W. Mike Edmunds

Fluoride in Natural Waters

The element fluorine has long been recognised to have benefits for dental health: low-fluoride intake has been linked to development of dental caries and the use of fluoride toothpastes and mouthwashes is widely advocated in mitigating dental health problems. Fluoridation of water supplies to augment naturally low fluoride concentrations is also undertaken in some countries. However, despite the benefits , optimal doses of fluoride appear to fall within a narrow range. The detrimental effects of ingestion of excessive doses of fluoride are also well documented. Chronic ingestion of high doses has been linked to the development of dental fluorosis, and in extreme cases, skeletal fluorosis. High doses have also been linked to cancer (Marshall 1990), although the association is not well-established (Hamilton 1992).

A 700-year history of groundwater recharge in the drylands of NW China

A 700-year semi-quantitative history of diffuse groundwater recharge in the Badain Jaran Desert (Inner Mongolia) is proposed on the basis of solute data from multiple unsaturated zone groundwater profiles using mass balance of chloride to establish recharge rates and profile chronologies. Four relatively humid (1330—1430, 1500—1620, 1700—1780 and 1950—1990) and three relatively arid phases (1430—1500, 1620—1700 and 1900—1950) are discernable across the profiles. The recharge history broadly reflects multidecadal to centurial timescale precipitation changes in the northern Tibetan Plateau and suggests that variations in East Asian Summer Monsoon intensity affect desert recharge rates. Uncertainties in the records owing to assumptions about the Cl inputs are examined by comparing deterministic and stochastic Cl input scenarios. Such records are valuable for assessing spatial aspects of climate changes in the region, as well as for informing sustainable water resource management strategies for northwestern Chinas drylands.

Renewable and non-renewable groundwater in semi-arid and arid regions

Abstract For thousands of years humans have adapted to live within the limits of the water cycle. Groundwater has generally provided reliability in supplied in semi-arid and arid regions through periods of drought, but now, within a generation, a global water crisis has developed,due to poor resource management since the scientific evidence has been clear, that water withdrawals exceed natural rates of renewal. For groundwater it is vital that finite amounts of any renewable resource can be recognised and quantified. In areas with low rainfall geochemical techniques are well-suited to recharge estimation. Unsaturated zone data using the chloride mass balance, linked to regional studies are described from sandy area of the African Sahel, which can provide reliable estimates of renewable amounts of water, taking into acount also the spatial variability. Results using this approach from around the world indicate that a cut-off in significant recharge at the regional scale occurs at around 200 mm/yr mean annual rainfall, although some preferential recharge may still occur via river channels. Under more arid conditions mining of non-renewable palaeowaters is being widely practiced. Chemical and isotopic indicators are able to confirm the timing and mode of emplacement of these waters as a guide to their non-renewability. Water quality issues also emerge which can threaten and further diminish the amounts of the renewable reserves. Salinity encroachment from excessive pumping (in addition to salinisation due to agriculture) poses considerable threats. Other issues considered include naturally occurring high nitrate concentrations related to past vegetation cover and in some cases the high baseline concentrations of certain elements arising from natural geological environments. A sound scientific basis is yet required for improved water management — for improved definition of the renewable resource and indications of non-renewable waters, water quality distribution and stratification and in providing early warning of change and the design of monitoring strategies. Above all an integration of available scientific evidence into policy making is badly needed.

Groundwater recharge in an arid grassland as indicated by soil chloride profile and multiple tracers

&NA; Previous studies have shown that shallow groundwater in arid regions is often not in equilibrium with near‐surface boundary conditions due to human activities and climate change. This is especially the case where the unsaturated zone is thick and recharge rate is limited. Under this nonequilibrium condition, the unsaturated zone solute profile plays an important role in estimating recent diffuse recharge in arid environments. This paper combines evaluation of the thick unsaturated zone with the saturated zone to investigate the groundwater recharge of a grassland in the arid western Ordos Basin, NW China, using the soil chloride profiles and multiple tracers (2H, 18O, 13C, 14C, and water chemistry) of groundwater. Whereas conventional water balance and Darcy flux measurements usually involve large errors in recharge estimations for arid areas, chloride mass balance has been widely and generally successfully used. The results show that the present diffuse recharge beneath the grassland is 0.11–0.32 mm/year, based on the chloride mass balance of seven soil profiles. The chloride accumulation age is approximately 2,500 years at a depth of 13 m in the unsaturated zone. The average Cl content in soil moisture in the upper 13 m of the unsaturated zone ranges from 2,842 to 7,856 mg/L, whereas the shallow groundwater Cl content ranges from 95 to 351 mg/L. The corrected 14C age of shallow groundwater ranges from 4,327 to 29,708 years. Stable isotopes show that the shallow groundwater is unrelated to modern precipitation. The shallow groundwater was recharged during the cold and wet phases of the Late Pleistocene and Holocene humid phase based on palaeoclimate, and consequently, the groundwater resources are nonrenewable. Due to the limited recharge rate and thick unsaturated zone, the present shallow groundwater has not been in hydraulic equilibrium with near‐surface boundary conditions in the past 2,500 years.

Chapter 5.3:Groundwater Age and Quality

The pressures on groundwater quality and quantity have increased dramatically during the past 50 years due to increasing demands for freshwater and contamination from a wide range of human activities. Before 1950 the human impact on groundwater quality was insignificant or limited, and the groundwat...

An accessible hydrogeological tool to monitor critical groundwater resources in hard-rock aquifers

Groundwater resources are increasingly being relied on in rural areas for income generation and food security. However, there is currently a lack of simple, yet accessible hydrogeological tools to monitor critical groundwater resources, both for quantity and quality. This is particularly true in developing countries underlain by fractured hard rock aquifers, with low productivities. Electrical conductivity (EC) meters are presented here as an easy-to-use tool that can provide real-time data collection to enhance routine groundwater monitoring in rural areas. A program was established within a fractured hard rock watershed for over a year in Rajasthan, India to determine the effectiveness and controls over EC as a monitoring tool. The initial groundwater quality in this region was largely influenced by rainfall, modified by evapotranspiration with recognizable input from water-rock interaction in the later months following the monsoon season. Chloride concentrations were linearly correlated with EC in all of the sampled groundwater, but the strength of the correlation attenuated in the months following the monsoon. Recharge rates were estimated using the chloride mass balance (CMB) approach, and then compared to the recharge rates derived from using EC as a surrogate for in what is referred to here as the CMB-EC approach. Recharge rates estimated from the CMB and CMB-EC methods were statistically similar (p=0.44).

Agricultural Structure Adjustment and Ecosystem Restoration Planning at the Village Level to Combat Desertification: A Pilot Study in the Minqin Basin, Northwest China

A village-scale approach was developed to break the cycle between desertification and poverty by providing sustainable employment and income, promoting environmental restoration by reducing water consumption, and integrating poverty amelioration with environmental restoration to ensure that solving one problem does not create new ones. The advantages of high-efficiency water-saving planting, a profitable livestock system, a sand-processing industry, and sand control and afforestation are integrated into what we call the Zhengxin pattern, which offers overall ecological and environmental benefits superior to those of competing approaches. The overall output efficiency of the Minqin basin water resources will increase threefold.