Mesohaline Waters Research Articles

Planktonic habitats in the Amazon Plume region of the Western Tropical North Atlantic

The Western Tropical North Atlantic is a highly dynamic marine system where the Amazon River Plume (ARP) generates a patchwork of environmental conditions that favor different phytoplankton groups. To study phytoplanktonic community structure in such heterogeneous conditions, we used a set of five standard ship-based measurements taken from oceanographic surveys between 2010 and 2021 to characterize different habitat types. We then utilized a variety of multiparametric approaches to examine phytoplankton biodiversity in the different habitats to assess the biological relevance of our delineated habitats. Our approach generated a consistent set of habitat types across cruises carried out in multiple different years and the Amazon’s two predominant (wet and dry) seasons. Our phytoplankton community analyses revealed strong distinctions among all habitats along the plume gradient using in-vivo fluorescence and diagnostic pigments, and clear contrasts of diazotroph community along the mesohaline waters using direct cell-count, a pattern consistent with niche partitioning among similar species. The few apparent mismatches we found between phytoplankton community composition and habitat may reflect recent hydrographic changes driven by mixing and/or upwelling and thus may be a useful index to biologically-relevant temporal variation. Our habitat classification approach is straightforward and broadly applicable in identifying biologically distinct areas within heterogeneous and dynamic regions of the ocean.

Evaluating population trends of juvenile Atlantic Sturgeon at low abundance in a dynamic estuarine environment (Hudson River, New York)

AbstractEvaluating population trends in dynamic estuarine environments can be challenging, especially when survey data include a high percentage of zero observations. In fishery‐independent surveys, zeros that come from reduced susceptibility to sample gears and reduced availability of the population to the survey impact survey catchability and negatively bias relative abundance indices. A zero‐inflated negative binomial model was used to standardize a juvenile Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) relative abundance index (Hudson River, New York) that included a high proportion (42%) of zero observations and intra‐ and interannually variable covariates. Reduced susceptibility was related to low water temperature, with the percentage of zeroes increasing rapidly below 7°C. Availability was influenced by temperature and distance to salt front, as catch rates increased with temperature and peaked in mesohaline waters ~27 km downstream of the predicted salt front. An alternative index suggested significant population growth (r = 0.15; p‐value = 0.007) occurred from 2004 to 2015. The zero‐inflated model helped better understand Hudson River juvenile Atlantic Sturgeon ecology and relative trends in abundance, to better inform future management and monitoring decisions along the Atlantic Coast.

Influence of environmental factors on the formation of zooplankton communities in a large lake system in Uzbekistan

Currently, the Aidar-Arnasai Lake System (AALS) is of great environmental and commercial importance for Uzbekistan. The article discusses the influence of mineralisation, temperature and diversity of biotopes on the change in the species composition in the lakes. The largest number of species is recorded in oligohaline water in the lakes’ littoral zones. They are dominated by the Rotifera and Cladocera and show a greater number of species in the spring. Areas with mesohaline water are dominated by Copepoda, showing the largest number of species in the winter in both littoral and pelagic zones. Biomass of zooplankton poorly correlates with salinity. Depth impacts reliably the distribution of zooplankton biomass, while the spatial accumulation of zooplankton biomass depends on temperature.

Distinct stages of the intestinal bacterial community of Ampullaceana balthica after salinization.

Environmental disturbances influence bacterial community structure and functioning. To investigate the effect of environmental disturbance caused by changes in salinity on host-protected bacterial communities, we analyzed the microbiome within the gastrointestinal tract of Ampullaceana balthica in different salinities. A. balthica is a benthic gastropod found in fresh- and mesohaline waters. Whereas the total energy reserves of A. balthica were unaffected by an increase of salinity to 3, a high mortality rate was detected after a shift from freshwater to salinity 6 suggesting a major disruption of energy homeostasis. The shift to salinity 6 also caused a change in the gastrointestinal bacterial community composition. At salinity 3, the bacterial community composition of different host individuals was related either to the freshwater or salinity 6 gastrointestinal bacterial community, indicating an ambivalent nature of salinity 3. Since salinity 3 represents the range where aquatic gastropods are able to regulate their osmolarity, this may be an important tipping point during salinization. The change in the intestinal microbiome was uncoupled from the change in the water bacterial community and unrelated to the food source microbiome. Our study shows that environmental disturbance caused by salinity acts also on the host-protected microbiome. In light of the sea-level rise, our findings indicate that salinization of the near-shore freshwater bodies will cause changes in organisms’ intestinal microbiomes if a critical salinity threshold (presumably ∼3) is exceeded.

Intertidal foraminifera from the Mar Chiquita Coastal Lagoon, Buenos Aires Province, Argentina

The present study aims to analyze the composition and distribution of the intertidal foraminiferal assemblages of the Mar Chiquita Coastal Lagoon (southeast coast of Buenos Aires Province). For this purpose, the abundance and diversity of the living and dead fauna were determined; the taphonomic features of the tests were analyzed; and physico-chemical measurements were taken at 10 sites of the lagoon. The assemblages were constituted mainly by autochthonous fauna. The sediment grain size and salinity are the main variables that determine the distribution of species and discerned three assemblages, associated with three sub-environments. The first sub-environment of coarse sediment and mesohaline waters corresponds to non-vegetated plains in the mouth of the lagoon. It contains Buccella peruviana, Elphidium discoidale, and Quinqueloculina patagonica. The second sub-environment of fine sediment and mesohaline waters corresponds to non-vegetated plains in the inlet of the lagoon. It includes Elphidium gunteri, B. peruviana, Ammonia parkinsoniana, Ammonia tepida, Miliolinella subrotunda, Rosalina williamsoni, Pyrgo ringens, Discorbis peruvianus, and Q. patagonica. The third sub-environment of coarse sediment - waters ranging from polyhaline to mixoeuhaline and fine sediment - oligohaline waters corresponds to vegetated and non-vegetated plains and floodplains far from the mouth of the lagoon. It contains Ammonia spp, and E. gunteri.

Life history of spinyhead croaker Collichthys lucidus (Sciaenidae) differentiated among populations from Chinese coastal waters

Otolith microchemistry provides valuable information about the environmental history of individual fish, but few studies have considered the influence of population or stock on life history traits. This study used the Sr/Ca ratio as an index of habitat use of spinyhead croakerCollichthys lucidusfrom 2 different populations (northern and southern China populations), including lifetime otolith microchemistry profiles (n = 63 fish) and determinations of natal habitat selection (n = 352 fish). The otolith data revealed 3 life history patterns inC. lucidus: Pattern 1 individuals spent most of their lifetime (>95%) in mesohaline waters (Sr/Ca range: 3-7 mmol mol-1), particularly during early growth; Pattern 2 individuals migrated from hyperhaline waters (Sr/Ca ≥ 7 mmol mol-1) to mesohaline waters; and Pattern 3 individuals migrated from oligohaline waters (Sr/Ca < 3 mmol mol-1) to mesohaline waters. Pattern 2 and Pattern 3 were specific to the northern and southern China populations, respectively, and Pattern 1 was shared by the 2 populations. The otolith core Sr/Ca ratios showed that mostC. lucidusselected mesohaline waters as their natal habitat (i.e. 90.6% of 352 total individuals); 12.5% (19 of 152) selected hyperhaline waters and fell within the northern China population, and 7% (14 of 200) selected oligohaline waters and fell within the southern China population. These results indicate that life history diversity exists in this species, as the pattern of habitat use largely differed between the northern and southern China populations. The overall findings highlight that the behavior of different populations should be considered when determining fish migration histories.

Разнообразие сообществ водной растительности озер Обь-Иртышского междуречья (Западная Сибирь)

The information on the syntaxonomic diversity of aquatic vegetation in the Ob-Irtysh interfluve (south of West Siberia), which was revealed using the ecological-floristic approach (Braun-Blanquet, 1964) is summarized. Lake ecosystems of the studied region are exposed to cyclical changes in accordance with the cyclicity of the hydrological regime of the lakes. Periodic fluctuations in the water level in lakes are accompanied by changes in mineralization, and therefore the biological regime of the lakes is unstable. The studies were carried out from 2001 to 2014 in Novosibirsk Region and Altai Territory. 164 complete geobotanical relevés made by the author on 80 lakes are used (Fig. 1, table 1); a list of studied lakes is given. Field work was carried out during the period of the lowest water level (summer dry season) — July–August. The following scale was used for abundance estimation: r — the species is extremely rare; + — rare, small cover; 1 — the number of individuals is large, the cover is small or individuals are sparse, but the cover is large; 2 —cover of 5–25 %; 3 — 26–50 %; 4 — 51–75 %; 5 — more than 75 %. Computer programs Turboveg for Windows 2.117 (Hennekens, Schaminée, 2001) and Juice 7.0.45 (Tichý, 2002) were used for data treatment. The syntaxonomic affiliation of phytocenoses was determined using modern literature (Bobrov, Chemeris, 2006; Vegetace…, 2011; Chepinoga, 2015; Landucci et al. 2015; Mucina, 2016). The coenotic diversity of aquatic vegetation in the studied lakes is 43 associations and 2 communities from 12 alliances, 6 orders, 5 classes (Tables 2–11). Eight associations belong to the class Lemnetea; 18 associations — Potamogetonetea; 3 associations and 2 communities — Stigeoclonietea tenuis; 9 associations — Charetea intermediae; 5 associations — Ruppietea maritimae. This rather high value of phytocenotic diversity is due to the high diversity of ecological conditions of specific lakes, in turn, determined by the different origin of lakes, the nature and composition of soils, salinity and chemical composition of waters, and temperature regime. Two new associations – Najadetum majoris ass. nov. and Ranunculetum subrigidi ass. nov. — are described. Table 10 shows the values of the frequency of associations (aquatic communities) in the lakes of the Novosibirsk region. We have identified phytocenotic complexes on the basis of data on the ranges of halotolerance of associations and in accordance with the frequency of associations in the lakes of different mineralization. Four phytocenotic complexes can be distinguished for the studied lakes of the Baraba Lowland and Kulunda Plain: freshwater, oligo-mesohaline, meso-hyperhaline, and euryhaline (Fig. 12). As for the ranges of halotoleration of lake communities, it is obvious that it is impossible to establish the universal ranges of halotolerance of species and communities of macrophytes for a number of reasons 1) regional differences in the salt composition of waters, 2) seasonal fluctuations in water salinity; 3) varying methods of mineralization measuring (ionometrically or analytically and also different analytical methods — by the sum of ions, and by the dry residual). However, several general trends can be distinguished. The main trend is a decrease in the species and coenotic diversity of aquatic and semi-aquatic vegetation with mineralization growth (Hammer, 1988; Williams, 1998; our data, etc.) This universal pattern is true for all groups of biota (Hammer, 1986; Williams, 1998; Kipriyanova et al., 2007, etc.). Communities of the assosiations Lemnetum trisulcae, Lemno–Utricularietum vulgaris, Potamogetono–Ceratophylletumsubmersi, Najadetum marinae, Potamogetonetum perfoliati were more resistant to high mineralization (up to 5 g/dm3 according to our data). The highest halotolerance among aquatic plant communities is found for the associations Ruppietum maritimae and Ruppietum drepanensis, as well as for Cladophoretum fractae. Based on the results of our research, it has been shown that in the continental lakes of the southeast of Western Siberia, such specific cenoses of continental water bodies of Siberia, as the communities of the assosiations Stuckenietum macrocarpae and Cladophoro fractae–Stuckenietum chakassiensis (Kipriyanova, 2017), mainly occur in oligo- and mesohaline waters in the range of mineralization 0.5–18.0 g/dm3. Stratiotetum aloidis, Nymphaeo–Nupharetum luteae, Nymphaeetum candidae associations were common in the freshwater lakes (up to 0.5 g/dm3), another ones were met moderately and less frequently. Associations Lemnetum trisulcae, Lemno minoris Ceratophylletum demersi were common in the β-oligohaline (0.5–1 g/dm3) lakes. Lemno–Utricularietum vulgaris, Myriophylletum sibirici, Potamogetonetum pectinati, Potamogetonetum perfoliati, Stuckenietum macrocarpae were moderately frequent, the rest were rare and solitary. Associations Lemnetum trisulcae, Lemno minoris–Ceratophylletum submersi, Stuckenietum macrocarpae, and Cladophoro fractae–Stuckenietum chakassiensis were common in the α-oligohaline lakes (1–5 g/dm3). The rest were moderately and less frequent. In mesohaline waters (5–18 g/dm3), associations Cladophoro fractae–Stuckenietum chakassiensis and Ruppietum maritimae were common. The rare in the studied lakes communities of the associations Najadetum marinae, Ruppietum maritimae, Ruppietum drepanensis, Charetum tomentosae, Nitellopsidetum obtusae are need in protection, since they include the species listed in the Red Data Book of the Novosibirsk Region (Krasnaya ..., 2018).

Tracking oxy-thermal habitat compression encountered by Chesapeake Bay striped bass through acoustic telemetry

Abstract In many coastal ecosystems, habitat compression is caused by seasonal combinations of hypoxia and supraoptimal temperatures. These conditions commonly induce avoidance behaviours in mobile species, resulting in the concentrated use of marginal habitats. Using 3 years of acoustic telemetry and high-resolution water quality data recorded throughout Chesapeake Bay, we measured the seasonal movements and exposure of striped bass (Morone saxatilis) to oxy-thermal habitat compression. Striped bass moved to tidal freshwaters in spring (March–May), mesohaline waters in summer (June–August) and fall (September–November), and mesohaline and polyhaline waters in winter (December–February): seasonal patterns consistent with known spawning, foraging, and overwintering migrations. Analyses of habitat selection suggest that during conditions of prevalent sub-pycnocline hypoxia (June–September), striped bass appeared to select surface waters (i.e. they may avoid bottom hypoxic waters). Striped bass detections indicated tolerance of a wide range of surface water temperatures, including those >25°C, which regional regulatory bodies stipulate are stressful for this species. Still, during summer and fall striped bass selected the lowest-available temperature and avoided water temperature >27°C, demonstrating that Chesapeake Bay striped bass can encounter habitat compressions due to the behavioural avoidance of bottom hypoxia and high temperatures.

Total buffering capacity of CaCO3-undersaturated and saturated waters buffered with agricultural limestone or hydrated lime and its importance to the liming of shrimp culture ponds

The pond's alkaline reserve (AR; particulate CaCO3) plus its total alkalinity (TA; dissolved HCO3−, CO3−2) would be equal to the pond's total buffering capacity (TBC). The present work aimed at determining the TBC of CaCO3-undersaturated and saturated waters buffered with CaCO3 and Ca(OH)2, and to discuss the TBC importance to the liming of shrimp culture ponds. Suitable volumes of seawater and distilled water were mixed up to prepare a batch of mesohaline water (CaCO3-saturated water; salinity = 11.2 g/L; LSI, Langelier Saturation Index ≈ 0). Besides, a batch of distilled water was used as a freshwater control (CaCO3-undersaturated water; LSI = −2.2). One single application of 1.00 g analytical-grade CaCO3 and Ca(OH)2 were carried out in 10-L gallons of each water type. For each water type and liming product, there were three applications of 1.0 mL HCl solution made at two-week intervals. The waters' pH, specific conductance, TA, total hardness, calcium hardness and Ca+2 were periodically monitored over a 55-day period. Three days after the 1st acidification, the pH of water increased for both liming products, mainly in the CaCO3-undersaturated water gallons. The grand TBC were as follows: −69.6% and − 80.1% for the CaCO3-undersaturated waters provided with CaCO3 and Ca(OH)2, respectively; −80.3% and − 78.7% for the CaCO3-saturated waters with CaCO3 and Ca(OH)2, respectively. It has been concluded that the application of agricultural limestone or hydrated lime in CaCO3-saturated waters, although pointless in the short term, might prove useful over time as an alkaline reserve of the shrimp's pond to be mobilized in cases of acidic inputs such as the occurrence of strong and persistent rains.

Evidence for stage-based larval vulnerability and resilience to acidification in Crassostrea virginica

ABSTRACT Using image analysis of scanning electron micrographs (SEMs), we compared differences in growth of D-stage veligers [i.e. prodissoconch I and II (PI and PII) larvae] of eastern oysters Crassostrea virginica grown in mesohaline water under high- and low-CO2 conditions. We found SEMs to reveal no evidence of dissolution or shell structure deformity for larval shells in either of the CO2 treatments but detected prominent growth lines in the PII regions of larval shells. The number of growth lines closely approximated the duration of the experiment, suggesting that growth lines are generated daily. Mean growth line interval widths were 20% greater for larval shells cultured in low- vs high-CO2 conditions. Crassostrea virginica veliger larvae were shown to tolerate high CO2 levels and aragonite saturation states (Ωarag) < 1.0, but larval growth was slowed substantially under these conditions. Differences in growth line interval width translate into substantial changes in shell area and account for previously observed differences in total shell area between the treatments, as determined by light microscopy and image analysis. Other studies have documented high mortality and malformation of D-stage larvae in bivalves when pre-veliger life stages (i.e. eggs, gastrula and trochophores) were exposed to elevated CO2. Our experiments revealed statistical differences in rates of larval survival, settlement and subsequent early-stage spat mortality for veligers reared in high- and low-CO2 conditions. Although each of these rates was measurably affected by high CO2, the magnitude of these differences was small (range across categories = 0.7–6.3%) suggesting that the impacts may not be catastrophic, as implied by several previous studies. We believe the apparent disparity among experimental results may be best explained by differential vulnerability of pre-veliger stage larvae and veligers, whereby PI and PII larvae have greater physiological capacity to withstand environmental conditions that may be thermodynamically unfavourable to calcification (i.e. Ωarag < 1.0).

Physicochemical characteristics of the Dombrovska pit lake (Ukraine) formed in an opencast potassium salt mine and the genome response of Chironomus salinarius Kieffer (Chironomidae, Diptera) to these conditions

This study focuses on the Dombrovska pit lake, near the city of Kalush in Ukraine, which is a former potassium salt mine filled with brine and freshwater. The water level is still increasing and as a result the salinity is decreasing. We analyzed the benthic fauna communities and the genome instability by assessing the rearrangements in the polytene chromosomes of Chironomus salinarius and the physicochemical parameters of the near-bottom water (pH, conductivity, mineralization, major ions, NO3−, NH4+, metals Cd, Pb, Cu, Mn, and Fe) and sediment (pH, organic matter and metals Cd, Pb, Cu, Zn, Mn, and Fe) at four sites. The water mineralization ranged from 17.3 to 26.2 g dm−3 which are classified as mesohaline and polyhaline waters, respectively. The biodiversity of the benthic fauna was low, and the dominant species was C. salinarius. The density of C. salinarius varied spatially and changed from 637 ind./m2 at a depth of 5 m to 8167 ind./m2 at a depth of 2.5 m. The genome instability was analyzed by examining the structural and functional changes in the salivary gland chromosomes of C. salinarius. The exposure of C. salinarius damaged the chromosomes and the activities of key structures, such as the Balbiani ring and nucleolar organizer, were partially or completely suppressed.

Impact of Salinity on the Gastrointestinal Bacterial Community of Theodoxus fluviatilis.

Differences in salinity are boundaries that act as barriers for the dispersal of most aquatic organisms. This creates distinctive biota in freshwater and brackish water (mesohaline) environments. To test how saline boundaries influence the diversity and composition of host-associated microbiota, we analyzed the microbiome within the digestive tract of Theodoxus fluviatilis, an organism able to cross the freshwater and mesohaline boundary. Alpha-diversity measures of the microbiome in freshwater and brackish water were not significantly different. However, the composition of the bacterial community within freshwater T. fluviatilis differed significantly compared with mesohaline T. fluviatilis and typical bacteria could be determined for the freshwater and the mesohaline digestive tract microbiome. An artificial increase in salinity surrounding these freshwater snails resulted in a strong change in the bacterial community and typical marine bacteria became more pronounced in the digestive tract microbiome of freshwater T. fluviatilis. However, the composition of the digestive tract microbiome in freshwater snails did not converge to that found within mesohaline snails. Within mesohaline snails, no cardinal change was found after either an increase or decrease in salinity. In all samples, Pseudomonas, Pirellula, Flavobacterium, Limnohabitans, and Acinetobacter were among the most abundant bacteria. These bacterial genera were largely unaffected by changes in environmental conditions. As permanent residents in T. fluviatilis, they may support the digestion of the algal food in the digestive tract. Our results show that freshwater and mesohaline water host-associated microbiomes respond differently to changes in salinity. Therefore, the salinization of coastal freshwater environments due to a rise in sea level can influence the gut microbiome and its functions with currently unknown consequences for, e.g., nutritional physiology of the host.

Automatic detection of the Cyprideis torosa (Jones, 1856) sieve pores from backscattered Electron Scanning Electron Microscopy images and development of morphometric tools for their shape identification

Abstract Round-shaped sieve pores of Cyprideis torosa have negative correlation with salinity and are a useful proxy for reconstructing paleo-salinity trends, especially for oligohaline to mesohaline waters. However, given its time-consuming character, this method has only been used rarely. A protocol for the automatic detection of sieve pores from Backscattered Electron Scanning Electron Microscopy (SEM-BSE) images and ImageJ-FIJI software has been developed. The use of SEM-BSE images has optimized the sieve pore contrasts and extend the observation possibilities of sieve pores on less well-preserved valves. Automatic detection significantly reduces analysis times, by avoiding individual pore measurements and applying batch processes on samples. Rosenfeld and Vesper (1977) proposed an elongation index (length/beam) to discriminate round and elongated shapes, but the identification of irregular shapes only depends on the operator's appreciation. Due to the rapid acquisition of morphometric data with the automatic detection method, it is possible to systematize the use of metrical tools to discriminate sieve pore shapes. Two methods were developed from a repository based on metric variables obtained by manually digitalized 1490 sieve pores: (i) a Functional Discriminant analysis based on 5 variables (Feret's aspect ratio, roundness, aspect ratio and two ratios: Apore/AMinimum Bounding Circle and Ppore/PMinimum Bounding Circle) and (ii) an irregularity index (Roundness/(Apore/AMinimum Bounding Circle), as a complement to the elongation index. In addition, a bootstrap on 1774 sieve pores indicates that is useful to analyze over 10 valves per sample in order to estimate the proportions of these sieve pore shapes with an acceptable level of precision.

Dissolution rates of hydrated lime, Ca(OH) 2 in fresh, oligohaline, mesohaline and euhaline waters and its significance for liming of shrimp culture ponds

This study aimed at assessing the dissolution rates of hydrated lime, Ca(OH)2 in fresh, oligohaline, mesohaline and euhaline waters and discussing its significance for liming of shrimp culture ponds. Appropriate volumes of seawater and distilled water were mixed to prepare oligohaline (1–4 g/L) and mesohaline waters (4–15 g/L). One gram of analytical grade calcium carbonate, CaCO3, or one gram of analytical grade calcium hydroxide, Ca(OH)2, were applied in 10-L gallons filled with seawater (39.9 g/L), 10.7 g/L, 4.2 g/L and distilled water (0.0 g/L). The final TA of water was significantly higher for Ca(OH)2 than for CaCO3 only at salinities 4.2 and 10.7 g/L. It was concluded that hydrated lime, Ca(OH)2 is a better liming option than agricultural limestone, CaCO3 for moderately saline, hard and/or buffered waters (−4.5 ≤ Langelier saturation index, LSI ≤ −0.7). In poorly saline, hard and/or buffered waters (LSI < −4.5), limestone and lime would increase water TA similarly. Neither limestone nor lime should be applied on highly saline, hard and/or buffered waters (LSI > −0.7) because a TA decrease is expected.

The Holocene salinity history of Lake Lop Nur (Tarim Basin, NW China) inferred from ostracods, foraminifera, ooids and stable isotope data

Abstract Terminal lakes without outlet respond directly to climate change and human impact, and provide important evidence for environmental conditions prior to times of instrumental monitoring. Lop Nur in northwestern China is a terminal lake which was still one of the world's largest lakes in historical times. Sediments from the excavated section YKD0301 in its presently dry basin were investigated to reconstruct the Holocene salinity history of the lake. Ostracod shells of Cyprideis torosa and Eucypris mareotica, tests of the foraminifer Ammonia tepida, and fruits of Ruppia maritima are abundant in the early Holocene part of the section. Two stratigraphic units in the middle Holocene part of the section contain ostracod shells typical of fresh to mesohaline waters such as Limnocythere inopinata, Cypridopsis vidua, Ilyocypris sp. and Darwinula stevensoni. Three units do not contain fossils or only few remains regarded as allochthonous. Ooids are abundant in the upper half of the section, and are here reported for the sediments of Lop Nur or sub-recent sediments from China for the first time. Ooids from YKD0301 are aragonitic and either subspherical around a detrital nucleus, or elongate and probably formed around fecal pellets of brine shrimps. The recorded fossils from Lop Nur indicate that lake waters were poly- to hyperhaline (20–100‰) at ca. 9.0 ka, oligo- to mesohaline (0.5–18‰) between ca. 8.7–7.5 ka and probably mesohaline (5–18‰) from 6.0–5.0 ka. In the intervening periods and after 5.0 ka, Lop Nur was a hyperhaline (>100‰) lake. The period of freshest conditions of Lop Nur (ca. 8.7–7.5 ka) coincides with wettest Holocene conditions reconstructed from other lake records in the region although a uniform temporal pattern of wettest Holocene climate conditions in NW China and adjacent regions cannot be inferred.

Spatial Variability and Co-acclimation of Phytoplankton and Bacterioplankton Communities in the Pearl River Estuary, China.

Phytoplankton and bacterioplankton play significant roles in estuarine systems. It is important to demonstrate the spatial variability of bacterial and microalgal communities and understand the co-acclimation of these organisms to different environmental factors. In this study, MiSeq sequencing and morphological identification were applied to analyze the variations in bacterial and microalgal communities in the Pearl River Estuary, respectively. Molecular ecological network analysis was used to investigate the potential interactions between microalgae and bacteria and illustrate the responses of these interactions to environmental gradients. The results revealed that microalgal/bacterial communities in freshwater samples were distinct from those in mesohaline water samples. Microalgae affiliated to the genus Skeletonema dominated the mesohaline water phytoplankton communities, while Melosira was the more abundant genus in freshwater communities. Actinobacteria, Alphaproteobacteria, Betaproteobacteria, and Acidimicrobiia dominated bacterial communities in freshwater samples, while Gammaproteobacteria, Bacilli, and Synechococcophycideae were more abundant in mesohaline water samples. Tightly correlations were observed between phytoplankton and bacterioplankton. These interactions were regarded to be key factors in shaping the community structures. Further, the KEGG database and PICRUSt were used to predict the functions of bacterioplankton in the process of nitrogen cycling. The results indicated that denitrification could play an important role in nitrogen loss and might alleviate the eutrophication in the Pearl River Estuary. Collectively, the results in this study revealed that substantial changes in phytoplankton and bacterioplankton communities were correlated with the gradients of environmental parameters in the Pearl River Estuary. The results also demonstrated that the interactions between phytoplankton and bacterioplankton were important for these organisms to acclimate to changing environments.

Short-term low salinity mitigates effects of oil and dispersant on juvenile eastern oysters: A laboratory experiment with implications for oil spill response activities.

Following the Deepwater Horizon oil spill, eastern oyster (Crassostrea virginica) reefs in the northern Gulf of Mexico were exposed to oil and various associated clean-up activities that may have compromised oyster reef health. Included in the exposure was oil, dispersant, and in some locales, atypical salinity regimes. Oil and dispersants can be detrimental to oysters and the effects of salinity depend on the level. In addition to these extrinsic factors, genetic diversity of oyster populations may help the oysters respond to stressors, as demonstrated in other systems. We used a 3×3×2 factorial design to experimentally examine the effects of oil/dispersed oil, intraspecific genetic diversity, and salinity on juvenile (ca. 25 mm shell height) oyster survivorship and growth during a 21-d exposure in a closed, recirculating system. The genetic effect was weak overall, oil and dispersed oil negatively affected juvenile oyster survivorship, and low salinity mitigated mortality in oil and dispersed oil treatments. Survivorship was about 40% greater in low-salinity than in mesohaline water for both oil and dispersed oil treatments, bringing survivorship in low salinity oil-only treatments to a similar level with low salinity controls (no oil). Oyster growth was minimal after 21 d but appeared to be negatively affected by oil and dispersed oil, and had a significant interaction with salinity. Our results may be informative for future decisions regarding oil spill response activities and suggest that a pulse of low salinity water may be a viable short-term mitigation option for oysters if filtration characteristics, exposure time, and water temperatures are all considered, in addition to weighing the costs and benefits of this type of response on other organisms and habitats.

Regional environmental change versus local signal preservation in Holocene thermokarst lake sediments: A case study from Herschel Island, Yukon (Canada)

Thermokarst lakes cover nearly one fourth of ice-rich permafrost lowlands in the Arctic. Sediments from an athalassic subsaline thermokarst lake on Herschel Island (69°36′N; 139°04′W, Canadian Arctic) were used to understand regional changes in climate and in sediment transport, hydrology, nutrient availability and permafrost disturbance. The sediment record spans the last ~ 11,700 years and the basal date is in good agreement with the Holocene onset of thermokarst initiation in the region. Electrical conductivity in pore water continuously decreases, thus indicating desalinization and continuous increase of lake size and water level. The inc/coh ratio of XRF scans provides a high-resolution organic-carbon proxy which correlates with TOC measurements. XRF-derived Mn/Fe ratios indicate aerobic versus anaerobic conditions which moderate the preservation potential of organic matter in lake sediments. The coexistence of marine, brackish and freshwater ostracods and foraminifera is explained by (1) oligohaline to mesohaline water chemistry of the past lake and (2) redeposition of Pleistocene specimens found within upthrusted marine sediments around the lake. Episodes of catchment disturbance are identified when calcareous fossils and allochthonous material were transported into the lake by thermokarst processes such as active-layer detachments, slumping and erosion of ice-rich shores. The pollen record does not show major variations and the pollen-based climate record does not match well with other summer air temperature reconstructions from this region. Local vegetation patterns in small catchments are strongly linked to morphology and sub-surface permafrost conditions rather than to climate. Multidisciplinary studies can identify the onset and life cycle of thermokarst lakes as they play a crucial role in Arctic freshwater ecosystems and in the global carbon cycle of the past, present and future.

Early dolomitization in the Lower Cretaceous shallow-water carbonates of Southern Apennines (Italy): Clues about palaeoclimatic fluctuations in western Tethys

A multidisciplinary study of the dolomitized bodies present in the Lower Cretaceous platform carbonates of Mt. Faito (Southern Apennines – Italy) was carried out in order to explore the connection between early dolomite formation and fluctuating climate conditions.The Berriasian-Aptian investigated succession is 466m thick and mainly consists of shallow-water lagoonal limestones with frequent dolomite caps. The dolomitization intensity varies along the succession and reaches its peak in the upper Hauterivian-lower Barremian interval, where it is present a completely dolomitized interval about 100-m-thick. Field relations, petrography, mineralogy, and geochemistry of the analyzed dolomite bodies allowed identifying two populations of early dolomites, a fine-medium crystalline (FMdol) and a coarse crystalline dolomite (Cdol), both interpreted as the product of mesohaline water reflux. According to our interpretation, FMdol precipitated from concentrated brines in the very early stage of the reflux process, producing typical sedimentary features as dolomite caps. In the successive step of the process, the basin-ward ‘latent’ reflux precipitated Cdol from less concentrated brines.A peculiar feature of the studied succession is the great consistency between stratigraphic distribution of dolomite bodies and their geochemical signature. The completely dolomitized Hauterivian-Barremian interval, in fact, is characterized by geochemical values suggesting an origin from distinctly saltier brines. Considering that the observed near-surface dolomitization process is controlled by physical and chemical parameters reflecting the paleoenvironmental and paleoclimatic conditions during dolomite formation, we propose that the stratigraphically controlled dolomitization intensity reflects periodic fluctuations in the salinity of dolomitizing fluid, in turn controlled by long-term climate oscillations.The present work highlights that the stratigraphic distribution of early diagenetic dolomite may be used as proxy to define the climatic fluctuations that have influenced the sedimentary dynamics in the Early Cretaceous. Moreover, considering that a comparable early dolomite distribution is present also in the Dinaric Platform, we suggest that a regional scale climate control acted on early dolomite formation and distribution. Refining the knowledge of such a key control may have a significative impact on hydrocarbon reservoir characterization and exploration in the Periadriatic area.

Paleosalinity and water body type of Eocene Pinghu Formation, Xihu Depression, East China Sea Basin

Xihu Depression is a relatively new petroleum exploration area in East China Sea Basin. Pinghu Formation is one of the most important oil-bearing formations in the depression. Due to the low exploration level of the depression, paleosalinity and deposition environment of the depression in Pinghu stage is not clear. Element geochemical analysis of samples from different structural units is used to study ancient water salinity and reveal the depositional environment. B/Ga ratio, which is sensitive to paleosalinity in study area, is 0.9–4.0 and indicates characteristics of mixed water of fresh and salt water. There is a threshold for Sr/Ba in water salinity study in the study area. When Sr/Ba ratio is lower than 0.15, it cannot be used as an indicator for salinity and ancient water body type. Equivalent boron content calculated by Walker's method is lower than 150 ppm. Paleo salinity from boron content calculated by Couch's method is 2.97‰–9.61‰ and the average is 4.8‰. Based on the above mentioned results, ancient water body of Xihu Depression in Pinghu stage has typical characteristics of brackish water and it belongs to oligohaline and mesohaline water. Combining paleogeomorphology and sedimentary facies distribution in the study area, paleowater body in Xihu Depression during Pinghu stage is transitional mixed water influenced by terrigenous diluted water. Paleosalinity contour lines extend on plane from north to the south and are parallel to paleo-coastline. Paleosalinity increases from the west to the east. Influenced by freshwater of deltas at western part of the depression, high abnormal salinity values occur around the wells M1 and L1 where salinity contour lines curve westward.