Measurement and modelling of evaporation from a coastal wetland in Maputaland, South Africa

Abstract

Abstract. The surface renewal (SR) method was used to determine the long-term (12 months) total evaporation (ET) from the Mfabeni Mire with calibration using eddy covariance during two window periods of approximately one week each. The SR method was found to be inexpensive, reliable and with low power requirements for unattended operation.Despite maximum ET rates of up to 6.0 mm day −1 , the average summer (October to March) ET was lower (3.2 mm day −1 ) due to early morning cloud cover that persisted until nearly midday at times. This reduced the daily available energy, and the ET was lower than expected despite the available water and high average wind speeds. In winter (May to September), there was less cloud cover but the average ET was only 1.8 mm day −1 due to plant senescence. In general ET was suppressed by the inflow of humid air (low vapour pressure deficit) and the comparatively low leaf area index of the wetland vegetation. The accumulated ET over 12 months was 900 mm. Daily ET estimates were compared to the Priestley-Taylor model results and a calibration α = 1.0 (R 2 = 0.96) was obtained for the site. A monthly crop factor (K c ) was determined for the standardised FAO-56 Penman-Monteith. However, K c was variable in some months and should be used with caution for daily ET modelling.These results represent not only some of the first longterm measurements of ET from a wetland in southern Africa, but also one of the few studies of actual ET in a subtropical peatland in the Southern Hemisphere. The study provides wetland ecologists and hydrologists with guidelines for the use of two internationally applied models for the estimation of wetland ET within a coastal, subtropical environment and shows that wetlands are not necessarily high water users.

Climatic variability in Mfabeni peatlands (South Africa) since the late Pleistocene

“…The shallow, but extensive 350 km 2 St Lucia Lake dominates the park and forms part of the largest estuarine wetland system on the African continent (Vrdoljak and Hart, 2007). The Mfabeni fen lies on the eastern shores of Lake St Lucia, within an interdunal basin (Botha and Porat, 2007) measuring c. 10 × 3 km (Clulow et al, 2012), and up to 11 m in depth (Grundling et al, 2013). The fen's hydrology is influenced primarily by the unconfined Maputaland aquifer (Grundling et al, 2013;Taylor et al, 2006a) and local precipitation.…”

Biomarker records of palaeoenvironmental variations in subtropical Southern Africa since the late Pleistocene: Evidences from a coastal peatland

“…Within the park, the shallow 350 km 2 St Lucia Lake forms part of the largest estuarine wetland system on the African continent (Vrdoljak and Hart, 2007). On the eastern shores of Lake St Lucia, the Mfabeni fen lies within an interdunal valley (Botha and Porat, 2007) measuring c. 10 x 3 km (Clulow et al, 2012;Grundling et al, 2013), and up to 11 m deep (Grundling et al, 2013;Grundling, 2001). The fen's hydrology is influenced primarily by circum-neutral Ca 2+ and HCO 3dominated groundwater of the Maputaland aquifer, that is structurally controlled by the north-south aligned coastal dune corridor (Grundling et al, 2013;Taylor et al, 2006a;Venter, 2003), and local precipitation.…”

The impact of taro (Colocasia esculenta) cultivation on the total evaporation of aCyperus latifoliusmarsh

“…Comparable results were obtained by Clulow et al . () for a sedge wetland on the East Coast of South Africa where daily average ET rates were 3.7 mm for November 2009 and 4.2 mm for January 2010. Daily ET rates ranging between 2.0 and 5.5 mm were recorded in summer by Jarmain and Dye () above a P. communis reed bed.…”