In this section
Good quality streams with healthy invertebrate communities
If you’ve collected a great sample with many invertebrate taxa (well over 20), a high proportion of which were 'sensitive' members of the mayflies, stoneflies and caddisflies, you probably have a high quality stream that is worth protecting in its current state. Such streams are often well shaded due to bush cover, and protecting the streamside vegetation may be the best stream management tactic. There may be no need for expensive riparian planting.
Invertebrate communities dominated by sensitive taxa are also usually found in relatively undisturbed areas not significantly affected by urban or agricultural development. Maintaining the natural channel form (avoiding piping or channelisation), maintaining low catchment imperviousness (minimising sealed areas that stop rainwater entering groundwater), and maintaining natural water quality (keeping wastewater or contaminated stormwater out of the stream) are all important if we are to maintain the natural, high quality stream fauna.
If you or your community group wish to protect such high quality streams from inappropriate development, you may need to watch out for development proposals to clear streamside vegetation, divert or pipe the stream, create a pond in the stream channel, or discharge wastewater or stormwater to the stream. Development proposals that may significantly affect stream resources should go through a resource consent application process, which gives you the opportunity to make a submission where you can outline the current natural stream values, and your concerns that such values be protected.
Streams with moderate to good quality invertebrate communities
Streams that support invertebrate communities of moderate quality can be great candidates for stream rehabilitation work because such streams have the potential to improve without being so degraded that the stream biota has little chance of improvement. Many farmland streams and some urban streams support a few mayflies, stoneflies and caddisflies, along with a mixture of more tolerant groups. The presence of sensitive taxa indicates that habitat and water quality conditions are not beyond repair. These taxa may be drifting downstream from more natural habitats in the upper catchment, and these upstream populations are therefore a source of recruits if stream conditions are improved further downstream.
Most of our sensitive invertebrates prefer cool water temperatures and therefore shading streams with riparian vegetation can benefit such taxa. Many freshwater invertebrates also depend on riparian vegetation as a food source, or as resting habitats for the flying adults, or as a source of woody debris for instream habitat (especially in soft-bottom streams) so planting appropriate trees for shade and woody debris can have real benefits to stream faunas.
Some notes of caution though – don’t just charge in and plant stream margins without expert help. Seek advice from regional council or other experts about what should be planted where. Be aware that (1) plantings may need council approval, (2) many plants are useless or even hazardous in floodplains, (3) the species selected should be those found naturally in that area, and (4) you may need to organise stock exclusion and ongoing weed control.
Keep monitoring your stream to see if the stream fauna changes over the years, and as described above for the good quality streams, watch out for any resource consent applications that may affect your stream.
Streams with relatively poor quality invertebrate communities
If you found no mayflies, stoneflies or caddisflies (apart from the tolerant Oxyethira or Paroxyethira) and the stream is not tidally affected, finding out why may require further investigation, ideally with the help of your regional or local council. A lack of sensitive invertebrates may be because the stream:
- is too warm for sensitive invertebrates (such streams might be good candidates for riparian planting), or
- has low dissolved oxygen due to a contaminant source (needing council investigation), or
- has insufficient flow (council investigation needed to establish if this is natural or artificial), or
- is wetland-like (where slow flow and low dissolved oxygen may be natural), or
- has a toxic contaminant problem (council investigation may be needed to establish the source), or
- has had a significant sediment influx from upstream earthworks (again a council issue), or
- a combination of physical habitat and water quality modifications, as is the case in many urban streams.
Clearly regional council help may be needed to determine whether your invertebrate community is inhibited by natural or man-made factors, and if man-made, what can be done to improve conditions. Regional councils monitor the biology of many streams, and they will know about problem areas where piping, channelisation, stormwater networks changing flow regimes, contaminated discharges or poor riparian vegetation may be affecting stream faunas. Some urban streams have so many of these problems that it may not be realistic to expect sufficient rehabilitation to allow sensitive invertebrate taxa to return.
Stream faunas can be significantly inhibited by pollution from a particular discharge point. Community groups often discover and report such point sources to the relevant council, and this initiates the pollution investigation and response that may significantly improve stream water quality and faunas.
Streams with deteriorating or very poor quality invertebrate communities
Any significant pollution discovered by your community group (particularly dead or distressed fish or strongly coloured discharges) should be immediately reported to your regional council. Many councils run a pollution hotline (phone number in your local phone book) and this connects you to a pollution response team. Remember that there is a much better chance of the pollution source being identified and remedied if the pollution response team gets to the stream while the discharge is still occurring.
Invertebrate surveys can show the effects of serious recent or long-term contamination. Spillages of some toxins can kill all freshwater life including the most tolerant freshwater invertebrates, and this may be detected by a lack of any invertebrates, or by the presence of many decomposing invertebrates in your sample. Long-term discharges of organic waste, including sewage leakages, food processing waste or leachates from silage pits, can cause a build-up of decomposing organic matter and growths of pale slimy 'sewage fungus'. Such conditions may support populations of syrphid flies (rat tail maggots), which require decomposing organic matter to survive. Any occurrences of syrphid flies should be reported to your pollution hotline (and we suggest you disinfect your hands and anything that came into contact with the water).
Your invertebrate data might also show evidence of deterioration over time due to ongoing habitat or water quality problems. Again inform your regional council if your invertebrate community has obviously deteriorated, e.g. if a once mayfly-dominated community has recently changed to a mayfly-free community dominated by worms and true flies. Councils are best placed to address significant pollution problems because they will know of likely contaminant sources and discharge points, and because they may need to collect evidence for enforcement procedures including possible prosecutions.