When the mauri of freshwater ecosystems is intact, they provide habitats (food, water, cover, and space) so a diversity of plants, animals, insects, and other organisms can thrive. Biodiversity is a key component of ecosystem health, and underpins important ecosystem processes, such as decomposition and nutrient cycling.
Ecological condition of surveyed lakes varies
The lake submerged plant index provides an indication of the ecological condition of lakes, which is informed by the diversity and distribution of native and invasive plant species (de Winton et al, 2012). Of 210 lakes surveyed for lake submerged plant index between 2007 and 2016, 33 percent were in excellent or high ecological condition, 31 percent were in moderate condition, and 36 percent were in poor ecological condition or non-vegetated (see figure 24) (analysed by Ministry for the Environment and Stats NZ). Only 10 percent of surveyed lakes (excluding non-vegetated lakes) had only native vegetation.
This graph shows lake submerged plant index for surveyed lakes between 2007 and 2016. Visit the MfE data service for the full breakdown of the data.
For more detail see Environmental indicators Te taiao Aotearoa: Lake submerged plant index [Stats NZ].
Mauri of tested sites varies
New Zealand’s freshwater ecosystems are an important part of the culture and well-being of Māori. These ecosystems provide valuable resources, and support Māori values and practices such as mahinga kai (customary food gathering). The cultural health index (CHI) is one method that can be used to measure factors of cultural importance to Māori, giving an overall indication of the cultural health of a site on a water body. A CHI score cannot be applied without local indigenous knowledge.
A CHI score has three elements: site status (the association tangata whenua have with the site, and whether they would return); mahinga kai status (range of species present and species abundance); and cultural stream health status (water quality and land use).
CHI ratings were assessed at 41 sites between 2005 and 2016 by various iwi and hapū/runanga groups nationally (see figure 25). The majority of sites assessed were located in the South Island. Of the 41 sites assessed, 11 sites had a good or very good overall CHI rating. A further 21 sites had a moderate rating, and nine had a poor or very poor rating.
This graph shows the overall cultural health index score of assessed sites between 2005 and 2016. Visit the MfE data service for the full breakdown of the data.
Mahinga kai status is one element that makes up the CHI. Of 39 assessed sites, the mahinga kai status was poor or very poor at 28 sites, moderate at seven sites, and good or very good at four sites. See Kōura in the Te Arawa lakes for an example of the impact of degraded mauri and habitats on mahinga kai.
Kōura in the Te Arawa lakes
Kōura (freshwater crayfish) is an important food for Māori. Today, it is considered a taonga species by Te Arawa iwi and hapū, and is important for mahinga kai activities on the Te Arawa lakes.
Iwi cultural histories and anecdotal evidence suggests kōura abundance in the Te Arawa lakes has been declining. This decline is thought to be caused by pressures such as the introduction of exotic plant and fish species, and increased nutrient concentrations causing excessive growth of algae that reduce oxygen levels in the lakes.
Limited information on kōura abundance and ecology has made it difficult for Māori to manage lake-dwelling kōura. Until recently, the main reason for a lack of quantitative information was the absence of suitable sampling methods (Kusabs & Quinn, 2009). Tau kōura (see figure below), a traditional method for harvesting kōura, has been resurrected by the Te Arawa iwi to improve the monitoring of kōura abundance in Te Arawa lakes (Kusabs et al, 2015). Tau kōura was found to be a more effective monitoring technique for kōura in the Te Arawa lakes compared with conventional methods such as baited traps.
Source: Kusabs & Quinn, 2009, based on Hiroa, 1921
Note: Diagram A shows the tau kōura, a traditional Māori method for harvesting kōura (freshwater crayfish) after Hiroa (1921). Pekapeka (drop line), tumu (post), pōito (float), tāuhu (surface line), punga (anchor), whakaweku (fern bundles).
Diagram B shows the modern-day tau kōura. The depth and length of tau are indicative and can be varied depending on lake bathymetry.
For more detail see Environmental indicators Te taiao Aotearoa: Cultural health index for freshwater bodies [Stats NZ] and Tau kōura: freshwater crayfish traditional fishing method [Stats NZ].
Some ecosystems are poorly understood
We have incomplete knowledge about the health of our freshwater ecosystems and habitats. A lot of information on freshwater ecosystems and habitats for certain water bodies or catchments are collected by various organisations; however, national-scale data are limited.
There are aspects of freshwater ecosystems we still know little about. For example, we know that wetlands have declined in extent, but we do not know much about the health of the wetlands that still exist. We also have limited information, nationally, on fish and invertebrate communities. We lack information on big (non-wadeable) rivers. We know very little about the biological component of groundwater ecosystems, even though understanding the microbial (bacteria) activity within aquifers is important in understanding how nutrients are processed (Sirisena et al, 2013).