Prognosis of the state （eutrophication and pollution） of freshwater ecosystems on the example of long-term research into Lake Baikal

Systematic （monthly） observations of changes in the components of trophic status in the pelagic zone of Baikal were carried out during years of spring blooms of almost pure cultures： Gymnodinium （1965）, Aulocoseira bai-calensis （1968）, Synedra acus （1969）, Nitzschia acicularis （1984 and 1987）, picocyanobacteria （2004-2005）. The research period coincided with various anthropogenic impacts on Baikal ecosystem： （1） the period of the natural state of the lake （until 1969）; （2） the period of weak anthropogenic impact （until 1985）; and （3） the period of acute anthropogenic impact. In the third period the following was found in the deep-water part of the lake： the episodic appearance of ammonium and nitrite nitrogen; change in the components of suspended matter （SM）; disturbed patterns of seasonal changes in SM content, chlorophyll-a, organic forms of carbon, nitrogen and phosphorus; the average annual concentrations of suspended organic carbon, nitrogen and phosphorus have increased considerably; the vertical distribution pattern of minerals and organic forms of nitrogen and phosphorus have been disturbed; finally, an observed inverse correlation between winter nitrogen content and the spring concentration of chlorophyll-a （1986-1989） would indicate the presence of toxins in the lake. This led to the study of POPs in Baikal and the Baikal region. Investigations undertaken during 2004-2005 in the pelagic coastal zones of the lake indicated the presence of toxic pollutants in southern Baikal （the correlation between winter nitrogen content and spring concentration of chlorophyll-a is inverse and equals 0.99 and 1.00 respectively）. Toxicants that enter the lake during the iced-over period mainly enter the trophogenic layer, as wastewaters are warmer than the lake waters, depress the development of endemic spring diatomic algae and lead to a rise in the trophic status.     

Geochemistry of deep formation waters in the Canning Basin,Western Australia,and their relationship to Zn‐Pb mineralization

The Canning Basin contains several Mississippi Valley‐type Zn‐Pb sulphide prospects and deposits in Devonian carbonate reef complexes on the northern edge of the Fitzroy Trough, and in Ordovician and Silurian marine sequences on the northern margin of the Willara Sub‐basin. This study uses the ionic composition and 5D, δ¹⁸O, δ³⁴S, ⁸⁷Sr/⁸⁶Sr isotopic data on present‐day deep formation waters to determine their origin and possible relationship to the Zn‐Pb mineralizing palaeofluids.

The present‐day Canning Basin formation waters have salinity ranging from typically less than 5000 mg/L up to 250 000 mg/L locally. The brines are mixtures of highly saline water, formed by seawater which evaporated beyond halite saturation (bittern water), with meteoric water ranging in salinity from low (<5000 mg/L) to hypersaline water (up to about 50 000 mg/L) formed by re‐solution of halite and calcium sulphate minerals. The original marine chemical composition of the bittern‐dominated brines was changed to that of a Na‐Ca‐Cl water by addition of Ca and removal of Mg and SO₄, initially by bacterial sulphate reduction and later by dolomitization of carbonate. Other reactions with terrigenous components of the sediment have provided additional Ca and Sr, including a small proportion of ⁸⁷Sr‐rich material. The δ³⁴S values of the bittern‐containing waters are within the range over which marine sulphate has fluctuated from the Ordovician to the Holocene, although one of the hypersaline waters has a value of +6.8%, indicating SO₄ of non‐marine origin. The pH of the bittern‐containing waters is low (about 5) and they contain significant concentrations of dissolved Fe (up to 120 mg/L).

The Canning Basin bitterns appear similar in origin and chemical composition to highly saline marine brines in the Mississippi Salt Dome Basin, USA, which are known to be either metal or sulphide‐rich depending on the organic content of the host rock. In the Canning Basin, mixing of the bittern water with the various types of meteoric water has resulted in decreases in salinity, Na, Ca, Mg, K, Sr, Li and Fe, and increases in HCO₃, SO₄ and pH.

Mixing of the bitterns with other types of metalliferous fluids and/or with sulphate‐containing hypersaline meteoric waters formed from the same marine evaporite sequence should produce ore‐precipitating fluids which are relatively hot and saline, and the resulting ore deposit should be of high grade and contain abundant sulphate minerals. In the southern Canning Basin, this type of mixing and the corresponding style of ore deposit is evident in the evaporite‐associated areas of Zn‐Pb mineralization near the Admiral Bay Fault. If the bitterns mix with low salinity HCO₃‐waters in near‐surface environments, then the ore‐precipitating fluids should have relatively low salinities and carbonate minerals would precipitate during later stages of mixing. In the Lennard Shelf, the present‐day formation waters, the style of the Zn‐Pb deposits, and range of salinity and temperature of the ore‐forming palaeofluids are consistent with this type of mixing.     

Characterisation and isotopic evolution of saline waters of the Outokumpu Deep Drill Hole,Finland – Implications for water origin and deep terrestrial biosphere

The isotopic composition of water and dissolved Sr as well as other geochemical parameters at the 2516 m deep Outokumpu Deep Drill Hole, Finland were determined. The drill hole is hosted by Palaeoproterozoic turbiditic metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granitoids. Sodium–Ca–Cl and Ca–Na–Cl-rich waters (total dissolved solids up to ca. 70 g L⁻¹) containing significant amounts of gas, mainly CH₄ (up to 32 mmol L⁻¹), N₂ (up to 10 mmol L⁻¹), H₂ (up to 3.1 mmol L⁻¹) and He (up to 1.1 mmol L⁻¹) discharge from fracture zones into the drill hole. This water is distinct from the shallow fresh groundwater of the area, and has an isotopic composition typical of shield brines that have been modified during long-term water–rock interaction. Based on water stable isotopes and geochemistry, the drill hole water profile can be divided into five water types, each discharging from separate fracture systems and affected by the surrounding rocks. The δ²H varies from −90‰ to −56‰ (VSMOW) and δ¹⁸O from −13.5‰ to −10.4‰ (VSMOW), plotting clearly above the Global and Local Meteoric Water Lines on a δ²H vs. δ¹⁸O diagram. The ⁸⁷Sr/⁸⁶Sr ratios range between 0.72423 and 0.73668. Simple two-component mixing between ²H and ¹⁸O rich end-member brine and meteoric water cannot explain the water stable isotopic composition and trends observed. Instead, hydration of silicates by ancient groundwaters recharged under different climatic conditions, warmer than at present, is the most likely mechanism to have caused the variation of the δ²H and δ¹⁸O values. Water types correlate with changes in microbial communities implying that different ecosystems occur at different depths. The different water types and microbial populations have remained isolated from each other and from the surface for long periods of time, probably tens of millions of years.     

Stable sulfur and oxygen isotope ratios of the Świętokrzyski National Park spring waters generated by natural and anthropogenic factors (south-central Poland)

This paper presents the results of an isotopic study of spring waters in ?wi?tokrzyski (Holy Cross Mountain) National Park (?NP), south-central Poland. The δ³⁴S_V-CDT and δ¹⁸O_V-SMOW of soluble sulfates (n = 40) varied from 0.5‰ to 18.1‰ and from 3.5‰ to 12.2‰, respectively. The average δ³⁴S values are closely similar to those of rainwater, soils and rocks (comprising scattered pyrite). This suggests that soluble sulfates in the springs originated from mixing of recent and historic deposition, sulfates derived from pyrite oxidation, and CS-mineralization in soils and debris. An additional anthropogenic sulfur input (inorganic fertilizer) occurs in the water of spring S-61 located in the ?wi?tokrzyski National Park buffer zone. The δ¹⁸O_V-SMOW of spring waters (n = 4) were in the range of −10.6‰ to −10.2‰ indicating that they are derived from vadose groundwater in ?NP. This was the first isotope study of spring waters in the national parks of Poland. It enabled the determination of sulfur pathways and discrimination between natural and anthropogenic sources of this element in a relatively pristine area.     

Strontium isotope composition of the Arno River Valley waters （Tuscany, Italy） as a natural tracer of water-rock interaction and mixing processes

Sr isotope studies of surficial waters have highlighted that differences in the ^87Sr/^86Sr ratio and Sr concentration are primarily caused by mixing of waters of various origins with specific isotopic and chemical characteristics, resulting from water-rock interaction processes. In this paper we reported the first Sr isotopic ratios, coupled with water chemistry, the measurement was carried out on samples related to （1） the Amo River （Tuscany, central-northern Italy）, between the source and the mouth, （2） the most important tributaries and to （3） the thermal water discharges seeping out in the southern part of the basin. The main goals are： a） to use the ^87Sr/^86Sr ratio as a discriminative parameter of source areas, b） to define its variation along both the main course and principal tributaries, and c） to estimate the effects of the mixing process of the different end-embers. The outcropping rocks in the Amo River Basin are predominantly sedimentary, mainly made up of Mesozoic limestones, Oligocene sandstones and Plio-Pleistocene marine-lacustrine formations. Triassic and Mesosinian evaporites crop out in the Elsa and Era reaches, whereas Paleozoic quartzitic formations occur in the Mrs. Pisani area. Strontium isotopic composition is generally controlled by lithology and does not seem to be affected by anthropic input and flow rate. The ^87Sr/^86Sr ratios in the Arno Basin vary between 0.707963 and 0.712743, the highest ratios being related to waters circulating in the Palezoic rocks and Oligocene sandstone formations. Less radiogenic values pertain to the Elsa and Era tributaries where contributions related to the dissolution of evaporitic sequences, and mixing processes with the thermal discharges have been distinguished. The tributaries show that water samples in the pristine area have higher ^87Sr/^86Sr ratios than the respective tributaries from which water samples were collected near the confluence. Eventually, water samples collected along the Arno River, close to the mouth, tend to have Sr isotopic ratios similar to those of the present seawater.     

GPR and aerial imageries to identify the recent historical course of the Obra River and spatial extent of Obrzańskie Lake, altered by hydro-technical works

Ground penetrating radar (GPR) measurements have been conducted to retrace the natural course of the Obra River and changes of spatial extent of Obrzańskie Lake (western Poland). The Obra River valley was subjected to intensive anthropogenic transformation. Three artificial canals were constructed here in the beginning of the nineteenth century. The GPR surveys were done using a georadar MALA ProEx equipped with 250 MHz antenna. The measurement was verified by coring and analyses of historical maps, aerial photographs, and satellite images. The research has shown that there are at least three elongated depressions preserved in the modern land surface near the village of Solec, situated in the middle course of the valley. Several structures suggesting functioning of a multi-channel pattern in the past have been detected inside and in the vicinity of the depressions. Filling the channels with silts and peats might have been the effect of flow deceleration caused by the construction of the Obra Canals. Moreover, situation of two of the retraced depressions suggests that the landforms might be the remains of a river bed disappearing in wetlands. Further studies including groundwater flux measurements in the area between the depressions are needed to confirm such hypothesis. Furthermore, the study allowed retracing the spatial extent of Obrzańskie Lake. The sediment structures detected by the GPR measurements and calibrated with coring were interpreted to be the traces of the lake shoreline. The interpretation was supported by the findings inferred from aerial and satellite images. It was shown that Obrzańskie Lake had had at least three islands and had been directly connected with a network of braided channels before the anthropogenic intervention. The spatial extent of the lake was significantly altered by the construction of the North Obra Canal. Disconnecting the lake from the Canal resulted in more than 50 % decrease of the lake surface.     

Constraining the marine strontium budget with natural strontium isotope fractionations (Sr/Sr∗, δSr) of carbonates, hydrothermal solutions and river waters

We present strontium (Sr) isotope ratios that, unlike traditional ⁸⁷Sr/⁸⁶Sr data, are not normalized to a fixed ⁸⁸Sr/⁸⁶Sr ratio of 8.375209 (defined as δ^88/86Sr = 0 relative to NIST SRM 987). Instead, we correct for isotope fractionation during mass spectrometry with a ⁸⁷Sr-⁸⁴Sr double spike. This technique yields two independent ratios for ⁸⁷Sr/⁸⁶Sr and ⁸⁸Sr/⁸⁶Sr that are reported as (⁸⁷Sr/⁸⁶Sr∗) and (δ^88/86Sr), respectively. The difference between the traditional radiogenic (⁸⁷Sr/⁸⁶Sr normalized to ⁸⁸Sr/⁸⁶Sr = 8.375209) and the new ⁸⁷Sr/⁸⁶Sr∗ values reflect natural mass-dependent isotope fractionation. In order to constrain glacial/interglacial changes in the marine Sr budget we compare the isotope composition of modern seawater ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_Seawater) and modern marine biogenic carbonates ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_Carbonates) with the corresponding values of river waters ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_River) and hydrothermal solutions ((⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_HydEnd) in a triple isotope plot. The measured (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_River values of selected rivers that together account for ∼18% of the global Sr discharge yield a Sr flux-weighted mean of (0.7114(8), 0.315(8)‰). The average (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_HydEnd values for hydrothermal solutions from the Atlantic Ocean are (0.7045(5), 0.27(3)‰). In contrast, the (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_Carbonates values representing the marine Sr output are (0.70926(2), 0.21(2)‰). We estimate the modern Sr isotope composition of the sources at (0.7106(8), 0.310(8)‰). The difference between the estimated (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_input and (⁸⁷Sr/⁸⁶Sr∗, δ^88/86Sr)_output values reflects isotope disequilibrium with respect to Sr inputs and outputs. In contrast to the modern ocean, isotope equilibrium between inputs and outputs during the last glacial maximum (10-30 ka before present) can be explained by invoking three times higher Sr inputs from a uniquely “glacial” source: weathering of shelf carbonates exposed at low sea levels. Our data are also consistent with the “weathering peak” hypothesis that invokes enhanced Sr inputs resulting from weathering of post-glacial exposure of abundant fine-grained material.     

Carbon and hydrogen isotopic reversals in deep basin gas: Evidence for limits to the stability of hydrocarbons by Burruss and Laughrey (Organic Geochemistry 41, 1285–1296) – Discussion

This discussion reevaluates the data provided by Burruss and Laughrey (2010) (Carbon and hydrogen isotopic reversals in deep basin gas: Evidence for limits to the stability of hydrocarbons. Organic Geochemistry 41, 1285–1296). It indicates that gas diffusive migration plays an important role in regulating the isotopic reversals in samples from the Silurian and Ordovician formations in the Appalachian Basin. Carbon and hydrogen isotopic reversals in deep basin gas cannot be attributed to the stability of hydrocarbons in shale-gas and tight-sand-gas accumulations, if gas diffusive migration in the subsurface is not considered.     

Tectonic evolution of the deep crust: Variscan reactivation by extension and thrusting of Precambrian basement in the Bragança and Morais massifs (Tras-os-Montes,NE Portugal)

Abstract

The Braganca amd Morais Massifs (NE Portugal) comprise a pile of four nappes on lop of the Autochthon of the Central-Iberian Zone : a Parautochthon (PTC), a Lower Allochthon (LATC), an Ophiolitic Complex (OTC) and an Upper Allochton (UATC). This article focuses on the tectonic evolution of the prc-Variscan basement preserved in the Upper Allochthonous Thrust Complex. (1) In the Morais Massif, the UATC is mainly composed of orthogneisscs, micaschists and high-grade melamorphic rocks restricted to a small duplex between the orthogneisses and the ophiolitic complex. The orthogneisses are pervasively deformed by D6 (Variscan D1). characterized by NNW-SSE stretching lineation, C-S structures, and sense of shear to the SSE. The high-grade melamorphic rocks show at least three ductile deformation phases older than the gneisses deformation. The micaschists and the orthogneisses are cut by mafic sills and dykes transformed into amphibolites by the Variscan tec-tonometamorphic evolution. In a restricted domain where dykes arc less deformed, two deformation events can be recognized and arc considered to be pre-Variscan. The walls of the dykes show a N-S stretching and mineral lineation interpreted as resulting from D6 (Variscan D1). (2) In the Braganca Massif, the UATC comprises mafic to ultrainafic igneous and high-grade melamorphic rocks, and paragncisses with ky-eclogite lenses. Six ductile deformation phases are recognized. The D1 to D4 events may correspond to a complete pre-Variscan orogenic cycle, from subduction (D1) to collision (D2-DS) and thrusting of the high-grade metamorphic rocks to upper levels in the crust (D3-D4); D5 may result from the Lower Palaeozoic extensional event that marks the begining of the Variscan Wilson cycle; D6 is interpreted as the first Variscan orogenic event with southward movement. The UATC of the Cabo Ortegal anil Braganca Massifs comprise mainly upper mantle/lower erustal rocks. By contrast, the UATC of the Ordenes and Morais Massifs is mainly composed of middle to upper erustal rocks. Vic propose that this is the result of a regional ductile normal fault (extensional event) that was active prior to the Variscan orogeny, in Lower Palaeozoic times, and affected a Precambrian basement.     

A commentary on climate change, stone decay dynamics and the ‘greening’ of natural stone buildings: new perspectives on ‘deep wetting’

Environmental controls on stone decay processes are rapidly changing as a result of changing climate. UKCP09 projections for the 2020s (2010–2039) indicate that over much of the UK seasonality of precipitation will increase. Summer dryness and winter wetness are both set to increase, the latter linked to projected precipitation increases in autumn and spring months. If so, this could increase the time that stone structures remain wet and possibly the depth of moisture penetration, and it appears that building stone in Northern Ireland has already responded through an increased incidence of algal ‘greening’. This paper highlights the need for understanding the effects of climate change through a series of studies of largely sandstone structures. Current and projected climatic trends are therefore considered to have aesthetic, physical and chemical implications that are not currently built into our models of sandstone decay, especially with respect to the role played by deep-seated wetness on sandstone deterioration and decay progression and the feedbacks associated with, for example surface algal growth. In particular, it is proposed that algal biofilms will aid moisture retention and further facilitate moisture and dissolved salt penetration to depth. Thus, whilst the outer surface of stone may continue to experience frequent wetting and drying associated with individual precipitation events, the latter is less likely to be complete, and the interiors of building blocks may only experience wetting/drying in response to seasonal cycling. A possible consequence of deeper salt penetration could be a delay in the onset of surface deterioration, but more rapid and effective retreat once it commences as decay mechanisms ‘tap into a reservoir of deep salt’.     

Model of heat and mass transfer by fluid during formation of Mo-U deposits in the Strel’tsovka ore field,eastern Transbaikal region: Forced convection of solutions generated by a deep source

The Strel’tsovka and Antei uranium deposits located in the Strel’tsovka caldera are unique in ore resources. According to the considered mathematical model, the uranium source of these deposits was related to the middle-lower crustal silicic magma chambers or had mantle origin. Boundary conditions of the model are based on modern views of physicochemical conditions of hydrothermal process in the Strel’tsovka ore field and factors governing ore deposition therein. Modeling results are consistent with morphology of orebodies and ultimate uranium resources of the deposits and thus confirm indirectly that the physicochemical parameters of the ore-forming system are coherent. The maximal duration of uranium ore deposition is estimated at 500 ka.     

Tracking deep ancient crustal components by xenocrystic/inherited zircons of Palaeozoic felsic igneous rocks from the Altai–East Junggar terrane and adjacent regions,western Central Asian Orogenic Belt and its tectonic significance

The deep crustal continental components and architecture of the western Central Asian Orogenic Belt (CAOB) have long been a matter of debate. This article presents an integrated study of published geochronological and Hf-in-zircon isotopic data for inherited zircons from the Palaeozoic granitoid rocks and associated felsic volcanic rocks of the Chinese Altai, East Junggar, and nearby regions. The aim is to trace the age spatial distribution of deep old crustal components. Our data set comprises 463 published age data obtained by SHRIMP and LA-ICP-MS from felsic igneous rocks in these areas. Among these samples, zircon xenocrysts were observed in 69 granitic rocks and 15 felsic volcanic rocks from the Chinese Altai and 30 granitoid rocks and five felsic volcanic rocks in the East Junggar, respectively.

Three major zircon xenocrysts provinces are defined based on the distribution of these inherited zircon ages, combined with Hf-in-zircon isotopes. Province I, mainly situated in the eastern part of the central Chinese Altai, is characterized by the abundant inherited zircons with Meso-Proterozoic and Palaeo-Proterozoic ages (1000–1600 and 1600–2500 Ma, respectively), and variable ε_Hf(_t) values ranging from ?15 to +7 with ancient Hf crustal model ages (T_DMC) ranging from 1.5 to 2.9 Ga. A few scattered parts of province I are scattered situated in the East Junggar (individual areas, e.g. Taheir and Shuangchagou). Province II, situated mostly in the central Chinese Altai, is characterized by abundant xenocrystic zircons with Neo-Proterozoic ages (542–1000 Ma), ε_Hf(t) values ranging from ?6.8 to +8.1, and corresponding Hf crustal model ages of ~1.0–1.3 Ga. Province III contains abundant Phanerozoic (<541 Ma) xenocrystic zircons that show highly positive ε_Hf(t) values ranging from +5 to +16 and the youngest Hf crustal model ages (0.4–0.95 Ga). The main part of Province III occupies most areas of the East Junggar and the southernmost and northern parts of the Chinese Altai. Identification of the ancient (pre-Neoproterozoic) Hf crustal model ages in the eastern part of the central Chinese Altai (Province I) supports the suggestions that ancient concealed crustal components exist in the Chinese Altai. In contrast, Province III in the East Junggar predominantly displays young model ages, which indicates that it is mainly composed of juvenile components and likely a typical accretionary belt. Besides, a few small areas with ancient model ages are recognized in the East Junggar, providing evidence for the local existence of Precambrian crust or micro-blocks within the accretionary belt. The zircon xenocrysts provinces are consisted with the Nd isotopic province and provide further evidence for the ancient and juvenile compositions in deep. In addition, the tectonic division of the region is discussed based on the distribution of deep crustal components. The Erqis fault zone can be regarded as the boundary between the Chinese Altai and East Junggar regions and its western extension is constrained to be closer to the Altai–Qinghe Fault than previously considered. The central Chinese Altai can be subdivided into two distinct tectonic units.     

Rebuttal to “The case of the Biscayne Bay and aquifer near Miami,Florida: density-driven flow of seawater or gravitationally driven discharge of deep saline groundwater?” by Weyer (Environ Earth Sci 2018, 77:1–16)

A recent paper by Weyer (Environ Earth Sci 2018, 77:1–16) challenges the widely accepted interpretation of groundwater heads and salinities in the coastal Biscayne aquifer near Miami, Florida, USA. Weyer (2018) suggests that the body of saltwater that underlies fresh groundwater just inland of the coast is not a recirculating wedge of seawater, but results instead from upward migration of deep saline groundwater driven by regional flow. Perhaps more significantly, Weyer (2018) also asserts that established hydrologic theory is fundamentally incorrect with respect to buoyancy. Instead of acting along the direction of gravity (that is, vertically), Weyer (2018) claims, buoyancy acts instead along the direction of the pressure gradient. As a result, Weyer (2018) considers currently available density-dependent groundwater flow and transport modeling codes, and the analyses based on them, to be in error. In this rebuttal, we clarify the inaccuracies in the main points of Weyer’s (2018) paper. First, we explain that Weyer (2018) has misinterpreted observed equivalent freshwater heads in the Biscayne aquifer and that his alternative hypothesis concerning the source of the saltwater does not explain the observed salinities. Then, we review the established theory of buoyancy to identify the problem with Weyer’s (2018) alternative theory. Finally, we present theory and cite successful benchmark simulations to affirm the suitability of currently available codes for modeling density-dependent groundwater flow and transport.     

Comment on “Timing and nature of the Xinlin–Xiguitu Ocean: constraints from ophiolitic gabbros in the northern Great Xing’an Range,eastern Central Asian Orogenic Belt” by Feng et al. (2016)

International Journal of Earth Sciences - We disagree the transitional supra-subduction zone model of Feng et al. (Int J Earth Sci (Geol Rundsch) 105:491–505, 2016) for the tectonic setting...