Sediment records of the 2016-2017 flood from Notwane dam, Upper Limpopo basin, Botswana

Seven cores of sediments were collected at scattered locations in the Notwane dam over 2 days (22/11/2017 and 19/02/2018) for further sedimentological and geochemical analyses. Core collection was realised with 50 mm diameter PVC pipes though use of a push corer equipped with extension rods from shore or from a small boat. They were subsequently stored the same day at 4 ˚C in a refrigerator at the Botswana International University of Science and Technology (BIUST) to allow for water retention. Before analysis, core were split in half, photographed and sub-sampled at selected intervals for lab analysis. Grain size distribution for each interval was obtained through dispersing a few grams of sediment into distilled water which was analysed with a Malvern Mastersizer 3000 laser diffraction particle size analyser at BIUST. The organic matter (OM) content was measured at BIUST through measuring the loss on ignition (LOI) of bulk sediments after calcination in a muffle furnace. The porcelain crucibles were pre-heated in a muffle furnace for 1 hour at 375°C and after cooling transferred into a desiccator for further cooling and weighed. Samples were dried at 105°C for 24 hours and weighed. The dried samples were then heated for 16h at 550°C. 95 samples of sediments from selected intervals of the cores were further analysed for trace metal distribution (Fe, Zn, Cu, Cr and Pb) using an Agilent 4200 Microwave Plasma-Atomic Emission Spectrometer (MP-AES) at BIUST. About 1 g of sample was treated with 10-15 ml of 65% nitric acid at 60°C for a period of 4 hours. The samples were then filtered at <0.45 µm and brought to 50 ml adding Milli-Q distilled water. Average standard deviations were as follows: Fe %RSD = 1.81; Zn %RSD = 4.02; Cu %RSD = 1.43; Cr %RSD = 0.82; Pb %RSD = 1.72. Detection limits for the metals reported here (as weight of dry sediment) were as follows: Cr = 0.8 µg kg-1, Fe = 1.7 µg kg-1; Cu = 0.5 µg kg-1; Zn = 28 µg kg-1; Pb = 2.5 µg kg-1

This dataset is included in the following collections

Impacts for the 2016-2017 extreme rainfall and floods on water resources quality and quantity in SE Botswana