Appendix 6: Water Quality Criteria Boffa Miskell Ltd | Waihi North Project: Freshwater Ecological Assessment | Table 6-1: WRC guidelines and standards used to assess water quality for ecological health Water quality variable (units) Relevance Categories Excellent Satisfactory Unsatisfactory Dissolved oxygen (% of saturation) Oxygen for aquatic animals to breathe >90 80–90 <80 pH (acidity) Can affect plants and fish 7–8 6.5–7 or 8–9 <6.5 or >9 Turbidity (NTU) Can restrict plant growth <2 2–5 >5 Ammonia (g N/m3) Toxic to fish <0.1 0.1–0.88 >0.88 Temperature (°C) Fish spawning May-Sep <10 10–12 >12 Fish health Oct-Apr <16 16–20 >20 Total phosphorus (g/m3) Causes nuisance plant growth <0.01 0.01–0.04 >0.04 Total nitrogen (g/m3) Causes nuisance plant growth <0.1 0.1–0.5 >0.5 Table 6-2:Provisional biomass and cover guidelines for periphyton growing in gravel/cobble bed streams for three main instream values (AFDM = ash-free dry mass) (from Biggs 2000). Instream value/variable Diatoms/cyanobacteria Filamentous algae Aesthetics/recreation 60%>0.3 cmthick 30%>2 cm long (1November–30April) Maximum cover of visible stream bed Maximum AFDM (g/m 2 ) N/A 35 Maximum chlorophyll a (mg/m 2 ) N/A 120 Benthic biodiversity 15 15 Mean monthly chlorophyll a (mg/m 2 ) Maximum chlorophyll a (mg/m 2 ) 50 50 Trout habitat andangling N/A 30%>2 cm long Maximum cover of whole stream bed Maximum AFDM (g/m 2 ) 35 35 Maximum chlorophyll a (mg/m 2 ) 200 120
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