Groundwater Assessment at Manukan Island,Sabah: Multidisplinary Approaches

A rapid increase in the number of tourists has placed a heavy demand for freshwater on Manukan Island, a small island located offcoast of Kota Kinabalu, Sabah. Hydrochemical and numerical approaches have been applied in this study to evaluate the groundwater quality of unconfined aquifer lying in Manukan Island, Sabah, East Malaysia. This is vital to enhance better understanding about groundwater management. Hydrochemical analysis output indicated NaCl water type in sampling locations. Seawater intrusion is marked by its relatively high Na⁺, Mg²⁺, Cl⁻ and SO₄ ²⁻ concentrations. Hydrochemical analysis output clearly showed the influence of seawater in groundwater of Manukan Island. The numerical model output proved the influence of seawater in groundwater of Manukan Island by indicating the upconing process at the beneath of the pumping well. Current status of seawater intrusion in Manukan Island is about 14.6% of freshwater and seawater mixing ratio in low lying area of Manukan Island as simulated by SEAWAT-2000 model output. Numerical model SEAWAT-2000 output showed clearly that the upconing process is the possible route of seawater to influence the fresh groundwater aquifer chemistry in Manukan Island. The results have enhanced the current understanding of seawater intrusion in the study area. Future studies will focus on using numerical models to simulate and suggest suitable groundwater management plans in Manukan Island.     

Characterization of Mechanisms and Processes Controlling Groundwater Recharge and its Quality in Drought-Prone Region of Central India (Buldhana,Maharashtra) Using Isotope Hydrochemical and End-Member Mixing Modeling

A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO₃ facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ²H, δ¹⁸O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences.

     

Groundwater Balance and Safe Yield of the coastal aquifer system in NEastern Korinthia, Greece

The northern coastal part of Korinthia prefecture can be characterized as an agrotourism center that has grown and urbanized rapidly. The area is formed of recent unconsolidated material consisting of sands, pebbles, breccias and fine clay to silty sand deposits. These deposits host the main aquifer system of the area, which depends on groundwater as a water resource. Groundwater is the main source for irrigation in the area. A total water volume of 29.2×10⁶–34.3×10⁶ m³ yr⁻¹ was estimated to recharge the aquifer system from direct infiltration of rainfall, streambed infiltration, irrigation return, artificial recharge via flood irrigation and lateral subsurface inflows. The present annual abstraction ranges between 39.2×10⁶ and 44.6×10⁶ m³ yr⁻¹. Groundwater abstraction in dry years exceeds renewable freshwater resources by more than 38%. Approximately 79% of the total abstraction is consumed for agriculture supply. Water balance in the coastal aquifer system is in disequilibrium; a deficit, which ranges from 4.9×10⁶ to 15.4×10⁶ m³ yr⁻¹ exists. The safe yield of the coastal aquifer system has been estimated at 37.1×10⁶ m³ yr⁻¹ for normal hydrological year and 32×10⁶ m³ yr⁻¹ for severely dry hydrological year. The total abstraction is greater than the recharge and the safe yield of the aquifer. The aquifer system has shown signs of depletion, seawater intrusion and quality contamination. The integrated water resources management, securing water in the future, should include measures that augment groundwater budget in the coastal aquifer of the study area.     

The influence of floodplain geohydrology on the distribution of Sarcocornia pillansii in the Olifants Estuary on the West Coast, South Africa

The distribution of Sarcocornia pillansii (Moss) A.J. Scott was determined by water-table depth and electrical conductivity (EC) of the groundwater. Where the groundwater was accessible (<1.5 m) and had a low EC (<80 mS cm⁻¹), S. pillansii extended its roots down to the water-table where a suitable water potential gradient was shown to exist between the soil and roots. In areas where the groundwater was too deep and/or hypersaline, the plants grew on hummocks. The unconfined aquifer below the floodplain is linked to the estuary and although diurnal tidal waves were dampened, water-table level fluctuations were recorded between tidal events. The complex geomorphology of the floodplain influences groundwater flow, in turn affecting the distribution of the salt marsh vegetation.     

Hydrogeochemistry of Groundwater and Its Suitability for Drinking and Agricultural Use in Nahavand,Western Iran

Groundwater is the major source of drinking water in Nahavand city. However, the groundwater quality at the agricultural areas has been deteriorating in recent years. Ground water quality monitoring is a tool which provides important information for water management and sustainable development of the water resources in Nahavand. Hydrochemical investigations were carried out in an agricultural area in Nahavand, western Iran, to assess chemical composition of groundwater. In this study, 64 representative groundwater samples were collected from different irrigation wells and analyzed for pH, electrical conductivity, major ions, and nitrate. The results of the chemical analysis of the groundwater showed that concentrations of ions vary widely and the most prevalent water type is Ca–Mg–HCO₃, followed by other water types: Ca–HCO₃, Ca–Na–HCO₃, and Na–Cl, which is in relation with their interactions with the geological formations of the basin, dissolution of feldspars and chloride and bicarbonate minerals, and anthropogenic activities. Thirty-seven percent of the water samples showed nitrate (NO₃ ⁻) concentrations above the human affected value (13 mg L⁻¹). The phosphorous (P) concentration in groundwater was between 0.11 and 0.90 mg L⁻¹, with an average value of 0.30 mg L⁻¹, with all of the samples over 0.05 mg L⁻¹. The most dominant class C2-S1 (76.5%) was found in the studied area, indicating that sodicity is very low and salinity is medium, and that these waters are suitable for irrigation in almost all soils. Agronomic practices, such as cultivation, cropping, and irrigation water management may decrease the average NO₃ ⁻ concentration in water draining from the soil zone.     

Hydrochemical Characteristics and Sodification of Groundwater in the Shirin Sou, Hamedan, Western Iran

Salinity and sodicity of groundwater are the principal water quality concerns in irrigated areas of arid and semi-arid regions. The hydrochemical characteristics and sodicity of groundwater in the Shirin Sou area, western Iran were investigated in this study by chemical analyses of groundwater samples from 49 wells. Chemical analysis of the groundwater showed that the mean concentration of the cations was in the order: Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, while that for anions was SO₃ ²⁻ > Cl⁻ > HCO₃ ⁻ > NO₃ ⁻. The most prevalent water type is Na–SO₄ followed by water types Na–Cl and Ca–SO₄. The chemical evolution of groundwater is primarily controlled by water–rock interactions: mainly weathering of aluminosilicates, dissolution of sulfate minerals, and cation exchange reactions. Sulfate dissolution and pyrite weathering may both contribute to the SO₄ ²⁻ load of the groundwater. High Na⁺ concentrations in groundwater participate in ion-exchange processes, resulting in the displacement of base cations into solution and raised concentrations in groundwater. The principal component analysis (PCA) performed on groundwater identified three principal components controlling variability of groundwater chemistry. Electrical conductivity, Ca²⁺, Mg²⁺, Na⁺, SO₄ ²⁻, and Cl⁻ content were associated in the same component (PC1) (salinity), most likely linked to anthropogenic activities.     

Extractable and total Fe and Mn contents of three sand dune soils in NW Nigeria

The profile distribution of total, diethylene triamine penta-acetic acid (DTPA)- and 0·1 HCl-extractable Fe and Mn were determined in 12 pedons formed on three contiguous sand dunes in the semi-arid savanna of Nigeria. The total Fe and Mn contents varied from 100 to 3750 and 40 to 11,375 μg g⁻¹, respectively. Values of 0·1 HCl-extractable Fe and Mn varied from 8·0 to 123 and 1·5 to 43·5 μg g⁻¹, respectively. The corresponding values of DTPA-extractable Fe and Mn were 4·5 to 16·0 and 1·0 to 38·8 μg g⁻¹. Total Fe and Mn correlated significantly with clay in nearly all the dunes (p≤ 0·01) but were not significantly correlated with organic matter. The 0·1 HCl-extractable Mn had a positive significant correlation with soil pH (r= 0·58*) in Illela dunes but a negative significant correlation with pH in the Sangiwa dunes (r= −0·75***). The values of extractable Fe and Mn in the sand dune soils are above the critical limits reported in other literature, thus deficiencies of these micronutrients do not pose a problem to crop production in the study area.     

Geophysical Exploration of Shallow Groundwater Aquifers in Arid Regions: A Case Study of Siwa Oasis,Egypt

Geophysical and geological studies play a fundamental role in the strategic and sustainable utilization of natural resources, especially that of fossil groundwater, in arid regions. The geophysical exploration of shallow groundwater aquifers is common in arid regions. In this work, a feasibility study of future development plans in the Siwa Oasis, Egypt, was carried out. A land electric resistivity survey was conducted, and approximately 14 vertical electric soundings were measured covering the Siwa Oasis, northwestern desert, Egypt. A detailed surface geology study was also conducted to study the underground water aquifer. Digital filters were applied to the reduced to pole-available magnetic data covering the area. The normalized source strength transformation and tilt depth were calculated and applied to delineate the possible structures that may control the shallow and deep aquifers in the area. The integrated interpretation showed the presence of four main geoelectric layers forming the shallow section of the Siwa Oasis down to 220 m. These layers varied in their resistivity and rock constituents from very low (0.2 Ω m) to very high (6200 Ω m) values. The calculated hydraulic parameters showed that the uppermost central area and the eastern area were the most promising areas for the required water development. Finally, based on the integrated interpretation and the estimated shallow aquifer potentiality, a land use map for the Siwa Oasis was produced to assist future strategic development of the region.

     

Supply and accumulation of metals in two Egyptian desert plant species growing onwadi-fill deposits

Sandy soils of thewadisin the Eastern Desert of Egypt have a poor retentive capacity for metals. The contents of Ca, Mg, K, Na, Fe, Al, Mn, Co, Ni, Cu and Zn in 37 soils from this area were highly variable. The metal contents of two dominant plant species of the Eastern Desert (Senna alexandrinaandCleome droserifolia) showed no correlation with soil metals. Metals accumulated in the leaves, withCleomehaving overall higher contents of Fe, Al, Mn, Co, Ni, Na and Si thanSenna, even thoughCleometended to grow in soil with low contents of these metals.     

Groundwater control on the suspended sediment load in the Na Borges River, Mallorca, Spain

Groundwater dominance has important effects on the hydrological and geomorphological characteristics of river systems. Low suspended sediment concentrations and high water clarity are expected because significant inputs of sediment-free spring water dilute the suspended sediment generated by storms. However, in many Mediterranean rivers, groundwater dominance is characterised by seasonal alternations of influent and effluent discharge involving significant variability on the sediment transport regimes. Such areas are often subject to soil and water conservation practices over the centuries that have reduced the sediment contribution from agricultural fields and favour subsurface flow to rivers. Moreover, urbanisation during the twentieth century has changed the catchment hydrology and altered basic river processes due to its ‘flashy’ regime. In this context, we monitored suspended sediment fluxes during a two-year period in the Na Borges River, a lowland agricultural catchment (319 km²) on the island of Mallorca (Balearic Islands). The suspended sediment concentration (SSC) was lower when the base flow index (i.e., relative proportion of baseflow compared to stormflow, BFI) was higher. Therefore, strong seasonal contrasts explain the high SSC coefficient of variation, which is clearly related to dilution effects associated with different groundwater and surface water seasonal interactions. A lack of correlation in the Q-SSC rating curves shows that factors other than discharge control sediment transport. As a result, at the event scale, multiple regressions illustrate that groundwater and surface water interactions are involved in the sedimentary response of flood events. In the winter, the stability of baseflow driven by groundwater contributions and agricultural and urban spills causes hydraulic variables (i.e., maximum discharge) to exert the most important control on events, whereas in the summer, it is necessary to accumulate important volumes of rainfall, creating a minimum of wet conditions in the catchment to activate hydrological pathways and deliver sediment to the drainage network. The BFI is also related to sediment delivery processes, as the loads are higher with lower BFI, corroborating the fact that most sediment movement is caused by stormflow and its related factors. Overall, suspended sediment yields were very low (i.e., < 1 t km^− 2 yr^− 1) at all measuring sites. Such values are the consequence of the limited sediment delivery attributable to soil conservation practices, low surface runoff coefficients and specific geomorphic features of groundwater-dominated rivers, such as low drainage density, low gradient, steep valley walls and flat valley floors.     

Potential water sources for Late Quaternary Megalake Jilantai-Hetao,China, inferred from mollusk shell <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr ratios

Lake Jilantai-Hetao, a megalake, was formed some time before 60–50 ka, along the Great North Bend of the Yellow River. The basin is now dry, with most of the area covered by aeolian sand. We are investigating this profound hydrologic change using a number of research approaches. Paleoshorelines of this megalake are best preserved in the Jilantai area in the southwestern portion of the megalake basin. We collected aquatic mollusk shells from littoral sediments at different altitudes around Jilantai and measured their strontium isotope compositions. ⁸⁷Sr/⁸⁶Sr ratios in shell carbonates are different between the high lake phase (~1,080–1,050 m altitude) and the low lake phase (~1,044–1,030 m altitude), with a small shift in average strontium ratios to more radiogenic values during the low lake phase. Based on regional hydrology and physical geography, we conclude that water from the Yellow River was the dominant water source supplying this megalake. ⁸⁷Sr/⁸⁶Sr ratios of modern water samples suggest the Yellow River was the dominant water source during the high lake phase, but that the relative contribution of Yellow River water to the megalake was reduced, and that the relative contributions of local precipitation and groundwater increased, during the low lake phase.     

Groundwater vulnerability and risk mapping for the Basaltic aquifer of the Azraq basin of Jordan using GIS, Remote sensing and DRASTIC

Water consumption in Jordan already exceeds renewable freshwater resources by more than 20% and, after the year 2005, freshwater resources are likely to be fully utilised. Over 50% of supply derives from groundwater and this paper focuses on a small part of the northern Badia region of Jordan that is underlain by the Azraq groundwater basin where it has been estimated that annual abstraction stands at over 100% of the projected safe yield. While water supply is a crucial issue, there is also evidence to suggest that the quality of groundwater supplies is also under threat as a result of salinisation and an increase in the use of agrochemicals. Focusing on this area, this paper attempts to produce groundwater vulnerability and risk maps. These maps are designed to show areas of greatest potential for groundwater contamination on the basis of hydro-geological conditions and human impacts. All of the major geological and hydro-geological factors that affect and control groundwater movement into, through, and out of the study area were incorporated into the DRASTIC model. Parameters included; depth to groundwater, recharge, aquifer media, soil media, topography, and impact of the vadose zone. The hydraulic conductivity of the aquifer was not included in calculating the final DRASTIC index for potential contamination due to a lack of sufficient quantitative data. A Geographical Information System (GIS) was used to create a groundwater vulnerability map by overlaying the available hydro-geological data. The resulting vulnerability map was then integrated with a land use map as an additional parameter in the DRASTIC model to assess the potential risk of groundwater to pollution in the study area. The final DRASTIC model was tested using hydrochemical data from the aquifer. Around 84% of the study area was classified as being at moderate risk while the re mainder was classified as low risk. While the analysis of groundwater chemistry was not conclusive, it was encouraging to find that no well with high nitrate levels was found in the areas classified as being of low risk suggesting that the DRASTIC model for this area provided a conservative estimate of low risk areas. It is recognised that the approach adopted to produce the DRASTIC index was limited by the availability of data. However, in areas with limited secondary data, this index provides important objective information that could be used to inform local decision making.     

Calibration of Shallow Borehole Drilling Sites Using the Electrical Resistivity Imaging Technique in the Granitoids of Central Region,Ghana

The electrical resistivity imaging (ERI) technique has been used to calibrate existing successful and dry borehole drilling locations in the Cape Coast Granitoid Complex of the Central Region of Ghana. The area has a low groundwater potential and most of the communities do not have access to potable water. Surface water is generally expensive to treat and is therefore not considered as a good water supply option in such rural and dispersed communities where incomes are low. Supply of water to communities from existing boreholes is inadequate. Therefore, there was the need to construct more boreholes to increase access to potable water to meet coverage targets. Results show that the ERI technique is capable of detecting shallow bowl-shaped conductive zones up to 75 m represented by low resistivity values mainly due to weathered granitoids and/or fractures within the granitoids. Resistivity values typically less than 500 Ω-m obtained between depths of 10–50 m on model resistivity sections accounted for about 80% of successful productive boreholes. Resistivity values in the range 500–1,500 Ω-m represented marginally successful borehole locations which could be suitable for hand-pump installation and values greater than 1,500 Ω-m were confirmation for dry borehole locations.     

Roles of saltcedar (Tamarix spp.) and capillary rise in salinizing a non-flooding terrace on a flow-regulated desert river

Tamarix spp. (saltcedar) secretes salts and has been considered to be a major factor contributing to the salinization of river terraces in western US riparian zones. However, salinization can also occur from the capillary rise of salts from the aquifer into the vadose zone. We investigated the roles of saltcedar and physical factors in salinizing the soil profile of a non-flooding terrace at sites on the Cibola National Wildlife Refuge on the Lower Colorado River, USA. We placed salt traps under and between saltcedar shrubs and estimated the annual deposition rate of salts from saltcedar. These were then compared to the quantities and distribution on of salts in the soil profile. Dense stands of saltcedar deposited 0.159 kg m⁻² yr⁻¹ of salts to the soil surface. If this rate was constant since seasonal flooding ceased in 1938 and all of the salts were retained in the soil profile, they could account for 11.4 kg m⁻² of salt, about 30% of total salts in the profile today. Eliminating saltcedar would not necessarily reduce salts, because vegetation reduces the upward migration of salts in bulk flow from the aquifer. The densest saltcedar stand had the lowest salt levels in the vadose zone in this study.     

Evaluation of soil physical properties of long-used cultivated lands as a deriving indicator of soil degradation,north Ethiopia

Soil degradation causes low land productivity. To tackle soil degradation, soil management practices have been implemented in the study area. However, less attention has been given to the management of physical soil quality. Hence, the objective of this study is to evaluate soil physical properties of long-used cultivated lands. Twelve Land Mapping Units (LMUs) were identified by overlaying slope and soil maps. Twelve composite and 12 undisturbed soil samples were collected from the 12 LMUs, and soil physical properties analyzed. Soil bulk density varied from 1.22 g cm^?3 in LMU3 to 1.68 g cm^?3 in LMU4. Available water capacity ranged from 0.09 in LMU4 to 0.17 in LMU3. Stability index (SI) values ranged from a low of 3.58 at LUM10 to 62.5 at LMU3; stability quotient (SQ) values ranged from 79.4 at LMU9 to 2782.8 at LUM3. Highest and lowest soil crust index values were found to be 1.53 in LMU5 and 0.29 in LMU9. This study indicated that poor soil management practice in the study area has caused soil physical degradation. Therefore, this study provides insight into improved land management of long-used cultivated land in the semi-arid region of the study area and other similar environments.     

Hydrogeophysical Characteristics of Pan-African Aquifer Specified Through an Alternative Approach Based on the Interpretation of Vertical Electrical Sounding Data in the Adamawa Region,Central Africa

This study was carried out in the Adamawa region, which connects Cameroon, Central African Republic, and Nigeria together. The main objective of this work is to assess the geophysical aspects of the local Pan-African hydraulic conductivity (K), using the vertical electrical sounding technique (VES) as an alternative approach to pumping test. This economical, less-time consuming, and easy-to-process alternative technique provides more accurate hydraulic conductivity values than the traditional pumping test technique. The K values obtained by the VES technique (ranging between 0.4 and 6.0 m/day) match those obtained by the pumping tests results. A thorough analysis of the transmissivity values reveals the existence of two aquifer trends in the region: Trend-1 with transmissivity values ranging from 34.22 to 39.27 m²/day with an average value of 35.44, and Trend-2, with transmissivity values of 7.87–34.44 m²/day with an average value of 16.56. Maps of transmissivity (T), resistivity (ρ), thickness (h), transverse resistance (TR), and hydraulic conductivity (K) of the Pan-African aquifer, derived from quantitative VES data interpretation, are established. These parameters are of paramount importance to the management of groundwater resources. They are important in the sense that geological contexts similar to that of Pan-African aquifer cut across Africa and South America. Therefore, this article will be valuable to regions worldwide that are geologically similar to the Adamawa Region.

     

A geospatial assessment of flood hazard in north-eastern depressed basin,Bangladesh

Floods are a frequently occurring calamity in deltaic Bangladesh. This paper aims to assess the temporal expansion of waterbodies during flooding using geospatial techniques. Several water indices were applied to classify the satellite images at various temporal scales. Among them, the Normalized Difference Water Index (NDWI) showed the highest correlation (r = 0.831; where p = 0.01) with rainfall data. Specifically, the NDWI results showed that perennial waterbodies measured 37 km² and 60 km² in Sunamganj District in 2017 and 2019, respectively. The area of waterbodies notably increased 52-fold from March to April (37 km² to 1958 km²) during the pre-monsoon flash flood of 2017. During the July 2019 monsoon flood, waterbodies started to extend after May and flooded 2784 km² in area. NDVI analysis showed that in 2019, floodwater submerged 361.7 km² of vegetation cover. At the same time, the Surma River's flooding resulted in a 73.9 per cent inundation of the total area of the Sunamganj District. We hope that this study will provide better understanding of the varying nature of floods that occur in the low lying bowl shaped Haor region which will in turn assist the government with flood mitigation.     

Groundwater Assessment for Current and Future Water Demand in the Daka Catchment,Northern Region,Ghana

The use of untreated surface water for domestic purposes has resulted in the infection of some people by guinea worm and other water borne diseases in the Northern Region of Ghana. The aim of this study is to assess the current groundwater quantity and quality conditions in the 7,820 km² Daka catchment and project the water demand in 2025. Results of groundwater analyses generally show good water quality for domestic use. Borehole analyses indicate that the catchment’s groundwater system can be characterized by a regolith aquifer underlain by a deeper fractured rock aquifer in some areas. The current per capita water demand is estimated at 40 l/day although 60 l/day is the desired amount, indicating that with the current population of 363,350, the projected water demand for the communities is 21,800 m³/day. With a projected population of 555,500 in 2025, an expected 33,300 m³/day of water is required. The estimated optimum potential groundwater available for use in the catchment is 154 × 10⁶ m³/year (4.24 × 10⁵ m³/day). However, the current total groundwater abstraction is only 8,876 m³/day or 2% of the optimum. In comparison, the projected total current and 2025 water demands are only 5 and 8%, respectively, of the optimum potential groundwater available for use in the catchment. In addition, only 1,780 m³/day (0.65 × 10⁶ m³/year) or 0.06% of the average annual flow of 1,016 × 10⁶ m³/year of the Daka River is treated for domestic use. These figures reveal that a significantly very large water resource potential exists for both surface and groundwater development in the Daka catchment. It is suggested that their development should proceed conjunctively.     

Water relations and the effects of clearing invasive Prosopis trees on groundwater in an arid environment in the Northern Cape,South Africa

Several Prosopis species have been introduced into South Africa in the last century and many of them have become invasive. This study investigates the water relations, effects of clearing, and the seasonal dynamics of groundwater use by invasive Prosopis trees. The trees were growing on deep sandy soils in the floodplain of an episodic river in the arid Northern Cape Province of South Africa. Data were collected on tree water uptake, evapotranspiration and water table depth over different seasons. Effects of tree clearing on groundwater were quantified by comparing data from a Prosopis invaded and an adjacent cleared area. Transpiration rates were less than 1.0 mm/d throughout the year and the trees showed structural and physiological adaptations to the combined low rainfall and low water holding capacity of the soils by developing very narrow sapwood areas and by closing their stomata. The trees abstracted groundwater as evidenced by the decline in borehole water levels in the Prosopis stand before the rainy season. Groundwater savings of up to 70 m³/month could be achieved in spring for each hectare of Prosopis cleared. The study suggests that clearing of invasive Prosopis would conserve groundwater in the arid parts of South Africa.     

The controls on phosphorus availability in a Boreal lake ecosystem since deglaciation

The sediment record from a 5.3-m core from Sargent Mountain Pond, Maine USA indicates strong co-evolutionary relationships among climate, vegetation, soil development, runoff chemistry, lake processes, diatom community, and water and sediment chemistry. Early post-glacial time (16,600–12,500 Cal Yr BP) was dominated by deposition of mineral-rich sediment, low in organic matter and secondary hydroxides of Al and Fe; pollen indicate tundra conditions; diatom taxa indicate pH between 7.5 and 8, and total P concentrations of about 25 μg L⁻¹, favoring higher productivity. Chemical weathering was rapid, with high alkalinity, pH, Ca, and P in runoff. As climate ameliorated, about 12,500 Cal Yr BP, forest vegetation became established; soils would have developed vertical zonation, including organic matter accumulation, and incipient podzolic horizons, with accumulating secondary hydroxides of Al and Fe that sequestered P in the soils. Labile minerals (primarily apatite, Ca₅(PO₄)₃(OH,F,Cl)) became depleted in the soil, further reducing the supply of P to the lake. Dissolved organic carbon (DOC) from soil organic matter mobilized Al and Fe to the lake where Al(OH)₃ (primarily) and Fe(OH)₃ (minor) were precipitated. The sedimenting hydroxides adsorbed P from the water column, further reducing bioavailable P. These long-term trends of moderating climate, and changing terrestrial biology, soils, and aquatic chemistry and phytoplankton were interrupted by the 1,000-year long Younger Dryas cooling, which led to a temporary reversal of these processes, a period that ended with the major onset of Holocene warming. The sequestration of P by soils would have strengthened because of long-term soil acidification and pedogenesis. The lake was transformed from a more productive, high P, high pH, low DOC system into an oligotrophic, relatively low P, acidic, humic lake over a period of 16,600 years, a natural trend that continues. In contrast to many human-affected lakes that become increasingly eutrophic, many lakes become more oligotrophic during their history. The precursors for that are: (1) absence of human land-use in watersheds, (2) bedrock lithology and soil with a paucity of soluble Ca-rich minerals, and (3) vegetation that promotes the accumulation of soil organic matter, podzolization, and increased export of metal-DOC complexes, particularly Al.