scholarly journals Methods in Capturing the Spatiotemporal Dynamics of Flow and Biogeochemical Reactivity in Sandy Beach Aquifers: A Review

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 782
Author(s):  
Kyra H. Kim ◽  
James W. Heiss
Keyword(s):  
Sandy Beach ◽  
Reaction Rates ◽  
Variable Density ◽  
Nutrient Loads ◽  
Primary Control ◽  
Biogeochemical Processes ◽  
Sample Collection ◽  
Fresh Groundwater ◽  
Present Measurement ◽  
Measurement Framework

Sandy beach aquifers are complex hydrological and biogeochemical systems where fresh groundwater and seawater mix. The extent of the intertidal mixing zone and the rates of circulating flows within beaches are a primary control on porewater chemistry and microbiology of the intertidal subsurface. Interplay between the hydrological and biogeochemical processes at these land-sea transition zones moderate fluxes of chemicals, particulates, heavy metals, and biota across the aquifer-ocean interface, affecting coastal water quality and nutrient loads to marine ecosystems. Thus, it is important to characterize hydrological and biogeochemical processes in beach aquifers when estimating material fluxes to the ocean. This can be achieved through a suite of cross-disciplinary measurements of beach groundwater flow and chemistry. In this review, we present measurement approaches that have been developed and employed to characterize the physical (geology, topography, subsurface hydrology) and biogeochemical (solute and particulate distributions, reaction rates) properties of and processes occurring within sandy intertidal aquifers. As applied to beach systems, we discuss vibracoring, sample collection, laboratory experiments, variable-density considerations, instrument construction, and sensor technologies. We discuss advantages and limitations of typical hydrologic field sampling methods when used to investigate beach aquifers and provide a measurement framework for researchers seeking to sample and collect data from these systems.

scholarly journals A three-dimensional palaeohydrogeological reconstruction of the groundwater salinity distribution in the Nile Delta Aquifer

2019 ◽  
Vol 23 (12) ◽  
pp. 5175-5198 ◽  
Author(s):  
Joeri van Engelen ◽  
Jarno Verkaik ◽  
Jude King ◽  
Eman R. Nofal ◽  
Marc F. P. Bierkens ◽  
...  
Keyword(s):  
Steady State ◽  
Nile Delta ◽  
Three Dimensional ◽  
Computer Code ◽  
Variable Density ◽  
Groundwater Salinity ◽  
Fresh Groundwater ◽  
Marine Transgression ◽  
Transient Simulations ◽  
Clay Layers

Abstract. Holocene marine transgressions are often put forward to explain observed groundwater salinities that extend far inland in deltas. This hypothesis was also proposed in the literature to explain the large land-inward extent of saline groundwater in the Nile Delta. The groundwater models previously built for the area used very large dispersivities to reconstruct this saline and brackish groundwater zone. However, this approach cannot explain the observed freshening of this zone. Here, we investigated the physical plausibility of the Holocene-transgression hypothesis to explain observed salinities by conducting a palaeohydrogeological reconstruction of groundwater salinity for the last 32 ka with a complex 3-D variable-density groundwater flow model, using a state-of-the-art version of the SEAWAT computer code that allows for parallel computation. Several scenarios with different lithologies and hypersaline groundwater provenances were simulated, of which five were selected that showed the best match with the observations. Amongst these selections, total freshwater volumes varied strongly, ranging from 1526 to 2659 km3, mainly due to uncertainties in the lithology offshore and at larger depths. This range is smaller (1511–1989 km3) when we only consider the volumes of onshore fresh groundwater within 300 m depth. In all five selected scenarios the total volume of hypersaline groundwater exceeded that of seawater. We also show that during the last 32 ka, total freshwater volumes significantly declined, with a factor ranging from 2 to 5, due to the rising sea level. Furthermore, the time period required to reach a steady state under current boundary conditions exceeded 5.5 ka for all scenarios. Finally, under highly permeable conditions the marine transgression simulated with the palaeohydrogeological reconstruction led to a steeper fresh–salt interface compared to its steady-state equivalent, while low-permeable clay layers allowed for the preservation of fresh groundwater volumes. This shows that long-term transient simulations are needed when estimating present-day fresh–salt groundwater distributions in large deltas. The insights of this study are also applicable to other major deltaic areas, since many also experienced a Holocene marine transgression.

scholarly journals A three-dimensional palaeo-reconstruction of the groundwater salinity distribution in the Nile Delta Aquifer

2019 ◽  
Author(s):  
Joeri van Engelen ◽  
Jarno Verkaik ◽  
Jude King ◽  
Eman R. Nofal ◽  
Marc F. P. Bierkens ◽  
...  
Keyword(s):  
Steady State ◽  
Sea Water ◽  
Nile Delta ◽  
Steady State Solution ◽  
Variable Density ◽  
Groundwater Salinity ◽  
Fresh Groundwater ◽  
Marine Transgression ◽  
Wide Range ◽  
Saline Zone

Abstract. The Nile Delta is an important agricultural area with a fast-growing population. Though traditionally irrigated with surface water, the delta increasingly relies on groundwater. However, saline groundwater extends far land inward, rendering groundwater close to the coastal zone useless for consumption or agriculture. To aid groundwater management decisions, hydrogeologists reconstructed this saline and brackish groundwater zone using variable-density groundwater models with very large dispersivities. However, this approach cannot explain the observed freshening of this zone as observed by hydrogeochemists, who hypothesize that the coastal saline zone is the effect of the Holocene transgression. Here, we investigated physical plausibility of this hypothesis by conducting a palaeo-reconstruction of groundwater salinity for the last 32 ka with a complex 3D variable-density groundwater flow model, using state-of-the-art model code that allows for parallel computation. Several scenarios with different lithologies and hypersaline groundwater provenances were simulated, of which five were selected that showed the best match with the observations. Amongst these selections, total fresh water volumes varied strongly, ranging from 1526 to 2659 km3, mainly due to uncertainties in the lithology offshore and at larger depths. This range is smaller (1511–1989 km3) when we consider the volumes of onshore fresh groundwater within 300 m depth. Regardless of the variance, in all cases the total volume of hypersaline groundwater exceeded that of sea water. We also show that during the last 32 ka, the total fresh groundwater volumes significantly declined, with a factor ranging from 1.9 to 5.4, due to the rising sea-level. Compared to a steady-state solution with present-day boundary conditions, the palaeo-reconstruction improved our validation for the saline zone (5 g/L–35 g/L TDS). Also, under highly permeable conditions the marine transgression simulated with the palaeo-reconstruction led to a steeper fresh-salt interface compared to its steady-state equivalent, while low permeable clay layers allowed for the preservation of volumes of fresh groundwater. This shows that long-term transient simulations are needed when estimating present-day fresh-salt groundwater distribution in large deltas. The insights of this study are also applicable to other major deltaic areas, given the wide-range of lithological model scenarios used in this study and since many deltas also experienced a Holocene marine transgression.

scholarly journals Kajian Hidrostratigrafi Bentanglahan Kepesisiran Tipologi Marine Deposition Coast Kecamatan Ngambur Provinsi Lampung

2021 ◽  
Vol 2 (1) ◽  
pp. 11-24
Author(s):  
Evi mivtahul Khoirullah ◽  
I.g.L. Setyawan Purnama ◽  
Margaretha Widyastuti
Keyword(s):  
Coastal Area ◽  
Sampling Method ◽  
Sandy Beach ◽  
Research Area ◽  
Soil Resistivity ◽  
Fresh Groundwater ◽  
Constituent Material ◽  
Measurement Results ◽  
Research Show

This research was conducted on coastal area located in Ngambur Subdistrict, Pesisir Barat Regency, Lampung Province. Geomorphologically, typology of this coastal area formed of marine deposition coast. Which is consist of sandy beach (M1), beach ridge (M2), and fluviomarine (Fm). The purpose of this reasearch is to reconstruct and analyze charactreistic of hydrostratigraphy which is includes of soil stratigraphy system and properties, and physical properties of groundwater in the research area. Vertical distribution of soil resistivity obtained by measuring 24 of measuring points with depth of penetration’s up to 150 meters. Determination of measurement points are selected using purposive sampling method. Furthermore, the resistivity value of the measurement results is calculated using IP2Win software. Results of the calculation matched with soil resistivity tables. Results of the research show that vertically the type of aquifers identified are aquifer, aquitard, and aquifug. The constituent material is dominated by alluvium containing fresh groundwater which acts as an aquifer and sandstone materials which acts as aquitard. The electrical conductivity value (DHL) measured <1,200mmhos / cm which indicates that the groundwater in ths area is classified as fresh groundwater.

The sustainability of fresh groundwater resources in major deltas around the world

2021 ◽  
Author(s):  
Joeri van Engelen ◽  
Gualbert Oude Essink ◽  
Marc Bierkens
Keyword(s):  
Sea Water ◽  
Salt Water ◽  
Groundwater Resources ◽  
Three Dimensional ◽  
Variable Density ◽  
Current Status ◽  
Irrigated Agriculture ◽  
Fresh Groundwater ◽  
Precise Knowledge ◽  
The World

&lt;p&gt;Increasing population, growth of cities and intensifying irrigated agriculture in the world&amp;#8217;s deltas promote the demand for fresh water resources, accelerating groundwater extraction. This, in turn, leads to sea water intrusion and salt water upconing, which threaten near-future water and food security. Proper water management in deltas requires precise knowledge about the current status of the deltas&amp;#8217; fresh groundwater resources, in the form of a groundwater salinity distribution. However, this knowledge is scarcely present, especially at larger depths. In this research, we applied three-dimensional variable-density groundwater model simulations over the last 125 ka to estimate present-day fresh groundwater volumes for several major deltas around the world. We also compared these to current extraction rates and estimated the time until in-situ fresh groundwater resources are completely exhausted (ignoring local-scale problems), partly leading to groundwater level decline and mostly replacement with river water or saline groundwater. In this presentation we will share our findings, for example which deltas&amp;#8217; groundwater reserves presumably are under stress.&lt;/p&gt;

scholarly journals C-GEM (v 1.0): a new, cost-efficient biogeochemical model for estuaries and its application to a funnel-shaped system

2014 ◽  
Vol 7 (4) ◽  
pp. 1271-1295 ◽  
Author(s):  
C. Volta ◽  
S. Arndt ◽  
H. H. G. Savenije ◽  
G. G. Laruelle ◽  
P. Regnier
Keyword(s):  
Reactive Transport ◽  
Reaction Rates ◽  
Global Scale ◽  
Scheldt Estuary ◽  
Salt Transport ◽  
Biogeochemical Model ◽  
Biogeochemical Processes ◽  
Two Dimensional ◽  
Computationally Efficient ◽  
Parameter Values

Abstract. Reactive transport models (RTMs) are powerful tools for disentangling the complex process interplay that drives estuarine biogeochemical dynamics, for assessing the quantitative role of estuaries in global biogeochemical cycles and for predicting their response to anthropogenic disturbances (land-use change, climate change and water management). Nevertheless, the application of RTMs for a regional or global estimation of estuarine biogeochemical transformations and fluxes is generally compromised by their high computational and data demands. Here, we describe C-GEM (Carbon-Generic Estuary Model), a new one-dimensional, computationally efficient RTM that reduces data requirements by using a generic, theoretical framework based on the direct relationship between estuarine geometry and hydrodynamics. Despite its efficiency, it provides an accurate description of estuarine hydrodynamics, salt transport and biogeochemistry on the appropriate spatio–temporal scales. We provide a detailed description of the model, as well as a protocol for its set-up. The new model is then applied to the funnel-shaped Scheldt estuary (BE/NL), one of the best-surveyed estuarine systems in the world. Its performance is evaluated through comprehensive model–data and model–model comparisons. Model results show that C-GEM captures the dominant features of the biogeochemical cycling in the Scheldt estuary. Longitudinal steady-state profiles of oxygen, ammonium, nitrate and silica are generally in good agreement with measured data. In addition, simulated, system-wide integrated reaction rates of the main pelagic biogeochemical processes are comparable with those obtained using a high-resolved, two-dimensional RTM. A comparison of fully transient simulations results with those of a two-dimensional model shows that the estuarine net ecosystem metabolism (NEM) only differs by about 10%, while system-wide estimates of individual biogeochemical processes never diverge by more than 40%. A sensitivity analysis is carried out to assess the sensitivity of biogeochemical processes to uncertainties in parameter values. Results reveal that the geometric parameters LC (estuarine convergence length) and H (water depth), as well as the rate constant of organic matter degradation (kox) exert an important influence on the biogeochemical functioning of the estuary. The sensitivity results also show that, currently, the most important hurdle towards regional- or global-scale applications arises from the lack of an objective framework for sediment and biogeochemical process parameterization. They, therefore, emphasize the need for a global compilation of biogeochemical parameter values that can help identify common trends and possible relationships between parameters and controlling factors, such as climate, catchment characteristics and anthropic pressure.

Estimating regional to global fresh-brackish-salt groundwater occurrence to support future projections

2020 ◽  
Author(s):  
Marc F.P. Bierkens ◽  
Jude A. King ◽  
Joeri van Engelen ◽  
Jarno Verkaik ◽  
Daniel Zamrsky ◽  
...  
Keyword(s):  
Sea Level ◽  
Nile Delta ◽  
Initial Conditions ◽  
Groundwater Resources ◽  
Variable Density ◽  
Coastal Areas ◽  
Estimation Methods ◽  
Fresh Groundwater ◽  
Surface Sealing ◽  
Groundwater Occurrence

&lt;p&gt;Coastal areas, including deltas, are hotspots for population growth and economic development. The rising demand for fresh water that results from these developments has resulted in increased rates of groundwater pumping and an associated enhanced risk of groundwater salinization. Future sea-level rise, climate change and surface sealing due to urbanisation are likely to further increase salinization risk in the near future. In order to correctly project the future fate of fresh groundwater resources in coastal areas under climate and socio-economic change, a correct estimate of the current fresh-brackish-salt groundwater occurrence is imperative. The reason for this is that future salinity projections are very sensitive to initial conditions, due to the large inertia of variable-density groundwater systems. Here, we make a case that estimating the current fresh-brackish-salt groundwater distribution by itself is a major challenge. The presence of conductivity contrasts in coastal areas, the past occurrence of sea-level transgressions and the aforementioned system inertia makes that traditional estimation methods such as interpolations between in-situ salinity observations or equilibrium (steady-state) modelling approaches are incapable of producing sufficiently realistic fresh-brackish-salt groundwater distributions. Using examples from the Rhine-Meuse delta, the Nile delta and the global coast, we show that advancements in airborne geophysics and high-resolution paleo-groundwater modelling may be key to providing distributions that are both realistic and accurate.&lt;/p&gt;

scholarly journals Hortonian Scaling of Coupled Hydrological and Biogeochemical Responses Across an Intensively Managed River Basin

2021 ◽  
Vol 3 ◽  
Author(s):  
Soohyun Yang ◽  
Enrico Bertuzzo ◽  
Dietrich Borchardt ◽  
P. Suresh C. Rao
Keyword(s):  
River Basin ◽  
Analytical Model ◽  
Spatial Patterns ◽  
Large Scale ◽  
Removal Rate ◽  
River Basins ◽  
Nutrient Loads ◽  
Biogeochemical Processes ◽  
Anthropogenic Pressures ◽  
Human Settlements

Structural and functional attributes across fractal river networks have been characterized by well-established and consistent hierarchical, Hortonian scaling patterns. In most of the global river basins, spatial patterns of human settlements also conform to similar hierarchical scaling. However, emergent spatial hierarchical patterns and scaling of heterogeneous anthropogenic nutrient loads over a river basin are less known. As a case study, we examined here a large intensely managed river basin in Germany (Weser River; 46K km2; 8M population). Archived data for point-/diffuse-sources of total Phosphorus (Ptot) input loads were combined with numerical and analytical model simulations of coupled hydrological and biogeochemical processes for in-stream Ptot removal at the network scale. We find that Ptot input loads scale exponentially over stream-orders, with the larger scaling constant for point-source loads from urban agglomerations compared to those for diffuse-source contributions from agricultural and forested areas. These differences in scaling patterns result from hierarchical self-organization of human settlements, and the associated clustering of large-scale, altered land-cover. Fraction of Ptot loads removed through in-stream biogeochemical processes also manifests Hortonian scaling, consistent with predictions of an analytical model. Our analyses show that while smaller streams are more efficient in Ptot removal, in larger streams the magnitude of Ptot loads removed is higher. These trends are consistent with inverse scaling of nutrient removal rate constant with mean discharge, and downstream clustering of larger cumulative input loads. Analyses of six nested sub-basins within the Weser River Basin also reveal similar scaling patterns. Our findings are useful for projecting likely water-quality spatial patterns in similar river basins in Germany, and Central Europe. Extensions and generalizations require further examination of diverse basins with archetype spatial heterogeneities in anthropogenic pressures and hydroclimatic settings.

scholarly journals From submarine to lacustrine groundwater discharge

2015 ◽  
Vol 365 ◽  
pp. 72-78 ◽  
Author(s):  
J. Lewandowski ◽  
K. Meinikmann ◽  
F. Pöschke ◽  
G. Nützmann ◽  
D. O. Rosenberry
Keyword(s):  
Submarine Groundwater Discharge ◽  
Groundwater Discharge ◽  
Nutrient Concentrations ◽  
Water Interface ◽  
Nutrient Loads ◽  
Biogeochemical Processes ◽  
Nitrogen And Phosphorus ◽  
Submarine Groundwater ◽  
Near Shore ◽  
Aquifer Characteristics

Abstract. Submarine groundwater discharge (SGD) and its role in marine nutrient cycling are well known since the last decade. The freshwater equivalent, lacustrine groundwater discharge (LGD), is often still disregarded, although first reports of LGD are more than 50 years old. We identify nine different reasons why groundwater has long been disregarded in both freshwater and marine environments such as invisibility of groundwater discharge, the size of the interface and its difficult accessibility. Although there are some fundamental differences in the hydrology of SGD and LGD, caused primarily by seawater recirculation that occurs only in cases of SGD, there are also a lot of similarities such as a focusing of discharge to near-shore areas. Nutrient concentrations in groundwater near the groundwater–surface water interface might be anthropogenically enriched. Due to spatial heterogeneity of aquifer characteristics and biogeochemical processes, the quantification of groundwater-borne nutrient loads is challenging. Both nitrogen and phosphorus might be mobile in near-shore aquifers and in a lot of case studies large groundwater-borne nutrient loads have been reported.

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