Convective crystal dissolution

The effect of free and forced convection on crystal dissolution is examined both theoretically and experimentally. Well-established relationships for heat and mass transfer are applied to obtain approximate expressions for the dissolution velocity and the associated thickness of the compositional boundary layer. These expressions are found to be in good agreement with experimental observations of the dissolution of quartz crystals in basalt and NaCl crystal in water. When applied to light felsic crystals in basaltic magmas, the expressions predict that forced convection will produce a boundary layer thickness of about 100 μm and a dissolution velocity of order 10⁻⁶ cm s⁻¹. These velocities are too slow for xenocrysts to be dissolved significantly during magma ascent in dykes, but are sufficient for cm-size crystals to dissolve in the interior of a convecting magma chamber. Larger crystals are likely to accumulate at the chamber's roof, where free convection is predicted to dissolve them at velocities of order 10⁻⁷ cm s⁻¹. In an Appendix, the dissolution of the chamber's walls is also considered, and a velocity of order 10⁻⁸cm s⁻¹ is predicted. Editorial responsibility: T.L. Grove     

Primary production in Long Island sound

Daily and annual integrated rates of primary productivity and community respiration were calculated using physiological parameters measured in oxygen-based photosynthesis-irradiance (P-I) incubations at 8 stations throughout central and western Long Island Sound (cwLIS) during the summer and autumn of 2002 and 2003 and the late spring of 2003. Each calculation takes into account actual variations in incident irradiance over the day and underwater irradiance and standing stock with depth. Annual peak rates, ±95% confidence interval of propagated uncertainty in each measurement, of gross primary production (GPP, 1,730±610 mmol O₂ m⁻² d⁻¹), community respiration (R_c, 1,660±270 mmol O₂ m⁻² d⁻¹), and net community production (NCP, 1,160±1,100 mmol O₂ m⁻² d⁻¹) occurred during summer at the western end of the Sound. Lowest rates of GPP (4±11 mmol O₂ m⁻² d⁻¹), R_c (−50±300 mmol O₂ m⁻² d⁻¹), and NCP (−1,250±270 mmol O₂ m⁻² d⁻¹) occurred during late autumn-early winter at the outer sampled stations. These large ranges in rates of GPP, R_c, and NCP throughout the photic zone of cwLIS are attributed to seasonal and spatial variability. Algal respiration (R_a) was estimated to consume an average of 5% to 52% of GPP, using a literature-based ratio of R_a:R_c. From this range, we established that the estimated R_a accounts for approximately half of GPP, and was used to estimate daily net primary production (NPP), which ranged from 2 to 870 mmol O₂ m⁻² d⁻¹ throughout cwLIS during the study. Annual NPP averaged 40±8 mol O₂ m⁻² yr⁻¹ for all sampled stations, which more than doubled along the main axis of the Sound, from 32±14 mol O₂ m⁻² yr⁻¹ at an eastern station to 82±25 mol O₂ m⁻² yr⁻¹ at the western-most station. These spatial gradients in productivity parallel nitrogen loads along the main axis of the Sound. Daily integrals of productivity were used to test and formulate a simple, robust biomass-light model for the prediction of phytoplankton production in Long Island Sound, and the slope of the relationship was consistent with reports for other systems.     

Light Requirements for Growth and Survival of Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) in Pacific Northwest (USA) Estuaries

We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon flux density (PPFD) of about 350–550 μmol quanta m⁻² s⁻¹. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term survival required at least 3 mol quanta m⁻² day⁻¹ on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m⁻² day⁻¹. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta m⁻² day⁻¹ during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m⁻² day⁻¹.     

Trends in phosphatase activity along a successional gradient of tidal freshwater marshes on the Cooper River South Carolina

Phosphatase activity was measured in sediments from tidal freshwater habitats adjacent to the Cooper River in South Carolina representing different stages of ecological succession. It was found that sediment (0–5 cm) acid phosphatase activity, alkaline phosphatase activity and phosphodiesterase activity increased with increasing successional stage and phytomass. Acid phosphatase activity in creased from 7.5±1.2 (±1 SD) in subtidal sediment from a shallow open water habitat without vegetation to 61.2±4.9 μmol g⁻¹ hr⁻¹ (μmol of p-nitrophenol released per gram of dry sediment per hour) in intertidal sediments colonized by emergent macrophytes, while alkaline phosphatase activity increased from 2.1±0.1 to 19.01±1.5 μmol g⁻¹ hr⁻¹. Phosphodiesterase activity increased from 1.8±0.1 to 20.2±2.0 μmol g⁻¹ hr⁻¹ along the same gradient. Acid phosphatase activity was highly correlated (R²=0.92, P<0.001) with the organic matter content of the sediment. A study of phosphatase kinetics showed that V_max of all phosphatases also increased along the successional gradient. Trends in phosphatase activity and V_max correlated positively with plant biomass and negatively with concentrations of soluble reactive phosphorus in porewater, sediment extractable phosphorus, and total phosphourus. The porewater N∶P atom ratio decreased along the succession gradient from 25.3 in an early stage, open water community to 13.0 in a community dominated by emergent vegetation. The data also show that the distribution of the forms of phosphorus changed with successional stage. The change in distribution and the increased biological demand for phosphorus that paralleled succession were mediated by the activity of phosphatase enzymes.     

Variations in long term wind speed during different decades in Arabian Sea and Bay of Bengal

A study has been carried out by comparing the extreme wind speeds estimated based on NCEP/NCAR reanalysis data for 100 years return period using Fischer Tippet-1 (commonly known as Gumbel) and Weibull distributions for three locations (off Goa, Visakhapatnam and Machilipatnam) in the north Indian Ocean. The wind dataset for Goa is compared with that from ERA-40 data. For higher wind speeds (12–20m s⁻¹), NCEP wind speed has higher percentage of occurrence than that of ERA-40. Analysis has shown slight upward trend in the annual maximum wind for location off Machilipatnam with an increase of 1.2 cm s⁻¹ per year and a decreasing trend of −1.3 cm s⁻¹ per year in the case of Goa. The Weibull distribution with shape parameter 2 fits the annual maximum wind data better than FT-1 distribution.     

Diffusion-controlled growth of albite and pyroxene reaction rims

The growth rates of albite and pyroxene (enstatite + diopside + spinel) reaction rims were measured at 1000°C and ˜700 MPa and found to be parabolic indicating diffusion-controlled growth. The parabolic rate constants for the pyroxene (+ spinel) rims in samples with 0.5 wt% H₂O added or initially vacuum dried at 25°C and 250°C are 1.68 ± 0.09, 0.54 ± 0.05 and 0.25 ± 0.06 μm²/h, respectively. The values for albite rim growth in samples initially dried at 60°C and with 0.1 wt% H₂O added are 0.25 ± 0.04 and 0.33 ± 0.03 μm²/h, respectively. The latter values were used to derive the product of the grain boundary diffusion coefficient D′_A, where A = SiO₂, NaAlO₂, or NaAlSi₋₁, and the grain boundary thickness δ in albite. The calculated D′_SIO2δ in the albite aggregate for the situations of two different water contents are about 9.9 × 10⁻²³ and 1.4 × 10⁻²² m³ s⁻¹, respectively. Both the rate constants and the calculated D′_Aδ demonstrate that the effect of water content on the grain boundary diffusion rate in monomineralic albite and polymineralic pyroxene (+ spinel) aggregates is small, consistent with recent studies of monomineralic enstatite and forsterite rims. Received: 1 July 1995 / Accepted: 1 August 1996     

Spatial structure of hydrography and flow in a Chilean fjord,Estuario Reloncaví

Underway current velocity profiles were combined with temperature and salinity profiles at fixed stations to describe tidal and subtidal flow patterns in the middle of the northernmost Chilean fjord, Estuario Reloncaví. This is the first study involving current velocity measurements in this fjord. Reloncaví fjord is 55 km long, 2 km wide, and on average is 170 m deep. Measurements concentrated around a marked bend of the coastline, where an 8-km along-fjord transect was sampled during a semidiurnal tidal cycle in March 2002 and a 2-km cross-fjord transect was occupied, also during a semidiurnal cycle, in May 2004. The fjord hydrography showed a relatively thin (<5 m deep), continuously stratified, buoyant layer with stratification values >4 kg m⁻³ per meter of depth. Below this thin layer, the water was relatively homogeneous. Semidiurnal tidal currents had low amplitudes (<10 cm s⁻¹) that allowed the persistence of a surface front throughout the tidal cycle. The front oscillated with a period of ca. 2.5 h and showed excursions of 2 km. The front oscillations could have been produced by a lateral seiche that corresponds to the natural period of oscillation across the fjord. This front could have also caused large (2 h) phase lags in the semidiurnal tidal currents, from one end of the transect to the other, within the buoyant layer. Tidal phases were relatively uniform underneath this buoyant layer. Subtidal flows showed a 3-layer pattern consisting of a surface layer (8 m thick, of 5 cm s⁻¹ surface outflow), an intermediate layer (70 m thick, of 3 cm s⁻¹ net inflow), and a bottom layer (below 80 m depth, of 3 cm s⁻¹ net outflow). The surface outflow and, to a certain extent, the inflow layer were related to the buoyant water interacting with the ambient oceanic water. The inflowing layer and the bottom outflow were attributed to nonlinear effects associated with a tidal wave that reflects at the fjord's head. The weak subtidal currents followed the morphology of the bend and caused downwelling on the inside and upwelling on the outside part of the bend.     

Detection of radio recombination lines of hydrogen ionized by cosmic-ray protons in the cool interstellar medium

The emission of hydrogen radio recombination lines from a cloud of cool interstellar matter toward the radio source Cassiopeia A has been detected. The formation of the radio recombination lines is initiated by cosmic rays. The rate of ionization of the interstellar hydrogen by cosmic-ray protons measured from the radio recombination lines using the most direct method is ζ_H = (1 ± 0.25)×10⁻¹⁶ s⁻¹. This value of ζ_H is compared with measurements obtained using other methods.     

Direct evidence of imbalanced seagrass (Posidonia oceanica) shoot population dynamics in the Spanish Mediterranean

Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots m⁻², absolute shoot mortality from 5±0 to 249±53 shoots m⁻² yr⁻¹, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m⁻²yr⁻¹. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot density, varied from 0.015±0.006 to 0.282±0.138 yr⁻¹ and 0.018±0.005 to 0.302±0.093 yr⁻¹, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment. The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass meadows.     

Iron Diffusion in Single-Crystal Diopside

 Iron tracer diffusion experiments in diopside have been performed using natural and synthetic single crystals of diopside, and stable iron tracers enriched in ⁵⁴Fe, at temperatures in the range 950–1100 °C, total pressure 1 atm, for times up to 29 days. Iron isotope diffusion profiles were determined with an ion microprobe. For experiments performed at log pO₂ = −13, in directions parallel to the c axis and the b axis of two natural, low iron (Fe ∼ 1.8 at %) diopsides, the data obey a single Arrhenius relationship of the form D = 6.22_−5.9 ^+49.6×10⁻¹⁵ exp(−161.5 ± 35.0 kJ mol⁻¹/RT) m² s⁻¹. A single datum for iron diffusion in iron-free, single-crystal diopside at 1050 °C, is approximately 1 order of magnitude slower than in the natural crystals. The pO₂ dependence of iron diffusion in natural crystals at 1050 °C (power exponent = 0.229 ± 0.036) indicates a vacancy mechanism; this is consistent with the results of unpublished atomistic simulation studies. There is no evidence of anisotropy for iron diffusion in diopside. Received: 16 March 1999 / Accepted: 10 April 2000     

Microzooplankton Grazing in Green Water—Results from Two Contrasting Estuaries

We measured seasonal variations in microzooplankton grazing in Long Island Sound (LIS) and San Francisco Bay (SFB). There was consistent evidence of nutrient limitation in LIS, but not SFB. We found higher chlorophyll a concentrations in LIS compared with SFB. In spite of differences in phytoplankton, there were no differences in microzooplankton abundance (summer: LIS, 12.4 ± 1.8 × 10³ indiv. L⁻¹; SFB, 14.1 ± 3.0 × 10³ indiv. L⁻¹), biomass (summer: LIS, 30.4 ± 5.0 μg C L⁻¹; SFB, 26.3 ± 5.9 μg C L⁻¹), or grazing rates (summer: LIS, 0.66 ± 0.19 day⁻¹; SFB, 0.65 ± 0.18 day⁻¹) between the two estuaries. In common with many other investigators, we found many instances of saturated as well as insignificant grazing. We suggest that saturation in some cases may result from high particle loads in turbid estuarine systems and that insignificant grazing may result from extreme saturation of the grazing response due to the need to process non-food particles.     

Interannual Variation in Photosynthetically Significant Optical Properties and Water Quality in a Coastal Blackwater River Plume

Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m³s⁻¹) was only 25% of the wet year discharge (429 ± 337 m³s⁻¹). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter (CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a _CDOM (412)] ranged from 0.05 to 8.25 m⁻¹ with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater river inputs, CDOM may exert a major limiting influence over near-shore primary production.     

Soil organic carbon storage changes in Yangtze Delta region,China

Soil carbon sequestration plays an essential role in mitigating CO₂ increases and the global greenhouse effect. This paper calculates soil organic carbon (SOC) storage changes during the course of industrialization and urbanization in Yangtze Delta region, China, based on the data of the second national soil survey (1982–1985) and the regional geochemical survey (2002–2005), with the help of remote sensing images acquired in periods of 1980, 2000, 2005. The results show that soils in the top 0–20 and 0–100 cm depth in this region demonstrate the carbon sink effect from the early 1980s to the early 2000s. The SOC storage in 0–20 cm depth has resulted in increase from 213.70 to 238.65 Tg, which corresponds to the SOC density increase from 2.94 ± 1.08 to 3.28 ± 0.92 kg m⁻², and mean carbon sequestration storage and rate are 1.25 Tg a⁻¹, 17.14 g m⁻² a⁻¹, respectively. The SOC storage in 0–100 cm depth has resulted in increase from 690.26 to 792.65 Tg, which corresponds to the SOC density increase from 9.48 ± 4.22 to 10.89 ± 3.42 kg m⁻², and mean carbon sequestration storage and rate are 5.12 Tg a⁻¹, 70.32 g m⁻² a⁻¹, respectively. Urban area in Yangtze Delta region, China, increased more than 3,000 km² and the urban growth patterns circled the central city region in the past 20 years. The SOC densities in 0–20 cm depth decrease gradually along urban–suburban–countryside and the urban topsoil is slightly enriched with SOC. Compared to the data of the second national soil survey in the early 1980s, the mean SOC density in urban area increased by 0.76 kg m², or up 25.85% in the past 20 years. With the characteristics of SOC storage changes offered, land-use changes, farming system transition and ecological city construction are mainly attributed to SOC storage increases. Because of lower SOC content in this region, it is assumed that the carbon sink effect will go on in the future through improved soil management.     

Heat capacity and thermodynamic properties of GdPO<Subscript>4</Subscript> in the temperature range 0–1600 K

The heat capacity of gadolinium orthophosphate (GdPO₄) measured in the temperature range 11.15–344.11 K by adiabatic calorimetry and available literature data were used to calculate its thermodynamic functions at 0–1600 K. At 298.15 K, these functions are as follows: C _p ⁰(298.15 K) = 101.85 ± 0.05 J K⁻¹ mol⁻¹, S ⁰(298.15 K) = 123.82 ± 0.18 J K⁻¹ mol⁻¹, H ⁰(298.15 K)–H ⁰(0) = 17.250 ± 0.012 kJ mol⁻¹, and Φ ⁰(298.15 K) = 65.97 ± 0.18 J K⁻¹ mol⁻¹ The calculated Gibbs free energy of formation from the elements of GdPO₄ is Δ _f G ⁰ (298.15 K) = −1844.3 ± 4.7 kJ mol⁻¹.     

Oxygen diffusion in anhydrous sanidine feldspar

Oxygen exchange experiments have been performed between single crystals of sanidine feldspar and oxygen gas enriched in ¹⁸O, at temperatures in the range 869–1053 °C, total pressure 1 atmosphere, for times up to 28 days. Oxygen isotope diffusion profiles in a direction perpendicular to (001) were determined with an ion microprobe. The experimental data obey a single Arrhenius relationship of the form D = 8.4 × 10⁻¹¹ exp. (−245 ± 15 kJ mol⁻¹/RT) m²s⁻¹. The results indicate that oxygen diffusion in anhydrous sanidine feldspar is marginally slower than oxygen diffusion in anhydrous anorthite. Comparison with published atomistic simulation studies suggests that oxygen transport in feldspar is by an interstitial mechanism. Received: 17 October 1997 / Accepted: 6 July 1998     

Estimation of methane emission from whole waste landfill site using correlation between flux and ground temperature

A methodology to estimate a methane emission in a waste landfill site was developed. The methane flux at a waste landfill site in summer, autumn, and winter was within the following ranges: from −1.3×10⁻² to 16, from −6.4×10⁻² to 7.5, and from −1.6×10⁻³ to 1.5×10⁻² g-CH₄ m⁻² h⁻¹, respectively. In those seasons, the mean methane emission rate and coefficient of variation were 1.1 g-CH₄ m⁻² h⁻¹ ±290%, 0.57 g-CH₄ m⁻² h⁻¹ ±347%, and 5.4×10⁻² g-CH₄ m⁻² h⁻¹ ±370%, respectively. These results simultaneously showed that fluctuations of methane emission from the landfill surface were both of spatial and temporal variability. In each season, an exponential relationship was observed between the methane flux density and the ground temperature. Total methane emissions were estimated to be 5.7×10⁻², 7.1×10⁻³, and 1.7×10⁻³ g-CH₄ m⁻² h⁻¹ in the summer, autumn, and winter surveys, respectively, using a temperature surrogated-kriging method. The results of this study would improve upon the labor-intensive closed-chamber method, and could be a more practical way to estimate methane emissions from waste landfills.     

Crystallographic preferred orientation and microstructure of experimentally deformed Braubach galena ore with emphasis on the relation to diffusional processes

Sample cylinders of two galena ore hand specimens from Braubach, Germany were axially shortened in the strain rate range 5 × 10⁻⁵ s⁻¹–5 × 10⁻⁷ s⁻¹ at a confining pressure of 200 (300) MPa and at temperatures of 20 °C–600 °C. Neutron diffraction analyses of the crystallographic preferred orientation (texture) were carried out before and after experimental deformation on the same sample cylinder. Up to a deformation temperature of 300 °C and a strain rate of 5 × 10⁻⁶ s⁻¹ a more or less complete <110> fiber texture develops, the strength of the fiber texture only depending on strain and the strength of the original preferred orientation. At slower strain rate and higher temperature, there is a distinct decrease of the fiber texture development. Diffusional mass transfer starts to become a significant deformation mechanism. Deformation at 500 °C changes the original texture only slightly, which indicates a rapid increase of importance of diffusional flow processes. The alteration of the accompanying sulfosalts indicates that the temperature is high enough for the movement of atoms. The microstructure only reveals remarkable deformation structures at higher strains and in areas of locally higher stresses. Received: 10 June 1997 / Accepted: 14 May 1998     

Pb diffusion in rutile

Diffusion of Pb was measured in natural and synthetic rutile under dry, 1 atmosphere conditions, using mixtures of Pb titanate or Pb sulfide and TiO₂ as the sources of diffusant. Pb depth profiles were then measured with Rutherford Backscattering Spectrometry (RBS). Over the temperature range 700–1100 °C, the following Arrhenius relation was obtained for the synthetic rutile: D=3.9 × 10⁻¹⁰exp(−250 ± 12 kJ mol⁻¹/RT) m²s⁻¹. Results for diffusion in natural and synthetic rutile were quite similar, despite significant differences in trace element compositions. Mean closure temperatures calculated from the diffusion parameters are around 600 °C for rutile grains of ∼100 μm size. This is about 100 °C higher than rutile closure temperature determinations from past field-based studies, suggesting that rutile is more resistant to Pb loss through volume diffusion than previously thought. Received: 28 June 1999 / Accepted: 29 December 1999     

Transport properties of low-sanidine single-crystals, glasses and melts at high temperature

Thermal diffusivity (D) was measured using laser-flash analysis from oriented single-crystal low-sanidine (K_0.92Na_0.08Al_0.99Fe³⁺ _0.005Si_2.95O₈), and three glasses near KAlSi₃O₈. Viscosity measurements of the three supercooled liquids, in the range 10^6.8 to 10^12.3 Pa s, confirm near-Arrhenian behavior, varying subtly with composition. For crystal and glass, D decreases with T, approaching a constant near 1,000 K: D _sat ∼ 0.65 ± 0.3 mm² s⁻¹ for bulk crystal and ∼0.53 ± 0.03 mm² s⁻¹ for the glass. A rapid decrease near 1,400 K is consistent with crossing the glass transition. Melt behavior is approximated by D = 0.475 ± 0.01 mm² s⁻¹. Thermal conductivity (k _lat) of glass, calculated using previous heat capacity (C _P) and new density data, increases with T because C _P strongly increases with T. For melt, k _lat reaches a plateau near 1.45 W m⁻¹ K⁻¹, and is always below k _lat of the crystal. Melting of potassium feldspars impedes heat transport, providing positive thermal feedback that may promote further melting in continental crust.     

Radioactivity in sediments and gross alpha–beta activities in surface water of Fırtına River, Turkey

The concentrations and distribution of natural and artificial radionuclides in sediment and water samples collected from Fırtına River in the Eastern Black Sea region of Turkey were investigated with an aim of evaluating the environmental radioactivity and radiation hazard. Natural gross α and gross β activities were determined for 21 different water samples, and the activity concentrations were obtained for ²²⁶Ra, ²¹⁴Pb, ²¹⁴Bi, ²²⁸Ac, ²⁰⁸Tl, ⁴⁰K and ¹³⁷Cs in 20 different sediment samples. The obtained results showed that natural gross α and gross β activity concentrations in water samples range from 12.4 ± 3.4 to 66.2 ± 9.2 mBq l⁻¹ and from 27.9 ± 3.3 to 133.3 ± 4.1 mBq l⁻¹, respectively. The mean activity concentrations were 32.6 ± 3.8 mBq l⁻¹ for gross α and 69.9 ± 4.4 mBq l⁻¹ for gross β. Generally, the gross β activities were higher than the corresponding gross α activities. The average concentrations of ²³⁸U and ²³²Th daughter products vary from 11 to 167 Bq kg⁻¹ and from 16 to 107 Bq kg⁻¹, respectively. The concentrations of ⁴⁰K and ¹³⁷Cs vary from 51 to 1,605 Bq kg⁻¹ and from 0.8 to 42 Bq kg⁻¹, respectively. Sediment characterization was also investigated using grain size, thin section and XRD analysis.