Ken W. F. Howard

The sensitivity of parameters in the Penman evaporation equations and direct recharge balance

Abstract The various parameters in the Penman equations and direct recharge balance are varied to determine their influence on the calculated evaporation and recharge amounts. The sensitivity analysis is applied to data from an area of the north Lincolnshire Chalk. Evaporation estimates are found to be particularly sensitive to albedo, radiation constants and wet-bulb temperature. The resultant differences in turn significantly affect recharge estimates. The study also indicates the need to use daily computations of recharge in place of the normally used ten-daily or monthly computations.

Building a new and sustainable “Silk Road economic belt”

The building of the Silk Road economic belt is an exciting prospect that may bring immense economic benefits to Eurasian countries. However, intensive human activities to be induced by it may double the water crisis in central Asia, deteriorate the vulnerable environment, and accelerate energy consumption in this area. To build a new and sustainable Silk Road economic belt, advancing scientific research, reinforcing international collaboration and enhancing education are necessary steps. With careful planning, sound research, good data and the support from governments and the people, the Silk Road economic belt can be developed in an environmentally sustainable manner that is a credit to all involved.

Groundwater recharge in the Victoria Nile basin of east Africa: support for the soil moisture balance approach using stable isotope tracers and flow modelling

Across equatorial Africa, increasing demand for groundwater has raised concerns about resource sustainability and has highlighted the need for reliable estimates of groundwater recharge. Recharge investigations in this environment are typically inhibited by a shortage of good quality meteorological and hydrogeological records. Moreover, when recharge studies are attempted they tend to rely on a single technique and frequently lack corroborating evidence to substantiate recharge predictions. In recent studies undertaken in the Aroca catchment of the Victoria Nile basin in central Uganda, the timing and magnitude of recharge determined by a soil moisture balance approach are supported by stable isotope data and groundwater flow modelling. The soil moisture balance study reveals that recharge averages in the order of 200 mm year−1 and is more dependent on the number of heavy (more than 10 turn day−1) rainfall events than the total annual volume of rainfall. Stable isotope data suggest independently that recharge occurs during the heaviest rains of the monsoons, and further establish that recharge stems entirely from the direct infiltration of rainfall, an assumption implicit in the soil moisture balance approach. Deforestation over the last 30 years is shown to have more than doubled the recharge estimate. Aquifer flow modelling supports the recharge estimates but demonstrates that the vast majority (over 99%) of recharging waters must be transmitted by the aquifer in the regolith rather the underlying bedrock fractures which have traditionally been developed for rural water supplies.

Hydrogeochemical implications of groundwater contamination by road de-icing chemicals

Abstract This hydrogeochemical study concerns the distribution, origins and behaviour of groundwaters in Quaternary sediments of southern Ontario, Canada, containing elevated concentrations of chloride. Major-ion, minor-ion and trace-metal analyses of 37 potential chloride sources and over 400 well waters, 70 urban springs and 30 pore waters are reported. Source chloride concentrations ranged up to 230,000 mg L−1 for brines from southwestern Ontario; for groundwaters in Quaternary sediments, the chlorides range up to 700 mg L−1 for domestic wells, 2,840 mg L−1 for urban springs and 13,700 mg L−1 for shallow pore waters. Regional studies performed in support of the study suggest that very little chloride enrichment is associated with natural chemical evolutionary processes. Background concentrations are in the range 15–20 mg L−1 and these levels are exceeded in over half the wells in the area; potential sources include road salts, landfill leachates, agricultural fertilizers and saline bedrock waters. Most of these sources are found to be chemically pure with 2 or 3 major ions occurring to the virtual exclusion of all other constituents. Source trace-metal concentrations are low and none are diagnostic of origin. Only iodide and fluoride prove useful indicators of source. Iodide is especially useful for differentiating between road salts and saline bedrock waters, sources which are normally indistinguishable using major-ion criteria alone. From an inorganic water quality perspective, trace-metal concentrations in the chloride sources do not appear to be an environmental concern and only the primary chemical components constitute a serious threat to groundwater potability.

Denitrification in a major limestone aquifer

Abstract The Chalk aquifer of eastern-central England is seriously affected by nitrates leached from agricultural land and, like many similar aquifers, its future as a potable resource must depend considerably on the nature and rates of denitrification. The regional distribution of nitrate supports a viewpoint based on thermodynamic criteria that denitrification is actively occurring and that the problem will be short-lived. More detailed considerations based on major-ion and environmental isotope data, however, indicate that denitrification is not significant and that the apparent lowering of nitrate concentration (from > 10 to −1 NO 3 -N) in the apparent direction of flow is due primarily to mixing between waters of different origins. Presence of reduced nitrogen species is possible evidence of denitrification in some older waters (> 4000 yr. B.P.). It is concluded that denitrification can not be relied upon to reduce elevated concentrations of nitrate in modern recharge waters.

Assessment of groundwater vulnerability in the Yinchuan Plain, Northwest China using OREADIC

Groundwater vulnerability assessments provide a measure of the sensitivity of groundwater quality to an imposed contaminant load and are globally recognized as an essential element of all aquifer management and protection plans. In this paper, the vulnerability of groundwaters underlying the Yinchuan Plain of Northwest China is determined using OREADIC, a GIS-based assessment tool that incorporates the key characteristics of the universally popular DRASTIC approach to vulnerability assessment but has been modified to consider important additional hydrogeological factors that are specific to the region. The results show that areas of high vulnerability are distributed mainly around Qingtongxia City, Wuzhong City, Lingwu City, and Yongning County and are associated with high rates of aquifer recharge, shallow depths to the water table, and highly permeable aquifer materials. The presence of elevated NO3− in the high vulnerability areas endorses the OREADIC approach. The vulnerability maps developed in this study have become valuable tools for environmental planning in the region and will be used for predictive management of the groundwater resource.

Post-palaeozoic evolution of weathered landsurfaces in Uganda by tectonically controlled deep weathering and stripping

A model for the evolution of weathered landsurfaces in Uganda is developed using available geotectonic, climatic, sedimentological and chronological data. The model demonstrates the pivotal role of tectonic uplift in inducing cycles of stripping, and tectonic quiescence for cycles of deep weathering. It is able to account for the development of key landforms, such as inselbergs and duricrust-capped plateaux, which previous hypotheses of landscape evolution that are based on climatic or eustatic controls are unable to explain. Development of the Ugandan landscape is traced back to the Permian. Following late Palaeozoic glaciation, a trend towards warmer and more humid climates through the Mesozoic enabled deep weathering of the Jurassic/mid-Cretaceous surface in Uganda during a period of prolonged tectonic quiescence. Uplift associated with the opening South Atlantic Ocean terminated this cycle and instigated a cycle of stripping between the mid-Cretaceous and early Miocene. Deep weathering on the succeeding Miocene to recent (African) surface has occurred from Miocene to present but has been interrupted in the areas adjacent to the western rift where development of a new drainage base level has prompted cycles of stripping in the Miocene and Pleistocene.

Lithological evidence for the evolution of weathered mantles in Uganda by tectonically controlled cycles of deep weathering and stripping

Abstract Landscape evolution in terrains that have been unaffected by glacial or aeolian erosion, occurs by cycles of deep weathering and stripping. Several factors have been proposed to control these cycles including sea level, climate and tectonics. In this study, a tectonic model of landscape evolution recently developed for Uganda, was tested by detailed study of the weathered mantle. The study involved an analysis of weathered-mantle stratigraphy, texture, mineralogy and elemental geochemistry, and was conducted in two catchments of central and southwestern Uganda which feature contrasting geomorphic processes (deep weathering and stripping) and different (post mid-Miocene) evolutionary histories. Application of graphical (sedimentological) logs to weathered-mantle stratigraphy is introduced in this work and represents an improvement upon more subjective classification schemes employed previously. The stratigraphy, texture, mineralogy and elemental geochemistry of the weathered mantle support cycles of deep weathering and stripping predicted by the tectonic model of landscape evolution. In central Uganda, deep weathering of the landsurface as a result of tectonic quiescence since the mid-Miocene is indicated by thick (30 m) weathered profiles that result from prolonged chemical denudation. This is evident from the progressive alteration of crystalline rock from relatively unweathered bedrock fragments at the base of the profile to a ferricrete crust at the top. Lithological evidence indicates that the weathered mantle has developed in situ and that the water table separates environments of different weathering intensity. In southwestern Uganda, stripping of the landsurface following mid-Pleistocene uplift is reflected by thinner, truncated weathered profiles that are not capped by ferricrete and are composed primarily of coarser, less weathered material.

Modeling the transient response of saline intrusion to rising sea-levels.

Sea levels are expected to rise as a result of global temperature increases, one implication of which is the potential exacerbation of sea water intrusion into coastal aquifers. Given that approximately 70% of the worlds population resides in coastal regions, it is imperative to understand the interaction between fresh groundwater and sea water intrusion in order to best manage available resources. For this study, controlled investigation has been carried out concerning the temporal variation in sea water intrusion as a result of rising sea levels. A series of fixed inland head two-dimensional sea water intrusion models were developed with SEAWAT in order to assess the impact of rising sea levels on the transient migration of saline intrusion in coastal aquifers under a range of hydrogeological property conditions. A wide range of responses were observed for typical hydrogeological parameter values. Systems with a high ratio of hydraulic conductivity to recharge and high effective porosity lagged behind the equilibrium sea water toe positions during sea-level rise, often by many hundreds of meters, and frequently taking several centuries to equilibrate following a cease in sea-level rise. Systems with a low ratio of hydraulic conductivity to recharge and low effective porosity did not develop such a large degree of disequilibrium and generally stabilized within decades following a cease in sea-level rise. This study provides qualitative initial estimates for the expected rate of intrusion and predicted degree of disequilibrium generated by sea-level rise for a range of hydrogeological parameter values.

Hydrogeological impacts of road salt from Canada's busiest highway on a Lake Ontario watershed (Frenchman's Bay) and lagoon, City of Pickering.

The quantity of deicing salt applied to paved surfaces in urban watersheds in cold regions has had a significant and cumulative effect on groundwater quality. Whereas road deicing salt is known in general to impact groundwater and surface water quality, quantitative information on the impact of large transport routes is lacking. In this study, we provide a chloride mass balance for an urban stream crossed by a large transport route in south-central Ontario, Canada and quantify likely long-term impacts of salt loading on surface and groundwater resources. The chloride mass balance, supported by hydrochemical analysis, reveals that approximately 50% of the total road salt applied to Pine Creek (1700 tonnes per winter) is removed annually via overland flow with the remainder accumulating in the shallow subsurface resulting in severe degradation of groundwater quality. Moreover, results show that road salt migration is the primary reason for enhanced mineral weathering in the shallow aquifer. During the 2004-05 salting season, runoff and baseflow transport of road salts were responsible for chloride concentrations in the stream of up to 2000 mg L(-1), and delivered approximately 850 tonnes of chloride (about 1400 tonnes of salt) to a shallow (<3.5 m) semi-enclosed lagoon on the shore of Lake Ontario (Frenchmans Bay; 0.85 km(2)). The total chloride delivery to the lagoon from its entire watershed is estimated at 3700 tonnes each year with up to 48% of the total load delivered by baseflow, the remainder from surface water runoff. Present day groundwater chloride concentrations are estimated to be about 80% of long-term concentrations when the system reaches steady state.