Ecological condition of lakes in New Zealand

The Lake SPI Index: A combination of the Native condition index (an indicator of the biodiversity and extent of native vegetation within a lake) and the Invasive impact index (an indicator of the degree of impact from invasive weed species). It provides an overall indicator of lake ecological condition. A high LakeSPI is desirable (0–20 percent, poor ecological condition; 20–50 percent, moderate ; 50–75 percent, high ecological; 75–100 percent, excellent). Non-vegetated lake status is associated with extreme lake eutrophication/deterioration.

Figure.NZ calculated the relevant summary statistics to mirror the data presented in the Environmental Reporting Series (see http://stats.govt.nz/browse_for_stats/environment/environmental-reporting-series/environmental-indicators/Home/Fresh%20water/lake-submerged-plant-index.aspx Figure 1)

Since 2007, 210 lakes have been surveyed. This is a very small percentage of lakes in New Zealand, so we advise caution when interpreting results as they may not be representative of all lakes.

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Submerged plants are good indicators of the ecological quality of lakes. Because they are attached to the bed of lakes, submerged plants are easy to observe and identify, and they are unable to move away from environmental changes. The plant species found within lakes can tell us about their level of habitat degradation and exotic weed invasion.

The lake submerged plant index (LakeSPI) uses observations of aquatic plants collected by trained divers, scuba divers, and snorkellers using standardised methods (de Winton et al, 2012).
Information on submerged plants’ structure and composition is used to calculate three indexes (de Winton et al, 2012).