Hydrodynamics and suspended particulate matter retention in macrotidal estuaries located in Amazonia-semiarid interface (Northeastern-Brazil)

The aim of the current study was to determine the nature of the seasonal variability of the Suspended Particulate Matter (SPM) fluxes from the drainage basin to the estuary in a macrotidal region (Northeastern Brazil), and the estuarine response to a seawater intrusion regarding sediment deposition, which will support the understanding of the global transport of materials at the continent-ocean interface. Thermohaline structure data was acquired using a Conductivity, Temperature, and Depth (CTD) probe with a sampling frequency of 4 Hz. Suspended particulate material was measured by gravimetric measurements applied to exact filtered volume samples. The outflows were measured through the use of an Acoustic Doppler Current Profiler (ADCP) with frequency of 1.5 MHz. The horizontal thermal and saline gradients varied from warmer and less saline waters (2014) to cooler and saline waters (2015). The gradient behavior when linked to volume transport and SPM flows, suggests a minimization of the fluvial flows in 2015, easing the advance of coastal water (CW) towards the inner estuary, leading to an inversion of the baroclinic pressure gradient. The bottom saline front, generated by the entrance of coastal water masses, caused an increase in SPM concentrations due to increased fluid density, resuspension of previously deposited sediment, and erosion of banks. High concentrations of SPM indicate higher volume transport suggesting a hydraulic barrier due to the change/inversion of the baroclinic pressure gradient, resulting in water and material retention. Material deposition was observed during neap tide, while during spring tide the material is resuspended, increasing the concentration, generating cycles of deposition and erosion during the neap-spring tides. The sediment in suspension that reach the estuary, even with low fluvial volume, stay in this environment forming new islands because of deposition. High deposition rates or sediment cycling, if generated by the hydraulic barrier, may indicate that the flows of SPM from the continental drainage to the estuary and adjacent continental shelf are interrupted and the residence time is increased.     

The formation and environmental significance of calcite rafts in tropical tufa-depositing rivers of northern Australia

Spring‐fed rivers of the Barkly karst in tropical northern Australia form an array of tufa and related freshwater carbonate deposits. One of these deposits, calcite rafts, is precipitated at the water–air interface principally as a consequence of CO₂ degassing and evaporation. Calcite rafts have been reported in cave environments but have not been described in detail from fluvial systems. Observations using scanning electron microscopy coupled with water chemistry data reveal that they form by a combination of physical, chemical and biological processes. They grow downwards into the water column and form a dentate lower surface, while a flat upper surface occurs at the water–air interface. The rafts are readily inhabited by microorganisms, particularly diatoms, which frequently become entombed by calcite as the rafts develop. The decay of the biological material leaves voids, creating a pock‐marked texture. The rafts are subject to secondary calcite growth along the crystal edges. Once they become submerged in the water column after disturbance of the water surface, they may become completely covered by this overgrowth, creating a homogeneous veneer. The rafts form in quiescent settings, principally behind tufa dams in large, lake‐like water bodies along each river. Therefore, they can be used in conjunction with adjacent exposures of other tufa facies to decipher palaeohydrological conditions. Although the rafts are extremely thin and fragile, they are readily preserved within fossil waterhole facies, and their occurrence has been identified in rocks from the Quaternary to the Tertiary.     

Effects of nitrogen on the ecosystem respiration,CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions to the atmosphere from the freshwater marshes in northeast China

Freshwater marshes could be a source of greenhouse gases emission because they contain large amounts of soil carbon and nitrogen. These emissions are strongly influenced by exogenous nitrogen. We investigate the effects of exogenous nitrogen on ecosystem respiration (CO₂), CH₄ and N₂O emissions from freshwater marshes in situ in the Sanjiang Plain Northeast of China during the growing seasons of 2004 and 2005, using a field fertilizer experiment and the static opaque chamber/GC techniques. The results show that there were no significant differences in patterns of seasonal variations of CO₂ and CH₄ among the fertilizer and non-fertilizer treatments, but the seasonal patterns of N₂O emission were significantly influenced by the exogenous nitrogen. Seasonal averages of the CO₂ flux from non-fertilizer and fertilizer were 987.74 and 1,344.35 mg m ⁻² h ⁻¹, respectively, in 2004, and 898.59 and 2,154.17 mg m ⁻² h ⁻¹, respectively, in 2005. And the CH₄ from the control and fertilizer treatments were 6.05 and 13.56 mg m ⁻² h ⁻¹ and 0.72 and 1.88 mg m ⁻² h ⁻¹, respectively, in 2004 and 2005. The difference of N₂O flux between the fertilizer and non-fertilizer treatments is also significant either in 2004 and 2005. On the time scale of 20-, 100-, and 500-year periods, the integrated global warming potential (GWP) of CO₂ + CH₄ + N₂O released during the two growing seasons for the treatment of fertilizer was 97, 94 and 89%, respectively, higher than that for the control, which suggested that the nitrogen fertilizer can enhance the GWP of the CH₄ and N₂O either in long time or short time scale.     

Absolute dating of the youngest sediments of the Swiss Molasse basin by apatite fission track analysis

A set of ash layer samples within the uppermost Upper Freshwater Molasse (OSM) sediments (N and E of Frauenfeld, Switzerland) was dated by apatite fission track (FT) means. The ages indicate an early Tortonian (perhaps latest Serravallian) eruption and sedimentation age of 11.5 ± 0.3 Ma. The age is in agreement with time constraints by Mammalian relicts which point to MN7-8. Due to the position of the ash layers close to the erosional gap and overlying Quaternary cover, the age represents a maximum age for the cessation of OSM sedimentation in the Swiss Molasse Basin. However, the end of Molasse sedimentation in this region had not stopped before the cover of OSM sediments by volcanic ash layers at the Höwenegg volcano (southern Germany), an event further constrained by an apatite FT age of 9.8 (?0.7/+0.8) Ma from a hornblende-bearing ash layer at Höwenegg. An isolated bentonitic ash layer occurring 25 km to the WSW of the main set of dated ashes (near Humlikon) has an age component identical to the OSM ash layers near Frauenfeld. The age suggests a source for this material within the Hegau, but is too young to be related to the volcanic activity at the Kaiserstuhl.The apatites from the ash layer samples show two distinct compositional populations, one very close to a Cl end member and one with apatites of equal proportions of Cl and OH end member. These populations are interpreted to have possibly originated from at least two distinct igneous sources for the ashes, separated by their eruption site or eruption time or both. The distinct compositional data on the volcanic apatites may provide a basis to clarify their origin in future work.     

Modeling the influence of river discharge on salt intrusion and residual circulation in Danshuei River estuary,Taiwan

A 3-D, time-dependent, baroclinic, hydrodynamic and salinity model was implemented and applied to the Danshuei River estuarine system and the adjacent coastal sea in Taiwan. The model forcing functions consist of tidal elevations along the open boundaries and freshwater inflows from the main stream and major tributaries in the Danshuei River estuarine system. The bottom friction coefficient was adjusted to achieve model calibration and verification in model simulations of barotropic and baroclinic flows. The turbulent diffusivities were ascertained through comparison of simulated salinity time series with observations. The model simulation results are in qualitative agreement with the available field data.     

Does the Actual Drop in Dead Sea Level Reflect the Development of Water Sources Within its Drainage Basin?

As a part of Jordan’s efforts to quantify the effect of the Dead Sea level decline on the precious groundwater resources of the surrounding aquifers, the authors analyzed the historic or predevelopment inflows and outflows of the Dead Sea basin and the resulting water balance which included precipitation, evaporation, surface‐ and groundwaters. The predevelopment situation was taken as the point of departure for the sake of this study. Furthermore, the present situation was analyzed in an attempt to quantify the groundwater inflows into the Dead Sea as a result of drop in the Dead Sea level. The groundwater component and the corresponding saltwater/freshwater interface were taken as the variables to balance the levels of the sea that would have been reached without the contribution of the uncontrolled groundwater inflows as a result of the salt/freshwater interface seaward migration. The present day water balance that includes all the water diversion projects from all riparians indicates serious declines in the Dead Sea level. The effects of the present day level declines on the fresh groundwater/saltwater interface indicate that considerable amounts of groundwater are driven into the Sea as a result of the seaward migration of the freshwater/saline water interface.     

东南极拉斯曼丘陵区的湖泊

拉斯曼丘陵区的湖泊均为淡水湖,总数近150个,湖泊总面积6.3km~2,占陆地总面积的3.15％。东部地区湖泊数量少但多深大湖,西部地区数量多但多浅小湖。湖泊地貌发育初始,A_1/A_c之值较大,湖岸地貌形态不发育,全年封冻期长达300天,限制了湖水动力对地貌和沉积物形成的作用强度,冰雪融水量与湖面蒸发量控制了湖水平衡和湖面变化过程。湖积物厚度小,颗粒粗,分选差,风力混杂堆积作用明显。夏季水温变化复杂,并常有明显的逆温现象。水体pH值介于6.0～8.0之间,Na~+占绝对优势。     

Influences of ammonia-nitrogen and dissolved oxygen on lysosomal integrity in green-lipped mussel Perna viridis: laboratory evaluation and field validation in Victoria Harbour, Hong Kong

Lysosomal integrity in mussels has been applied as a biomarker to detect the pollution of trace organics and metals in the natural environments. However, few studies have examined the effects of water quality on the response of lysosomal integrity, in particular total ammonia-nitrogen (TAN) and dissolved oxygen (DO). This study demonstrated that high level of TAN (2.0 mg/l) and low DO (2.5 mg O₂/l) could significantly reduce the lysosomal integrity in green-lipped mussel Perna viridis, respectively by 33% and 38%, whereas the mussel lysosomal integrity decreased by 70% in the combined treatment of TAN and low DO under laboratory conditions after one week. The mussel lysosomal integrity of all treatment groups could return to the control level after a three week recovery period. In the field validation in Victoria Harbour, Hong Kong during an one-year study period, lysosomal integrity in P. viridis identified the cleanest site east to the harbour, where the lowest TAN and highest DO concentrations were found. While lysosomal integrity in mussels seemed not affected by seasonal changes, approximately 40% of the variation of this biomarker could be attributable to the changes in TAN and DO in seawater. In conclusion, the response of the mussel lysosomal integrity can be confounded by both TAN and DO prevailing in the natural environments and thus caution must be exercised in relating the observed changes in lysosomal integrity to any specific pollutant in coastal water quality monitoring studies.     

A 3-D numerical study of salinity variations in the Bohai Sea during the recent years

Salinity is an important component of the marine system. Previous studies indicated that the mean salinity in the Bohai Sea had increased by 2.0 psu in the second half of the 20th century, mainly due to a sharp decrease in the Yellow River runoff, and also the effects of large-scale climatic variations and the intrusions of the North Yellow Sea Water (NYSW). Since 2002, the Yellow River Conservancy Commission has carried out the flow regulation at the beginning of every flood season, resulting in more discharge of the Yellow River freshwater into the Bohai Sea. In this study, the variations of salinity in the Bohai Sea during the recent years are investigated using a well-established three-dimensional baroclinic model, HAMburg Shelf Ocean Model (HAMSOM). The simulation results show that the Yellow River diluted water was mainly discharged into the Laizhou Bay, so the remarkable increase in the Yellow River runoff after 2002 led to a regime shift of salinity in the Laizhou Bay. However, in other parts of the Bohai Sea, salinity variation was influenced by the surrounding rivers or the intrusions of NYSW, and has little relation with the Yellow River runoff. As a whole, advection is more important than diffusion in the salinity distribution, and seasonal oscillation is the main feature of salinity variation. Via several case studies, evaporation and precipitation rates are found to be important in the long-term simulation of salinity.     

Water column monitoring near oil installations in the North Sea 2001-2004

Fisheries have been vital to coastal communities around the North Sea for centuries, but this semi-enclosed sea also receives large amounts of waste. It is therefore important to monitor and control inputs of contaminants into the North Sea. Inputs of effluents from offshore oil and gas production platforms (produced water) in the Norwegian sector have been monitored through an integrated chemical and biological effects programme since 2001. The programme has used caged Atlantic cod and blue mussels. PAH tissue residues in blue mussels and PAH bile metabolites in cod have confirmed exposure to effluents, but there was variation between years. Results for a range of biological effects methods reflected exposure gradients and indicated that exposure levels were low and caused minor environmental impact at the deployment locations. There is a need to develop methods that are sufficiently sensitive to components in produced water at levels found in marine ecosystems.