Changes In Aquatic Environment Research Articles

Horizontal visibility of an underwater low-resolution video camera modeled by practical parameters near the sea surface

Underwater video cameras can be used for fisheries, aquacultures, and marine ecology to monitor the existence of fish. In order to assess marine structures, monitoring is also important to understand the effects on the local fish community. Underwater vision is sometimes degraded due to the condition of the water and sunlight. In particular, horizontal visibility is not easily obtained with regard to water quality. So far, an empirical relationship with horizontal visibility has been described according divers' vision, and it states that divers' horizontal visibility is approximately equal to 0.7 times the Secchi depth (Wright and Colling, 1995). If the video camera has a high resolution, visibility may be similar, however, if the camera has a low resolution, detectable distance can deteriorate. For practical usage, a video camera with low resolution has the advantage of reducing storage of data and it is easy to transmit video remotely, in other words, real-time monitoring. Real-time data will provide a prompt understanding of aquatic environmental changes. In order to obtain such data, a low-resolution video camera is still required for usage in a field. There are few models that describe horizontal visibility using a camera in water, therefore this study aims to model one. This paper showed a new approach to model horizontal visibility by water depth and Secchi depth, which are practical and obtainable parameters for underwater monitoring. In addition to this, global solar radiation is adopted for modeling. The model is expressed as relative contrast between target and background. Based on two observations near the sea surface (less than Secchi depth), the model is created. The model showed plausible horizontal visibility using an underwater video camera for real-time monitoring of fish and marine environment.

Struktur Komunitas Makrobentos Pada Kawasan Budidaya dan Non Budidaya Di Pulau Tembelas, Kabupaten Karimun Kepuluan Riau

The macrobenthos community structure of living organisms in aquatic base, can function as a bioindicator of changes in aquatic environments, are sensitive to any disturbance of environmental changes within a waters. This research aims to determine the effect of different structures of macrobenthos communities in the cultivation environment and noncultivation environment. The research was conducted for 4 months on Tembelas island in 2 areas that were monoculture cultivation and reference area. Abiotic data obtained were substrate grain analysis and total organic analysis of carbon and nitrogen, as well as abiotic environmental parameters such as temperature, pH, salinity and dissolved oxygen. The biotic data obtained in the form of macrobenthos species that were found and the amount in the area was then calculated using non parametric index that were the level of diversity, eveness and abundance, and T test. The identification result showed the number of species found as many as 24 species in the monoculture location and 42 species at the reference location. Dominant species found in monoculture locations were Costoanachis sp and Anodontia sp. dominant species found in the reference sites were Nuculana sp and Ellobium sp. Shannon-Wiener (H') diversity index value at monoculture location was 2,43, while reference index value index had bigger index value 2,83. The abiotic quality of monoculture and reference aquatic environments was categorized as good. Based on the result of the research, it can be concluded that reference environment had better macrobenthos diversity value than monoculture environment. Keywords: Makrobenthos, Monoculture, Reference Environment

Less water renewal reduces effects on social aggression of the cichlid Pterophyllum scalare

Changes in aquatic environments can affect fish behavior. Water renewal, for example, can dilute chemical signals, which are a social communication tool used by some fish species, and this dilution increases aggressive interactions in the group. Fierce and prolonged fights can affect fish welfare by increasing the probability of injuries, stress, and detrimental impacts on fish health. We tested whether the amount of water changed was associated with social aggression in the angelfish Pterophyllum scalare, a popular ornamental Amazonian cichlid. We designed an experiment with social groups (3 fish) that were assigned to one of three treatments (with 15 replicates of each treatment): 1) 50% water renewal; 2) 25% water renewal; or 3) 0% renewal (i.e., water removed and returned to the aquarium as a control). These treatments were referred to as T50%, T25%, and T0%, respectively. Fish behavior was video-recorded immediately before water renewal (baseline) and also 1min, 1h, 2h, and 24h after water renewal. The frequencies of attacks (overt fights) and displays (threats) were compared using the general linear model (GLM), with the treatment as the categorical factor, observation sessions as the repeated measures, and social rank as a continuous factor. Attacks increased after the water was changed, and they were higher in T50% than in T25% (P=0.0001). In T25%, aggression returned to baseline levels after 1h (P=0.32), but remained increased after 24h in T50% (P=0.000001). Changing only a small volume of water at a time was therefore found to prevent exaggerated aggressive interactions among P. scalare specimens and to reduce the probability of injuries, stress, and detrimental impacts on fish welfare.

Aquatic environmental changes and ecological implications from the combined effects of sea-level rise and land reclamation in Deep Bay, Pearl River Estuary, China

Rising sea levels due to climate change are altering the hydrodynamic and solute transport conditions in estuarine regions worldwide. At the same time, anthropogenic projects such as land reclamation could change the potential effects of sea-level rise (SLR). In this study, Deep Bay in the Pearl River Estuary of China was used as a case study to investigate the combined effects of SLR and reclamation. A numerical model was applied to simulate the changes of hydrodynamic and solute transport with 0.0, 0.3, and 0.5m of SLR in two groups of scenarios (i.e., before and after land reclamation). SLR alone substantially affected the hydrodynamics and strengthened the tidal influence. SLR resulted in a loss of intertidal regions and an increased tidal prism in the bay. Reclamation further magnified SLR’s effects on both the hydrodynamics and solute transport. The tidal energy entering the bay during each tidal phase increased by 39.2% and 66.4% with 0.3 and 0.5m of SLR (respectively) before reclamation, versus 40.7% and 68.9% (respectively) after reclamation. The reclamation projects in the bay helped the saline sea water to intrude further upstream, and magnified the effects of SLR on variations in seasonal salinity. SLR also decreased the bay’s ability to exchange water. However, the reclamation accelerated the solute circulation inside the bay, considerably reduced the water age, and offset the SLR’s effects on the bay’s ability to exchange water with the adjacent sea. The increase in salinity variation due to the combined effects of SLR and reclamation might exert stress on the ecological system of the inner bay, which contains a Ramsar wetland.

OSTRACODE BIOFACIES AND SHELL CHEMISTRY REVEAL QUATERNARY AQUATIC TRANSITIONS IN THE POZUELOS BASIN (ARGENTINA)

Here we present the first use of calcareous microfossils to examine the late Quaternary paleoecology of the endorheic Pozuelos Basin (Argentina). Modern deposition in the basin centers on Laguna de los Pozuelos (LP), a shallow playa-lake that is fed by axial rivers and groundwater and dominantly accumulates siliciclastic sediments. Today, the distribution of limnocytherid and cypridoidean ostracodes across southern LP is strongly influenced by distance to the Rio Cincel delta, whereas the northern end of the playa-lake is characterized by a paucity of ostracodes due to frequent sub-aerial exposure. Ten ostracode biofacies define a sediment core retrieved from LP, which reveal progressive changes in aquatic environments that varied in salinity, depth, and proximity to deltas over the late Pleistocene. Closed lakes occupied the basin from ∼ 37.6–30.7 ka, ∼ 28.0–25.0 ka, and ∼ 23.0–16.6 ka, whereas saline wetlands occurred when these lakes contracted. Extant LP has no analog in the late Pleistocene record; it formed after ∼ 7.2 ka, following a hiatus that removed the Pleistocene–Holocene transition. Paleoecological evidence indicates that the core site was influenced by deltaic inflows from the eastern basin margin until ∼ 24.3 ka, an area where today dry alluvial fans are found. Reorganization of the watershed by normal faulting, most likely at ∼ 18.0 ka, appears to have reduced the influence of these deltaic inflows. Extensional neotectonics, perhaps induced by incorporation of the Pozuelos Basin into the Andean hinterland, is a mechanism that along with tropical climate change is potentially important to water balance and ecology in high-altitude convergent orogenic basins.

Seasonal variation in the growth responses of some chlorophytic algal flora of the Red Sea

Seasonal variation in growth responses and antioxidant activities of four chlorophytic algal species, namely Ulva lactuca, Enteromorpha flexuoca, Cladophora prolifera, Chaetomorpha linum was investigated. Seasonal variation in the physico-chemical characteristics of water at the study site of the Red Sea was also determined. A significant variation was observed in water quality parameters in different seasons. All the algal species show higher accumulation of photosynthetic and accessory pigments in July and October and a significant decrease in January. Higher NPK content in all the four algal species was recorded in July, however, the contents were low in other months. Total protein contents were higher in July and October. Total carbohydrates in U. lactuca and E. flexuoca were significantly higher in July but in the other two species, C. prolifera and C. linum, maximum accumulation was observed in October. Antioxidant activities in all the species were most significant in January as compared to the other months. All the chlorphytic algae show prominent growth responses and antioxidant activities and are better adapted to changing climatic conditions. Due to their prompt responses even to minor changes in aquatic environment, they can be used as ecological indicators in coastal marine ecosystems.

Aquatic environmental changes and anthropogenic activities reflected by the sedimentary records of the Shima River, Southern China

Reconstructing historical sedimentary records is essential for better understanding the effects of anthropogenic activities on river environments. We used lead-210 to date riverine sediment core from the Shima River in China. We obtained a sedimentary history of 34 years (1982–2015) for core S2, which had a length of 34 cm. The sedimentation rate of 0.304–2.04 cm y−1 was controlled by both flood events and anthropogenic activities. The conservative element content depth profiles remained relatively constant, suggestive of a relatively stable sediment provenance; therefore, the increase in the sedimentation rate over time was mainly the result of domestic and industrial wastewater effluent and the construction of a rubber dam at the middle and lower reach of the Shima River. From 1982 to 2015, the nutrient and trace metal depth profiles could be divided in three periods based on their trends. From 1982 to 1993, the vertical profiles of nutrients (organic carbon, total phosphorus, and total nitrogen) and three trace metals (nickel, zinc, and manganese) were relatively stable; however, the gradual decrease in copper and cadmium was likely associated with a reduction in agricultural chemical application. From 1993 to 2003, a population explosion and rapid industrialization were responsible for an increase in the input of pollutants into the Shima River, which was partly attenuated by water from the Dong River, leading to a gradual increase in nutrient and trace metal contents. Finally, from 2003 to 2015, the Shima River stopped being used as a source of water due to its deteriorating water quality. The relatively lower velocity of the water flow after the recovery of its flow direction and the reconstruction of the rubber dam in 2009 provided advantageous sedimentary conditions, promoting nutrient accumulation and significant trace metal enrichment.

Phenotypic plasticity of aquatic plants in heterogeneous environments: a review

Aquatic plants are the ecological group that mainly consists of herbaceous plants with habitats that are closely associated with water. Most aquatic plants have strong clonality. In response to changes in aquatic environments, aquatic plants exhibit significant plasticity in morphological, behavioral and physiological traits, and thus adapt well to heterogeneous aquatic environments. Compared with extensive studies on phenotypic plasticity of terrestrial plants, less attention has been paid to test how phenotypic plasticity of aquatic plants responds to heterogeneous environments. In this review, we briefly clarified the major types of phenotypic plasticity and their relationships in clonal plants in heterogeneous environments, identified the uniqueness of aquatic environments in relation to environmental heterogeneity, and analyzed the theoretical possibilities of aquatic plants showing high phenotypic plasticity. Furthermore, we probed into how aquatic plants adapted to heterogeneous aquatic environments by means of phenotypic plasticity involved with morphological plasticity, foraging behavior, clonal integration, intraclonal labour division, and risk spreading. Finally, we identified shortcomings in current studies on phenotypic plasticity of aquatic plants, and highlighted some issues deserving more attention in future studies, which include: (1) the changing pattern and mechanism of phenotypic plasticity; (2) the influence of clonal integration on community and ecosystem stability; •综述• 第 2 期 黎磊等: 异质生境中水生植物表型可塑性的研究进展 217 (3) the trade-offs between clonal integration and fragmentation; (4) the differences of phenotypic plasticity in different types of clonal architecture, and their mechanisms; (5) the adaptive evolution of phenotypic plasticity; (6) the interaction of aquatic plants with species in other taxa or at different tropic levels; and (7) the response of aquatic ecosystems to global change.

Dissolved inorganic carbon speciation in aquatic environments and its application to monitor algal carbon uptake

Dissolved inorganic carbon (DIC) speciation is an important parameter that enables chemical and ecological changes in aquatic environments, such as the aquatic environmental impact of increasing atmospheric CO2 levels, to be monitored. We have examined and developed a sensitive and cost-effective ‘back-titration’ method to determine the DIC species and abundance in aqueous environments that is more accurate and reproducible than existing methods and is applicable in a range of fresh, brackish and sea waters. We propose the use of pHHCO3 (bicarbonate-dominant pH) and pH3.5 as the titration end points in the back-titration technique to accurately determine carbonate alkalinity. The proposed method has a higher accuracy and precision than other modified Gran's methods that are currently in use. The detection limit was found to be ~5μmolkg−1 with an accuracy within 1% and a precision (CV) within 0.2% and 0.5% at high and low level of carbonates, respectively. This method was successfully applied to monitor DIC in the aqueous medium of Nannochlopsis salina cultivation separately carried out with NaHCO3 and CO2 as the respective inorganic carbon source. The cells were able to grow in the NaHCO3 medium with a similar growth curve to cells with 0.039% CO2 (air). Increases in CO2 level stimulated lipid accumulation by diverting the fixed carbon from protein to lipids. The increased concentration of gaseous CO2 and the accompanying lower pH appears to significantly inhibit the growth of algae despite the presence of HCO3− when 20% CO2 was employed.

Isotopic and geochemical characterization of invader tilapia fishes from water bodies of West Bengal and Karnataka, India.

The otoliths (N = 12) of freshwater invasive species tilapia (Tilapia mossambicus) collected from two water bodies located at Kolkata and Bangalore, India, were analyzed for stable isotopes (δ18O, δ14C) and major and trace elements in order to assess the suitability of using otoliths as a tracer of aquatic environmental changes. The stable isotope analysis was done using the dual inlet system of a Finnigan-MAT 253 isotope ratio mass spectrometer (Thermo-Fisher, Bremen, Germany). Concentrations of major and trace elements were determined using a Thermo X-Series II quadrupole mass spectrometer. The stable isotope composition in tilapia otolith samples from Bangalore and Kolkata water bodies are quite good agreeing with that of the respective lake/pond and rain water. Elemental composition revealed in a pattern of Ca>Fe>Na>Sr>K>Ba>Cr>Mg>As>Mn>Zn>Co>Cu>Cd>Pb. The otoliths from Kolkata pond water are more enriched in Ba, Zn, Pb, Mn, Se, Cu, Zn, Cd, and Ni whereas Cr and As were found to be higher in otolith samples from Bangalore lake. The enrichment factor (EF) values of Cr were higher for both the sampling location in comparison with other metals, although all the studied metals exhibited EF values>1. The PCA shows clustering of metals in the otolith which are related either with the metabolic and physiological attributes or waterborne source. The study demonstrated the potential of stable isotope techniques to distinguish otolith specimens from varied climatic zone, while elemental composition recorded the quality of water at both the locations. The role of climate driving the quality of water can be understood by detailed and continuous monitoring of otolith specimens in the future. Future method allows reconstruction of climate and water quality from old specimens from field exposures or museum collection.

Evaluation of Cytotoxicity and Cell Death Induced In Vitro by Saxitoxin in Mammalian Cells

Since the cyanotoxin saxitoxin (STX) is a neurotoxin and induces ecological changes in aquatic environments, a potential risk to public and environmental health exists. However, data on STX-mediated cytotoxic and genotoxic effects are still scare. In order to gain a better understanding of the effects of this toxin, the cytotoxic and genotoxic potential of STX was examined in two mammalian cell lines. Neuro 2A (N2A), a neuroblastoma mouse cell line, and Vero cell line, derived from Vero green monkey kidney cells, were exposed to several concentrations of STX ranging from 0.5 to 64 nM to determine cell viability, induction of apoptosis (DNA fragmentation assay), and formation of micronuclei (MN) (cytokinesis-block micronucleus assay; CBMN) following 24 h of incubation. The half maximal effective concentration (EC50) values for STX calculated in cell viability tests were 1.01 nM for N2A and 0.82 nM for Vero cells. With increasing STX concentration there was evidence of DNA fragmentation indicating apoptosis induction in Vero cells with a 50% increase in DNA fragmentation compared to control at the highest STX concentration tested (3 nM). The results demonstrated no significant changes in the frequency of micronucleated binucleated cells in N2A and Vero cells exposed to STX, indicating the absence of genotoxicity under these test conditions. There was no apparent cellular necrosis as evidenced by a lack of formation of multinucleated cells. In conclusion, data reported herein demonstrate that STX produced death of both cell types tested through an apoptotic process.

Effects of hydrological regulation and anthropogenic pollutants on Dongting Lake in the Yangtze floodplain

AbstractDongting Lake, a wetland of international importance under the Ramsar Convention, is the hydrological lynchpin of the Yangtze floodplain. It is subjected to eutrophication and heavy metal pollution, but little is known of recent rapid degradation of its aquatic environment and potential causes. Here, we use sedimentary records of particle size, elements and pigments, combined with historical hydrological and limnological data, to assess aquatic environmental changes since ca 1960. Coarse particles in the sediments increased after 2003, while concentrations of K, Li, Al and Mg declined. These changes are probably linked to strong erosion of the downstream riverbed and declining supply of ion‐rich material from the upper Yangtze reaches after the Three Gorges Dam (TGD) began to operate. Furthermore, enrichment of sedimentary heavy metals and total phosphorus since the 1990s can be attributed to the influx of anthropogenic pollutants. Biotic responses are manifested in higher concentrations of fossil algal pigments, especially those from chlorophytes and siliceous algae after the TGD impoundment. Multivariate analysis revealed that changes in fossil pigments were significantly correlated with total phosphorus and Pb and three indicators for hydrological conditions (i.e. coarse particles, water exchange ratio and sediment discharge), indicating that influx of anthropogenic pollutants and hydrological regulation by the TGD are main drivers of algal community change. Our results provide reference conditions for restoration of Dongting Lake and highlight the importance of hydrological connection with the mainstream and pollution control for continuing efforts to restore Dongting Lake, as well as other similar floodplain lakes worldwide. Copyright © 2015 John Wiley & Sons, Ltd.

Thermodynamic analysis of fatty acid harvesting by novel carbon-based adsorbent.

In this study, separation and concentration of fatty acids (FA) from the synthetic food processing wastewater containing low concentration of FA (250mg/L) were investigated using expanded graphite (EG) as a novel adsorbent at different temperatures (298~318K). The adsorption results were further analyzed to verify adsorption mechanisms and thermodynamics of FA onto EG. Results show that the adsorption of FA onto EG was explained well by the Langmuir model with the maximum adsorption capacity up to 8.01gFA/gEG at 298K, and considerably affected by temperature. The adsorption kinetics fitted with pseudo-second-order kinetic model and the adsorption mechanism analysis showed that the intraparticle diffusion was not the rate-limiting step, but the coalescence of FA droplets played the significant role for novel adsorption of FA onto EG. The calculated activation energy and thermodynamic parameters such as Gibbs free energy change (ΔG(0)), enthalpy change (ΔH(0)), and entropy change (ΔS(0)) indicated that the adsorption of FA onto EG was very feasible, was highly spontaneous, occurred physically, was exothermic in nature, and was stable in aquatic environmental changes. Overall, FA can be effectively harvested and concentrated from the food processing wastewater by EG even at low concentration.

Chironomids as indicators in freshwater ecosystems: an assessment of the literature

Abstract Freshwater assessment studies have been used changes on individuals and populations of Chironomidae assemblages as bioindicators to assay aquatic ecosystems changes and environmental quality. To assess the contribution of the studies with this family to response aquatic environmental changes, we carried out a scientometric analysis of the papers published from 1992 to 2012. We imported papers from ISI Web of Knowledge database (Thomson Reuters) in November 2013. A total of 2967 papers were evaluated and we carried out descriptive analysis to assay the main trends on Chironomidae research in freshwater assessments. The main ideas and approaches in these studies were related to the impact of human influence on aquatic ecosystems and the status of conservation of this environments, as well as to limitations and difficulties in the applications of the assessments. In view of our results, we suggest some ideas to contribute to the conservation of aquatic ecosystems, mainly in threatened environments in southern Hemisphere countries. However, Chironomidae identification for assessing aquatic environments, as well as the limitations of suitable tools and metrics, which still are strong issues that need more attention to make more robust approaches to assay aquatic ecosystems.

Tet genes as indicators of changes in the water environment: Relationships between culture-dependent and culture-independent approaches

The aim of this study was to identify tetracycline resistance determinants that could be used as molecular indicators of anthropogenic changes in aquatic environments. Two parallel approaches were used to examine the prevalence of tet genes: a culture-based method involving standard PCR and a method relying on quantitative PCR. The studied site was the Łyna River in Olsztyn (Poland). The culture-dependent method revealed that the concentrations of doxycycline-resistant bacteria harboring the tet(B) gene were higher in wastewater and downstream river samples than in upstream water samples. The tet(B) gene was transferred from environmental bacteria to Escherichia coli. The results generated by the culture-independent method validated statistically significant differences in tet(B) concentrations between upstream and downstream river sections, and revealed that tet(B) levels were correlated with the presence of other tetracycline resistance genes, dissolved oxygen concentrations, temperature and doxycycline concentrations in water. Our findings indicate that doxycycline-resistant bacteria, in particular E. coli harboring tet(B) or increased concentrations of tet(B), are potentially robust indicators of changes in water environments.

Assessing the changes in land use and ecosystem services in an oasis agricultural region of Yanqi Basin, Northwest China.

The Yanqi Basin, one of the most productive agricultural areas, has a high population density in Xinjiang, Northwest China. Land use changes, mainly driven by oasis expansion, significantly impact ecosystem services and functions, but these effects are difficult to quantify. The valuation of ecosystem services is important to clarify the ecological and environmental changes caused by agriculturalization of oasis. This study aimed to investigate variations in ecosystem services in response to land use changes during oasis agricultural expansion activities in the Yanqi Basin from 1964 to 2009. The methods used were based on formula of ecosystem service value (ESV) and ESV coefficients. Satellite data were combined with the ESV coefficients to quantify land use changes and ecosystem service changes in the study area. Sensitivity analysis determined the effect of manipulating the coefficients on the estimated values. The results show that the total ESVs in the Yanqi Basin were $1,674, $1,692, $1,471, $1,732, and $1,603 million in 1964, 1973, 1989, 1999, and 2009, respectively. The net deline in ESV was $71 million in the past 46years, but the ESVs of each types of landscape changed significantly. The aggregated ESVs of water areas and wetlands were approximately 80% of the total ESV. Water supply and waste treatment were the two largest service functions and contributed approximately 65% of the total ESV. The estimated ESVs in this study were elastic with respect to the value coefficients. Therefore, the estimations were robust in spite of uncertainties on the value coefficients. These significant changes in land use occur within the entire basin over the study period. These changes cause environmental problems, such as land degradation, vegetation degeneracy, and changes in aquatic environment.

Phytoplankton strategies for photosynthetic energy allocation.

Phytoplankton physiology is dynamic and highly responsive to the environment. Phytoplankton acclimate to changing environmental conditions by a complex reallocation of carbon and energy through metabolic pathways to optimize growth. Considering the tremendous diversity of phytoplankton, it is not surprising that different phytoplankton taxa use different strategies to partition carbon and energy resources. It has therefore been satisfying to discover that general principles of energetic stoichiometry appear to govern these complex processes and can be broadly applied to interpret phytoplankton distributions, productivity, and food web dynamics. The expectation of future changes in aquatic environments brought on by climate change warrants gathering knowledge about underlying patterns of photosynthetic energy allocation and their impacts on community structure and ecosystem productivity.

Palynological evidence of natural and anthropogenic impacts on aquatic environmental changes over the last 150 years in Dongping Lake, North China

Dongping Lake is located in Dongping County, west of Shandong Province, North China. It is the only large reservoir for flood control and detention in the lower reaches of the Yellow River, and an important regulator for the Eastern Route of South-to-North Water Diversion Project in China. In order to retrieve past historical changes of aquatic vegetation in Dongping Lake, a sediment core was drilled from the lake. Based on the high-resolution chronological sequence which was established according to 210Pb and 137Cs methods, changes in physical conditions and water quality associated with the disturbance of the Yellow River, as well as the reactions of aquatic species to environmental conditions and human activities in Dongping Lake are discussed. The data suggest that the lake has undergone considerable aquatic environmental change, resulting in remarkable change of aquatic vegetation (development period, mass disappearing period, restoration and development period, thriving period), which are attributed to both natural and anthropogenic impacts over the past 150 years. From 1855 to 1865, aquatic pollen was in great abundance, attributed to occasional disturbance by floods of the Yellow River during this period. Frequent influence of the Yellow River (high water level, turbid water, low transparency and strong hydrodynamic condition) could be responsible for the near absence of Typha and Myriophyllum from 1865 to 1940. The high and stable accumulation rate of 0.29 g cm−2 y−1 during this period also supports this. The Yellow River captured the Huai River and discharged to the Yellow Sea in 1938. Without disturbance of the Yellow River, the improved growing conditions in the lake from 1938 led to a partial recovery of aquatic vegetation. The rapid decline of the sedimentary flux also supports this. The lake was disturbed by the Yellow River again in 1947, and the decreasing sediment concentration was recorded by the continuing decreased sedimentary flux. As the water level rose, a noticeable increase of Myriophyllum and a decrease of Typha were observed. High abundance of Myriophyllum and Typha and frequent appeared Nymphoides and Trapa/Nymphea from 1963 could be related to a change in sediment supply, stable environmental conditions, and eutrophication-related changes. The increasing abundance of Pediastrum and low stable sedimentary flux also support this. However, the remarkable rise of sedimentary flux and decrease of Pediastrum from 1995 might be a reflection of enhanced human activities in recent years.

Genotoxicity in Astyanax bimaculatus (Twospot Astyanax) Exposed to the Waters of Engano River (Brazil) as Determined by Micronucleus Tests in Erythrocytes

Changes in aquatic environments are potentially large, and effects on biota are highly variable. In Santa Catarina State, Brazil, the main sources of pollution in headwaters are wastewater, pesticides, and animal waste, which contain chemical and organic additives, and there is little knowledge about their effects on aquatic organisms. This study was aimed at investigating the possible genotoxic effects of the waters of the Engano River through the micronucleus (MN) test in Astyanax bimaculatus erythrocytes. Samplings were performed at two sites on the river, and there were six temporal repetitions with collection of blood from six individuals per site/repetition. For the negative-control treatment, we used fish from organic culture; cyclophosphamide was inoculated to constitute the positive-control treatment. MN was obtained in 3,000 erythrocytes/individual. Kruskal-Wallis analysis of variance, Scott-Knott test, and Spearman correlation were employed for data analysis. We found 124 MN in fish from the river, with 70 and 54 MN, respectively, for each site and 16 and 59 MN in negative and positive controls, respectively. The results showed a statistical difference for the formation of MN between river fish and fish in the positive-control treatment. Considering the average MN, we found the formation of three distinct groups: (1) fish from site no. 1 and those in the negative-control group, (2) fish from site no. 2, and (3) fish in the positive-control group. The greater values of chromosomal damage were found during periods of lower rainfall. The test used indicated the presence in the water of substances likely to cause clastogenic and aneugenic effects.

十三湖におけるヤマトシジミ浮遊幼生数への汽水環境の影響解析

Lake Jusan is a brackish lake located in the down reaches of Iwaki River system and is a fishing place of Corbicula japonica. However, the annual catches of C. japonica have been fluctuated over time presumably because of aquatic environmental changes. To maintain sustainable fishery, it is necessary to understand the causal factors on reclamation processes of C. Japonica in relation to brackish environmental conditions of the lake. In this study, field measurements were conducted on salinity, water temperature, and distribution of larvae of C. Japonica. From the results, empirical formulation was made to estimate number of the larvae in the lake. By combining that formulation with numerical hydraulic simulation, a methodology was proposed to evaluate the influence of hydrological changes in the watershed on reclamation of C. japonica.