Freshwater Habitat Quality

Creeks, minor waterways and wetlands

Norman Creek upstream from Birdwood Rd Holland Park West looking a bit crowded. Scenes like this are a clear indication that the water quality is pretty good !

Norman Creek near Birdwood Road


Red Arrow Dragonfly at Arnwood Place. An abundance of insects is usually a good sign.

Red Arrow Dragonfly


Bowies Flat Wetland, this cormorant has ruined any chance of the Egret catching a fish :-)
The vastly different methods used by these birds suggests there's a variety of prey available.

Eastern Great Egret and Little Black Cormorant


Norman Creek upstream from Birdwood Rd again, a Torresian Crow, some Pacific Black Ducks and Dusky Moorhens all keeping to themselves.

Crow, Pacific Black Ducks and Dusky Moorhens near Birdwood Road

Water Temperature

If you ignore industrial, influences ( eg. cooling water discharge into a lake from an electrical power station ) and non atmospheric influences such as artesian or other subterranean input, then trees and ( to a lesser extent ) other vegetation along a creek bank combined with geographical latitude, topography plus direction and rate of flow will determine the degree to which sunlight will raise the water's temperature. The warming influence this has on a typical creek is far and away the major factor determining water temperature diurnal and seasonal maxima and minima.

Oxygen is more readily absorbed into water at lower temperatures demonstrating the need for appropriate riparian vegetation, principally as a means of providing some thermal regulation, ie: limiting the maxima.
With sea level atmospheric pressure and water temperature at 4°C the maximum concentration ( ie: saturation point ) of dissolved oxygen is approx. 14.6mg per litre, at the other end of the scale, the saturation point at 40°C drops to approx. 6mg per litre. 1

These generalised approximations are presented as indicators, variations in overall hydrology ( including salinity, turbidity, pH, etc ), climate, specific aquatic species, surrounding vegetation, etc, [ the usual suspects :-) ] will skew the various parameters and/or requirements necessitating localised measurements, comprehensive faunal surveys and extended observations particularly looking for unusual or exaggerated behaviour, eg. if oxygen is low freshwater mullet will jump and splash frequently as a means of aerating the water. Although these observations don't contribute to the high degree of precision required to accurately ascertain any significant parametric departure(s) they are nonetheless important. If a particular behaviour is correlated to a measured parameter then a future, casual observation of such behaviour may provide a " heads up " to a depleted oxygen level.

The accepted generalised short term minimum is 4 - 5mg dissolved oxygen per litre, but once again is dependent on the usual suspects. Minor discrepancies are insignificant, eg. it would be foolish to suggest that fish will be ok at 4.000000mg/ltr but start dying at 3.999999mg/ltr. Whilst this may in fact occur in one individual fish it would be necessary to test each individual for their specific mortality level ........ yes, I'm joking !!!!

Graph showing the comparison of water temperature in °C to dissolved oxygen saturation level in mg/L. 1   Click to enlarge graph.

chart comparison of water temperature to dissolved oxygen saturation

As shown oxygen solubility variations in fresh water are inversely proportional to temperature variations, conversely the oxygen uptake requirements of aquatic fauna are directly proportional to temperature placing these characteristics in direct opposition.
Clearly oxygen absorption is enhanced by lower temperatures making the shading effect of riparian vegetation, particularly trees, of paramount importance to the overall quality of an aquatic habitat.
Obviously there are limiting factors here as virtually all aquatic and some semi-aquatic creek dwellers are ectothermic ( cold blooded ), eg. fish, frogs, reptiles, and invertebrates ( ie: insects, worms, etc ) whilst others may be poikilothermic ( I had to look that up and there appears to be some disagreement over it's proper meaning ) which is sort of cold blooded or sort of warm blooded, more about this under the heading " Freshwater Fauna ".

As a practical guide to the significance of O2 levels, the following points are noteworthy :-

  • < 3mg / L too low for fish
  • 3 - 5mg / L short term tolerable ( allowable diurnal minima )
  • 5 - 7mg / L small population
  • 7 - 9mg / L large population
  • >9mg / L risk of boom/bust cycle if not sustained or diurnal maxima

Also note that O2 concentrations will not be uniform within any given stretch of water as ( "all else being equal") there is necessarily going to be a reasonable amount of agitation and flushing action resulting from consistent, unimpeded water flow which would also minimise the loss of oxygen due ( for example ) to biomass decomposition. 2

Note 1: 1mg per litre closely equates to 1 part per million ( p.p.m. ), also these concentrations are ideal maximums which will rarely if ever be achieved.
One way to achieve a theoretical saturation point for any initial dissolved oxygen to water temperature ratio, is to increase the temperature of the water until dissolved oxygen begins to be expelled. This expulsion will only occur once the saturation point for the increased temperature is reached.
This could occur naturally in a creek where the upper reaches of the creek are well shaded and agitated. As the water flows on it may become heated by the sun to a point where dissolved oxygen is expelled.

Note 2: There's potentially more at stake here than just dissolved oxygen depletion. Water which is static or near static may stagnate promoting a proliferation of mosquito larvae. Further, the presence of a suitable putrid medium such as a decomposing carcase, animal or human faeces or a carelessly discarded dairy product / fast food scraps might give rise to E. coli, botulism, salmonella or even giardia. This combined with large numbers of mosquitoes could be disastrous and possibly deadly.
Accidental ingestion of contaminated water downstream is also a distinct possibility, ie: children playing, dogs paddling and then shaking, etc.


Water cascading over the weir at Arnwood Place into a deep pool in Norman Creek.

Norman Creek Arnwood Place

A lot of aeration, swirling and agitation taking place with a substantial volume of water so dissolved oxygen level here should be quite high. It's also aesthetically pleasing :-)



Water flowing rapidly over rocks in Sandy Creek.

Rocks in Sandy Creek

Feeding aerated water into the following deep channel near the confluence with Norman Creek providing good agitation and some swirling thereby helping to optimise the dissolved oxygen level further along. This is an example of using rocks to create a riffle and pool structure much favoured in creek rehabilitation projects.



Australian Wood Ducks next to shallow water along Norman Creek near Birdwood Rd Holland Park West.

Australian Wood Ducks

The water here is remarkably clear. This stretch of Norman Creek is frequented by quite a large number of birds and water fowl at times so it must provide a good source of food.

Freshwater Fauna

The body temperature of true ectotherms is controlled solely by their environment they have no biological mechanism for maintaining body temperature, in the case of freshwater streams around here you'll often see Eastern Water Dragons basking in the sun, if they get too hot they simply move into shade or go for a swim to cool off and vice versa, they can tolerate a wide range of environmental temperatures and hence body temperature, but they have to manage it themselves in order to facilitate this tolerance. Fish are true ectotherms also and manage their body temperature similarly to the dragons but without actually leaving the water, staying close to the surface for warmth and shade or deep water to cool down.

Poikilotherms ( as I understand ) have a primitive and not very effective biological body temperature regulation. Even so they are able to tolerate a wider range of environmental temperatures than "average" ectotherms because their body temperature isn't solely dependant on their environment and ( I think ) they can achieve a body temperature above their environment, ( I'm not too sure about this as some references quote poikilothermy as the antonym of homeothermy ).

Poikilotherms ( it seems ) don't need to bask or swim as do the water dragons but may do so if the influence of climatic conditions exceeds their ability to maintain a suitable body temperature. "Officially" there is only one mammal ( which I can't remember ), that falls into this category again this depends on who you ask, others say there are no poikilothermic mammals.

For the purpose of this writing I'm only going to cite Water Rats ( hydromys chrysogaster ) as an example, ( purely from observation, ie. no scientific basis whatsoever, I reckon [ no-one else does ] ), that they are poikilothermic.

I've had a rethink on this and it would seem more appropriate to assign the term poikilothermic to any creature warm or cold blooded which effectively or necessarily uses hibernation ( or brumation ) as a substitute for seasonal migration ( I think ), some examples being bears, snakes and turtles.
If this is the case then you can throw quite a lot more aquatic critters into this category, ie: Eastern Water Dragons ( Intellagama lesueurii ) , Water Rats, etc.

I am pleased to announce that amid this confusion and disagreement I've decided to launch a special category just for Water Rats ( Hydromys chrysogaster ) wait for it ...... chrysotherm :-)
Somewhere between ecto and endothermic but not a true poikilotherm either. Defined as Chrysotherm - A mammal whose nominal ( median ) body temperature is substantially lower than typical ectothermic mammals with a greatly reduced tolerance for climatic temperature extremes.
In other words susceptible to both hypothermia and hyperthermia.

Despite being unrelated to Water Rats yet living in virtually identical habitats, having a very similar diet and displaying similar behaviour, the Platypus ( ornithorhynchus anatinus ) differs significantly in terms of nominal ( median ) body temperature ( 32°C vs 25°C ) and tolerance to very cold water, this tolerance being mostly due to thicker fur. The Water Rat loses much more body heat when swimming in cold water than does a platypus, the difference can be attributed to 2 main factors, 1) surface area vs body mass, 2) thermal insulating property of the fur.
Consider an instantaneous water temperature of ( say ) 20°C - the Water Rats fur has only 5°C thermal differential skin to water whereas the Platypus' fur will have 12°C skin to water. If the water temperature drops below where the Water Rat is comfortable it will seek refuge in its burrow.
If necessary a Water Rat will leave the water altogether for as long as it takes for the water temperature to rise to a suitable level. Capable of foraging over a range hundreds of metres, Water Rats have this as an ultimate survival strategy.

Clearly the Water Rat's fur is not as effective as a thermal insulator. Whilst vascular and skin area to body mass ratio variations would account for some of the difference, I really think it mainly comes down to the fur.
Regardless of the reason(s) for the difference the platypus doesn't qualify as a chrysotherm.

Introducing yet another "therm" might seem like foolishness unless you've looked at all the references I have which contain statements obviously written by someone who is either plagiarising someone else's drivel, re-iterating what they've been led to believe by someone who has never observed a Water Rat in it's natural environment or are making it up as they go along. Interspersed with all this you'll find a scattering of comments along the lines of " compared to most species of mammals not much is known about these rather secretive creatures ..... "

Well blimey there's a lot of categorical statements flying around about an animal that relatively little is known about!! ...... ranting digression ends
Water Rats are indirectly reliant on water temperature and (DO) levels mainly because their primary sources of food are aquatic.
As such Water Rats serve as a good indicator of the health of their habitat which is why I think they are so important, if there's one or two long term resident Water Rats in a creek it follows that the water quality will be pretty good.

As their life span is only quite short " long term " in this context may only be 3 years or so. It should be noted here that Water Rats will happily forage on land and travel considerable distances doing so. If observed spending an inordinate amount of time on land this would indicate the water quality is degraded. This might be countered to some extent if there's a nearby source of an easy meal such as pet food left out in a backyard not far away.

A good comparison can also be made between Water Rats and Freshwater Catfish, such as those found in Kingfisher Creek. Catfish are ( of course ) ectothermic and so rely on water temperature directly, they are also a good indicator of water quality because their preferred diet is very similar to the aquatic diet of Water Rats and Platypus.


Though it might seem corny and clichéd, the fact is that all the creatures in the pictures on this page are utterly reliant on the quality of their habitat.
If the creeks and their environs sustain a supportive, healthy ecology then the birds, fish and lizards, etc will flourish.

Pollution of any waterway can have a severe impact not only in the immediate vicinity but far reaching follow-on effects for a number of reasons, eg: a boom/bust cycle, eradication of one or more species of either flora or fauna leading to a major disruption to any dependent species, and so on.
Whether or not the high level ( ie: visible from a distance ) fauna flourish or fail / remain or move away ( possibly to their ultimate demise ) can be directly attributed to the success or failure of macro and micro organisms.

Benthic macroinvertebrates ( ie: immature stages of aquatic insects, crayfish, etc ) are often used in studies to accurately gauge water quality because of their expected high numbers, and dependence on the land environment around the stream and the fact that they are visible with the naked eye, ( depends how good your eyesight is ).
The presence or absence of reasonable numbers of mature insects ( and their predators ) can serve as a good 1st impression indicator. Macroinvertebrates are a vital link in the food chain connecting ( for example ) algae and aquatic biomass decomposition ( think microbial decay ) to fish.

A number of high level semi-acquatic creatures ( eg: water rats ) are also good 1st indicators of water quality. They do this much more by their presence and observable behaviour than by their absence. Whilst the birds being very mobile will simply move on if things aren't suitable, a great many other creatures will perish due to increased vulnerability from weakness whilst some will alter their feeding behaviour, eg. water rats will spend much more time out of the water foraging overland ranging further from the water and for longer times than normal.

Local native fauna collectively provide as good an indicator as you'll get. If you observe reasonable populations of fish, water dragons, birds, etc then it's a fair assumption that water pollution levels are low and therefore the lower order aquatic organisms are doing ok also. It's a fairly safe bet that you'd find a wide variety of native flora in and around the waterway also.

If for no other reason than to preserve the wildlife our local creeks should never be used as drains or rubbish tips, they're wildlife habitats with complex and delicately balanced ecologies, the water quality really matters as it's the foundation upon which everything else relies.

This issue has been the subject of much discussion and ( previously ) precious little action. The major contributors are pollutant chemicals ( think automotive degreaser fluids and the like, detergents, etc ) general parkland litter and groundwater runoff all of which adversely impact water quality by altering pH levels, disolved oxygen levels, water temperature, etc.
Brisbane City Council has installed a number of ground water filtration systems over the last few years as part of the Lord Mayor's Cleaner Waterways initiative.
These natural filters which utilise dispersion, ground filtering and plant uptake have been very successful and BCC intends to progressively roll out more.

Due to a lot of existing drainage infrastructure substantial amounts of contaminants from footpaths, residential driveways and roadways will continue to wash straight into local creeks. The scale of this problem means that fixing it will be a drawn out and expensive exercise. Street sweeping machines, grids and notices on drainage entry points and public education are helping to limit the amount of polutant run-off.

Dissolved Oxygen and Dissolved Nitrogen

In nature the quality of freshwater aquatic wildlife habitats comes down to two common, day to day natural phenomena :-

  1. the quantity of dissolved Oxygen (DO) in the water, more is better
  2. the quantity of dissolved Nitrogen (DN), as ammonia (NH3), less is better

If these two characteristics are within suitable limits then intrapolating ( extrapolating backwards, there's no real word for it so I made one up, kinda like reverse engineering ) from this will show that pretty much everything that influences overall water quality will also be balanced out.

Sounds simple enough doesn't it, trouble is oxygen and nitrogen levels are at the mercy of a myriad of influences. Just about anything you can think of has an effect on dissolved oxygen and nitrogen levels.

Note: Nitrogen as Nitrate (NO3) is an essential nutrient for plant growth hence has only an indirect influence. Ideally the concentration of NO3 should remain <1mg/L. Nitrate concentration above 10mg/L combined with an equivalently high Phosphate concentration can lead to eutrophication.

Singling out just the chemistry might seem to be a rather narrow view, it is intentionally just that. Accurate chemical analysis will give a definitive indication of true water quality from which further deductions can be made. Other aspects of the hydrology, eg. temperature, depth and flow can significantly effect (DO) / (DN), therefore the factors which control these aspects of a waterway need to be in order also and can be suitably assessed by observation or simple measurements.

It should be noted here that many of the reactions that take place in water, eg. rusting of ferrous metals, decay of biomass, etc do not involve the component oxygen of the water ( the reactions do not release hydrogen and because someone will no doubt pick me up on it neither are there any resultant hydroxyl radicals ) dissolved oxygen is consumed thereby lowering the (DO) level.

Anthropogenic effects such as non-toxic turbidity could be counted as a third major factor, eg. a burst water main washing mud, clay etc into a creek and usually short term. Turbidity can dramatically affect water temperature and therefore oxygen levels.

Basically, turbidity is cloudiness or muddiness created by suspended, possibly microscopic particulate matter which may act as a non-infectious pathogen. Yes, I know that's as close to a contradiction of terms as I can easily get but it's the only way I can think to explain that the ( possibly microscopic ) particles suspended in the water may not be biologically active or inherently toxic but could ( for example ) damage a fish's gills thereby potentially killing the fish. Toxic pollution throws a whole other dimension into the ecological mix with the potential for causing irreparable damage.



Positive Indicators

Brisbane Short Necked Turtle in Norman Creek at Arnwood Place.

Brisbane Short Necked Turtle

It's not unusual to see 20 - 30 of these turtles here during the warmer months which is a good sign.


A Little Egret trying to ambush anything eatable swept along by the unusually fast flowing current of Norman Creek just downstream from Arnwood Place, the remnant result of some heavy rain.

Little Egret

If the water quality was poor there'd be no tasty morsels for the Egret so it wouldn't be there.


Again in Norman Creek a bit further downstream from where the Egret was standing, a small section of a much larger school of Freshwater Mullet.

Freshwater Mullet

Remaining in the shallows where it's warmer for any length of time is only possible if there's sufficient dissolved oxygen. Whilst only small, their numbers would have added up to a considerable oxygen take-up. They seemed happy just meandering about for quite some time and only retreated when startled.


Unfortunately pest species are just as reliant on water quality and can displace native species :-(
This Mozambique Tilapia was one of a few spotted in Norman Creek near Arnwood Place. In the couple of years since their population has increased enormously  :-(

Mozambique Tilapia

Water rats are a good indicator of water quality. Whilst they will happily reside in brackish water which affords them a measure of privacy their preferred aquatic diet dictates some excursions into cleaner waters.
If they spend most of their time in and around the creek it's a sure sign the food resources provided by the creek are adequate.

Water Rat crossing Norman Creek at Arnwood Place.

Water Rat Arnwood Place

An abundance of the Water Rat's aquatic diet is a clear indication that major water quality parameters are well within acceptable ranges. This is only possible if a great many things are in order hence the overall ecology must be in good shape.


Catfish in Kingfisher Creek near Moorhen Flats.

Catfish in Kingfisher Creek

Similarly to Water Rats, Catfish are are a good indicator of water quality. As permanent residents their preferred diet is very similar to the aquatic diet of Water Rats but without the option of foraging on land. The presence of sizeable populations of Catfish indicate a plentiful supply of food and hence good water quality.


Bridgewater Creek in Wembley Park Coorparoo.

Bridgewater Creek Wembley Park

Looking down stream away from the netball courts, lots of shade from trees alongside the creek keep water temperature down during Summer.
The shade and natural vegetation also provide a haven for native fauna especially birds. In Summer the air temperature here is noticeably lower compared to non shaded areas. As this shading extends for a considerable distance it follows that the water temperature will also be lower.



Water Depth

We're talking about creeks, in particular their upper reaches and tributaries. Shallow can be as little as a constant few millimetres, deep can range from ( say ) 600mm up to chest height on an average adult, ie: just over Wellington boot height to just over waders ( am I a true cynic or what ? ). Some of the deeper parts can be over 2 metres ( eg. small sections of Norman Creek ) but these are usually narrow, eroded trenches so in terms of quantity and hence contribution to the overall hydrology of the creek they're not particularly significant. There are many good articles available on the web regarding water quality in creeks and the only conclusion I can come to is don't drink any of it ! .... but I digress ( again ) .....

"Still waters run deep" an old and eternally true saying. Temperatures towards the bottom of the deeper parts of creeks will be significantly lower and therefore there is the potential for an enhanced rate of oxygen absorption and a potentially higher saturation level. Much of this temperature differential will likely result from greater shadowing rather than the actual depth per se - "greater" shadowing here by virtue of the angle of solar declination combined with steep, possibly high banks compared to more stereotypical cross-sections combined with turbidity.

If little or no agitation occurs ( ie: there is insufficient flow to cause useful swirling ( note convection currents may compensate in some small part but the ratio Δ°C/ΔTime will surely be very small indeed and hence not a significant influence) there will be virtually no atmospheric contact and therefore oxygenation below a few centimetres will be almost solely dependant on ( sub aquatic ) plant expiration during photosynthesis. Of course the existence of such plants is reliant on factors like suitable nutrient levels, a lack of contaminants, the requisite amount of sunshine, attacks by (for example) Purple Swamp Hens, etc, etc (getting the picture ?).

If however water cascades over a weir or down a rocky incline ( referred to as a riffle in creek speak ) into a deeper area then there will be some oxygenation from this action and the resulting agitation will facilitate direct exposure to the atmosphere which will oxygenate the water as it circulates.

A riffle and pool construct is most favoured by bushcare groups when rehabilitating creeks for this very reason and the fact that it creates a more regulated water flow.
It follows that in areas where deep water exists the actual volume of water is much greater and whilst ( as noted earlier ) this large, localised volume is not hydrologically significant overall if this water is effectively oxygenated and free flowing there will be an attendant increase in the total available oxygen which determines the population that a given body of water can sustain, diurnal maxima and minima notwithstanding.

Delivery and hence take-up of the total available oxygen is scalable as the product of flow rate and dissolved oxygen level, ( Δflow*ΔO2 ) ie: if you've got plenty of available oxygen then a slow flow rate is ok, if you have less oxygen then you'll need a higher flow rate, naturally this isn't open ended. The objective is to provide a suitable amount of oxygen in a given timeframe, ( ΔO2/ΔTime ), oxygen take-up by fish is usually specified in terms of consumption per unit of weight per hour, the exact biological requirement is primarily dictated by activity level. The activity level referred to here is not related to exaggerated gill actions or inactivity in the face of hypoxia, rather high aerobic activity such as that associated with predation down to the near motionless hovering frequently associated with Tilapia or Catfish.

An arbitrary but not unreasonable example -
a freshwater fish at a common exploratory activity level and an ambient temperature of 10°C requires 200mg of oxygen per Kg of body mass per hour. Dissolved oxygen saturation in freshwater at 10°C is ≈12mg/Litre, if our fish weighs 100grams and his ( her ) gills are 100% efficient then ≈1.67 litres of water must pass over his ( her ) gills every hour, clearly a very achievable result.

How about when "things" aren't so good. Raise the temperature to 20°C which reduces the dissolved oxygen saturation level to ≈9.1mg/Litre and reduce the fish's gill efficiency to 90%. At the same activity level and an ambient temperature now of 20°C our fish requires 300mg of oxygen per Kg of body mass per hour. Therefore now ≈3.3 litres of water must pass over his ( her ) gills every hour or double what was required at the lower temperature.
Remember these dissolved oxygen concentrations are at saturation, ie: as high as it gets which won't necessarily be achieved in reality. Throw in some pollutants, the odd rotting biomass, etc and the real dissolved oxygen concentration could easily be a LOT lower.


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