A New Well and the Disappearing Frogs
A wetland of about 2 hectares lies beside a village. It supports frogs, reed warblers, dragonflies and a small fish population. Villagers have traditionally grazed cattle at its edge and cut reeds for thatching. A developer proposes draining 60% of the wetland to grow maize and sinking a well to irrigate it. An environmental officer surveys the site and finds 14 frog species, three of which are found nowhere else within 50 km. Villagers say the frogs are 'useless' and that the maize will feed families. The developer says the wetland is 'just a swamp'.
1. Explain the ecological roles of the wetland and its frogs, and assess the likely effects of draining 60% of it.
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Ecological roles of the wetland:
- Habitat: It provides breeding sites, shelter and food for frogs, dragonflies, fish and birds. Frogs need standing water for eggs and tadpoles and damp vegetation for adults.
- Food web support: Frogs eat insects, including mosquitoes and crop pests, and are themselves eaten by birds and snakes. Removing frogs can increase insect numbers, including disease vectors.
- Water regulation: Wetland vegetation slows water flow, reduces flooding downstream, filters sediment and nutrients, and helps recharge groundwater.
- Productivity: Reeds and grazing are renewable resources that depend on the wetland staying wet.
Effects of draining 60%:
- Habitat loss: Only 40% (about 0.8 ha) remains. Species that need large or connected areas may not survive in a fragment. The three endemic frog species are at particular risk because they have no other local population.
- Edge effects: The remaining strip has more edge relative to its area, so it is more exposed to sun, wind, pesticide drift from the maize and silt runoff.
- Food web disruption: Fewer insects eaten by frogs, fewer frogs for birds; reed warblers lose nesting reed beds if cutting and drainage remove them.
- Hydrological change: A well for irrigation lowers the water table, which may dry the remaining wetland in the dry season even if it is not drained directly. This is a key risk the developer's plan does not address.
- Loss of services: Flood buffering and water filtration decline, affecting villagers downstream.
Judgement: The claim that the wetland is 'just a swamp' ignores these functions. The loss of three locally unique species is effectively irreversible.
2. Propose a plan that balances food production with conservation, and state two indicators the officer should monitor to judge whether the plan is working.
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Balanced plan:
- Protect a core area: Leave at least the 40% containing the breeding pools of the endemic frogs undrained, with a buffer of natural vegetation around it. Fencing the core from cattle prevents trampling of egg-laying sites.
- Limit drainage: Drain no more than a smaller fraction, or use raised beds and dry-season cropping rather than permanent drainage, so the wetland can recover in wet years.
- Control the well: Set a maximum abstraction rate and monitor the water table. Irrigation should be scheduled so the wetland does not dry out; drip irrigation and mulching reduce demand.
- Buffer strips: Keep a vegetated strip between maize and the wetland to trap silt and pesticide runoff.
- Sustainable reed harvest: Cut reeds in rotation, leaving patches for nesting birds.
- Community benefit: Involve villagers in managing the core area and share maize yields, so conservation is not seen as opposing food needs.
Indicators to monitor:
- Frog abundance and species richness: Count calling males or survey tadpoles at fixed points each season. A fall in the three endemic species is an early warning.
- Water table depth and wetland extent: Measure the water level in dip wells and map the wet area each dry season. If the wet area shrinks beyond the agreed limit, abstraction must be reduced.
Other useful indicators include insect and bird counts, water turbidity and maize yield. The key is to set thresholds in advance and agree what action follows if they are crossed.