Sand Groundwater Research Articles

Nitrogen Migration and Transformation Mechanism in the Groundwater Level Fluctuation Zone of Typical Medium

Because of the nitrogen pollution problem in groundwater, the migration conversion mechanism of nitrogen in groundwater level fluctuations was analyzed. Technology and methods through indoor experiments and theoretical analysis were used to study coarse sand, medium sand, and fine sand groundwater level fluctuation in the aeration zone and saturated zone under the situation of nitrogen distribution characteristics, revealing groundwater level fluctuation with the nitrogen migration mechanism. The experimental results showed that the variation range of the nitrate-nitrogen (NO3−−N) concentration with the water level is medium sand > fine sand > coarse sand. The ammonium nitrogen (NH4+−N) concentration showed a downward trend after water level fluctuations, and there were more apparent fluctuations in coarse sand and medium sand. The nitrite nitrogen (NO2−−N) in coarse sand and medium sand first increased the water level and then gradually reached a balance. The sampling points below the water level in fine sand showed a downward trend with fluctuation of the water level, and then gradually reached equilibrium. The results provide a scientific basis for the remediation and treatment of soil and groundwater pollution.

Influence of Freshwater Discharges on Biogeochemistry and Benthic Communities of a Coral Reef Ecosystem (La Réunion Island, Indian Ocean)

We investigated the influence of freshwater discharges on biogeochemistry and benthic communities of La Saline fringing reef, the largest coral reef system of La Reunion Island (France, Indian Ocean). Sampling was conducted in February-March 2012 along a land-ocean continuum, including rivers, groundwater, reef waters, and oceanic waters. Our results indicated the discharges of basalt groundwater (enriched in nitrates) in the southern part of the reef, and the discharges of sand groundwater and river waters (enriched in organic matter) in sites located northward. These discharges mainly impacted fore reef surface waters, while groundwater resurgences were more diffuse and not clearly detected in depth. We highlighted the relationship Si(OH) 4 /NO 3 − to identify basalt groundwater discharges. We also put forward the relationships humic-like fluorescence/NH 4 + and tryptophan-like fluorescence/PO 4 3− to identify sand groundwater discharges and wastewater pollutions, respectively. We observed the eutrophication of the southern part of the reef through higher phytoplankton biomasses, a massive presence of fleshy algal formations and a low coral coverage. The spatial homogeneity of the benthic community structures onto the entire slope contrasted with the spatial heterogeneity of chemical variables in water. This reflected the different spatial and temporal scales involved in biological and chemical processes in coral reef ecosystems.

MONUMENTS OF NATURE AND HISTORICAL AND CULTURAL OBJECTS OF THE DNISTROVSKYI RLP: THE STATE OF PROTECTION AND THE PROSPECTS OF TOURIST USE

The existing nature conservation objects that are part of the Dnistrovskyi Regional Landscape Park are characterized and mapped. There are more than sixty different types of WFD objects in and around the park. All objects are tabulated. Also, geological, geomorphological, hydrological objects have been identified that have scientific, recreational and educational value, which gives grounds for granting them conservation status. This is a large number of rocks of different ages (Silurian, Devonian, Jurassic, Cretaceous), which makes it possible to study the history and condition sof the territory. The location is mapped. Also on the map as places of interest are the places of manifestation of modern geomorphological processes. Fluvial, karst, gravity, erosion and other processes are most evidentin the park. The dynamics of karst processes haveled to the formation of numerous caves and cave formations, which are valuable from the scientific and recreational plan. A mong the hydrological and hydro-geological features are waterfalls, marshe sand ground water exits to the surface in the form of springs. Historical and cultural sites occurring with in and around the park are characterized and mapped. The seare objects of Paleolithic heritage (the oldestin Bukivna, Horodnytsia), Kievan Rus' period, ruins of ancient castles (Rakovetsky and Chekrnelitsky) and fotresses, lordlye states, ancient churches, of which there are more than thirty, existing and in active in the region. The most ancient are the village of Michalce), monuments of liberation competitions (hiding places) and places of great historical battles. It maps and describes the existing route sand objects of the tourist infrastructure of the Dnistrovskyi RLP. The park and surrounding areas haves ignificant natural and recreational potential. The presence of a large number of diverse natural sites make sit possible to create attractions for tourism development in the region. The presence of historical and cultural heritage en hances the use of the territory. New routes and proposals for improvement of the tourist infrastructure of the territory were developed: creation of an eco-educational visit center, placement of agroosel complexes, arrangement of places for stops during the Dniester alloys, creation of a network of tourist points at the places of passage of route sand places of rest of residents, development and in stallation of new information standsne are xisting tourist natural and historical sites in the study area. Key words: Dnistrovskyi RLR, Nature Reserve objects, historical and cultural sites, nature monuments, recreational resources, tourism.

Vanadium geochemistry along groundwater flow paths in contrasting aquifers of the United States: Carrizo Sand (Texas) and Oasis Valley (Nevada) aquifers

Vanadium (V) concentrations were measured along the flow paths in two contrasting aquifer systems to study how changing solution composition and redox conditions affect V cycling and transport in groundwater flow systems. The Oasis Valley groundwater system in Nevada is an unconfined system where groundwaters generally remain oxic along the flow path, whereas the Carrizo Sand aquifer is a deep, confined coastal plain aquifer in Texas that contains well-defined Fe(III) and SO42− reduction zones along the flow path. Speciation modeling predicts that in groundwaters from the Oasis Valley, V chiefly occurs as the vanadate oxyanion (e.g., H2VO4−, HVO42−), which is mobile along the entire flow path because of vanadate's solubility in oxic and alkaline waters. Furthermore, the data indicate that V concentrations increase in groundwaters along the flow path suggesting that mineral dissolution and/or desorption reactions progressively contribute V to groundwaters of the Oasis Valley system. Geochemical modeling is consistent with dissolution of mafic phenocrysts that are common in the local tuffaceous aquifer rocks as a probable source of V to Oasis Valley groundwaters. Within the Carrizo Sand aquifer, groundwater V concentrations decrease with flow beyond the recharge zone and into the confined portion of the aquifer. Thereafter, total V concentrations remain low and relatively constant along the remainder of the studied flow path, exhibiting no systematic variations across the Fe(III) and SO42− reduction zones. Groundwaters from the Carrizo Sand aquifer are generally reducing, and as such, geochemical modeling suggests that both V(V) and V(IV) species occur in Carrizo Sand groundwaters, and furthermore, that the proportion of V(IV) species increases concurrent with the decrease in total V concentrations along the flow path. Results from sequential extraction experiments on Carrizo Sand aquifer sediment samples suggest that V adsorption onto Fe(III)/Mn(IV) oxides/oxyhydroxides acts to decrease the aqueous V concentrations in Carrizo Sand groundwater. Furthermore, geochemical modeling is consistent with complexation of V(IV) with dissolved organic matter (DOM) within the Carrizo Sand aquifer groundwaters, which, owing to the low DOM concentrations, appears to buffer V at low, but relatively constant concentrations within the confined and reducing Carrizo Sand groundwaters. These results support previous reports of V(IV)–DOM binding and imply that aquifer material maintains an essential role in not only determining the availability of V to enter aqueous solution but also in influencing partitioning between solid and aqueous phases.

Geochemical cycling of mercury in a deep, confined aquifer: Insights from biogeochemical reactive transport modeling

Total dissolved mercury concentrations (HgT) were measured in groundwaters collected along a flow path within a deep, confined aquifer (i.e., the Carrizo Sand) in southeastern Texas, USA, along with major solutes, pH, and redox sensitive parameters that include dissolved iron species [Fe(II), Fe(III)] and sulfide [S(-II)] concentrations. Mercury concentrations range from below detection (<0.43pmolkg−1) to close to 8pmolkg−1, and increase 6-fold along the first 13km of the flow path, coincident with the region of the aquifer where dissimilatory Fe(III) reduction buffers the redox conditions. With groundwater flow beyond the Fe(III) reducing zone and into the region of the aquifer dominated by sulfate reduction, the dissolved HgT concentrations decrease by close to a factor of 3. Dissolved HgT is positively correlated with dissolved Fe(II) concentrations (r=0.61), and to a lesser extent with dissolved organic carbon (DOC) concentrations (r=0.54), and inversely related to both pH (r=−0.56) and dissolved S(-II) concentrations (r=−0.41), although this latter relationship is not statistically significant. Solution complexation modeling indicates that Hg is chiefly complexed with dissolved sulfide and that organic complexes with Hg are generally negligible. Biogeochemical reactive transport modeling demonstrates that the distinct zones of high Fe(II) followed by high S(-II) groundwaters observed along the flow path are consistent with microbially mediated Fe(III) reduction followed by SO42- reduction that occurs sequentially along the flow path. Furthermore, the modeling suggests that Hg is released to Carrizo Sand aquifer groundwaters by dissimilatory reduction of the Fe(III) oxides/oxyhydroxides (goethite and hematite), which are common in the aquifer, occurring as coatings on sand grains (chiefly quartz). Subsequently, the model suggests that Hg is removed from Carrizo Sand groundwater further down gradient along the flow path by adsorption onto goethite and hematite. Adsorption onto, or co-precipitation with, Fe-sulfide minerals like mackinawite, sorption onto sedimentary organic matter, and/or precipitation of HgS(s) may also play important roles in Hg removal from Carrizo Sand groundwaters.

Identification of the nitrate contamination sources of the Brusselian sands groundwater body (Belgium) using a dual-isotope approach

Isotopic fingerprinting is an advanced technique allowing the classification of the nitrate source pollution of groundwater, but needs further development and validation. In this study, we performed measurements of natural stable isotopic composition of nitrate (15N and 18O) in the groundwater body of the Brussels sands (Belgium) and studied the spatial and temporal dynamics of the isotope signature of this aquifer. Potential nitrogen sources sampled in the region had isotopic signatures that fell within the corresponding typical ranges found in the literature. For a few monitoring stations, the isotopic data strongly suggest that the sources of nitrate are from mineral fertiliser origin, as used in agriculture and golf courses. Other stations suggest that manure leaching from unprotected stockpiles in farms, domestic gardening practices, septic tanks and probably cemeteries contribute to the nitrate pollution of this groundwater body. For most monitoring stations, nitrate originates from a mixing of several nitrogen sources. The isotopic signature of the groundwater body was poorly structured in space, but exhibited a clear temporal structure. This temporal structure could be explained by groundwater recharge dynamics and cycling process of nitrogen in the soil-nitrogen pool.

Role of aquifer heterogeneity in fresh groundwater discharge and seawater recycling: An example from the Carmel coast, Israel

A case study is shown in which the pattern of submarine groundwater discharge and of seawater recycling is controlled by local hydrogeological variability. The coastal aquifer in Dor Bay is composed of two units: a partly confined calcaranitic sandstone (Kurkar) and an overlying loose sand. Groundwater in the Kurkar has elevated activities of 222Rn (∼390 dpm/L) and relatively low 224Ra/223Ra activity ratios (3–4), while the sand groundwater is significantly less radiogenic (6–90 dpm/L) and shows higher 224Ra/223Ra ratios. Groundwater discharging from sand‐covered areas of the bay has salinities of 16–31 and an average 222Rn activity of 168 dpm/L, which lies on a mixing line between Rn‐rich Kurkar fresh water and Rn‐poor seawater. Another key observation is that seawater infiltrates to some extent into onshore sand groundwater, while the fresh water within the submarine Kurkar can be traced up to 40 m offshore. This implies that while fresh water mainly discharges from the Kurkar unit, seawater recycling is limited to the loose sand, and that the discharge from sand‐covered areas is a mixture of Kurkar water with recycled seawater. Advection rates from the bay floor were calculated from Rn time series and found to vary between 0 and 36 cm/d, correlating negatively with bay water depth. The average flux was 8.1 cm/d, and it did not seem to change much during March, May, and July 2006. The average amount of fresh water discharging to the bay was 5.0 m3/d per meter of shoreline. Radon activity in the sand groundwater also fluctuates due to influx of Kurkar‐type groundwater.

A field tracer study of attenuation of atrazine, hexazinone and procymidone in a pumice sand aquifer.

A field tracer experiment, simulating point source contamination, was conducted to investigate attenuation and transport of atrazine, hexazinone and procymidone in a volcanic pumice sand aquifer. Preliminary laboratory incubation tests were also carried out to determine degradation rates. Field transport of the pesticides was observed to the significant under non-equilibrium conditions. Therefore, a two-region/two-site non-equilibrium transport model, N3DADE, was used for analysis of the field data. A lump reduction rate constant was used in this paper to encompass all the irreversible reduction processes (e.g. degradation, irreversible adsorption, complexation and filtration for the pesticides adsorbed into particles and colloids) which are assumed to follow a first-order rate law. Results from the field experiment suggest that (a) hexazinone was the most mobile (retardation factor R = 1.4) and underwent least mass reduction; (b) procymidone was the least mobile (R = 9.26) and underwent the greatest mass reduction; (c) the mobility of atrazine (R = 4.45) was similar to that of rhodamine WT (R = 4.10). Hence, rhodamine WT can be used to delimit the appearance of atrazine in pumice sand groundwater. Results from the incubation tests suggest that (a) hexazinone was degraded only in the mixture of groundwater and aquifer material (degradation rate constant = 4.36 x 10(-3) day-1); (b) procymidone was degraded not only in the mixture of groundwater and aquifer material (rate constant = 1.12 x 10(-2) day-1) but also in the groundwater alone (rate constant = 2.79 x 10(-2) and-1); (c) atrazine was not degraded over 57 days incubation in either the mixture of aquifer material and groundwater or the groundwater alone. Degradation rates measured in the batch tests were much lower than the total reduction rates. This suggests that not only degradation but also other irreversible processes are important in attenuating pesticides under field conditions. Hence, the use of laboratory-determined degradation rates could underestimate reduction of pesticides in field conditions.

Flow of ground water in sands of nonuniform thickness: 3. Flow to wells

This is the third of a sequence of papers dealing with ground-water flow in sands of nonuniform thickness. It is concerned with unsteady flow toward wells completely penetrating an aquifer whose thickness may be assumed to vary exponentially in the direction of x while remaining uniform in the y direction. The drawdown induced around a flowing well (well of constant head) or around a well that is pumped at a constant rate is obtained for aquifers that can be considered effectively infinite in areal extent. The flow toward steadily discharging wells near a fairly straight and an effectively long stream, or near an impermeable boundary which completely cuts through the aquifer, is also considered. The results are compared with those which would be obtained if the aquifer were of uniform thickness.

Flow of ground water in sands of nonuniform thickness: Part 1. Flow in a wedge-shaped aquifer

Formulas of ground-water flow through wedge-shaped aquifers are obtained for several flow systems of practical interest. It is assumed that the flow has no significant component of velocity in the y direction so that its pattern is the same in all parallel vertical xz planes. The results are presented in terms of functions that are already available in tabular form, making these analytical expressions as easy to use as any other simple formula. These results show that the flow in wedge-shaped aquifers cannot be approximated by the flow in aquifers of uniform thickness (as currently practiced) except during very short periods which become longer for points closer to the source of the flow.

Flow of ground water in sands of nonuniform thickness: Part 2. Approximate theory

Several flow problems in an aquifer whose thickness varies linearly or exponentially in the x direction while remaining uniform in the y direction are treated. Their solutions are based on a differential equation that has been set up to approximate the flow in such aquifers. Several initial and boundary conditions are considered. Some of the results are compared with those rigorously obtained in the first of this sequence of papers. It is concluded that the approximate solutions yield good results in sands confined by beds whose angles of dip have tangents less than 0.20. Also, the flow in wedge-shaped aquifers cannot be approximated by that which would exist if the aquifer were of uniform thickness except during very short periods which become longer for points closer to the source of flow.