A cluster of artesian springs encircled by mounds of marsh and wet meadows was discovered near the equator in Kenya, East Africa. Each spring is capped by a dense fibrous root mat that covers a mound of clayey peat with a blister of water in the center. Individual mounds are ∼15 m wide, 1–2 m high, and affect an area of ∼50 m2. The central water-blister volume is <1 m3. The arched semi-permeable vegetation cap appears to be buoyed upward by slow artesian flow that leaks through the cap and moves slowly away. Lush plant growth (Poaceae and Cyperaceae, algae, diatoms, and filamentous cyanobacteria) is supported even through the dry season (Dec.–Feb.). The term “artesian blister wetland” is proposed for this unusual marsh, which has not been described previously. Approximately 20 small, circular-to-oval artesian blister wetlands occur within a large spring and wetland complex (∼1.3 km2) that includes several freshwater Typha marshes fed by ground-water seeps. The springs discharge along a rift-related fracture system near the contact between volcanic bedrock and late Quaternary sediments. Cores (1–2 m) through the mounds revealed a dense root mat underlain by water in the center and a clayey peat that is locally pebbly at the base surrounding the blister. LOI in the clayey peat decreases from 75% at surface to ∼10% at 0.4–1.2 m. Blister water is cool, fresh, and dysaerobic (T = 30–33 °C; pH = 6.2–7.2; conductivity ∼600 ìS/cm; and DO = 50%; 0.6–3.5 mg/l). The spring/wetland mounds likely form by the blanketing of the land around the spring orifice with vegetation (paludification). Plants and cyanobacteria seem to trap sediment transported by surface run-off and wind. The mound grows with time, but its height is limited by the magnitude of the hydraulic head. These ecological niches are important freshwater resources for animals and humans in semi-arid environments.
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Vol. 22 • No. 4