Lake submerged plant index

  • Image, Lake submerged plant index.

    The lake submerged plant index (LakeSPI) measures the ecological condition of lakes. Ecological condition is informed by the diversity and extent of native and invasive plant species. New Zealand’s native aquatic plants help maintain lake ecosystem processes and provide food and habitat for other aquatic organisms. Invasive aquatic plants can negatively impact on native species and lake ecosystem processes. Lakes with high ecological condition have a high number and diversity of native aquatic plants, and an absence or a low number and diversity of invasive aquatic plants. LakeSPI includes three indexes: ecological condition, invasive impact index, and native condition index.

    We classified Lake submerged plant index as a case study.

    Key findings

    Of 210 lakes surveyed from 2007 to 2016, 32.9 percent are in excellent or high ecological condition, 31.0 percent are moderate, and 36.2 percent are in poor ecological condition or are non-vegetated (the most-deteriorated state). 

    • In 10.1 percent of surveyed lakes (excluding non-vegetated lakes), only native aquatic plants were observed.
    • In 2.4 percent of surveyed lakes (excluding non-vegetated lakes), only introduced aquatic plants were observed.

    Figure 1

    Note: Non-vegetated lake status is associated with extreme lake eutrophication/deterioration.

    Figure 2

    Definition and methodology

    Aquatic plants can be used to assess lake ecological condition. They are commonly found in lakes all year round and, because of their size, are easy to observe and identify when diving. Because aquatic plants are unable to move in response to environmental changes, they provide a reliable measure of overall lake condition.

    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).

    1. Native condition index – an indicator of the biodiversity and extent of native vegetation within a lake.
    2. Invasive impact index – an indicator of the degree of impact from invasive weed species.
    3. Native condition and invasive impact indexes are used together to generate the LakeSPI index, which 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 ).

    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.

    Data quality

    Topic Classification   Relevance Accuracy 
     Freshwater species, taonga species, and genetic diversity  Case study

     relevance-direct
    Direct

    Image, Medium accuracy.

    Medium 

    See Data quality information for more detail.

    References

    De Winton, MD, Clayton, JS, & Edwards, T (2012). Incorporating invasive weeds into a plant indicator method (LakeSPI) to assess lake ecological condition. Hydrobiologia 691(1), 47–58.

    Published 27 April 2017

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