Current Freshwater State

The NPSFM attributes from both the 2020 and 2023 reports show generally good results for the Awatere FMU. Improvements for E. Coli at two sites is a good result, particularly given this attribute has the poorest measures regionally. We do however see mixed results and some declines for Dissolved Reactive Phosphorus (DRP) and new reporting for the Clarity attribute.

Ammonia and Nitrate are both in the A bands for all sites and both years. The E.Coli attribute improved from two B scores and one non assessed site (Black Birch) in 2020 to two A band results and one B in 2023 – with Black Birch scoring an A grade.

The MCI B and C bands measured show that ecological heath is somewhat impacted but is not poor, despite the higher turbidity recordings from the SOE monitoring. These bands were unchanged from 2020 to 2023. Although high turbidity is known to affect the ecological health of rivers, the relatively good and unchanged B/C macroinvertebrate score (MCI) for the Awatere River does suggest that aquatic life has adapted and can still thrive. The related APSM attribute – explained fully in the SOE reports – is B band across all three sites and unchanged between the 2020 and 2023 reports.

The other C band measure is Dissolved reactive phosphorus (DRP) – the amount of phosphorus in the water column that can easily be taken up by plants. The 2023 SOE report shows mixed results with an improvement for the Black Birch site but declines for the others. The Awatere River monitoring sites have much lower DRP despite their higher levels of human activity in the catchments compared to other areas in the FMU. This points to the impact of different geology and other factors.

The NPSFM has limits for clarity rather than turbidity. Turbidity is further discussed in the WQI section below; Water Clarity serves as a surrogate for sediment concentrations. Council has conducted parallel monitoring of both surrogate measures, enabling site-specific conversion of turbidity to Water Clarity. Historically, clarity was not routinely measured in Marlborough as it was less practical, potentially more subjective, and introduced greater Health and Safety concerns compared to the measurement of turbidity. It also cannot be measured continuously.

The current NPSFM allows limits for clarity to be converted into turbidity limits using site-specific correlations. At the 2020 report, the majority of monitoring sites were either not established or did not have enough data to derive a trend. At the 2023 report, the Awatere FMU sites had enough data to derive a trend which is shown in the outer circle on the chart above. Both Awatere River sites score within the D band for clarity, whereas the Black Birch sites has scored within the A band. This results comes down to a number of factors but importantly the natural geology of the area. This is further discussed in the WQI section below.

Periphyton monitoring is conducted on a monthly basis and demands considerably more staff time compared to other monthly parameters. Historically, it has only monitored at a select number of sites across the region. In 2022, a number of new monitoring sites were established across Marlborough to fill gaps in the programme and ensure the council is able to measure and record all required attributes. Two of these new sites are in the Awatere FMU and both will be measured for periphyton going forward.

We can see from the table that the Water Quality Index has been relatively stable in this FMU with the only change being an improvement at the Mid Awatere Site.

The Black Birch stream site has the best WQI of the three monitored. The surrounding landscape directly impacts on this outcome. For example, the Black Birch site is in a catchment area almost completely covered by mature, native vegetation. This assists with shading the waterway, keeping water temperatures low which in turn supports the freshwater habitat. This also assists with reducing turbidity as discussed below.

The Turbidity parameter is key for the Awatere River in particular. This is directly related to the geology and land cover of the catchment area. The highly erodible mudstone soil type in this area causes comparatively high turbidity. Erosion is accelerated by bare land such as cultivated or harvested fields which are common on the river margins. However, because so little native vegetation remains, it is difficult to determine the contribution of human activity to the river’s high turbidity. For this reason, the Awatere River is only characterised by clear water after longer dry spells. In comparison, the Black Birch monitoring site has much lower turbidity. The Black Birch stream is located further up the catchment, is surrounded by native vegetation, and the geology is likely different. All of this contributes to the lower turbidity measures.

The opposite is true for Dissolved reactive phosphorus (DRP) in this FMU. DRP Black Birch has the highest DRP of the three sites, despite being almost un-impacted by human activity and is likely caused by phosphorus-rich rock in this catchment. This situation highlights the importance of natural characteristics such as soil type and their resulting impact on water quality measures.