Unique Hydrological Characteristics Research Articles

Distribution and Abundance of Microplastics in Underground Rivers in the South Malang Karst Area: First Evidence in Indonesia

Introduction: The presence of microplastics in the environment increases the diversity of types of pollutants in waters, including clean water sources on the surface and underground. Karst areas have unique hydrological characteristics, with cracks and fissures between the rocks that can be potential routes for the transport and accumulation of microplastics in underground river flows. In this study, we want to know the distribution and abundance of microplastics in underground rivers in the karst area of South Malang, Indonesia. Methods: Samples were collected purposively from underground river of Lowo, Banyu and Sengik. Microplastics were prepared using a diluted solvent of 30% H2SO4 and 30% H2O2. The sediment sample was dried and then filtered twice using 300-mesh size nylon filters until microplastic particles accumulated. Results and Discussion: Microplastics were detected in all water samples, with an average abundance ranging from 1.8 to 2.3 particles per liter. Fibers were the dominant microplastic type, followed by fragments and films, while the color distribution includes blue, white, red, yellow, black, green, pink, and brown. Conclusion: Microplastic contamination has been found in underground river flows in the karst area of South Malang, Indonesia. Karst soil, traditionally viewed as a natural filter, is not impervious to plastic pollution. This suggests significantly higher surface contamination than previously assumed. Therefore, reducing surface pollution is essential to safeguard the precious quality of underground aquifers and protect public health above.

Improving a herbicide risk assessment model in paddy rice cultivation

Herbicides play a pivotal role in paddy rice cultivation by effectively controlling weeds, thus ensuring optimal resource utilisation and higher crop yields, making them indispensable for efficient rice production systems. However, herbicide applications could be related to potential environmental impacts such as water contamination and harm to non-target species, requiring special attention in their management to ensure the long-term sustainability of rice farming practices. The development and utilisation of robust risk assessment indicators for pesticides are essential tools in evaluating and mitigating potential environmental and human health hazards associated with pesticide use in agricultural practices. The Environmental Potential Risk Indicator for Pesticides (EPRIP) is not suitable for rice paddy cultivation due to its limitations in accurately assessing pesticide risk in this specific agricultural context. This is primarily attributed to the unique hydrological characteristics and ecosystem dynamics of paddy fields, which significantly differ from other agricultural systems. To address this issue and to enhance the accuracy of pesticide risk assessment in rice paddy fields, EPRIP has been improved and validated in two agricultural seasons. A synergistic approach involving field experiments and enhanced EPRIP model simulations was employed to assess the risk associated with the application of two herbicides in Italian paddy rice systems. The observed and model-predicted surface water (SW) concentrations exhibited a close alignment, though an overestimation was observed for groundwater (GW). In general, the estimated Risk Points (1 for SW and 4 for GW) were largely in accord with those derived from the field experiments (1 for SW and 3 for GW), suggesting that the refined EPRIP model holds promise for conducting reliable risk assessments following herbicide applications in such contexts.

Opinions and considerations on some hydrological characteristics of Bukhara region

Currently, as a result of the extensive use of water resources worldwide, their quantitative reduction and quality deterioration are causing a number of problems. Therefore, studying the hydrological characteristics of existing water resources in the Bukhara region is considered one of the urgent problems. Bukhara region has its own unique hydrological characteristics due to the fact that it is completely in the desert zone, the climate changes sharply, the temperature is high, warm winds constantly blow, and it does not have its own natural water source.

Wetland mapping based on feature optimization and Google Earth Engine in Zhalong Nature Reserve

Wetlands have very important and irreplaceable ecological service functions in protecting biodiversity and maintaining ecological balance. Due to the unique hydrological characteristics of wetlands, large-scale wetland mapping methods are usually time-consuming, labor intensive, and expensive. With the rise of big data and cloud computing platforms, there are opportunities for long time series and large-scale spatial data processing that improve large-scale wetland mapping. In this study, the Sentinel-1, Sentinel-2, and digital elevation model derived from the Google Earth Engine were used to extract the wetland extent in the Zhalong Nature Reserve based on the Jeffries–Matusita (JM) distance for feature optimization and random forest. Research shows the following: (1) The JM distance for each feature showed that the optical features had the highest separation in all five features and (2) the classification after feature optimization performed best. User accuracy (UA) and producer accuracy (PA) for wetland reached 89.64% and 83.00%, respectively, and overall accuracy reached 90.76%. After feature optimization, PA and UA of wetland were each increased 4.26% and 1.07%, respectively, and the number of features was reduced from 46 to 28. The method used in this study is highly accurate in wetland mapping and can effectively avoid the problem of data redundancy.

Screening and scoping-level assessment of beneficial management practices in a Canadian prairie watershed

In the Canadian prairies, eutrophication is a widespread issue, with agriculture representing a major anthropogenic nutrient source in many watersheds. However, efforts to mitigate agricultural nutrient export are challenged by the lack of coordinated monitoring programs and the unique hydrological characteristics of the prairies, notably, the dominance of snowmelt in both water flows and nutrient loads, variable runoff, variable contributing area and the issues of understanding how scale affects nutrient concentrations and prevalence of dissolved nutrient transport (over total nutrients). Efforts are being made to integrate these characteristics in process-based water quality models, but the models are often complex and are not yet ready for use by watershed managers for prioritizing implementation of beneficial management practices (BMPs). In this study, a screening and scoping approach based on nutrient export coefficient modeling was used to prioritize BMPs for the 55,700 km2 Qu’Appelle Watershed, Saskatchewan. By integrating land use information, in-stream monitoring data, stakeholder input and nutrient export coefficient modeling, the study assessed potential efficiencies of six BMPs involving fertilizer, manure, grazing, crop and wetland management in nutrient load reductions for nine tributaries of the watershed. Uncertainty around the effectiveness of the BMPs was assessed. Field-level export coefficients were adjusted with nutrient delivery ratios for estimating watershed-level exports. Of the BMPs examined, in general, wetland restoration had the greatest potential to reduce both nitrogen and phosphorus loads in most tributaries, followed by fertilizer management. The importance of wetland restoration was supported by positive, significant, linear correlations between nutrient delivery ratios and drainage intensity in the tributaries (nitrogen: R 2 = 0.67; phosphorus: R 2 = 0.82). Notably, the relative ranking of BMP efficiencies varied with tributaries, as a result of differing landscape characteristics, land uses and nutrient inputs. In conclusion, the approach developed here acknowledges uncertainty, but provides a means to guide management decisions within the context of an adaptive management approach, where BMP implementation is partnered with monitoring and assessment to revise ongoing plans and ensures selected practices are meeting goals for nutrient abatement.

The potential of GRACE in assessing the flood potential of Peninsular Indian River basins

ABSTRACT The existence of fewer gauging sites along with sparse network of rain gauges make the monitoring of floods difficult, especially over regions characterized with hydrologic heterogeneity. The availability of observations from satellite sensors makes it possible to study hydrological behaviour of such under-observed river basins. In this study, we explore the utility of GRACE derived terrestrial water storage estimates to monitor the flood events of varying magnitudes over the river basins on Indian Peninsula, that is known to be a region of high heterogeneity. We use terrestrial water storage estimates from Gravity Recovery and Climate Experiment (GRACE) satellite mission, rainfall and temperature data from India Meteorological Department (IMD), discharge data from Central Water Commission (CWC) and groundwater level data from Central Ground Water Board (CGWB) to evaluate and compare the variability of flood potential of six major river basins, which show unique hydrological characteristics. The flood potential is evaluated for these major basins in Peninsular India using Reager’s Flood Potential Index (FPI) and the skill of FPI is assessed over these basins, for the period from 2003 to 2016. Significant variations are observed in the terrestrial water storage and FPI estimates of these basins, which reflects the diverse hydrological behaviour of the basins. Mahanadi basin shows extremely high positive FPI values, while Cauvery basin shows extremely high negative values, thereby confirming their respective flood and drought prone characteristics. The ability of FPI is established especially for basins with discharge values higher than 2000 m3 s–1. Moreover, good accuracy (> 90%) is observed over Mahanadi, Godavari and Narmada basins that are exposed with frequent mild, moderate and severe floods, using the threshold values of FPI. Among all the basins, Mahanadi basin shows high threshold FPI values of 0.40, 0.32 and 0.27 for severe, moderate and mild floods respectively. Godavari and Narmada basins have relatively lesser thresholds. The FPI values corresponding to severe, moderate and mild floods for Godavari basin are 0.25, 0.14 and 0.09, while those for Narmada basin are 0.25, 0.11 and 0.04. We hence, conclude that the index has the ability to monitor different levels of floods, over basins exhibiting diverse hydrological characteristics. These observations establish that GRACE derived terrestrial water storage anomaly (TWSA) can be used for flood monitoring applications, when discharge data is rarely available and the incorporation of terrestrial water storage estimates with the rainfall data in hydrological modelling may greatly help in assessing hydrological extremes.

Comparing fishway designs for application in a large tropical river system

River infrastructure poses a serious threat to diverse and productive fish stocks in many tropical river-floodplain systems; particularly the Lower Mekong River, where the fisheries are vital for food security. Dams and weirs block fish migration pathways and prevent access to feeding, spawning or nursery habitat. Fishways are becoming increasingly important for mitigating the effects of barriers; however, knowledge regarding their effectiveness for the biodiverse tropical river systems is still scant. This study examined the effectiveness of differing low-cost fishway designs for rehabilitating degraded floodplain fisheries in the Lower Mekong Basin (LMB) in Laos: (1) vertical slot; (2) submerged orifice — 150 mm square opening; and (3) submerged orifice — 300 mm square opening. Day and night in situ field experiments were undertaken to compare the abundance, biomass, species richness and size range of fish able to pass through each design with relatively low drops between pools (i.e. 150 mm each) and low water velocities (i.e. 1.71 ms−1). Passage of a total of 73 species was supported by the fishway designs at a similar abundance, biomass, species richness and size range of fish, during both the day and night; although, the vertical slot design supported a different suite of fish species to that of the other two designs during the day. This suggests that each of these fishway designs could be successfully used to support the rehabilitation of fisheries in the LMB and potentially other large tropical river systems with relatively diverse migratory fish communities and variable hydrological characteristics. However, the vertical slot provides greater design and operational flexibility over the submerged orifice designs particularly in tropical systems with inherently variable hydrology. The final fishway design choice ultimately depends on the fish species and size classes being prioritised for restoration and the unique hydrological characteristics of the site.

Effects of environmental variation on stable isotope abundances during typical seasonal floodplain dry season litter decomposition

Unique hydrological characteristics and complex topography can create wide-ranging dry season environmental heterogeneity in response to groundwater level across China's Jiangxi Province Poyang Lake wetland. Soil traits are one of several fluctuating environmental variables. To determine the effects of soil variables on stable isotope (δ13C and δ15N) abundances during decomposition, we performed a field experiment using Carex cinerascens along a groundwater level gradient (GT-L: −25 to −50cm, GT-LM: −15 to −25cm, GT-MH: −5 to −15cm, GT-H: 5 to −5cm) in a shallow lake. Twelve soil properties—including total organic carbon (TOC), nitrogen (N), pH, moisture, bulk density, clay, silt, sand, peroxidase, cellulase, microbial biomass carbon (MBC), and microbial biomass nitrogen—were measured in surface soil samples to assess soil environmental conditions. Analyses were performed to determine the effects of soil traits and lignin degradation on changes in stable isotope abundances. This study revealed that stable isotope abundances were significantly lower at high groundwater levels than at low groundwater levels. Lignin degradation was associated with a decrease in both δ13C and δ15N abundances. These two stable isotopes were positively related with soil N and bulk density, but negatively with pH and microbial quotient (MBC/TOC). Variation partitioning analysis (VPA) showed that soil variables and lignin decay rates explained 80.1% of the δ13C variation and 42.8% of the δ15N variation. Soil chemical and biological variables exhibited significant interactions with lignin decay rates, indicating they may affect stable isotope abundances via complex mechanisms. Our results indicate that the change in stable isotope abundances during decomposition may be affected directly by soil variables or indirectly through lignin degradation. Our results provide useful insight for understanding the roles of litter decomposition and soil traits in changing environmental conditions of seasonal floodplain wetlands.

Analisis Karakteristik Hidrogeokimia Airtanah Di Pulau Koral Panggal, Kepulauan Seribu, DKI Jakarta

The small island has a very unique hydrological characteristics. The unique character are low rainfall, rain catchment narrow and high vulnerability to seawater intrusion. This study aims to (1) analyze the groundwater hydrogeochemistry facies in Panggang Cay and (2) to analyze the evolution of groundwater hydrogeochemistry in Panggang Cay. Data used include major element analysis results of the groundwater samples taken from the study site. Hidrogeochemistry fasies of groundwater determined the type of diagram analysis stiff, while the analysis of the hydrogeochemistry evolution of groundater analyzed using piper diagram. Groundwater hydrochemical facies in Panggang Cay is MgCl2 with hydrogeochemical evolution of CaCO3 into MgCl2. The evolution of hydrogeochemistry fasies that occur indicate the sea water intrusion process.

A pollution fate and transport model application in a semi-arid region: Is some number better than no number?

Fate and transport models are powerful tools that aid authorities in making unbiased decisions for developing sustainable management strategies. Application of pollution fate and transport models in semi-arid regions has been challenging because of unique hydrological characteristics and limited data availability. Significant temporal and spatial variability in rainfall events, complex interactions between soil, vegetation and topography, and limited water quality and hydrological data due to insufficient monitoring network make it a difficult task to develop reliable models in semi-arid regions. The performances of these models govern the final use of the outcomes such as policy implementation, screening, economical analysis, etc. In this study, a deterministic distributed fate and transport model, SWAT, is applied in Lake Mogan Watershed, a semi-arid region dominated by dry agricultural practices, to estimate nutrient loads and to develop the water budget of the watershed. To minimize the discrepancy due to limited availability of historical water quality data extensive efforts were placed in collecting site-specific data for model inputs such as soil properties, agricultural practice information and land use. Moreover, calibration parameter ranges suggested in the literature are utilized during calibration in order to obtain more realistic representation of Lake Mogan Watershed in the model. Model performance is evaluated using comparisons of the measured data with 95%CI for the simulated data and comparison of unit pollution load estimations with those provided in the literature for similar catchments, in addition to commonly used evaluation criteria such as Nash-Sutcliffe simulation efficiency, coefficient of determination and percent bias. These evaluations demonstrated that even though the model prediction power is not high according to the commonly used model performance criteria, the calibrated model may provide useful information in the comparison of the effects of different management practices on diffuse pollution and water quality in Lake Mogan Watershed.

Calculation and Analysis of Degradation Ability under Different Hydrological Conditions in Poyang Lake

According to the unique hydrological characteristics of “a flood in high water level, a line in low water level”, Poyang lake is partitioned. Based on the hydrological datas, 2003, 2005 and 2010 are selected as typical years of dry year, average year and wet year respectively. The model of the pollutant degradation ability is selected to calculate the degradation coefficient during hydrological periods in typical years. The results show that the degradation ability of pollutants is greater in high water period than in normal water period. There was no obvious rule in the degradation ability because water level and flow velocity are random during low water period in different hydrological year. The degradation ability of river into the lake area is greater than in the north lake district during high and normal water period. The south lake district is the least. The degradation of pollutants depends on hydrological conditions. Physical degradation is main generally.

Environmental dynamics of dissolved black carbon in wetlands

Wetlands are ecosystems commonly characterized by elevated levels of dissolved organic carbon (DOC), and although they cover a surface area less than 2 % worldwide, they are an important carbon source representing an estimated 15 % of global annual DOC flux to the oceans. Because of their unique hydrological characteristics, fire can be an important ecological driver in pulsed wetland systems. Consequently, wetlands may be important sources not only of DOC but also of products derived from biomass burning, such as dissolved black carbon (DBC). However, the biogeochemistry of DBC in wetlands has not been studied in detail. The objective of this study is to determine the environmental dynamics of DBC in different fire-impacted wetlands. An intensive, 2-year spatial and temporal dynamics study of DBC in a coastal wetland, the Everglades (Florida) system, as well as one-time sampling surveys for the other two inland wetlands, Okavango Delta (Botswana) and the Pantanal (Brazil), were reported. Our data reveal that DBC dynamics are strongly coupled with the DOC dynamics regardless of location, season or recent fire history. The statistically significant linear regression between DOC and DBC was applied to estimate DBC fluxes to the coastal zone through two main riverine DOC export routes in the Everglades ecosystem. The presence of significant amounts of DBC in these three fire-impacted ecosystems suggests that sub-tropical wetlands could represent an important continental-ocean carrier of combustion products from biomass burning. The discrimination of DBC molecular structure (i.e. aromaticity) between coastal and terrestrial samples, and between samples collected in wet and dry season, suggests that spatially-significant variation in DBC source strength and/or degree of degradation may also influence DBC dynamics.

A comparison study on distributed hydrological modelling of a subarctic wetland system

Wetlands occupy 14% of the Canadian territory and mainly exist as bogs, fens, swamps, marshes, and shallow water. Recently, arctic and subarctic wetlands have attracted much attention due to their unique hydrological characteristics, and vulnerability to climate condition changes. To gain insight of the interactions between hydrology and atmosphere of the second largest wetland in Canada - the Hudson Bay Lowlands (HBL), extensive field investigations were conducted from 2006 to 2008 in the Deer River watershed near Churchill, Manitoba, Canada. Hydrologic and geographic conditions, such as frost table, soil moisture and temperature, and streamflow were monitored to advance the understanding of the wetland systems. Following up the field investigation, two semi-distributed hydrological models, Semi-distributed Land Use-based Runoff Processes (SLURP) and WATFLOOD, were employed to simulate the water cycle in the Deer River watershed. They were further compared from the aspects of modelling structures, formulations, parameters, and simulation results. Regardless the distinct simulation concepts (i.e., aggregated simulation area in SLURP and group response unit in WATFLOOD), the results indicated that snowmelt and peaks of spring runoffs simulated by SLURP were earlier than those simulated by WATFLOOD. This may be explained by the exponentially increasing snowmelt rate adopted by SLURP. Lack of considering the existence of permafrost and seasonal ponds in both models tended to underestimate the peaks of spring runoffs. It was also observed that the Morton CRAE method used in SLURP slightly underestimated the summertime evapotranspiration, meanwhile it was overestimated by the Hargreaves Equation employed in WATFLOOD. This study not only helped to fill the knowledge gaps in how well the two widely used models could fit the requirements of subarctic wetlands modelling, but also showed their strength and limitations as well as the potential for improvement.

Bioassessment of artesian springs in the Bonneville Basin, Utah, USA

In recent years, the loss and degradation of desert artesian springs has resulted in the loss of endemic species while other species have received “sensitive” designations. Bioassessment procedures have not been developed for groundwater-fed springs in the United States. Assessing the integrity of artesian springs is a challenge because of variable physico-chemical conditions among springs coupled with their unique hydrologic characteristics (a constant inflow of unpolluted water). We collected physico-chemical data and macroinvertebrates from 125 springs. Thirty-three springs clustered into three minimally impacted reference classes. We matched 39 test sites with one of these three classes. An integrated approach combining diversity indices, and aspects of multivariate analyses and multimetrics was more useful than any single method. Multivariate analyses (NMDS, ANOSIM and SIMPER) were particularly helpful in detecting trends at the community level and identifying specific indicator taxa (e.g., amphipods). However, macroinvertebrates in some springs did not respond to the potentially adverse effects of livestock grazing, perhaps because a variety of large ungulates historically frequented these springs (buffalo, elk, deer, etc.). Also, macroinvertebrate diversity increased with increasing disturbance; rare taxa were probably more easily detected as their densities increased with increased food availability in impaired sites. Expanding the scope of this study to artesian springs of the entire Great Basin Province may produce additional reference classes (e.g., > 20°C water temperatures) and provide a way to assess the integrity of all springs.

Mapping dry/wet snow cover in the Indian Himalayas using IRS multispectral imagery

Application of remote sensing data has been made to differentiate between dry/wet snows in a glacierized basin. The present study has been carried out in the Gangotri glacier, Himalayas, using IRS-LISS-III multispectral data for the period March–November 2000 and the digital elevation model. The methodology involves conversion of satellite sensor data into reflectance values, computation of NDSI, determination of the boundary between dry/wet snows from spectral response data, and threshold slicing of the image data. The areas of dry snow cover and wet snow cover for different dates of satellite overpasses have been computed. The dry snow area has been compared with non-melting area obtained from the temperature lapse rate method, and the two are found to be in close mutual correspondence (< 15%). It is observed that there occur four water-bearing zones in the glacierized basin: dry snow zone, wet snow zone, exposed glacial ice and moraine-covered glacial ice, each of which possesses unique hydrological characteristics and can be distinguished and mapped from satellite sensor data. It is suggested that input of data on the position and extent of specifically wet snow and exposed glacial ice, which can be directly derived from remote sensing, should improve hydrological simulation of such basins.

JET‐SUSPENDED, CALCITE‐BALLASTED CYANOBACTERIAL WATERWARTS IN A DESERT SPRING1

We describe a population of colonial cyanobacteria (waterwarts) that develops as the dominant primary producer in a bottom‐fed, O2‐poor, warm spring in the Cuatro Ciénegas karstic region of the Mexican Chihuahuan Desert. The centimeter‐sized waterwarts were suspended within a central, conically shaped, 6‐m deep well by upwelling waters. Waterwarts were built by an Aphanothece‐like unicellular cyanobacterium and supported a community of epiphytic filamentous cyanobacteria and diatoms but were free of heterotrophic bacteria inside. Sequence analysis of 16S rRNA genes revealed that this cyanobacterium is only distantly related to several strains of other unicellular cyanobacteria (Merismopedia, Cyanothece, Microcystis). Waterwarts contained orderly arrangements of mineral crystallites, made up of microcrystalline low‐magnesium calcite with high levels of strontium and sulfur. Waterwarts were 95.9% (v/v) glycan, 2.8% cells, and 1.3% mineral grains and had a buoyant density of 1.034 kg·L−1. An analysis of the hydrological properties of the spring well and the waterwarts demonstrated that both large colony size and the presence of controlled amounts of mineral ballast are required to prevent the population from being washed out of the well. The unique hydrological characteristics of the spring have likely selected for both traits. The mechanisms by which controlled nucleation of extracellular calcite is achieved remain to be explored.

Spatial variability of soils developing on basalt flows in the Potrillo volcanic field, southern New Mexico: prelude to a chronosequence study

If the systematic spatial variability of soils in a chronosequence is identified and accounted for, the accuracy of quantitative data derived from soil chronosequence studies will be increased. A sample design using landscape positions with minimal variability could result in more accurate chronofunctions from these studies. Four basalt flows in the Potrillo volcanic field, southern New Mexico, with ages ranging between 20 ka and 260 ka (40Ar/39Ar and/or cosmogenic 3He methods) provide a sound basis for a soil chronosequence study. Basalt flow surface relief in the Potrillos reduces with time as depressions fill with basalt rubble and aeolian dust. Soil variability is primarily a function of landscape position with respect to ridges and swales in the original basalt flow topography. Soils developing over original topographic lows (swale soils) form primarily in aeolian dust, have larger amounts of total carbonate and soluble salts, and display greater variability than soils developing over original topographic highs (ridge soils). It is thus concluded that ridge soils, which have minimal variability, should be employed for a soil chronosequence study of basalt surfaces in the Potrillo volcanic field. The spatial variability of swale soils results in part from the significant hydrologic variability of low-lying landscape positions. Depth profiles of chloride concentrations suggest that hydrologic variability systematically correlates with the size and shape of depressions in which soils are forming. The infilling of depressions with aeolian material results in increasingly arid hydrologic conditions both by increasing the volume of aeolian material that is being drained and by reducing the catchment area for runoff into the depression. Depressions fill at different rates, however, depending on their size, shape and catchment area. Small, narrow depressions fill quickly, and their associated soils form under more arid conditions and have stronger development than soils in large depressions. Therefore, a number of geomorphic surfaces of varying age may develop on a single isochronous basalt flow. Each of these surfaces will have unique hydrologic characteristics and consequently different degrees of soil development. The pre-burial high water flux evident in depressions suggests that basalt flows may play an important role in aquifer recharge in this area of New Mexico. Copyright © 1999 John Wiley & Sons, Ltd.

Spatial variability of soils developing on basalt flows in the Potrillo volcanic field, southern New Mexico: prelude to a chronosequence study

If the systematic spatial variability of soils in a chronosequence is identified and accounted for, the accuracy of quantitative data derived from soil chronosequence studies will be increased. A sample design using landscape positions with minimal variability could result in more accurate chronofunctions from these studies. Four basalt flows in the Potrillo volcanic field, southern New Mexico, with ages ranging between 20 ka and 260 ka (40Ar/39Ar and/or cosmogenic 3He methods) provide a sound basis for a soil chronosequence study. Basalt flow surface relief in the Potrillos reduces with time as depressions fill with basalt rubble and aeolian dust. Soil variability is primarily a function of landscape position with respect to ridges and swales in the original basalt flow topography. Soils developing over original topographic lows (swale soils) form primarily in aeolian dust, have larger amounts of total carbonate and soluble salts, and display greater variability than soils developing over original topographic highs (ridge soils). It is thus concluded that ridge soils, which have minimal variability, should be employed for a soil chronosequence study of basalt surfaces in the Potrillo volcanic field. The spatial variability of swale soils results in part from the significant hydrologic variability of low-lying landscape positions. Depth profiles of chloride concentrations suggest that hydrologic variability systematically correlates with the size and shape of depressions in which soils are forming. The infilling of depressions with aeolian material results in increasingly arid hydrologic conditions both by increasing the volume of aeolian material that is being drained and by reducing the catchment area for runoff into the depression. Depressions fill at different rates, however, depending on their size, shape and catchment area. Small, narrow depressions fill quickly, and their associated soils form under more arid conditions and have stronger development than soils in large depressions. Therefore, a number of geomorphic surfaces of varying age may develop on a single isochronous basalt flow. Each of these surfaces will have unique hydrologic characteristics and consequently different degrees of soil development. The pre-burial high water flux evident in depressions suggests that basalt flows may play an important role in aquifer recharge in this area of New Mexico. Copyright © 1999 John Wiley & Sons, Ltd.