scholarly journals Recharge Estimation Using CMB and Environmental Isotopes in the Verlorenvlei Estuarine System, South Africa and Implications for Groundwater Sustainability in a Semi-Arid Agricultural Region

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1362
Author(s):  
Andrew Watson ◽  
Anya Eilers ◽  
Jodie A. Miller
Keyword(s):  
South Africa ◽  
Groundwater Recharge ◽  
Low Flow ◽  
Mean Annual Precipitation ◽  
Severe Drought ◽  
Estuarine System ◽  
Groundwater Mixing ◽  
Dry Spell ◽  
Recharge Rates ◽  
Semi Arid

Groundwater recharge remains one of the most difficult hydrogeological variables to measure accurately, especially for semi-arid environments where the recharge flux is much smaller than in humid conditions. In this study, groundwater recharge was estimated using chloride mass balance (CMB) in the Verlorenvlei catchment, South Africa where the effects of recent severe drought conditions in an already semi-arid environment have impacted both agricultural activity as well as the RAMSAR-listed Verlorenvlei estuarine system. Chloride, 18O and 2H tracers were used to improve understanding of the groundwater flow patterns and allowed the fresh parts of the groundwater system, defined by Ca2+-HCO3− groundwater types, to be separated from those where additional salts were being introduced through groundwater mixing, and thus characterized as Na+-Cl− groundwater types. Recharge rates calculated from CMB in the fresh parts of the system were between 4.2–5.6% and 11.4–15.1% of mean annual precipitation for the headwater valley and mountains of the Krom Antonies and are largely consistent with previous studies. However, much lower recharge rates in the valleys where agriculture is dominant contrasts with previous results, which were higher, since groundwater-mixing zones were not recognised. Although the chloride concentration in precipitation is based on only one year of data between 2015 and 2016, where 2015 had on average 28% less precipitation than 2016, the results provide a snapshot of how the system will respond to increasing drought frequency in the future. The results suggest that low rates of groundwater recharge under dry spell conditions will impact on low flow generations which are required to sustain the Verlorenvlei estuarine lake system. Overall, the study highlights the importance of combining hydrochemical tracers such as bulk chloride and stable isotopes with numerical modelling in data-scarce catchments to fully understand the nature of hydrological resilience.

scholarly journals Floristic analysis of semi-arid mountain ecosystems of the Griqualand West centre of plant endemism, Northern Cape, South Africa

2020 ◽  
Vol 21 (5) ◽  
Author(s):  
Nanette Van Staden ◽  
STEFAN JOHN SIEBERT ◽  
DIRK PETRUS CILLIERS ◽  
DIAN WILSENACH ◽  
ARNOLD WALTER FRISBY
Keyword(s):  
South Africa ◽  
Indicator Species ◽  
Habitat Specialization ◽  
Mean Annual Precipitation ◽  
Endemic Plant ◽  
Mountain Ecosystems ◽  
Floristic Analysis ◽  
Northern Cape ◽  
Plant Endemism ◽  
Semi Arid

Abstract. Van Staden N, Siebert SJ, Cilliers DP, Wilsenach D, Frisby AW. 2020. Floristic analysis of semi-arid mountain ecosystems of the Griqualand West centre of plant endemism, Northern Cape, South Africa. Biodiversitas 21: 1989-2002. The Griqualand West Centre (GWC) is one of 13 centres of plant endemism in South Africa. Despite its unique flora, it remains poorly conserved and studied. A recent study identified an extensive geographical core area for the GWC, but endemic plant species were found to be absent from certain parts within these borders. To address this, we refined the current GWC borders based on an ecological niche model, which predicted that endemic species are restricted to four mountain ranges within GWC. Mountain floras within these refined borders were then floristically compared to assess whether they are hotspots of endemicity. Floristically, the Asteraceae, Fabaceae, Malvaceae, and Poaceae were the dominant plant families. Mountain ecosystems differed from one another at species level, with indicator species explaining the compositional differences. Distribution patterns of indicator species were determined by mean annual precipitation, Ca: Mg ratios, soil pH, cation exchange capacity, iron, and sand content. These environmental factors are possible drivers of niche partitioning, environmental filtering and habitat specialization in each mountain ecosystem. Limestone and banded ironstone habitats were identified as conservation priority areas, since they contained the highest numbers of rare and threatened GWC restricted-range species, of which six were narrow endemics.

scholarly journals Using multiple methods to investigate the effects of land-use changes on groundwater recharge in a semi-arid area

2021 ◽  
Vol 25 (1) ◽  
pp. 89-104
Author(s):  
Shovon Barua ◽  
Ian Cartwright ◽  
P. Evan Dresel ◽  
Edoardo Daly
Keyword(s):  
Land Use ◽  
Groundwater Recharge ◽  
Water Table ◽  
Land Use Changes ◽  
Arid Area ◽  
Land Clearing ◽  
Water Table Fluctuations ◽  
Recharge Rates ◽  
Effects Of Land Use ◽  
Semi Arid

Abstract. Understanding the applicability and uncertainties of methods for documenting recharge rates in semi-arid areas is important for assessing the successive effects of land-use changes and understanding groundwater systems. This study focuses on estimating groundwater recharge rates and understanding the impacts of land-use changes on recharge rates in a semi-arid area in southeast Australia. Two adjacent catchments were cleared ∼180 years ago following European settlement, and a eucalypt plantation forest was subsequently established ∼15 years ago in one of the catchments. Chloride mass balance analysis yields recharge rates of 0.2 to 61.6 mm yr−1 (typically up to 11.2 mm yr−1). The lower of these values probably represents recharge rates prior to land clearing, whereas the higher likely reflects recharge rates following the initial land clearing. The low pre-land-clearing recharge rates are consistent with the presence of old groundwater (residence times up to 24 700 years) and the moderate-to-low hydraulic conductivities (0.31 to 0.002 m d−1) of the aquifers. Recharge rates estimated from tritium activities and water table fluctuations reflect those following the initial land clearing. Recharge rates estimated using water table fluctuations (15 to 500 mm yr−1) are significantly higher than those estimated using tritium renewal rates (0.01 to 89 mm yr−1; typically <14.0 mm yr−1) and approach the long-term average annual rainfall (∼640 mm yr−1). These recharge rates are unrealistic given the estimated evapotranspiration rates of 500 to 600 mm yr−1 and the preservation of old groundwater in the catchments. It is likely that uncertainties in the specific yield results in the water table fluctuation method significantly overestimating recharge rates, and despite the land-use changes, the present-day recharge rates are relatively modest. These results are ultimately important for assessing the impacts of land-use changes and management of groundwater resources in semi-arid regions in Australia and elsewhere.

scholarly journals Using multiple methods to understand groundwater recharge in a semi-arid area

2020 ◽  
Author(s):  
Shovon Barua ◽  
Ian Cartwright ◽  
P. Evan Dresel ◽  
Edoardo Daly
Keyword(s):  
Groundwater Recharge ◽  
Water Table ◽  
Groundwater Resources ◽  
Land Use Changes ◽  
Arid Area ◽  
Plantation Forest ◽  
Land Clearing ◽  
Water Table Fluctuations ◽  
Recharge Rates ◽  
Semi Arid

Abstract. Understanding recharge in semi-arid areas is important for the sustainable management of groundwater resources. This study focuses on estimating groundwater recharge rates and understanding the impacts of land-use changes on recharge in a semi-arid area. Two adjacent catchments in southeast Australia were cleared ~180 years ago following European settlement; in one of these catchments eucalypt plantation forest was subsequently established ~ 20 years ago. Chloride mass balance yields recharge rates of 0.2 to 61.6 mm yr−1 (typically up to 11.2 mm yr−1). The lower of these values probably represent recharge rates prior to land clearing, whereas the higher likely reflects recharge rates following initial land clearing. The low pre-land clearing recharge rates are consistent with the presence of groundwater that has residence times that are up to 24,700 years (calculated using radiocarbon) and the moderate to low hydraulic conductivities (0.31 to 0.002 m day−1) of the clay-rich aquifers. Recharge rates estimated from tritium activities and water table fluctuations reflect those following the initial land clearing. However, recharge rates estimated using water table fluctuations (15 to 500 mm yr−1) are significantly higher than those estimated using tritium renewal rates (0.01 to 89 mm yr−1; typically

scholarly journals Evaluation of Drought Characteristics in Iraq using SC-PDSI

2018 ◽  
Vol 6 (4) ◽  
pp. 177-182
Author(s):  
Thaer K. Jawad ◽  
Osama T. Al-Taai ◽  
Yaseen K. Al-Timimi
Keyword(s):  
Severity Index ◽  
Climatic Research Unit ◽  
Drought Severity ◽  
Arid Zones ◽  
Severe Drought ◽  
Drought Characteristics ◽  
Dry Spell ◽  
Desert Zone ◽  
Semi Arid ◽  
Run Theory

Evaluation of drought characteristics in Iraq by analysis annual growing season of Self-Calibrating Palmer Drought Severity Index (SC-PDSI) for three climatic zones using run theory method. The efficiency of SC-PDSI for drought monitoring was examined from compared with Rainfall Departure from the mean (RD) for three zones (Arid and Semi-Arid, Steppes and Desert) for the period 1981-2015, were derived from Climatic Research Unit (CRU). The spatial interpolation techniques in ArcGIS package has been used, to cover the whole extent of country and extracting the zones. Statistical methods were applied to compute the probability of drought events at every zone. The results showed the years 1999, 2000, 2008 and 2009 experienced droughts in all zones except the desert zone where was experienced severe drought in 2012, while the years 1982 and 1988 experienced received precipitation above-average in all zones. The values of standard deviation of precipitation were compared with precipitation anomalies for each zone, the drier seasons are (2007-2008) and (1998-1999) in all Zones. The wetter seasons are (1987-1988) in Arid and Semi-Arid and Steppes zone, (1994-1995) and (1997-1998) are wetter seasons in Desert zone. Using run theory, the steppes zone have experienced more severe droughts than other zones evaluated in this study and the most susceptible areas to dry spell are steppes and Arid and Semi-Arid Zones during study period. While the desert zone experienced less droughts.

scholarly journals Groundwater recharge rates and surface runoff response to land use and land cover changes in semi-arid environments

2016 ◽  
Vol 5 (1) ◽  
Author(s):  
S. O. Owuor ◽  
K. Butterbach-Bahl ◽  
A. C. Guzha ◽  
M. C. Rufino ◽  
D. E. Pelster ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Groundwater Recharge ◽  
Surface Runoff ◽  
Land Cover Changes ◽  
Arid Environments ◽  
Recharge Rates ◽  
Semi Arid

scholarly journals SWB Modeling of Groundwater Recharge on Catalina Island, California, during a Period of Severe Drought

Water ◽  
2018 ◽  
Vol 11 (1) ◽  
pp. 58 ◽  
Author(s):  
Jeanette Harlow ◽  
Benjamin Hagedorn
Keyword(s):  
Land Cover ◽  
Groundwater Recharge ◽  
Open Space ◽  
Field Studies ◽  
Soil Water Balance ◽  
Sensitivity Analyses ◽  
Severe Drought ◽  
Spatial Trend ◽  
Mass Balance Method ◽  
Recharge Rates

This study applied a soil water balance (SWB) model to simulate groundwater recharge on Catalina Island, California, for the years 2008–2014, a period that coincided with a severe drought. Island-wide average recharge ranged from 0.05 mm/year in 2013 to 82.3 mm/year in 2008, with a 7-year mean of 23.0 mm/year. High recharge is primarily associated with east-facing mountain fronts and the land cover types “developed, open space” and “herbaceous”. This spatial trend is also reflected in recharge estimates for groundwater well locations produced by the Cl mass balance method. Only in 2008 did all areas of the island experience recharge, while the recharge was very low during the drought years 2009 and 2012–2014. Sensitivity analyses indicate an unresolved discrepancy in land cover classification (i.e., herbaceous grass dominated vs. chaparral and coastal sage dominated) to be a significant factor. In a scenario where herbaceous grass dominates, as field studies from the early 1980s imply, recharge estimates nearly double. Nevertheless, the overall low recharge rates presented herein and the fact that drought conditions in Southern California have worsened since 2014 suggest that large parts of the island may not have received any recharge in nearly a decade.

scholarly journals Evaluation of Drought Characteristics in Iraq using SC-PDSI

2018 ◽  
Vol 6 (3) ◽  
pp. 94-99 ◽  
Author(s):  
Thaer K. Jawad ◽  
Osama T. Al-Taai ◽  
Yaseen K. Al-timimi
Keyword(s):  
Severity Index ◽  
Climatic Research Unit ◽  
Drought Severity ◽  
Arid Zones ◽  
Severe Drought ◽  
Drought Characteristics ◽  
Dry Spell ◽  
Desert Zone ◽  
Semi Arid ◽  
Run Theory

Evaluation of drought characteristics in Iraq by analysis annual growing season of Self-Calibrating Palmer Drought Severity Index (SC-PDSI) for three climatic zones using run theory method. The efficiency of SC-PDSI for drought monitoring was examined from compared with Rainfall Departure from the mean (RD) for three zones (Arid and Semi-Arid, Steppes and Desert) for the period 1981-2015, were derived from Climatic Research Unit (CRU). The spatial interpolation techniques in ArcGIS package has been used, to cover the whole extent of country and extracting the zones. Statistical methods were applied to compute the probability of drought events at every zone. The results showed the years 1999, 2000, 2008 and 2009 experienced droughts in all zones except the desert zone where was experienced severe drought in 2012, while the years 1982 and 1988 experienced received precipitation above-average in all zones. The values of standard deviation of precipitation were compared with precipitation anomalies for each zone, the drier seasons are (2007-2008) and (1998-1999) in all Zones. The wetter seasons are (1987-1988) in Arid and Semi-Arid and Steppes zone, (1994-1995) and (1997-1998) are wetter seasons in Desert zone. Using run theory, the steppes zone have experienced more severe droughts than other zones evaluated in this study and the most susceptible areas to dry spell are steppes and Arid and Semi-Arid Zones during study period. While the desert zone experienced less droughts.

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