Freshwater Zone Research Articles

Distribution and grazing of the dominant mesozooplankton species in the Yenisei estuary and adjacent shelf in early summer (July 2016)

Estuaries of large Siberian rivers, Yenisei and Ob, play a pivotal role in transformation and sedimentation of the suspended matter from the riverine runoff. The mesozooplankton community is one of the key players in estuarine functioning. Most of the studies in the Yenisei region were performed at the end of the productive season (August–September) and concentrated on the structure of zooplankton community. The main goal of this study was to characterize structure and grazing of the zooplankton community in the Yenisei estuarine and plume-affected shelf region in early summer soon after the discharge maximum. More specifically, we assessed zooplankton biomass and analyzed the distribution patterns of the dominant species in July; assessed herbivorous feeding rates; and grazing pressure of these species during the period of high phytoplankton production. Zooplankton were collected and feeding rates were studied along a quasi-latitudinal transect in the Yenisei Estuary and the adjacent shelf in July 2016. Freshwater zone (FWZ), frontal zone of the Yenisei plume (YFZ) and shelf zone outside the plume (MSZ) were distinguished according to salinity and temperature. Highest biomass (12–101 mg DW m−3) was recorded in the YFZ. Several specific aspects of distribution and grazing were distinguished. Cladocera were highly abundant in the FWZ and grazed up to 14% of phytoplankton there. Species which dominated zooplankton in the YFZ avoided the upper freshened layer, and maximum abundance of both marine and brackish species coincided with the gradient layer. The brackish Limnocalanus macrurus penetrated far into the north where this species was supposedly exported earlier with the maximal runoff. Low ingestion (0.1–0.9% body carbon) and demographic structure of L. macrurus suggest termination of seasonal development of the population. Herbivorous feeding of the marine copepods exceeded their metabolic demands in the estuarine zone and was insufficient in the marine shelf zone. The highest daily grazing pressure in the YFZ (up to 21% phytoplankton biomass) was exerted by Calanus glacialis. Analysis of our results together with the published data implies that timing of ice retreat is among the main factors controlling seasonal development of the dominant zooplankton populations.

An investigation of the spatial and temporal variability of the saline interface in a sandy aquifer subject to storm wave runup and rainfall recharge

Investigations at Hat Head in northern New South Wales, Australia, have shown that the depth and location of the saline interface changes significantly in response to storm-induced wave runup, rainfall recharge and regional groundwater discharge. The interplay between these three factors creates moving zones of fresh and salty water that displace each other over time, leading to the development of complex geochemical patterns. The results of an extensive hydrogeological investigation incorporating surface and borehole geophysics, drilling, monitoring and hydrochemical sampling on multiple occasions has demonstrated that the mixing zone between fresh groundwater and seawater occurs as zones of variable chemical composition which extend further inland and to greater depths than anticipated. The location and magnitude of these mixing zones varies over time scales of weeks. The chemical processes within these mixing zones are dominated by redox reactions that may never reach an equilibrium, with the system being episodically disturbed by new storm events. Diel changes from tides do not have an observable impact on the interface. An improved understanding of these processes will require regular monitoring and sampling from a range of vertical sampling points in the coastal zone, combined with routine monitoring using borehole induction logs.

A Model Analysis of the Tidal Engine That Drives Nitrogen Cycling in Coastal Riparian Aquifers

AbstractIn coastal rivers, tides facilitate surface water‐groundwater exchange and strongly coupled nitrification‐denitrification near the fluctuating water table. We used numerical fluid flow and reactive transport models to explore hydrogeologic and biogeochemical controls on nitrogen transport along an idealized tidal freshwater zone based on field observations from White Clay Creek, Delaware, USA. The capacity of the riparian aquifer to remove nitrate depends largely on nitrate transport rates, which initially increase with increasing tidal range but then decline as sediments become muddier and permeability decreases. Over the entire model reach, local nitrification provides a similar amount of nitrate as surface and groundwater contributions combined. More than half (~66%) of nitrate removed via denitrification is produced in situ, while the vast majority of remaining nitrate removed comes from groundwater sources. In contrast, average nitrate removal from surface water due to tidal pumping amounts to only ~1% of the average daily in‐channel riverine nitrate load or 1.77 kg of nitrate along the reach each day. As a result, tidal bank storage zones may not be major sinks for nitrate in coastal rivers but can act as effective sinks for groundwater nitrate. By extension, tidal bank storage zones provide a critical ecosystem service, reducing contributions of groundwater nitrate, which is often derived from septic tanks and fertilizers, to coastal rivers.

Defining a Riverine Tidal Freshwater Zone and Its Spatiotemporal Dynamics

AbstractTidal freshwater zones (TFZs) are transitional environments between terrestrial and coastal waters. TFZs have freshwater chemistry and tidal physics, and yet are neither river nor estuary based on classic definitions. Such zones have been occasionally discussed in the literature but lack a consistent nomenclature and framework for study. This work proposes a measurable definition for TFZs based on three longitudinal points of interest: (1) the upstream limit of brackish water, (2) the upstream limit of bidirectional tidal velocities, and (3) the upstream limit of tidal stage fluctuations. The resulting size and position of a TFZ is transient and depends on the balance of tidal and riverine forces that evolves over event, tidal, seasonal, and annual (or longer) timescales. The concept, definition, and transient analysis of TFZ position are illustrated using field observations from the Aransas River (Texas, USA) from July 2015 to July 2016. The median Aransas TFZ length was 59.9 km, with a late summer maximum of 66.0 km and a winter minimum of 53.6 km. The TFZ typically (annual median) began 11.8 km upstream from the river mouth (15.4 km winter/11.2 km summer medians) and ended 71.7 km upstream (69.0 km/77.2 km). Seasonally low baseflow in the Aransas River promoted gradual coastal salt encroachment upstream, which shortened the TFZ. However, sporadic large rainfall/runoff events rapidly elongated the TFZ. The TFZ definition establishes a quantifiable framework for analyzing these critical freshwater systems that reside at the nexus of natural and human‐influenced hydrology, tides, and climate.

The assessment of water quality in river Molo water basin, Kenya

The monitoring of water quality for both domestic and commercial use is absolutely essential for policy formulation that affects both public and environmental health. This study investigates the quality of water of river Molo system which lies in the Kenyan Rift Valley. The river is considered a vital source of water for the residents and industrial activities in Nakuru and Baringo Counties. Six water samples were collected during the dry season of December 2017. Various physicochemical parameters were determined in situ by use of a portable pH meter. These parameters included pH, temperature, electrical conductivity and total dissolved solids (TDS). Anions such as fluorides, sulfates, phosphates, nitrates, chlorides, carbonates and bicarbonates were determined using conventional methods such as titrimetry and (ultra-violet visible) UV–Vis techniques. The cations including sodium, potassium, calcium and magnesium were determined using flame photometry. The results showed that the water had pH values ranging from 7.90 to 9.66 units, temperature ranged from 14.02 to 31.5 °C, while electrical conductivity ranged from 181 to 1637 μS/cm, TDS (69–823 mg/L), F (2.76–3.28 mg/L), sulfates (4.97–85.66 mg/L), phosphates (0.13–11.06 mg/L), nitrates (1.73–6.16 mg/L), chlorides (38.5–69.4 mg/L), carbonates (18–148 mg/L), bicarbonates (54–384 mg/L), sodium (19–1800 mg/L), potassium (8.9–121 mg/L), magnesium (4.8–106.8 mg/L) and calcium (13.4–77.4 mg/L). The pH, temperature, fluorides and sodium were above the World Health Organization permissible limits for drinking water in S4 and S5. All the water samples fall under bicarbonate or freshwater zone. The sampling points can be classified into five water types: Na–Mg–Ca–HCO3, Na–HCO3, Na–Ca–Mg–HCO3–CO3, Na and Na–Ca–HCO3–CO3. Chemical indices such as sodium adsorption ratio, magnesium hazard, percent sodium and permeability index are reported. Accordingly, the findings from this work indicate that the river Molo water in general is good for irrigation.

Association of geomorphic features with groundwater quality and freshwater availability in coastal regions

Seawater intrusion into coastal aquifers is a global problem as it limits the freshwater availability in coastal regions. A study has been conducted with the aims to identify the processes controlling seawater/freshwater distribution and demarcate potential freshwater zones in an aquifer along the coast of Bay of Bengal. Sixty-eight groundwater samples were collected from 900 sq. km spread along the coast and were analyzed for various physicochemical parameters. Most of the samples show brackish to saline characteristics. The anionic ratio indicates that 65% of groundwater samples are slightly to moderately affected by seawater, while 25% are severely affected. Seawater–freshwater mixing and freshening have been identified as the dominant processes in controlling the groundwater chemistry. Seawater has been traced in 88% of collected samples, and it is found that only 1% mixing of the seawater makes the groundwater unsuitable for drinking purposes. The fraction of seawater in individual samples has been calculated using chloride as a tracer. Thematic maps of seawater tracers have indicated that groundwater with higher salinity is located in the inland areas, whereas patches of fresh groundwater are found near the coast. With the help of satellite imageries, it has been found that the freshwater patches are typically located on paleochannels and sand dunes, which act as local reservoirs to retain freshwater in the seawater affected region. Such geomorphic features are common in coastal environments. Their identification and subsequent utilization as freshwater sources can be of vital importance to deal with freshwater scarcity in the coastal regions across the globe.

Mapping Shallow Aquifers Intruded by Saltwater in the Coastal Area of Benin River in Western Niger Delta fromDar-Zarrouk Parameters

Shallow aquifers are the major source of groundwater to the inhabitants of the coastal area of the Niger Delta. Groundwater is harnessed by hand-dug wells because they are easier and inexpensive to construct compared to boreholes. The closeness of groundwater water table to the surface encourages the construction of dug wells. The coastal area under investigation is faced with acute groundwater quality and assessment problems arising from saltwater intrusion. Dar-Zarrouk parameter comprising of longitudinal unit conductance(S) and transverse unit resistance (T) were coupled with resistivity to discriminate freshwater from saltwater zones. S across the area ranged from 0.03 to 2.96 Siemens and T from 1.4 to 790 Ω m2. S values greater and lesser than 0.3Siemens were considered as saltwater and freshwater zones respectively, while T values that ranged from 1.32 to 161.33Ω m2 were regarded as saltwater zones. Resistivity high of 185Ωm to 1511.58Ωm was assigned freshwater zones. The resistivity data considered showed evidence of freshwater at depth of 27.6m and saltwater at 34.3m. The lateral interface between saltwater and freshwater is situated at 565m from the sea. The intrusion revealed by the study does not suggest over-withdrawal of groundwater because of the small population of inhabitants but to natural hydrodynamic forcing connected with aquifer adjacent to the sea. However, the tendency of upconing of saltwater into the freshwater aquifer is probably at the depth of 3.9 to 12.3m by over-withdrawing of groundwater may not be ruled out in the future. Induced polarization is suggested as a follow-up investigation to unravel ambiguity that may be associated with resolution of resistivity data.Key words: Benin River, Niger Delta, Saltwater intrusion, Dar-Zarrouk Parameters, longitudinal unit conductance, transverse unit resistance.

Pseudobranch mimics gill in expressing Na+K+-ATPase 1 α-subunit and carbonic anhydrase in concert with H+-ATPase in adult hilsa (Tenualosa ilisha) during river migration.

In hilsa (Tenualosa ilisha), pseudobranch comprises a row of parallel filaments bear numerous leaf-like lamellae arranged on both sides throughout its length. The purpose of this study was to elucidate involvement of pseudobranchial Na+, K+-ATPase (NKA) 1 α-subunit, and carbonic anhydrase (CA) in concert with H+-ATPase (HAT) compared to their branchial counterparts in freshwater acclimation of hilsa during spawning migration from off-shore of the Bay of Bengal to the Bhagirathi-Hooghly zones of the Ganga river system in India. Adult hilsa fish were collected from seawater (SW), freshwater 1 (FW1), and freshwater 2 (FW2) locations, where the salinity level was 26-28‰, 1-5‰, and 0-0.04‰, respectively. Hilsa migrating through freshwater showed a consistent decrease in the plasma osmolality, sodium (Na+) and chloride (Cl-) ion levels indicates unstable ionic homeostasis. The mRNA expression and activity of NKA 1 α-subunit in pseudobranch as well as in true gills declined with the migration to upstream locations. The pseudobranchial CA activity almost mirrors its branchial counterpart most notably while hilsa entered the freshwater zone, in the upstream river suggesting its diverse role in hypo-osmotic regulatory acclimation. Nevertheless, the H+-ATPase activity of both the tissues increased with the freshwater entry and remained similar during up-river movement into the freshwater environment. The results confirm that the pseudobranchial NKA 1 α-subunit mRNA expression and activity mimic its branchial counterpart in the process of ionoregulatory acclimation during migration through salt barriers. Also, the increase in the activities of pseudobranchial and branchial CA in concert with H+-ATPase (HAT) during freshwater acclimation of hilsa suggests their critical involvement in ion uptake.

Hydrogeologic Controls of Surface Water‐Groundwater Nitrogen Dynamics Within a Tidal Freshwater Zone

AbstractMicrobial processing of reactive nitrogen in stream sediments and connected aquifers can remove and transform nitrogen prior to its discharge into coastal waters, decreasing the likelihood of harmful algal blooms and low oxygen levels in estuaries. Canonical wisdom points to the decreased capacity of rivers to retain nitrogen as they flow toward the coast. However, how tidal freshwater zones, which often extend hundreds of kilometers inland, process and remove nitrogen remains unknown. Using geochemical measurements and numerical models, we show that tidal pumping results in the rapid cycling of nitrogen within distinct zones throughout the riparian aquifer. Near the fluctuating water table nitrification dominates, with high nitrate concentrations (>10 mg N/L) and consistent isotopic composition. Beneath this zone, isotopes reveal that nitrate is both denitrified and added over the tidal cycle, maintaining nitrate concentrations >3–4 mg N/L. In most of the riparian aquifer and streambed, nitrate concentrations are <0.5 mg N/L, suggesting denitrification dominates. Model results reveal that oxygen delivery to groundwater from the overlying unsaturated soil fuels mineralization and nitrification, with subsequent denitrification in low‐oxygen, high organic matter regions. Depending on flow paths, tidal freshwater zones could be sources of nitrate in regions with permeable sediment and low organic matter content.

Groundwater microbial diversity and antibiotic resistance linked to human population density in Yucatan Peninsula, Mexico.

Microbial community composition in selected karst groundwater sites in the Yucatan Peninsula, Mexico, was assessed to determine the environmental variables influencing groundwater microbial diversity. The karst aquifer system is a groundwater-dependent ecosystem and is the world's second largest underwater karst cave system. The area's geology allows precipitation to infiltrate into the groundwater system and prevents accumulation of surface water; as such, groundwater is the only source of fresh water on the peninsula. The sampling locations consisted of three karst sinkholes that extend through the freshwater zone into the saline water, and an abandoned drinking water well of an ocean-side resort, during the dry and rainy seasons. The analysis showed that highly diverse microbial communities are present in the Yucatan groundwater, sustained by permanently warm temperatures and high nutrient input from human activity. Proximity to densely populated areas, such as tourist resorts, is the most important factor influencing both the diversity and presence of fecal bacteria and the antibiotic resistance profile.

Water Pollution, Fish Migration and the Plight of Fish Famers: A Biblical-Contextual Analysis

The relationship between unethical activities in the water zones and fish migration in ancient Israel and contemporary Rivers State (R/S) cannot be overemphasized. This study focused on the linkage between unethical activities and fish migration in ancient Israel and especially, contemporary R/S of Nigeria. This work utilised the Historical-Grammatical method for analysis of Biblical text of Hosea 4:3c and survey method for gathering of data from 583 respondents in R/S. The data collated were subjected to Simple Percentage Ratings and Content analyses. Accordingly, findings revealed that in Hosea 4:1-2, dysfunctional community relationships ( w e ’en-chesed ) manifested in destructive activities ( pārats ), while Hosea 4:3c echoed the attendant consequences as fish migration owing to excessive fishing motivated by greed. Similarly, in Rivers State, the unethical use of chemical and explosive as fishing gear was attested to by 89.4% of the Residents. Equally, a whopping 84.9% of the respondents believed that there was a reduction in the amount of fish brought home from fishing activities due to recent use of chemicals and explosives as part of fishing strategies. Residents from fresh water zone applied gammalin20 while those of saline water zone used dynamite as fishing techniques. This resulted in non-selective mortal damage, which left water sources stinking after two days. Thus, was detrimental to the economic life of families that depended on fishing for livelihood. Therefore, the role of residents and the government remains imperative for the environmental remediation in Rivers State as this will ameliorate the economic downturn of fish farmers. Keywords: gammalin20/dynamite, fishing strategies, fish migration, coastal rivers state, family livelihood, hosea 4:3c DOI : 10.7176/JEES/9-9-04 Publication date :September 30 th 2019

Integrating hydrogeological, geophysical, and remote-sensing data to identify fresh groundwater resources in arid regions: a case study from Western Iraq

There is a limited availability of fresh groundwater in the western part of Iraq due to the aridity of the region, and new water supplies are required to meet the demands of potential industrial, mining, and agricultural projects. Consequently, the factors that influence the quality, availability, and distribution of fresh groundwater in the region were assessed by combining hydrogeological, geophysical, and remote-sensing data within a GIS environment. For this purpose, the Shuttle Radar Topography Mission elevation data, geophysical data (gravity and magnetic), and hydrogeological database were used in an integrated approach. It was concluded that both a regionally extensive, deep intergranular aquifer and shallow-fractured and karstified carbonate aquifers have the potential to contain fresh groundwater in the region. It was inferred from the hydrochemical statistics that the main factors controlling groundwater chemistry are the dissolution of evaporite minerals and the weathering of carbonate rocks. Gravity (measured and satellite) data and magnetic data were processed and interpreted to identify the locations and characteristics of subsurface structures. Source Parameter Imaging was applied to calculate depth to the magnetic basement map from gridded magnetic data. The decompensative anomaly maps showed that zones with fresh groundwater are distributed on gravity lows which coincide with areas with a large depth to basement. Most of the fresh groundwater zones in the region are distributed between the pre-Tertiary and Tertiary axes of the Ha’il Arch due to increased recharge along this structure caused by intense fracturing. The extension of the gravity high outside the Iraq territory may suggest similar freshwater zones of groundwater occur in Syria, Jordan, and Saudi Arabia.

Integrated seawater intrusion study of coastal region of Thiruvallur district, Tamil Nadu, South India

The groundwater is the main resource of water for irrigation activity in river lacking area. The freshwater–seawater interface in the study region that has existed 3 km away from the coast in the year 1969 has been found to be migrated to distance of 13 km from the coast during the year 2007 noticed by the Central Ground Water Board (Central ground water board’s district groundwater brochure, Thiruvallur district, Tamil Nadu, 2007). Integrated geochemical and geophysical techniques were carried out in the study area to decode subsurface geologic pattern and delineate the seawater–freshwater zones. Total numbers of 50 samples were collected from the entire study area and analyzed for major ions. The considerable samples are brackish scenery of groundwater water at low depth. Chadha and Piper’s plots categorize the coastal groundwater into Na–HCO3, Ca–Na–HCO3, Ca–HCO3, and Na–Cl water facies, with Ca–HCO3 as the dominant. Cl/CO3 + HCO3 ratio, Cl/HCO3, and ionic strength, Mg/Ca and Cl/HCO3 ratios show that most of the samples in the study area are affected by seawater intrusion, which is also confirmed by the geophysical method. The results of vertical electrical sounding carried out in the study area reveal the low transverse resistance and high longitudinal conductance. It suggests the brackish nature of the groundwater in the eastern part of the study area may be due to the seawater intrusion. The final map using GIS platforms productively delineates the location that is really undergoing seawater and freshwater zone is migrated toward the inland. The article suggested further studies to arrest the migration of sea/freshwater interface into the land and avoid overexploitation of groundwater to further development.

GIS Based Land Use Change Analysis of a Coastal Area of Bangladesh

Satkhira is a coastal district of Bangladesh where lives of millions of people are transforming due to natural hazards and anthropogenic stimuluses, specifically water bodies are facing the bulk of the transformation owing to salinity. The study area of this research includes part of Satkhira Sadar and the work is done based on Betna river influenced zone. Sundarban and the Bay of Bengal are close to this river and its highly influenced by saline water. The natural pristine environment of the area went through major changes during the last few decades, especially after the 1980’s because of human interventions as well as natural causes. This research was an attempt to find out the transformations that took place in the area with remotely sensed imagery of 2018 and toposheet map of 1982, the underlying reasons of change and their consequences. The collected data were analyzed with Remote Sensing and Geographic Information System (GIS) software’s for better interpretation and an in-depth understanding. Features which came into consideration frequently are river, shrimp farms, settlement, agriculture, embankment, salinity intrusion, increasing population, frequent hazard and riparian vegetation. The outcome of the work tells that the change in land use occurred mainly because of shrimp farming and salinity intrusion while Betna river took the major blow. Although economically beneficial, shrimp culture created a saline environment and modification of water bodies resulted in frequent waterlogging and escalated salinity in the area previously known as freshwater zone. While Bangladesh is scare in land resource, the coastal area such as the study site of this research is even more stressed owing to climate change and recurring natural hazards. Propositions are made at the end of the work to use the presented data and information mentioned in this study by corresponding authorities.

Application of VES and ERT for delineation of fresh-saline interface in alluvial aquifers of Lower Bari Doab, Pakistan

Geophysical methods are effectively used to delineate intrusion boundary between the fresh and saline aquifers because of their intrinsic capability to assess the lateral variations in the pore-water salinity. In this study, an integrated geophysical approach of vertical electrical sounding (VES) and electrical resistivity tomography (ERT) has been conducted to delineate the contaminated aquifers in the Lower Bari Doab, Pakistan. Electrical resistivity tomography (ERT) using Schlumberger array with 5 m electrode spacing was conducted along eleven profiles at three selected sites (LBD1, LBD2 and LBD3) in the investigated area. The surface geoelectrical method was performed by sixty electrical resistivity soundings using the same array with maximum current electrode spacing (AB = 150 m). The integration of formation resistivity with ten boreholes reveals four discrete subsurface layers i.e., clay having saline aquifer, clay-sand containing brackish aquifer, sand with fresh aquifer and gravel-sand containing fresh aquifer. Estimation of Dar-Zarrouk Parameters (i.e., longitudinal resistivity, transverse resistance and longitudinal conductance) from different combinations of aquifer thickness and resistivity delineated the fresh, brackish and saline water zones with specific values range through mapping and graphical analysis. Geochemical method was performed on forty wells for main cations (K+, Na+, Ca2+ and Mg2+), anions (SO42−, Cl−, HCO3– and NO3−) and other parameters (As, EC, TDS and pH) to validate the results obtained from the geophysical methods. The fresh/saline aquifers delineated by the inclusion of ERT and geoelectrical method are in good agreement with those revealed by the physicochemical analysis and the local hydrogeological data. The results suggest that the use of non-invasive geophysical methods can reduce the number of expensive boreholes to obtain an interface between the fresh and saline water for the exploitation of fresh groundwater resources in any large area of homogeneous or heterogeneous aquifers.

Estimating active storage of groundwater quality zones in alluvial deposits of Faisalabad area, Rechna Doab, Pakistan

The quantification and assessment of groundwater are of great significance for the urbanization and town planning in an area. The current study has been carried out for quantification and assessment of groundwater quality zones by using geo-electrical technique in Faisalabad area (73° 06′ 08″–73° 11′ 59″ E; 31° 35′ 00″–31° 40′ 39″ N) of Pakistan. Vertical electrical soundings (VES) at six locations were conducted by Schlumberger configuration up to 300-m depth of investigation. Modeling technique is used for the interpretation of apparent resistivity, and the true resistivities of various subsurface lithologies were recorded from 2.10 to 55 Ω m for the depth of investigation. Three sand-dominant aquifers were identified at depth intervals of 0–50 m, 50–100 m, and 100–300 m. The VES results are compared and calibrated with the available borehole data taken from the tube wells drilled in the vicinity of the study area. The GIS technique is applied for the preparation of water quality zonation maps. Some of the groundwater quantification parameters such as total volume of the alluvium, total volumes of the water content, and active storage are estimated through GIS applications. Top geo-electrical layer (0–50 m) is dominated by low resistivity zone (10–25 Ω m), having an active storage of 0.71 km3. Intermediate geo-electrical layer (50–100 m) comprised coarse sand with low-to-medium resistivity zone of 10–35 Ω m, showing a low active storage (1.01 km3). Deep geo-electrical layer (100–300 m) is dominant by very low resistivity zone (< 10 Ω m) in the whole area. This 200-m-thick zone is possibly an admixture of fine sand, clay, and silt, having a high active storage (4.06 km3). The quality of water deteriorates with depth, and aquifer zones saturated with marginal-to-saline groundwater are interpreted below the fresh water zone at all the probe sites. The active storage of the lower geo-electrical layer (100–300 m) indicates a huge water potential but it is trapped in medium sand and alternative layers of clay. The intermediate geo-electrical layer (50–100 m) is comparatively better in quality but has low ground water potential.

Saltwater Intrusion Zone Mapping on Shallow Groundwater Aquifer in Selat Baru, Bengkalis Island, Indonesia

Saltwater intrusion becomes a common problem in coastal area. Northern coast of Bengkalis Island in Riau, Indonesia that contiguously to Malacca Strait is experiencing the problem particularly in Selat Baru area which considered as developing area and most of the people live close to the sea. Dug well is the main source of groundwater that had been used by the population in Selat Baru and as the increasing of land occupation, the demand of clean water is rising up followed by the number of dug well. A study of groundwater monitoring was conducted to identify the zone of saltwater intrusion. Field observation had done by measuring the water level and physical parameters of groundwater such as taste, pH, electrical conductivity (EC) and total dissolved solid (TDS) from 110 existing dug wells. Some conus feature had found from groundwater elevation map which indicated lower water level caused by excessive groundwater pumping. Generally, pH shows values from 6-8 that was still in range of water quality standard, but there are 20 wells (18%) that have pH below the water quality standard (slightly acidic water). Similar pattern had been observed from Electrical Conductivity (EC) and Total Dissolved Solid (TDS) map, higher value of EC and TDS was dominant in the northern part of study area and lower value in the south. Groundwater taste map also revealed the identical condition with EC and TDS map which dominated by brackish and saline water in the northern part. Therefore, the study area had been divided into two zones of groundwater saline water zone possibly caused by the saltwater intrusion in the northern part and freshwater zone from the center to the southern part.

Sediment dynamic equilibrium, a key for assessing a coastal anthropogenic disturbance using geochemical tracers: Application to the eastern part of the Bay of Seine

Geochemical studies are becoming more and more frequent in the context of the increasing pressure of human activities on marine coastal ecosystems and represent an appropriate tool to assess anthropogenic disturbances. Moreover, it is difficult to find discriminant markers. The eastern part of the Bay of Seine (English Channel) is highly impacted by the presence of harbour activities, fishing and sediment extraction. Dredged sediment from the Grand Port Maritime du Havre (GPMH) are deposited at the subtidal Octeville site, in the north-eastern part of the mouth of the Seine estuary (mixed sediment area). To understand natural and anthropogenic sedimentary mechanisms in this area, a geochemical and sedimentological study was conducted at the beginning of 2016. A dense sampling campaign including 179 stations was carried out between Cap de La Hève and Cap d’Antifer. For comparison, sampling was carried out in the harbour (13 samples in basins strongly or very weakly dredged), in the dredged grab itself and in the Seine estuary sediment (one station in the brackish zone and two stations in the river freshwater zone). Elemental compositions were determined by X-Ray Fluorescence spectrometry and infrared spectrometry. Using PCA (Principal Component Analysis), seven constituents were selected (Si, As, S, Pb, Rb, organic Br and TOC) to determine the area influenced by dumped spoil and the sediment transport directions. Sediment areas in dynamic equilibrium display a TOC gradient perpendicular to the coastline, linked to granulometric variations due to a combination of the swell and tidal currents. In the study area, dredged sediment are finer grained and have undergone changes due to the influence of diagenetic processes characteristic of the harbour environment. As a result, these sediment are enriched in sulphides, Pb, TOC and Rb, which allows us to highlight the in-situ deposited sediment spoil. Dumped sediment and the area subject to their influence are clearly identified since they locally disrupt the natural dynamic equilibrium state.

Characteristics of geochemical fractions of phosphorus and its bioavailability in sediments of a largest brackish water lake, South Asia

The spatio-temporal distribution of geochemical fractions of phosphorus and its bio-availability for Asia's largest brackish water lake has been carried out. One way ANOVA analysis revealed that both iron bound phosphorus (Fe-P) (p<0.05, n=360) and calcium bound phosphorus (Ca-P) (p<0.05, n=360) showed a significant variation on a spatio-temporal scale which may be attributed to pH and salinity of overlying water column. Pearson's correlation matrix revealed that sediment texture played a major role in the quantification of phosphorus species. The relationship between Ca-P and Ca was not established for the sediments of the lake Chilika, which suggested its authigenic origin. The concentration of bio-available phosphorus (BAP) in different sectors of the lake varied in the order of northern sector (45.64%)>central sector (42.22%)>outer channel (36.63%)>southern sector (29.27%) of total phosphorus (TP). This is supported by the fact that bioavailable P is comparatively higher in the freshwater zone than in the brackish water zone. The principal component analysis (PCA) revealed a good relationship between dissolved phosphate concentrations of water column with benthic population density. It showed that TP availability in the sediment of the lake is mostly bounded with Al, Fe and organic matter (OM). Positive association of total carbon (TC), total nitrogen (TN) and OM with negatively loading of Eh indicates towards the fact that, deposition of TN and TC is largely governed by OM availability in sediment.

Oil and Gas Wells: Enhanced Wellbore Casing Integrity Management through Corrosion Rate Prediction Using an Augmented Intelligent Approach

Wellbore integrity management for oil and gas wells plays a vital role throughout the typical lifespan of a well. Downhole casing leaks in oil- and gas-producing wells significantly affect their shallow water horizon, the environment, and fresh water resources. Additionally, downhole casing leaks may cause seepage of toxic gases to fresh water zones and the surface, through the casing annuli. Forecasting of such leaks and proactive measures of prevention will help eliminate their consequences and, in turn, better protect the environment. The objective of this study is to formulate an effective, robust, and accurate model for predicting the corrosion rate of metal casing string using artificial intelligence (AI) techniques. The input parameters used to train AI models include casing leaks, the percentage of metal loss, casing age, and average remaining barrier ratio (ARBR). The target parameter is the corrosion rate of the metal casing string. The dataset from which the AI models were trained was comprised of 250 data points collected from 218 wells in a giant carbonate reservoir that covered a wide range of practically reasonable values. Two AI tools were used: artificial neural networks (ANNs) and adaptive network-based fuzzy inference systems (ANFISs). A prediction comparison was made between these two tools. Based on the minimum average absolute percentage error (AAPE) and the highest coefficient of determination (R2) between the measured and predicted corrosion rate values, the ANN model proposed here was determined to be best for predicting the corrosion rate. An ANN-based empirical model is also presented in this study. The proposed model is based on the associated weights and biases. After evaluating the new ANN equation using an unseen validation dataset, it was concluded that the ANN equation was able to make predictions with a significantly lower AAPE and higher R2. Use of the proposed new equation is very cost-effective in terms of reducing the number of sequential surveys and experiments conducted. The proposed equation can be utilized without an AI engine. The developed model and empirical correlation are very promising and can serve as a handy tool for corrosion engineers seeking to determine the corrosion rate without training an AI model.