Michelle Goman

ARTESIAN BLISTER WETLANDS, A PERENNIAL WATER RESOURCE IN THE SEMI-ARID RIFT VALLEY OF EAST AFRICA

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.

Multiproxy paleoecological reconstruction of prehistoric land-use history in the western region of the lower Río Verde Valley, Oaxaca, Mexico

Paleoecological archives from three paleomeander sites and one archeological feature located in the lower Río Verde Valley, Oaxaca, Mexico, are used to develop a spatial understanding of the patterns of prehistoric agricultural land use over the last ~3000 years. Multiproxy paleoecological data at each site (i.e. magnetic susceptibility, micro- and macroscopic charcoal, pollen and stable carbon isotopes) provide a history of land use. By examining the spatial differences in agricultural indicators at all the sites through time, augmented with our understanding of changes in demography and settlement patterns determined through the archeological record, we are able to reconstruct the complex human/land interactions in the western portion of the valley.

Diversity and distribution of macrophytes in a freshwater wetland, Loboi Swamp (Rift Valley) Kenya

ABSTRACT An inventory of Loboi swamp was undertaken to determine the macrophyte diversity and distribution. A total of 36 vascular plant species in 13 families were recorded, with Cyperaceae forming over 30% of macrophytes. Two vegetation zones were observed, characterised by the presence of Typha and papyrus. The Typha zone, comprising over 70% of the swamp, is dominated by T. domingensis and is species rich with 35 plant species whereas the papyrus zone includes the dominant Cyperus papyrus and only one other macrophyte species. Distribution of macrophytes is correlated with depth and period under water, with the Typha zone seasonally flooded while the papyrus zone is permanently under water at depths over 0.5m. Water chemistry has little influence on the distribution of macrophytes in the swamp, but at the edges there is predominance of Cyperus laevigatus in high alkalinity soils. Current uses of the swamp include dry season grazing, harvesting of papyrus and other plant material for mat making and house thatching, and use of the swamp water for domestic and irrigation agriculture. Further monitoring is needed to evaluate the effect of the resource uses on the swamp.