The main rivers have generally low DISSOLVED NUTRIENTS, although the Tutaekurī levels are slightly elevated. Dissolved phosphorus is quite high in some of the tributaries and dissolved nitrogen is also elevated. These nutrients in combination with flow, substrate and temperature and can cause algae to grow more quickly and affect the types of algae that grow. The relationship between all of these factors on algae, including phormidium growth can be very complex
Figure 2: Numbers of Macroinvertebrates across the TANK catchments
ALGAE levels in the Mangatutu and Maraekakaho can occasionally exceed guidelines for recreation and phormidium (a type of algae that sometimes includes toxic strains) and can be high in the Poporangi and Mangatutu Rivers. The lower reaches of the Tutaekurī can also exceed algae guidelines for recreational values. The TANK Group wishes to focus on algae management in these areas.
The management of E. COLI levels in relation to swimming and other values including those of tāngata whenua continues to be of concern for the Group. The need for water to be clean for mahinga kai values was discussed, and although washing or cooking food before eating it reduces contamination, the need for water quality to be free of significant bacteria was identified as important.
E.coli levels in the main rivers and most of the tributaries meet the quality required for swimming nearly all of the time. However, while the Ohiwa and Tutaekurī-Waimate rivers meet the standards required for secondary contact (such as kayaking) and for stock drinking water, they don’t meet swimming water quality requirements. E. coli in urban streams has also been raised as a potential concern although no data has been received so far by the TANK Group. Further work on this is being carried out by the Stormwater Working Group.
The TANK Group will consider the state and trend of the Waitangi estuary health in relation to deposited sediment and nutrients at its next meeting, and are aware of the need to take these aspects into consideration.