UWCScholar :: Browsing by Author "Xu, Yongxin"

Browsing by Author "Xu, Yongxin"

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Application of enviromental and hydrochemical analysis to characterize flow dynamics in the Sakumo Wetland, Ghana
(University of the Western Cape, 2018) Laar, Cynthia; Xu, Yongxin
This research focused on understanding the current hydrogeology of the Sakumo wetland by developing a conceptual flow model and simulating the groundwater flow system. The purpose of the model is to assist in understanding the groundwater flow system and quantify the water fluxes contributing to the wetland water storage. The research adapted quantitative, qualitative and mixed analysis to characterize the water flow in the basin. This involved the use of numerical modelling techniques to determine the zones of groundwater discharge to the wetland and zones of wetland water released for groundwater recharge. Field investigation were carried out to estimate the hydraulic parameters and sample rainwater, wetland water and groundwater. The Sakumo wetland aquifer is situated in the quaternary unit consisting of sandy clay and weathered quartzite. The average annual precipitation in the study area from 1970 to 2016 was estimated at 760 mm/yr. Groundwater recharge rate was estimated as 5% of the mean annual rainfall which provided inputs into the numerical groundwater flow model. Evaporation from the wetland and evapotranspiration from the basin estimated using the Hargreaves and Samani method were 1341 mm/a and 546 mm/a, respectively. The hydrogeologic conceptual model was developed from the geology, borehole lithology, groundwater and wetland water levels.
Assessment of groundwater management for domestic use from IWRM perspective in upper Limphasa river catchment, Malawi
(University of the Western Cape, 2012) Kanyerere, T.; Xu, Yongxin; Saka, John
The research problem for this study is the limited and unsuccessful implementation of the IWRM concept. This thesis has argued that comprehensive assessment of physical and socioeconomic conditions is essential to provide explanation on factors that limit the successful execution of the IWRM approach. It has further argued that the local IWRM works as proxy for full and successful implementation of the IWRM approach.To contextualise this thesis, the prevailing physical and socioeconomic factors in Malawi in relation to current management and usage of water resources were explained.With 1,321m3 per capita per year against index thresholds of 1,700-1,000m3 per capita per year, this study showed that Malawi is a physically water stressed country but not physically water scarce country although economically it is a water scarce country. This novelty is against some literature that present Malawi as a water abundant country.Again, this study showed that executing a full and successful IWRM in Malawi remains a challenge because of the prevailing socioeconomic situation in terms of water policies,water laws, institutions and management instruments. These aspects have not been reformed and harmonised to facilitate a successful operation of the IWRM approach.The main water-related problem in Malawi is the mismanagement of the available water resources. This is largely due to the lack of implementing management approaches which can generate systematic data for practical assessment of water resources to guide the coordinated procedure among water stakeholders working in catchments. This lack of implementing a coordinated management approach commonly known as integrated water resources management (IWRM) can be attributed to various reasons that includei) lack of comprehensive assessment of factors that can explain lack of successful IWRM implementation at catchment level and ii) lack of methods to demonstrate data generation and analysis on quantity, quality and governance of water that show practical operation of IWRM at community level using groundwater as a showcase among others.This study revealed that introducing local IWRM requires a prior knowledge of the evolution and role of the full IWRM concept in the international water policy which aimed at addressing broader developmental objectives. Globally, the current status of the IWRM concept has potential to address such broader developmental objectives, but sustaining IWRM projects where they have been piloted showed slow progress. Basing on the factors that slow such a progress, local IWRM approach has emerged as a proxy to execute the full IWRM as demonstrated in chapter 8 in this thesis. However, the observed lack of sustainable resources to fund continual functioning of local IWRM activities will defeat its potential solution to water management challenges. The main threat for sustainable local IWRM activities is the tendency of national governments to decentralise roles and responsibilities to local governments and communities without the accompanying financial resources to enable the implementation of the local participation, investments and initiatives at local level. If this tendency could be reversed, the contribution by local IWRM towards solving management problems in the water sector will be enormous. Chapter four has provided the general case-study approach used in this study in terms of research design, data collection methods, data analysis methods, ethical consideration and limitation of the current study within the context of water resource management with a focus on groundwater management.Using geologic map, satellite images, photographs and hydrogeologic conceptual model, the following results emerged: 1) that the Upper Limphasa River catchment has fractured rock aquifer with limited permeability and storage capacity; 2) The topographic nature and north-south strikes of the lineaments explained the north-south flow direction of groundwater in the catchment; 3) The drainage system observed in the Kandoli and Kaning’ina Mountains to the east and west of the Upper Limphasa River catchment respectively (Fig. 5.1; Fig.5.2) formed a groundwater recharge boundary; 4)The regional faults in the same mountains (Fig. 5.1; Fig.5.2) formed structural boundar as well as hydrogeologic boundary which controlled flow direction of the groundwater;5) the hydrogeologic conceptual model showed the existence of the forested weathered bedrock in the upland areas of the entire catchment which formed no-flow boundary and groundwater divide thereby controlling the water flow direction downwards (Fig. 5.9);6) The major agricultural commercial activities existed in Lower Limphasa catchment while only subsistence farming existed in Upper Limphasa catchment. This knowledge and visualization from the map (Fig. 5.3) and conceptual model (Fig.5.9) showed interactions between upland and lowland areas and the role of physical factors in controlling groundwater flow direction in the catchment. It also provided the enlightenment on implications of socioeconomic farming activities on water management. These insights enabled this study to recommend the need for expedited implementation of holistic effective management for sustainable water utilization.Using different physical factors, water scarcity indices and methodologies, this study showed that Malawi is a physically water stressed as well as an economic water scarce country. This novelty is against some literature that present Malawi as a water abundant country. Again, despite the high proportion (85%) of Malawians relying on groundwater resource, groundwater availability (storage in km3) is relatively low (269 km3 in Table 6.10) compared to other countries within SADC and Africa. Given the complexity of groundwater abstraction, the available groundwater for use is further reduced for Malawians who depend on such a resource for their domestic and productive livelihoods. Such insights provided the basis for discussing the need for IWRM.Although daily statistics on groundwater demand (i: 21.20 litres; 116.91 litres;80,550.99 litres), use (ii: 16.8 litres; 92.55 litres; 63,766.95 litres) and abstracted but not used (iii: 4.4; 24.36; 16,784.04 litres) were relatively low per person, per household and per sub-catchment respectively, such statistics when calculated on monthly basis (i.Demand: 636 litres; 3,507.30 litres; 2,416,529.70 litres; ii.Use:504 litres; 2,776.5 litres;1, 913, 008.5 litres iii. Abstracted but not used: 132 litres; 730 litres; 503, 521.2); and on yearly basis (i. Demand: 7,632 litres; 42,087.6 litres; 28,998,356.4 litres; ii. Use: 6,048 litres; 33,318 litres; 22, 956, 102 litres; iii: Abstracted but not used: 1,584 litres; 8,769.6 litres; 6,042,254.4 litres) per person, per household and per sub-catchment provided huge amount of groundwater (Table 6.5). Given the limited storage capacity of fractured rock aquifer in the basement complex geology, the monthly and yearly groundwater demand and use on one hand and abstracted but not used on the other was considered enormous. With the population growth rate of 2.8 for Nkhata Bay (NSO, 2009) and the observed desire to intensify productive livelihoods activities coupled with expected negative effects of climate change, the need to implement IWRM approach for such groundwater resource in the study catchment remains imperative and is urgently needed.In addition to identifying and describing factors that explain the limited groundwater availability in the study catchment, the study developed a methodology for calculating groundwater demand, use and unused at both households and sub-catchment levels.This methodology provided step-by-step procedure for collecting data on groundwater demand and use as a tool that would improve availability of data on groundwater.Implications of such results for IWRM in similar environments were discussed. Despite the time-consuming procedure involved in using the developed methodology, the calculations are simple and interpretation of results is easily understood among various stakeholders. Hence, such an approach is recommended for the IWRM approach which requires stakeholders from various disciplines to interact and collaborate. Nonetheless, this recommends the use of this method as its further refinement is being sought. The analysis on groundwater quality has shown that the dominant water type in the aquifers of Upper Limphasa catchment was Ca-HCO3, suggesting that the study area had shallow, fresh groundwater with recent recharged aquifer. Analyses on physicochemical parameters revealed that none of the sampled boreholes (BHs) and protected shallow dug wells (PSWs) had physical or chemical concentration levels of health concern when such levels were compared with 2008-World Health Organisation(WHO) guidelines and 2005-Malawi Bureau of Standards (MBS). Conversely, although the compliance with 2008-WHO and 2005-MBS of pathogenic bacteria (E.coli) in BHs water was 100% suggesting that water from BHs had low risk and free from bacteriological contamination, water from PSWs showed 0% compliance with 2008-WHO and 2005-MBS values implying high risk to human health. The overall assessment on risk to health classification showed that PSWs were risky sources to supply potable water, hence the need to implement strategies that protect groundwater.On the basis of such findings, the analysis in this study demonstrated the feasibility of using IWRM approach as a platform for implementing environmental and engineering interventions through education programmes to create and raise public awareness on groundwater protection and on the need for collaborative efforts to implement protective measures for their drinking water sources. The use of different analytical methods which were applied to identify the exact sources of the observed contaminants in the PSWs proved futile. Therefore, this study concluded that rolling-out PSWs either as improved or safe sources of drinking water requires further detailed investigations.However, this research recommended using rapid assessment of drinking water-quality (RADWQ) methods for assessing the quality of groundwater sources for drinking. Despite the study area being in the humid climatic region with annual rainfall above 1,000 mm, many of the physical factors were not favourable for availability of more groundwater in the aquifers. Such observation provided compelling evidence in this study to commend the local IWRM as a proxy for the full IWRM implementation for sustainable utilization of such waters. Although institutional arrangements, water laws and water policy were found problematic to facilitate a successful implementation of full IWRM at national level in Malawi, this thesis demonstrated that local institutional arrangements, coordination among institutions, data collection efforts by local community members (active participation), self-regulation among local community committees were favourable conditions for a successful local IWRM in the Upper Limphasa River catchment. This research recommends continuation of such local participation, investment and initiatives as proxy for the full and successful IWRM beyond the study catchment. However, the observed lack of financial resource from central government to facilitates local IWRM activities were seen as counterproductive.In addition, this thesis recommended further studies which should aim at improving some observed negative implications of self-regulations on community members and the limited decentralisation elements from the Department of Water Development.Finally, one of the contributions from this study is the scientific value in using different methods to assess the quality of groundwater as presented in chapter 7. The second value is the demonstration of applying practical techniques to evaluate factors that explain the amount of groundwater storage in the aquifers that can be understood by water scientists, water users, water developers and water managers to implement IWRM collaboratively using groundwater as a showcase. The third contribution is the provision of the procedure to systematically generate data on demand (abstraction) and use of groundwater in unmetered rural areas which has the potential to guide water allocation process in the catchment. Fourthly, the thesis has provided a hydrogeologic conceptual model for the first time for Limphasa River catchment to be used as a visual tool for planning and developing management practices and addressing current water problems.Fifthly, the study has shown how local IWRM works at community level as a proxy for the full implementation of IWRM despite the absence of Catchment Management Agencies. The last contribution is the dissemination of results from this study made through publications and conference presentations as outlined in the appendix.
Assessment of managed aquifer recharge using GIS based modeling approach in West Coast, South Africa
(University of the Western Cape, 2019) Zhang, Heng; Xu, Yongxin
Due to climate change, rapid urbanization, and population expansion, the water demand and supply is showing increasing fluctuations, especially in the arid or semi-arid regions. One of the most important water resource management strategies to improve water security in these drought-prone areas is managed aquifer recharge (MAR), which is developed to recharge groundwater purposefully and increase its storage to overcome the temporal imbalance between local water demand and availability, thus improving water security of the water supply. Assessment of an MAR project requires the integration of many types of methods, data and information from many disciplines, which makes it a challenge. This thesis addressed a GIS based modeling approach for assessing the implementation of MAR in terms of suitable sites as well as appropriate scheme in drought-prone area. The West Coast of South Africa was studied as a case. Langebaan Road
Assessment of microbial contamination of groundwater in upper Limphasa River catchment, located in a rural area of northern Malawi
(Water Research Commission, 2012) Kanyerere, Thokozani; Levy, Jonathan; Xu, Yongxin; Saka, John
In rural Africa, scientific evidence is often lacking to guide the scaling-up of groundwater as the safest source of potable water. An investigation was conducted in the Upper Limphasa Catchment in northern Malawi to determine the safety of groundwater sources and to explore factors influencing water quality. Water samples from 17 boreholes, 6 hand-dug wells and 90 households were analysed for selected parameters. Portable incubators, multi-parameter probe and colorimetric standard methods were used for field measurements, and standard methods were used for laboratory water analysis. Results were compared to specified guidelines of the World Health Organization and Malawi Bureau of Standards to establish the potability of water. Statistical results using non-parametric t-tests indicated that the wells were more contaminated with E. coli bacteria than boreholes (p=6.2x10-6), suggesting non-consideration of local hydrogeologic factors in groundwater development. Water from boreholes that tested negative for pathogens at source tested positive at some households (total coliform: p=0.0042 and E. coli p=7.8x10-7) suggesting the effect of handling practices. Water from wells that was not treated with chlorine showed higher levels of E. coli than treated water from the same sources, confirming the effectiveness of chlorine in reducing pathogenic bacteria in households’ stored drinking-water, reinforcing the scientific basis for scaling up chlorine as effective disinfectant. However, this study demonstrated that chlorine failed to effectively eliminate all pathogens in drinking water. As a case study in tropical rural environments in Africa, these findings on the suitability of using chlorine as disinfectant and on factors explaining groundwater contamination, though provisional, provide a scientific basis for assessing cost-effectiveness and sustainability of scaling-up the use of chlorine as a curative remedy and of systematically investigating local hydrogeologic factors in order to implement measures to protect groundwater quality in poverty-prone rural communities.
Assessment of sustainable groundwater utilization with case studies from semi-arid Namibia
(University of the Western Cape, 2016) Sarma, Diganta; Xu, Yongxin
The thesis addresses sustainability of groundwater utilization in arid and semiarid regions of Namibia. Recharge in this hydrogeological setting occurs as discrete events to aquifers that are bounded in extent. Case studies involving fractured hardrock and alluvial aquifers with aquifer-ephemeral river interaction were considered. The nature of recharge to arid region bounded aquifers was explored. In arid region aquifers, roundwater storage is depleted during extended dry periods due to pumping and natural discharge. Steady state conditions are rarely achieved. With lowering of the water table, evapotranspiration is reduced thus decreasing aquifer discharge. However, depletion of ephemeral river flow is the primary source of water to boreholes. Physical constraints such as river bed and aquifer hydraulic properties set a limit to the degree of natural replenishment possible during flow events. An approach to assessing sustainable yield of a fractured rock aquifer associated with ephemeral river flow is discussed using a case study from rural semi-arid Namibia. Limited data required the simulation results to be verified against geological and hydrogeological constraints. The aquifer’s gain in storage is estimated through numerical simulation. It provides a basis for groundwater scheme management that rely on limited data in semi-arid conditions in sub-Saharan Africa. Aspects related to ephemeral river flow and groundwater recharge to strip alluvial aquifers was addressed in the second case study. The processes controlling infiltration, significance of surface water and groundwater losses, and possible artificial recharge options were investigated through numerical simulation. It was concluded that recharge processes in arid alluvial aquifers differ significantly from those in humid systems. Conjunctive use of surface and groundwater resources require artificial augmentation of aquifer recharge due to constrains in natural infiltration rates. The study provides a reference for sustainable management of alluvial aquifer systems in similar regions. It is seen from the study that high rates of groundwater exploitation deplete surface water resources needed downstream while failure to capture surface flow during flood events cause loss of potential recharge. It is concluded that as water demand in Namibia increases, basin wide combined surface water and groundwater resource evaluation and management have become a necessity.
Book review: estimating groundwater recharge
(Springer Verlag, 2011) Xu, Yongxin
Book review: urban geology
(Springer Verlag, 2012) Xu, Yongxin;
Borehole dilution experiment in a Karoo aquifer in Bloemfontein
(Water Research Commission, 1997) Xu, Yongxin; van Tonder, Gerrit J.; van Wyk, B.; van Wyk, E.; Aleobua, B.
This paper shows that a borehole dilution experiment using common salt is a useful technique for better understanding of some hydrogeological features of a fractured aquifer. A sense of such tracer experiments was performed in the campus site aquifer, a hydrological experiment site of the Institute for Ground Studies at the University of the Orange Free State in Bloemfontein. It is demonstrated that the model for use in homogeneous aquifers may be adapted in fractured aquifers. Results have revealed valuable information on hydraulic parameters of the fracture system at different scales. Profiles of electrical conductivities monitored in several boreholes can be used to locate horizontal fracture zones in the aquifer. These results may provide an important guide to formulate realistic conceptual models for borehole protection zoning. The experiment can also serve as a reference to future experiments of this kind in Karoo aquifers which cover some 50% of the subcontinent of Southern Africa.
Capture zone simulation for boreholes located in fractured dykes using the linesink concept
(Water Research Commission, 2002) Xu, Yongxin; van Tonder, Gerrit J.
Delineation of capture zones for groundwater source protection is normally performed by using numerical codes which are based on the porous medium flow equation. However, boreholes are often sited in or along permeable dykes or single fracture zones through which aquifers are drained. It is very important to take into account dyke-influenced aquifers. This paper makes use of Linesink to simulate permeable dyke or fractured zones and utilises the pathline distribution to delineate the capture zones. Conditions when the influence of a fractured dyke can be considered negligible are also discussed through comparison with stagnation point in a uniform flow field. The approach may be sufficient to illustrate protection zoning requirements when dyke aquifers are considered.
Characterization of macropore structure of Malan loess in NW China based on 3D pipe models constructed by using computed tomography technology
(Elsevier, 2018) Li, Yanrong; He, Shengdi; Deng, Xiaohong; Xu, Yongxin
Malan loess is a grayish yellow or brownish yellow, clastic, highly porous and brittle late Quaternary sediment formed by the accumulation of windblown dust. The present-day pore structure of Malan loess is crucial for understanding the loessification process in history, loess strengths and mechanical behavior. This study employed a modern computed tomography (CT) device to scan Malan loess samples, which were obtained from the east part of the Loess Plateau of China. A sophisticated and efficient workflow for processing the CT images and constructing 3D pore models was established by selecting and programming relevant mathematical algorithms in MATLAB, such as the maximum entropy method, medial axis method, and node recognition algorithm. Individual pipes within the Malan loess were identified and constructed by partitioning and recombining links in the 3D pore model. The macropore structure of Malan loess was then depicted using quantitative parameters. The parameters derived from 2D images of CT scanning included equivalent radius, length and aspect ratio of pores, porosity, and pore distribution entropy, whereas those derived from the constructed 3D structure models included porosity, coordination number, node density, pipe radius, length, length density, dip angle, and dip direction. The analysis of these parameters revealed that Malan loess is a strongly anisotropic geomaterial with a dense and complex network of pores and pipes. The pores discovered on horizontal images, perpendicular to the vertical direction, were round and relatively uniform in shape and size and evenly distributed, whereas the pores discovered on vertical images varied in shape and size and were distributed in clusters. The pores showed good connectivity in vertical direction and formed vertically aligned pipes but displayed weak connectivity in horizontal directions. The pipes in vertical direction were thick, long, and straight compared with those in horizontal directions. These results were in good agreement with both numerical simulation and laboratory permeability tests, which indicate that Malan loess is more permeable in the vertical direction than in the horizontal directions.
Climate change and its influence on the Karst groundwater recharge in the Jinci Spring Region, Northern China
(MDPI, 2017) Jia, Zhenxing; Zang, Hongfei; Zheng, Xiuqing; Xu, Yongxin
Due to climate change and human activities over the last fifty years, the spring flow volume of karst groundwater has sharply diminished in China. Climate change is one of the critical factors that initiates a series of karst hydrogeologic and water ecological environmental problems, because the precipitation shows a decreasing trend while the temperature shows an increasing trend. The Jinci Spring is one of the largest, most famous springs in northern China. This study employed data from the Taiyuan Meteorological Station and ten precipitation stations in and around the Jinci Spring region as well as the runoff data gathered from two hydrological monitoring stations during 1960-2012. The sliding average method and the Mann-Kendall test were used to analyze the variation tendency of precipitation, temperature, and land evaporation in this area. Finally, the following were calculated: the varying pattern of the karst groundwater recharge amount and the response of the recharge amount to precipitation, land evaporation, and river runoff by quantitative analysis. The results indicated that the precipitation and land evaporation amount decreased at first and then subsequently increased. Likewise, the variation trend of the karst groundwater recharge amount in the spring region was roughly consistent with the precipitation variation pattern. In contrast, the temperature displayed an increasing trend. The climate change resulted in a reduction of the karst groundwater recharge amount, and it had the greatest influence in the 1990s, which caused the karst groundwater recharge amount to decrease 26.75 mm as compared to that of the 1960s (about 39.68% lower than that of the 1960s). The Jinci Spring had zero flow during this period. The reduction in precipitation was one of main factors that caused the cutoff of the Jinci Spring.
A conceptual model for the development and management of the Cape Flats aquifer, South Africa
(Water Research Commission, 2010) Adelana, Segun; Xu, Yongxin; Vrbka, Petr
This paper provides an integrated approach to the analysis of the geological, hydrological and hydrogeological characteristics of the Cape Flats: a coastal plain sand formed within the mountains of the Cape Town metropolitan area. The study is mainly based on evaluation of available data, on surface water and groundwater, rainfall and selected springs, to describe the Cape Flats aquifer. Qualitative analysis has shown that both surface water and groundwater of the investigated area are of good quality; whereas sources of contamination indicated are restricted to certain parts of the area. Interpretation of hydrogeological data and aquifer parameters revealed that the Cape Flats aquifer has good storage characteristics to support its development for water supply, although the generally unconfined conditions render it highly susceptible to pollution from the surface. From the analysis of long-term climate data in Cape Town, it is evident that fluctuation exists in the pattern of rainfall; this rainfall pattern has implications for recharge and water management issues in the city. Therefore, a conceptual hydrogeological model was developed to elucidate groundwater flow and recharge mechanisms in the Cape Flats.
Conceptualization of urban hydrogeology within the context of water sensitive urban design: case study of Cape Flats Aquifer
(University of the Western Cape, 2018) Gxokwe, Siyamthanda; Xu, Yongxin; Kanyerere, Thokozani
Urban hydrogeology can be used to facilitate a decision-making process regarding the implementation of water sensitive urban design (WSUD) to manage water systems of periurban cities. This thesis was aimed at providing explanation of how that approach can be applied in Cape Town using Cape Flats Aquifer as a case study. To achieve this main objective, three specific objectives were set, namely, objective 1 which focused on estimating aquifer parameters using Theis analytical flow solution, in order to identify areas for implementation of managed aquifer recharge (MAR) suggested by WSUD principles; Objective 2 focused on conceptualizing groundwater flow system of Cape Flats Aquifer using the Finite Difference Method (FDM), in order to predict aquifer behaviour under stresses caused by the implementation of WSUD; Objective 3 focused on assessing gw-sw interaction using Principal Aquifer Setting, environmental isotope, and hydrochemical analysis, in-order to identify where and when groundwater surface water interaction is occurring, and thus informing the prevention strategies of the negative effluence of such exchanges on WSUD. The analysis of data collected through pumping test approach which were conducted in March, October 2015 and June 2016, showed that average transmissivity ranged from 15.08m2/d to 2525.59m2/d, with Phillipi Borehole (BG00153) having the highest and Westridge borehole 1 (G32961) having the lowest transmissivity values based on Theis solution by Aqua test analysis. Theis solution by excel spreadsheet analysis showed that average transmissivity ranged from 11.30m2/d to 387.10m2/d with Phill (BG00153) having the highest transmissivity and Bellville 2 (BG46052) having the lowest transmissivity. Storativity values ranged from 10-3 to 10-1 with Phillipi borehole (BG00153) having the highest storativity and Lenteguer borehole 1(BG00139) having the lowest values from both analysis. Average transmissivity visual maps showed that highest transmissivity values within the Cape Flats Aquifer can be obtained around the Phillipi area towards the southern part of the aquifer. Storativity maps also showed that the greatest storativity values can be obtained around Phillipi and Lenteguer area. These findings reveal that MAR would be feasible to implement around the Phillipi and Lenteguer area, where aquifer storage and discharge rates are higher.
Conservation status of large branchiopods in the Western Cape, South Africa
(Springer Verlag, 2007) De Roeck, Els R.; VanSchoenwinkel, Bram J.; Day, Jenny A.; Xu, Yongxin; Raitt, Lincoln; Brendonck, Luc
Temporary wetlands are an ecologically and economically important habitat in South Africa. They harbor large branchiopods, known to be flagship species of nonpermanent aquatic habitats, and sensitive to land use changes. In this study we review the current status of large branchiopods in the Western Cape, a South African province subject to increasing agriculture and urbanization. We studied the species diversity and distribution of large branchiopods by sampling 58 temporary wetlands in an area covering about 30% of the Western Cape. Information obtained from field samples was supplemented by incubating resting egg banks from the sampled wetlands. Our data were compared with all known distribution records for large branchiopods in the target region. Based on this combined information, the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List category was assessed for each species. Four of the eight large branchiopod species known to occur in the sampling area were collected. Of all wetlands sampled, 40% harbored large branchiopods. Most anostracan populations were small, and species co-occurred in only one wetland. From the entire Western Cape, 14 species have been recorded in the past. Two of these are already included in the IUCN Red List. Insufficient data are available to determine the IUCN Red Data Category of six other species. A large variation in the telsonic appendages of S. dendyi was found across the studied area. In view of possible ongoing speciation and subsequent radiation, individual populations need protection. Since little information is available, it is difficult to evaluate recent changes in the conservation status of large branchiopods. Their populations are currently very low and have probably diminished in the last few decades. More knowledge about the functioning of temporary systems is needed to manage these vulnerable habitats and conserve their threatened species.
Editor’s message: Building capacity and partnerships towards sustainable utilization of groundwater in Africa
(Springer, 2008) Xu, Yongxin
This Editor’s Message advises the international groundwater fraternity of new opportunities in hydrogeological developments in Africa. It is a fact that groundwater plays a vital role in socio-economic and ecological services in the continent but it has been largely neglected in the past. With the 6th Ordinary Session of AMCOW (African Ministers’ Council on Water) held in Brazzaville, Congo in late May 2007, the profile of groundwater in the continent has been raised.
Effect of temperature on microorganisms and nitrogen removal in a multi-stage surface flow constructed wetland
(MDPI, 2023) Wang, Huiyong; Xu, Yongxin; Chai, Beibei
The effect of low temperature on microbial nitrogen metabolism in constructed wetlands has yet to be extensively investigated. In this study, we analyzed the effects of temperature changes on nitrogen-associated microorganisms and nitrogen metabolism functional genes in a multi-stage surface flow constructed wetland (MSSFCW) using metagenomic sequencing. The treatment of polluted river water in the MSSFCW, which had a mean water temperature (MWT) of ≤17 °C, resulted in a low removal efficiency (RE) for total nitrogen (TN; average RE: 23.05% at 1–17 °C) and nitrate nitrogen (NO3−-N; average RE: −2.41% at 1–17 °C). Furthermore, at a MWT of ≤11 °C, the REs were low for ammonium nitrogen (NH4+-N; average RE: 67.92% at 1–11 °C) and for chemical oxygen demand (COD; average RE: 27.45% at 1–11 °C). At 0.24 m3 m−2 d−1 influent load, the highest REs for TN (66.84%), NO3−-N (74.90%), NH4+-N (83.93%), and COD (52.97%) occurred in July and August, when water temperatures were between 26 and 28 °C.
Estimation of recharge using a revised CRD method
(Water Research Commission, 2001) Xu, Yongxin; van Tonder, Gerrit J.
The cumulative rainfall departure (CRD) method, based on the water-balance principle, is often used for mimicking of water level fluctuations. Because of its simplicity and minimal requirement of spatial data, the CRD method has been applied widely for estimating either effective recharge or aquifer storativity, and consequently gained a focus in South Africa. This paper critically reviews this method and proposes expanded algorithm. Validation of the method under typical South African conditions is discussed based on model-generated and known cases. The study is aided with a user-friendly Excel program called Recharge Estimation Model in Excel (REME).
Evaluation of groundwater flow theories and aquifer parameters estimation
(University of the Western Cape, 2014) Xiao, Liang; Xu, Yongxin; Lin, Lixiang
This thesis deals with some fundamental aspects of groundwater models. Deterministic mathematical models of groundwater are usually used to simulate flow and transport processes in aquifer systems by means of partial differential equations. Analytical solutions for the deterministic mathematical models of the Theis problem and the transient confined-unconfined flow in a confined aquifer are investigated in the thesis. The Theis equation is a most commonly applied solution for the deterministic mathematical model of the Theis problem. In the thesis, a most simplified similarity transformation method for derivation of the Theis equation is proposed by using the Boltzmann transform. To investigate the transient confined-unconfined flow towards a fully penetrating well in a confined aquifer, a new analytical solution for the deterministic mathematical models of interest is proposed in the thesis. The proposed analytical solution considers a change of hydraulic properties (transmissivity and storativity) during the confined-unconfined conversion. Based on the proposed analytical solution, a practical method to determine distance of the conversion interface from pumping well and diffusivity of the unconfined region is developed by using a constant rate test. Applicability of the proposed analytical solution is demonstrated by a comparison with previous solutions, namely the MP and the Chen models. The results show that the proposed analytical solution can be used to assess the effect of the change of diffusivity on the transient confined-unconfined flow. The MP model is only accepted if the transmissivity during the confined-unconfined conversion is constant. The Chen model, given as a special case of the proposed analytical solution, is limited to the analysis of the transient confined-unconfined flow with a fixed diffusivity. An important application of groundwater models is to estimate parameters, such as hydraulic properties and flow dynamics, of groundwater systems by assessing and analysing field data. For instance, the pumping and the hydrochemistry and environmental tracer tests are two effective ways to obtain such data. To evaluate hydraulic properties of aquifer systems by derivative interpretation of drawdown data from pumping tests, a new diagnostic analysis method is proposed based on a lg-lg drawdown derivative, dlgs/dlgt, and the differentiation algorithm namely Lagrange Interpolation Regression (LIR) in the thesis. Use of a combined plot of dlgs/dlgt and a semi-lg drawdown derivative (ds/dlgt) is made to identify various flow segments during variable discharge tests with infinite conditions, constant rate tests in bounded aquifers and tests involving double-porosity behaviours. These can be applied to further characterize pumped aquifers. Compared to traditional diagnostic analysis method using plot of ds/dlgt alone, the combined drawdown derivative plot possesses certain advantages identified as: (1) the plot of dlgs/dlgt is strikingly sensitive for use in unveiling differences between pumping and its following recovery periods in intermittent variable discharge tests; (2) storativity (S) of pumped aquifers can be evaluated by using the combined plot; and (3) quantitative assessments of double-porosity behaviours can also be achieved. Based on two case studies, advantages and disadvantages of uses of the LIR and other existing differentiation methods in calculations of numerical drawdown derivative are demonstrated in practice. The results suggest that the LIR is a preferred method for numerical differentiation of drawdown data as it can be used to effectively minimise noisy effects. The proposed derivative approach provides hydrologists with an additional tool for characterizing pumped aquifers. Use of hydrochemistry and environmental tracer tests to assess flow dynamics of groundwater systems is demonstrated via a case study in the dolomite aquifer of South Africa. An emphasis is on determining mean residence times (MRTs) of the dolomite aquifer by means of an appropriate box model with time series of 14C values of dissolved inorganic carbon (14C-DIC) and initial 14C activities of spring samples during 1970s and 2010s. To obtain the calibrated 14C MRTs, 13C values of dissolved inorganic carbon (δ13C-DIC) of the spring samples are applied to estimate mineral dissolution in the dolomite aquifer and calculate the initial 14C activities. The results indicate that the spring samples have about 50%-80% initial 14C activities. By using the appropriate box model, the calibrated 14C MRTs of the spring system are given within a range from ≤ 10 to 50 years. Additionally, the flow dynamics, including the recharge source and area, the effect of climate change on the temporal trend of the groundwater MRTs and the groundwater flow circulation, of the dolomitic spring system are also discussed for further possible management interventions in the dolomite aquifer.
Foreword to special section: groundwater in Africa
(Wiley-Blackwell, 2010) Bradbury, Kenneth R.; Xu, Yongxin
Geological and hydrgeological characteristics of acid mine drainage from an abandoned coal mine: A case study of Shandi coal mine in Niangziguan spring catchment, Shanxi
(University of Western Cape, 2022) Wang, Zhaoliang; Xu, Yongxin
As Shanxi Province is rich in coal resources, the output of raw coal approximately accounts for one quarter of China's production. It is one of the most important energy and heavy chemical bases and plays a significant role in the sustainable development of the national economy and energy security. With the continuing exploitation of coal resources in Shanxi, water environmental problems such as the destruction of water resources and deterioration of water quality have become increasingly prominent. Especially with the closure of many depleted coal mines, water pollution caused by acid mine drainage (AMD) has become more and more serious, which aggravated the shortage of water resources and threatens the safety of local drinking water supply. Since 2008, more than 100 coal mines have been abandoned in the Yangquan coalfield of Shanxi, and the AMD has polluted the surface water and groundwater in the Niangziguan spring catchment.

Browsing by Author "Xu, Yongxin"

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