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Maun (Botswana)


Location

Okavango Delta

Botswana, Mopane woodland

Latitude -19.92
Longitude 23.56

Botswana, Floodplain

Latitude -19,61
Longitude 23,27

Botswana, Grassland

Latitude -19,66
Longitude 23,35

Botswana, Swamp

Latitude -19,01
Longitude 22,40

Overview

  • 1999-2003
  • Colaboration with Okavango Research Center (University of Botswana)
  • Mopane fixed tower
  • Measuring campaigns
  • Eddy covariance (CO2, water)
  • Solar station
  • Gas exchange measurements
  • Canopy measurements
  • Vegetation surveys
  • Soil sampling

Project

CARBOAFRICA

Description, History

Fixed Tower - Mopane woodland

The study site was located in northern Botswana, ca. 20 km east of the town Maun.
Colophospermum mopane comprises the typical woodlands of southern Africa, found growing on slightly heavy soils and in areas with annual precipitation between 300–800 mm (Timberlake, 1995). Average annual rainfall in Maun is 460 mm, of which typically at least 80% fall in the four-months-period November to February. The pattern is highly irregular, however, with scattered, small rain events (<20 mm over one to two days) occurring into May or as early as September, whereas weeklong dry spells are being observed even during the height of the rainy season (Veenendaal et al., 2004).

Soils are hard setting sands with a maximum volumetric water holding capacity of just below 20% in the top 50 cm. A layer of calcrete is found at a depth of 2–6 m.

In the area around Maun, Mopane forms a near singlespecies canopy of approximately 8 m tall trees with a maximum leaf area index of around 1.2 in February and March. Afew Acacia erioloba are present. Mopane is a drought deciduous species but has a relatively irregular pattern of leaf fall (Veenendaal et al., 2004).

Campaigns - Floodplain, Grassland, Swamp

Three study sites of different hydrology within the Okavango River Delta, Botswana were selected. The Okavango River flows from the Angolan highlands into Botswana where it spreads into a complex, dynamically changing mosaic of perennial swamps, seasonal swamps, floodplains, and rain-fed grasslands and savannas. The herbaceous types of vegetation, which dominate much of the Delta, are dominated by C4 grasses and sedges, but also contain a number of C3 species, especially in the moister areas (Ellery et al., 1992).

One of the study areas was chosen in the central region of these perennial swamps, close to the Jao distributary channel. In this area, peat has gradually accumulated, indicating a prevalence of inundated conditions.

The second study area represented a typical seasonal floodplain with the sedges Schoenoplectus coryombosus and Cyperus articulatus growing in its lowest parts. The clay, representing the predominant soil material here, becomes blackish in colour when wet. Panicum repens dominated slightly higher areas with less seasonal inundation, and I. cylindrica was found on the upper, drier areas of the floodplain (Mantlana et al., 2008). Panicum repens and I. cylindrica were found in areas that have soils with a sandy-loam character.

The third area investigated was a rain-fed grassland, located in an area that had not received flooding for several years, and possibly for decades. Here, the top 30  cm of the soil consisted predominantly of sand. The vegetation was dominated by annual and perennial grasses (Mantlana et al., 2008).

At the seasonal floodplain, half-hourly rainfall, air temperature, and air water vapour saturation deficit at 3 m height were measured at a nearby eddy-covariance flux tower.

At the perennial swamp and the semi-arid rain-fed grassland similar meteorological data, at 7 m and 3 m height, respectively, were collected at a nearby mobile tower using equipment similar to that used in the seasonal floodplain.

Variables & Instruments

Fluxes

  • Eddy covariance - CO2, water vapor, momentum, heat (Gill R3, LI6262)

Meteorology

  • Wind velocity - cup anemometer, Thies
  • Air pressure - barometer RPT 410, Druck Inc.
  • Air pressure - PTB101B, Vaisala
  • Air temperature and humidity - temperature-humidity-sensor HMP45D, Mela
  • Air temperature - , Friedrichs
  • Precipitation - tipping bucket rain gauge Model 52202, Young
  • Net radiation - pyrradiometer LXG055,
  • Albedo - pyranometer CM14, Kipp & Zonen
  • Photosynthetically active radiation - PAR sensor LI-190SA, LiCor

Soil conditions

  • Soil temperature localy - temperature probe HMP45A, Vaisala
  • Soil moisture localy - soil moisture sensor HH2 + Theta probe ML-2x, Delta-T
  • Soil moisture in 12 positions - soil moisture probes ML-2x, Delta-T
  • Soil heat flux in 5 locations - soil heat flux plates HP3/CN3, Rimco

Data acquisition

  • Meteorological data - datalogger CR23X, Campbell Scientific
  • Flux data - notebook

Power

  • Solar station

Publications

Arneth, A., Veenendaal, E. M., Best, C., Timmermans, W., Kolle, O., Montagnani, L., Shibistova, O. (2006). Water use strategies and ecosystem-atmosphere exchange of CO2 in two highly seasonal environments. Biogeosciences, 3(4), 421-437.

Mantlana, K. B., Arneth, A., Veenendaal, E. M., Wohland, P., Wolski, P., Kolle, O., Wagner, M., Lloyd, J.(2007). "Inter-site and species specific differences in photosynthetic properties of C-4 plants growing in an African savanna/wetland mosaic." South African Journal of Botany 73(2): 330-330.

Mantlana, K. B., Arneth, A., Veenendaal, E. M., Wohland, P., Wolski, P., Kolle, O., Wagner, M., Lloyd, J.(2007). "Seasonal and inter-annual Soil CO2 efflux in savanna/wetland mosaic in the Okavango Delta, Botswana." South African Journal of Botany 73(2): 300-300.

Mantlana, K. B., Arneth, A., Veenendaal, E. M., Wohland, P., Wolski, P., Kolle, O., Lloyd, J. (2008). Seasonal and inter-annual photosynthetic response of representative C4 species to soil water content and leaf nitrogen concentration across a tropical seasonal floodplain. Journal of Tropical Ecology, 24(Part 2), 201-213. doi:10.1017/S0266467408004859.

Mantlana, K. B., Arneth, A., Veenendaal, E. M., Wohland, P., Wolski, P., Kolle, O., Wagner, M., Lloyd, J. (2008). Photosynthetic properties of C4 plants growing in an African savanna/wetland mosaic. Journal of Experimental Botany, 59(14), 3941-3952. doi:10.1093/jxb/ern237.

Veenendaal, E. M., Kolle, O., Lloyd, J. (2004). Seasonal variation in energy fluxes and carbon dioxide exchange for a broad-leaved semi-arid savanna (Mopane woodland) in Southern Africa. Global Change Biology, 10(3), 318-328.

Bird, M. I., Moyo, C., Veenendaal, E. M., Lloyd, J., Frost, P. (1999). Stability of elemental carbon in a savanna soil. Global Biogeochemical Cycles, 13(4), 923-932. doi:10.1029/1999GB900067