Are aquatic invertebrates useful for assessing wetland condition? : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management at Massey University, Manawatu, New Zealand
Freshwater wetlands are one of the most biodiverse ecosystems and at the same time of
the most threatened globally. New Zealand has lost 90% of its wetlands and of those
remaining, 60% are considered degraded. Establishing accurate wetland inventories and
assessing wetland condition are priorities for the management and conservation of these
important ecosystems. Aquatic invertebrates are used worldwide to assess the condition
of other aquatic ecosystems such as rivers and lakes; however, their use for assessing
wetland condition has not been extensive.
A wetland’s hydroperiod is considered one of the most important environmental
variables affecting wetland biota and one that has also been most altered by anthropogenic
stresses. The second chapter of this thesis analyses the effect of hydroperiod on the
macroinvertebrate communities of the Ō Tū Wharekai (Ashburton lakes) wetland system
in New Zealand. A total of 40 taxa from 11 orders were recorded from 4 permanent lakes,
3 semi-permanent ponds, and 7 temporary ponds in September 2016. The
macroinvertebrate assemblages in lakes were distinct to those in semi-permanent and
temporary ponds. Overall, temporary ponds were slightly more diverse than the semipermanent
ponds and lakes. Semi-permanent and temporary ponds were most similar to
each other in macroinvertebrate composition. They host more species of small crustaceans
such as cladocerans and ostracods, while species belonging to the Trichoptera, Odonata
and Hirudinea orders were only present at permanent sites. The results emphasize the need
to include small and seasonal wetlands in freshwater conservation efforts since they often
hold unique biotic communities.
In the third chapter, the potential to use macroinvertebrate communities in wetland
assessment is evaluated. The macroinvertebrate communities of 14 freshwater wetlands
in the lower North Island were sampled. The sites represent a gradient of wetland
condition and include urban lagoons, agricultural swamps and lacustrine wetlands with
recognized ecological value. A total of 63 invertebrate taxa were identified, of which
crustaceans were the most abundant. There appeared to be no link between the
composition and diversity of macroinvertebrate communities and wetland condition.
However, of the habitat characteristics measured at each site, nutrient enrichment
appeared to be the most important variable in determining macroinvertebrate
assemblages. On the other hand, macrophyte communities appear to be more reflective of
wetland condition. There are considerable knowledge gaps regarding invertebrate
response to environmental change in freshwater wetlands and this limits their suitability
as a biomonitoring tool.
Assessing wetland condition accurately is one of the greatest challenges for the
management and conservation of these threatened ecosystems. Aquatic invertebrates are
used as biomonitoring tool for many freshwater ecosystems but not wetlands. This is
because the way wetland invertebrates respond to environmental change remains unclear.
So far, in New Zealand, there appears to be no link between wetland condition scores and
invertebrate communities. Thus, the final section of this thesis proposes a simple
dichotomous wetland condition scoring system exemplified with information from the 14
freshwater wetland sampled in the North Island. The method has limitations, but allows
the integration of biotic data into wetland condition assessment.