| Australians are coming
to realise how important healthy river systems are to the national welfare
— both agricultural and recreational. One important indicator
of the health of fresh water systems is the aquatic organisms that live
in them.
But the quality of the water in Australia’s lakes, rivers and
creeks depends not only on what is living in the water, but also on
what goes on under and around it, in soils and sediments. If these are
functioning properly, they can cushion the waterways against many of
the problems facing them.
The decline in water quality in many of Australia’s fresh water
systems through pesticide residues and chemical by-products, fertilisers
and acidification make the soils and sediments an increasingly important
resource. For these systems to function properly, the right organisms
must be present.
Scientists from CSIRO Entomology, supported by the Australian Biological
Resources Study, have been looking at factors affecting water quality
from a different angle. They have been getting to the bottom of things
and examining the oozy sludge under the water. In particular, they were
looking for the things that live in it because the presence of the right
organisms is vital to maintaining a healthy system and their presence
or absence provides an indication of what is happening in the system.
Australians have recently seen many images of drought showing dry, cracked
mud. It isn’t obvious that in this mud, either hiding or dormant
as eggs or resting stages, are many organisms waiting for rain to bring
them to life again.
The freshwater systems and their surrounding soils and sediments are
a two way system. What is in sediment can end up in the water and all
the things which get into water end up lurking in sediment with the
potential to cause problems in the future — for example, nutrients
like nitrogen and phosphorus, pesticides, herbicides and heavy metals.
If the sediment is functioning normally, it is a wonderful safeguard
against these nasties as the things living in it can help detoxify polluting
chemicals.
In healthy sediment, the unseen but useful tiny organisms such as bacteria,
fungi, algae, protists (slime moulds, protozoa and primitive algae),
worms, snails and arthropods, are constantly at work transforming nutrients,
immobilizing or transforming nasty chemicals and stabilising the sediment.
The importance of their function only becomes obvious when, for some
reason, they are not doing their job — when the water turns green
because of an algal bloom, or black because everything except the most
resistant microbes has died from a lethal dose of a toxic chemical.
But the sludge also contains unwanted organisms and telling the useful
organisms from problem ones is not easy. CSIRO scientists have been
looking at one group, nematodes or roundworms. As a result of their
work, the nematodes found in soils and sediments from the Murray-Darling
Basin and south-eastern Australia can now be identified on the web (www.ent.csiro.au/science/nematode.html).
This identification system is simple enough for amateur naturalists
to use and this means local communities can now monitor their own freshwater
systems. The website also provides information on the distribution and
ecology of the nematodes — such as known associations with other
organisms and what they eat.
This interactive key also covers some terrestrial nematodes which are
plant parasites because they could turn up in waterways and some free-living
terrestrial nematodes because they are sometimes mistaken for plant
parasites. It will also allow work on the many beneficial nematodes
which have been ignored till now because of a lack of identification
tools. Finally, the key also includes some organisms that are not nematodes,
because they are frequently misidentified as nematodes.
Nematodes are small, white worms, almost invisible to the naked eye,
which can occur in huge numbers. They are only about one mm long but
are so numerous that if all the nematodes in the Murray River sediments
were laid end to end, they would more than encircle the equator. The
species present are a mixture of useful and problem species.
Most people have heard of nematodes which are intestinal parasites,
such as Barber’s pole worm in ruminants or hookworms and pinworms
in humans. There are also circulatory parasites like heartworm in dogs
or kidney worm in humans.
Of the nematodes which parasitise insects, some are now used as biological
control agents for pests such as scarab larvae. The vast majority of
nematodes are quite harmless even beneficial, as they recycle nutrients
and consume pathogenic organisms — for example Rhabditis, which
eats bacteria.
Nematodes are also parasites of plants — for example, root lesion
nematode, Pratylenchus spp. — and cause an estimated $400 million
in crop losses in Australia every year. Occasionally it finds its way
into rivers. One quirk of nematodes is that if there is a common name
it is generally a pest species.
When a pest nematode such as this gets into waterways, it is important
to know it is there as there is potential to spread them in irrigation
water. It is also important to know how frequently they are being spread
this way, and whether, as the last few drops are drained from a dam,
a lot of problems are being sucked up too.
The CSIRO web site is the first step to providing this information and
makes CSIRO a world leader in providing nematological information on
the web.
The ease of using the web site belies the amount of research needed
to tell these tiny worms apart. The effort ranged from information theory,
through mathematical deconstruction of shapes and biology to extensive
collecting of samples.
This first ever survey in Australia to determine the nematode fauna
in Australia’s fresh waters was conducted over three years with
the team sampling throughout the Murray-Darling River System as well
as all the major coastal river catchments from north of the NSW/Queensland
border, through NSW, the ACT and Victoria, to near the mouth of the
Murray in South Australia. In the process, they created a biological
collection of over 10,000 nematodes, which is one of the most comprehensive
in the world. It was during these surveys that they found the root lesion
nematodes in rivers.
Other nematodes discovered were in the genus Monhystera, which occurs
in all the rivers of the Murray–Darling Basin and coastal freshwater
streams of south-eastern Australia. But different species of this genus
seem to occur in waters of different quality: one species is common
in water which is periodically under stress, while another seems to
prefer cleaner waters.
These nematodes live in intimate contact with the sediment, and any
nasties it may contain. So can they be used as biomonitors to show what
is happening in sediments? Can they help to determine what has happened
in the past or what may happen if conditions change?
The research that has been done provides some of the tools that will
help answer these questions. There are serious water quality issues
which are emerging —pesticide by-products and acid generators
are two of them. These new tools will help in monitoring these problems.
All the collecting that has been done, in every major river catchment
of the southeast, has provided an incredible baseline data set for monitoring
what is happening to Australia’s fresh waters. To ensure that
all specimens and data are stored properly, they have been lodged in
the National Nematode Collection.
This will enable scientists in the future to determine what, if any,
changes have taken place in the nematodes present. This will provide
one measure of how climate change affects our waterways.
It is interesting, but logical, that many of the nematodes in sediments
under rivers occur in the land beside the rivers too as sediment under
the water is an extension of the land on either side.
Not only can nematodes help identify problems in waterways, but they
could, in some instances, offer solutions. For example, one species
contains yellow crystals which may be a detoxifying mechanism for some
of the nasties in the sediment. There are numerous other possibilities
yet to be documented.
Now there is a simple way to identify the nematodes found in our freshwater
systems, other issues can be addressed:
• Can good nematodes be used to consume harmful microbes
and enhance bacterial turnover?
• Should the frequency and effects of plant-parasitic nematodes
being transported down rivers then applied to crops with irrigation
water be investigated further?
• How can the data be used to monitor the conditions of river
sediments and riparian verges in 50 years?
• Can use be made of species which can detoxify some of the
chemicals that find their way into waterways?
|
