Sand Plain Research Articles

Sediment yield, detachment, and runoff from soil under selected parent materials in Southeastern Nigeria.

Soil degradation due to water erosion among other causes has been a major problem in southeastern Nigeria, therefore a study was conducted to determine sediment yield, detachment, and runoff from soil under selected parent material in southeastern Nigeria. The objective was to characterize the selected soils in terms of their physical and chemical parameters, carry out rainfall simulation, and to establish some relationships that exist among studied parameters with selected soil properties. Soil samples were collected in three replicates from twenty locations, 5 location each from 4 geologic formations namely Asu River Group, Bende Ameki Group, Coastal Plain Sand and False bedded Sandstone at a depth of 0 – 20 cm using soil auger. Standard laboratory procedures were followed for samples for routine analyses while the rest was subjected to rainfall simulation at an intensity of 190 mm/hr for a period of 30 minutes under dry and wet conditions of the soils. Result showed that significant P<0.05) differences among studied parameters. Sediment yield under wet and dry states ranged from 0.56 - 3.95 kg m-2 hr-1 and from 0.80 - 4.97 kg m-2hr-1. The highest sediment yield under both conditions was recorded at Ishiagu, Bende, Obinze and Okigwe from ARG, BAG, CPS and FBS derived parent materials, respectively. Detachment under both conditions ranged from 0.04 - 0.13 kg m-2hr-1 and from 0.03 - 0.21 kg m-2 hr- . Similarly, runoff ranged from 79.80 - 125.30 mm and 28.00 – 106.90 mm under wet and dry states. Result also indicated a negative relationship between clay fraction and sediment yield (r= - 0.62) under dry and ( r= - 0.27) under wet condition. Conclusively, the study noted that rainfall has great impact on studied soils as higher values of sediment yield and detachment were noted mostly under dry than in wet conditions.

Woody islands in South Brazilian coastal grasslands: effects of spatial variations on the structure of plant communities

Brazilian costal sand plains (restingas) are widely known for their many vegetation types, often responding to small landform variations which in turn cause quite distinct soil conditions. One interesting and still poorly known physiognomy is the woody patches or islands dispersed over sparse to dense herbaceous matrixes. Our main objective in this paper was to assess how spatial variables, as area and volume of the patches, affect the floristic composition and the community structure of woody patches in south Brazilian coastal grasslands. We analyzed 48 woody patches in four study sites in central coastal Rio Grande do Sul, Brazil. Each woody island was measured, and all vascular plant species above 30 cm were registered and quantified according to an abundance scale. Each species received values from one to five depending on the occurrence in five possible segments of each woody patch. Woody patches varied roughly between 4 and 204 m2. The floristic inventory resulted in 102 species in 49 families, Myrtaceae and Bromeliaceae being the most diversified, with eight and seven species, respectively. A total of 12 life-forms were recognized, the most diversified being trees or potential trees (27 species), herb–subshrub (17), climbers (20), and epiphytes (15). Species richness increased significantly with the size of woody islands, corroborating one of the basic premises of Theory of Island Biogeography. Diversity and abundance of life-forms in the contrary were not significantly different along the different sizes. The comparison of all woody islands from the four study sites indicated a higher similarity within each site, suggesting regional variation in soil properties, past disturbances, or landscape contexts.

Agricultural potentials of floodplain soils with contrasting parent material in Cross River State, Nigeria

This paper reports the soil properties and agricultural potential of floodplain soil in Obufa Esuk Orok, Calabar and Awi, Akamkpa, Cross River State and characterized the soils to develop a baseline for soil improvement and increased agricultural productivity. Floodplain soil developed on coastal plain sand and basement complex soils were examined with regards to their physical and chemical properties. The results showed that both soils were coarse-textured with a high content of sand exceeding 70 %, giving dominant textural classes of loamy sand and sandy loam. The soils were strongly to slightly acid in reaction with mean surface pH values of 5.54 and 5.43 for soil developed on coastal plain sand and basement complex. The surface soil developed in coastal plain sand within Obufa Esuk Orok, Calabar contains moderate amount of exchangeable Mg (0.8-2.2 cmol/kg), available P (10.0 -11.83 mg/kg), total N (0.20-0.25 %) and organic carbon (2.51-3.05 %) and was high in base saturation (93.11-95.50 %) and low in exchangeable acidity. Conversely, the floodplain soil developed on basement complex in Awi, Akamkpa was rated low in key fertility indicators. Hence, floodplain soil under this study notably, those developed on coastal plain soil can be exploited for the cultivation of rice, oil palm, coconut, plantain, pineapple, pepper, fluted pumpkin and sugar cane with judicious application of lime, and N and K fertilizer.Keywords: Floodplain Soil, Soil Fertility, Coastal Plain Soil, Basement Complex

Response of Okra to Incorporating Humic Acid-Derived Active Molecules into NPK Fertilizer and Lime on Coastal Plain Sand in Calabar, Nigeria

This study evaluated the response of okra to NPK fertilizer with humic acid and lime at the University of Calabar, Teaching and Research Farm between October 2015 and January 2016 cropping season. The experiment was laid out in a randomized complete block design (RCBD) with four replications. The experiment consisted of NPK with humic acid and liming materials as treatments. The test crop was okra. The result of initial analysis of the chemical properties of the soil before the experiment showed that the soil was acidic and was low in exchangeable bases, organic matter (1.13%), total nitrogen (0.14%) and ECEC but high in available phosphorus (26.63 mg/kg) and base saturation. After application of treatment, the result showed that 6.2 g of lime and 4.6 g of NPK with humic acid increase the soil pH from 5.6 units in the control to 5.8 in NPK with Humic Acid, 6.0 in NPK with Humic Acid and lime and 6.4 in lime. Organic carbon content, total nitrogen and available phosphorus also increase in like manner. The results for the growth parameters showed that okra height, number of leaves, and pod yield were significantly (p≤0.05) different from the control. Based on the result of this study further research is recommended in other locations to fully ascertain the effects of this treatment using a different combination.

Application of Geophysical Borehole Logs For Aquifer Characterization in Coastal Environment of Lagos, Southwestern Nigeria

Well correlation and aquifer characterization were successfully carried out across a part of Lekki, Lagos state, Nigeria. The formation stratification sequence comprises predominantly of sand and clay with intercalations of both occurring as clayey sand and sandy clay. Three distinct fluid types (saline water, brackish water and fresh water) were delineated. The bulk resistivity (formation and fluid resistivity) ranged from 0 - 80Ωm for saline water sand and clay, 80 – 120 Ωm for the brackish water sand and clay and 120 – 620 Ωm for fresh water. Salinity occurrence was observed throughout the entire study area with depth of occurrence ranging between 14 – 152m. The depth to saline/fresh water interface range from 123 – 167m. Two aquifer types (unconfined and leaky confined aquifers) were observed in the study area. A maximum of five aquifers were delineated across the borehole sections. The depths to the delineated aquifers ranged from 163 – 249m with the aquifer thickness ranging from 10 to 56m. The maximum saline water depth extent was at about 152m (BH7 and BH5). Brackish water (the saline water interface) ranges from about 123.5 – 167m while the minimum depth to freshwater was about 163.5m (BH4) and maximum depth was about 175m (BH8) for all observed logs. The hydrogeological importance of the Coastal Plain Sand (a good aquifer unit) in the study area is under severe threat of continued seawater (saline water) intrusion on its coastal flank as observed from the vulnerability analysis of the study area. The study area is under intense stress from probably heavy abstraction as more than 80% of the observed boreholes were characterized as highly vulnerable and all of the observed boreholes already exceeded the standard range of values for some of the vulnerability parameters particularly.

Spatial-temporal analysis of soil water storage and deep drainage under irrigated potatoes in the Central Sands of Wisconsin, USA

Knowledge of soil water storage and deep drainage is important for improving irrigation efficiency, maximizing crop water use, and understanding groundwater table fluctuation. This is particularly important in sandy soils that depend on irrigation to produce high crop yields. In sandy soils under potato in the Wisconsin Central Sand Plains, soil water storage using tension probes was measured in three irrigation zones over the 2014 and 2015 growing seasons. Soil water storage was estimated across a 78 ha field using apparent electrical conductivity maps. Deep drainage was estimated using the Richards’ equation and Hydrus-1D software. It was found that the average soil water storage ranged from 74 to 110 mm in the top 0.45 m in three irrigation zones in 2014, and from 70 to 95 mm in 2015. Rainfall and irrigation was 387 and 269 mm in 2014, and 328 and 281 mm in 2015. Estimated deep drainage was uniform in three irrigation zones, and ranged from 222 to 244 mm in 2014, and from 167 to 180 mm in 2015. A negative correlation was found between soil water storage and potato yields possibly due to over-irrigation. The methods used in this study can be applied to improve irrigation and water use efficiency.

Soil microbial community size and composition changes along a tanglehead (Heteropogon contortus) gradient in a semiarid region

Invasive plants are a serious concern throughout many rangelands in North America because of their detrimental effects on vegetation community composition, diversity and wildlife habitat. Growing evidence shows that invasive plants affect ecosystem processes such as energy and nutrient cycling and soil microbial associations. Tanglehead (Heteropogon contortus [L.] P. Beauv. ex Roem and Schult.) is a C4, perennial caespitose grass that is rapidly increasing throughout the Coastal Sand Plain in southern Texas. In a field study, we examined the response of soil microbial community size and structure over a 3-year period (2013–2015) along a tanglehead invasion gradient represented by the natives-without-tanglehead plant communities (<15% tanglehead), natives-with-tanglehead mixtures (15–70% tanglehead), and tanglehead-dominated (>70% tanglehead) plant communities. Soil microbial size [microbial biomass carbon (MBC), nitrogen (MBN), and total fatty acid methyl esters (FAME)] differed between natives-without-tanglehead and tanglehead-dominated sites in 2013 and 2015 (dry years). MBC averaged ~200 mg kg−1 soil in natives-without-tanglehead sites but <70 mg kg−1 soil in invaded sites, and total FAME averaged 36 and 41 nmol g−1 soil in native-without-tanglehead and invaded sites, respectively, in 2013 and 44 and 55 nmol g−1 in 2015. Invaded sites had higher saprophytic fungi:bacteria ratios than sites with <15% tanglehead (0.64 vs. 0.53) over all 3 years. We conducted a separate inoculation experiment where tanglehead was planted in native soils that lacked tanglehead to investigate effects of tanglehead inoculation on soil microbial community dynamics; introduction of tanglehead to native soils did not change microbial community structure, size, or relative abundance of key microbial FAME indicators over the course of 18 months. Field study results revealed different soil microbial communities associated with tanglehead, but at what point these communities change during invasion is not clear, and how these effects are related to overall habitat degradation associated with this invasive plant requires further study.

Differential speciation and availability of copper in soils derived from different parent materials in Imo State, southeastern Nigeria

Effective and efficient management of copper (Cu) in soils for optimum crop production and environmental conservation depends on proper knowledge of the various copper forms and fractions in soils as well asparent material. The distribution of forms of Cu in soils of different parent materials (coastal plain sands, alluvium, false-bedded sandstones and Imo clay shale) in Imo State, Southeastern Nigeria was evaluated using sequential extraction procedure, comprising of six fractions; water soluble (WS), exchangeable (EX), specifically sorbed/CO3 bound (SSC), Fe-Mn bound (Fe-Mn), organic matter bound (OMB) and residual bound (RE) fractions. Soil was sampled at 0-15, 15-30, 30-45, 45-60 and 60-75 cm depths from each soil. Data obtained were subjected to analysis of variance and means separation was done by the procedure of Least Significant Difference at 5% probability level. Correlation analysis of the various Cu forms and some soil properties was also carried out. Results showed that the water soluble, specifically sorbed/carbonate bound, Fe-Mn bound, organic matter bound (OMB) and residual bound (RE Cu fractions differed significantly among the soils of the different parent materials. The Fe-Mn bound copper was the dominant fraction in most of the soils, contributing 41.53-46.63% to the total Cu, being highest in the alluvial soil (6.389 mg kg-1) and lowest in the Imo clay shale soil (2.231 mg kg-1). Moderate concentrations of available Cu (0.694-1.456 mg kg-1) were observed and significant differences were observed among the soils. Correlations among the different Cu forms (WS vs EX r - 0.48; EX vs Fe-Mn r −0.46) and some soil properties (OM vs Fe-Mn r −0.86; Ca vs RE r −0.59; Clay Vs Fe-Mn r −0.53) were determined.Key words: copper fractions, copper availability, parent materials, soil properties, southeastern Nigeria

Termite activities and surface characteristics of coastal plain sands

This study evaluated the effect of mound building termites on the increase in the quantity of fine particles of the dimension of clay on the surface of coastal plain sands of south-eastern Nigeria. Six termite mounds were selected in different locations, destroyed completely and sampled in three replications. Surface and subsurface soils were sampled within the periphery of the termite mounds in similar replications as the mounds. Samples were processed and analyzed in the laboratory. Data were analysed using ANOVA, correlation and principal component. Termite mounds were not common but massive, with base diameter more extensive than height. The major determinants (responsible for 28%) of the effects of termite activities on the surface characteristics are total sand, clay and silt + clay. Termite mounds were similar to the surface soil in available phosphorus, exchangeable sodium and potassium, effective cation exchange capacity, fine sand and silt. These similarities result from homogenization through erosion and redistribution of the mound material within the surface soil vicinity. The fortified mound materials redistributed in surface soil vicinity is responsible for the high clay, elevated pH, enhanced effective cation exchange capacity, improved structural stability, minimized leaching and subsequently improved fertility of coastal plain sands.Key words: termite mounds, pedogenesis, acid sands, biopedoturbation, surface fining

Late Quaternary Aboriginal hunter-gatherer occupation of the Greater Swan Region, south-western Australia

The Greater Swan Region is an archaeological study area on the Indian Ocean coast in south-western Australia. It covers the central Swan Coastal Plain and the adjacent part of the formerly emergent Rottnest Shelf. Assessment of Aboriginal hunter-gatherer activity throughout this late Quaternary coastal landscape is based on dated records of open-air sites within their environmental settings, informed by historical accounts of mainland subsistence activities. Artefacts flaked from Eocene fossiliferous chert and other stone, identified, in situ, in dated dune soils on the mainland and in palaeosols and Tamala Limestone successions on Rottnest Island, show that during regressive sea levels human groups were distributed across a sand plain reaching from the Darling Scarp 70 km westward across the emergent Rottnest Shelf. On the mainland, open-air site settings near freshwater sources and terrestrial and estuarine habitats give insight into adaptive strategies of Aboriginal occupiers. A similar occupation pattern is proposed for the emergent shelf. Early Holocene records of terrestrial plant species and freshwater microfauna from Barker Swamp on Rottnest Island imply that freshwater sources and terrestrial habitats were comparable to those of the mainland. Further archaeological investigations on the Rottnest Shelf should include extant and former freshwater swamps on Rottnest Island.

The CO2CRC Otway Shallow CO2 Controlled Release Experiment: Geological Model and CO2 Migration Simulations

CO2CRC is undertaking a feasibility study for a planned CO2 controlled release and monitoring experiment on a shallow fault at the CO2CRC Otway Research Facility. In the first phase of the project, a series of geophysical surveys and groundwater permeability assessments were conducted at the Otway Research Facility to characterise the prospective experimental site and confirm the presence of a shallow fault. The data from the surveys have been integrated into a 3D model of the upper faulted shallow geology of the CO2CRC Otway site. Five properties (hydrostratigraphic unit, horizontal permeability, vertical permeability, fault permeability and P-velocity from refraction tomography) were populated in the 3D grid to produce the final static model. The model has been developed to assist with designing the experiment and conceptualising the shallow stratigraphy and fault structure at the Otway site. Dynamic modelling simulations based on the static model suggest that under certain scenarios it is possible that CO2 could migrate up the fault to the base of the Hanson Plain Sand if injected at approximately 30 m depth. This suggests that the planned fault injection experiment is feasible but additional data is required to validate the geological model and better constrain the modelling simulations.

Radiogenic heat production in the Coastal Plain Sands of Ipokia, Dahomey Basin, Nigeria

This study is aimed at establishing the radiogenic heat production in the Benin Formation of Dahomey Basin using in-situ measurements of elemental concentrations of uranium, thorium and potassium over a kaolin deposits in Ifonyintedo, Ipokia LGA, Ogun State. Super-Spec gamma ray spectrometer is used to obtain varied data of naturally occurring radionuclides over eleven different stations in the Coastal Plain Sands at 1 m height above the ground. The mean heat produced by uranium, thorium and potassium are 294.3, 410.5 and 0.001 ρW kg−1 respectively. The total heat produced in the study area varied from 544.0 to 902.1 ρW kg−1, which classified the study area as Low-to-Moderate Heat Production Potential zone. This classification corresponds to the radiogenic heat characteristics of Benin Formation in Niger Delta.•In-situ measurements of three radioisotopes were made over Coastal Plain Sands of Dahomey Basin.•The mean heat produced by uranium, thorium, potassium and the total radiogenic heat are 294.3, 410.5, 0.001 and 704.79 ρW kg−1 respectively.•The study area is characterized by Low-to-Moderate Heat Production Potential.

Micro-aggregate Indices and Structural stability of Soils under Different Management

Low water stability of soil micro-aggregates accentuated by increased intensity of cultivation and soil degradation are among the significant issues that draw the atten- tion of Soil Scientists due to their effects on soil physical conditions. The study was carried out to quantify changes in micro-aggregate stability indices of soils on coastal plain sands under contrasting land use and management. Soil samples were collected from cassava plots, plantain, maize, rubber plantation, oil palm and 2-season fallow plots with Calapogonium mucunoides. Results revealed significant changes in micro-and macro-aggregate stability indices. Clay dispersion index (CDI) was 0.46 and 0.39 respectively in cassava and maize plots. Parameters such as aggregated silt and clay (ASC), clay flocculation index (CFI) and saturated hydraulic conductivity (Ksat) used as estimates of soil structural stability were significantly (p &lt; 0.05) increased due to 2-season fallow and 10-year oil palm plantation. Two-year fallow increased ASC and CFI by 57 % and 86.5% respectively compared with continuous maize culti- vation. Ten-year cultivation to cassava and maize increased sand content by 18 and 9% respectively and decreased the mean weight diameter (MWD) of water stable aggregates and Ksat. Relationships showed significant (p &lt; 0.05) positive correlation between ASC and CFI and Ksat. Two-year fallow with Calapogonium mucunoides and 10-year oil palm plantation improved the soil micro- and macroaggregate indices. They could be used to conserve the soil and reduce the degradation of soil resources.

Predicting Nitrate Retention at the Groundwater‐Surface Water Interface in Sandplain Streams

AbstractGroundwater‐surface water ecotones present opportunities for nitrate retention because changes in organic carbon availability, redox potential, and nitrate demand often occur at these locations. Although there have been many measurements of nitrate retention and denitrification at the groundwater‐surface water interface, few investigators have quantitatively predicted where nitrogen transformation occurs in this zone. Our main objective was to describe and predict spatial variation in nitrate retention and removal in shallow groundwater among and within streams in the central sand plains of Wisconsin. We predicted that nitrate transformation rates would be positively related to nitrate and particulate organic carbon availability, a negative nonlinear function of dissolved oxygen availability, and would peak at intermediate rates of groundwater discharge. Five sites on four streams were chosen that spanned an order of magnitude in groundwater nitrate concentration. Nitrate retention and N2 production were quantified by determining how nitrate and N2 fluxes changed along nominal 55‐cm groundwater flow paths. Nitrogen transformation was widespread but highly variable within the study sites. Partial least squares regression models explained a much larger amount of variation in nitrate retention and N2 production at the local scale than at the regional scale. Dissolved oxygen availability and groundwater discharge were the most consistent predictors of nitrate retention at both scales. We conclude that nitrate retention at the groundwater‐surface water interface can be predicted but that more research is necessary to determine if nitrate transformation at this ecotone can be modeled at broader scales.

Small mammal and reptile persistence in desert grasslands during a period of low rainfall – Part 1

The abundance of Australia's arid zone vertebrates is typically driven by fluctuations in rainfall, which dictate productivity across functional groups. Many species fluctuate from highly abundant during high rainfall periods to low abundance during low rainfall periods. Although these fluctuations are well documented, little is known regarding the factors affecting fauna persistence during periods of low rainfall. We examined the relationship between several influential factors and the richness and abundance of nocturnal small mammal and reptiles in the spinifex sand plains of central Australia. The study was conducted during a period of low rainfall following the decline of most vertebrate species in the area. Mammals showed species-specific responses, with varying dependencies on cover and climatic factors, whilst reptiles showed a surprisingly limited response to resource abundances and rainfall. The most consistent factor associated with small mammal and reptile abundances was the presence of large predators. Cats had greater suppressive effects on small mammals whilst reptiles declined with greater wild dog presence. These results likely represent a combination of selective foraging and seasonal fluctuations in activity of the two predators. Our results highlight the importance of controlling predator numbers during low rainfall periods to reduce their potential suppressive effects.

Persistence of ground-dwelling invertebrates in desert grasslands during a period of low rainfall – Part 2

Current knowledge on the life history of Australia's arid zone invertebrates is sparse. From the studies conducted in arid zones globally, the primary drivers of invertebrates are thought to be climate, particularly temperature and rainfall. In Australia, a limited number of studies have shown vegetation and inter-species interactions are also highly influential. We investigated the effects of multiple potential drivers on ground-dwelling invertebrates in the spinifex sand plains of central Australia. The study was conducted during a period of low rainfall immediately following several years of higher than average rainfall. Results supported the trends found globally, with rainfall and temperature the most consistent drivers. Vegetation cover was not found to be an important driver; however increased abundance of large vertebrate predators coincided with greater abundance of many invertebrate orders. Areas supporting greater invertebrate abundances likely attract predators, particularly during periods when resources are low, and potentially play an important role in sustaining their populations during these periods. No suppressive effects were found, indicating many invertebrates can withstand the higher predator pressure apparent during low rainfall periods. This study highlights the important roles invertebrates play in ecosystem functioning and a need to gain a greater understanding of this little known group.

Population ecology of some keystone tree species in the Jebel Marra region of Darfur

Populations of Albizia amara, Acacia senegal, Anogeissus leiocarpus, and Balanites aegyptiaca were monitored in five habitats in the Jebel Marra region: clay plains, sand plains, wadis, northern slopes, and southern slopes of the Jebel Marra (mountain) region. The plains and wadi habitat types had been regularly disturbed because of cycles of shifting cultivation. When land was prepared for cultivation, seedlings and juvenile plants were removed, leaving only larger adult plants, and, therefore, unstable tree populations, lacking juveniles, and growing in fallow lands. A. amara and A. senegal were more abundant than A. leiocarpus and B. aegyptiaca. The healthiest populations, with more juvenile recruits, were found in the grazing lands at higher elevations. However, A. amara and A. senegal showed stable size structure in both grazing and fallow lands. In general, in the four study species, we see a decline in growth and reproduction (with growth measured as tree height and number of branches, and reproduction assessed in terms of number of fruits per tree and dry weight of seeds) along a progression from fallow lands to the grazing lands, and, separately, from lower to higher altitudes. The resilience potential of each species in the fallow lands indicated two distinct population resilience strategies: (1) we saw faster rebound in the case of A. amara and A. senegal and (2) slow recovery from disturbance in the case of A. leiocarpus and B. aegyptiaca which showed low juvenile recruitment in fallow lands.

Tanglehead in Southern Texas: A Native Grass with an Invasive Behavior

On the Ground • Tanglehead is a native bunchgrass with a pan-tropical distribution. Historically, tanglehead was common but not abundant in southern Texas and was considered a decreaser whose presence indicated good range condition. • Beginning in the late 1990s, the Texas Coastal Sand Plain ecoregion witnessed dramatic increases in the abundance and distribution of tanglehead: thousands of acres of former grasslands were replaced by dense monotypic stands of tanglehead, reducing habitat quality for livestock and wildlife. • Our research has focused on understanding factors related to tanglehead's expansion, its effects on habitat quality, and management practices that can improve range condition and habitat quality.

Aquifer Mapping in the Niger Delta Region: A Case Study of Edo State, Nigeria

In Nigeria, potable water is in short supply to the greater population and where available, groundwater accounts for over 90% of the supply. Oil exploration and exploitation activities are carried out in the Niger Delta region of Nigeria and this has affected the environment in this region. However, naturally occurring traces of petroleum products in strata or petroleum losses through spillages can contaminate groundwater, thus aquifer mapping in the Niger Delta Region becomes crucial. The study involves collection, collation and analysis of relevant information and data required for successful development of groundwater in Edo state. Groundwater in Edo State occurs under different conditions in the various aquifers defined by the following geological units, namely: Coastal Plain Sands of the Benin Formation, Ogwashi- Asaba, Bende- Ameki and Imo Shale Group of the Tertiary Deposits, False-bedded Sandstones and the Nkporo Shale Group of the Cretaceous deposits and the Basement Complex Rocks which only contain groundwater in the overburden, faults and joints. From the information collated, groundwater levels are deepest in the Ishan Plateau where it is about 171 metres above mean sea level at Ekpoma. Away from the pleateau, groundwater rises southwards and northwards. At Aduwawa/Ikpoba Hill (Benin City), the groundwater level is 40 metres, at Iguiye (Lagos Road, Benin City) to the west, the groundwater level is 55 metres and at Fugar to the north, the groundwater level is 95 metres. The groundwater flow direction is from the Plateau to all other areas with higher groundwater levels. Therefore, aquifer mapping in the Niger Delta region is necessary, as it will help in assessing the availability and development methods to be adopted.

Root xylem characteristics and hydraulic strategies of species co-occurring in semi-arid Australia

Xylem traits such as xylem vessel size can influence the efficiency and safety of water transport and thus plant growth and survival. Root xylem traits are much less frequently examined than those of branches despite such studies being critical to our understanding of plant hydraulics. In this study, we investigated primary lateral and sinker roots of six co-occurring species of semi-arid Australia. Two species are restricted to a floodplain, two were sampled only from the adjacent sand plain, and two species co-occur in both habitats. We assessed root wood density, xylem traits (i.e., vessel diameter, fibre and vessel wall thickness), outer pit aperture diameter and calculated theoretical hydraulic conductivity and vessel implosion resistance. We hypothesized that (1) roots have larger xylem vessel diameters and lower wood density than branches of the same species and that (2) there is an inverse correlation between theoretical sapwood hydraulic conductivity and vessel implosion resistance for roots. Variation in root wood density was explained by variations in xylem vessel lumen area across the different species (r2 = 0.73, p = 0.03), as hypothesized. We rejected our second hypothesis, finding instead that the relationship between theoretical hydraulic conductivity and vessel implosion resistance was not maintained in roots of all of our studied species, in contrast to our previous study of branches from the same species. Xylem traits were found to depend upon habitat and eco-hydrological niche, with the groupings including (i) arid-adapted shrubs and trees with shallow lateral roots (Acacia aneura and Psydrax latifolia), (ii) trees restricted to the floodplain habitat, both evergreen (Eucalyptus camaldulensis) and deciduous (Erythrina vespertilio) and (iii) evergreen trees co-occurring in both floodplain and adjacent sand plain habitats (Corymbia opaca and Hakea sp.).