vernon Lagoons. I . I . l 9 l ' 2. PHYSICAL DESCRIPTION ~ ' 2.1. Geomorphology The lower reaches of the Wairau River flow across a flat plain resulting from the outwash of glacial material and subse quent reworking of this by both rivers and the sea during periods· of rise and fall in sea level. Geomorphologically the area surrounding the Wairau River estuary is very complex (Figs 1.1 and 2.1). A remarkable feature is the very extensive lagoon system lying to the south of the estuary and opening into it near the mouth. A smaller river, the Opawa, enters the estuary a short distance upstream from the entrance to the Vernon Lagoons.