Shawan Dogramaci - Academia.edu (original) (raw)
Papers by Shawan Dogramaci
![Research paper thumbnail of Corrigendum to “Hydrochemical and stable isotope indicators of pyrite oxidation in carbonate-rich environment; the Hamersley Basin, Western Australia” [J. Hydrol. 545 (2017), 288–298]](https://attachments.academia-assets.com/114999232/thumbnails/1.jpg)
](Journal of Hydrology, Dec 1, 2018
Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 2016
HIGHLIGHTS (max 85 characters) • Biomarkers and n-alkane δ 13 C were extracted from sediment with... more HIGHLIGHTS (max 85 characters) • Biomarkers and n-alkane δ 13 C were extracted from sediment with total C = 0.4-1.4% • Distribution of biomarkers reflected a decrease of aridity in the last ~2000 years • Arid based Bayesian model of n-alkanes δ 13 C suggested increase of riparian C3 input
Aquatic Sciences, Feb 26, 2020
Streams in hot, arid environments often exist as a series of isolated pools along main 21 channel... more Streams in hot, arid environments often exist as a series of isolated pools along main 21 channels. During these periods, shallow alluvial throughflow may strongly influence key 22 ecological processes within pools. We measured diel changes in δ C values of dissolved 23 inorganic carbon (DIC) and dissolved oxygen (DO) in two pools of ephemeral, dryland 24 streams. We quantified alluvial water connectivity through stable isotope analysis (δ 18 O and 25 δ 2 H) of pool and alluvial water. We also estimated gross primary productivity (GPP) and 26 ecosystem respiration (ER) rates across a wider set of pools in both streams. δ 13 CDIC values 27 displayed regular diel cycles, where both pools displayed small but similar daily amplitude 28 (0.7-0.9‰) despite contrasting amplitudes of change in DO (0.8 mg L-1 vs. 2.8 mg L-1) and 29 contrasting alluvial water connectivity (connected vs. disconnected). Water temperature was 30 the strongest predictor of both δ 13 CDIC values and rates of change in δ 13 CDIC across both 31 pools. Across both streams, all pools were net heterotrophic. GPP (0.35 to 1.73 g O2 m-2 d-1) 32 and ER (0.49 to 2.64 g O2 m-2 d-1) rates were linked to aquatic vegetation cover. The 33 disconnect between diurnal amplitudes of δ 13 C values and DO concentrations thus suggests 34 that ecological drivers of gas exchange became increasingly localised as pools contracted.
Journal of Hydrology, Nov 1, 2019
Evaporative flux from soils in arid and semi-arid climates can be very high and may substantially... more Evaporative flux from soils in arid and semi-arid climates can be very high and may substantially reduce soil moisture retained between infrequent rainfall events. Direct measurement of the evaporative losses from soils is technically challenging; however, environmental tracers such as stable hydrogen and oxygen isotope composition can be used to calculate evaporation rates if the initial signature of the infiltrating rainwater is distinct from the signature of residual soil moisture. Large tropical cyclones typically result in rainfall events of large volume and very negative δ 18 O signatures that are significantly lower than the signatures of the usual precipitation. These very negative stable isotope signatures are retained in the soil and can be used to understand the depth of water infiltration, retention and subsequent rate of evaporation from the soil. At our study site in dry subtropical northwest Australia, we repeatedly sampled rainwater and soil moisture prior to, during and after tropical cyclones Heidi and Lua in 2012. Site inundation from Cyclone Heidi (rainfall 213 mm, δ 18 O-17.6 ‰) replenished soil moisture in the unsaturated zone for several months, completely replacing soil moisture down to depths of ~3.5 m and contributing to groundwater recharge. The transient momentary evaporative losses from wet soil at the time of sampling (recalculated as an annual rate) varied between 76 and 220 mm×yr-1. During the prolonged dry period between cyclones, evaporative losses decreased to between 8 and 30 mm×yr-1. Consequently, mean long-term groundwater recharge for the study period was low (<6 mm×yr-1) and primarily driven by infrequent but high-volume cyclones that are an important source of soil moisture and therefore an essential water source for vegetation in the semi-arid environment. However, upscaling from a local to a regional scale model for ecological water demand would be challenging due to the high variability in δ 18 O observed in soil profiles, which varies with lithology, position in the landscape and time since the last inundation.
Journal of Hydrology, Feb 1, 2017
Sulphur (S) is a commonly occurring element in most aquifers, primarily in oxidised (sulphates) a... more Sulphur (S) is a commonly occurring element in most aquifers, primarily in oxidised (sulphates) and reduced (sulphides) forms. Sulphides often constitute a risk to groundwater quality due to acid rock drainage, especially in catchments that are subject to mining excavations or groundwater injection. However, in semi-arid regions detection of the acid rock drainage risk can be challenging and traditional methods based on observations of increasing SO 4 concentrations or SO 4 /Cl ratios in surface and groundwater, are not necessarily applicable. In addition, decreasing pH, usually accompanying pyrite oxidation, can be masked by the high pH-neutralisation capacity of carbonate and silicate minerals. Analysis of 73 surface and groundwater samples from different water bodies and aquifers located in the Hamersley Basin, Western Australia found that most of the samples are characterised by neutral pH but there was also a large spatial variability in the dissolved sulphate (SO 4) concentrations that ranged from 1 mg/L to 15,000 mg/L. Not surprisingly, groundwater in aquifers that contained pyrite had high sulphate concentrations (>1000 mg/L). This was associated with low d 34 S SO4 values (+1.2‰ to +4.6‰) and was consistent with the values obtained from aquifer matrix pyritic rock samples (À1.9‰ to +4.4‰). It was also found that the SO 4 concentrations and acidity levels were not only dependent on d 34 S SO4 values and existence of pyrite but also on the presence of carbonate minerals in the aquifer matrix. The groundwater in aquifers containing both pyrite and carbonate minerals had a neutral pH and was also saturated with respect to gypsum and had high magnesium concentrations of up to 2200 mg/L suggesting dedolomitisation as the process buffering the acidity generated by pyrite oxidation. Based on the findings from this study, a classification scheme has been developed for identification of the acid rock drainage contribution to groundwater that encompasses a myriad of geochemical processes that occur in aqueous systems. The classification uses five proxies (SO 4 , SO 4 /Cl, SI of calcite, d 34 S SO4 and d 18 O SO4) to improve assessment of the oxidation of sulphide potential contribution to overall sulphate ion concentrations regardless of acidity levels of the aqueous system.
EGU General Assembly Conference Abstracts, Apr 1, 2017
AGU Fall Meeting Abstracts, Dec 18, 2014
Earth Surface Processes and Landforms, Aug 14, 2019
Groundwater dolocretes may exert an important geomorphic control on landscape evolution within su... more Groundwater dolocretes may exert an important geomorphic control on landscape evolution within sub-humid to arid regions. However, the geomorphic and hydrogeological settings of dolocrete remain poorly described. The hydrochemical conditions of dolomite precipitation in groundwater environments are also not well known. Classic models of dolocrete formation explain dolomite precipitation from highly evolved groundwaters at the terminus of major drainage but do not explain dolocrete distributed in regionally elevated landscapes, upgradient of major drainage. This study investigated the mineralogy, micromorphology and stable carbon and oxygen isotope compositions of three dolocrete profiles within a regionally elevated sub-basin of the Hamersley Ranges in the Pilbara region of northwest Australia. We sought to establish the environmental and hydrochemical conditions and present a model for dolocrete formation. We found that dolocrete formed within zones of emerging groundwater under saline-evaporitic conditions within internally draining sub-basins, most likely during the Late Miocene and Pliocene. Saline-evaporitic conditions were indicated by: i) the mineralogy, dominated by dolomite, palygorskite and smectite; ii) desiccation features and the presence of phreatic and vadose cements, indicative of a shallow fluctuating water table, and; iii) dolomite δ 18 O values (median =-5.88‰). Dolomite precipitation was promoted by evaporation and CO2 degassing from shallow Mg-rich groundwater. These factors appear to have been the major drivers of dolocrete development without a requirement for significant down-dip hydrochemical modification. Primary dolomite precipitation was possible due to the presence of microbial extracellular polymeric substances (EPS). EPS provided negatively charged nucleation sites, which bound Mg 2+ , overcoming kinetic effects. High microbial activity within groundwater systems suggest these processes may be This article is protected by copyright. All rights reserved. important for dolocrete formation worldwide and that groundwater dolocretes may be more pervasive in landscapes than currently recognised.
Quaternary Science Reviews, Jul 1, 2016
Here we report a ~2000-year sediment sequence from the Fortescue Marsh (Martuyitha) in the easter... more Here we report a ~2000-year sediment sequence from the Fortescue Marsh (Martuyitha) in the eastern Pilbara region, which we have used to investigate changing hydroclimatic conditions in the arid subtropics of northwest Australia. The Pilbara is located at the intersection of the tropical Indian and Pacific Oceans and its modern rainfall regime is strongly influenced by tropical cyclones, the Intertropical Convergence Zone (ITCZ) and the Indo-Pacific Warm Pool. We identified four distinct periods within from the record. The most recent period (P1: CE ~1990-present) reveals hydroclimatic conditions over recent decades that are the most persistently wet of potentially the last ~2000 years. During the previous centuries (P2: ~CE 1600-1990), the Fortescue Marsh was overall drier but likely punctuated by a number of extreme floods, which are defined here as extraordinary, strongly episodic floods in drylands generated by rainfall events of high volume and intensity. The occurrence of extreme floods during this period, which encompasses the Little Ice Age (LIA; CE 1400-1850), is coherent with other southern tropical datasets along the ITCZ over the last 2000 years, suggesting synchronous hydroclimatic changes across the region. This extreme flood period was preceded by several hundred years (P3: ~CE 700-1600) of less vigorous but more regular flows. The earliest period of the sediment record (P4: ~CE 100-700) was the most arid, with sedimentary and preservation processes driven by prolonged drought. Our results highlight the importance of developing paleoclimate records from the tropical and subtropical arid zone, providing a long-term baseline of hydrological conditions in areas with limited historical observations.
AGU Fall Meeting Abstracts, Dec 17, 2014
Journal of Hydrology, 2017
Hydrogeology Journal, Jan 11, 2020
Hydraulic head and groundwater age data are effective in building understanding of groundwater sy... more Hydraulic head and groundwater age data are effective in building understanding of groundwater systems. Yet their joint role in detecting and characterising low-permeability geological structures, i.e. hydrogeologic barriers such as faults and dykes, has not been widely studied. Here, numerical flow and transport models, using MODFLOW-NWT and MT3D-USGS, were developed with different hydrogeologic barrier configurations in a hypothetical aquifer. Computed hydraulic head and groundwater age distributions were compared to those without a barrier. The conjoint use of these datasets helps in detecting vertically-oriented barriers. Two forms of recharge were compared: (1) applied across the entire aquifer surface (uniform), and (2) applied to the upstream part of the aquifer (upgradient). The hydraulic head distribution is significantly impacted by a barrier that penetrates the aquifer’s full vertical thickness. This barrier also perturbs the groundwater age distribution when upgradient recharge prevails; however, with uniform recharge, groundwater age is not successful in detecting the barrier. When a barrier is buried, such as by younger sediment, hydraulic head data also do not clearly identify the barrier. Groundwater age data could, on the other hand, prove to be useful if sampled at depth-specific intervals. These results are important for the detection and characterisation of hydrogeologic barriers, which may play a significant role in the compartmentalisation of groundwater flow, spring dynamics, and drawdown and recovery associated with groundwater extraction. Les données piézométriques et de datation des eaux souterraines permettent de mieux comprendre les systèmes hydrogéologiques. Pourtant, leur rôle conjoint dans la détection et la caractérisation des structures géologiques à faible perméabilité, les barrières hydrauliques telles que les failles et dykes, n’est que très peu étudié. Ici, des modèles numériques de flux et de transport, utilisant MODFLOW-NWT et MT3D-USGS, ont été élaborés avec différentes configurations de barrières hydrauliques dans un aquifère hypothétique. Les distributions des charges hydrauliques et des âges des eaux souterraines modélisés ont été comparés à celles en l’absence de barrière. L’utilisation conjointe de ces ensembles de données aide à détecter les barrières verticales. Deux formes de recharge ont été comparées: (1) la première est appliquée sur toute la surface de l’aquifère (uniforme) et (2) la deuxième est appliquée seulement sur la partie amont de l’aquifère (amont). La distribution de la charge hydraulique est fortement impactée par une barrière qui pénètre toute l’épaisseur verticale de l’aquifère. Cette barrière perturbe également la distribution des âges des eaux souterraines lorsque la recharge en amont prévaut. Cependant, avec une recharge uniforme, l’âge des eaux souterraines ne permet pas de détecter de barrière. Lorsqu’une barrière est recouverte (par des sédiments plus récents par exemple), les données piézométriques ne permettent pas non plus d’identifier clairement cette barrière. Par contre, les données de datation des eaux souterraines se révèlent utiles si elles sont échantillonnées à des intervalles de profondeur spécifiques. Ces résultats sont importants pour la détection et la caractérisation des barrières hydrauliques, qui peuvent jouer un rôle important dans le compartimentage des circulations des eaux souterraines, la dynamique des sources, le rabattement et la remontée des niveaux piézométriques associés à l’exploitation des eaux souterraines. Los datos de altura hidráulica y de edad del agua subterránea son efectivos en la construcción de la comprensión de los sistemas de agua subterránea. Sin embargo, su papel conjunto en la detección y caracterización de estructuras geológicas de baja permeabilidad, es decir, barreras hidrogeológicas como fallas y diques, no ha sido ampliamente estudiado. Aquí se desarrollaron modelos numéricos de flujo y transporte, utilizando MODFLOW-NWT y MT3D-USGS, con diferentes configuraciones de barreras hidrogeológicas en un hipotético acuífero. Se compararon las distribuciones calculadas de la altura hidráulica y la edad del agua subterránea con las que no tenían una barrera. El uso conjunto de estos conjuntos de datos ayuda a detectar las barreras de orientación vertical. Se compararon dos formas de recarga: (1) aplicarse en toda la superficie del acuífero (uniforme), y (2) aplicarse en la parte de aguas arriba del acuífero (gradiente arriba). La distribución de la altura hidráulica es impactada significativamente por una barrera vertical que penetra todo el espesor del acuífero. Esta barrera también perturba la distribución de la edad del agua subterránea cuando prevalece la recarga de nutrientes. Sin embargo, con una recarga uniforme, la edad del agua subterránea no tiene éxito en la detección de la barrera. Cuando una barrera es enterrada (como por ejemplo por sedimentos más jóvenes), los datos de la altura…
EGU General Assembly Conference Abstracts, Apr 1, 2017
Hydrology and Earth System Sciences, Feb 15, 2023
Persistent surface water pools along non-perennial rivers represent an important water resource f... more Persistent surface water pools along non-perennial rivers represent an important water resource for plants, animals, and humans. While ecological studies of these features are not uncommon, these are rarely accompanied by a rigorous examination of the hydrological and hydrogeological characteristics that create or support persistent river pools. Here we present an overarching framework for understanding the hydrology of persistent pools. Perched surface water, alluvial water throughflow, and groundwater discharge are the key hydraulic mechanisms that control the persistence of pools along river channels. Groundwater discharge can be further categorized into that controlled by a geological contact or barrier and discharge controlled by topography. Emphasis is put on clearly defining throughflow of alluvial water and the different drivers of groundwater discharge. The suite of regional-scale and pool-scale diagnostic tools available for elucidating these hydraulic mechanisms are summarized and critiqued. Water fluxes to pools supported by throughflow alluvial and groundwater discharge can vary spatially and temporally, and quantitatively resolving pool water balance components is commonly non-trivial. This framework allows for the evaluation of the susceptibility of persistent pools along river channels to changes in climate or groundwater withdrawals. Finally, we demonstrate the application of this framework using a suite of the available tools to conduct a regional and pool-scale assessment of the hydrology of persistent river pools in the Hamersley Basin of northwestern Australia.
Quaternary Science Reviews, Apr 1, 2018
Groundwater dolocrete occurring within the Fortescue Marsh, a large inland wetland in the Pilbara... more Groundwater dolocrete occurring within the Fortescue Marsh, a large inland wetland in the Pilbara region of northwest Australia, has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the Quaternary Period. Two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete, based on differences in depth, δ 18 O values and mineral composition. Group 1 (G1) occurs at depth 20 to 65 m b.g.l. (below ground level) and contains stoichiometric dolomite with δ 18 O values of-4.02 to 0.71‰. Group 2 (G2) is shallower (0 to 23 m b.g.l.), occurring close to the current groundwater level, and contains Ca-rich dolomite ± secondary calcite with a comparatively lower range of δ 18 O values (-7.74 and-6.03‰). Modelled δ 18 O values of paleogroundwater from which older G1 dolomite precipitated indicated highly saline source water, which had similar stable oxygen isotope compositions to relatively old brine groundwater within the Marsh, developed under a different hydroclimatic regime. The higher δ 18 O values suggest highly evaporitic conditions occurred at the Marsh, which may have been a playa lake to saline mud flat environment. In contrast, G2 dolomite precipitated from comparatively fresher water, and modelled δ 18 O values suggested formation from mixing between inflowing fresher groundwater with saline-brine groundwater within the Marsh. The δ 18 O values of the calcite indicates formation from brackish to saline groundwater, which suggests this process may be associated with coeval gypsum dissolution. In contrast to the modern hydrology of the Marsh, which is surface water dependent and driven by a flood and drought regime, past conditions conducive to dolomite precipitation suggest a 3 groundwater dependent system, where shallow groundwaters were influenced by intensive evaporation.
Journal of Hydrology, Nov 1, 2016
Very small groundwater outflows have the potential to significantly impact the hydrochemistry and... more Very small groundwater outflows have the potential to significantly impact the hydrochemistry and salt accumulation processes of notionally terminal basins in arid environments. However, this limited groundwater outflow can be very difficult to quantify using classical water budget calculations due to large uncertainties in estimates of evaporation and evapotranspiration rates from the surface of dry lake beds. In this study, we used a dimensionless time evaporation model to estimate the range of groundwater outflow required to maintain salinity levels observed at the Fortescue Marsh (FM), one of the largest wetlands of semi-arid northwest Australia (~1,100 km 2). The groundwater outflow from aquifers underlying the FM to the Lower Fortescue catchment is constrained by an extremely low hydraulic gradient of <0.0001 and a small 'alluvial outlet' of 0.35 km 2 because of relatively high bedrock elevation. However, FM groundwater salinity is far below saturation with respect to halite (TDS <160 g/L), episodic flood water is fresh to brackish, and salt efflorescences are very sparse and evident only when the FM is dry. We show that if the FM was 100% "leakage free" i.e., a true terminal basin, groundwater would have achieved halite saturation (> 300 g/L) after ~45 ka. We calculated that only a very small seepage of ~2 GL/yr (~0.03% of the FM water volume) is sufficient to maintain current salinity conditions. The minimum time required to develop the current hydrochemical groundwater composition under the FM ranges from ~60 to ~165 ka. We conclude that a dimensionless time evaporation model versus inflow over outflow ratio model is likely more suitable than classical water budget calculations for determining outflow from large saline lakes and to estimate groundwater seepage from hydrologically terminal basins.
Hydrology and Earth System Sciences, Apr 29, 2015
Long-term hydrologic records provide crucial reference baselines of natural variability that can ... more Long-term hydrologic records provide crucial reference baselines of natural variability that can be used to evaluate potential changes in hydrologic regimes and their impacts. However, there is a dearth of studies of the hydrologic regimes for tropical drylands where intraseasonal and interannual variability in magnitude and frequency of precipitation are extreme. Here, we sought to identify the main hydroclimatic determinants of the strongly episodic flood regime of a large catchment in the semi-arid, subtropical northwest of Australia and to establish the background of hydrologic variability for the region over the last century. We used a monthly sequence of satellite images to quantify surface water expression on the Fortescue Marsh, the largest water feature of inland northwest Australia, from 1988 to 2012. We used this sequence together with instrumental rainfall data to build a statistical model with multiple linear regression and reconstruct monthly history of floods and droughts since 1912. We found that severe and intense regional rainfall events, as well as the sequence of recharge events both within and between years, determine surface water expression on the floodplain (i.e. total rainfall, number of rain days and carried-over inundated area; R 2 adj = 0.79; p value < 0.001, E RMSP = 56 km 2). The most severe reconstructed inundation over the last century was in March 2000 (1000 km 2), which is less than the 1300 km 2 area required to overflow to the adjacent catchment. The Fortescue Marsh was completely dry for 32% of all years, for periods of up to four consecutive years. Extremely wet years (seven of the 100 years) caused the Marsh to remain inundated for up to 12 months; only 25 % of years (9 % of all months) had floods of greater than 300 km 2. The prolonged, severe and consecutive yearly inundations between 1999 and 2006 were unprecedented compared to the last century. While there is high inter-annual variability in the system, if the frequency and intensity of extreme rainfall events for the region were to increase (or be similar to 1999-2006), surface water on the Marsh will become more persistent, in turn impacting its structure and functioning as a wetland.
Persistent surface water pools along non-perennial rivers represent an important water resource f... more Persistent surface water pools along non-perennial rivers represent an important water resource for plants, animals, and humans. While ecological studies of these features are not uncommon, these are rarely accompanied by a rigorous examination of the hydrological and hydrogeological characteristics that create or support the pools. Here we present an overarching framework for understanding the hydrology of persistent pools. We identified perched water, alluvial through flow and groundwater discharge as mechanisms that control the persistence of pools along river channels. Groundwater discharge is further categorized into that controlled by a geological contact or barrier (not previously described in the literature), and discharge controlled by topography. Emphasis is put on clearly defining through-flow pools and the different drivers of groundwater discharge, as this is lacking in the literature. A suite of diagnostic tools (including geological mapping, hydraulic data and hydrochemical surveys) is generally required to identify the mechanism(s) supporting persistent pools. Water fluxes to pools supported by through-flow alluvial and bedrock aquifers can vary seasonally and resolving these inputs is generally non-trivial. This framework allows the evaluation of the susceptibility of persistent pools along river channels to changes in climate or groundwater withdrawals. Finally, we present three case studies from the Hamersley Basin of northwestern Australia to demonstrate how the available diagnostic tools can be applied within the proposed framework.
Geophysical Research Letters, Dec 1, 2022
Analyzing groundwater systems in transient state is essential for understanding the response of g... more Analyzing groundwater systems in transient state is essential for understanding the response of groundwater recharge to changing environments. Radioactive isotopes have long been used to track recharge behavior, typically under steady state conditions. This study tests the limitations of using radioactive isotopes in confined aquifers and under transient conditions to sense changes in groundwater recharge rates over time. Four system parameters determine the bounds of this approach: the isotope half‐life, the Péclet number (Pe), and mobile‐immobile zone interactions. This study revealed that in confined groundwater systems where Pe ≥ 10, isotopes reflect transience when the half‐life matches the water travel time down the flow path or the time elapsed from the change in velocity. This response is evident regardless of mobile‐immobile interaction, suggesting that appropriate isotope selection is key to establishing past recharge regardless of aquifer lithology or geometry.
Journal of Hydrology, Dec 1, 2018
Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 2016
HIGHLIGHTS (max 85 characters) • Biomarkers and n-alkane δ 13 C were extracted from sediment with... more HIGHLIGHTS (max 85 characters) • Biomarkers and n-alkane δ 13 C were extracted from sediment with total C = 0.4-1.4% • Distribution of biomarkers reflected a decrease of aridity in the last ~2000 years • Arid based Bayesian model of n-alkanes δ 13 C suggested increase of riparian C3 input
Aquatic Sciences, Feb 26, 2020
Streams in hot, arid environments often exist as a series of isolated pools along main 21 channel... more Streams in hot, arid environments often exist as a series of isolated pools along main 21 channels. During these periods, shallow alluvial throughflow may strongly influence key 22 ecological processes within pools. We measured diel changes in δ C values of dissolved 23 inorganic carbon (DIC) and dissolved oxygen (DO) in two pools of ephemeral, dryland 24 streams. We quantified alluvial water connectivity through stable isotope analysis (δ 18 O and 25 δ 2 H) of pool and alluvial water. We also estimated gross primary productivity (GPP) and 26 ecosystem respiration (ER) rates across a wider set of pools in both streams. δ 13 CDIC values 27 displayed regular diel cycles, where both pools displayed small but similar daily amplitude 28 (0.7-0.9‰) despite contrasting amplitudes of change in DO (0.8 mg L-1 vs. 2.8 mg L-1) and 29 contrasting alluvial water connectivity (connected vs. disconnected). Water temperature was 30 the strongest predictor of both δ 13 CDIC values and rates of change in δ 13 CDIC across both 31 pools. Across both streams, all pools were net heterotrophic. GPP (0.35 to 1.73 g O2 m-2 d-1) 32 and ER (0.49 to 2.64 g O2 m-2 d-1) rates were linked to aquatic vegetation cover. The 33 disconnect between diurnal amplitudes of δ 13 C values and DO concentrations thus suggests 34 that ecological drivers of gas exchange became increasingly localised as pools contracted.
Journal of Hydrology, Nov 1, 2019
Evaporative flux from soils in arid and semi-arid climates can be very high and may substantially... more Evaporative flux from soils in arid and semi-arid climates can be very high and may substantially reduce soil moisture retained between infrequent rainfall events. Direct measurement of the evaporative losses from soils is technically challenging; however, environmental tracers such as stable hydrogen and oxygen isotope composition can be used to calculate evaporation rates if the initial signature of the infiltrating rainwater is distinct from the signature of residual soil moisture. Large tropical cyclones typically result in rainfall events of large volume and very negative δ 18 O signatures that are significantly lower than the signatures of the usual precipitation. These very negative stable isotope signatures are retained in the soil and can be used to understand the depth of water infiltration, retention and subsequent rate of evaporation from the soil. At our study site in dry subtropical northwest Australia, we repeatedly sampled rainwater and soil moisture prior to, during and after tropical cyclones Heidi and Lua in 2012. Site inundation from Cyclone Heidi (rainfall 213 mm, δ 18 O-17.6 ‰) replenished soil moisture in the unsaturated zone for several months, completely replacing soil moisture down to depths of ~3.5 m and contributing to groundwater recharge. The transient momentary evaporative losses from wet soil at the time of sampling (recalculated as an annual rate) varied between 76 and 220 mm×yr-1. During the prolonged dry period between cyclones, evaporative losses decreased to between 8 and 30 mm×yr-1. Consequently, mean long-term groundwater recharge for the study period was low (<6 mm×yr-1) and primarily driven by infrequent but high-volume cyclones that are an important source of soil moisture and therefore an essential water source for vegetation in the semi-arid environment. However, upscaling from a local to a regional scale model for ecological water demand would be challenging due to the high variability in δ 18 O observed in soil profiles, which varies with lithology, position in the landscape and time since the last inundation.
Journal of Hydrology, Feb 1, 2017
Sulphur (S) is a commonly occurring element in most aquifers, primarily in oxidised (sulphates) a... more Sulphur (S) is a commonly occurring element in most aquifers, primarily in oxidised (sulphates) and reduced (sulphides) forms. Sulphides often constitute a risk to groundwater quality due to acid rock drainage, especially in catchments that are subject to mining excavations or groundwater injection. However, in semi-arid regions detection of the acid rock drainage risk can be challenging and traditional methods based on observations of increasing SO 4 concentrations or SO 4 /Cl ratios in surface and groundwater, are not necessarily applicable. In addition, decreasing pH, usually accompanying pyrite oxidation, can be masked by the high pH-neutralisation capacity of carbonate and silicate minerals. Analysis of 73 surface and groundwater samples from different water bodies and aquifers located in the Hamersley Basin, Western Australia found that most of the samples are characterised by neutral pH but there was also a large spatial variability in the dissolved sulphate (SO 4) concentrations that ranged from 1 mg/L to 15,000 mg/L. Not surprisingly, groundwater in aquifers that contained pyrite had high sulphate concentrations (>1000 mg/L). This was associated with low d 34 S SO4 values (+1.2‰ to +4.6‰) and was consistent with the values obtained from aquifer matrix pyritic rock samples (À1.9‰ to +4.4‰). It was also found that the SO 4 concentrations and acidity levels were not only dependent on d 34 S SO4 values and existence of pyrite but also on the presence of carbonate minerals in the aquifer matrix. The groundwater in aquifers containing both pyrite and carbonate minerals had a neutral pH and was also saturated with respect to gypsum and had high magnesium concentrations of up to 2200 mg/L suggesting dedolomitisation as the process buffering the acidity generated by pyrite oxidation. Based on the findings from this study, a classification scheme has been developed for identification of the acid rock drainage contribution to groundwater that encompasses a myriad of geochemical processes that occur in aqueous systems. The classification uses five proxies (SO 4 , SO 4 /Cl, SI of calcite, d 34 S SO4 and d 18 O SO4) to improve assessment of the oxidation of sulphide potential contribution to overall sulphate ion concentrations regardless of acidity levels of the aqueous system.
EGU General Assembly Conference Abstracts, Apr 1, 2017
AGU Fall Meeting Abstracts, Dec 18, 2014
Earth Surface Processes and Landforms, Aug 14, 2019
Groundwater dolocretes may exert an important geomorphic control on landscape evolution within su... more Groundwater dolocretes may exert an important geomorphic control on landscape evolution within sub-humid to arid regions. However, the geomorphic and hydrogeological settings of dolocrete remain poorly described. The hydrochemical conditions of dolomite precipitation in groundwater environments are also not well known. Classic models of dolocrete formation explain dolomite precipitation from highly evolved groundwaters at the terminus of major drainage but do not explain dolocrete distributed in regionally elevated landscapes, upgradient of major drainage. This study investigated the mineralogy, micromorphology and stable carbon and oxygen isotope compositions of three dolocrete profiles within a regionally elevated sub-basin of the Hamersley Ranges in the Pilbara region of northwest Australia. We sought to establish the environmental and hydrochemical conditions and present a model for dolocrete formation. We found that dolocrete formed within zones of emerging groundwater under saline-evaporitic conditions within internally draining sub-basins, most likely during the Late Miocene and Pliocene. Saline-evaporitic conditions were indicated by: i) the mineralogy, dominated by dolomite, palygorskite and smectite; ii) desiccation features and the presence of phreatic and vadose cements, indicative of a shallow fluctuating water table, and; iii) dolomite δ 18 O values (median =-5.88‰). Dolomite precipitation was promoted by evaporation and CO2 degassing from shallow Mg-rich groundwater. These factors appear to have been the major drivers of dolocrete development without a requirement for significant down-dip hydrochemical modification. Primary dolomite precipitation was possible due to the presence of microbial extracellular polymeric substances (EPS). EPS provided negatively charged nucleation sites, which bound Mg 2+ , overcoming kinetic effects. High microbial activity within groundwater systems suggest these processes may be This article is protected by copyright. All rights reserved. important for dolocrete formation worldwide and that groundwater dolocretes may be more pervasive in landscapes than currently recognised.
Quaternary Science Reviews, Jul 1, 2016
Here we report a ~2000-year sediment sequence from the Fortescue Marsh (Martuyitha) in the easter... more Here we report a ~2000-year sediment sequence from the Fortescue Marsh (Martuyitha) in the eastern Pilbara region, which we have used to investigate changing hydroclimatic conditions in the arid subtropics of northwest Australia. The Pilbara is located at the intersection of the tropical Indian and Pacific Oceans and its modern rainfall regime is strongly influenced by tropical cyclones, the Intertropical Convergence Zone (ITCZ) and the Indo-Pacific Warm Pool. We identified four distinct periods within from the record. The most recent period (P1: CE ~1990-present) reveals hydroclimatic conditions over recent decades that are the most persistently wet of potentially the last ~2000 years. During the previous centuries (P2: ~CE 1600-1990), the Fortescue Marsh was overall drier but likely punctuated by a number of extreme floods, which are defined here as extraordinary, strongly episodic floods in drylands generated by rainfall events of high volume and intensity. The occurrence of extreme floods during this period, which encompasses the Little Ice Age (LIA; CE 1400-1850), is coherent with other southern tropical datasets along the ITCZ over the last 2000 years, suggesting synchronous hydroclimatic changes across the region. This extreme flood period was preceded by several hundred years (P3: ~CE 700-1600) of less vigorous but more regular flows. The earliest period of the sediment record (P4: ~CE 100-700) was the most arid, with sedimentary and preservation processes driven by prolonged drought. Our results highlight the importance of developing paleoclimate records from the tropical and subtropical arid zone, providing a long-term baseline of hydrological conditions in areas with limited historical observations.
AGU Fall Meeting Abstracts, Dec 17, 2014
Journal of Hydrology, 2017
Hydrogeology Journal, Jan 11, 2020
Hydraulic head and groundwater age data are effective in building understanding of groundwater sy... more Hydraulic head and groundwater age data are effective in building understanding of groundwater systems. Yet their joint role in detecting and characterising low-permeability geological structures, i.e. hydrogeologic barriers such as faults and dykes, has not been widely studied. Here, numerical flow and transport models, using MODFLOW-NWT and MT3D-USGS, were developed with different hydrogeologic barrier configurations in a hypothetical aquifer. Computed hydraulic head and groundwater age distributions were compared to those without a barrier. The conjoint use of these datasets helps in detecting vertically-oriented barriers. Two forms of recharge were compared: (1) applied across the entire aquifer surface (uniform), and (2) applied to the upstream part of the aquifer (upgradient). The hydraulic head distribution is significantly impacted by a barrier that penetrates the aquifer’s full vertical thickness. This barrier also perturbs the groundwater age distribution when upgradient recharge prevails; however, with uniform recharge, groundwater age is not successful in detecting the barrier. When a barrier is buried, such as by younger sediment, hydraulic head data also do not clearly identify the barrier. Groundwater age data could, on the other hand, prove to be useful if sampled at depth-specific intervals. These results are important for the detection and characterisation of hydrogeologic barriers, which may play a significant role in the compartmentalisation of groundwater flow, spring dynamics, and drawdown and recovery associated with groundwater extraction. Les données piézométriques et de datation des eaux souterraines permettent de mieux comprendre les systèmes hydrogéologiques. Pourtant, leur rôle conjoint dans la détection et la caractérisation des structures géologiques à faible perméabilité, les barrières hydrauliques telles que les failles et dykes, n’est que très peu étudié. Ici, des modèles numériques de flux et de transport, utilisant MODFLOW-NWT et MT3D-USGS, ont été élaborés avec différentes configurations de barrières hydrauliques dans un aquifère hypothétique. Les distributions des charges hydrauliques et des âges des eaux souterraines modélisés ont été comparés à celles en l’absence de barrière. L’utilisation conjointe de ces ensembles de données aide à détecter les barrières verticales. Deux formes de recharge ont été comparées: (1) la première est appliquée sur toute la surface de l’aquifère (uniforme) et (2) la deuxième est appliquée seulement sur la partie amont de l’aquifère (amont). La distribution de la charge hydraulique est fortement impactée par une barrière qui pénètre toute l’épaisseur verticale de l’aquifère. Cette barrière perturbe également la distribution des âges des eaux souterraines lorsque la recharge en amont prévaut. Cependant, avec une recharge uniforme, l’âge des eaux souterraines ne permet pas de détecter de barrière. Lorsqu’une barrière est recouverte (par des sédiments plus récents par exemple), les données piézométriques ne permettent pas non plus d’identifier clairement cette barrière. Par contre, les données de datation des eaux souterraines se révèlent utiles si elles sont échantillonnées à des intervalles de profondeur spécifiques. Ces résultats sont importants pour la détection et la caractérisation des barrières hydrauliques, qui peuvent jouer un rôle important dans le compartimentage des circulations des eaux souterraines, la dynamique des sources, le rabattement et la remontée des niveaux piézométriques associés à l’exploitation des eaux souterraines. Los datos de altura hidráulica y de edad del agua subterránea son efectivos en la construcción de la comprensión de los sistemas de agua subterránea. Sin embargo, su papel conjunto en la detección y caracterización de estructuras geológicas de baja permeabilidad, es decir, barreras hidrogeológicas como fallas y diques, no ha sido ampliamente estudiado. Aquí se desarrollaron modelos numéricos de flujo y transporte, utilizando MODFLOW-NWT y MT3D-USGS, con diferentes configuraciones de barreras hidrogeológicas en un hipotético acuífero. Se compararon las distribuciones calculadas de la altura hidráulica y la edad del agua subterránea con las que no tenían una barrera. El uso conjunto de estos conjuntos de datos ayuda a detectar las barreras de orientación vertical. Se compararon dos formas de recarga: (1) aplicarse en toda la superficie del acuífero (uniforme), y (2) aplicarse en la parte de aguas arriba del acuífero (gradiente arriba). La distribución de la altura hidráulica es impactada significativamente por una barrera vertical que penetra todo el espesor del acuífero. Esta barrera también perturba la distribución de la edad del agua subterránea cuando prevalece la recarga de nutrientes. Sin embargo, con una recarga uniforme, la edad del agua subterránea no tiene éxito en la detección de la barrera. Cuando una barrera es enterrada (como por ejemplo por sedimentos más jóvenes), los datos de la altura…
EGU General Assembly Conference Abstracts, Apr 1, 2017
Hydrology and Earth System Sciences, Feb 15, 2023
Persistent surface water pools along non-perennial rivers represent an important water resource f... more Persistent surface water pools along non-perennial rivers represent an important water resource for plants, animals, and humans. While ecological studies of these features are not uncommon, these are rarely accompanied by a rigorous examination of the hydrological and hydrogeological characteristics that create or support persistent river pools. Here we present an overarching framework for understanding the hydrology of persistent pools. Perched surface water, alluvial water throughflow, and groundwater discharge are the key hydraulic mechanisms that control the persistence of pools along river channels. Groundwater discharge can be further categorized into that controlled by a geological contact or barrier and discharge controlled by topography. Emphasis is put on clearly defining throughflow of alluvial water and the different drivers of groundwater discharge. The suite of regional-scale and pool-scale diagnostic tools available for elucidating these hydraulic mechanisms are summarized and critiqued. Water fluxes to pools supported by throughflow alluvial and groundwater discharge can vary spatially and temporally, and quantitatively resolving pool water balance components is commonly non-trivial. This framework allows for the evaluation of the susceptibility of persistent pools along river channels to changes in climate or groundwater withdrawals. Finally, we demonstrate the application of this framework using a suite of the available tools to conduct a regional and pool-scale assessment of the hydrology of persistent river pools in the Hamersley Basin of northwestern Australia.
Quaternary Science Reviews, Apr 1, 2018
Groundwater dolocrete occurring within the Fortescue Marsh, a large inland wetland in the Pilbara... more Groundwater dolocrete occurring within the Fortescue Marsh, a large inland wetland in the Pilbara region of northwest Australia, has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the Quaternary Period. Two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete, based on differences in depth, δ 18 O values and mineral composition. Group 1 (G1) occurs at depth 20 to 65 m b.g.l. (below ground level) and contains stoichiometric dolomite with δ 18 O values of-4.02 to 0.71‰. Group 2 (G2) is shallower (0 to 23 m b.g.l.), occurring close to the current groundwater level, and contains Ca-rich dolomite ± secondary calcite with a comparatively lower range of δ 18 O values (-7.74 and-6.03‰). Modelled δ 18 O values of paleogroundwater from which older G1 dolomite precipitated indicated highly saline source water, which had similar stable oxygen isotope compositions to relatively old brine groundwater within the Marsh, developed under a different hydroclimatic regime. The higher δ 18 O values suggest highly evaporitic conditions occurred at the Marsh, which may have been a playa lake to saline mud flat environment. In contrast, G2 dolomite precipitated from comparatively fresher water, and modelled δ 18 O values suggested formation from mixing between inflowing fresher groundwater with saline-brine groundwater within the Marsh. The δ 18 O values of the calcite indicates formation from brackish to saline groundwater, which suggests this process may be associated with coeval gypsum dissolution. In contrast to the modern hydrology of the Marsh, which is surface water dependent and driven by a flood and drought regime, past conditions conducive to dolomite precipitation suggest a 3 groundwater dependent system, where shallow groundwaters were influenced by intensive evaporation.
Journal of Hydrology, Nov 1, 2016
Very small groundwater outflows have the potential to significantly impact the hydrochemistry and... more Very small groundwater outflows have the potential to significantly impact the hydrochemistry and salt accumulation processes of notionally terminal basins in arid environments. However, this limited groundwater outflow can be very difficult to quantify using classical water budget calculations due to large uncertainties in estimates of evaporation and evapotranspiration rates from the surface of dry lake beds. In this study, we used a dimensionless time evaporation model to estimate the range of groundwater outflow required to maintain salinity levels observed at the Fortescue Marsh (FM), one of the largest wetlands of semi-arid northwest Australia (~1,100 km 2). The groundwater outflow from aquifers underlying the FM to the Lower Fortescue catchment is constrained by an extremely low hydraulic gradient of <0.0001 and a small 'alluvial outlet' of 0.35 km 2 because of relatively high bedrock elevation. However, FM groundwater salinity is far below saturation with respect to halite (TDS <160 g/L), episodic flood water is fresh to brackish, and salt efflorescences are very sparse and evident only when the FM is dry. We show that if the FM was 100% "leakage free" i.e., a true terminal basin, groundwater would have achieved halite saturation (> 300 g/L) after ~45 ka. We calculated that only a very small seepage of ~2 GL/yr (~0.03% of the FM water volume) is sufficient to maintain current salinity conditions. The minimum time required to develop the current hydrochemical groundwater composition under the FM ranges from ~60 to ~165 ka. We conclude that a dimensionless time evaporation model versus inflow over outflow ratio model is likely more suitable than classical water budget calculations for determining outflow from large saline lakes and to estimate groundwater seepage from hydrologically terminal basins.
Hydrology and Earth System Sciences, Apr 29, 2015
Long-term hydrologic records provide crucial reference baselines of natural variability that can ... more Long-term hydrologic records provide crucial reference baselines of natural variability that can be used to evaluate potential changes in hydrologic regimes and their impacts. However, there is a dearth of studies of the hydrologic regimes for tropical drylands where intraseasonal and interannual variability in magnitude and frequency of precipitation are extreme. Here, we sought to identify the main hydroclimatic determinants of the strongly episodic flood regime of a large catchment in the semi-arid, subtropical northwest of Australia and to establish the background of hydrologic variability for the region over the last century. We used a monthly sequence of satellite images to quantify surface water expression on the Fortescue Marsh, the largest water feature of inland northwest Australia, from 1988 to 2012. We used this sequence together with instrumental rainfall data to build a statistical model with multiple linear regression and reconstruct monthly history of floods and droughts since 1912. We found that severe and intense regional rainfall events, as well as the sequence of recharge events both within and between years, determine surface water expression on the floodplain (i.e. total rainfall, number of rain days and carried-over inundated area; R 2 adj = 0.79; p value < 0.001, E RMSP = 56 km 2). The most severe reconstructed inundation over the last century was in March 2000 (1000 km 2), which is less than the 1300 km 2 area required to overflow to the adjacent catchment. The Fortescue Marsh was completely dry for 32% of all years, for periods of up to four consecutive years. Extremely wet years (seven of the 100 years) caused the Marsh to remain inundated for up to 12 months; only 25 % of years (9 % of all months) had floods of greater than 300 km 2. The prolonged, severe and consecutive yearly inundations between 1999 and 2006 were unprecedented compared to the last century. While there is high inter-annual variability in the system, if the frequency and intensity of extreme rainfall events for the region were to increase (or be similar to 1999-2006), surface water on the Marsh will become more persistent, in turn impacting its structure and functioning as a wetland.
Persistent surface water pools along non-perennial rivers represent an important water resource f... more Persistent surface water pools along non-perennial rivers represent an important water resource for plants, animals, and humans. While ecological studies of these features are not uncommon, these are rarely accompanied by a rigorous examination of the hydrological and hydrogeological characteristics that create or support the pools. Here we present an overarching framework for understanding the hydrology of persistent pools. We identified perched water, alluvial through flow and groundwater discharge as mechanisms that control the persistence of pools along river channels. Groundwater discharge is further categorized into that controlled by a geological contact or barrier (not previously described in the literature), and discharge controlled by topography. Emphasis is put on clearly defining through-flow pools and the different drivers of groundwater discharge, as this is lacking in the literature. A suite of diagnostic tools (including geological mapping, hydraulic data and hydrochemical surveys) is generally required to identify the mechanism(s) supporting persistent pools. Water fluxes to pools supported by through-flow alluvial and bedrock aquifers can vary seasonally and resolving these inputs is generally non-trivial. This framework allows the evaluation of the susceptibility of persistent pools along river channels to changes in climate or groundwater withdrawals. Finally, we present three case studies from the Hamersley Basin of northwestern Australia to demonstrate how the available diagnostic tools can be applied within the proposed framework.
Geophysical Research Letters, Dec 1, 2022
Analyzing groundwater systems in transient state is essential for understanding the response of g... more Analyzing groundwater systems in transient state is essential for understanding the response of groundwater recharge to changing environments. Radioactive isotopes have long been used to track recharge behavior, typically under steady state conditions. This study tests the limitations of using radioactive isotopes in confined aquifers and under transient conditions to sense changes in groundwater recharge rates over time. Four system parameters determine the bounds of this approach: the isotope half‐life, the Péclet number (Pe), and mobile‐immobile zone interactions. This study revealed that in confined groundwater systems where Pe ≥ 10, isotopes reflect transience when the half‐life matches the water travel time down the flow path or the time elapsed from the change in velocity. This response is evident regardless of mobile‐immobile interaction, suggesting that appropriate isotope selection is key to establishing past recharge regardless of aquifer lithology or geometry.