2 Nutrient cycling in floodplains

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Figure 3 The nutrient cycle on a floodplain Meadow. Numbers represent amount of phosphorus in kg ha^-1 y^-1. Bold arrows denote the major flux through the system.

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A diagram showing the floodplain meadow system, with three domains: the river channel, the floodplain meadow and the wider environment. Phosphorus moves through the system with the dominant flux being from the river via sediment to the meadow and then via haymaking to the wider environment..

Figure 3 The nutrient cycle on a floodplain Meadow. Numbers represent amount of phosphorus in kg ha^-1 y^-1. Bold arrows denote the major ...

The availability of nutrients in floodplains is determined by the input from floods and the output, primarily in the form of a hay crop. A comparison of these fluxes is called a nutrient budget.

If nutrient arriving in floods exceeds the amount removed in hay, the soils will increase in fertility and tall, competitive species of grass (such as tall oat and cocksfoot) will dominate the meadow, reducing both botanical diversity and hay quality. On the other hand, if the floods deliver less nutrient than the hay crop removes, then the hay yield will start to decline.

Grazing animals have relatively little effect on the nutrient budget because, while they consume grass and extract nutrients for body growth, the majority (>90%) reappears at the other end as manure and returns to the soil. Managing floodplain as pasture therefore allows nutrients to build up over time and eventually leach back into the river.

Activity 1

Timing: Allow about 5 minutes

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Figure 2 (repeated) How hay from floodplain meadows balances the nutrient inputs.

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A diagram showing how sediment is deposited on a floodplain during a flood and those nutrients can subsequently be absorbed by plants and be exported as hay.

Figure 2 (repeated) How hay from floodplain meadows balances the nutrient inputs.

Examine the infographic. It shows how nutrients cycle through a floodplain meadow. What would happen if the hay cut were not taken?

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Discussion

The hay cut balances the nutrients that are deposited in a flood, so if it was not taken, the soil fertility would increase and plant diversity would decrease.