Freshwater environmental quality parameters
Because almost all water bodies are dynamic in their composition, the relevant quality parameters are typically expressed as a range of expected concentrations.
As a consequence the majority of ground-water data comes from samples taken from springs, wells, water supply bore-holes and in natural caves.
Lakes and ponds can be very large and support a complex eco-system in which environmental parameters vary widely in all three physical dimensions and with time.
The chemical interactions are not just simple mixing but may be complicated by biological processes from submerged macrophytes and by water joining the channel from the hyporheic zone or from springs draining an aquifer.
A river flowing across very ancient precambrian schists is likely to have dissolved very little from the rocks and maybe similar to de-ionised water at least in the headwaters.
Oxygen is probably the most important chemical constituent of surface water chemistry, as all aerobic organisms require it for survival.
Fast, turbulent streams expose more of the water's surface area to the air and tend to have low temperatures and thus more oxygen than slow, backwaters.
Oxygen can be limiting if circulation between the surface and deeper layers is poor, if the activity of animals is very high, or if there is a large amount of organic decay occurring such as following Autumn leaf-fall.
The pH change is most marked in rivers with very low concentrations of dissolved salts as these cannot buffer the effects of the acid input.
In parts of Scandinavia and West Wales and Scotland many rivers became so acidic from oxides of sulphur that most fish life was destroyed and pHs as low as pH4 were recorded during critical weather conditions.
In most environmental situations the presence or absence of an organism is determined by a complex web of interactions only some of which will be related to measurable chemical or biological parameters.
Flow rate, turbulence, inter and intra specific competition, feeding behaviour, disease, parasitism, commensalism and symbiosis are just a few of the pressures and opportunities facing any organism or population.
However both colour and turbidity reduce the amount of light penetrating the water and can have significant impact on algae and macrophytes.
Many rivers draining high moor-lands overlain by peat have a very deep yellow brown colour caused by dissolved humic acids.
Some organic constituents such as synthetic hormones, pesticides, phthalates have direct metabolic effects on aquatic biota and even on humans drinking water taken from the river.
Significant levels of copper are unusual in rivers and where it does it occur the source is most likely to be mining activities, coal stocking, or pig farming.
Thus high levels of nitrogenous compounds tends to lead to eutrophication with extreme variations in parameters which in turn can substantially degrade the ecological worth of the watercourse.
As the plants die in the late summer they fall into the cool water layers underneath - the hypolimnion - and decompose.
Inert solids are produced in all montane rivers as the energy of the water helps grind away rocks into gravel, sand and finer material.
[5] Many other types of solids from agriculture, mining, quarrying, urban run-off and sewage may block-out sunlight from the river and may block interstices in gravel beds making them useless for spawning and supporting insect life.
Both agriculture and sewage treatment produce inputs into rivers with very high concentrations of bacteria and viruses including a wide range of pathogenic organisms.
Even in areas with little human activity significant levels of bacteria and viruses can be detected originating from fish and aquatic mammals and from animals grazing near rivers such as deer.
Upland waters draining areas frequented by sheep, goats or deer may also harbour a variety of opportunistic human parasites such as liver fluke.
In rivers used for contact recreation such as swimming, safe levels of bacteria and viruses can be established based on risk assessment.
Under certain conditions bacteria can colonise freshwaters occasionally making large rafts of filamentous mats known as sewage fungus – usually Sphaerotilus natans.
[6] Enterobacteria may also persist in the environment in mud, sediments, sand and soil for considerable lengths of time.
[7] pH in rivers is affected by the geology of the water source, atmospheric inputs and a range of other chemical contaminants.
