miniDOT Loggers Observing Eutrophication in New Zealand

miniDOT Loggers Observing Eutrophication in New Zealand

Over the course of the 2017/18 southern hemisphere summer, 20 miniDOT loggers were deployed by researchers from the National Institute of Water and Atmospheric Research (NIWA) in Hamilton, New Zealand. The loggers, are part of a larger research initiative to observe the eutrophication effects on a catchment scale.

The loggers were deployed to record dissolved oxygen (DO) and temperature. The loggers were placed in streams within a catchment primarily subject to agriculture, and dairy farming, with hopes of learning more about the characteristics of the dissolved oxygen.

Streams in these areas are low gradient with soft-bottom substrate that supports large amounts of aquatic plant life. They  generally have depressed DO concentrations, particularly overnight, as a result of the high plant biomass combined with low flows and high temperatures.

In NZ, proposed national thresholds for DO are based on oxygen minima (either 1- or 7-day minima values) and therefore require continuous monitoring to assess the DO state.

Next summer, the researchers at NIWA are planning to double the number of miniDOT loggers deployed to continue their efforts. In addition, they also plan to trial the miniWIPER automatic wiper system, at some of their key locations.

The miniDOT loggers were chosen for this research as they provided an economic means of monitoring DO continuously across multiple sites within a catchment. Contact us to see what a miniDOT logger could do for your research.

A big thank you to Dr. Craig Depree, Environmental Chemist at NIWA for providing this information and images.


DO concentration time-series

Figure shows 6-week DO concentration time-series on a 4th order stream in the Piako catchment (Waikato, New Zealand – see picture below showing high macrophyte biomass). The red dashed line represents the recommended ‘bottom-line’ threshold value of 4 g/m3. Diel minima at this site were continuously below this value (often <1 g/m3) for most of the monitoring period. The period in early January where the minima was >4 g/m3 corresponded to a storm event that increased stream the flow rate.