Variations In Water Temperature Research Articles

Towards i5 Ecohydraulics: Field Determination of Manning’s Roughness Coefficient, Drag Force, and Macroinvertebrate Habitat Suitability for Various Stream Vegetation Types

Ecohydraulic models have commonly used the flow velocity, water depth, and substrate type (i3 models) as the three fundamental determinants of the distribution of freshwater biota, but a fourth determinant has largely been neglected: stream vegetation. In this study, we provide the hydraulic and habitat information required to develop vegetation-adapted ecohydraulic models (i4 models) in streams. We calculated drag forces and Manning’s roughness coefficients (nV) for nine types of submerged, emergent, and overhanging stream vegetation. In addition, we developed habitat suitability curves (HSCs) for benthic macroinvertebrates for these stream vegetation types. Hydraulic modules can now be upgraded to simulate stream vegetation by including the vegetation-adapted nV values within an additive approach in which nV is added to the n value of the inorganic substrate to which the vegetation is rooted. Habitat modules can also be upgraded to include macroinvertebrate HSCs for stream vegetation, again by adding the vegetation-adapted habitat suitability to that of the inorganic substrate to which the vegetation is rooted. In combination, i4 ecohydraulic models (including vegetation) can now be designed and applied, and we suggest that ecohydraulic research should further focus on including a fifth variable (water temperature) to ultimately advance to i5 ecohydraulic models that will optimally simulate the hydroecological reality.

The Analytical Solution of an Unsteady State Heat Transfer Model for the Confined Aquifer under the Influence of Water Temperature Variation in the River Channel

The effect of water temperature variation in a river channel on groundwater temperature in the confined aquifer it cuts can be generalized to a one-dimensional thermal convection-conduction problem in which the boundary water temperature rises instantaneously and then remains constant. The basic equation of thermal transport for such a problem is the viscous Burgers equation, which is difficult to solve analytically. To solve this problem, the Cole–Hopf transform was used to convert the second-order nonlinear thermal convection-conduction equation into a heat conduction equation with exponential function-type boundary conditions. Considering the difficulty of calculating the inverse of the image function of the boundary function, the characteristics and properties of the Laplace transform were used to derive the theoretical solution of the model without relying on the transformation of the boundary function, and the analytical solution was obtained by substituting the boundary condition into the theoretical solution. The analytical solution was used to analyze the temperature response laws of aquifers to parameter variation. Subsequently, a 40-day numerical simulation was conducted to analyze the boundary influence range and the results from the analytical method were compared to those from the numerical method. The study shows that: (1) the greater the distance from the river canal and the lower the aquifer flow velocity, the slower the aquifer temperature changes; (2) the influence range of the river canal boundary increases from 18.19 m to 23.19 m at the end of simulation period as the groundwater seepage velocity v increases from 0.08 m/d to 0.12 m/d; (3) the relative errors of the analytical and numerical methods are mostly less than 5%, confirming the rationality of the analytical solution.

Responses of Water Temperature and Level to Large Earthquakes in Tibet

Well water levels can reflect the stress placed on a confined subsurface aquifer system in a similar manner to a strain meter. Based on observations of the geophysical field in Lhasa combined with digital data recorded at an underground fluid well at the Lhasa geomagnetic station in recent years, we comprehensively analyzed the characteristics of co-seismic changes caused by 14 different-magnitude M ≥ 5 earthquakes recorded in the well. The results show that (1) the co-seismic changes in water temperature and water level are different; the water level exhibits oscillation-type changes, while the water temperature variations indicate first heating and subsequent recovery. (2) The co-seismic changes are related to the epicentral distance, magnitude and focal depth of the earthquake. The closer the epicenter is to the well, the earlier the co-seismic responses occur, but the time interval between the co-seismic changes in the water level and temperature differs. (3) The co-seismic ratio of the water temperature is higher than that of the water level; this may be related to faulty water level instrumentation or segmented records.

A methodology to uncertainty quantification of essential ocean variables

The goal of this study is to provide a universally applicable procedure for a systematic evaluation of in situ measured data from single sensors regarding quantifying the uncertainty of the measurement results. As determining uncertainty for an environmental parameter also depends on the parameter itself, the focus here will be set on the variable water temperature in the first place. A separate analysis for salinity and other data will follow in later publications. With this first of a series of planned manuscripts on different parameters, we aim at providing a common understanding of how measurement uncertainty on single sensor measurements can be derived. Using an experimental in situ set-up with 6 different standard CTD sensors of two different brands, we created a four month-long, high-quality data set to be used to develop a reliable method for quantifying measurement uncertainties. Although the CTDs were deployed in a mooring in a coastal environment the described method can be extended to other deployment configurations as well. The described procedures have evolved as a stepwise process that takes the different perspectives of the involved authors into account, as well as the special conditions for environmental measurements, which are collected while the observed volume/area is undergoing a constant change. By sharing the ideas with other stakeholders, the basic concept can be extended to other observing programs and to other essential ocean variables.

Modelling spatial and temporal variability of water temperature across six rivers in Western Canada

AbstractIncreasing river water temperature in response to the warming climate is concerning for water quality and ecosystem health of rivers. This study provides an assessment of the spatio‐temporal variability of the ongoing and potential future river water temperature (Tw) change in western Canada. We use the air2stream model to reconstruct historical Tw dataset for 17 stations across six rivers, and employ the reconstructed Tw to analyze hydro‐climatic controls, trends, and sensitivities in relation to air temperature (Ta) and discharge. Results provide insights on the contrasting summer (July and August) Tw responses. While Tw is primarily Ta controlled for the northern rivers, discharge exerts increasing influence that approaches Ta control for the southern rivers. Trends in Tw are increasing and spatially varied, with significant increases and occurrences above the critical 18 and 20°C thresholds for the southern Fraser and Similkameen Rivers. A sensitivity analysis indicated 0.5–1.5°C Tw increases for a 2.0°C Ta increase, and 0.2–0.6°C Tw increases for a 20% summer discharge decline. Overall, the results provide critical information for understanding the river ecosystem health, such as cold‐water species habitat.

Coastal upwelling generates cryptic temperature refugia

Understanding the effects of climate-mediated environmental variation on the distribution of organisms is critically important in an era of global change. We used wavelet analysis to quantify the spatiotemporal (co)variation in daily water temperature for predicting the distribution of cryptic refugia across 16 intertidal sites that were characterized as ‘no’, ‘weak’ or ‘strong’ upwelling and spanned 2000 km of the European Atlantic Coast. Sites experiencing weak upwelling exhibited high synchrony in temperature but low levels of co-variability at monthly to weekly timescales, whereas the opposite was true for sites experiencing strong upwelling. This suggests upwelling generates temporal thermal refugia that can promote organismal performance by both supplying colder water that mitigates thermal stress during hot Summer months and ensuring high levels of fine-scale variation in temperature that reduce the duration of thermal extremes. Additionally, pairwise correlograms based on the Pearson-product moment correlation coefficient and wavelet coherence revealed scale dependent trends in temperature fluctuations across space, with a rapid decay in strong upwelling sites at monthly and weekly timescales. This suggests upwelling also generates spatial thermal refugia that can ‘rescue’ populations from unfavorable conditions at local and regional scales. Overall, this study highlights the importance of identifying cryptic spatiotemporal refugia that emerge from fine-scale environmental variation to map potential patterns of organismal performance in a rapidly changing world.

The Influence of Reservoirs on Water Temperature in the Downstream Part of an Open Watercourse: A Case Study at Botovo Station on the Drava River

The air temperature trends measured at the central meteorological station Varaždin and the water temperature measured at the Botovo station on the Drava River were analyzed from 1 January 1969 to 31 December 2021. Analyses were performed for three different time scales: year, month, and day. Mann–Kendall testing statistically determined the significant trends over the analyzed period and found increasing air and water temperatures. From 1975 to 1989, three reservoirs of different volumes and water surface areas were built. The Botovo water measuring station is 11 km from the third largest reservoir and 28 km from the mouth. Applying the day-to-day (DTD) method, we determined that the variations in the daily air temperatures are significantly higher than the simultaneous variations in the daily water temperatures. Also, the rise in water temperatures at the downstream water measuring station Botovo was influenced by the construction of reservoirs. The commissioning of the second reservoir in 1982 caused a significant rise in water temperature at the Botovo station. Trends in water temperature increase during all months of the year were statistically significant, while air temperature trends were statistically significant during the warm parts of the year.

A downcore calibration of the [formula omitted] temperature proxy for the Baltic Sea

The Baltic Sea is a marginal sea sensitive to climate change. Relatively high sedimentation rates allow reconstructing Holocene climate variability with a high temporal resolution. The different TEX86 proxies (TEX86, TEX86L and TEX86H) based on Thaumarchaeota membrane lipids (isoprenoid glycerol dialkyl glycerol tetraethers; iGDGTs) represent a unique opportunity to estimate past water temperature variability as other temperature proxies are not applicable in the Baltic Sea. Although numerous TEX86 calibrations are available, the Baltic Sea represents a particular environment characterized by brackish and permanently stratified waters. Since surface sediments used to establish temperature calibrations are restricted in space and time, a downcore calibration approach is proposed here, which consists of comparing TEX86, TEX86L and TEX86H values from a well-dated sediment core with observed water temperatures in the central Baltic Sea over the last 45 years. The most reliable relationship is between TEX86L and water temperature at 80–120 m, the depth range in which Thaumarchaeota are thriving in the Baltic Sea. This result is corroborated by the absence of a seasonal pattern in the TEX86L index derived from a sediment trap time series. Comparing TEX86L water temperature estimates from a sediment core covering the last 160 years with hindcast simulations suggests that TEX86L estimates might be affected by changes in redox conditions. This is most likely related to a change in the depth habitat of Thaumarchaeota. The application of the new calibration on a long sediment core from the central Baltic Sea validates its efficiency to reconstruct subsurface water temperature in the Baltic Sea over the mid-to late Holocene.

Improving assessments of coastal ecosystems – Adjusting coastal fish indicators to variation in ambient environmental factors

The application of ecological indictors for assessing the environmental status of ecosystems play an important role for effective management. However, natural variability may limit the indicators’ ability to provide relevant information about anthropogenic pressures and guide management action. Coastal fish species are not only a resource for commercial and recreational fisheries but also key ecosystem components in the Baltic Sea, and is therefore used as management objectives within the EU Marine Strategy Framework Directive and the HELCOM Baltic Sea Action Plan. A challenge, however, is that the distribution and abundance of coastal fish populations in Baltic Sea is also influenced by spatial and temporal variation in ambient environmental factors. Here, using 16 years of monitoring data, over a latitudinal range of 56 – 66°N along the Swedish Baltic Sea coast, we evaluated the effect of variability in water temperature and depth, and wave exposure for three indicators of environmental status assessment in the Baltic Sea: Abundance of perch, Abundance of Cyprinids, and Abundance of Piscivores. Generalized linear mixed models (GLMM) revealed an overall positive linear relationship between water temperature for all indicators, and overall negative linear relationships to depth and wave exposure. When adjusting indicator values using the parameter estimates from the GLMM models, the variability and 95 % confidence interval for all three indicators were reduced. The adjustment, however, did not have a strong impact on the assessment of the ecological state of the indicator. Our results suggest that adjusting coastal fish indicators to variation in local ambient environmental factors will increase their precision, and hence, the confidence in the assessment of environmental status.

Wind-Induced Variability of Warm Water on the Southern Bellingshausen Sea Continental Shelf.

The Bellingshausen Sea hosts heat transport onto the continental shelf, potentially enhancing ice shelf basal melt. Here, we use the GLORYS12V1 1993-2018 reanalysis to identify physical processes that set seasonal and interannual variability of water mass properties in the Eltanin and Latady Bays on the southern Bellingshausen Sea continental shelf. Annual means of potential temperature from 300m to the seabed reveal interannual variability and allow separation into warm and cold regimes. The Amundsen Sea Low (ASL) is more intense and extends further east during the warm regime than the cold regime. In the warm regime, a wind-induced reduction of sea ice concentration near the coast increases surface heat loss, convection, and formation of cold dense water in winter, associated with a decrease in heat content of the southern Bellingshausen Sea over time and a net northward heat transport. In contrast, in the cold regime, increased sea ice concentration reduces surface heat loss and thus formation of cold, dense water. Combined with an increase in heat content over time and a net southward heat transport, this results in a warming of the southern Bellingshausen Sea. This suggests that variability in the deep water temperature in the southern Bellingshausen Sea is primarily due to local surface heat fluxes above the shelf. The variability of surface heat fluxes is related to the variability of the ASL and its influence on sea ice extent and local formation of cold, dense water in winter.

Detection of surface water temperature variations of Mongolian lakes benefiting from the spatially and temporally gap-filled MODIS data

• We applied an effective spatiotemporal gap-filled method to improve the LSWT from MODIS. • The long-term variations of the annual and seasonal mean LSWTs of Mongolian lakes were provided. • The LSWT of Mongolian lakes confirmed the phenomenon “global warming hiatus”. Lakes provide critical water resources for human activities and ecosystems, particularly in the Mongolian Plateau (MP), which is characterized by a dry climate and a harsh environment. As a region that is sensitive to anthropogenic warming, tracking lake surface water temperature (LSWT) changes in Mongolian lakes is crucial for understanding the consequences of a warming climate on lake ecosystems. However, the long-term monitoring of LSWT is restricted by the spatiotemporal gaps in the raw imagery of remote sensing-based land surface temperature (LST), e.g., the commonly used Moderate Resolution Imaging Spectroradiometer (MODIS) LST products. This study applied an improved gap-filling method by utilizing the discrete cosine transform-based penalized least squares (DCT-PLS) strategy in the spatial domain combined with the linear interpolation (LI) algorithm in the temporal domain. The method was applied to fill gaps in the LSWT imagery of 12 representative lakes across MP. The randomly sampled high-quality MODIS LSWT values in the spatial and temporal domains were excavated as false data gaps and considered “virtual true” validation datasets. The spatial validation results showed that the estimated LSWT for all the lake cases were comparable with the “virtual true” LSWT values, with the average values of the coefficient of determination, mean absolute error, mean square error, and root mean square error being 0.98, 0.38 °C, 0.45 °C, and 0.59 °C, respectively. Meanwhile, the error of nighttime LSWT results was relatively lower than that of daytime LSWT. For temporal interpolation validation, the LI algorithm exhibited relatively better performance and could more objectively indicate the variation in LSWT. Benefiting from the spatially and temporally well-constrained data, we analyzed the interannual and intra-annual change characteristics of the LSWTs of the 12 lakes. The long-term variations of annual and seasonal mean LSWTs in the 12 selected lakes exhibited no evident trends in 2000–2020, while presented apparent interannual fluctuations. The slight changes in the average LSWTs of the 12 selected lakes were in excellent synchronization with the surrounding LST derived from the reanalysis datasets, confirming the widely reported phenomenon of “global warming hiatus” that occurred in the early 21st century. This study improves the understanding of the LSWT variations in Mongolian lakes in response to global climate change. It has the potential to provide an effective approach for monitoring LSWT changes in other large-scale studies.

Spatial–temporal characteristics of surface thermal environment and its effect on Lake surface water temperature in Dianchi Lake basin

The surface thermal environment plays an important role in urban sustainable development and ecological environment protection. Existing researches mainly focus on the formation process and mechanism of the surface thermal environment and lack the analysis of its effect on the lake ecological environment under the influence of human activities. Therefore, based on the analysis of the variations in land surface temperature (LST) and lake surface water temperature (LSWT) of Dianchi Lake at multiple spatio-temporal scales, this study evaluated the response of LSWT by using the methods of spatial influence, the center of gravity migration trajectory, trend analysis, and correlation analysis. The results show that: (1) Urbanization has a greater warming effect on LSWT than on LST, and the warming effect at night is greater than that at daytime. From 2001 to 2018, the warming trend of LSWT in daytime and night was 0.01°C/a and 0.02°C/a, respectively, while the cooling trend of LST in daytime was −0.03°C/a and the warming trend of LST in night was 0.01°C/a. (2) Areas with high human activity are warming faster, both in the eastern and northern coastal areas of lake and the heavily urbanized sub-basins. (3) The spatial influence of LST and LSWT are highly correlated, and the response of the outer buffer in the range of 2 km is obvious, and the direction of gravity center migration trajectory is consistent. The results are of great significance for the control and improvement of urban heat island and ecological environment protection of Dianchi Lake in Kunming and can provide data support and decision support for urban planning, promoting the construction of the ecological civilization city in Kunming, and reducing the accumulation of urban surface heat.

Population Structure of Wild Schizothorax kozlovi in the Upper Yangtze River Based on mtDNA and Stable Isotopes, and Their Relationship with Ambient Temperature

Schizothorax kozlovi, as an endemic and vulnerable fish of the upper Yangtze River in China, faces many threats. In order to expose the population structure of wild S. kozlovi, the carbon and oxygen isotopic ratios in the otoliths, and the gene sequences of two common mitochondrial markers (Cytb and COI) were investigated in four sampling locations, and then their relationship with ambient temperature was further investigated. In general, it exhibits limited geographic population structuring of S. kozlovi in the upper Yangtze River by both mtDNA and stable isotopes. The values of otolith stable isotope ratios varied from −15.30‰ to −12.37‰ for δ18O and from −10.10‰ to −6.13‰ for δ13C. Significant relationships were revealed between stable isotope ratios and specific mean monthly water temperature variables (from November to March), indicating low temperature effect on otolith stable isotope ratios. Haplotype diversity and nucleotide diversity were 0.928 and 0.00778, both exhibiting high levels. A median-joining haplotype network indicated a mixture of geographical distribution but exhibited two distinct haplotype lineages (Clade I and Clade II). AMOVA detected that the higher percentage of genetic variance was within sampling locations (96.94%) and between two haplotype lineages (72.82%). Most FST values between sampling locations showed small levels of genetic differentiation except the differentiation between population SJ (Sanjiangkou) and JP (Jinping). Therefore, two haplotype lineages and population JP of S. kozlovi in the upper Yangtze River are suggested as three management units for conservation due to their moderate-to-great genetic differentiation and isolated habitat.

Warming of surface water in the large and shallow lakes across the Yangtze River Basin, China, and its driver analysis.

A variety of physical, chemical, and biological processes within the lakes relies on the surface water temperature while the spatial pattern of large lakes of different warming trends and their connections with climate change remain unclear. Using correlation analysis, regression tree analysis (RTA), and general linear models (GLMs), we have estimated the warming trends of 192 lakes since 2000 in the populated Yangtze River Basin, China, to identify dominant climate drivers and quantify their contributions. The results show that surface water temperature has increased substantially in the majority of the investigated lakes (179 from a total of 192 lakes) at a rate of 0.29 (- 0.12 to 0.62)°C/decade (median and 95% confidence interval). The shallower lakes (< 13.1m in depth) usually have the faster median warming rates than the deeper lakes (i.e., 0.37°C/decade versus 0.16°C/decade). We find that in the shallow lakes, rising air temperatures and declining wind speeds can explain the majority of variation in surface water temperature (i.e., 31.4‒80.3% and 13.0‒21.0%, respectively). In contrast, in deeper lakes, change of air temperatures plays a dominant role in water warming (75.4‒91.2%). This study has emphasized the importance of declining wind speed in water warming in large and shallow lakes and illustrated a difference of dominant climatic drivers in water warming between the shallow and deep lakes.

Analysis of the eutrophication in a wetland using a data-driven model.

Eutrophication is a major problem in the international Anzali wetland (northern Iran). The present research initially aimed to determine the trophic state index (TSI) in ten sampling sites in the main parts of the Anzali wetland (western, eastern, central, and Siahkeshim parts). After determining the TSI in the wetland, a data-driven method (classification tree model with a J48 algorithm) was implemented to predict the trophic condition in the wetland based on a set of water quality and physical-structural variables. One hundred twenty samples related to chlorophyll-a (the model's output) and environmental variables (the model's inputs) were measured monthly during 1-year study period (2017-2018). Based on the TSI calculation, the western, Siahkeshim, eastern, and central parts of the wetland are classified as eutrophic, super-eutrophic, hyper-eutrophic, and hyper-eutrophic, respectively. When all environmental variables were introduced to the model (with five-time randomization effort, pruning confidence factor = 0.01, and seven-fold cross-validation), eight variables (bicarbonate, pH, water temperature, electric conductivity, dissolved oxygen, total phosphorus, water depth, and water turbidity) were predicted by the model. The model predicted that an increase in total phosphate, water turbidity, and electric conductivity concentration may contribute to the hyper-eutrophic state of the wetland. In contrast, the hyper-eutrophic of the wetland is associated with a decrease in water depth, dissolved oxygen, and pH concentration. According to ANOVA test, the trophic condition in the wetland can be affected by spatial and temporal patterns. Anthropogenic pressures such as the influx of chemicals particularly the nutrients (phosphorus and nitrogen) are the main cause of water enrichment (eutrophication problem) in main parts of the Anzali wetland ecosystem.

Key hydrodynamic principles for controlling algal blooms using emergency reservoir operation strategies

Reservoir operation strategies with low cost and high efficiency have been proposed to control algal blooms. However, the key hydrodynamic principle for performing reservoir operation strategies is still unknown, posing an obstacle to practical applications. To address this challenge, we proposed short-term emergency reservoir operation strategies (EROSs), established a three-dimensional (3D) eutrophication model of the Zipingpu Reservoir, and designed six 14-day reservoir operation cases to explore the mechanism of EROSs in controlling algal blooms. Large outflows with rapid water exchange should be adopted early in EROSs to control algal blooms in the reservoir. Small variations in the surface water temperature or the mixed layer depth/euphotic layer depth (Zmix/Zeu) ratio were found for different EROSs, indicating that these variations might not have been responsible for the differences in the algal blooms in the reservoir. The EROSs induced high surface flow velocity (Vs) and depth-averaged velocity (Vd) values in the reservoir, thereby controlling algal blooms by inhibiting algal growth and disrupting algal accumulation in the upper water layers. The flow of Vs against the direction of the water intake was detected during the execution of the EROSs, suggesting that increasing Vs might enhance water retention in the reservoir. Increasing Vd not only promoted water exchange to disrupt algal accumulation but also enhanced Vs to inhibit algal growth. Moreover, Vd demonstrated a strong linear relationship with the inhibition ratio of algal blooms. These results demonstrate that Vd is the key hydrodynamic indicator for performing EROSs and that accelerating Vd to exceed 0.039 m s−1 in the near-dam region can control algal blooms. Overall, in this study, we develop a novel EROS and elucidate corresponding principles for the use of EROSs to control algal blooms in reservoirs.

Sexual reproduction and biometry of the non-zooxanthellate papillose cup coral Paracyathus pulchellus

Basic information on the reproductive biology of many scleractinian corals species is limited or entirely lacking, particularly from temperate zones, though it is essential for a better understanding of their ecology. This study describes the morphological aspects and the annual cycle of gametogenesis and biometric parameterss of the papillose cup coral Paracyathus pulchellus collected at Palinuro (Italy, Southern Tyrrhenian Sea), filling a knowledge gap about the reproductive biology of a widespread Mediterranean and Northern Atlantic coral. Samples of P. pulchellus were collected by SCUBA diving between 5- and 10-meters depth during 18 monthly collections from June 2010 to December 2011. Sexually active polyps displayed either oocytes or spermaries, indicating that P. pulchellus was gonochoric. The sex ratio of sexually active polyps was 1:1. Gametogenesis began with undifferentiated germ cells arose in the gastrodermis that migrated towards the mesoglea of the mesentery where they completed the development. During spermatogenesis, spermary diameter increased from 25 to 83 µm. Oocyte diameter ranged from 9 to 146 µm and during oogenesis the nucleus/cytoplasm ratio decreased due to the accumulation of yolk. The nucleus migrated to the periphery of the oocyte adhering closely to the cell membrane. No embryo was observed in the coelenteric cavity of the polyps, suggesting an external development of planktotrophic larvae due to the small-sized mature oocytes and a possible broadcast spawning reproductive mode. Gonadal index of both females and males increased significantly from August until November and fertilization took place from November to January. Only sexually inactive individuals were observed from February to April, suggesting a quiescence period in both males and females. Seasonal variations in water temperature and photoperiod may have a key role in regulating gametogenesis. The analysis of the main biometric parameters (polyp width, height, dry skeletal mass, volume, surface/volume ratio and bulk skeletal density) showed a negative correlation between size and skeletal density, and no sexual dimorphism.

Recent changes of the thermal structure in Three Gorges Reservoir, China and its impact on algal bloom in tributary bays

Despite the fact that the water temperature of the Yangtze River has changed substantially due to the construction of Three Gorges Reservoir (TGR), little is known about how the thermal structure of TGR responded to the implementation of two large upstream reservoirs in 2013. We investigated the seasonal variations of water temperature and discharge in the middle reaches of the Yangtze River by analyzing multi-year (2004–2018) hydrological and water temperature data. The effects of upstream dams on the thermal regime, density currents and phytoplankton blooms in TGR were examined. The results show that water temperature in TGR increased in spring (+1.1 °C) and winter (+0.8 °C) seasons after the filling of upstream reservoirs compared to the years before. Longer duration of stratification is associated with a smaller discharge and a longer water residence time. Moreover, the increase of inflow, which was at least partially due to upstream dam construction, lead to the weakening of stratification during the spring season. As a consequence of the higher water temperature in TGR in spring, the density-driven exchange flows between the main reservoir and tributary bays have changed. Overflows became more frequent, which promoted the deepening of the surface mixing layer, and resulted in a dramatic reduction in the frequency and biomass of phytoplankton blooms in tributary bays of TGR.

Spectral changing during a massive bloom event of Dinophysis cf. accuminata in south Brazil

Harmful algal blooms (HABs) are deleterious ecological phenomena that can severely impact coastal ecosystems, fisheries resources, and public health worldwide. Different HABs species have distinct spectral characteristics due to the specific absorption of their accessory pigments, allowing us to monitor them through remote sensing. In June 2016, a massive Dinophysis cf. acuminata bloom hit the southern Brazilian coast causing damage to the local mariculture along its trajectory. In order to observe its passage and evolution, we performed weekly sampling cruises in the coastal waters of Paraná, Brazil. Remote sensing reflectance (Rrs) data were performed with FieldSpec ASD, along with oceanographic variables (water temperature, salinity, Secchi depths, chlorophyll fluorescence, and particulate matter concentration). Satellite images from MODIS and OLI were used to quantify the magnitude of the HAB. During its peak, the bloom reached an area of 201 km 2 along the Paraná coast with abundances of 6.85 × 106 cells.L−1, the highest cell density ever recorded for this species. The event was associated with low salinity and temperature from a high chlorophyll plume from the La Plata River. The in situ Rrs were grouped by hierarchical clustering, separating the spectral signature of the Dinophysis bloom through principal component analysis. The same spectral shape was observed in the K-means clustering of both MODIS and OLI images, attesting to the method’s suitability. We address the first characterization of a Dinophysis bloom, and the results can contribute to a better understanding of the spectral response of this toxic dinoflagellate and optimize the satellite algorithms for the detection of HABs.

Dynamic Response of Surface Water Temperature in Urban Lakes under Different Climate Scenarios-A Case Study in Dianchi Lake, China.

Lake surface water temperature is a fundamental metabolic indicator of lake ecosystems that affects the exchange of material and energy in lake ecosystems. Estimating and predicting changes in lake surface water temperature is crucial to lake ecosystem research. This study selected Dianchi Lake, a typical urban lake in China, as the research area and used the Air2water model combined with the Mann-Kendall mutation statistical method to analyze the temporal and spatial variation in the surface water temperature of Dianchi Lake under three climate models. The research results show that, under the RCP 5-8.5 scenario model, the surface water temperature change rate for Dianchi Lake from 2015 to 2100 would be 0.28 ℃/10a, which was the largest change rate among the three selected scenarios. The rate of change during 2015–2100 would be 9.33 times higher than that during the historical period (1900–2014) (0.03 °C/10a). Against the background of Niulan River water diversion and rapid urbanization, the surface water temperature of Dianchi Lake experienced abrupt changes in 1992, 2016, 2017, and 2022. Against the background of urbanization, the impact of human activities on the surface water temperature of urban lakes will become greater.