5. Discussion and Conclusions

NIWA report: Freshwater quality monitoring by Environment Southland, Taranaki Regional Council, Horizons Regional Council and Environment Waikato.

5.1: Do regional councils have effective methods to gather information about and monitor the quality of freshwater?

In our opinion, the four regional council monitoring networks provide a good basis for assessing the quality of freshwater. All four councils now have networks that have reasonable numbers of SoE sites for rivers, lakes and groundwater that are distributed over their regions in a fairly representative manner (i.e. where the number of sites in different catchments or types of water bodies is in proportion to the overall importance and quantity of water bodies of that type). We also found that all four councils were monitoring a common suite of water quality variables.

We made a specific test of the adequacy of the river SoE monitoring networks in the regions. Our test of adequacy was based on asking whether the networks had sufficient statistical power (numbers of sites relative to the variability of the site medians) to detect statistically significant large scale patterns, defined by River Environment Classification (REC) categories, in water quality state and trends. We used the river water quality data for the 10 year period ending 2009 that met our criteria for trend analysis to conduct this test (i.e. that had been collected at quarterly or monthly on at least 80% of sampling occasions). The river water quality monitoring data for Southland and Waikato comprised sufficient sites that met these criteria that we were able to detect detailed patterns in both state and trends (i.e. statistically significant differences in state and significant overall trends were found for many REC categories and variables). The data for Taranaki comprised only 12 sites but this was sufficient to detect patterns albeit for fewer REC categories and variables than for Southland and Waikato. The dataset for Horizons comprised 17 sites and was barely adequate to describe large scale patterns in water quality state and trends in the region. This is because, in the past, Horizons have employed a system of "rolling SoE sites" whereby some sites have been monitored on a rolling basis, i.e. once every three years 12 months of monthly sampling has been undertaken. This practice is no longer carried out by Horizons Regional Council and the number of SoE sites in the monitoring network has been increased.

We found that councils have given due consideration to QA/QC and data storage issues. Environment Southland and Horizons need to consider lowering detection for some variables, notably DRP and Ammoniacal-N, because high detection limits will mask trends in currently high quality water bodies. Councils could consider tightening up on hydrometric infrastructure under-pinning water quality monitoring, for example, by establishing quantified relationships between flow at sampling sites and flow gauging stations. An indication of the uncertainties associated with flow estimates will be valuable for future load calculations, even if not strictly needed for flow-adjustment in trend analysis. We also consider that storage of water quality data in a database is highly desirable because this allows easy interrogation of the data and datasets to be restructured efficiently.

There were large differences between regions in the numbers of SoE sites that met our criteria for inclusion in the trend and state analysis. In all four cases council staff indicated that they are currently monitoring a larger number of sites than we assessed in this report, and the approximate sizes of their existing networks has been reported. The difference between analysed sites and the size of existing networks reflects an ongoing effort by regional councils to increase monitoring coverage. The relatively small number of SoE sites from TRC and Horizons that were included in our analysis reflects disruptions and changes to monitoring programs over the previous ten years. We have provided supplementary material that shows whether there was data provided by the councils for each site, in each month over the ten year period by water quality variable. These graphs indicate when sites were opened, analysed variables were changed and whether there were disruptions to the program. The important point is that if monitoring is to be of maximum benefit it must be consistent and this requires an ongoing commitment by the regional councils.

There were inconsistencies between regions in terms of certain detailed aspects of SoE monitoring. These inconsistencies include sampling protocols (such as frequency), laboratory analysis methods, QA/QC procedures and storage of water quality data. Inconsistencies between regions is not an issue for individual regions, however it is a national issue in that it leads to difficulties in collating data and also prevents robust comparison or amalgamation of data or statistics (e.g., trends). The Ministry for Environment (Tanya Gray pers. comm.) is currently leading efforts (supported by the Regional Council SWIM group Graham Sevicke-Jones, Hawkes Bay Regional Council pers. comm.) to improve monitoring consistency across all of the regions and territorial local authorities.

5.2: What is the state and trends in water quality as indicated by state of the environment monitoring data?

5.2.1: Water quality state

The assessment of water quality state shows that water quality was highly variable throughout the individual regions. Median nutrient concentrations at sites frequently exceeded the ANZECC (2000) trigger values and median clarity at sites was frequently lower than guidelines. Faecal bacterial levels were also high, with E. coli numbers exceeding the MfE/MoH (2003) action value at many sites (based on the 95th percentiles).

Land-use impacts on water quality state were clear, with poor water quality (high nutrients and faecal pollution, and low visual clarity) being associated with pastoral land cover and even poorer water quality in urban streams. These patterns with land cover are consistent with reports by other authors in previous studies, (e.g., Ballantine and Davies-Colley, 2009; Hamill and McBride, 2003; Larned et al., 2003; Larned et al., 2004; Snelder and Scarsbrook, 2002).

5.2.2: Water quality trends

The trend analyses indicate that trend strength and direction is highly variable across sites in the four study regions. We used the binomial test to indicate whether there were "overall trends" in sites grouped in several ways. We found overall degrading trends in clarity in Taranaki and Waikato, degrading trends in conductivity in Waikato, improving trends in DRP in Southland, Taranaki and Waikato, a degrading trend in E.coli in Waikato, improving trends in NH4-N in Horizons and Waikato and a degrading trend in NH4-N in Taranki, degrading trends in NOx-N in Southland and Waikato, a degrading trend in TN in Southland and Waikato and improving trend in TP in Horizons and Waikato. When these trends were broken down by REC categories there was a predominance of degrading trends in Low-elevation and Hill Topography and Pasture Land-cover categories. These results suggest that water quality decreased over the ten year period in Low-elevation areas and in catchments dominated by pastoral land cover. There were however, generally improving trends in DRP and TP in all of the regions.. The improving trend in phosphorus shown in this study (consistent with a recent national study by Ballantine et al. 2010) may be attributable to two factors. First, there has been increase in phosphorus fertiliser costs over the last decade (an 86% rise in 2008 alone). Second, there has also recently been very active management of soil phosphorus (Olsen-P) levels by the pastoral industry. However, nitrogen has increased due to increased farm production. For example, there has been a 20% rise in dairy-farm production. This increase in production is associated with leaching of nitrogen from pasture soils for which there are not currently adequate mitigation methods

A point of caution need to be borne in mind in using the state and trends analysis in this report to draw conclusions concerning regional councils' management of freshwater. We compared the existing state to guideline values. To fully assess whether regional councils are meeting (their own) standards, the standards defined in statutory plans would need to be compared with the state information derived in this study. Second, trends provide information about change in water quality over time and also need to be considered within the broader statutory framework that regional councils have set. The analysis is outside the scope of this report.