Impact of recent climate variability on an aquifer system in north Belgium

The last decade it has been realised that climate and global change can (and very likely will affect) groundwater reserves. This will have impact on both the economical (groundwater exploitation) and ecological (ecosystems) aspects of aquifer systems. A key issue is the intrinsic variability in hydrodynamics due to natural fluctuations of meteorological conditions. In this paper the results of a modelling study are presented that reconstructs the hydrodynamic evolution of the important Neogene aquifer system in North-East Belgium, between 1833 and 2005. Boundary conditions are defined on a monthly basis. The results show that besides the yearly seasonal fluctuations also multi-year to decadal variations occur. These are especially important in the topographic higher regions like on the Campine plateau and the Campine cuesta, and can severely affect local groundwater dependent ecosystems as found in some protected areas and nature reserves. The same cyclicity is recognized in the intensity and extent of seepage of deep Neogene groundwater in the Nete basin

Groundwater overexploitation and seawater intrusion in coastal areas of arid and semi-arid regions

The exploitation of groundwater resources is of high importance and has become very crucial in the last decades, especially in coastal areas of arid and semi-arid regions. The coastal aquifers in these regions are particularly at risk due to intrusion of salty marine water. One example is the case of Tripoli city at the Mediterranean coast of Jifarah Plain, North West Libya. Libya has experienced progressive seawater intrusion in the coastal aquifers since the 1930s because of its ever increasing water demand from underground water resources. Tripoli city is a typical area where the contamination of the aquifer in the form of saltwater intrusion is very developed. Sixty-four groundwater samples were collected from the study area and analyzed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters Electrical Conductivity, Na+, K+, Mg2+, Cl- and SO42-, which can be attributed to seawater intrusion, where Cl is the major pollutant of the aquifer. The water types according to the Stuyfzand groundwater classification are mostly CaCl, NaCl and Ca/MgMix. These water types indicate that groundwater chemistry is changed by cation exchange reactions during the mixing process between freshwater and seawater. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 25 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high NO3- concentration in the region

Mobility and removal of nitrate in heterogeneous Eocene aquifers

n a study of the principles of lateral and vertical nitrate mobility and removal in unconfined heterogeneous fine sandy Eocene aquifers by long-term observation, no significant nitrate reduction could be observed over short distances (90 m) in the lateral flow direction. Decreasing oxygen contents and limited flow velocity in a downward direction (caused by clay lenses and layers) resulted in a more efficient but incomplete nitrate removal with increasing depth. Chemo-organotrophic and chemo-lithotrophic denitrification coexist in the aquifers. Recharge input of organic matter and the reactivity of sedimentary organic sources, as well as the amounts of pyrite and Fe2+-bearing minerals, control which microbiologically catalysed process finally occurs. Sharp boundaries between different redox zones do not exist due to locally changing availability of organic and inorganic electron donors used for nitrate reduction. Furthermore, preferential flow paths result in a wide spread occurrence of low concentrations of nitrate below the main denitrification zone

Analysis of the groundwater resource decline in an intramountain aquifer system in Central Iran

The Shahrekord aquifer is located in an intramountain basin in Central Iran (90 km SW of Isfahan) and is the main resource of irrigation water for the intensively developed agriculture in the Shahrekord Plain. Early exploitation of the aquifer started back around 1950 but has intensified severely during the last decades. Irrigation water is provided by three means: spring water is tapped, water is pumped from around 650 wells and in historic times more than 100 karizes (or ghanats, deep underground channels that drain the water table and are accessed by shafts) were constructed and provide an additional source of water. However, groundwater levels have declined severely during the last decade, and although systematic piezometric monitoring already started in 1984, it stayed unclear whether the declining trend is related to increased water demand and exploitation or is due to climatic reasons, as around 2000 a severe drought lasted for three years. In this paper, exploitation and precipitation data are combined with the measured piezometric levels to analyse their relationship and help to understand the observed trend in declining groundwater storage. This aquifer is an example of a system that can easily deliver large amounts of groundwater because of a high transmissivity and considerable thickness, but has, for climatic reasons, a limited recharge. This imbalance makes the present level of exploitation unsustainable

Quantification of groundwater exploitation and assessment of water quality risk perception in the Dar Es Salaam Quaternary Aquifer, Tanzania

This study quantified groundwater exploitation and assessed water quality risk perception in the Dar es Salaam quaternary aquifer through a socio-economic survey. Annual total groundwater exploitation was estimated, using the daily per capita consumption of groundwater derived from the household survey. A logistic regression analysis was performed to ascertain the influence of sex, marital status, education level, employment, income, and cost of water on groundwater quality risk perception. It was revealed that most residents of Dar es Salaam use groundwater as a main source of water supply. The results of this study further showed that 78% consider groundwater as a reliable source. Averting strategies for insufficient quantity of groundwater consist of minimizing less necessary water uses, while for poor quality, buying bottled water and water treatment by boiling and using chemicals. The chance for water quality risk perception is 0.205 times greater for married than unmarried household heads, and it is 623 times higher for employed versus unemployed household heads. To get an overall view of the importance of groundwater for domestic needs in Dar es Salaam it is imperative to combine a time series data of groundwater and surface water exploitation

Quantification of submarine groundwater discharge in the Gaza strip

Gaza Strip has suffered from seawater intrusion during the past three decades due to low rainfall and high abstraction from the groundwater resource. On a yearly basis, more than 170 million m(3) of groundwater is abstracted, while the long-term average recharge from rainfall is 24.4 million m(3)/year. Submarine groundwater discharge (SGD) has never been studied in the Gaza Strip, due to lack of experience in this field, next to the ignorance of this subject due to the seawater intrusion process taking place. Continuous radon measurements were carried out in six sites along the Gaza Strip to quantify the SGD rate. The final result shows SGD to occur in all sampled sites. The range of SGD rates varies from 0.9 to 5.9 cmday(-1). High values of SGD are found in the south (Rafah and Khan Younis governorates). The high values are probably related to the shallow unconfined aquifer, while the lowest values of SGD are found in the middle of Gaza Strip, and they are probably related to the Sabkha formation. In the north of Gaza Strip, SGD values are in the range of 1.0 to 2.0 cmday(-1). Considering that SGD would occur with the measured rates in a strip of 100 m wide along the whole coast line, the results in a quantity of 38 million m(3) of groundwater being discharged yearly to the Mediterranean Sea along Gaza coast. Nutrient samples were taken along Gaza Strip coastline, and they were compared to the onshore wells, 600 m away from the Mediterranean Sea. The results show that SGD has higher NO3- + NO2- than nutrient-poor seawater, and that it is close to the onshore results from the wells. This confirms that the source of SGD is groundwater, and not shallow seawater circulation. In a coastal strip of 100 m wide along the Gaza coast, a yearly discharge of over 400 tons of nitrate and 250 tons of ammonium occurs from groundwater to the Mediterranean Sea

Impact of precipitation trends and the North Atlantic Oscillation on phreatic water levels in Low Belgium

A set of 10 representative multi-decade long time series of piezometric levels of phreatic aquifers were selected in different parts of Low Belgium to investigate correlations between groundwater levels, precipitation rates and the North Atlantic Oscillation (NAO) index. Correlations between piezometric levels and precipitation rates are always high and significant at the 5% level for all series. A direct relation between groundwater levels and the NAO is only possible if there is a correlation with aquifer recharge, which in north Belgium is limited to the winter period. Correlation between monthly precipitation and monthly NAO indices are highly temporal, with two distinct periods during which the correlation is significant at the 5% level. In summer (July and August) there is a negative correlation, in winter time (December and January) a positive one. As in summer aquifer recharge is negligible, only the winter NAO index can have an impact on groundwater levels. Of the ten investigated series, only two have a significant correlation at the 5% level, between piezometric levels and the December-January NAO values. Both wells lie in the same region, in the upper part of the lithologically heterogeneous Campine Complex. The local hydrogeological conditions here seem to increase sensitivity to winter NAO modus