122 20.4.3 Dissolved Reactive Phosphorus (DRP) 20.4.3.1 NOF limits The NOF sets out limits for DRP for ecosystem health (water quality) for freshwaters (rivers) in New Zealand. These limits relate to DRP limits and are set out in attribute bands for condition of water quality for ecosystem health that require an Action Plan. In the case of DRP no NBL has been set. The limits for each attribute band are set out based on impacts on ecological communities, changes in primary production, macroinvertebrate and fish communities, and respiratory and decay rates. The NOF attribute bands for DRP are set out in Appendix 12. 20.4.3.2 DRP in the Ohinemuri River We have set out the concentrations of DRP recorded from the Ohinemuri River at Waihi as the numeric attribute state limits of the NOF (i.e., annual median and 95th percentile derived from monthly monitoring over five years) in Table 37. It is evident that for the most part over the record of data available that water quality of the Ohinemuri River meets Attribute A for the median and 95th percentile for DRP at all sites of the river at Waihi. The treated water discharge is not contributing to any changes in the DRP concentrations in the Ohinemuri River. 20.4.4 Dissolved oxygen 20.4.4.1 NOF limits The NOF sets out limits for dissolved oxygen for ecosystem health (water quality) for freshwaters (rivers) in New Zealand (specifically for below points sources). In the case of dissolved oxygen the NBL has been set as 5.0 g/m3 (7-day mean minimum over the summer period), and 4.0 g/m3 (1-day minimum over the summer period). The limits for each attribute band are set out based on stress levels on aquatic organisms. The NOF attribute bands for dissolved oxygen are set out in Appendix 12. 20.4.4.2 Dissolved oxygen in the Ohinemuri River Records for DO within the Ohinemuri River at Waihi are limited, and at best only available from 2003 to 2010, and then only as spot temperatures. It is difficult to draw meaningful conclusions from such a sparse data set. Furthermore, the data is not collected as the same numeric measures required for the NOF (7-day mean minimum and 1- day minimum) as no continuous oxygen monitoring has been undertaken or is required as a condition of the current consents. Nevertheless, we provide the available dissolved oxygen data in Table 38. Spot recordings are generally a poor representation of what is happening with DO in the river as DO typically varies over a 24-hour period as it responds to the biotic and abiotic factors within the river system. DO is generally highest during afternoons when photosynthetic activity is at its greatest (excess DO production over DO use through respiration) and DO is lowest shortly before dawn when productivity is at its lowest (DO demand from respiration is occurring in the absence of DO-producing photosynthesis). In addition, DO levels occur in an inverse relationship with temperature, i.e., as temperature levels increase less DO is available. We consider that although lowered DO levels have the potential to result in adverse effects on the aquatic values there is no evidence to suggest that low DO levels have in fact resulted from the treated water discharge and resulted in any adverse effects on the aquatic ecological values within the Ohinemuri River at Waihi. Nevertheless, we have recommended a condition of consent that requires the collection of DO (and temperature) data during summer low flows to
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