Στην παρούσα διπλωματική εργασία πραγματοποιήθηκε επεξεργασία και ανάλυση δεδομένων που συλλέχθηκαν κατά την περίοδο μελέτης της περιοχής της Στούπας στην Νοτιοανατολική Μεσσηνία, στον όρμο της Καλόγριας, με απώτερο στόχο την διερεύνηση του φαινομένου των υποθαλάσσιων εκροών υπογείων υδάτων. / --

In this thesis, the response of uranium minerals and poorly crystalline phases to changes in geochemical conditions through geological time has been assessed in order to understand the mobility of natural uranium in the fracture network of a proposed site for a spent nuclear fuel repository in Forsmark, Sweden. Identification and characterization of solid phase uranium have been performed through electron microprobe analysis and optical petrography (Article I). The identified uraninite, haiweeite, and uranophane crystals have been dated using U-Pb and Pb-Pb isotope ratios obtained from secondary ion mass spectrometry and laser ablation-inductively coupled plasma-mass spectrometry (Article II). The mobility of uranium in current Forsmark groundwaters and fracture system has been modelled using the PHREEQC geochemical program and Ra and Rn isotope systematics (Article IV). The rate of submarine groundwater discharge (SGD) from the Forsmark coast to Öregrundsgrepen has also been modelled using Ra isotopes (Article V). Results from these studies support a geologically early (~1200 Ma) oxidation of U(IV) to U(VI). It is further suggested that the old U(VI) minerals present in the bedrock are soluble at the pe values and alkalinities observed in the Forsmark groundwaters. At pe &lt; −4.6 and alkalinity &lt; 60 mg/L, U(VI) can be reduced to U(IV) and deposited in the fracture network. Although a non-negligible rate of SGD has been observed, this cannot be attributed to the discharge of deep (&gt;200 m.b.s.l.) Forsmark groundwaters on the basis of current data. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: In press. Paper 4: Manuscript. Paper 5: Manuscript.</p>

For this dissertation I studied phosphorus (P) sorption dynamics in the shallow groundwater of the southern Everglades. In particular, I examined how the ambient water type governs soluble reactive P (SRP) availability through adsorption/desorption reactions with the aquifer matrix. Chapter 2 investigated how P sorption dynamics of the mangrove root zone sediment are affected by high bicarbonate brackish groundwater compared to both fresh groundwater and saltwater. The results from chapter 2 show that the sediment exhibited exceptionally low sorption efficiency in the high bicarbonate brackish water, which would allow ambient water SRP concentration to be maintained at a higher level. Chapter 3 is a detailed analysis of how P sorption dynamics in two bedrock samples are affected by incremental increases in saltwater content in a freshwater-saltwater transition zone. The results of chapter 3 indicate that a sorption edge occurs at 3 mM Cl- concentration. In water exceeding this Cl- concentration, SRP would be expected to desorb from the bedrock due to a sharp decrease in sorption efficiency between the freshwater saltwater. These results suggest that SRP is active in the ion exchange front of saltwater intrusion, with a rapid increase in SRP availability expected at the leading edge of saltwater intrusion. A landward incursion of 3 mM Cl- concentration water would be expected to raise ambient SRP concentration along the affected aquifer zone, in turn increasing SRP availability in the ecosystem where the transitional waters discharge to the surface. Chapter 4 investigates the kinetics SRP release accompanying saltwater intrusion using a column of carbonate aquifer solids and alternating inflow between fresh groundwater and saltwater. The results show an immediate and high magnitude increase in SRP concentration when saltwater flows into the column. The combined results of this dissertation show that, in the southern Everglades and possibly other carbonate coastlines as well, water type strongly controls P sorption behavior of the sediment and bedrock, and may have a direct influence on the local ecology through increased P availability. A fundamental understanding of the abiotic exchange mechanisms between SRP and the aquifer solids can aid in the successful management and protection of this unique and important ecosystem.

No description available.

The dissertation is comprised of three manuscripts presenting rare earth element (REE) and neodymium (Nd) isotopic analyses for the groundwaters, surface waters, sediments, and bedrocks of two estuaries along the eastern coast of the United States: Indian River Lagoon, Florida, and Pettaquamscutt Estuary, Rhode Island. This research was performed to understand the behavior of REEs in subterranean estuaries, the REE SGD fluxes, and the Nd isotopic composition of SGD. The selection of these sites offers contrasting geology (carbonate/sand matrix aquifer versus glacial till aquifer sourced from granitoids) and contrasting subterranean estuary structure. In the first site, the flux of REEs to the Indian River Lagoon, FL is comprised of a nearshore source of terrestrial SGD displaying a HREE-enriched fractionation pattern, and LREE- and MREE-enriched sources that originate from the reductive dissolution of Fe (III) oxide/hydroxides in the subterranean estuary and transported by bioirrigation to the overlying lagoon. The εNd(0) value the Indian River Lagoon groundwater is much more radiogenic than those of the surface water and sediments which could be due to the use of fertilizers in adjacent communities. The surface waters Nd isotopic composition appears to be a mixture of weathering of the Anastasia Formation and dissolution of eolian-transported Saharan Dust. In contrast at the second site, phosphate minerals control the surface and groundwaters of the Pettaquamscutt estuary, RI. The weathering of apatite and precipitation of secondary REE phosphate minerals most likely produce the MREE-enriched fractionation patterns of the Pettaquamscutt groundwaters. The further precipitation of the secondary REE phosphates in the surface waters of the Pettaquamscutt yields HREE-enriched fractionation patterns. The radiogenic Nd isotopic ratios of the Pettaquamscutt waters relative to the bedrock further suggest that apatite is the source of REEs. The Nd flux of SGD for both sites is roughly equal to the respective river fluxes; however, the Nd flux of SGD to the Pettaquamscutt is approximately 3 times greater than the SGD flux to the Indian River Lagoon. More research is needed in both environments to evaluate the impact of SGD on the Nd isotopic budget of the oceans. / acase@tulane.edu

Submarine Groundwater Discharge (SGD) through seafloor sediments is gaining recognition as an important component of coastal water quality. Stratigraphic features creating geologic heterogeneity, such as incised paleochannels, may influence preferential pathways for SGD. The central Mississippi Sound is underlain by paleochannels that were incised into Pleistocene sediments while the area was subaerially exposed during the last glacial maximum and are now buried by transgressive Holocene deposits. In this thesis, newly collected chirp, previously published seismic reflection, and sediment core data are used to characterize the three-dimensional structure of the Holocene-Pleistocene contact. Results indicate that Pleistocene paleochannels cross-cut the study area, exhibiting depths from 7.3–23.4 m, widths from 0.2–2.5 km, infilling with higher acoustic impedance fluvial sediments, and burial by transgressive Holocene sediments. Results suggest that this shallow subsurface stratigraphy may mediate locations of SGD and aid in predicting SGD pathways and associated contaminant loading into the coastal ocean.

The feasibility of predicting porewater salinity based on calibrated surface electromagnetic methods is discussed in a coastal wetland on the southern banks of Tampa Bay in West-Central Florida. This study utilizes a new method to float commercial land based electromagnetic (EM) instruments in shallow marine waters of less than 1.5 meters. The floating EM-31 (Geonics, Ltd.) effectively sensed the magnitude and lateral extent of high and low salinity porewaters within mangrove lined ditches and ponds. Resistivity and EM geophysical methods are merged with direct sampling data to calibrate layers in electromagnetic models to infer shallow (<30m) groundwater salinity patterns. Initial marine resistivity surveys are necessary to discriminate between equivalent EM model solutions for seafloor conductivities beneath shallow (0.1-1.5m) marine (~30 ppt) waters. Using formation factors computed from nearby resistivity surveys, porewater conductivity predictions based on surface EM-31 and EM-34 measurements are successful at distinguishing overall porewater salinity trends. At the Tampa Bay study site, the most distinctive terrain conductivity anomalies are associated with mangroves bordering marine waters. Highly elevated porewater conductivities are found within 5m of the mangrove trunks, falling sharply off within 10m, presumably due to saltwater exclusion by mangrove roots. Modeling indicates the shallow water EM-31 measurements probably lack the resolution necessary to image more subtle porewater conductivity variations, such as those expected in association with diffuse submarine groundwater discharge. However, the technique has potential application for locating high contrast zones of freshwater discharge and other salinity anomalies in shallow and nearshore areas not accessible to conventional marine resistivity or land-based arrays, and hence may be useful for interdisciplinary studies of coastal wetland ecosystems.

<p>Water and vapour flows from land to sea and the atmosphere are important for water resources, coastal ecosystems and climate. This thesis investigates possible methods for modelling these flows under often encountered unmonitored hydrological conditions and data limitations. Two contrasting types of drainage basin and associated data limitation/availability cases are considered: the Swedish unmonitored near-coastal catchment areas Forsmark and Simpevarp, for which detailed spatial but not much temporal variability data is available; and the much larger Aral Sea Drainage Basin (ASDB), for which spatial hydrological information is limited, while there is relatively well-known temporal change occurring in the Aral Sea itself and in the land and water use of the region over the last 50 years.</p><p>The hydrologic modelling for the Forsmark and Simpevarp catchment areas showed that the relatively large focused stream flows, and the mean values and total sums of the diffuse small stream-groundwater flow fields in between the large stream flows from land to sea are largely constrained by the catchment hydrological balances and relatively robust and certain to estimate. The ASDB hydrologic modelling indicated an evapotranspiration return flow to the atmosphere from the irrigation water input on irrigated land that is much higher than previous estimates in atmospheric modelling, implying possible considerably larger than previously estimated non-local water and climate effects of the world’s irrigated areas. The more detailed groundwater-seawater dynamics modelling carried out for the coastal parts of the ASDB showed that regional topography and bathymetry largely influence coastal water fluxes during sea level lowering, with the Aral Sea shrinkage decreasing the seawater intrusion risk into the coastal groundwater considerably more for steeper than for flatter coastal topography parts of the region.</p>

Water and vapour flows from land to sea and the atmosphere are important for water resources, coastal ecosystems and climate. This thesis investigates possible methods for modelling these flows under often encountered unmonitored hydrological conditions and data limitations. Two contrasting types of drainage basin and associated data limitation/availability cases are considered: the Swedish unmonitored near-coastal catchment areas Forsmark and Simpevarp, for which detailed spatial but not much temporal variability data is available; and the much larger Aral Sea Drainage Basin (ASDB), for which spatial hydrological information is limited, while there is relatively well-known temporal change occurring in the Aral Sea itself and in the land and water use of the region over the last 50 years. The hydrologic modelling for the Forsmark and Simpevarp catchment areas showed that the relatively large focused stream flows, and the mean values and total sums of the diffuse small stream-groundwater flow fields in between the large stream flows from land to sea are largely constrained by the catchment hydrological balances and relatively robust and certain to estimate. The ASDB hydrologic modelling indicated an evapotranspiration return flow to the atmosphere from the irrigation water input on irrigated land that is much higher than previous estimates in atmospheric modelling, implying possible considerably larger than previously estimated non-local water and climate effects of the world’s irrigated areas. The more detailed groundwater-seawater dynamics modelling carried out for the coastal parts of the ASDB showed that regional topography and bathymetry largely influence coastal water fluxes during sea level lowering, with the Aral Sea shrinkage decreasing the seawater intrusion risk into the coastal groundwater considerably more for steeper than for flatter coastal topography parts of the region.

The Otway Basin of southeast Australia is the subject of this thesis, which incorporates pre-existing geological, hydraulic and major element hydrogeological data with new isotope hydrogeochemical investigations. The region is an Upper Cretaceous–Tertiary basin, filled with siliciclastic and calcareous aquifers and aquitards and characterised by late volcanic activity, pervasive faulting and karstification. (For complete abstract open document.)