Calibration of a Bio-optical Model in the North River, North Carolina (Albemarle–Pamlico Sound): A Tool to Evaluate Water Quality Impacts on Seagrasses

Seagrasses are typically light limited in many turbid estuarine systems. Light attenuation is due to water and three optically active constituents (OACs): nonalgal particulates, phytoplankton, and colored dissolved organic matter (CDOM). Using radiative transfer modeling, the inherent optical properties (IOPs) of these three OACs were linked to the light attenuation coefficient, K _PAR, which was measured in North River, North Carolina, by profiles of photosynthetically active radiation (PAR). Seagrasses in the southern portion of Albemarle-Pamlico Estuarine System (APES), the second largest estuary in the USA, were found to be light limited at depths ranging from 0.87 to 2 m. This corresponds to a range of K _PAR from 0.54 to 2.76 m^?1 measured during a 24-month monitoring program. Turbidity ranged from 2.20 to 35.55 NTU, chlorophyll a from 1.56 to 15.35 mg m^?3, and CDOM absorption at 440 nm from 0.319 to 3.554 m^?1. The IOP and water quality data were used to calibrate an existing bio-optical model, which predicted a maximum depth for seagrasses of 1.7 m using annual mean water quality values and a minimum light requirement of 22% surface PAR. The utility of this modeling approach for the management of seagrasses in the APES lies in the identification of which water quality component is most important in driving light attenuation and limiting seagrass depth distribution. The calibrated bio-optical model now enables researchers and managers alike to set water quality targets to achieve desired water column light requirement goals that can be used to set criteria for seagrass habitat protection in North Carolina.     

Effects of landscape patterns on soil erosion processes in a mountain–basin system in the North China

This study was taken up to investigate the effects of landscape patterns on the soil erosion processes in a mountain–basin watershed. The revised universal soil loss equation and sediment delivery distribution models were used to estimate the soil erosion processes. The landscape patterns include the landscape metrics at the landscape level, landscape composition and configuration indicators on the basis of source–sink landscape theory. In the study area, the grassland, bare land, farmland and construction land were the sediment-source landscape; the forest and shrub were the sediment-sink landscape. The correlation analysis results showed that the soil erosion processes were significantly associated with the landscape patterns of the study area. At the landscape level, fragmentation metric was positively correlated with soil erosion; diversity metric was negatively related to soil erosion and sediment yield at the sub-basin scale. Among the source–sink landscape composition and configuration indicators, the composition indicator was positively correlated with soil erosion rate and sediment yield. In the configuration landscape indices, the shape index was negatively correlated with soil erosion rate and sediment yield; the fragmentation index was positively correlated with soil erosion rate and negatively correlated with sediment delivery rate. These results indicated that the optimization measures, such as increase in the area, connectivity and regularity of sediment-sink landscape, or decrease in the proportion, connectivity and regularity of sediment-source landscape, were favorable for soil conservation. Furthermore, the landscape indicators based on the source–sink theory could provide more information for landscape pattern optimization to reduce soil erosion.     

Role of Quaternary stratigraphy on arsenic-contaminated groundwater from parts of Barak Valley, Assam, North–East India

Groundwater arsenic survey in Cachar and Karimganj districts of Barak Valley, Assam shows that people in these two districts are drinking arsenic-contaminated (max. 350 μg/l) groundwater. 66% of tubewells in these two districts have arsenic concentration above the WHO guideline value of 10 μg/l and 26% tubewells have arsenic above 50 μg/l, the Indian standards for arsenic in drinking water. 90% of installed tubewells in these two districts are shallow depth (14–40 m). Shallow tubewells were installed in Holocene Newer Alluvium aquifers are characterised by grey to black coloured fine grained organic rich argillaceous sediments and are mostly arsenic contamination in groundwater. Plio-Pleistocene Older Alluvium aquifers composed of shale, ferruginous sandstone, mottle clay, pebble and boulder beds, which at higher location or with thin cover of Newer Alluvium sediments are safe in arsenic contamination in groundwater. 91% of tubewell water samples show significantly higher concentrations of iron beyond its permissible limit of 1 mg/l. The iron content in these two districts varies from 0.5 to as much as 48 mg/l. Most of the arsenic contaminated villages of Cachar and Karimganj districts are located in entrenched channels and flood plains of Newer Alluvium sediments in Barak-Surma-Langai Rivers system. However, deeper tubewells (>60 m) in Plio-Pleistocene Older Alluvium aquifers would be a better option for arsenic-safe groundwater. The arsenic in groundwater is getting released from associated Holocene sediments which were likely deposited from the surrounding Tertiary Barail hill range.     

Geophysical Effects of the Eruption of Hunga–Tonga–Hunga–Ha’apai Volcano on January 15, 2022

Doklady Earth Sciences - The results of instrumental observations for meteoparameters, microbaric variations, and variations in an electric field are analyzed at the Mikhnevo Observatory and the...     

Genesis of Coal Metamorphism of Late PalaeozoicCoals in the South of North China——A Further Approach to the Effects of ThermalGroundwater on Coal Metamorphism

The close relationship between the genesis of coal metamorphism and the evolution of the regional tectonic framework is expounded on the basis of an analysis of the geological factors causing the metamorphic zonation of the Late Palaeozoic coals in southern North China; in terms of the mechanism for the formation of palaeogeothermal anomalies, the effects of thermal groundwater on coal metamorphism is highlighted and a geological model for thermal groundwater metamorphism of coal established; with the concept of the palaeogeotherm-coal metamorphism system, the genesis of coal metamorphism is analysed according to the distribution pattern of three geological factors: heat source, heat-carrier and channel, and heat-collector.     

Assessment of the Effects of Freeze–Thaw and Salt Crystallization Ageing Tests on Anahita Temple Stone,Kangavar, West of Iran

Building stone of Anahita Temple seriously suffers from weathering due to long term freezing-thawing and salt crystallization processes. This article investigates possible changes of physical and mechanical characteristics of this stone subjected to freeze–thaw and salt crystallization ageing tests. Fresh samples obtained from the Chelmaran quarry (the main quarry supplying for Anahita Temple stone) were tested under freeze–thaw and salt crystallization experiments. The freeze–thaw and sodium sulfate salt crystallization are suggested to be the most effective factors affecting in apparent deterioration of the stone in compare to the magnesium sulfate salt crystallization test. Significant decreases in mechanical properties of the stone were observed after freeze–thaw and salt crystallization tests. However, more mechanical losses were recorded after the salt crystallization cycles than the freeze–thaw cycles. This is probably due to crystallization pressure of salt crystals in compare to ice wedging force, which promoted more development of micro-fractures in the specimens. Probably, intrinsic factors of the stone such as frequent calcite veins and stylolites, are the main factors that control the durability of Anahita Temple stone. Preferential weakening along these features during freeze–thaw and salt crystallization cycles led to physical destruction and strength loss of the stone. Based on comparison between experimentally induced damages and field observations, reasonably freeze–thaw process is major factor in weathering of Anahita Temple stone. It should be noted that recorded 102 frozen days for the region imply high destruction potential of the stone during freeze–thaw cycles.     

Effects of errors and biases on the scaling of earthquake spatial pattern: application to the 2004 Sumatra–Andaman sequence

This study discusses the scaling properties of the spatial distribution of the December 26, 2004, Sumatra aftershocks. We estimate the spatial correlation dimension D ₂ of the epicentral distribution of aftershocks recorded by a local network operated by Geological Survey of India. We estimate the value of D ₂ for five blocks in the source area by using generalized correlation integral approach. We assess its bias due to finite data points, scaling range, effects of location errors, and boundary effects theoretically and apply it to real data sets. The correlation dimension was computed both for real as well as synthetic data sets that include randomly generated point sets obtained using uniform distributions and mimicking the number of events and outlines of the effective areas filled with epicenters. On comparing the results from the real data and random point sets from simulations, we found the lower limit of bias in D ₂ estimates from limited data sets to be 0.26. Thus, the spatial variation in correlation dimensions among different blocks using local data sets cannot be directly compared unless the influence of bias in the real aftershock data set is taken into account. They cannot also be used to infer the geometry of the faults. We also discuss the results in order to add constraints on the use of synthetic data and of different approaches for uncertainty analysis on spatial variation of D ₂. A difference in D ₂ values, rather than their absolute values, among small blocks is of interest to local data sets, which are correlated with their seismic b values. Taking into account the possible errors and biases, the average D ₂ values vary from 1.05 to 1.57 in the Andaman–Nicobar region. The relative change in D ₂ values can be interpreted in terms of clustering and diffuse seismic activity associated with the low and high D ₂ values, respectively. Overall, a relatively high D ₂ and low b value is consistent with high-magnitude, diffuse activity in space in the source region of the 2004 Sumatra earthquake.

     

Experimental study on water–rock interactions during CO2 flooding in the Tensleep Formation,Wyoming, USA

The conditions for mineral alteration and formation damage during CO₂ treatment of Tensleep sandstone reservoirs in northern Wyoming, USA, were examined through core-flooding laboratory experiments carried out under simulated reservoir conditions (80°C and 166 bars). Subsurface cores from the Tensleep sandstone, which were cemented by dolomite and anhydrite, and synthetic brines were used. The brines used were (Ca, Mg, Na)SO₄–NaCl solution (9.69 g/l total dissolved solids) for Run 1 and a 0.25 mol/l NaCl solution for Run 2. The solution used in Run 1 was saturated with respect to anhydrite at run conditions, which is characteristic of Tensleep Formation waters.Three major reactions took place during flooding, including (1) dissolution of dolomite, (2) alteration of K-feldspar to form kaolinite, and (3) precipitation (in Run 1) or dissolution (in Run 2) of anhydrite. All sample solutions remained undersaturated with respect to carbonates. The permeability of all the cores (except one used in Run 2) decreased during the experiments despite the dissolution of authigenic cement. Kaolinite crystal growth occurring in pore throats likely reduced the permeability.Application of the experimental results to reservoirs in the Tensleep Formation indicates that an injection solution will obtain saturation with respect to dolomite (and anhydrite) in the immediate vicinity of the injection well. The injection of NaCl-type water, which can be obtained from other formations, causes a greater increase in porosity than the injection of Tensleep Formation waters because of the dissolution of both dolomite and anhydrite cements.     

Geochemical,Sr–Nd–Pb isotope,and zircon U–Pb geochronological constraints on the origin of Early Permian mafic dikes,northern North China Craton

Dolerite dike swarms are widespread across the North China Craton (NCC) of Hebei Province (China) and Inner Mongolia. Here, we report new geochemical, Sr–Nd–Pb isotope, and U–Pb zircon ages for representative samples of these dikes. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb analysis yielded consistent Permian ages of 274.8 ± 2.9 and 275.0 ± 4.5 Ma for zircons extracted from two dikes. The dolerites have highly variable compositions (SiO₂ = 46.99–56.18 wt.%, TiO₂ = 1.27–2.39 wt.%, Al₂O₃ = 14.42–16.20 wt.%, MgO = 5.18–7.75 wt.%, Fe₂O₃ = 8.03–13.52 wt.%, CaO = 5.18–9.75 wt.%, Na₂O = 2.46–3.79 wt.%, K₂O = 0.26–2.35 wt.%, and P₂O₅ = 0.18–0.37 wt.%) and are light rare earth element (LREE) and large ion lithophile element (LILE, e.g. Rb, Ba, and K, and Pb in sample SXG1-9) enriched, and Th and high field strength element (HFSE, e.g. Nb and Ta in sample SXG1-9, and Ti) depleted. The mafic dikes have relatively uniform (⁸⁷Sr/⁸⁶Sr)_i values from 0.7031 to 0.7048, (²⁰⁶Pb/²⁰⁴Pb)_i from 17.77 to 17.976, (²⁰⁷Pb/²⁰⁴Pb)_i from 15.50 to 15.52, (²⁰⁸Pb/²⁰⁴Pb)_i from 37.95 to 38.03, and positive ?_Nd(t) (3.6–7.3), and variable neodymium model ages (T_DM1 = 0.75–0.99 Ga, T_DM2 = 0.34–0.74 Ga). These data suggest that the dike magmas were derived from partial melting of a depleted region of the asthenospheric mantle, and that they fractionated olivine, pyroxene, plagioclase, K-feldspar, and Ti-bearing phases without undergoing significant crustal contamination. These mafic dikes within the NCC formed during a period of crustal thinning in response to extension after Permian collision between the NCC and the Siberian Block.     

A Before–After–Control–Impact Analysis of the Effects of a Mississippi River Freshwater Diversion on Estuarine Nekton in Louisiana, USA

Since 1991, the Caernarvon Freshwater Diversion has been reintroducing Mississippi River water into a previously hydrologically isolated estuary in an effort to restore wetlands. To determine the effect of freshwater inflow on estuarine nekton community structure, a Before?CAfter?CControl?CImpact study design was applied. As a result of the opening, salinities in the impact area decreased, and the nekton community structure in the estuary changed significantly. Species of economical or ecological importance either increased in biomass or exhibited no response to the opening of the diversion. Higher abundances of small fish were observed in the area receiving freshwater flow, which is an indication that the area serves as a refuge from large marine predators. Because a salinity gradient was established, as opposed to a uniform but lower salinity regime, aquatic habitat was available to nekton species from a wide spectrum of salinity tolerances.     

Geological,fluid inclusion,and O–C–S–Pb–He–Ar isotopic constraints on the genesis of the Honghuagou lode gold deposit,northern North China Craton

The Honghuagou Au deposit is located in the Chifeng-Chaoyang region within the northern margin of the North China Craton. The auriferous quartz veins are mainly hosted in the mafic gneiss and migmatite of the Neoarchean Xiaotazigou Formation along NNW- and NE-striking faults, with pyrite as the predominant ore mineral. The gold mineralization process can be divided into two stages, involving stage I quartz-pyrite and stage II quartz-calcite-polymetallic sulfide. Three types of fluid inclusions (FIs) have been identified in the Honghuagou deposit, namely, carbonic inclusions, aqueous‑carbonic inclusions, and aqueous inclusions. Quartz of stage I contains all types of FIs, whereas only aqueous inclusions are evident in stage II veins. The FIs of stages I and II yield homogenization temperatures of 275–340 °C and 240–290 °C with salinities of 3.4–10.7 wt% and 1.4–9.7 wt% NaCl eqv., respectively. The ore-forming fluids are characterized by medium temperature and low salinity, belonging to the H₂O–NaCl–CO₂ system. The δ¹⁸O_H2O values of the ore fluids are between 2.1‰ and 5.9‰, within the range of enriched mantle-derived fluids in the North China Craton. The carbon isotope compositions of calcite (δ¹³C_PDB = −4.4‰ to −4‰) are also similar to mantle carbon. He-Ar isotope data (³He/⁴He = 0.38–0.44 Ra; ⁴⁰Ar/³⁶Ar = 330–477) of fluid inclusions in pyrite indicate a mixed crustal and mantle source for the ore-forming fluids. Whereas, S-Pb isotope compositions of sulfides reveal that ore metals are principally derived from crustal rocks. On the basis of available geological and geochemical evidence, we suggest that the Honghuagou deposit is an orogenic gold deposit.     

Paleoproterozoic crustal evolution of the Hengshan–Wutai–Fuping region, North China Craton

An arguable point regarding the Neoarchean and Paleoproterozoic crustal evolution of the North China Craton（NCC）is whether the tectonic setting in the central belt during the mid-Paleoproterozoic（2.35-2.0 Ga）was dominated by an extensional regime or an oceanic subduction-arc regime.A review of the midPaleoproterozoic magmatism and sedimentation for the Hengshan-Wutai-Fuping region suggests that a back-arc extension regime was dominant in this region.This conclusion is consistent with the observation that the 2.35-2.0 Ga magmatism shows a typical bimodal distribution where the mafic rocks mostly have arc affinities and the acidic rocks mainly comprise highly-fractioned calc-alkaline to alkaline（or A-type）granites,and that this magmatism was coeval with development of extensional basins characteristic of transgressive sequences with volcanic interlayers such as in the Hutuo Group.Although the final amalgamation of the NCC was believed to occur at ～1.85 Ga,recent zircon U-Pb age dating for mica schist in the Wutai Group suggests a collisional event may have occurred at ～1.95 Ga.The metamorphic ages of ～1.85 Ga,obtained mostly from the high-grade rocks using the zircon U-Pb approach,most probably indicate uplifting and cooling of these high-grade terranes.This is because（i）phase modeling suggests that newly-grown zircon grains in highgrade rocks with a melt phase cannot date the age of peak pressure and temperature stages,but the age of melt crystallization in cooling stages;（ii）the metamorphic P-T paths with isobaric cooling under 6-7 kb for the Hengshan and Fuping granulites suggest their prolonged stay in the middle-lower crust;and（iii）the obtained metamorphic age data show a continuous distribution from 1.95 to 1.80 Ga.Thus,an alternative tectonic scenario for the Hengshan-Wutai-Fuping region involves：（i）formation of a proto-NCC at ～2.5 Ga;（ii）back-arc extension during 2.35-2.0 Ga resulting in bimodal magmatism and sedimentation in rifting basins on an Archean basement;?     

Effects of alkaline earth metals on the surface,structure, and reactivity of α-alumina

A series of strontium- and barium-doped alumina samples were prepared by hydrolysis, in neutral medium, starting from commercial Al₂O₃, SrCO₃, and BaCO₃ materials. The precursors thus obtained were calcined under air at 700 °C; then, the bulk and surface properties of the resulting mixed oxides were characterized by nitrogen physisorption, X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), thermogravimetry (TGA), and differential thermal analysis (DTA). Contrary to SrCO₃, an addition of BaCO₃ to α-Al₂O₃ increases slightly the specific surface area. XRD patterns essentially reveal the characteristic reflections assigned to α-Al₂O₃. In agreement with TGA and XRD analysis, strontium and barium carbonates remain after calcination at 700 °C, their decomposition starting above 800 °C. Let us note that this decomposition occurs more readily on AlSr-100 than on AlBa-100 with no apparent relationship with the evolution observed on the specific surface areas. H₂-TPR experiments underline a significant bulk reduction of barium and strontium carbonates taking place significantly above 900 °C with similar trend noticed during TGA regarding their thermal decomposition. However, the most relevant observation is related to a sharp enhancement of the reducibility of AlSr-y with the appearance two reduction ranges highlighting the existence of different types of interactions with strontium and the alumina substrate.     

Effects of acid rain on physical,mechanical and chemical properties of GGBS–MgO-solidified/stabilized Pb-contaminated clayey soil

Acta Geotechnica - Reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS) is a newly developed binder for soil stabilization/solidification. It can be used as an alternative...