River PollutionPollution is an addition to the

environment with consequent adverse effects to that environment

The main causes of pollution in rivers are:• Agricultural Pollution - the effects of excess fertilisers and

pesticides and farm slurry• Industrial Pollution - inorganic and organic waste that directly

contaminates rivers• Dumps - spoil heaps and refuse tips release harmful chemicals

that may leach into rivers• Domestic Pollution - treated effluent from sewage works is

discharged into many of our rivers• Thermal Pollution - warm waste water from cooling towers

and other industrial processes raises the temperature of the water and lowers oxygen solubility

• Atmospheric Pollution - pollution of the atmosphere with nitrogen and sulphur oxides produces acid rain that modifies the pH of rivers which, in certain conditions, has lethal effects on the river organisms

• Oil Pollution - can result from river traffic

Water tumbling downa hillside from its source

is crystal clear and unpolluted

As rivers flow through towns, agricultural land and industrial areas, various pollutants enter the water

body and influence the distribution andcomposition of aquatic life

As pollution loads increase, species diversity declines and the abundance of pollution-tolerant species increases

This river is becoming increasingly polluted as organic and inorganic materials ‘run off’ from the surrounding agricultural land

Thermal Pollutionfrom cooling towers

IndustrialWaste

FarmyardWaste

Effluent fromsewage works

Fertiliserrun off

Acid Rain

Oil Pollution

Measuring River Pollution

Methods for detecting and measuring river pollution include:

• Sampling the populations of river invertebrates; river invertebrates are indicator organisms that serve as indicators of the state of the river by their presence or absence

• Chemical testing to determine the amount of dissolved oxygen in the water

• Chemical testing for determining levels of specific chemicals such as ammonia, nitrates and phosphates

• Physical testing such as measurements of the turbidity of the water and the quantity of suspended solids

The amount of dissolved oxygen in the water is a major determinant for the presence and abundance of

invertebrates in river ecosystemsThe discharge of organic material into rivers lowers the oxygen

availability and sensitive organisms are unable to survive

PlecopteraStonefly nymphs

EphemeropteraMayfly nymphs

These invertebrates areintolerant of pollution

and low oxygen concentrations; they feed

on detritus and otherinvertebrates and have

flattened bodies and clawsfor crawling over the

surface of stones

Mayfly and stonefly nymphs are clean water fauna and

indicators of well-oxygenated unpolluted water

TrichopteraCaddis-fly larva

Gammarus pulexFreshwater Shrimp

These invertebrates are tolerant of mild pollution and reappear in rivers polluted with organic material as

oxygen levels return to normal

Asellus aquaticuswater hog-louse

LimnaeaFreshwater Snail

HirudineaFreshwater Leech

These invertebrates are tolerant of moderate pollution and reappear downstream from the polluting source

AnnelidaTubificid worms

in cases

Eristalis teneaxLarva of bee-fly

(rat-tailed maggot)

Chironomus thummiBloodworm – midge larva

These invertebrates are tolerant of high pollution and are adapted to survive the low oxygen levels in polluted water

Tubificid and Chironomus larvae possess a form of haemoglobin in their blood that exhibits a high affinity for oxygen

Rat-tailed maggots possess a breathing tube at their rear end which penetrates the river surface enabling these organisms to obtain

oxygen from the atmosphere

Clean water organismsintolerant of pollution

Organisms tolerant of mild pollution that reappear as rivers recover from organic pollution

Organisms tolerant of mild pollution that reappear as rivers recover from organic pollution

The bright-red colour of Chironomus is due to the presence of haemoglobin,

adapting this organism for survival in conditions of low oxygen concentration

Clean water faunaFauna tolerantof high

pollution

Fauna tolerantof moderate

pollution

Fauna tolerant of slight pollution Fresh water fauna return

The Effectof Organic

Pollution onRiver Fauna

• http://www.youtube.com/watch?v=UGqZsSuG7ao

• http://www.youtube.com/watch?v=h-zncNp-X-E (song)

Dissolvedoxygen

Ammonium ions

(NH4+)

Nitrates(NO3)

Suspended solidsBiologicalOxygenDemand(BOD)C

on

ce

ntr

ati

on

(A

rbit

rary

Un

its)

SEWAGE

DISTANCE DOW NSTREAM

The Effect of Raw Sewage on the Chemical Compositionof a River Ecosystem

Explain the graph

Dissolvedoxygen

Ammonium ions(NH4

+)

Nitrates(NO3)

Suspended solids

Co

nc

en

tra

tio

n (

Arb

itra

ry U

nit

s)

SEWAGE

DISTANCE DOW NSTREAM

BiochemicalOxygenDemand(BOD)

Entry of sewage intothe river increases the quantity of suspended

solids, and light availability to oxygen-

producing aquatic plants is reduced

Organic material in the discharge

provides an abundant source of food for bacteria and other

decomposers resulting in a rapid growth of their populationsThe oxygen level falls dramatically as it is utilised

by decomposers for respiration and the BOD is highThe Biochemical Oxygen Demand reflects the demand for oxygen by the decomposers; it is a measure of the

dissolved oxygen taken up by microorganisms in decaying the available organic matter

Ammonium ions are released as decomposers oxidise the organic matter and these are rapidly oxidised to

nitrates by nitrifying bacteria

Nitrates stimulatethe growth of algae

Organic material is gradually broken

down and the river recovers from the

polluting effects as it flows

downstream

River invertebrates are indicators of the degree of pollution in the river

Species diversity decreases with high pollution and graduallyincreases again as the river recovers

The increased nitrate levels, resulting from

microbial decomposition of organic material,

stimulates the growth of algae

Pollution from Nitrogen Fertilisers

• Nitrogen based fertilisers have many benefits such as increased productivity in plants/crops but they have had detrimental effects:

• Reduced species diversity – grass/nettles prefer nitrogen rich soil, so they out compete other species e.g. silage fields

• Leaching – Rain water removes nitrates from soil and then into streams/rivers. This can be harmful if water is a source of drinking water. High nitrate levels can lead to inefficient oxygen transport in babies and stomach cancer.

• Eutrophication – Fertilisers leaching into watercourses.

Eutrophication• Eutrophication is a natural process but can be made worse by over use of

fertilisers (usually inorganic).• In most lakes and rivers, nitrates exist in low amounts and are limiting factor

for plant and algal growth• Over use of fertiliser on agricultural land near watercourses can lead to

leaching of nitrates into lakes and rivers, leading to nitrate levels increasing.• Algal and plant growth increases exponentially. Algal growth is mainly on

surface and upper layers – leads to ‘algal bloom’• This dense layer absorbs most sunlight and prevents it from penetrating lower

layers. Light is now limiting factor for lower plant life – starts to die.• Dead plants and algae provide food for saprobiotic bacteria, so their

population number grows exponentially.• These decomposers require more oxygen for respiration, so the concentration

of oxygen decreases but nitrates increase due to decomposition.• Oxygen levels are now limiting factor for population of aerobic organisms

(fish, invertebrates) and these die off.• Less competition for anaerobic organisms. These continue to grow in

numbers.• Dead material is further broken down releasing more nitrates and toxic waste

such as Hydrogen Sulphide – Water becomes putrid.

• Complete troubled waters activity

Biotic DataBiotic data was used to calculate the

Simpson’s Diversity Index and the Trent Biotic Index for each site

The Biotic Index is given as a Roman Numeral which describes the quality of the stream, from 0 for

very polluted, to X for very clean

The index is dependent upon the presence or absence of certain indicator species, as well as the

composition of the community

Instructions for determining the index are provided in the workbook

TRENT BIOTIC INDEXAfter F Woodiwiss, Trent River Authority

0-1 2-5 6-10 11-15 16+

-0 I II -

VI

I II III IV -

II III IV V

VII

III IV V VI VII

IV IV V VI

VIII

- V VI VII VIII

- V VI VII

IX

- VI VII VIII IX

- VI VII VIII

Composition Score

- VII VIII IX XHow many species of Plecoptera

(stoneflies) in sample?

How many species of Ephemeroptera (mayflies)

excluding Baetis rhodani (olive mayfly larvae)?

How many species of Trichoptera (caddis flies) (include B.rhodani

here if present)?

Were Gammarus (freshwater shrimps) present in sample?

Were Asellus (water hog lice) present?

Were Tubifex worms and/or red chironomid larvae (bloodworms)

present?

All above animals absent. Were any macro invertebrates present?

Biotic Index 0.Very polluted

START

None

None

No

No

No

No

No

The Biotic Index is given as a Roman Numeral which describes the quality of the stream, from 0 for very polluted, to X for very clean. The index is dependent on the presence or absence of certain indicator species, as well as the composition of the community.

To work out the Index from the table on the right you need to add up a Community Composition Score , and then work through the flow chart. The intersection of the appropriate flow box row and column gives the Biotic Index for the site.

Community Composition Score : You score points for taxonomic groups of animals which are relatively easy to identify. Score one point for each of the following in the sample.

Each species of Platyhelminthes (flatworms)The phylum Annelida (true worms and leeches)Each species of Hirudinae (leeches)Each species of Mollusca (snails etc)Each species of Crustacea (water louse, shrimps) excluding the Cladocera (water fleas)Each species of Plecoptera (stoneflies)Each species of Ephemeroptera (mayflies)Each family of Trichoptera (caddis flies)Each species of Neuroptera (alderflies)The family Chironomidae (midge larvae) excepting Chironomus thummi (bloodworms)Chironomus thummi if presentThe family Simulidae (black flies)Each other species of Diptera (true flies), eg crane fliesEach species of Coleoptera (beetles and beetle larvae)Each species of Hydracarine (water mites)

More than one

More than one

More than one

One

One

One

Yes

Yes

Yes

Yes

Trent Biotic index (After F. Woodiwiss, Trent River Authority