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The marked decline in tree island cover across the Everglades over the last century, has been attributed to landscape-scale hydrologic degradation. To preserve and restore Everglades tree islands, a clear understanding of tree island groundwater-surface water interactions is needed, as these interactions strongly influence the chemistry of shallow groundwater and the location and patterns of vegetation in many wetlands. The goal of this work was to define the relationship between groundwater-surface water interactions, plant-water uptake, and the groundwater geochemical condition of tree islands. Groundwater and surface water levels, temperature, and chemistry were monitored on eight constructed and one natural tree island in the Everglades from 2007-2010. Sap flow, diurnal water table fluctuations and stable oxygen isotopes of stem, ground and soil water were used to determine the effect of plant-water uptake on groundwater-surface water interactions. Hydrologic and geochemical modeling was used to further explore the effect of plant-groundwater-surface water interactions on ion concentrations and potential mineral formation. A comparison of groundwater and surface water levels, along with calculated groundwater evapotranspiration rates, revealed that the presence of a water table depression under the islands was concurrent with elevated groundwater uptake by the overlying trees. Groundwater chemistry indicated that the water table depression resulted in the advective movement of regional groundwater into the islands. A chloride budget and oxygen isotopes indicated that the elevated ionic strength of tree island groundwater was a result of transpiration. Geochemical modeling indicated that the elevated ionic strength of the groundwater created conditions conducive to the precipitation of aragonite and calcite, and suggests that trees may alter underlying geologic and hydrologic properties. The interaction of tree island and regional groundwater was mediated by the underlying soil type and aboveground biomass, with greater inputs of regional groundwater found on islands underlain by limestone with high amounts of aboveground biomass. Variations in climate, geologic material and aboveground biomass created complex groundwater-surface water interactions that affected the hydrogeochemical condition of tree islands.

The decline of freshwater ecosystems, generally result from land use activities in the river catchment and is of great concern worldwide. This study was conducted along Umtata River in the Eastern Cape province of South Africa between May 2010 and April 2011. The study was aimed at identifying macrophytes families (to species level) and determining the stable isotope signatures (C:N ratios, δ13C and δ15N) and to relate their isotopic signatures to the land use activities along the river catchment. Analysis of variance was performed to test the effect of sites and sampling period on the C:N ratios, δ13C and δ15N signatures. There were 16 macrophyte families represented by 26 species recorded along the river. There was only a significant difference in sites and sampling period in δ15N (p< 0.05). The highest C:N ratios value (30.75±9.65‰) was recorded in the upper reaches while the lowest value (6.10±2.35‰) occurred in the lower reaches. The δ13C values varied throughout the length of the river with highest values (-19.63±5.44‰) obtained in the middle reaches. Spatial variation was evident in δ15N throughout the length of the river and showed increase from the upper reaches to middle reaches and decreased towards lower reaches. The δ15N ranged from 3.92±2.43‰ in the upper reaches to 10.02±4.56‰ in the middle reaches. Temporal variation in δ15N was also evident throughout the sampling period with highest peak in May (9.77± 4.49‰) and lowest in February (0.50±2.49‰) respectively. The highest values of isotope signatures at spatial level demonstrated the true reflection of urban development, sewage discharge and agricultural activities taking place along the river system. Continued monitoring is recommended that may ultimately come up with a better management options for the communities living within the study area, and also to better enhanced land utilization.

This study is part of a project aiming for the long-term burying of nuclear wastes in Kincardine, Ontario. Bedrock formations as well as their associated waters were analyzed in drill cores from the Michigan sedimentary basin, southwest Ontario. This research utilizes geochemistry combined to strontium and rubidium isotope ratios in order to determine the origin of porewaters from Ordovician shales and limestones. It is demonstrated that these waters are the result of a mixing line between the Silurian (Guelph) and Cambrian groundwaters. This last end-member was also mixed with Precambrian brines to some extent. Strontium and rubidium isotopes also demonstrated rubidium in clays were leached by porewaters over time. Once in solution, radioactive rubidium decayed into strontium over time. This process explains the accumulation of radiogenic strontium observed in porewaters. An age estimate for the deposition of carbonates and other evaporates was calculated with the Rb-Sr isotope system. The calculated age is 453.7 million years before present for dolomites, which is consistent with the history of the site. It was possible to gen an approximate age of 339.7 million years for the formation of illites. This corresponds to the illitization process that occurred after the deposition of rocks, when the Silurian brines infiltrated the deeper Ordovician shale. It was also possible to estimate of porewaters ages.

EPR spectra of Fe³⁺ in a natural crystal of brookite have been investigated at X- and Q-band frequencies at room temperature and 573°K. Part of the paramagnetic resonance spectrum observed has been interpreted on the assumption that Fe³⁺occupies eight equivalent Ti⁴⁺ sites in brookite, with four inequivalent orientations.. The spectra show an "intermediate" zero-field splitting at X-band and a "normal" zero field splitting at Q-band frequencies. The spin Hamiltonian parameters which fit the spectra are the following: g = 2.002 ± 0.005 . D = (1170 ± 30) x 10⁻⁴cm⁻¹ E = (330 ± 20) x 10⁻⁴cm⁻¹ [pa + (l/l2)qF]₀₁₀ = (13±10) x 10⁻⁴cm⁻¹ [pa + (l/l2)qF]₁₀₀ = (-13±15) x l0⁻⁴cm⁻¹ [pa + (l/l2)qF]₀₀₁ = (-66±4) x l0⁻⁴cm⁻¹ / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Despite the importance of tropical rivers to the global carbon cycle, the nature of carbon cycling within these watersheds has been dealt with by only a handful of studies. The current work attempts to address this lack of information, using stable isotope and concentration measurements to constrain sources and sinks of carbon in two Peninsular Malaysian watersheds. The basins are located on the central-western and northeastern coasts of the Malaysian Peninsula, and are drained by the Langat and Kelantan Rivers, respectively. Water samples were collected from three points along the two rivers twice a month, in addition to the sampling of groundwater in adjacent aquifers. Principal component analyses (PCA) on water chemistry parameters in the Langat and Kelantan Rivers show the dominance of geogenic and anthropogenic influences, grouped in 4 to 6 components that comprise over 50 % of the total dataset variances. The geogenic input is reflected by components showing strong loadings by Ca, Mg, Mn, Si, and Sr, while anthropogenic influences via pollution are indicated via strong loadings by NO3, SO4, K, Zn and Cl. The carbon isotope and concentration data appear unrelated to these groups, suggesting that the riverine carbon cycle in both locations is dominated by other factors. These may include alternative sources of organic pollution, or inputs from the local vegetation and soils. The mean riverine 13CDOC of -27.8 ± 2.9 ‰ and -26.6 ± 2.2 ‰ in the Langat and Kelantan Basins, respectively, are consistent with the dominance of C3-type vegetation in both watersheds. Riverine 13CDIC signatures approach C3-like values at high DIC concentrations, with measurements as low as -19 ‰ in the Kelantan Basin and -20 ‰ observed in the Langat Basin, consistent with a biological origin for riverine DIC. However, the average 13CDIC in river water is 13C-enriched by about 10 ‰ relative to the expected C3 source in both rivers, and this 13C- enrichment appears to be largest with smaller DIC concentrations. Because of the overpressures of CO2 in the rivers, entrainment of isotopically-heavy atmospheric CO2 is not a likely explanation for the observed 13C-enrichment. Theoretically, dissolution of carbonates could be an alternative source of 13C-enriched carbon, but this lithology is scarce, particularly in the Langat watershed. The increase in DIC downstream and generally high pCO2 values in most river sections argues against aquatic photosynthesis as a primary causative factor for the observed isotopic enrichment. This elimination process leaves the speciation of riverine DIC and the evasion of CO2 as the most likely mechanisms for 13C-enrichment in DIC, via isotope fractionation during HCO3- hydration and CO2 diffusion. Potentially, methanogenic activity could also be, at least partially, responsible for the 13C-enrichment in DIC, particularly immediately downstream of the Langat Reservoir, but due to the absence of empirical data, this must remain only a theoretical proposition. The aquatic chemistry and dissolved carbon data suggests that pollution discharge into the Langat and Kelantan Rivers is the major factor that is responsible for the considerable CO2 overpressures and high DIC and DOC concentrations in the river waters, particularly in the downstream sections. This pollution is likely of biological origin, via sewage and palm oil mill effluent (POME) discharge, and therefore isotopically indistinguishable from natural C3 plant sources. Carbon budgets of the Langat and Kelantan River show CO2 degassing to be a significant mechanism of fluvial carbon loss, comprising roughly 50 %, or more, of the total riverine carbon export in both watersheds. The remainder of the river carbon is transported to the ocean in the form of DIC, DOC and POC in broadly comparable proportions. However, the combined riverine carbon export from the Kelantan and Langat Basins amount to 2 % or less of the total carbon sequestration of the watersheds. Thus, most of the sequestered carbon is returned to the atmosphere via respiration, with smaller amounts incorporated into ecosystem biomass . These results highlight the complexity of carbon cycling in tropical rivers, and agree with previous studies in showing riverine systems to be more than simple conduits of carbon from the land to the ocean.

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