Characterising wetland hydrology and water quality in streams and wetlands of Khalong-la-Lithunya, Lesotho (original) (raw)
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Soil Science - Emerging Technologies, Global Perspectives and Applications [Working Title], 2022
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PHYSICAL HYDROLOGY OF THE MIDDLE MOHLAPITSI WETLAND, CAPRICORN DISTRICT, SOUTH AFRICA
Anthropogenic intervention in wetlands water dynamics is thought to have created significant changes in water table fluctuations in the Middle Mohlapitsi Wetland. For example, clearing or drainage of wetlands can lead to losses of stored organic carbon (C) to atmospheric carbon dioxide (CO2). By doing this, wetlands mitigate climate change. Changes from flooded to drained conditions in soils stimulate changes from aquatic to terrestrial vegetation and decrease the algal contribution to total primary production. The objective of this paper is to analyse and quantify the dynamics of water generation and retention within the wetland. The study involved both fieldwork and laboratory analyses. Twenty (20) piezometers made from 65 mm diameter PVC tubes were installed along three transects namely T4, T5 and T6. T4 is the widest transect (596.50m); with nine piezometers that were kept in place until the end of 2012. T5 is the second widest transect (450.70 m) with a total of eight piezometers and is located in the left bank of the river. Among this group of transects, T6 is the narrowest (198.90m) with only three piezometers. Long-term groundwater table (GWTL) levels were monitored in order to understand water table fluctuations. GWTL fluctuations were measured by an electronic water level recorder and the readings were sent to the authors for desktop analyses. Five funnel-shaped rain gauges were installed in 2005 within the wetland and readings were taken after every rain events until 2012. These readings were used for all calculations. Streamflow readings from 1970 through 2012 were taken from Department of Water Affairs (DWA) weir, located 1 km downstream of the wetland. Between 10/02/2010 and 02/04/2010, the study wetland received some 214 mm of rainwater, and it was observed that GWTLs in all three transect increased. Thereafter, all piezometers did not show any increase or decrease until the end of study period. Statistical analysis showed that there is a significant moderate positive correlation between rainfall and streamflow. However, there is no relationship between rainfall and groundwater. Such complex situations between in groundwater table and rainfall could be caused by rainfall far from the study area. Hydrological processes in the upper and surrounding catchments impact water balance of the wetland under study. Keywords- Mohlapitsi Wetland, water table, transect, piezometer.
Quantification of water purification in South African palmiet wetlands
Water Science and Technology, 2018
Despite the importance of water purification to society, it is one of the more difficult wetland ecosystem services to quantify. It remains an issue in ecosystem service assessments where rapid estimates are needed, and poor-quality indicators are overused. We attempted to quantify the water purification service of South African palmiet wetlands (valley-bottom peatlands highly threatened by agriculture). First, we used an instantaneous catchment-scale mass balance sampling approach, which compared the fate of various water quality parameters over degraded and pristine sections of palmiet wetlands. We found that pristine palmiet wetlands acted as a sink for water, major cations, anions, dissolved silicon and nutrients, though there was relatively high variation in these trends. There are important limitations to this catchment-scale approach, including the fact that at this large scale there are multiple mechanisms (internal wetland processes as well as external inputs) at work that ...
Abstract In East Africa where wetlands are becoming essential systems for waste water treatment and potable water supply, hydrological characterisation is crucial to understand the dynamics of their functioning on a spatial and temporal scale. Beside ecosystem services, basic ecological properties such as vegetation structure and nutrient cycling of wetland ecosystems depend on hydrology. Nabajjuzi wetland, in central Uganda, East Africa is internationally recognised as a Ramsar site and currently used for potable water supply in addition to other essential ecological and social economic services to the riparian communities. To contribute to the limited and scanty information of this ecosystem, the study focussed on hydrological and water quality characterisation using a water-nutrient mass balance as the major output. Also, the flow dynamics of Fe and allochthonous suspended solids loading into the wetland were investigated. Results show that the water balance of Nabajjuzi wetland is dominated by surface flow, which is influenced by rainy and dry periods. During peak flow, the estimated hydraulic retention time was found to be 1 month compared to 1.5 months during the low flow period. Also, water loss flux due to evapotranspiration in this region is high and in Nabajjuzi wetland, it is twice the daily rate of abstraction. Analysis of long term flow data also revealed that the current water abstraction rate can potentially result in hydrological stress to the system during extremely low flow periods. However, the wetland N and P loading is very low compared to other urban disturbed wetlands. Consequently, high concentration of Fe and suspended solids loading are the major constraints to the surface water quality hence potable water supply. Generally, there is need for a more comprehensive hydrological-water quality study and careful planning of the future catchment land use strategies. This can enhance management and conservation of the wetland to guarantee the crucial ecosystem services it provides. Keywords: Hydrology, Riverine wetland, Hydrological gradient, Surface-flow, Nutrients, Iron, Mass-balance, Lake Victoria basin.
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