Hydrological Periods Research Articles

Unravelling a specialised diet of an Amazonian catfish in a controlled flood-pulse area by combining stomach-content and stable-isotope analyses

Context Hydrological dynamics are crucial in fish ecology. Aims To evaluate the effect of the flood pulse on the feeding ecology of Doras higuchii in the reduced-flow section of the Belo Monte dam, Xingu River, Brazil. Methods Collections were conducted between December 2020 and November 2021. The fish were measured and had their stomachs removed. Muscle tissue was also extracted for stable-isotope analysis. Stomach contents were inspected to assess diet, testing the influence of hydrological periods by using GLM. In addition, we evaluated the effect of the flood pulse on the δ13C and isotopic ratios of individuals Results In total, 362 specimens of D. higuchii were analysed, highlighting a diet mainly on the basis of sediment (74.9%) and aquatic insects (24.8%), not varying between periods characterising the species as a specialist for having detritivorous habit, as well as the extension of the trophic niche. There was variation in food intensity, with higher average food consumption in the flood period. The isotopic composition (δ13C and δ15N) also did not differ between periods. Finally, δ15N did not vary by length class. Conclusions This information helps understand the interface between environmental and biological factors in an environment affected by a hydroelectric dam. Implications Our results may help fill gaps in knowledge about the diet of doradid fishes.

Evaluation of the Offsets of Artificial Recharge on the Extra Run-Off Induced by Urbanization and Extreme Storms Based on an Enhanced Semi-Distributed Hydrologic Model with an Infiltration Basin Module

Urbanization and climate change exacerbate groundwater overexploitation and urban flooding. The infiltration basin plays a significant role in protecting groundwater resources because it is a prevalent technology of managed aquifer recharge. It could also be utilized as a retention pond to mitigate city waterlogging. The goal of this study was to explore the offsets of artificial recharge on the extra runoff induced by urbanization and extreme storms via infiltration basins. To achieve this objective, a lumped infiltration basin module was developed and integrated into a semi-distributed hydrologic model. Then, the enhanced model was applied to an agriculture watershed with urban areas. Finally, the functionalities of the infiltration basins were evaluated under the scenarios of the predicted urbanization and extreme storms. The results demonstrated the capability of the infiltration basins to influence both artificial recharge and flood mitigation. To mitigate floods, especially peak flows, larger areas are needed for infiltration basins than for artificial recharge purposes only. Based on different demands, the intermittent regulation of infiltration basins according to different hydrologic periods is recommended. The offsets of artificial recharge on the extra surface runoff provide insight into the comprehensive preservation and management of surface water resources and groundwater resources.

Long-term study of phytoplankton dynamics in a supply reservoir reveals signs of trophic state shift linked to changes in hydrodynamics associated with flow management and extreme events

This study analyses over a decade (2009–2022) of monitoring data to understand the impact of hydrological characteristics on water quality and phytoplankton dynamics in Prospect Reservoir, a critical water supply for Greater Sydney, Australia, known for its excellent water quality. Water quality and phytoplankton dynamics were related to hydrodynamics, linked to flow management and the water quality of inflows. Phytoplankton biovolume increased after a prolonged drawdown and subsequent refill event, mainly driven by dinoflagellates, and corresponded to increases in total phosphorus and water temperature. The hydrological period following the 2019/2020 summer bushfires (post-bushfire) that impacted connected reservoirs, was marked by increased flow activity and nutrient loading, leading to significant shifts in the phytoplankton community. Functional group classification and ordination analysis indicated a transition from taxa typically dominant in oligotrophic conditions to meso‑eutrophic. This transition correlated with elevated nutrient levels and chlorophyll-a (Chl-a), and reduced Secchi depth and dissolved oxygen, providing evidence of eutrophication. Q index indicated good water quality post-bushfire, contrasting with a eutrophic status assessment using Chl-a. Our findings highlight the importance of analysing long-term datasets encompassing varied hydroclimatological conditions for a deeper understanding of reservoir behaviour. A comprehensive approach to water quality assessment is recommended, combining functional group classification, Q index and Chl-a measurements for effective reservoir health assessment. This research provides novel insights into the effects of disturbances such as bushfires, on water quality and phytoplankton dynamics in an underrepresented geographic region, offering valuable knowledge for managing water resources amidst growing climate variability.

Spatial factors overcome seasonality regulating the consumption of allochthonous food resources by fishes from tropical lotic ecosystems

Abstract In lotic ecosystems, a higher availability of allochthonous food resources is expected during floods and rainfall events, which may yield a higher consumption of these resources by consumers. However, allochthonous input and seasonality in environmental conditions are locally dependent. Thus, dietary responses of freshwater consumers to seasonality should also be locally dependent. Herein, we applied a meta‐analytical approach to identify the spatial and seasonal environmental variables associated with the relative consumption of allochthonous food resources by fishes from tropical lotic ecosystems in different seasons. We gathered 566 observations of the diet of fish populations (i.e., restricted to the same sampling event) from 38 studies conducted in 70 localities across the tropics during flood and drought periods (hereafter, high‐water and low‐water periods, respectively). We retrieved latitude, seasonal channel width, elevation and two proxies for allochthonous input for each locality: terrestrial biomass (without considering seasonality) and the normalised difference vegetation index (NDVI; considering seasonality). Then, we applied meta‐regression models using these environmental variables as predictors and the proportion of allochthonous food resources in each consumer's diet (%Allo) as the response variable. Our models revealed that the diet of fishes from tropical lotic ecosystems is mostly autochthonous‐based, independent of the hydrological period (high‐water or low‐water), and aquatic invertebrates were the most consumed food items. Terrestrial vegetation biomass and elevation predicted increasing allochthony in the diet of tropical fishes for high‐water, but only terrestrial biomass predicted allochthony at low‐water periods. We found no relationship between latitude, channel width or NDVI with allochthony. Our study highlights the importance of considering the hierarchical level of biological organisation and fish trophic guilds for understanding seasonal patterns of relative consumption of allochthonous and autochthonous food resources by fishes. We also argue that variations in seasonality across the tropics are likely to have undermined its influence on allochthony in fish diets. The absence of a non‐relationship between channel width and allochthony provides evidence that the River Continuum Concept is better suited to temperate lotic ecosystems. Our results provide novel insights and the big‐picture of seasonal pattern in the diets of tropical fishes for use in future local empirical studies, improving forecasting of the relationship between the factors underpinning the availability of allochthonous and autochthonous food resources, and the diet of freshwater fishes.

Local environmental factors are the main drivers of phytoplankton biovolume in subtropical streams of Brazil

The ecological attributes of phytoplankton in freshwater environments are strongly influenced by limnological factors and temporal variability. In this study, we investigated the importance of local environmental and regional (spatial and landscape) predictors in structuring stream phytoplankton from the perspective of metacommunity theory. We seasonally sampled phytoplankton and abiotic variables from nine streams in three subtropical basins. Variation partitioning was used to investigate the influence of environmental, landscape, and spatial predictors on phytoplankton biovolume. Independent of the hydrological period (dry and rainy), the phytoplankton communities were predominantly structured by local environmental factors. In addition, the different land uses considered (landscape) showed weak significance during the dry season, with emphasis on the rural category. Biovolume values remained low, and diatoms and green algae were the most representative groups. Our findings are consistent with recognized ecological patterns for potamoplankton and emphasize local environmental filters as a fundamental regulator of phytoplankton biodiversity in lotic environments.

Agricultural drought assessment in dry zones of Tolima, Colombia, using an approach based on water balance and vegetation water stress

Soil water balance is an essential element to consider for the management of droughts and agricultural land use. It is important to evaluate the water consumption of a crop in each of its phenological phases and the status of water reserves during critical hydrologic periods. This study developed an agricultural drought index (Standardized Soil Moisture Deficit Index - SMODI) conceptualized with a water balance model considering the vegetation stress caused by soil moisture deficit. This contribution was based on meteorological information, soil moisture from satellite images, hydrophysical properties of the soil and crop evapotranspiration. Information from 61 weather stations located in the dry zone of Tolima was used for estimating the water balance. SMODI was compared with the most common drought indexes: Standardized Precipitation - Evapotranspiration Index (SPEI), the Palmer Self-Calibrated Drought Index (scPDSI), and other eleven macroclimatic indexes. Pearson's correlation coefficients (r), Tukey's test, and analysis of variance were applied to analyze the degree of association between SMODI and the contrasting indexes on a quarterly basis. SMODI considers factors influencing soil moisture distribution and retention and the water stress thresholds that plants have evolved to withstand during drought periods. Consequently, this integrated approach enhances the assessment of agricultural drought by relying on pertinent physical processes. SMODI identified extremely dry, severe, moderate and normal drought 5 %, 3 %, 20 % and 72 % respectively conditions in areas characterized by Entisols, Inceptisols, and Andisols, where rice and fruit crops and pasturelands are cultivated. The SMODI has a good correlation with macroclimatic indexes (0.70 < r < 0.74).

Actinella gessneri Hustedt (Eunotiaceae, Bacillariophyceae), a rare and endemic species in Amazonian blackwater, Brazil

Actinella gessneri Hustedt is a rare and poorly known Amazonian diatom species. Low records and restricted distribution to acid waters suggest that this species may be threatened with extinction. We record a new occurrence of Actinella gessneri Hustedt in Amazonian blackwaters, providing detailed images on LM and SEM, and approaching ecological aspects concerning habitat, quality water and hydrological periods.

Development and Evaluation of the Plankton Biological Integrity Index (P-IBI) in Dry and Wet Seasons for Dianchi Lake

As an important component of lake ecosystems, plankton are often used as indicators to evaluate the health of aquatic ecosystems, such as lakes and reservoirs. The plankton integrity index (P-IBI) is a highly utilized method for evaluating the ecological health of the lakes. This study took Dianchi Lake, located in the Yangtze River Basin, as the research object and analyzed the phytoplankton, zooplankton communities, and environmental factors at 11 sampling points in this lake during the wet season (July) in 2022 and the dry season (February) in 2023. The P-IBI was established to evaluate the health status of this lake ecosystem. The results showed that a total of 83 species of phytoplankton and 31 species of zooplankton were identified in Dianchi Lake, and the number of plankton species in the dry season was significantly higher than that in the wet season. The P-IBI evaluation results for the two hydrological periods were generally “good”. Linear regression analysis showed that there was a certain negative correlation between the P-IBI value and the comprehensive trophic level index (TLI), and the evaluation results were generally in line with the actual situation of the water body. Redundancy analysis (RDA) showed that there was a significant correlation between the P-IBI and its constituent parameters and individual water quality environmental factors, such as total nitrogen (TN) and electrical conductivity (EC). In summary, by reducing errors caused by spatial and temporal changes across various hydrological periods, P-IBI represents a more scientifically rigorous technique for lake water ecological health assessments within a certain time range.

Hydrological alteration drives chemistry of dissolved organic matter in the largest freshwater lake of China (Poyang Lake)

As the largest reactive organic carbon pool, dissolved organic matter (DOM) plays an important role in various biogeochemical processes in lake ecosystems. Recently, climate change-induced extreme events (e.g., floods and droughts) have significantly modified the hydrological patterns of lakes worldwide, and regulated the quality and quantity of DOM. However, the responses of DOM chemistry to hydrological alteration in lakes remain poorly understood. Here we investigated the influences of hydrological alteration on sources, composition, and characteristics of DOM in Poyang Lake, the largest freshwater lake in China, using a combination of bulk chemical, optical and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques. Results show various sources of DOM (autochthonous, allochthonous, and anthropogenic inputs) and significant variations in DOM chemistry across four hydrological periods (the retreating, dry, rising, and flooding periods) in Poyang Lake. During the retreating, rising, and flooding periods, DOM was characterized by higher aromaticity, humification degree, and recalcitrance, and exhibited pronounced allochthonous signatures. In contrast, DOM contained more S-containing molecules and aliphatic compounds during the dry period, displaying relatively stronger autochthonous features. Terrestrial inputs and the lignin-CHOS formation process are likely the primary underlying mechanisms shaping the differences in DOM chemistry in Poyang Lake. Our research demonstrates the significant impacts of hydrological alteration on DOM dynamics, and provides an improved understanding of DOM biogeochemical cycles and carbon cycling in large aquatic systems under global climate change.

A cheia não causou homogeneização taxonômica e funcional da comunidade de Chironomidae (Diptera) em uma planície de inundação neotropical

Abstract: Aim We investigated the hypothesis that flood decreases the taxonomic and functional beta diversity of Chironomidae (Diptera) larvae among floodplain lakes, causing biotic homogenization. Methods We collected benthic samples using a modified Petersen grab in 18 lakes in a flood period (March 2011) and a drought period (September 2011) in the Upper Paraná River floodplain. We compared the taxonomic and functional beta diversity of Chironomidae among lakes in flood and drought periods using a multivariate dispersion analysis (PERMDISP). Results We found similar taxonomic and functional beta diversity of the Chironomidae between hydrological periods. Conclusions We did not find evidence of biotic homogenization due to flood pulse. Our findings suggest other mechanisms besides increasing connectivity and environmental similarity due to flood pulse that may structure the benthic community, such as variation in the identity of flood-tolerant morphospecies across lakes.

STREAMFLOW GENERATION OF RIVER NIGER BASIN KOGI USING MODIFIED THOMAS FIERRING MODEL

There is a concerted effort towards protection of environment as a result of incessant change of climate and its resultant effects on human live and property. Studies have shown that flooding is ranked the most devastating natural disaster in the world; and it is a common natural environmental hazard in various parts of Nigeria. In recent times, flooding has been reported to constitute a major challenge to about 1.5 billion people or 19% of the world population; whereas 70 million people globally exposed to flooding every year while over 800 million people are living in flood-prone areas. The 2022 destructive flooding in River Niger Basin Lokoja Nigeria has attracted attention of experts with a view to curtailing the future reoccurrence. Based on this rationale, this study aimed to determine the trend in the hydrometric dataset and to provide extensive time series analysis of the streamflow in the study area using Modified Thomas Fierring Model (MTFM). In order to achieve the objectives of the study, the dataset for 20 years was sourced from the NIWA (National Inland Waterway Authority) whereby the daily and monthly data was extensively analyzed and the (Thomas Fierring) T-F model the data for the “n” years was divided into 12 sections while the data of each month was re-aggressed to the previous month so that there were 12 linear regressions. Also, MTFM was used to predict the monthly flows from River Niger from 2000 to 2019 so as to compute 36 parameters (12) means (), standard deviations (), and Lag-1 autocorrelation coefficients (r1)). After the estimation of the parameters of the MTFM, the series of historical monthly flows for 20 years were generated. These series were compared with the recorded monthly flows of River Niger for the hydrological period of 20 years (2000-2019), with the use of basic statistical characteristics like mean, standard deviation, maximum, minimum, coefficient of variation, skewness and Kurtosis as shown in Table 1 and Figure 2. The findings revealed that monthly discharge time series of River Niger Basin from 2000 to 2019 are consistent with slightly variation in the trends after modified modified Thomas Fierring Model application; and the study further underscored the relevance of MTFM for analyzing streamflow of River Niger Basin Lokoja. Among others, the study recommended up-to-date hydrometric data of River Niger Basin for optimum control and management of streamflow in the study area; and concluded that up-to-date information in this direction will help future researcher to consolidate on the existing body of knowledge in the field.

Effects of “source-sink” landscape on spatiotemporal differentiation of phosphorus output in multiple watersheds in mountainous areas based on the modified location-weighted landscape index

Optimizing the landscape structure and spatial configuration of the basin is one of the most important ways to reduce the harm of non-point source pollution (NPSP) to water bodies. The coupling relationship between the “source-sink” landscape pattern and NPSP process had long been a research hotspot of “source-sink” landscape theory. However, the “source-sink” landscape index represented by the classic location-weighted landscape index (LWLI) is suitable only for watersheds with similar environmental backgrounds, and cannot reflect the spatiotemporal heterogeneity of phosphorus output between watersheds with large differences in environmental backgrounds. In this study, 15 tributary watersheds in the Poyang Lake Basin were selected as the case study. The characteristics of “source-sink” landscape structure in 2020 were described by using landscape area structure indices. Moreover, the classical LWLI was modified by adding the topographic wetness index, soil erodibility index and vegetation interception index, and by evaluating the spatiotemporal differences in the effect of “source-sink” landscape patterns on phosphorus export in three hydrological periods (normal, wet and dry) by pearson correlation analysis and redundancy analysis. We found that (1) the proportion of “sink” landscape (greater than 58%) was greater than that of “source” landscape (less than 40%) in all sub-watersheds. In addition, the results of Lorentz curves showed that when the elevation and slope increased, the proportion of “source” landscape decreased and the proportion of “sink” landscape increased. (2) the classical and modified LWLI values were less than 0.5, which indicated that the potential contribution of the “sink” landscape was greater than that of the “source” landscape. (3) The correlation between the classical LWLI and total phosphorus (TP) in the wet period and normal period was stronger than the correlation between all “source-sink” landscape area structure indices and TP, indicating that the LWLI was more effective in describing TP loss than were the “source-sink” landscape area structure indices. (4) the correlation of the modified LWLI with TP in the three periods were stronger than those of the classical LWLI with TP, which indicated that the modified LWLI could better indicate the coupling relationship between the “source-sink” landscape pattern and the phosphorus output by introducing the factors of terrain runoff, soil erodibility and vegetation interception. This study can help with the evaluation of the spatial and temporal heterogeneity of nutrient loss in different watersheds with various landscape patterns, and provide a basis for scientific prevention and control of NPSP.

Numerical simulation of water environment capacity from wet, normal, and dry years: taking the Luo River as an example

Abstract Water pollution is a globally significant issue. Water environment simulation is an important tool to study water pollution. In order to investigate the impact of hydrological periods, water quality indicators and cross-sections on the water environment capacity, we took the Luo River in Luoyang City as an example, and used MIKE21-coupled hydrodynamic and water quality model and the segmentation method to calculate the water environment capacity of COD, TP, and NH3-N in wet, normal, and dry periods under L1 (Gao Yazhai-Lilou), L2 (Li Lou-Baimasi), and L3 (Baimasi-G207 Highway Bridge) section. The results of the study showed that from the hydrological period, the water environmental capacity was the largest in the wet period due to the dilution effect caused by higher precipitation; from the water quality indexes, the COD concentration was the largest due to industrial pollution, but the higher degradation coefficients result in the largest water environment capacity for COD; from the cross-section, L1 has the longest channel, thus the highest capacity of the water environment was L1. This result can broaden ideas for the application of the MIKE21 model, provide a basis for the calculation of the dynamic water environment capacity and water pollution control in the river.

Differences in biodiversity and assembly mechanisms between planktonic and benthic diatom communities in riverine ecosystems: A case study in the Ashi river

Diatoms are an indispensable component of river ecosystem biodiversity and play an important role in aquatic ecosystems. The community assembly mechanism of diatoms has always been a central issue in the study of aquatic ecology. In recent years, many measures have been implemented in the Ashi River Basin (ASRB) to promote social and economic development, such as bridge construction, river bottom sand mining, agricultural irrigation, and urban expansion. However, there are few studies on the effects of these activities on the mechanism of diatom community assembly. First, we found that the α- and β-diversity of planktonic diatoms was higher in the normal season, while the α- and β-diversity of benthic diatoms was higher in the dry season, and the α- and β-diversity of both planktonic and benthic diatoms was reduced in the wet season. Second, the community structures of planktonic and benthic diatoms were significantly different in different hydrological periods, and the differences between planktonic diatoms communities were more evident than those between benthic diatom communities. Third, distance-decay analysis indicated that the distribution of the two types of diatom communities in the ASRB was influenced by both dispersal limitation and environmental selection. Finally, variance partitioning analysis revealed that dispersal limitation was the dominant driving factor for the spatial and temporal differentiation of planktonic and benthic diatoms. Our study reveals the important role of dispersal limitation in the community assembly of planktonic and benthic diatoms in rivers under different hydrological conditions. This study provides new insights for further understanding the relative importance of niche theory and neutral theory to aquatic microbial community assembly. Our research provides key information for analysing the structure of aquatic ecosystems and basic data for designing biodiversity conservation strategies in China's cold watersheds.

Fish diversity of a tributary of the Meta River, in the flat highlands of the colombian Orinoquia

The distribution and abundance of fish for the Orinoco River basin drainages are influenced by hydrometric seasonality and the structural complexity of the habitat, so understanding how fish assemblages are structured on a temporal and spatial scale is essential for biological conservation. Therefore, the purpose of this study was to describe the fish assemblage for the Mitimiti stream and test the hypothesis of spatial and temporal variation. To do this, collections were made at four sampling stations on the Mitimiti stream, during three contrasting rainfall seasons, with the help of a 10 m x 1.5 m trawl net and a 2 mm mesh eye. The diversity of fish assemblages was analyzed using Hill numbers, abundance-based dissimilarity, and a Canonical Correspondence Analysis (CCA). In total, 2493 individuals and 115 species were recorded, where the orders with the highest dominance were Characiformes and Blenniiformes. Regarding the diversity of order q = 0, no significant differences were found between the hydrological periods and the sampling stations, however, the low water period and St3 exhibited the highest species richness. The most dissimilar hydrological period was the high water season and the variables that significantly influenced fish assemblage were water temperature (p = 0.02) and dissolved oxygen (p = 0.05).

Tree Ring Width Responses of Pinus densiflora and Robinia pseudoacacia to Climate Variation in the Mount Tai Area of Northern China

To effectively combat climate change and put plans in place to enhance the health and quality of forests, research on the connections between long-term climate change and tree ring width is essential. Here, Pinus densiflora Siebold &amp; Zucc. and Robinia pseudoacacia L. in the Mount Tai area were studied. Specifically, their tree ring width characteristics were investigated according to the principles of dendrochronology, based on the analysis of multiyear climate data (1972–2022). The results showed that (1) the variation in tree ring width of Pinus densiflora Siebold &amp; Zucc. generally decreased. Its basal area increment sequence presented a “growth-decline” change process. The trend for Robinia pseudoacacia L. was stability at first and then a reduction. Its basal area increment sequence presented a “growth-stabilization” change process. (2) The standard chronologies of both tree species contained more environmental information than the residual chronologies, rendering the former more appropriate for analysis. (3) The tree ring width of Pinus densiflora Siebold &amp; Zucc. was positively correlated with the mean maximum temperature in February, March, and July, the mean temperature in May, and the mean precipitation in December of the previous year and June of the current year. The tree ring width of Robinia pseudoacacia L. was positively correlated with the mean and maximum temperatures in October of the previous year, the mean maximum temperature in May of the current year, and the mean temperature in July of the current year. This variable was positively correlated with the mean precipitation in November of the previous year and July of the current year but negatively correlated with the mean minimum temperature in November of the previous year and the mean temperature in December of the current year. (4) During 1987–1988, 1994–1995, 2005–2006, and 2018–2019, the tree ring width was restricted by rising temperatures and low precipitation, with variations in tree ring width observed in various hydrological periods. (5) The moisture index, followed by the warmth index, precipitation and temperature, was the primary climate factor determining the tree ring width in both tree species.

Is water resources management at the expense of deteriorating water quality in a large river-connected lake after the construction of a lake sluice?

River-connected lakes with floodplain characteristics have substantial effects on terrestrial hydrologic cycles and are highly sensitive to external disturbances; thus, large-scale hydraulic projects are often constructed in such lakes to mitigate problems in the water environment. However, the spatiotemporal dynamics of the water environment in river-connected lakes and the differences in the water environment before and after the hydraulic project operation have received little attention. Here, a well-established coupled hydrodynamic–water quality model was applied to estimate the effects of the Chenglingji Sluice (CS) operation on the hydrodynamic features and water quality of Dongting Lake, a typical river-connected lake in China. The model successfully reproduced the water level and water quality dynamics of Dongting Lake, with a Root Mean Square Error (RMSE) of 0.29–1.24 m for water level and a Mean Relative Error (MRE) of 5.76–10.28% and 6.25–8.14% for total nitrogen (TN) and permanganate index (CODMn), respectively. The spatiotemporal fluctuation of lake water levels was observed over different hydrological periods. Water quality varied considerably spatially, with considerable pollution in East Dongting Lake and the Xiang River inlet. Concentrations of NH3-N (ammonia nitrogen), TN, and total phosphorus (TP) first decreased and then increased during the study period, whereas CODMn concentrations displayed the opposite trend. After the CS operation, the water level increased to 27.11 m and the water surface area increased by 19.29% in the dry period; furthermore, the water quality in the CS operation scenario had low concentrations compared to that of the baseline scenario in the dry period, with concentrations ranging from 0.03 to 0.24 mg/L for TN, 0.001 to 0.015 mg/L for TP, 0.006 to 0.09 mg/L for NH3-N, and 0.02 to 0.22 mg/L for CODM, effectively improving the water environment of Dongting Lake. However, the subsequent reaction of the lake environment to changes in hydrological conditions after the CS operation requires further attention.

Hydrodynamic and dissolved oxygen–biochemical oxygen demand transport characteristics at the river confluence in China's largest alluvial plain—A modeling study

AbstractThe Yellow River flows through multiple provinces in China, shaping the North China Plain, the largest alluvial plain in China. As the control node of basin ecological environment, the confluence of Weihe River and Yellow River is deemed as the gateway to North China Plain. In this study, a numerical simulation of the Weihe River–Yellow River confluence is conducted using a 2D hydrodynamic model and a coupled transport model for dissolved oxygen–biochemical oxygen demand. The results show that: (i) The typical flow field with multiple backflow areas is formed at the stagnant area where main stream and tributary converge and abrupt channel change area in different hydrological periods. The spur dike here mainly affects the velocity of the Weihe River outlet. (ii) There is an obvious concentration transition mixing zone downstream of the confluence, and the width of the mixing zone gradually linear increases with the direction of water flow. (iii) The self‐purification ability of the confluence is strongest in dry period, weaker in level period, and weakest in wet period. Water bodies have stronger self‐purification capacity on riverbanks than in the middle, and it is stronger in the upper reaches of Weihe River compared to Yellow River. Lower reaches also have a stronger self‐purification capacity than upper reaches. The study results can serve as a scientific reference for protecting the ecological environment of the Yellow River.

Environmental and spatial factors play different roles in phytoplankton community assembly in different hydrological seasons in Lake Wuchang, China

Lake phytoplankton communities are affected by environmental and spatial factors. We studied the relative importance of environmental and spatial factors on the phytoplankton community assembly in Lake Wuchang across three hydrological seasons, which were divided into dry (December to March), normal (April to June, October to November) and wet seasons (July to September) based on the water level and depth. Spatial and temporal patterns of environmental factors and phytoplankton community composition and diversity were studied using Kruskal–Wallis test, Wilcoxon test and NMDS. CCA, Mantel and partial Mantel tests, and PLS-PM were used to investigate the effects of environmental and spatial factors on phytoplankton community characteristics. Results showed that phytoplankton assemblages at the eight study sites were composed of totally 244 species belonging to 9 phyla, which changed from Bacillariophyta and Chlorophyta to Cyanophyta across the whole hydrological period. There was significantly higher abundance and biomass in the normal and wet seasons than that in the dry season. Phytoplankton alpha diversity exhibited uniform temporal distribution patterns with higher values in the dry season than in the normal and wet seasons. The Mantel and partial Mantel tests revealed that environmental (physicochemical conditions of lake water) and spatial factors (geographic distances among sites) jointly affected the phytoplankton community structure and beta diversity across the hydrological seasons, while spatial factors were more important in the wet season. Partial least squares path models showed that spatial factors exhibited a significant positive correlation with the phytoplankton diversity with the path coefficients of 0.53 and 0.71 in the normal and wet seasons, respectively. Phytoplankton composition had significant correlation with on phytoplankton diversity with the path coefficient of −0.75 and 0.61 in the normal and wet seasons, respectively. Our findings revealed that both environmental and spatial factors affected the phytoplankton community assembly in Lake Wuchang. Environmental factors played a more important role in the dry season, while spatial factors were more important in the wet season. With the exception of the abiotic factors (environmental and spatial), the impacts of biotic factors on phytoplankton community cannot be ignored. Therefore, it is also necessary to strengthen further research on the top-down control over phytoplankton communities in Lake Wuchang.

Assessing relationships between environmental stress and benthic diatoms in lentic habitats in the western Mediterranean basin (Turkey).

Hydrological (rainy and dry) periods can affect the water quality of lentic ecosystems, which may be useful for understanding their ecological condition in the watershed. Ecological status of various lentic ecosytems (both brackish and freshwater) in the western Mediterranean basin was evaluated by using various diatom metrics throughout rainy (May) and dry (August and October) periods to explain the diatom-stressor interactions using multivariate approaches. Canonical correspondence analysis separated freshwater habitats under the pressures of nitrate and total organic carbon from brackish ecosystems under the pressures of conductivity, nitrite, sulphate, calcium, and copper, which were characterized by different phytoplankton species. Ecological integrations of diatom species varied in the ecosystems throughout rainy and dry periods. Different ecological regional diatom indices were used to find the best index/indices indicating the ecological status of lakes and reservoirs in the basin during the two hydrological periods. The trophic diatom index developed for lakes was not found to be suitable for assessing lentic habitats. European diatom indices generally showed the distinction in the assessment of these ecosystems in the rainy and dry seasons, but others could not. Among the diatom indices, only the trophic index Turkey (TIT) showed a statistically significant correlation with TP. The TIT not only showed degradation of the water quality of ecosystems during the dry season compared to the rainy season, but it has also been successful in distinguishing the ecological conditions of lentic ecosystems.