Water Table Regime Research Articles

A survey of groundwater levels and hydrogeochemistry in irrigated fields in the Karamay Agricultural Development Area, northwest China: Implications for soil and groundwater salinity resulting from surface water transfer for irrigation

Analysis of the water budget, along with hydrochemistry and stable isotopes in shallow groundwater were carried out in the Karamay Agricultural Development Area (KADA) in order to assess the impact of transfer of irrigation water from the IrtySh River, in particular in relation to the mechanisms of salinization and the nature of the water table regime. In terms of aquifer dynamics, the addition of the irrigation water without any groundwater abstraction has caused a sharp rise in the water table is and the development of serious soil salinity, together with an almost complete attenuation of inter-seasonal water table oscillations. The mean rise in the groundwater table from September 1997 to October 2009 was 6.9 m, representing an accumulated total water storage change of close to 150 million cubic meters. The analysis of aquifer water budget shows that infiltration of irrigation water occupied over 90% of the total recharge of the groundwater in the KADA. Sources of groundwater recharge and mechanisms of salinization in the KADA were also investigated using geochemical and isotopic techniques. The groundwater is characterized by Cl(SO 4 )–Na type, generally becoming more Na and Cl dominated with increasing salinity. The total dissolved solids (TDS) content of the groundwater ranges from 0.5 g/L to over 65 g/L, with greater TDS values in areas of low topographic relief and shallow water tables. Where the sediments are more permeable (e.g. due to the presence of palaeochannels), TDS values are generally lower and the seasonal water table fluctuations greater. The ratios of K/Cl, Ca/Cl, Na/Cl, and Mg/Cl decrease with increasing Cl − concentrations especially in the shallow groundwater from 10 to 15 m depth, indicating hydrogeochemical evolution via minor water-rock interaction (feldspar weathering) and significant evaporation. The stable isotopic compositions show a characteristic evaporation effect in the shallow groundwater and confirm that direct infiltration of precipitation is generally not a volumetrically important source of recharge to the shallow aquifer. Preferential recharge of river water after irrigation events and/or precipitation from rare heavy rain events is likely responsible for the depleted δ 2 H and δ 18 O values in some of the groundwater samples. The negative relationship between deuterium excess and δ 18 O values indicates that even in groundwater with relatively depleted δ 2 H and δ 18 O values, evaporation has occurred to a significant degree. Careful management of water quantity and quality and implementation of salinity management strategies are considered necessary in order to reduce the risk of further salt accumulation and damage to farming and local ecosystems.

A Multi-Year Record of Methane Flux at the Mer Bleue Bog, Southern Canada

The Mer Bleue peatland is a large ombrotrophic bog with hummock-lawn microtopography, poor fen sections and beaver ponds at the margin. Average growing-season (May–October) fluxes of methane (CH4) measured in 2002–2003 across the bog ranged from less than 5 mg m−2 d−1 in hummocks, to greater than 100 mg m−2 d−1 in lawns and ponds. The average position of the water table explained about half of the variation in the season average CH4 fluxes, similar to that observed in many other peatlands in Canada and elsewhere. The flux varied most when the water table position ranged between −15 and −40 cm. To better establish the factors that influence this variability, we measured CH4 flux at approximately weekly intervals from May to November for 5 years (2004–2008) at 12 collars representing the water table and vegetation variations typical of the peatland. Over the snow-free season, peat temperature is the dominant correlate and the difference among the collars’ seasonal average CH4 flux is partially dependent on water table position. A third important correlate on CH4 flux is vegetation, particularly the presence of Eriophorum vaginatum, which increases CH4 flux, as well as differences in the potential of the peat profile to produce and consume CH4 under anaerobic and aerobic conditions. The combination of peat temperature and water table position with vegetation cover was able to explain approximately 44% of the variation in daily CH4 flux, based on 1097 individual measurements. There was considerable inter-annual variation in fluxes, associated with varying peat thermal and water table regimes in response to variations in weather, but also by variations in the water level in peripheral ponds, associated with beaver dam activity. Raised water level in the beaver ponds led to higher water tables and increased CH4 emission in the peatland.

Plant-Soil-Hydrology Relationships in Three Carolina Bays in Bladen County, North Carolina

Abstract This study provides quantitative ecological targets for restoring degraded peat-based Carolina Bays in the Carolina Flatwoods Ecoregion. Cluster analysis of vegetation data from three Carolina Bay reference sites in Bladen County, North Carolina, indicated four plant communities present: pond pine (Pinus serotina) woodland, non-riverine swamp forest dominated by swamp gum (Nyssa biflora), high pocosin dominated by evergreen shrubs with scattered pond pine, and bay forest dominated by loblolly bay (Gordonia lasianthus). We classified bay soils according to surface organic layer thickness (OLT) into mineral, histic, shallow organic, and deep organic types. We monitored the water table of each soil type in one bay throughout one growing season. The soil types with corresponding water table regimes were: mineral (9.4 cm mean OLT with a rooting zone water table [RZWT] 39% of the monitoring period), histic (27.5 cm OLT and 76% RZWT), shallow organic (63.9 cm OLT and 84% RZWT), and deep organic (102.5 c...

Effects of soil water table regime on tree community species richness and structure of alluvial forest fragments in Southeast Brazil

In order to determine the influence of soil water table fluctuation on tree species richness and structure of alluvial forest fragments, 24 plots were allocated in a point bar forest and 30 plots in five forest fragments located in a floodplain, in the municipality of São Sebastião da Bela Vista, Southeast Brazil, totalizing 54, 10 X 20 m, plots. The information recorded in each plot were the soil water table level, diameter at breast height (dbh), total height and botanical identity off all trees with dbh > 5 cm. The water table fluctuation was assessed through 1 m deep observation wells in each plot. Correlations analysis indicated that sites with shallower water table in the flooding plains had a low number of tree species and high tree density. Although the water table in the point bar remained below the wells during the study period, low tree species richness was observed. There are other events taking place within the point bar forest that assume a high ecological importance, such as the intensive water velocity during flooding and sedimentation processes.

The influence of hydrological regimes on sex ratios and spatial segregation of the sexes in two dioecious riparian shrub species in northern Sweden

River management practices have altered the hydrological regimes of many rivers and also altered the availability of regeneration niches for riparian species. We investigated the impact of changed hydrological regimes on the sex ratios and the Spatial Segregation of the Sexes (SSS) in the dioecious species Salix myrsinifolia Salisb.–phylicifolia L. and S. lapponum L. by studying the free-flowing Vindel River and the regulated Ume River in northern Sweden. We surveyed sex ratios of these species in 12 river reaches on the Vindel River and in 17 reaches on the Ume River. In addition, we surveyed the sex and location above mean river stage of 1,002 individuals across both river systems to investigate the SSS of both species. Cuttings were collected from male and female individuals of S. myrsinifolia–phylicifolia from both rivers and subjected to four different water table regimes in a greenhouse experiment to investigate growth response between the sexes. We found an M/F sex ratio in both river systems similar to the regional norm of 0.62 for S. myrsinifolia–phylicifolia and of 0.42 for S. lapponum. We found no evidence of SSS in either the free-flowing Vindel River or the regulated Ume River. In the greenhouse experiment, hydrological regime had a significant effect on shoot and root dry weight and on root length. Significantly higher shoot dry weights were found in females than in males and significantly different shoot and root dry weights were found between cuttings taken from the two rivers. We concluded that changed hydrological regimes are likely to alter dimensions of the regeneration niche and therefore to influence sex ratios and SSS at an early successional stage, making it difficult to find clear spatial patterns once these species reach maturity and can be sexed.

Evaluating a multi-level subsurface drainage system for improved drainage water quality

This paper describes a multi-level drainage system, designed to improve drainage water quality. Results are presented from a field scale land reclamation experiment implemented in the Murrumbidgee Irrigation Area of New South Wales, Australia. A traditional single level drainage system and a multi-level drainage system were compared in the experiment in an irrigated field setting. The single level drainage system consisted of 1.8 m deep drains at 20 m spacing. This configuration is typical of subsurface drainage system design used in the area. The multi-level drainage system consisted of shallow closely spaced drains (3.3 m spacing at 0.75 m depth) underlain by deeper widely spaced drains (20 m spacing at 1.8 m depth). Data on drainage flows and salinity, water table regime and soil salinity were collected over a 2-year period. Comparisons of water and solute movement between the multi-level drainage system and a single level drainage system are presented. Differences in the performance of the multi-level and single level drainage systems were found in the water table regime, drain water salinity and soil salinity.

A survey of soil salinity and groundwater level control systems in irrigated fields in the Jezre’el Valley, Israel

The Jezre’el Valley, Israel has inherent drainage problems; high water tables are common. Intensive irrigation has led to the development of salinity problems. A number of drainage system designs were installed in the same field to manage the prevailing causes of the salinity hazards. The shallow drainage system was designed to prevent damage to the winter crops and especially to enable early seeding of summer crops. The deep drainage system was designed to maintain a relatively low water table, thereby avoiding concentration of salts in the root zone. The combined drainage system with relief wells was designed to relief upward hydraulic pressure exerted by the semi-confined shallow aquifer. To study the mechanisms of salinization and the nature of the water table regime, soil salinity and water table monitoring systems were installed perpendicular to the parallel subsurface drains. The water table monitoring systems consisted of batteries of piezometers installed at different depths and located between the drainage lines. The most efficient method of drainage was found to be a combination of shallow and deep drains with relief wells wherever the semi-confined shallow aquifer was present. A noticeable improvement of the soil salinity, to below 4 dS/m, was observed 2–3 years after the drainage system was installed. It was found that the water table should be more than 1 m below the soil surface, in the spring season, to prevent soil salinization.

The spatial distribution of groundwater age for different geohydrological situations in the Netherlands: implications for groundwater quality monitoring at the regional scale

The spatial distribution of groundwater age is a key factor determining the distribution of dissolved contaminants in the subsurface when contamination loadings have increased in time. The effects of surficial drainage and aquifer heterogeneity on the spatial distribution of groundwater age in unconsolidated aquifers in flat areas were investigated, and consequences were presented for the monitoring of contaminants from diffuse sources. First, the effects were assessed using model simulations. Second, the groundwater age distribution was evaluated in the two regional monitoring networks of Noord-Brabant and Drenthe using tritium measurements. Theoretically, a simple spatial distribution of groundwater age is present in homogeneous aquifers with natural groundwater recharge, characterized by a horizontal pattern of residence time isochrones and a gradual increase of groundwater age with depth. The model simulations show that the isochrone pattern becomes distorted in areas with a surficial drainage network, resulting in relatively old groundwater at shallow depth and larger spatial variation in groundwater age at a specific depth. This drainage effect on the spatial distribution of groundwater age is relatively large compared with effects of regional scale aquifer heterogeneity or spatially varying groundwater recharge. The effects of surficial drainage on the spatial distribution of groundwater age were confirmed by tritium measurements made in the regional monitoring networks of two provinces in the Netherlands. At about 24 m depth, the proportion of post-1950 groundwater in drained areas was significantly less and the spatial variation of groundwater age was larger than in recharge areas that lack a drainage network. The age of the groundwater appeared to be related to the drainage network density and the water table regime. A preliminary survey showed that contamination patterns in the two networks agree well with the proportion of post-1950 groundwater.

Logistic Modeling to Spatially Predict the Probability of Soil Drainage Classes

Logistic models were developed to spatially predict the probability of drainage classes in a humid tropical area (58900 ha) using sampled terrain attributes from a digital elevation model, and vegetation indices from a LANDSAT‐5 Thematic Mapper image. Soil drainage classes were assigned on the basis of the local water table regime depth, determined by soil morphological indicators, to 295 pseudo‐randomly selected soil auger hole observations (calibration data set) and 72 soil pedon observations (validation data set). Six drainage classes were identified: excessively (D1), well (D2), moderately well (D3), imperfectly (D4), poorly (D5), and very poorly (D6). A nested dichotomous modeling strategy of progressively separating the six drainage classes was adopted, and resulted in five multivariate logistic models. The best performing model, predicting the probability of nonhydric (D1D2) soils versus hydric (D3D4D5D6) soils had a concordance of 99%, and the worst performing model, predicting the probability of imperfectly (D4) drained soils versus moderately well (D3) drained soils had a concordance of 65%. The most important spatial determinants were: elevation, slope, distance‐to‐the‐river channel (DC), and vegetation indices. The logistic models were combined in a geographic information system (GIS) to derive soil drainage class maps using the gridded data sets of the significant variables. The results showed that digital elevation models and vegetation indices from LANDSAT‐5 Thematic Mapper provide complementary information for developing statistical models to spatially predict and map soil drainage classes.

Evaluation of drainage and tillage effect on watertable depth and maize yield in wet inland valleys in southwestern Nigeria

A study was conducted in three wet inland valley bottoms, namely, high (MHW), medium (MMW) and low (MLW) watertable sites to evaluate the effect of drained (D) and control (Do), and mound-tillage (MT), ridge-tillage (RT) and no-tillage (NT) treatments on watertable depth and yield of maize in 1990 wet and 1990/1991 dry season in southwestern Nigeria. The watertable depth averaged 30.0 cm in the drained plot and <15.0 cm in the control plot in 1990. The watertable tended toward its lowest depth averaging 44.8 cm in the drained and 26.2 cm in the control plot in 1990/1991. Soil moisture content was lower ( P<0.01) and air-filled porosity greater ( P<0.01) in the mound-tilled compared with the ridge tilled and no-till soils in both drained and control plots in 1990 and 1990/1991. Equally, green maize yield from the mound-tillage and ditch drainage system was greater ( P<0.01) than the ridge-tillage and no-tillage systems in both seasons. Maize may be grown successfully with a ditch drainage and mound-tillage system in the wet soils in inland valley bottoms regardless of their watertable regimes in southwestern Nigeria.

Production, nutrient availability, and elemental balances of two meadows affected by different fertilization and water table regimes in The Netherlands

The restoration of degraded peat-grasslands is an important nature conservation goal in The Netherlands. We investigated the effects of ceased fertilization (15 years) combined with a groundwater-raised water table (6 years) on the production of the peat-grassland vegetation and soil nutrient availability in a meadow. Furthermore, we evaluated whether and how this difference between meadows affected the balances between nutrient inputs and outputs in the ecosystem. We used an adjacent fertilized meadow in which the water table followed agricultural practice as a control. Yield of the grassland vegetation was significantly lower in the wet than in the control meadow. The tissue concentrations of N, P, and K in the harvested vegetation were significantly lower, but those of Ca higher in the wet than in the control meadow. The difference between both meadows significantly affected the annual nitrification rate, but not the annual C and N mineralization rates and the annual net P and K release rates. The difference between both meadows also significantly affected the seasonal nitrification and K release rates. Season exerted a significant effect on the seasonal C and N mineralization and nitrification rates. The elemental balances and relative contributions of the balance terms to elemental inputs and outputs varied considerably with element. Annually, the wet meadow lost N, P and K, while the control meadow gained these elements. The elemental demand of the grassland vegetation in the wet meadow was met for N for a large part by mineralization and for the remainder by atmospheric deposition, for P it was in the same order of magnitude as the net soil-P release, as it was for K. It is to be expected that the soil resources of N, P and K will continue to decrease under a continued regime of ceased fertilization and a raised water table, with those of N decreasing with the same rate, of P morerapidly and of K more slowly than estimated from regressions.

CARBON DIOXIDE PRODUCTION FROM PEATLAND SOIL PROFILES: THE INFLUENCE OF TEMPERATURE, OXIC/ANOXIC CONDITIONS AND SUBSTRATE

The authors incubated intact peat cores from depth intervals of 5--15, 15--25, 25--35, and 35--45 cm from ombrotrophic bog, poor fen, and beaver pond margin sections of a cool-temperate peatland. CO{sub 2} production was measured over 12-day incubation periods at 4 and 14 C and under oxic and anoxic conditions. Rates ranged from 0.06 to 0.66 mg CO{sub 2} g{sup {minus}1} dry peat d{sup {minus}1} under oxic conditions and from 0.002 to 0.098 mg CO{sub 2} g{sup {minus}1} d{sup {minus}1} under anoxic conditions, and rates generally decreased with depth in the profiles. When expressed on a volumetric basis, production rates ranged from 0.3 to 23.4 g CO{sub 2} m{sup {minus}3} d{sup {minus}1}, and there was much less variation in CO{sub 2} production rates within profiles because the bulk density of peat increased with depth. The Q{sub 10} quotient, between 4 and 14 C, ranged from 1.0 to 7.7, depending on sample and incubation conditions, with an average of 2.0 for oxic and 2.7 for anoxic conditions. Oxic:anoxic ratios averaged 7:1, 16:1, and 12:1 for the bog, poor fen, and beaver pond margin samples, respectively. Degree of decomposition (von Post index) was the substrate property most strongly correlated with CO{sub 2}more » production. Based on temperature and incubation data for the peat profiles to a depth of 45 cm, annual decomposition values (k) ranged from 0.016 to 0.060 yr{sup {minus}1} under oxic conditions and from 0.001 to 0.007 yr{sup {minus}1} under anoxic conditions. A model of CO{sub 2} emission from the three sites, based on the incubation data and thermal and water table regime, gave good agreement with measured in situ CO{sub 2} emission rates, although summer emission rates were underpredicted, possibly because of the absence of a root production component in the incubations or because of underestimation of CO{sub 2} production rates in field conditions above the water table.« less

Shallow geophysical investigations on Tell el Farama, Northwest Sinai, Egypt

The main objective of the present study was to locate the buried archaeological remains in the area of Tell el Farama in northwestern Sinai, using shallow geophysical techniques. Magnetic and electric resistivity surveys were carried out on a selected area of about 300 m×330 m, which represents the present location of the ancient Citadel of el Farama. The field data have been collected, automatically analysed and presented in the form of maps and profiles, which show several magnetic and resistivity anomalies of different amplitudes and shapes. After the interpretation of these geophysical anomalies, a broader distribution of the buried archaeological features has been estimated and a simplified interpretative map is given to assist future plans for excavation of this area. This interpretation was based mainly on the magnetic results. The geoelectric resistivity method failed to give an indication of the distribution of the archaeological remains in this area due to the high salinization, shallow water table and soil moisture regime in the area of el Farama. Copyright © 1998 John Wiley & Sons, Ltd.

Effects of mining-induced earthquakes on water table in deep wells

Based on the systematical collection and processing of data on the influence of mining-induced earthquakes on water table regime in deep well Lu-15 in Taozhuang Coal Mine since 1980, we study the characteristics of coseismic effect of water table in deep well in this paper. We have found precursory phenomena of water table in deep well before mining-induced earthquake. Here we discuss the physical mechanism of coseismic effect of mining-induced earthquake on water table in deep well.

Water Table Gradient Effects on the Performance of Diverse Cowpea Cultivars

AbstractCowpea sown in tropical monsoon climates is often constrained by soil saturation and a high water table during growth. We hypothesized that a strong interaction exists between cowpea maturity class and the soil water table depth regime experienced during the growing season, and that the occurrence of shallow water table depths in the dry‐wet transition period before rice and the rapid decline in water table depth in the wet‐dry post‐rice period favor early maturing cultivars. The effects of three water table regimes on the performance of 24 diverse cowpea [Vigna unguiculat (L.) Walp] cultivars was studied on a Typic Tropudalf toposequence. The water table depths in the shallow (SWT), medium (MWT), and deep (DWT) water table regimes varied between 0.06 to 0.54 m, 0.28 to 0.96 m, and 0.68 to 1.44 m in the 2 yr of dry season (DS) experiments. In the wet season (WS), the three regimes were 0 to 0.27 m, 0.30 to 0.60 m, and 0.55 to 1.05 m. Most of the early maturing cultivars exhibited their best performance in the DWT regime, but the medium maturing cultivars were superior in seed yields in all water table regimes. The mean yields of the early maturing cultivars were reduced by 49% (1986–1987 DS) and 57% (1987–1988 DS) in SWT compared to DWT. They were reduced by 50% in the 1987 wet season. The mean yield reductions for the medium maturing cultivars were 40%, 54%, and 51%, respectively, in SWT compared to DWT. Pods per plant was the yield component most affected by excess moisture. Flowering in the SWT was delayed by 4 vs 5 d (DS) and 5 vs 7 d (WS) between the early and medium maturing cultivar groups, respectively. The superiority of the medium maturing cultivars was consistent among sites with a water table within the root zone for a major portion of the crop season.

Cowpea Water Relations and Growth Response on a Toposequence Water Table Gradient

AbstractCowpea sown after wetland rice in tropical monsoon climates is frequently subjected to soil saturation and a high water table during early growth. We compared the effects of variation in water table regime on the shoot and root growth, and plant water relations of two medium‐maturing (cv. TVX3236‐01G and TVX3410‐02J) and two early maturing (cv. BS6 and IT82D‐889) cowpea [Vigna unquiculata (L.) Walp] cultivars in three water table depth regimes on a Typic Tropudalf toposequence. Our objective was to elucidate the possible mechanisms of differential cultivar adaptation to shallow water table conditions. The shallow water table regime (SWT) significantly reduced the total dry matter accumulation and harvest index for BS6, an early maturing cultivar (reductions in stems, leaves, pods, and total dry matter by 82, 77, 88, and 84% respectively), while the least reductions (reductions by 44, 3, 57 and 55%, respectively) was observed for TVX 3410‐02J, a medium‐maturing cultivar. Roots of the medium cultivars were more concentrated in the top 0.2m in the SWT Site than those of the early‐maturing cultivars. Roots of the medium cultivars later penetrated to 0.8‐m maximum depth compared to 0.6‐m maximum depth for the early cultivars, and extracted soil water from 20 cm deeper in the soil profile than the early maturing cultivars. The medium‐maturity cultivars maintained higher leaf water potentials and lower canopy temperatures throughout the season. This was associated with greater end‐of‐season total soil profile water extraction. The medium‐maturing cultivars showed better adaptation to shallow water table conditions due to superior plant water status, rooting pattern, and biomass production and partitioning.

Influence of Water Table Depth on Sugarcane Grown in Sandy Soils in Florida

A three-year study was conducted on sandy soils in Southwest Florida to determine the influence of water table management on root length, stalk growth, crop yield, and stand longevity of sugarcane (Saccharum spp., cv. CP 72-1210). Water table regimes used in the experiment were: a high water table of 0.45 m (HWT), a low water table of 0.75 m (LWT), and a declining water table of 0.15 m per year beginning at 0.45 m the first year (DWT). Annual pan evaporation was 1864 mm in 1988, 1865 mm in 1989, and 2006 mm in 1990. Pan evaporation exceeded rainfall by 73% in 1988, 52% in 1989, and 98% in 1990. In the first and second crop, total root lengths were similar, but in the third crop (Second ratoon), total root lengths in the HWT and DWT treatments were significantly longer than those in the LWT treatment. The rate of stalk growth during the rainy season (June-August) was not affected by water table depth. For the season, stalk growth in the HWT treatment was slightly higher than that for the LWT treatment, but the difference was not significant. Average cane yield for the three seasons were 92, 95, and 84 Mg/ha for the HWT, DWT, and LWT, respectively. Sugar yield from these treatments averaged 12.1, 12.3, and 11.0 Mg/ha. Average cane and sugar yields from the HWT did not differ significantly from cane and sugar yields from the DWT treatment, but average yield from the HWT and DWT treatments were significantly higher than average cane and sugar yields from the LWT treatment. The rate at which sugar yields declined was 1.75, 1.95, and 3.0 Mg/ha/year for HWT, LWT, and DWT treatments, respectively. The HWT treatment, which represented the water management level needed to reduce oxidation of organic soils, did not adversely affect the sugarcanes stand longevity on sandy soils.

Field determination of soil hydraulic properties for simulation of the optimum watertable regime

A field experiment to evaluate accurate cost and time efficient methodologies for determining soil hydraulic properties was done at the NIAB Research Station at Faisalabad, Pakistan. The experiment was performed on a freely draining loamy soil. This soil type is representative of 75% of the topsoil in a tile drainage area known as the Fourth Drainage Project. Redistribution of water was monitored at five locations, for seven depths, following a steady state infiltration for prolonged time. The data were analyzed with Darcian flow analysis, three simplified methods, and two parameter optimization programs to calculate unsaturated hydraulic conductivity. The Darcian flow analysis was used as a reference against which the simplified methods were compared. Two simplified methods produced satisfactory results with less effort. The drawback is that the simplified methods alone do not provide enough information for use in simulation models. The advantage of the two optimization programs — SFIT and RETC — is that they are based on a continuous function which describes complete h(ϑ) and K(ϑ) curves. This is a requirement for computer simulation of salt and water movement in the unsaturated soil. The results of the optimizations were evaluated by their correspondence to field measurements and to laboratory measurements and by their ability to simulate soil water flow. Both programs fit the observed field data well, but only the SFIT optimized parameters were suitable for soil water flow simulations.

Mineralogical and textural evolution of the economic manganese mineralisation in western Rhodope massif, N. Greece

AbstractThe western Rhodope massif contains a significant number of ‘battery grade’ Mn-oxide deposits which are best developed in the area near Kato Nevrokopi, Drama district, N. Greece. Economic Mn-oxide ore concentrations are confined to fault zones and related karsts in marbles. The mineralisation has formed by weathering of hydrothermal veins that were genetically related to Oligocene magmatism.At Kato Nevrokopi, progressive and continuous weathering of primary, hydrothermal veins of rhodochrosite, mixed sulphide, quartz and ‘black calcite’ (calcite and todorokite) has resulted in the formation of the assemblage MnO-gel-(amorphous Mn-oxide)-todorokite-azurite-goethite-cerussite in the veins and the assemblage MnO-gel-nsutite-chalcophanite-birnessite-cryptomelane-pyrolusite and malachite and amorphous Fe-oxides in karstic cavities.The fs2 and fO2 of the hydrothermal fluids increased with time. The breakdown of the hypogene Mn-carbonate was aided by the production of an acidic fluid due to the oxidation of sulphides. Precipitation of the supergene ores was caused by neutralisation of the fluids due to reaction with the host marble and to mixing of relatively reduced fluids with oxygenated surface water in a fluctuation water table regime. Zinc was also mobile during weathering and became concentrated in the intermediate Mn-oxides, effectively stabilising their structures. The mineral paragenesis records the progressive oxidation of the ore and the appearance of less hydrated Mn-oxides, low in alkalis and alkaline earths.

Water tables and soil colour as an indicator of saturation in some soils of the Waikato, New Zealand

Seasonal fluctuation in water tables in some alluvial soils in the Waikato was determined to establish time, depth and duration of saturation. Duration of saturation could then be related to soil colour to test whether colour could be used as an indicator of saturated conditions in these soils. The results confirmed that there were different watertable regimes between soil series and that there could be different depths and durations of water-table within a series. In the soils studied, colour can be used as a general indicator of whether or not saturated conditions have occurred. However, soil colour did not give any indication as to the time of year or continuous duration of a water table, or whether or not soil wetness had changed as a result of improved drainage. The results of this study highlight the dynamic water-table relationships between and within Waikato soils. For detailed land-use interpretations based on depth to a water table it is advisable to take watertable measurements at the site itself rather than to rely on assessments based on soil colour. When measurement is not practical, the worst conditions indicated by soil colour should be used for interpretations and planning soil management.