Hydro-period, surface-ground water interactions and water quality to assess wetland condition of Khalong-la-Lithunya

Wetland degradation may pose effects on wetland functioning. Wetland hydrology and water quality are important in understanding wetland systems in evaluating wetland functions and processes hence are used to assess the wetland condition. The study was carried out to assess the ecological functioning of Khalong-la-Lithunya wetland by determining hydro-period, surface – ground water interactions and the effect of the wetland on water quality. Wetland hydrology and water quality of the three sub-catchments were monitored. Water levels in piezometers were recorded once a month from October 2015 to March 2016 and the monthly water levels data for the years 2010, 2011, 2012 and 2013 previously recorded by the Millennium Challenge Account-Lesotho (MCA-L) project were also used. Rainfall, piezometers and streams water also collected once a month were analysed for δ2H and δ18O water stable isotopes and water quality parameters were determined. The estimated overall hydro-period of Khalong-la-Lithunya from the years 2010 to 2016 was 11.4% of the sampled time. The wetland showed delayed response of piezometer water levels to rainfall. However, there was additional source of water to the wetland through sub-surface flow during dry conditions. The piezometers water isotopes were highly depleted (-10.663 to -11.153‰ for δ2H and δ18O) while stream water (1.419 to -2.913‰ for δ2H and δ18O) had a mixture of both piezometer and rainfall water (7.6 to 64.0‰ for δ2H and 0.42 to 10.28‰ for δ18O) hence these showed that the water gets stored in the wetland for some time before it gets discharged to the stream. This indicates a positive interaction between ground and surface water. Most water quality parameters were higher in streams than in piezometers, however, they were mostly within WHO permissible limits. The concentrations of BOD (9.03mg/L) and PO4 (1.07mg/L) were extremely higher than WHO standards hence contributed to the poor water quality index in streams (59.71). While the high phosphate levels (4.15mg/L) contributed to the poor water quality index (53.67) in piezometers. The principal component analysis (PCA) indicated that the parameters that were responsible for the variation in water quality were related to natural hydro-chemical processes, anthropogenic factors as well as geology and soil constituents. Most water quality parameters were highest during dry months (October and December 2015). Short hydro-period, delayed interaction between surface and ground water together with poor stream water quality may indicate affected wetland ecological functioning.