Lake Kasumigaura Research Articles

Long-term changes in phytoplankton community, mainly cyanobacteria in Lake Kasumigaura, Japan

Long-term changes in phytoplankton community, mainly cyanobacteria in Lake Kasumigaura, Japan

Relationship between fish traits and the methane‐derived carbon contribution to fish in a shallow lake

Abstract Although the transfer of methane‐derived carbon (MDC) to benthic macroinvertebrates such as chironomid larvae and oligochaetes has been well documented, knowledge of the transfer of MDC to fish is limited. We investigated the MDC contribution to 28 fish species through their growth stages and examined the relationship between fish traits including body size, and MDC contribution to fish within species in Lake Kasumigaura, Japan. We used carbon stable isotope ratios and a two‐source mixing model (methane‐oxidation bacteria [MOB] and particulate organic matter) to estimate the MDC contribution to fish. The MDC contribution to individual fish ranged from 0% to 21.5%. Anguilla japonica showed the highest MDC contribution (mean 3.8%). Fish species were classified into four groups according to two criteria: (a) whether the correlation between the MDC contribution and fish size (within species) was significantly negative (negative vs. not significant; ns); and (b) whether the 90th percentile of MDC contribution was 0% or not. The mean MDC contribution was highest (2.18% ± 2.93%, 12 species) for the group with (a)ns/(b)>0%, including the high contribution species such as Abbottina rivularis (mean 5.5%) and Biwia zezera (mean 9.8%). This group (12 species) included relatively high numbers of benthic habitat use (eight species) and omnivores (nine species). The mean MDC contributions were almost zero for the group with (a)ns/(b)=0% (seven species), which included only two species of benthic habitat use and one species of omnivores. The mean MDC contributions were intermediate for the other groups with (a)negative/(b)>0% (1.30% ± 1.17%, seven species) and (a)negative/(b)=0% (0.10%, two species). The negative correlation between fish size within species and MDC contribution in groups with (a)negative/(b)>0% and (a)negative/(b)=0% indicated that ontogenetic habitat and dietary shifts induced changes in MDC transfer. Our results suggest that 21 out of 28 fish species were involved in the MDC transfer in a shallow lake, but variation in MDC transfer could be explained by fish traits (trophic guild and habitat use). Although the mean MDC contribution to all fish species was low (0.61% ± 1.97%), the roughly estimated annual consumption rate of fish on MOB corresponded to approximately 10% of the MOB production in the sediment, suggesting that fish contribute to methane dynamics from the perspective of biogeochemical cycles.

Estimating the concentration of total suspended solids in inland and coastal waters from Sentinel-2 MSI: A semi-analytical approach

Inland and coastal waters provide key ecosystem services and are closely linked to human well-being. In this study, we propose a semi-analytical method, which can be applied to Sentinel-2 MultiSpectral Instrument (MSI) images to retrieve high spatial-resolution total suspended solids (TSS) concentration in a broad spectrum of aquatic ecosystems ranging from clear to extremely turbid waters. The presented approach has four main steps. First, the remote sensing reflectance (Rrs) at a band lacking in MSI (620 nm) is estimated through an empirical relationship from Rrs at 665 nm. Second, waters are classified into four types (clear, moderately turbid, highly turbid, and extremely turbid). Third, semi-analytical algorithms are used to estimate the particulate backscattering coefficient (bbp) at a reference band depending on the water types. Last, TSS is estimated from bbp at the reference band. Validation and comparison of the proposed method with three existing methods are performed using a simulated dataset (N = 1000), an in situ dataset collected from global inland and coastal waters (N = 1265) and satellite matchups (N = 40). Results indicate that the proposed method can improve TSS estimation and provide accurate retrievals of TSS from all three datasets, with a median absolute percentage error (MAPE) of 14.88 %, 31.50 % and 41.69 % respectively. We also present comparisons of TSS mapping between the Sentinel-3 Ocean and Land Colour Instrument (OLCI) and MSI in Lake Kasumigaura, Japan and the Tagus Estuary, Portugal. Results clearly demonstrate the advantages of using MSI for TSS monitoring in small water bodies such as rivers, river mouths and other nearshore waters. MSI can provide more detailed and realistic TSS estimates than OLCI in these water bodies. The proposed TSS estimation method was applied to MSI images to produce TSS time-series in Lake Kasumigaura, which showed good agreements with in situ and OLCI-derived TSS time-series.

How useful are the lake surface temperature estimates from a geostationary satellite (Himawari-8) to detect seasonal and diurnal changes?

ABSTRACT The current geostationary satellite images have a time resolution of minutes. It is not clear how useful they are for detecting diurnal and seasonal changes. We tested this by comparing lake surface temperatures (LSTs) from Himawari-8 Advanced Himawari Imager (AHI) images with in situ measurements in Lake Kasumigaura, Japan, for one year. LST products of the Sentinel-3 satellites were also compared. We found that instantaneous LSTs can be estimated with an root mean square difference (RMSE) of 0.6°C. A large amount of data (N = 102–103) is available for each month, but N differs greatly in the range of 216–2771. A good agreement (RMSE of 0.9°C) was found between monthly mean LSTs from Himawari-8 and in situ measurements, and it is better than the RMSE of 1.2–1.7°C found for the Sentinel-3 LST products. The diurnal change detection was more difficult due to insufficient data numbers around noon. Practical remedies for this issue are suggested.

Will Planktothrix spp. become dominant again in Lake Kasumigaura? Analysis of phytoplankton community dynamics

Will Planktothrix spp. become dominant again in Lake Kasumigaura? Analysis of phytoplankton community dynamics

カモ類等によるレンコン食痕の形状と劣化の経過

To evaluate bird damage to lotus roots, Nelumbo nucifera Gaertn. （Proteales: Nelumbonaceae）, we collected 170 damaged roots from eight flooded lotus fields around Lake Kasumigaura. There were 258 samples of feeding marks, so-called “duck damage,” and 41 samples of disease damage. The shapes of the feeding marks were categorized into seven types: touch, sharp-peck, shallow-scoop, deep-scoop, boat, cross-section, and eat-up. We experimentally placed the lotus roots in a post-harvest lotus field and confirmed six types, excluding shallow-scoop, from our observation of the leftovers eaten by Eurasian Coots, Fulica atra L. （Gruiformes: Rallidae）, and Mallards, Anas platyrhynchos L. （Anseriformes: Anatidae）. To compare the shape of the damage with bill size, we tested on crows in captivity. While scars caused by numerous pecks impeded the identification of the suspect species, the width of a single sharp-peck by Eurasian Coots or Large-billed Crows, Corvus macrorhynchos Wagler （Passeriformes: Corvidae）, matched their bill width. In the mud of the lotus fields, the color around the feeding marks changed to purple-black after a couple of days, but the shapes did not change and differed from disease damage. Therefore, damaged roots claimed as “duck damage” were caused by ducks and coots’ feeding, and a single sharp-peck can be identified as being caused by coots’ pecking action.

Analysis of the complete mitogenome of Daphnia galeata from the Han River, South Korea: structure comparison and control region evolution.

Daphnia galeata is an important plankton in aquatic ecosystems. As a widely distributed species, D. galeata has been found throughout the Holarctic region. Understanding the genetic diversity and evolution of D. galeata requires the accumulation of genetic information from different locations. Even though the mitochondrial genome (mitogenome) sequence of D. galeata has already been reported, little is known about the evolution of its mitochondrial control region. In this study, D. galeata samples were collected from the Han River on the Korean Peninsula and its partial nd2 gene was sequenced for haplotype network analysis. This analysis showed that four clades of D. galeata were present in the Holarctic region. Moreover, the D. galeata examined in this study belonged to clade D and was specific to SouthKorea. The mitogenome of D. galeata from the Han River showed similar gene content and structure compared to sequences reported from Japan. Furthermore, the structure of control region of the Han River was similar to those of Japanese clones and differed substantially from European clone. Finally, a phylogenetic analysis based on the amino acid sequences of 13 protein-coding genes (PCGs) indicated that D. galeata from theHan River formed a cluster with clones collected from Lakes Kasumigaura, Shirakaba, and Kizaki in Japan. The differences in control region structure and stem and loop structure reflect the different evolutionary directions of the mitogenomes from Asian and European clones. These findings improve our understanding of the mitogenome structure and genetic diversity of D. galeata.

Evaporation and energy balance studies of Lake Kasumigaura

Evaporation and energy balance studies of Lake Kasumigaura

Synchronous decline of native bitterling population detected from 9 years of survey in rivers and agricultural ditches around Lake Kasumigaura, Japan

Synchronous decline of native bitterling population detected from 9 years of survey in rivers and agricultural ditches around Lake Kasumigaura, Japan

Vertical mixing and oxygen flux caused by daily sea breezes in a shallow stratified lake

Vertical transport caused by mixing is essential for understanding physical processes in lakes. However, mixing processes in shallow lakes are not well understood because of the lack of turbulence measurements. This study presents observations of vertical mixing and oxygen flux in a shallow lake, Lake Kitaura of the Lake Kasumigaura continuous lake system, which is located along the central eastern coast of the Japanese mainland. Mooring and microstructure surveys were conducted in August 2020. The vertical eddy diffusivity was estimated from the Ellison scale using high-frequency sampled temperature data from the mooring location, and the estimations were consistent with those observed from the microstructure profiler. The estimated eddy diffusivity revealed a mixing structure and oxygen flux in the lake during the study period. The daily cycle of stratification and mixing was caused by daily heating due to solar radiation and by winds from daily sea breezes, respectively. The daily stratification maximum occurred around noon, which suppressed vertical mixing. Vertical mixing was intensified due to sea breezes in the afternoon, which led to movement of oxygen from the surface layer to the bottom layer. The maximum vertical mixing was observed at 18:00. The oxygen concentration did not increase during nighttime when the negative surface heat flux was observed; thus, nighttime cooling may not primarily contribute to the vertical oxygen supply.

The composition of organic phosphorus in a river during the springtime irrigation period

Study regionThe study region was the Sakura River, a tributary of Lake Kasumigaura, Japan. Study focusWe asked whether particulate organic phosphorus (POP) contributed to the P cycle in rivers. Previous studies have focused on the interaction between PO43– and particulate inorganic P (PIP), but our study focused on whether POP could also be the source of PO43–. New hydrological insights for the regionAfter rain events during irrigation, concentrations of suspended particles and particulate P (PP) increased. POP accounted for 42.4 % of PP concentrations. The PIP and POP concentrations were both positively correlated with suspended particle concentrations. The PO43– concentrations were significantly higher during decomposition experiments when suspended particles were present in the water. Decomposition experiments revealed that the P composition changed and the proportion of organic P decreased as DNA-P disappeared from the PP. The fact that the DOP concentration was significantly lower in the treatment with suspended particles than without suspended particles suggested that DOP mineralization rates were increased by the presence of suspended particles. In addition to mineral-sorbed P, the POP derived from the irrigation of paddy fields may also be bioavailable.

Development of a Quantification and Detection Method for 2-MIB-producing Cyanobacteria

Consumers often complain about taste and odor (T&O) in drinking water and freshwater fishery. One of the common T&O compounds, 2-methylisoborneol (2-MIB), can be detected by humans even when the concentration is below 10 ng/L. A forecast method of T&O occurrence is required to control drinking water plants and fishery farms to determine the timing of exchange of activated carbon or exchange the water in earthy pond. Traditional monitoring methods such as PCR, microscopy, and chemical analysis require a long time, are high in cost, and have a complex operation. We conducted this study to develop whole-cell PCR and whole-cell qPCR assays for rapid detection and quantification of 2-MIB-producing cyanobacteria without DNA extraction to detect 2-MIB cyclase gene (mtc). Pseudanabaena foetida strain 1705-12 (Lake Kasumigaura), strain 1803-12 (Lake Kasumigaura), and strain PTG (Lake Biwa) of 2-MIB-producing cyanobacteria were used in the study. The positive correlation between the results of whole-cell PCR, whole-cell qPCR and chlorophyll a (Chl.a), and gene abundances illustrated that whole-cell PCR and whole-cell qPCR assays could rapidly and conveniently detect and quantify 2-MIB-producing cyanobacteria. Thus, this study provides a valuable tool for prediction of T&O events in drinking water and freshwater fishery.

Water temperature at the shore and center of Lake Kasumigaura during summer

Water temperature at the shore and center of Lake Kasumigaura during summer

Radiocesium accumulation in Lake Kasumigaura by riverine input and migration following the Fukushima Dai-ichi nuclear power plant accident

Vertical radiocesium concentration profiles and inventories in sediments were measured in Lake Kasumigaura following the 2011 Fukushima Dai-ichi Nuclear Power Plant accident. Further measurements of radiocesium concentrations in suspended solids (SS) have been conducted since September 2012 in the Koise and Sakura rivers inflowing into the lake. Cesium-137 (137Cs) accumulated intensively near the inflow outlets in the lake. At the lake center, the 137Cs inventory in sediments increased during 2011–2014; however, few changes were observed during 2014–2016. The 137Cs surface concentration and inventory decreased considerably in Tsuchiura-iri Bay until 3 years after the accident, indicating 137Cs migration. However, the rate of decrease subsequently slowed due to the 137Cs supply from the river. The 137Cs concentration in river SS declined during 2012–2015; however, it remained 1–2 orders of magnitude above its pre-accident level. The entrainment coefficient of particulate 137Cs in the inflows was initially higher in the Koise River but decreased exponentially more rapidly in the Koise River than in the Sakura River until 2015. Therefore, in the future, the difference in 137Cs concentrations will be smaller. The 137Cs concentration in the Koise River will continue to decrease; thus, the difference in the 137Cs inventory between the northern and southern parts of the lake will decrease. Total estimated amounts of 137Cs in the entire lake were 3.72 × 1012 Bq in December 2012 and 4.18 × 1012 Bq in August 2016. The accumulated amount of 137Cs in the entire lake based on sediment analysis was similar to the riverine input of particulate 137Cs based on riverine SS analysis from December 2012‒;August 2016, confirming the high trapping performance of the lake for particulate matter provided by the basin. Moreover, the amount of 137Cs accumulated in the lake in 2016 may have originated from comparable rates of atmospheric deposition and riverine input. These findings provide useful insights for future prediction and management of radiocesium contamination and the effects of riverine inputs in general shallow lakes.

Forecasting chlorophyll‐a concentration using empirical wavelet transform and support vector regression

AbstractAccurate forecast of chlorophyll‐a concentration of water bodies is important for aquatic management because it can support management decisions with future information. In this regard, this paper proposes a new chlorophyll‐a forecast method that combines empirical wavelet transform, support vector regression, and sine cosine algorithm. Chlorophyll‐a concentration data are decomposed by empirical wavelet transform, and then, support vector regression is employed to predict decomposed components, and finally, forecast value is obtained by reconstructing the predicted values for the decomposed components. Hyperparameters of support vector regression models are optimized by sine cosine algorithm. Our model is evaluated by chlorophyll‐a concentration data of Lake Kasumigaura, Japan. For the purpose of comparison, several other models are also developed. Result indicates that our method shows better forecast performance than other competitor models. This study demonstrates that data processing by empirical wavelet transform can significantly improve forecast accuracy and our method is a promising new forecast method for lake chlorophyll‐a concentration.

Does increased springtime solar radiation also increase primary production?

AbstractWe tested the hypothesis that long-term brightening of solar radiation and changes in the underwater light climate would increase the primary production of phytoplankton in the springtime in Lake Kasumigaura, Japan. Global solar radiation fluctuates on a decadal scale, and the solar radiation in May has been increasing since the 1990s in Japan. We developed a model of depth-integrated primary production (gC m−2 h−1) based on long-term monitoring data. The model based on photosynthesis-irradiance curve clarified that primary production increased by 13.2%, from 0.093 gC m−2 h−1 in 1992 to 0.105 gC m−2 h−1 in 2019, because of the combined effects of solar radiation and water temperature increases. Sensitivity analysis of the model showed that primary production was most sensitive to water quality parameters, i.e. the light attenuation coefficient and nutrient effects on Pmax. Nutrient effects were significantly correlated with the particulate organic carbon to nitrogen ratio, indicating that nitrogen shortage in phytoplankton cells may affect primary production. These results suggest that long-term springtime increases in solar radiation and water temperature increase primary production, but that water quality also controls primary production.

Temporal and interspecific dietary variation in wintering ducks in agricultural landscapes.

Farmlands are becoming more important as waterfowl foraging habitats, while natural wetlands are being lost globally. However, it is unclear how waterfowl coexist in agricultural landscapes by resource partitioning. We evaluated the diets of seven sympatric dabbling ducks foraging in rice paddy and lotus fields around Lake Kasumigaura, the second largest lake in Japan, during two wintering seasons (from November to February) by faecal DNA metabarcoding using chloroplast trnL and mitochondrial CO1 region sequences. We examined 420 faecal samples and found different patterns of dietary diversity and composition among the duck species. The pattern also differed between plant and invertebrate food. Dietary niche partitioning was clear in plant food. Large-bodied ducks intensively use crop plants, and other ducks might mediate competition by using terrestrial and aquatic plants that are suitable for their foraging behaviours or microhabitats. Dietary segregation among species was the most apparent in February, when the abundance of foraging ducks was the largest. This study illustrated the complex pattern of dietary niche partitioning of dabbling ducks in agricultural landscapes, which might be difficult to evaluate by conventional approaches. The availability of crop plants, as well as other plant food resources in flooted areas and farmland dikes, may enable ducks to coexist by spatial or behavioural resource partitioning.

Quantitative assessment of decadal water temperature changes in Lake Kasumigaura, a shallow turbid lake, using a one-dimensional model

To assess the decadal water temperature (WT) changes observed at the center of Lake Kasumigaura, a shallow turbid lake in Japan, we constructed a prediction model for WT. The thermal interactions among air, water, and sediment were simulated by a one-dimensional differential equation using hourly observations of meteorological and limnological parameters. The validated model showed good performance (i.e., <1 °C RMSE for the daily averaged WT) for 2012, 2013, and 2015, respectively, in both upper and lower water layers, which were attained by incorporating a physical sub-model regarding the surface water temperature (surface WT). The good description of seasonal, daily, and hourly changes in surface WT obtained with the sub-model was confirmed by the observed and simulated time series. We then quantified and evaluated the trends of the meteorological and limnological parameters influencing WT changes from 1979 to 2015 based on their effects on WT by using the prediction model with the increases in air temperature (AT), solar radiation (SR), wind velocity (WV), and turbidity during that period; then, WT in the former period (1979) was predicted according to the trends and compared with the measured WT. The observed WT changes during the period were quantitatively explained by the compound effects of the parameters' changes, i.e., the AT and SR raising the WT, and the WV and turbidity lowering the WT.

A Semianalytical Algorithm for Estimating Water Transparency in Different Optical Water Types from MERIS Data

Water transparency (or Secchi disk depth: ZSD) is a key parameter of water quality; thus, it is very important to routinely monitor. In this study, we made four efforts to improve a state-of-the-art ZSD estimation algorithm that was developed in 2019 on the basis of a new underwater visibility theory proposed in 2015. The four efforts were: (1) classifying all water into clear (Type I), moderately turbid (Type II), highly turbid (Type III), or extremely turbid (Type IV) water types; (2) selecting different reference wavelengths and corresponding semianalytical models for each water type; (3) employing an estimation model to represent reasonable shapes for particulate backscattering coefficients based on the water type classification; and (4) constraining likely wavelength range at which the minimum diffuse attenuation coefficient (Kd(λ)) will occur for each water type. The performance of the proposed ZSD estimation algorithm was compared to that of the original state-of-the-art algorithm using a simulated dataset (N = 91,287, ZSD values 0.01 to 44.68 m) and an in situ measured dataset (N = 305, ZSD values 0.3 to 16.4 m). The results showed a significant improvement with a reduced mean absolute percentage error (MAPE) from 116% to 65% for simulated data and from 32% to 27% for in situ data. Outliers in the previous algorithm were well addressed in the new algorithm. We further evaluated the developed ZSD estimation algorithm using medium resolution imaging spectrometer (MERIS) images acquired from Lake Kasumigaura, Japan. The results obtained from 19 matchups revealed that the estimated ZSD matched well with the in situ measured ZSD, with a MAPE of 15%. The developed ZSD estimation algorithm can probably be applied to different optical water types due to its semianalytical features.

Quantitative Assessment of Decadal Water Temperature Changes in Lake Kasumigaura, a Shallow Turbid Lake, Using a One-Dimensional Model

Quantitative Assessment of Decadal Water Temperature Changes in Lake Kasumigaura, a Shallow Turbid Lake, Using a One-Dimensional Model