Growth,abundance, morphometric and metabolic parameters of three populations of Diplodon chilensis subject to different levels of natural and anthropogenic organic matter input in a glaciar lake of North Patagonia

Three populations of Diplodon chilensis (Hiridae, Bivalvia) from North Patagonia (Lacar lake, Argentina) have been studied to determine how organic matter (OM) influence their growth, density, morphometric and metabolic parameters in two pristine sites (Yuco and Nonthué) and in a growing touristic locality (San Martín de los Andes Bay, site SMA) affected by urban discharges. In Nonthué (chemical and biological oxygen demand ratio COD/BOD ratio of 4.7), a dense neighboring forest provides higher quantities of vegetal detritus compared to Yuco, while in SMA the OM input increase is related to anthropogenic impact, mainly sewage discharges, which is more biodegradable (COD/BOD ratio of 1.7). Our results show that population's size distribution and growth rates are affected positively by increased OM, independently of its natural or anthropogenic origin. The modal shell length interval for SMA and Nonthué is two-fold higher (70 mm), in agreement to the growth rate increase (k = 0.079), compared to Yuco (35 mm, k = 0.045). The morphometric relationships between size–size and size–mass show a higher slope for SMA and Nonthué, which underline allometric differences between these two populations and the Yuco's one. The lower population densities in both sites (SMA 33 ind./m² and Nonthué 76 ind./m²) compare to Yuco (176 ind./m²) and the absence of individuals younger than 7 and 5 years old, respectively, in SMA and Nonthué could be related to the higher allochthonous OM content in the sediments and total suspended solids in water. Increased OM due to urban pollution in SMA bivalves leads to higher oxidative damage to lipids, which is not counterbalanced by the higher detoxification enzyme glutathione-S-transferase activity. Hence, we can conclude that pollution would explain the drastic reduction in population density, probably related to a high impair in the juvenile's survival/recruitment, the higher observed mortality and the lower population longevity. When increased OM is supply by the forest, like in Nonthué, this has less negative effect on population density and no effect on longevity at all. However, a negative effect of oxygen depletion due to increased OM (either anthropogenic or natural) on juvenile survival cannot be discarded, but further studies should be carried out to support this idea.     

河蚌养殖对水域环境的影响及养殖模式的优化

综述了河蚌养殖育珠对水域水质影响以及养殖模式优化,指出采用适当的养殖模式养殖育珠,可修复水域环境与改善水质状况.     

A 12.8-ka-long palaeoenvironmental record revealed by subfossil ostracod data from lacustrine freshwater tufa in Lake Sinijärv,northern Estonia

High-resolution quantitative analysis of ostracod assemblages from 4.3-m-thick freshwater tufa-rich sediments, deposited during the last 12.8 ka in Lake Sinijärv, northern Estonia, yielded information on water level, trophic state conditions, and temperature changes since the late glacial. AMS ¹⁴C dates from aquatic mosses provided time constraints on the palaeoenvironmental development of the region. In the ostracod assemblage structure, four faunal zones (OFZ) were determined. The most significant change in the ostracod fauna occurred at 10,590 cal. y BP, when a typical littoral, polythermophilic fauna was replaced by a mostly sublittoral, species-rich meso- to stenothermophilic fauna. The ostracod data indicate two major low-water-level periods in the lake at 12,800–10,590 and 7,600–3,700 cal. y BP. Sediment analysis indicates the most intensive tufa precipitation occurred during these low stand periods, rather than during the warmest climate in Estonia between 8,000 and 4,500 cal. y BP. The late glacial low water level in the groundwater-fed Lake Sinijärv at 12,800–10,590 cal. y BP coincides partly with the regression in the Lake Peipsi basin (14,000–12,100 cal. y BP) and with the last drainage event of the Baltic Ice Lake at 11,600 cal. y BP. The low-water-level period in Lake Sinijärv occurred earlier than in lakes in the SE sector of Scandinavian glaciation. The change from low to high water level in Lake Sinijärv at 10,590 cal. y BP preceded the first post-glacial transgression events in the small lowland lakes of Estonia, southern Sweden, Poles`ye in Belarus, and Valday in NW Russia. In general, the mid-Holocene low-water-level period in Lake Sinijärv between 7,600 and 3,700 cal. y BP is concurrent with the regressions in the lakes of the SE sector of Scandinavian glaciation.     

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.     

Multimetric Macroinvertebrate Index Flanders (MMIF) for biological assessment of rivers and lakes in Flanders (Belgium)

The European Water Framework Directive requires that member states assess all their surface waters based on a number of biological elements, including macroinvertebrates. Since 1989, the Flemish Environment Agency has been using the Belgian Biotic Index for assessing river water quality based on macroinvertebrates. Throughout the years, the Belgian Biotic Index has proven to be a reliable and robust method providing a good indication of general degradation of river water and habitat quality. Since the Belgian Biotic Index does not meet all the requirements of the Water Framework Directive, a new index, the Multimetric Macroinvertebrate Index Flanders (MMIF) for evaluating rivers and lakes was developed and tested. This index was developed in order to provide a general assessment of ecological deterioration caused by any kind of stressor, such as water pollution and habitat quality degradation. The MMIF is based on macroinvertebrate samples that are taken using the same sampling and identification procedure as the Belgian Biotic Index. The index calculation is a type-specific multimetric system based on five equally weighted metrics, which are taxa richness, number of Ephemeroptera, Plecoptera and Trichoptera taxa, number of other sensitive taxa, the Shannon-Wiener diversity index and the mean tolerance score. The final index value is expressed as an Ecological Quality Ratio ranging from zero for very bad ecological quality to one for very good ecological quality. The MMIF correlates positively with dissolved oxygen and negatively with Kjeldahl nitrogen, total nitrogen, ammonium, nitrite, total phosphorous, orthophosphate and biochemical and chemical oxygen demand. This new index is now being used by the Flemish Environment Agency as a standard method to report about the status of macroinvertebrates in rivers and lakes in Flanders within the context of the European Water Framework Directive.     

青藏高原中部色林错中晚全新世以来古气候变化特征

色林错位于青藏高原中部印度季风和西风环流的过渡地带,同时受西风环流和印度季风系统控制,是研究二者进退变化特征的理想场所。本文利用色林错SL-1钻孔中介形虫Limnocythere inopinata的丰度及其壳体微量元素Mg/Ca和Mn/Ca比值重建了色林错5.3 ka BP以来的古气候环境变化特征。5.3～2.9 ka BP,L.inopinata丰度较小,壳体的低Mg/Ca比值和高Mn/Ca比值表明此阶段气候偏冷湿;2.9～1.8 ka BP,L.inopinata丰度较前一阶段增加,壳体Mg/Ca比值略有增长但仍为低值表明气温虽然有所回升但仍然较低,Mn/Ca比值较前一阶段明显降低,指示湖泊水位下降;1.8 ka BP至今,L.inopinata丰度达到最大,壳体的高Mg/Ca和Mn/Ca比值指示湖泊温度和水位均呈显著的上升趋势。通过与西风区、过渡区以及印度季风区其他湖泊的环境沉积记录对比,本文认为青藏高原中部地区在中全新世晚期主要受西风环流影响,气温较低,西风带来大量水汽使得湖面呈扩张趋势;而到晚全新世西风环流逐渐北撤,色林错受季风影响更大,季风带来的降水和气温升高导致的冰川融...     

Influence of changes in developed land and precipitation on hydrology of a coastal Texas watershed

Freshwater inflows, among the most important factors in the overall health of estuarine environments, can be altered both by regional climatic influences as well as changes in land use and land cover. We conduct a scenario analysis to study the individual and combined impacts of changes in land use and land cover and in precipitation patterns in a coastal Texas watershed. The watershed is one of the major sources of freshwater for the estuarine area within the Mission-Aransas National Estuarine Research Reserve (NERR). Our scenario analysis suggests that climatic changes are more influential than land changes at the watershed level. However, localized impacts of land change may still be significant on habitats within the NERR site. Results from our watershed-level analysis poorly agree with the recommended freshwater flows established for the region, which deserve further scrutiny. Our findings suggest that geomorphic characteristics of the streams in the watershed need to be taken into consideration in hydrological modeling. Further research on the interactions between land change and hydrological dynamics should also aim for tighter temporal integration of the two sets of processes.     

The diffusion coefficient of dissolved silica revisited

The diffusion coefficient of dissolved silica was determined for two different salinities, 36 and 0, at temperatures ranging from 2 °C to 30 °C and at an average pH value of 8.1. Our results show limited influence of salinity and a variation by a factor of 2 to 3 of the silica diffusion coefficient within the temperature range considered in this study. The values obtained at 25 °C are in agreement with previous work carried out at room temperature for seawater and freshwater. The dependency on temperature and viscosity of the diffusion coefficient agrees well with the Einstein–Stokes equation. The composition of the solvent appears to be an important factor because it modifies the viscosity and allows for the complexation of the dissolved silica with less mobile ions, while its pH controls the dissolved silica speciation. In seawater, the higher viscosity and the presence of dissociated and polymeric species result in a decrease of the diffusion coefficient compared to freshwater systems.