Characterisation of groundwater recharge conditions and flow mechanisms in bedrock aquifers of the Johannesburg area, South Africa

Leketa, Khahliso; Abiye, Tamiru; Butler, Michael J.

doi:10.1007/s12665-018-7911-7

Cited by 15 publications

(19 citation statements)

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“…The rainfall-runoff relationship, which is controlled by the local geology and slope play important role in the contribution of rainfall to replenish the aquifer [55][56][57]. The unsaturated zone with low K could delay recharge and hence affecting the δ 18 O and δ 2 H composition.…”

Section: Stable Isotope Distributionmentioning

confidence: 99%

An Overview of Aquifer Physiognomies and the δ18O and δ2H Distribution in the South African Groundwaters

2021

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A comprehensive assessment of the stable isotope distribution in the groundwater systems of South Africa was conducted in relation to the diversity in the aquifer lithology and corresponding hydraulic characteristics. The stable isotopes of oxygen (18O) and hydrogen (2H) in groundwater show distinct spatial variation owing to the recharge source and possibly mixing effect in the aquifers with the existing water, where aquifers are characterized by diverse hydraulic conductivity and transmissivity values. When the shallow aquifer that receives direct recharge from rainfall shows a similar isotopic signature, it implies less mixing effect, while in the case of deep groundwater interaction between recharging water and the resident water intensifies, which could change the isotope signature. As aquifer depth increases the effect of mixing tends to be minimal. In most cases, the isotopic composition of recharging water shows depletion in the interior areas and western arid zones which is attributed to the depleted isotopic composition of the moisture source. The variations in the stable isotope composition of groundwater in the region are primarily controlled by the isotope composition of the rainfall, which shows variable isotope composition as it was observed from the local meteoric water lines, in addition to the evaporation, recharge and mixing effects.

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Section: Stable Isotope Distributionmentioning

confidence: 99%

An Overview of Aquifer Physiognomies and the δ18O and δ2H Distribution in the South African Groundwaters

2021

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“…Groundwater nutrient outfluxes were estimated using the findings of Leketa et al (2018) of a net loss of 2 000 000 m 3 from the dam and assumed nutrient concentrations matching those of the outflow canals. Groundwater nutrient influx is assumed to be included in river flows.…”

Section: Groundwater Influx and Outflux Estimationmentioning

confidence: 99%

Increasing nutrient influx trends and remediation options at Hartbeespoort Dam, South Africa: a mass-balance approach

Carroll

Curtis

2021

WSA

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The Hartbeespoort Dam, located 40 km west of Tshwane on the Crocodile River, is an extremely eutrophic water body. Situated in one of the most economically active areas of South Africa, it receives a high nutrient input from wastewater treatment works (WWTW), leaking sewers, as well as urban and agricultural runoff. The Metsi a Me programme, which ran from 2006 to 2016, aimed to mitigate in-lake nutrient stocks using biomanipulation, including the physical removal of Eichhornia crassipes (water hyacinth) and Microcystis aeruginosa (blue-green algae). Using Department of Water and Sanitation water quality and flow data, the annual influxes and outfluxes of total nitrogen (TN) and total phosphorus (TP) to the Hartbeespoort Dam were calculated. Through literature review and comparison with previous studies, the relative importance of nutrient removal from biomass harvesting in relation to retained nutrients was assessed. The average nutrient influx from rivers during hydrological years 2010/11 to 2016/17 was 582 t∙a−1 TP and 4 687 t∙a−1 TN, with trends for both TN and TP being significantly positive over this period. TP influx increased by 77.8 t∙a−1 every year and TN influx increased by 456 t∙a−1, reversing a long-term negative trend. Average annual dam retention + removal (calculated as the difference between river inputs and outputs, i.e., including sedimentation, biomass removal and denitrification losses) was 358 t P and 2 195 t N. A best estimation of nutrient removal from water hyacinth and algal harvesting was 2.1 t∙a−1 P and 11.5 t∙a−1 N, and 3.9 t∙a−1 P and 40 t∙a−1 N, respectively. An estimated 341 t∙a−1 P and 674–1 288 t∙a−1 N was sedimented. Denitrification losses are poorly quantified but are possibly comparable to sedimentation. River outfluxes increased by 28.4 t∙a−1 TP and 110 t∙a−1 TN, smaller rates than the influxes, suggesting increasing retention per annum. Upgrading WWTWs in the catchment and refurbishing leaking and overflowing sewers is the most appropriate long-term solution.

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“…Stable isotopes of water (δ 18 O and δ 2 H) have been widely used as tracers for the provenance of water in various reservoirs, including groundwater (Sami, 1992;Harris et al, 1998;Abiye et al, 2011;Ayadi et al, 2018;Leketa et al, 2018), soil water storage (Allison et al, 1983;Selaolo, 1998;Soderberg et al, 2012;Isokangas et al, 2017), groundwater-surface water interaction (Herczeg et al, 1992;Abiye et al, 2015) and vegetation (Evaristo and McDonnell, 2017;Shakhane et al, 2017). Moreover, various water resource assessment studies that incorporate the use of stable isotopes in South(ern) Africa have been documented in Abiye (2013).…”

Section: Introductionmentioning

confidence: 99%

“…The enrichment of groundwater often infers focused recharge occurring from a surface water body or existence of hot springs, while a depleted groundwater often infers direct diffuse recharge from rainfall (Sami, 1992;Healy, 2010). However, an extremely depleted groundwater sample could also infer an exchange of oxygen between CO2 and groundwater in dolomite-rich aquifers (Karolytė et al, 2017;Leketa et al, 2018;Leketa, 2019) rather than a recharge mechanism.…”

Section: Introductionmentioning

confidence: 99%

“…Durowoju et al (2019) specified the isotopic effects in rainfall of Thohoyandou in Limpopo Province and generated the Thohoyandou Local Meteoric Water Line (TLMWL) as δ 2 H = 7.56δ 18 O + 10.64‰ (n = 12). Leketa et al (2018) determined the Johannesburg Local Meteoric Water Line (JLMWL) using 3 years daily rainfall data (δ 2 H=6.7δ 18 O + 10‰, n = 260 and R 2 = 0.92) (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

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Investigating stable isotope effects and moisture trajectories for rainfall events in Johannesburg, South Africa

Leketa

Abiye

2020

WSA

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This study investigated the isotopic composition of daily rainfall in Johannesburg from November 2016 to October 2018. The moisture sources and trajectories for rainfall events of extreme isotopic signatures were deduced using the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT). The results from time series and regression analysis show temperature and amount effects, with low coefficient of determination (R2) values of 0.21 and 0.12, respectively. The rainfall with amounts of <20 mm yielded a meteoric water line (MWL) with a slope of +6.9 and deuterium excess (d-excess) of +11.9‰. Rainfall with amounts of ≥20 mm had slope and d-excess values of +8.2 and +18.6‰, respectively. The lower slope in rainfall of <20 mm indicated the preferential occurrence of sub-cloud re-evaporation on light rainfall. Considering the lack of re-evaporation in heavy rainfall (≥20 mm), its slope and d-excess were approximated to those of incoming or in-cloud moisture prior to condensation. Therefore, a high d-excess of +18.6‰ in incoming moisture indicates evaporation that mainly occurs under warm sea surface temperature and low relative humidity. HYSPLIT shows that the moisture for the most depleted and the most enriched rainfall originates in the higher latitudes but differs in trajectory. The moisture for the most depleted rainfall had long residence in the higher latitudes following a semi-direct trajectory to Johannesburg, over the Atlantic and Indian Oceans. The most enriched rainfall followed a curved anticlockwise trajectory with long residence in the lower latitudes over the Indian Ocean. Circulation of saturated moisture over the warm Indian Ocean leads to a loss of light isotopes, thereby enhancing enrichment in the moisture that moves further inland. HYSPLIT indicated the importance of atmospheric conditions along the moisture trajectory on the signature of Johannesburg rainfall.

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Characterisation of groundwater recharge conditions and flow mechanisms in bedrock aquifers of the Johannesburg area, South Africa

Cited by 15 publications

References 15 publications

An Overview of Aquifer Physiognomies and the δ18O and δ2H Distribution in the South African Groundwaters

An Overview of Aquifer Physiognomies and the δ18O and δ2H Distribution in the South African Groundwaters

Increasing nutrient influx trends and remediation options at Hartbeespoort Dam, South Africa: a mass-balance approach

Investigating stable isotope effects and moisture trajectories for rainfall events in Johannesburg, South Africa

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