Causes of Eutrophication

Developed by Richard Sandford with

contributions from Martin Bloxham and Paul Worsfold,

Eutrophication in the Sea of Azov. Source: SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAG

Eutrophication is caused by enhanced nutrient inputs (N and P) as a result of:

Inorganic fertilisers and animal wastes in crop

production

Wastes from animal production

Combustion of fossil fuel

Forestry practices

Phosphate detergents

Sewage discharges

Aquaculture

Draining of wetlands

Soil and sediment erosion, remobilisation,

leaching (from agriculture, mining, construction)

Example: Effects of Agricutlure on lakes

2.1 Enhanced nutrient inputs

Combustion of fossil fuel

Soil erosion

Sewage discharges

Wastes from animal production

Agricultural practices

Eutrophication – Causes

Eutrophication is also caused by Increased recycling/mobilisation of nutrients as a result of:

Forestry practices

Draining of wetlands

Water system impoundment (e.g. reservoirs)

Soil and sediment erosion, remobilisation,

leaching (e.g. As a result of agriculture, mining,

construction)

Question: What is a Causal Chain?

Forestry practices

Soil erosion

Water impoundment

Draining of wetlands

2.2 Increased recycling/mobilisation of nutrients

Eutrophication – Causes

Eutrophication is also caused by Trapping of nutrients (e.g. in river impoundments)as a result of:

Water system impoundment

Soil and sediment erosion, remobilization,

leaching (e.g. As a result of agriculture, mining,

construction)

Question: What uncertainties are there when determining causes?

Soil erosion

Water impoundment

Water impoundment

2.3 Trapping of nutrients (e.g. in river impoundments)

Eutrophication – Causes

There are over 600 small lakes in Northern Ireland. Research on the sediments in six of these has reconstructed a remarkable record of changes in total phosphorus concentration over the past 150 years that appears to be typical of lakes in most developed countries. The data shown above is for three lakes that have no point sources (e.g. sewage) draining into them, only the inputs from surrounding agriculture. Each of the lakes shows an increase in phosphorus, initially as a result of land clearances (ploughing releases phosphorus) and then a more pronounced increase since the 1950s. This recent large change is due to land drainage, fertiliser use and the indirect impact of rural sanitation. Impacts of these activities are accelerating the demise of the lakes. Each of the lakes is affected in a slightly different manner according to the characteristics of the particular drainage basin. Recent decreases may reflect more prudent use of fertilisers.

source: redrawn from Anderson, J. Freshwater. Biol. 38, 427-440, Fig. 9

Eutrophication – Causes

Immediatecauses

a. EnhancedNutrientInputsb. Increasedrecycling/Mobilizationc. Trapping ofnutr ients (e.g.Riverimpoundments)

Secondary causes

1. Use of ferti lizersin crop production(a)2. Use of animalwastes inagriculture (a)3. Wastes fromanimal production(a)4. Combustion offossil fuel (a)5. Forestry/Agriculturalpractices(a,b)6. Phosphatedetergents (a)7. Sewagedischarges (a)8. Aquaculture (a)9. Draining ofwetlands (a,b)

Tertiary causes

1. Enhanced foodproduction via useof fertilizers (a)2. Intensificationof animalproduction (a)3. Enhancedenergy demand(a,c)4. Urbanization (a)5. Enhancedaquaculturalproduction (a)6. Land-usechanges (a,b)7. Enhancementof navigation,dredging ofwaterways andharbours (b)8. Enhancementof water supplies(b,c)9. Hydrolelectricpowerdevelopment (b,c)

Policymanagementfailures

1. Lack ofinternalization ofcosts ofenvironmentaldegradation2. Inadequatedevelopmentand/orenforcement ofregulations

Causal chains

Enhanced nutrient input is the Immediate Cause of eutrophication.The Secondary Cause could be the use of fertilisers in crop production. The Tertiary Cause may be the intensification of animal production. This could be as a result of Policy Management Failures. This stepwise process is known as a Causal Chain.

A Causal Chain is a series of statements that demonstrate and summarise, in a stepwise manner, the linkages between problems and their underlying or 'root' causes.

Eutrophication – Causes

Uncertainties in determining causes

1. Relative importance of given sources in a given situation (temporal and spatial variance)

2. Level/input rates of nutrients that give rise to exceptional algal blooms

3. Limitations of information on the incidence and bio-availability of forms of

nutrients (N & P)

4. Uncertainties in the precision of comparisons among options

5. Uncertainty in the prediction of the outcome of management interventions

Eutrophication – Causes