Limnology

One of the challenges facing megacities in South Asian developing countries in their attempts to realize so-called urban rejuvenation is groundwater conditioned by canal seepage and immense sewage loads. To understand the connection between groundwater pollutants and urbanization, numerous studies were reviewed, and data obtained from a variety of national and international organizations were analyzed. In Delhi and Dhaka, urbanization has lowered the groundwater level as a result of severe overextraction, and its dense population makes Delhi particularly vulnerable to groundwater pollution. In the coastal areas of Karachi and Mumbai, such pollution is magnified by the proximity of seawater as well as the increasing populations of these areas. Among the groundwater pollutants associated with urbanization, chlorides and nitrates are the chief anthropogenic toxins; thus, they are examined in this study. This paper concludes with policy recommendations for minimizing the impact of urbanization on groundwater.

Understanding how the occurrence and abundance of invasive species vary over time and the environmental factors that cause such variation is important for managing and controlling invasive species. To date, studies with this perspective remain scarce in the Neotropics. We used a database describing 12 years of the occurrence of an invasive rotifer (Kellicottia bostoniensis) in a large neotropical wetland (230 km2) (upper Paraná River) since 2000. We investigated how multiple local abiotic and biotic environmental variables jointly affect occurrence and abundance of an invasive zooplankton species (K. bostoniensis). The abundance and occurrence of K. bostoniensis varied significantly over time, with a marked increase after 2009. Furthermore, biotic (native zooplankton abundance, chlorophyll-a) and abiotic (turbidity, and water level) variables were important drivers of K. bostoniensis. Whereas native zooplankton and turbidity were negatively associated with the occurrence and abundance of K. bostoniensis, chlorophyll-a and water level were positively related. Furthermore, as biotic and abiotic variables naturally fluctuate to extremes, the occurrence and abundance of K. bostoniensis were reduced. Collectively, our findings underline the important role of local variables, particularly, native zooplankton and turbidity to control the abundance and occurrence of K. bostoniensis. Our results also suggest that maintaining natural extreme oscillations of the local variables can be effective in the management of invasive species.

To identify the geosmin-producing organisms in Lake Shinji, Japan, we conducted preliminary chemical and biological investigations from April to July 2008, during which odor occurrence was observed. Geosmin was mainly detected in the suspended substance (SS) of lake water, and its concentration corresponded to the cell numbers of Coelosphaerium kuetzingianum (Cyanophyceae) and Monoraphidium contortum. C. kuetzingianum and Pseudodictyosphaerium minusculum (Chlorophyceae; which occurred only in April) were separated from the lake water of 30 April to the lighter, interlayers in a step density gradient medium. The highest concentration of geosmin was detected in the portion of the lightest layer separated from the water sample by gas chromatography mass spectrometry (GC/MS). Observation under optical microscope confirmed that abundant C. kuetzingianum with some P. minusculum and a very rare unknown material was retained in this portion. Similarly C. kuetzingianum was separated by the step density gradient medium from the sediment of 7 May. Abundant C. kuetzingianum with rare bacteria was recognized in the portion of the lightest layer, which contained the highest concentration of geosmin. The cell numbers of C. kuetzingianum correlated with the concentration of geosmin in the separated portions of water samples. These results suggest that C. kuetzingianum probably produced geosmin, although there has been no report about this to now.

Water bodies of West Siberia mainly belong to the Ob River basin, which is not connected to other basins by shipping canals. The relative isolation of the basin predetermined the major role of industrial fisheries and aquarium trade in alien invertebrate transfer into the basin reservoirs. About 60% of the alien species were introduced into water bodies of West Siberia through industrial fisheries, and about 40% through aquarium fisheries. This paper is the first attempt to supplement a list of alien aquatic invertebrates from the Ob River basin. The data on the spread of 21 known non-indigenous species of invertebrates in this area are available. It should be noted that 7 species were deliberately introduced to enhance food reserves for fish, 8 were released by aquarists, 5 were inadvertently released during fish and forage organism introduction, and 1 (a crayfish) was imported for human consumption. For species with a known establishment period, there was a prolonged lag time in cases of both intentional and inadvertent introduction. The high invasion rate in the relatively isolated water bodies of the Ob River basin is comparable to that in Europe; hence, establishment of control over fishery-induced movement of alien invertebrates is required.

The impact of Pseudorasbora parva, a common zooplanktivorous fish species in Japan, on a zooplankton community was analyzed in experimental tanks, half of which were stocked with the fish. Different zooplankton species showed different responses to the introduction of the fish. In the presence of the fish, the populations of the large cladoceran Ceriodaphnia and the predatory copepod Mesocyclops were reduced, but the population of the herbivorous copepod Eodiaptomus and the small cladocerans Bosmina fatalis and Bosminopsis deitersi increased relative to the controls. The increase of Mesocyclops seen in the control tanks might have suppressed the populations of the small cladocerans, which are vulnerable to invertebrate predation. The results suggest that the population densities of the large prey items preferred by the fish, Ceriodaphnia and Mesocyclops, were controlled directly by fish predation, but the population densities of the smaller and less preferred zooplankton were controlled indirectly through the food-web cascade.

An effective way to access processes of ecological communities and ecosystems is the use of functional traits; therefore, the use of the functional characteristics of diatoms in paleolimnological works has been growing. In this study, the variations in the abundance of functional traits of sedimentary diatoms were evaluated in two lakes (Garças Lake and Patos Lake), from a subtropical floodplain, which present different intensities of influence of dams. Diatom community functional diversity and functional beta decomposed were calculated. A core from each environment was collected and samples of approximately 50 years were used. According to the functional diversity results, the two lakes showed different patterns, with a greater functional variation in Garças Lake. Through functional beta diversity results, the lakes showed similar results. Both showed a reduction in the functional diversity values and substitution of traits, after the 1980s in Garças Lake, and after ~ 2008 in Patos Lake. In these periods, both environments showed dominance of the same functional categories related to high turbulence and lower waters. The results suggest hydrological changes in the two lakes, which may have been driven by dams close to the floodplain.

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.

Natural fluctuations in ecosystems, such as those associated with climate, are a fundamental factor structuring macroinvertebrate assemblages. Given that macroinvertebrates are widely used in biomonitoring of aquatic systems, it is necessary assess the potential effects of seasonality on this group to avoid confusing its effects with the effects of anthropogenic impacts. In the present study, the richness, assemblage composition, and abundance of macroinvertebrates of Amazonian streams (n = 23) were compared among four periods—the start and apex of dry period, and the start and apex of rainy period. For these comparisons, were considered the conditions of the streams in three categories: (i) pristine, (ii) impacted by deforestation, and (iii) impacted by deforestation and pollution with raw sewage. The results indicate no significant variation among periods in the richness (p = 0.397), abundance (p = 0.420), and assemblage composition (p = 0.274) of the macroinvertebrates, which respond to anthropogenic impact irrespective of the seasonal period. Given this, representative samples can be obtained during any given period of the year, reducing field costs and sample processing time, enabling the reliable and rapid diagnosis of streams.