Limnology最新文献

Organism size is considered a master trait influencing virtually every aspect of life, but the underlying mechanisms of phenotypic variation are still poorly understood. This study examined the valve size (length, height, width) of an ostracod species (Cyprideis torosa) collected from different lakes of the Mansfeld Lakes (ML), Central Germany. Size variability were investigated on different temporal (ecological and geological) scales and compared on different spatial (regional and local) scales. Statistical methods were applied to explore size variation between and within sample locations and the relationship between size traits and physical and chemical parameters (salinity, oxygen, temperature, pH). In ML no significant differences in size between contiguous lakes were detected but two morphotypes in males were identified in stratigraphically separated Holocene samples and co-occurring within Recent samples. Seasonal effects were detected for females (smaller size in spring than in autumn) and males (smaller size range in spring, higher variability in autumn). The correlation of size traits with environmental parameters revealed no general patterns, but a locally limited correlation between size and salinity in ML exists. On spatial and temporal scales, males and females show sex-specific size patterns, possibly due to differences in life history traits or selection pressure.

Stable isotope ratios of nitrate (NO₃⁻) can be used as a tool to investigate NO₃⁻ dynamics in watersheds over the world. However, most of the NO₃⁻ source analyses from watersheds using isotopes have been conducted during baseflow conditions, and more information is required on conditions during rainfall, which is a crucial period for nitrogen export to downstream ecosystems. Additionally, there is limited information regarding the sources of stable isotopes of NO₃⁻ in watersheds of Japan. We measured the nitrogen and oxygen isotopes of NO₃⁻ (δ¹⁵N–NO₃⁻ and δ¹⁸O–NO₃⁻) in the Yasu River during baseflow and rainfall events and those from major NO₃⁻ sources in the watershed. The δ¹⁵N–NO₃⁻ exported from forests and rice paddies showed small fluctuations, while there were large fluctuations in the δ¹⁵N–NO₃⁻ exported from sewage treatment plants, suggesting the need to obtain data on δ¹⁵N–NO₃⁻ exported from sewage treatment plants. The NO₃⁻ concentrations in the Yasu River during summer baseflow were too low to be explained by the mixing of NO₃⁻ sources within the watershed, suggesting that NO₃⁻ consumption processes within the river and groundwater influence the NO₃⁻ concentrations. Furthermore, the sources of NO₃⁻ exported from the watershed differed during baseflow and rainfall, with a larger contribution of forest-derived NO₃⁻ during rainfall. Monitoring during rainfall is therefore essential to determine the sources of NO₃⁻ exported from the watershed.

The environmental DNA (eDNA) method is potentially useful to detect the diurnal activity of aquatic organisms. Seasonal changes in the diurnal activities of the endangered semiaquatic water shrew, Chimarrogale platycephalus, were investigated to evaluate the efficiency of the eDNA method in their tracking. We conducted hourly field surveys for a period of 25 consecutive hours in two streams quarterly, using a species-specific primer and camera trap observations. Using qPCR, we compared the frequency and concentration of eDNA detected between day and night, seasons, and streams. In both streams, eDNA was detected consistently with temporal fluctuations during all seasons for nighttime. However, during daytime, eDNA was detected in all seasons except autumn, in which it was detected only in one stream. This suggests that species activity occurs throughout both daytime and nighttime in winter, spring, and summer, and potentially less during the daytime in autumn, probably due to the lack of competition and energy constraints during that season, as most individuals were non-breeding in autumn and avoided the habitation of areas with high density after the dispersal of their offspring. The high eDNA concentration in summer may be attributable to the higher density of non-breeding individuals after the offspring left the nest and/or to the increased activity owing to the competition for food or space. The diurnal activities of species detected using eDNA sampling allow us to obtain detailed ecological information, which is beneficial for managing conservation in the future.

The redox conditions in the littoral limnic sediments may be affected by the penetration of plant roots which provide channels for oxygen transport into the sediment while decomposition of the dead roots results in consumption of oxygen. The goal of this work was to study the impact of environmental parameters including penetration of roots of Cyperus articulatus L. into the sediments on cycling of the redox-sensitive elements in Lake Kinneret. We measured roots content, porosity, and chemical parameters including pH, sulfur, iron and manganese speciation in the sediments from the shore, littoral and sublittoral zones with and without vegetation. Our results show that at ≥ 12 m water depth, the upper 10 cm of the sediments are affected by the active sulfur cycling with concentrations of hydrogen sulfide > 70 μM near the sediment–water interface. Speciation of sulfur, iron, and manganese in the upper 10 cm of littoral sediments, which are covered by < 20 cm of water, are affected by their permeability and, to a lesser extent, by roots penetration. In the case when sediments are not covered by water, oxygen penetration to the sediments by desiccation is an additional important control of the redox zonation in the surface sediments. In the shore sediments, despite relatively high concentrations of sulfate in the pore-waters, sulfur cycling may be described as “cryptic” as expressed by very low concentrations of hydrogen sulfide in the pore-waters. This is most likely a result of its fast reoxidation by the abundant highly reactive Fe(III) and Mn(IV) phases.

The responses of assemblages and ecosystems to river intermittency are often considered on large spatial scales, such as those associated with the Köppen climate classification. However, river intermittency may naturally occur even in humid regions, and the effects may differ from those where intermittency occurs throughout the area. This study aimed to examine the differences in taxonomic and trait composition of aquatic insects between intermittent rivers in the Seto Inland Sea watersheds and neighboring humid-temperate rivers in Japan using national census data. While the climate in the most part of the Japanese Archipelago is categorized as humid-temperate, and rivers are usually perennial, local climate in the Seto Inland Sea watersheds has low summer precipitation compared with that in neighboring regions, thereby resulting in river intermittency. Consistent with the previous studies in the regions where rivers are intermittent on a large spatial scale, we observed that aquatic insects with multivoltinism and/or aerial respiration notably tolerated river intermittency. In contrast, the aquatic insect fauna in Japanese intermittent rivers represented subsets of those in the humid-temperate rivers, although previous studies such in Mediterranean regions have reported high endemism and species diversity in intermittent rivers. These results highlight the importance of exploring the role of river intermittency on small to medium spatial scales, as well as on large scales, to project effects of ongoing and future climate changes on species diversity.

Testate amoebae are widely used as proxies in palaeoecological reconstructions of lacustrine environments. However, our knowledge on their morphological adaptation to depth is still limited. This study aims to determine correlations between the morphological and size structure of testate amoeba communities and depth and some other environmental variables along a depth gradient from 0 to 57 m in mesotrophic Valdayskoe Lake, Russia. The morphological structure of testate amoeba communities in the bottom surface sediments of the lake and their distribution along the depth gradient were described. Redundancy analysis indicated that sampling depth, temperature, pH, and slope angle significantly explained the total variance in the community compositions, which were classified into three morphological groups. The set of morphotraits of testate amoebae communities differed drastically above and below the thermocline and may be used as an indicator of the depths. Above and below the thermocline, the morphological structure of testaceans is also determined by other environmental variables associated with the habitats they were found. The weighted and median body size of testate amoebae generally decreases with depth, but bottom relief influences the body size structure of the community via differences in the accumulation of organic matter on slopes and flat sites. These data may contribute to a better interpretation of palaeoecological records of subfossil testate amoebae in lacustrine surface sediments and serve as a basis for the development of a transfer function for reconstructing lake depths.

Herbivorous invaders promote changes in community structure and ecosystem functioning. The apple snail, Pomacea canaliculata, is an invader with strong impacts on wetland vegetation and aquatic crops. While able to feed on diverse trophic resources using different feeding mechanisms it is usually regarded as a macrophytophage. However, studies showing direct evidence of what they actually eat in natural waterbodies are few and their results do not fully support such a feeding habit. We analyzed the digestive contents of P. canaliculata using a micrographic technique to describe the spatiotemporal variation of its natural diet within its native range. Stomach and intestine contents were similar but the intestines were never empty and their volume and diversity were generally higher. Detritus was the dominant food item (84.1% of total abundance) and was consumed by all the snails whereas macrophytes were eaten by only half of the snails and represented only an 8.6% of total abundance; filamentous algae, animal remains and grasses showed lower than 5% of total abundance. The spatiotemporal variation in these feeding patterns was minor, despite the among site variation in macrophyte coverage and richness. In the Encadenadas del Oeste basin, P. canaliculata behaves as a specialist on detritus, with some individuals occasionally consuming other resources and can thus be described as an opportunistic generalist omnivore. The impacts of apple snail invasions on both detritus and on other detritivores have seldom been studied although they may have important negative and positive effects, respectively, on dead vegetal matter decomposition.

Sampling was done over a year (December 2020–November 2021) to study the distribution and species composition of phytoplankton in the southwestern Caspian Sea. Sea water from various depths was collected along four transects: Lisar, Anzali, Sefidrood and Chaboksar, with a total of 12 stations. A comparison was then made with the data collected in 1996 to look at the long-term changes. The increase in sea water temperature and salinity, especially in summer, was observed in the present study, which was possibly due to global warming and climate change. Amongst 48 identified phytoplankton species, Bacillariophyta (80.0%) and Cyanophyta (11.0%) were dominant. Phytoplankton abundance was measured as 99,775 ± 30,200 cell L⁻¹ on average. The highest abundance was a non-native species Pseudo-nitzschia seriata (H. Peragallo 1900) from Bacillariophyta with more than 17,000 cell L⁻¹, followed by another toxic species Nodularia spumigena (Mertens ex Bornet and Flahault 1888) from Cyanophyta. The N. spumigena species had the highest abundance as 5,000,000 cell L⁻¹ in July 2021 at the Anzali region. Nutrient increase of more than threefold in 2020–2021 has caused a sevenfold increase of chlorophyll-a as compared to that in 1996. The increases in nutrients levels, sea surface temperature (> 30 °C) and salinity are generally regarded as important factors to cause variations in phytoplankton abundance and composition. The sevenfold increase of phytoplankton abundance between 1996 and 2020–2021 and change of trophic state from oligotroph to mesotroph, indicated the increase of stress and pressure on the native phytoplankton community.

This study investigated morphological differences, habitat preference, and ecological niche overlap in two sympatric Capoeta species i.e., Capoeta. damascina and Capoeta umbla collected from the Sirvan river drainage. Ten environmental factors, including pH, temperature, electrical conductivity (EC), total dissolved solids (TDS), river width, river depth, flow velocity, altitude, slope, and dissolved oxygen (DO) were measured during sampling time. A total of 17 morphometric characteristics were measured using digital calipers for traditional morphometrics (TM). For the geometric morphometric method (GM), 2D pictures were taken from the left side of the fresh samples, by tpsDig2 software, and 16 landmark points were defined and digitalized to extract body shape data. The data were analyzed using t-test, Mann–Whitney, principal component analysis (PCA), and discriminant function analysis based on the P-value of Hotelling’s T-squared. The ratio of the common area under the graph to the total area of habitat suitability indices was defined as the ecological niche overlap. The results showed significant differences in eye diameter, predorsal, caudal peduncle length, preanal, preventral, ventral-pectoral, body depth, and caudal peduncle depth traits (P < 0.05) in TM, and those differences in the GM were related to the position of the snout, head and body depth and caudal peduncle length i.e., C. damascina had the deeper body shape and head, and anterior the snout and caudal peduncle length. Based on the results, C. damascina prefers areas with higher pH and temperature and by increasing other studied factors, its habitat suitability decreased. The preference for C. umbla with increasing river depth and DO was increased. These two species showed low niche overlap i.e., they avoid competition in their habitat by opting for different areas in terms of river width, flow velocity, and temperature that have more depth with higher slope microhabitats.

Freshwater invaders threaten both natural ecosystems and human activities. An invasive freshwater sponge Heterorotula multidentata (Weltner, 1895) has been found for the first time in continental waters of Europe (Spain). It is a species native to Australia and New Zealand, from which it spread to Japan, being considered invasive. The species has been found in water intake grids of irrigation and drinking water systems in the basins of the Guadalquivir and Tajo rivers, affecting their hydrological functions. It has also been found growing on the invasive mussel Dreissena polymorpha in the Guadalquivir River. To assess the risks associated with invasive alien organisms, a detailed knowledge of their taxonomic status and distribution is necessary. A morphological and molecular evaluation confirmed that the specimens found in Spain belong to the Japanese type. A full morphological description and the fouling problems caused by the species are also provided. It is not yet clear how H. multidentata arrived at Spain, but indirect transport by other invasive freshwater species cannot be ruled out either, as H. multidentata has been found fouling the invasive species zebra mussel.