Combined influence of meteorological,hydrological, and physicochemical factors on macrophyte overgrowth in agricultural reservoirs

Limnology - Maintaining moderate levels of aquatic plant cover in agricultural reservoirs is an important issue because aquatic plant development is closely related to diverse ecosystem functions,...     

The longitudinal distribution and community dynamics of zooplankton in a regulated large river: a case study of the Nakdong River (Korea)

The longitudinal distribution and seasonal dynamics of zooplankton were examined along a 200-km section of the middle to lower Nakdong River, Korea. Zooplankton was sampled twice a month from January 1995 to December 1997 at five sites in the main river channel. There was considerable longitudinal variation in total zooplankton abundance (ANOVA, p < 0.001). All major zooplankton groups (rotifers, cladocerans, copepodids and nauplii) increased significantly with distance downstream along the river. There also were statistically significant seasonal differences in zooplankton abundance at the sampling sites (ANOVA, p < 0.01). Zooplankton abundance was high in spring and fall and low in summer and winter. The seasonal pattern of rotifers was similar to that of total zooplankton. This reflected the fact that rotifers (Brachionus calyciflorus, B. rubens, Keratella cochlearis and Polyarthra spp.) strongly dominated the zooplankton community at all locations. Among the macrozooplankton, small-bodied cladocerans (e.g. Bosmina spp.) dominated; the abundance of large-bodied cladocerans (e.g. Daphnia) was negligible (0–5 ind. l^–1). Among the environmental variables considered, partial residence time seemed to play the most important role in determining characteristics of the river zooplankton community.     

Population Growth of the Cladoceran,Daphnia magna: A Quantitative Analysis of the Effects of Different Algal Food

In this study, we examined the effects of two phytoplankton species, Chlorella vulgaris and Stephanodiscus hantzschii, on growth of the zooplankton Daphnia magna. Our experimental approach utilized stable isotopes to determine the contribution of food algae to offspring characteristics and to the size of adult D. magna individuals. When equal amounts of food algae were provided (in terms of carbon content), the size of individuals, adult zooplankton, and their offspring increased significantly following the provision of S. hantzschii, but not after the provision of C. vulgaris or of a combination of the two species. Offspring size was unaffected when C. vulgaris or a mixture of the two algal species was delivered, whereas providing only S. hantzschii increased the production of larger-sized offspring. Stable isotope analysis revealed significant assimilation of diatom-derived materials that was important for the growth of D. magna populations. Our results confirm the applicability of stable isotope approaches for clarifying the contribution of different food algae and elucidate the importance of food quality for growth of D. magna individuals and populations. Furthermore, we expect that stable isotope analysis will help to further precisely examine the contribution of prey to predators or grazers in controlled experiments.     

Effect of flooding on fish assemblages in small streams in South Korea

The impact of Typhoon-Rusa-generated flood on fish assemblages was investigated in small streams in the northeastern part of South Korea. As a result of high precipitation (870 mm day⁻¹) during the typhoon, stream morphology and substrate composition changed. Stream depth and width decreased and slightly enlarged, respectively. Substantial amounts of mud and silt flowed into the streams and modified substrate composition to a simple state. Although the total number of individual fish significantly decreased after the flood, the dominant species remained the same relative to before the typhoon, and their relative abundance subsequently increased. However, the rank order of fish assemblages before and after the flood changed. Three years after the flood, fish assemblage recovered, but the number of individuals per site was still lower than prior to the flood. Flooding affects fish assemblages both directly and indirectly. Indirect impacts, such as habitat alteration, more critically affected the change in local fish assemblage and delayed recovery time. Nonetheless, fish assemblages persisted at sites where floods occurred.     

Talking about Climate Change and Global Warming

The increasing prevalence of social networks provides researchers greater opportunities to evaluate and assess changes in public opinion and public sentiment towards issues of social consequence. Using trend and sentiment analysis is one method whereby researchers can identify changes in public perception that can be used to enhance the development of a social consciousness towards a specific public interest. The following study assessed Relative search volume (RSV) patterns for global warming (GW) and Climate change (CC) to determine public knowledge and awareness of these terms. In conjunction with this, the researchers looked at the sentiment connected to these terms in social media networks. It was found that there was a relationship between the awareness of the information and the amount of publicity generated around the terminology. Furthermore, the primary driver for the increase in awareness was an increase in publicity in either a positive or a negative light. Sentiment analysis further confirmed that the primary emotive connections to the words were derived from the original context in which the word was framed. Thus having awareness or knowledge of a topic is strongly related to its public exposure in the media, and the emotional context of this relationship is dependent on the context in which the relationship was originally established. This has value in fields like conservation, law enforcement, or other fields where the practice can and often does have two very strong emotive responses based on the context of the problems being examined.     

Spatial and temporal dynamics of phytoplankton communities along a regulated river system, the Nakdong River, Korea

The longitudinal distribution and seasonal fluctuation of phytoplankton communities was studied along the middle to lower part of a regulated river system (Nakdong River, Korea). Phytoplankton biomass decreased sharply in the middle part of the river (182 km upward the estuary dam), and then increased downstream reaching a maximum at the last sampling station (27 km upward the estuary dam). In contrast, there was little downstream fluctuation in species composition, irrespective of pronounced differences in nutrient concentrations (TN, TP, NO₃, NH₄, PO₄) as well as in algal biomass. In the main river channel, small centric diatoms (Stephanodiscus hantzschii, Cyclotella meneghiniana) and pennate diatoms (Synedra, Fragilaria, Nitzschia) were dominant from winter to early spring (November–April). A mixed community of cryptomonads, centric and pennate diatoms, and coenobial greens (Pediastrum, Scenedesmus) was dominant in late spring (May–June). Blue-green algae (Anabaena, Microcystis, Oscillatoria) were dominant in the summer (July–September). A mid-summer Microcystis bloom occurred at all study sites during the dry season, when discharge was low, though the nutrient concentration varied in each study site. Nutrients appeared everywhere to be in excess of algal requirement and apparently did not influence markedly the downstream and seasonal phytoplankton compositional differences in this river.     

Patterning limnological characteristics of the Chilika lagoon (India) using a self-organizing map

In this study, a self-organizing map (SOM) was utilized to classify habitats in the Chilika lagoon located in India, the largest lagoon ecosystem in Asia (maximum length, 64.3 km; mean width, 20.1 km). The lagoon was marginally eutrophic (nitrate, 0.25 ± 0.22 mg L⁻¹; orthophosphate, 0.26 ± 0.22 mg L⁻¹; n = 1,980, respectively) for six years (1999–2004), and it used to be warm, shallow, turbid and predominantly brackish. The SOM model successfully identified the changing patterns of limnology in the lagoon using the monthly limnological dataset from 30 study sites (July 1999–December 2004). Comparative re-sectoring evaluation of current monitoring sites was accomplished based on the outcome of the modeling. The new site clustering that emerged from the model was similar to conventional ones, and several sites were reorganized. Water physicochemistry was affected by freshwater inflow during monsoon and the new lagoon mouth constructed in September 2000, which resulted in variations in site characteristics in terms of limnology. The results of this study may provide information on the limnological patterns in Chilika lagoon, and they leave room for further study into functional changes in the lagoon ecology with respect to changes in climatic factor, freshwater flow and lagoon morphology.     

Use of large web-based data to identify public interest and trends related to endangered species

Use of the Internet by an increasing number of people to search for information related to varying disciplines has led to more precise data on societal views and trends. We used web search log data from a 6-year period and examined characteristics related to public interest in endangered species. Web search data for 246 endangered species as determined by the Ministry of Environment of Korea were evaluated. Relative search volumes for species were correlated with the status of conservation practices, and a self-organizing map (SOM) was used to analyze the relationship among selected variables. The relative search volume for higher taxa, including mammals, birds, amphibians and reptiles, were ten times higher than those for other taxa. SOM clusters were mainly divided according to the rank designation of the endangered species and the existence of a conservation facility dedicated to the species. The relative search volume and amount of web materials were the highest for the most highly ranked species. A positive relationship between the relative search volume and number of printed media articles (β 2.68; R ² 0.45; p < 0.0,001) and a negative relationship between the length of the common name of a species and number of printed media articles (β ?125.7; R ² 0.48; p = 0.024) were found. The evaluation of endangered species by using web-based data can be useful to improve conservation tools, including using feedback to facilitate interaction among political, scientific, and socio-economic interests.     

Changes of fish assemblages after construction of an estuary barrage in the lower Nakdong River,South Korea

In the Nakdong River, an estuary barrage was constructed in 1987, and it divided the freshwater and the seawater, resulting in a change in the ecosystem. To estimate the impact of barrage construction on fish assemblages, we evaluated 20 years of monitoring data before and after the construction of the estuary barrage, and evaluated the role of fishways. The barrage construction generated entire changes of fish assemblages. After construction, the number of fish species dropped sharply, and 36 species disappeared. Conversely, 18 species appeared at this site, including eight freshwater species, seven of which were exotic or translocated species. Barrage construction affected freshwater fish more severely than it did estuarine and marine species because of the existence of an estuarine environment below the barrage. We did not detect any evidence of recovery of fish assemblages. A total of 31 species were collected at fishways, and the number of individuals collected at each fishway was positively correlated with the amount of discharge from the estuary barrage, mean daily tide level, and water temperature. Migratory fish using a fishway had obvious occurrence periods. Therefore, the efficiency of fishway use can be increased if an appropriate management plan is prepared and implemented.