The Health of the Manawatu

In attempting to answer the above question, several important factors, and their interaction, need to be evaluated. This question guided Year 11 Geography students at Freyberg High School to undertake research at several locations to help explore the Manawatu River environment.

The below map shows the pathway of the Manawatu River, six testing sites for which we have data, and the upstream watershed area from those testing sites. Each of the pop ups includes specific data for each location from an aggregate of data.

A waterway's health can be defined in several different ways and, by understanding the interaction of various parts of the environment, a full picture can be developed to understand the waterway's health.Depending on one's perspective, it is possible to evaluate the health of a waterway from a Mātauranga Māori perspective by using a lens that applies a mauri to the waterway, river, or watershed and its connected ecosystem. An alternative, but complementary viewpoint, would look at the health of the waterway from a Western-scientific perspective and attempt to analyse the specific water quality metrics that are measurable as well as through an analysis of the environmental influences upon a waterway. Some water quality metrics one could look at are temperature and dissolved oxygen, as well as pH, total dissolved solids, conductivity, and suspended sediment. The environmental influences one could look at might include the substrate, wildlife and vegetation, land cover, topography, water source, flow rate, and inputs. In order to identify a healthy waterway, one needs to look at the interaction between a range of these factors to evaluate the overall health of the system and the environment.

First, a mauri perspective on a healthy waterway stresses the importance of interconnection across a range of factors. As shown in the diagram above, this includes a range of factors that include spiritual and human connections to the waterway, waterway biodiversity, and pollution hazards. For example, a human connection might consist of one's tikanga around using the waterway as a a resource, while its biodiversity is connected to the taonga contained within the waterway. Similarly, a mauri perspective on pollution hazards would look at a range of inputs and attempt to understand how this would impact upon both of the previous factors.

Another important factor to consider the health of an environment would be the Western-scientific measurements used to assess waterway health. Again, there are a range of these and their interaction with one another is important; however, a particular focus could be paid to temperature and dissolved oxygen. As seen in the diagram above, low levels of oxygen availability means that plant and animal life would struggle to maintain itself. As such, if temperatures fluctuate drastically or are consistently high, the level of dissolved oxygen available for flora and fauna is lessened. If this is the case, the health of the environment suffers since it cannot maintain its biodiversity nor its mauri.

Another important factor to consider in determining the health of a waterway environment are the environmental factors that can influence the waterway. This can include a range of factors, but a particularly relevant one is the adjacent topography. If the topographical layout of the adjacent riverbank is particularly steep, this can increase sedimentation as erosion from rainfall is easily moved from the steep banks into the riverway. This can affect the clarity of the water, which is an important measure of water quality as well. In unpacking the interaction between a range of these environmental factors, as well as analyzing the mauri of the environment and its direct water metrics, the health of the environment becomes clearer. In the Tawa Loop Track stream, the topography is quite steep on both sides, however, it is also surrounded by native bush.

The map below shows a range of the environmental factors (photos in the pop-ups, as well as the different uses of land along the path of the river. This is then compared to urban use.

The data gathered by Year 11 Geography students is useful, but, when combined with secondary data from the council, begins to tell a clearer picture of interaction across a range of metrics that help determine the health of the Manawatu River.

The data shows a link between temperature and conductivity as measurements of water quality, with a general increase in temperature resulting in a general increase in conductivity. Since a higher temperature and higher conductivity are both signs of an unhealthy water, due to their being evidence of pollution, we can assume that a site with low temperature and conductivity would be healthier.

Similarly, there is a weak positive link between the pH of the water and its conductivity in the Manawatu River. Since both are measures of health, and a pH near to 7 is ideal, we can assume that those places with higher pH and higher conductivity are also unhealthy.

Finally, in the chartsbelow, we can clearly see a distribution of conductivity that shows the most common value being roughly 200 uS/cm. Since it is observed that a higher conductivity is linked to pollution, a good value should be below 200. Therefore, the healthier places of the Manawatu are likely to have a conductivity value below 200 uS/cm. As can be seen in the chart below, sites with a temperature near 10C or 11C have conductivity measurements below 200 uS/cm. Therefore, these sites can be assumed to be healthier. On the other side, those sites with a higher temperature (near 19C), seem to have a conductivity measurement greater than 200uS/cm, approaching 220. Therefore, these sites can be assumed to be less healthy.

The data gathered by two Year 11 classes leaves areas of water quality to be determined. Two key factors are important here: first, the number of sites surveyed is low and, as such, we don't have the full range of data available. Even with additional data, we don't have enough sites in the Manawatu region surveyed to adequately answer the question. The size of the Manawatu River basin means that we would need more data to fully answer our research question. Looking at LAWA data for the Manawatu River suggests there are over 80 sites that are routinely tested. As we only directly tested two sites ourselves, and only have six total sites on our data list, there are many locations that could be healthier than our sample. Therefore, our sample size is a limiting factor in understanding the health of the environment.

Similarly, even with the data we gathered, there are issues to be addressed. Most importantly, we don't know exact data points for each of the relevant water quality metrics. For example, we didn't test for dissolved oxygen or specific pollutant types. This would impact our ability to evaluate the narrow health at a particular site. Similarly, we have limited information on a range of environmental factors that might influence the water quality at different sites. For example, we don't have a full wildlife survey at each site, nor do we have details on the site's topography. This can have an impact on our results as well. Third, we don't have a particularly in-depth understanding or evaluation of the mauri of the river and its interconnection with the tangata whenua. As such, we cannot say that it is healthy or unhealthy in this way, either! Finally, the data acquisition that we did could have introduced problems - we tested similar, but not exactly the same, sites as a class and, as such, the data could be different.

Given the data above, and the limitations of this data, the healthiest point along the Manawatu River is...