water pollution

water pollution- when water is altered in composition or condition, directly or indirectly as a result of activities of man, so that it is less suitable for any or all of the purposes for which it would be suitable in its natural state.

 

Types of water pollutants

  1. Organic pollution

  • Sewage

  • Urban runoff

  • Industrial effluents

  • Farm wastes

  • Other sources

  1. Inorganic pollution (novel entities)

  • Inorganic nutrients (fertilisers)

  • Inorganic chemicals (elements/compounds)

  1. Suspended solids

 

Organic pollutants

Organic compounds that contain carbon (and usually carbon hydrogen bonds)

Organic pollutants are long bonds of molecules containing carbon.

Act as a substrate for microorganisms - bacteria, fungus and pathogens. (sewage)

Can also include manmade substances,(as long as till based in carbons),

  • Hydrocarbons (oils, grease, plastics)

  • Detergents (washing powder)

  • Pesticides and herbicides (persistent organic pollutants, POPs)

Example - historical management of domestic sewage:

  • Sewage disposal

  • Population growth and industrialisation created The Great Stink of 1858, River Thames known as a dumping ground combined with hot summer led to the creation of a sewage system.

Modern sources

Domestic sewage

  • Combined sewers (surface water is combined with sewerage)

  • Modern sewage treatment still releases organic compounds

Urban runoff - impermeable surfaces

  • Storm conditions - trace metals

  • Catchpits (gully pots)

  • Episodic

  • Anoxic and bacterial scum

 

First flush

Occurs after a period of dry weather, often associated with road run off and storm water.

  • Oil spills

  • Tyre and brake wear

  • Trace metals

Industrial effluents

  • Food processing

  • Brewing

  • Textiles

  • Abattoirs

Farm wastes

  • Slurries

  • Silage- liquor

  • Manure (4x more phosphorus than human waste)

Effects of organic pollution

Micro- organisms break down organic material in water and the pollution increases the number of microorganisms.

Increases the biochemical oxygen demand (BOD) - amount of oxygen needed by microorganims to decompose biological wastes.

As BOD increases dissolved oxygen (DO) decreases.

DO is scarce in water and any reduction can harm aquatic life that needs it.

Increased BOD and decreased DO.

Eutrophication is the enrichement of water by inogranic and organic plant nuteirents- low DO, high alge, low light, high nuteritns

Oligotrophic lake- low nutirnt levles, good light penetration, high DO, low algoe, less tolerant species.

 

Macroinvertebrates

 

Point and diffuse pollution

Point source pollution- release pollutants from discrete outflows such as a discharge pipe.

Main point source discharges are factories and sewage treatment plants which release treated wastewater.

Nonpoint source pollution- a combination of pollutants from a large area rather than from specific identifiable sources such as discharge pipes.

 

Reducing organic pollutants

Sewage treatment - (gravity fed system

  1. Preliminary (screening and maceration)

  • For removing large material

  1. Primary (sedimation= sludge)- allowed to settle in a settlement tank

  • Produces very useful biproduct as a source of energy

  1. Secondary (biological treatment)

  • Aeration allows microorganism to remove majority of suspended soilds- good microorganism removing pollutants

  1. Tertiary (removing nutrients)

  • Removes BOD, P and N

 

In developing countries

  • Untreated wastewater

  • Lack of treatment

  • Excessive BOD

  • Contaminated surface and ground water

  • Health implications on humans

 

Urban point sources of nutrients

Domestic sewage and lack of tertiary sewage treatment.

Industrial effluents- brewing, waste residues and cleaning agents.

  • Factories

  • Water treatment plants

 

Diffuse sources of nutrients

  • Atmospheric deposition/ fossil fuel burning

  • Rural housing

  • Urban runoff from impermable surfaces

  • Forestry - fertilisers, afforestation in uplands (fertilsers and sediment when deforested), plantations.

  • Agriculture and farmland - runoff of fertilisers after a storm (farmland)

 

Agriculture

N- nitrate P- phosphate K- potassium

Heavy use on arable farmland contributes to diffuse pollution and nutirent loss from farmland.

  • Drainage water- percolation

  • Runoff

  • Erosion

  • Phosphate bound to particulates

  • Solubility of nitrate

  • Confined animal feeding operations - organic waste is large from these.

 

Effect of eutrophication

  • Principle effect- increase in primary producivity (enhanced plant growth)

  • Algal blooms (single celled, energy producers)

  • By humans pumping nitrates and phosphates into the water.

Algal blooms

Physical, chemical and bioloigcal effects

  • Smell

  • Exterts BOD

  • Species composition/ diveristy

  • Loss of macrophytes (lillies submerged vegetation) - shading out

  • Sedimentation

  • Toxic

Sediment and suspended soils

  • Excessive amounts of suspended soil particles that orginiates from erison of agricultural lands, deforestation, degraded stream banks, overgrazing and construction.

  • Causes problems in aquatic ecosystems such as limits light penetration stopping photosynethsis , covers aquatic animals and plants - ones attached to rocks get removed by sediemnt and brings insolube toxins into waterways.

  • This is an example of alternate state theory

 

Effects of water pollution

  1. Oxygen depletion- excess organic matter

  • Stream ecology - lose habitats and species

  • Eutrophication - excess nutrients

  • Nutrient fluxes

  1. Soil and surface water acidification - excess acid ions from tracemetals.

  • Aluminium is toxic

  • Acid episodes in rivers

  • Biomagnification in food chain- concentration of dosage of a system chemical as it goes up the food chain effecting bigger predators.

  • Mercury

  1. Human affects

  2. Environmental degradation

 

Measurement vs monitoring

Survey- single measurements spread over space- water quality suvey

Monitoring= repeated measurements

 

Sampling methods

Spot (must be analysed with caution as water courseds are highly dynamic) vs continuous

Spatial vs temporal

 

Surveying environmental phenomena

  1. Chemical

  • Basic parameters

  • BOD

  • Nutrients

  • Metals

  1. Physical

  • Water quantity

  • Sediment

  • Concentration

  • Catchment terrain and land use

  • Soil properties

  • Fluvial geomorphology

  1. Biological

  • Plants

  • Invertebrates

  • Diatoms

Methods in- situ on bankside tend to be less accurate and replicable than in a lab.

Kick sampling uses a 1mm net

Assessing water quality from macro- invertebrates

  • All taxonomic groups of aquatic macroinvertebrates given a score from 1-10 (1 tolerant to low water quality)

  • Scores are then calculated for each sample- BMWP is calculated as score X number found in each sample, ASPT is calculated as sample score/ number of taxonomic groups found.

  • Cannot tell us what is causing the issues so has to be used in conjuction with others.