IB Geography A.3.2 Agricultural Consequences for Water Quality Notes

Nutrient Runoff Can Turn Productive Water into an Oxygen-Poor System

1. Eutrophication is nutrient enrichment that increases biological production and can degrade water quality.
2. Fertiliser and manure add nitrogen and phosphorus to farmland.
3. Rainfall, irrigation or eroded soil transfers part of these nutrients into streams, lakes and coastal water.
4. The added nutrients can produce rapid algal or plant growth when light, temperature and residence time are favourable.
5. Dense growth blocks light from submerged plants and changes the food web.
6. Bacteria consume dissolved oxygen as dead algae and plants decompose.
7. Hypoxia or anoxia can kill fish and bottom-dwelling organisms or force mobile species to leave.

Eutrophication Links an Upstream Farm to Downstream Ecosystem Loss

1. Nutrients move through tributaries, so the most severe oxygen depletion may occur far from the fields that supplied them.
2. A slow-flowing lake or estuary retains nutrients longer than a fast river and may develop a stronger bloom.
3. Some cyanobacterial blooms release toxins that raise treatment costs and restrict recreation, livestock watering or drinking-water use.
4. The Mississippi Basin transfers agricultural nutrients toward the Gulf of Mexico, where seasonal oxygen depletion creates a large coastal dead zone.

1. Farmers gain from fertiliser use, while fishers, water utilities and coastal communities may bear costs downstream.
2. Buffer strips, restored wetlands, covered manure stores and better timing of fertiliser can reduce the nutrient load before it reaches a channel.

Irrigation Can Concentrate Salt in Soil and Return It to Water

1. Salinization is the build-up of soluble salts in soil or water to levels that harm crops, ecosystems or water use.
2. Irrigation water contains dissolved salts even when it tastes fresh.
3. Evaporation and crop transpiration remove water but leave much of the salt in the soil.
4. Poor drainage can raise the water table and draw salty groundwater upward by capillary action.
5. Salt makes it harder for plant roots to take up water and can damage sensitive crops.
6. Drainage water can carry the salt into rivers or aquifers and shift the water-quality problem downstream.

Agricultural Water Management Must Control Both Inputs and Drainage

1. Precision application can reduce excess fertiliser without requiring farmers to stop using nutrients.
2. Vegetated buffer zones and wetlands trap sediment and absorb part of the nutrient flow before it enters open water.
3. Efficient irrigation lowers the volume applied, but salt still requires enough drainage or leaching water to leave the root zone.
4. Lined canals can reduce seepage where rising groundwater contributes to salinization.
5. Salt-tolerant crops reduce losses but do not remove salt from the soil or drainage water.
6. Effective policy combines monitoring, farm advice, incentives and limits on pollution because downstream water users cannot control upstream practice alone.