Riverine Zone Research Articles

Innovative interpretable AI-guided water quality evaluation with risk adversarial analysis in river streams considering spatial-temporal effects

Water security remains a critical issue given the looming threats of industrial pollution, necessitating comprehensive assessments of water quality to address seasonal fluctuations and influential factors while formulating effective strategies for decision makers. This study introduces a novel approach for evaluating water quality within a complex riverine zone in South Korea: Han River that encompasses five river streams situated at each junction of North and South streams (including Gyeongan Stream) that ultimately leading towards Paldang Lake. By utilizing the monthly water characteristic data from the year 2013–2022 across 14 different locations, the significant seasonal trends and potential influences on water quality are identified. The water quality here is calculated with the proposed method of sub-index water quality index (s-WQI). A combinatorial prediction approach of s-WQI for each location is conducted through a collective of data preprocessing approaches including Hampel filtering and feature selection in prior to the machine learning predictions. In return, light gradient boosting (LGB) is the most accurate predictor by outperforming other prediction algorithms, especially through LGB-Pearson and LGB-Spearman combinations for North and South stream intersections, and LGB-Pearson for Paldang Lake. To further evaluate the robustness of this evaluation and extending the results to a foreseeable scenario, a seasonal based Monte-Carlo Simulation with 10,000 attempts targeting the water characteristic distributions obtained from each location considered are carried out to identify the risk bounds within. The results are further interpreted with SHAP analysis on identifying the contributions of each water characteristics towards the water quality through local and global spectrum. This research yields practical implications, offering tailored strategies for water quality enhancement and early warning systems. The integration of AI-based prediction and feature selection underscores the transformative potential of computational techniques in advancing data-driven water quality assessments, shaping the future of environmental science research.

Influence of hydrological changes on the composition of phytoplankton and sediment diatoms in the Rio de la Plata estuary

ABSTRACT ENSO phases produce changes in precipitation and river flow in Eastern South America. We aimed to evaluate phytoplankton and surface sediment diatoms' response to ENSO within the Río de la Plata estuary. A 180-km-long transect off the Uruguayan coast was undertaken in May 2009 (La Niña) and May 2010 (El Niño), where physical, chemical and biological variables were measured. During El Niño we registered lower temperatures/salinities throughout the transect, and the riverine zone was specifically more homogeneous in terms of temperature, salinity, turbidity and chlorophyll-a than during La Niña. We observed changes in the species composition of both planktonic and sediment diatoms. Concomitantly, a significant depletion in planktonic diatom abundance and richness in both planktonic and benthic domain during El Niño was observed. In addition, there was a higher proportion of dinoflagellates than during La Niña, which was explained by a higher water column stability. The dominance of the chain-forming and meso-eutrophic diatom Aulacoseira was registered during El Niño in both domains, mainly in the fluvial zone, related to a high river discharge. Our findings are important to anticipate changes in microalgae composition related to oceanographic variability during potential ENSO events.

Bubbles dominated the significant spatiotemporal variability and accumulation of methane concentrations in an ice-covered reservoir

Climate-sensitive ice-covered reservoirs are critical components of methane (CH4) release. However, the mechanisms that influence CH4 dynamics during ice-covered periods remain poorly studied. To investigate the effects of bubbles on CH4 dynamics, we conducted intensive field and incubation experiments in an ice-covered reservoir (ice growth, stability, and melt period) in Northeast China. We found that the mean dissolved CH4 concentrations in the ice (625.9 ± 2419.7 nmol L−1) and underlying water (1218.9 ± 2678.9 nmol L−1) were high, making them atmosphere CH4 sources. The visible bubble bands (bubble area) in the riverine zone and the vertical profile of the CH4 concentration in the ice reflect the distribution of trapped bubbles. The mean CH4 concentration in the ice of the bubble area (1674.8 ± 3926.8 nmol L−1) was 2 orders of magnitude higher than that of no-bubble area (53.7 ± 9.2 nmol L−1). Moreover, a large amount of CH4 accumulated under the ice in the bubble area. These findings suggest that bubbles determine the CH4 storage in ice and CH4 accumulation in the underlying water. Ice growth increases CH4 storage in ice and the underlying water because of the entrapment and re-dissolution of CH4 bubbles. However, ice melting releases the CH4 accumulated in the ice and underlying water. A comparison of the field and incubation experiments indicated that the deep-water environment of the reservoir had a CH4 burial effect. Stepwise regression analysis revealed that higher sediment organic matter content, median particle size, and porosity increased the production and release of CH4 bubbles, trapping more CH4 bubbles in ice. Overall, this study improves the mechanistic understanding of CH4 dynamics and predictability of CH4 emissions during ice-covered periods.

Longitudinal Gradient and Historical Trends of Arsenic and Metals in a Tropical Reservoir

This study aimed to establish the longitudinal gradient and historical trends of arsenic and metals in a tropical reservoir. Water and sediment samples were collected along the Rio Bonito reservoir (Espírito Santo, Brazil), and a sediment core was obtained from the lacustrine zone. Plasma spectrometric techniques were employed to determine concentrations of As, Cd, Co, Cu, Fe, Mn, Ni, and Pb in water and sediment samples, and the sediment samples were dated using high-resolution gamma spectrometry. Higher concentrations of elements were observed in surface water samples from the riverine zone and bottom water samples from the transition zone. Concerning surface sediment samples, elevated concentrations were noted in the transition and lacustrine zones, where deposition is more intense. The sediment core was dated to 1940, before the reservoir dam construction, utilizing 210Pb dating. Certain elements exhibited progressively increasing concentrations over time. Enrichment factor, pollution load, and ecological risk indexes indicated the need for continuous monitoring of this reservoir

Dams and agricultural lands affect energy sources and the trophic position of fish in a floodplain

Abstract Landscape change caused by hydropower dam construction and invasion of agriculture in the riparian zone has been a catalyst for alterations in fish food web dynamics. The objectives of this study were to investigate the trophic state and land use of three rivers, one directly impacted by a dam; the trophic structure of four fish species of four trophic guilds; and the relationship between the trophic state and land use with trophic structure. We found a greater total allochthonous contribution in the dam-regulated river in contrast to its tributaries, along with less natural cover in the riparian zone, but a high percentage of natural vegetation on the islands. Additionally, we observed greater contribution of the riverine sources for all three rivers, independent of the trophic state and natural cover of the river. The trophic position was greater for the fish in the river in a protected area and lower in the rivers with a high percentage of agropastoral activities in the riparian areas. These findings show the importance of the conservation of the riverine zones mainly in dam-regulated rivers, because this vegetation provides the main energy source by fish.

Linking ecological characteristics with fish diversity, assemblage patterns and feeding guilds, and GIS applications along the temporal and spatial gradients in a large subtropical reservoir, India, for sustainable management

Abstract The objective of the investigation was to explore the abundance, composition, and diversity patterns of the fish fauna along the temporal and spatial scale and study the influence of environmental parameters on the fish assemblage in the Rihand reservoir, a large sub-tropical Indian reservoir in India. On the temporal scale, the highest abundance was recorded in the summer season and the lowest in the monsoon season, while on the spatial scale, the highest abundance was recorded from the riverine and the minimum from the lacustrine zone. The highest species richness and diversity were recorded from the riverine zone followed by the transitional and lacustrine zones, respectively. The analysis of the variance of fish abundance revealed insignificant differences between the riverine and the transitional zones. The trophic guild analysis indicated the dominance of carnivores. The output of canonical correspondence analysis depicted the significant influence of the physico-chemical traits on the abundance of fish species. The transparency and specific conductivity were found to be the most critical factors affecting fish assemblages in the Rihand reservoir. This study generated important baseline ecological information that would be useful for the monitoring, conservation, and management of the reservoir ecosystem.

Catchment scale assessment of macroplastic pollution in the Odaw river, Ghana

Catchment-scale plastic pollution assessments provide insights in its sources, sinks, and pathways. We present an approach to quantify macroplastic transport and density across the Odaw catchment, Ghana. We divided the catchment into the non-urban riverine, urban riverine, and urban tidal zones. Macroplastic transport and density on riverbanks and land were monitored at ten locations in December 2021. The urban riverine zone had the highest transport, and the urban tidal zone had the highest riverbank and land macroplastic density. Water sachets, soft fragments, and foam fragments were the most abundant items. Our approach aims to be transferable to other catchments globally.

Spatiotemporal variability and environmental effects of greenhouse gases, nutrients, and dissolved carbons in an ice-covered reservoir

Ice cover restructures the distribution of substances in ice and underlying water and poses non-negligible environmental effects. This study aimed to clarify the spatiotemporal variability and environmental effects of methane (CH4), nitrous oxide (N2O), total nitrogen (TN), total phosphorus (TP), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) in ice and water columns during different ice-covered periods. We surveyed the ice-growth, ice-stability, and ice-melt periods in an ice-covered reservoir located in Northeast China. The results showed that underlying water (CH4: 1218.9 ± 2678.9 nmol L−1 and N2O: 19.3 ± 7.3 nmol L−1) and ice (CH4: 535.2 ± 2373.1 nmol L−1 and N2O: 9.9 ± 1.5 nmol L−1) were sources of atmospheric greenhouse gases. N2O concentrations were the highest in the bottom water of the reservoir while CH4 accumulated the most below the ice in the riverine zone. These can be attributed to differences in the solubilities and relative molecular masses of the two gases. Higher concentrations of N2O, TN, TP, DOC, and DIC were recorded in the underlying water than those in the ice due to the preferential redistribution of these substances in the aqueous phase during ice formation. Additionally, we distinguished between bubble and no-bubble areas in the riverine zone and found that the higher CH4 concentrations in the underlying water than those in the ice were due to CH4 bubbles. In addition, we reviewed various substances in ice-water systems and found that the substances in ice-water systems can be divided into solute exclusion and particle entrapment, which are attributed to differences between dissolved and particulate states. These findings are important for a comprehensive understanding of substances dynamics during ice-covered periods.

The origin of suspended particulate matter in the Great Barrier Reef

River run-off has long been regarded as the largest source of organic-rich suspended particulate matter (SPM) in the Great Barrier Reef (GBR), contributing to high turbidity, pollutant exposure and increasing vulnerability of coral reef to climate change. However, the terrestrial versus marine origin of the SPM in the GBR is uncertain. Here we provide multiple lines of evidence (13C NMR, isotopic and genetic fingerprints) to unravel that a considerable proportion of the terrestrially-derived SPM is degraded in the riverine and estuarine mixing zones before it is transported further offshore. The fingerprints of SPM in the marine environment were completely different from those of terrestrial origin but more consistent with that formed by marine phytoplankton. This result indicates that the SPM in the GBR may not have terrestrial origin but produced locally in the marine environment, which has significant implications on developing better-targeted management practices for improving water quality in the GBR.

Seasonal and Spatial Distribution of Walleye Sex Ratios in a Large Nebraska Reservoir

Abstract The ratio of female to male Walleye Sander vitreus across the spatial scale of large reservoirs and during nonspawning times receives little attention, even though standardized sampling occurs during this time. This study evaluated whether the proportion of female Walleye collected from seasonal sampling at different spatial areas within a large reservoir fell within the 0.450–0.550 range, which would closely reflect a 1:1 female-to-male sex ratio. We used a Bayesian generalized linear mixed-effects model with a binomial probability distribution to assess the proportion of female Walleye, using season (spring and fall) and reservoir zone (riverine, transitional, and lacustrine) as fixed effects and year (2015 and 2016) as a random effect. We collected a total of 2,163 Walleye using standardized Nebraska Game and Parks Commission gill-netting methodology and determined sex on a random subsample of fish (n = 989) collected throughout each reservoir zone. There was no meaningful deviation from the 0.450–0.550 range in the mean posterior estimate of the proportion of female Walleye caught in the riverine and transitional zones during either spring or fall. The mean (SD) posterior estimate of the proportion of female Walleye in the lacustrine zone was 0.182 (0.024) in the spring and 0.621 (0.032) in the fall. These results are consistent with previous observations of increased male presence near spawning locations in the spring and demonstrate that increased fall female catch in the lacustrine zone could potentially bias sampling results. This study provides further insight into the distribution of sexes across the spatial gradient of a large Great Plains reservoir and demonstrates a need to sex Walleye during standardized fall surveys.

Estimation of phytoplankton carbon content in Jatigede Reservoir, Sumedang, West Java

Jatigede Reservoir is stagnant inland water formed from the damming of the Cimanuk river. Jatigede Reservoir, like any other reservoir, is horizontally divided into three areas, namely riverine, transition, and lacustrine. The different characteristics of each zone also impact the composition and community of phytoplankton, trophic status, and carbon content. This study aims to calculate the carbon content of phytoplankton in the waters of the Jatigede Reservoir in each zone with the composition and community of phytoplankton at a certain trophic status. The research stations were selected using purposive sampling with station selection based on the site in the reservoir, namely riverine, transition, and lacustrine. Analysis of trophic status and carbon content was used to determine the condition and presence of carbon in the Jatiged Reservoir. The trophic position of the Jatigede Reservoir based on the Nygaard Index and TSI (Tropic State Index) is categorized into the eutrophic level. Species from the Cyanophyceae class tend to have high abundances, but the higher carbon content is in the Dinophyceae class. Riverin, transitional, and lacustrine zoning have the same trophic status but have different compositions and phytoplankton communities. Based on the study results, the carbon content of phytoplankton was relatively high in the riverine and lacustrine zones and low in the transition zone.

Remote sensing of column-integrated chlorophyll a in a large deep-water reservoir

The accurate assessment of total algal biomass in large deep-water reservoirs is challenging because the characteristics of thermodynamic stratification in such reservoirs differ noticeably from those of other types of inland waters. To address this challenge, we proposed a novel remote sensing model to derive column-integrated chlorophyll a (CIC), a better indicator than water surface chlorophyll a concentration (Csurf), for evaluating total algal biomass. The proposed algorithm was utilized to construct the patterns of spatiotemporal change in CIC in the Xin’anjiang Reservoir (the largest freshwater human-made reservoir in East China, located in Zhejiang Province) based on 97 cloud-free Sentinel-2 satellite images from 2016 to 2020. The results showed that the best index for developing the CIC remote sensing model was the average chlorophyll a concentration within the euphotic layer, which could be derived from Csurf and euphotic depth. The proposed model demonstrated good performance in deriving CIC in the Xin’anjiang Reservoir from Sentinel-2 images (yielding a mean absolute percent error of 20.7% and a root mean square error of 16.3 mg/m2). The values of the five-year averaged CIC and total algal biomass within the reservoir were 62.38 mg/m2 and 22.31 t, respectively. The CIC in the Xin’anjiang Reservoir displayed noticeable spatial variation, with the highest CIC appearing in the riverine zone and the lowest CIC appearing in the lacustrine zone. Clear seasonal variation in CIC was observed, with CIC exhibiting the order summer > autumn > spring > winter. Although the model was developed for a specific reservoir, we believe that this research can serve as a case study that illustrates the benefits of using CIC for assessing spatiotemporal variation in phytoplankton.

Phytoplankton flora of asejire reservoir, Southwest Nigeria

An appraisal of the current ecological status of Asejire Reservoir was carried out using the reservoir phytoplankton composition and community structure. Monthly sampling was carried out in nine selected sites for twelve months. Data were analysed using descriptive statistics, analysis of variance, Shannon-Weiner and Evenness indices. One hundred and fifty-four phytoplankton taxa were identified. Taxa dominance was in the following order: Bacillariophycea>Chlorophycea>Charophycea>Cyanophycea>Euglenophycea>Ochrophycea>Dinophyceaa. Microcystis sp. were the most abundant species followed by Anabaena sp. and Closterium sp. The riverine zone accounted for 50.8% of the total phytoplankton population. One-way analysis of variance between the zones indicated that there was a significant difference (F=11.41, df=2, p=0.0000146) in the spatial distribution among the stations. Most of the recorded phytoplankton species are cosmopolitan with the presence of the following species: Staurastrum, Closterium, Cosmarium, Anabaena, and Oscillatoria. The presence of some pollution indicator species is a cause of concern and the need to ensure holistic and effective monitoring measure is put in place to safeguard the reservoir.

Freely dissolved organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) along the Indus River Pakistan: spatial pattern and risk assessment.

Freely dissolved OCPs and PCBs were measured by using polyethylene passive samplers at 15 sites during 2014 throughout the stretch of the Indus River to investigate the spatial pattern and risk assess. Levels (pg/L) of dissolved ∑OCPs and ∑PCBs ranged from 34 to 1600 and from 3 to 230. Among the detected OCPs, dissolved DDTs (p,p'-DDE, followed by p,p'-DDT) predominated with levels of 0.48 to 220pg/L. The order of occurrence for other studied OCPs was as follows: HCB, endosulfans, chlordanes, and HCHs. Spatially, dissolved (pg/L) ∑OCPs varied (p < 0.05) as the following: surface water of the alluvial riverine zone (ARZ) showed the highest levels (114) followed by the frozen mountain zone (FMZ) (52.9), low-lying zone (LLZ) (28.73), and wet mountain zone (WMZ) (14.43), respectively. However, our zone-wise PCB data did not exhibit significant differences (p > 0.05). Principal component analysis/multilinear regression results showed pesticide usage in the crop/orchard fields and health sector, electric and electronic materials, and widespread industrial activities as the main source of OCPs and PCBs along the Indus River. Our results showed that OCPs and PCBs contaminated water intake, playing an important role towards the considerable cancer/non-cancer risk (HI and CR values) along the Indus River Flood-Plain.

Effects of seasonal hypoxia on macroinvertebrate communities in a small reservoir

AbstractLocalized hypoxia can reduce available habitat, restrict movement and limit the abundance of aquatic invertebrates. Although cultural eutrophication, coupled with the effects of climate change, is likely to increase the frequency and extent of hypoxia in aquatic ecosystems, little is known about how oxygen gradients in small reservoirs influence spatial distribution and abundance of aquatic invertebrates. The present study evaluated the effects of environmental and biological attributes on seasonal and spatial variation of macroinvertebrates and explored how hypoxic conditions influenced littoral, benthic and pelagic macroinvertebrate communities in Lake Alvin, South Dakota. Data on reservoir conditions, in conjunction with macroinvertebrate sampling from May to October 2009–2011, were applied in an information theoretic approach to evaluate factors affecting invertebrate abundance. Hypoxic conditions were present from May to September in the lacustrine zone impacting 10%–39% of the water column. Benthic invertebrates were typically absent from the lacustrine zone during periods of severe hypoxia and were most abundant in the shallow, well‐oxygenated riverine zone. Littoral invertebrates were negatively related to the per cent of the hypoxic water column, suggesting fish, confined to shallow waters by hypoxia, may be consuming a larger portion of littoral invertebrates in their diets. Cladocera and Copepoda densities were influenced primarily by water depth and monthly precipitation. The larger size of Daphnia found in the hypoxic‐prone transitional and lacustrine zones suggested low oxygen concentrations may provide a refuge from fish predation. The results of the present study demonstrated spatial variations in near‐bottom oxygen concentrations were important predictors of macroinvertebrate and zooplankton abundance and size structure in Lake Alvin and that macroinvertebrates, particularly benthic and littoral invertebrates, could benefit from measures taken to reduce summer hypoxia.

Heavy metal impression in surface sediments and factors governing the fate of macrobenthic communties in tropical estuarine ecosystem, India.

The present study aims to investigate the contamination of heavy metals in the sediments of a tropical ecosystem, India, and to evaluate the factors responsible for the dominance of specific macrobenthic communities, particularly in estuarine sediments. For the analysis of Cu, Cr, Ni, Zn, Pb and Cd in sediments, acid digestion and subsequent quantification by microwave plasma atomic emission spectroscopy was performed, whereas for Hg determination, cold vapour atomic absorption spectrophotometry was used. The general trend of the heavy metal concentration was observed as Cr > Cu > Zn > Ni > Pb > Cd > Hg, regardless of any seasonal alteration. The estuarine region was considerably contaminated by Cu and Cr (C.F. > 2) irrespective of any seasonal difference, and by Cd in 2017 non-monsoon (CF > 3). Heavy metal contamination was most pronounced during the monsoon (2018). Estuarine and marine zone together considered as deteriorated zone especially during monsoon seasons (PLI > 1, 2018 monsoon) while riverine zone remained poorly contaminated (PLI < 1). Clay Loam/Clay/Heavy Clay textures preferred polychaetes and bivalves in the estuarine and marine zone as compared to other macrobenthic communities (OMC). Among the hydrochemical parameters, total dissolved solids in general and euryhaline and slightly alkaline pH preferred domination of bivalves followed by polychaetes in non-monsoon seasons. The trace metal contamination in estuarine sediments increases the concern of bioaccumulation tendency of dominant bivalves of the estuarine and coastal sediments.

Zooplanktonic Community Assessment over Space and Time: A biomonitoring Tool in an Artificial Lake

Aims: The prime objective of this study is to determine the taxonomic composition of the zooplankton fauna of Esa-Odo Reservoir in Osun State and determine the spatial (horizontal and vertical) and seasonal variations in the composition, distribution abundance, and community structure of the zooplankton community in the reservoir.&#x0D; Study design: sampling stations were selected horizontally and vertically to cover the entire zones of the reservoir. Planktonic samples were collected at two months intervals for two years.&#x0D; Methodology: Samples were collected from the depth using an improvised Meyer’s water sampler. Net and Total plankton were sampled by filtration and sedimentation methods. Planktonic samples were preserved as 5% formalin and 1% Lugol’s solution. Measurement, enumeration, and scaled pictures of the recorded zooplankton were taken using a photomicrograph. The taxonomic composition of zooplankton biota was determined using identification keys. Data analysis was done using PAST Statistical Package. ANOVA was used to determine the spatio-temporal variations.&#x0D; Results: Fiftyty-three (53) pecies of total zooplankton recorded in this study belong to 4 groups: Rotifera, Cladocera, Copepoda, and Insecta. Rotifera was the most represented group (61.21%). Horizontally, 24 species with the highest mean abundance characterized the lacustrine; while 12 species and 10 species were unique to the transition and riverine zones, respectively. Vertically, most species had their mean abundance decreased from the surface to the bottom of the reservoir. A total of nine (9), two (2) and one (1) species were peculiar to the surface, bottom and mid-depth, respectively. Zooplankton organisms were most abundant during the dry season.&#x0D; Conclusion: Esa-Odo Reservoir comprised highly diversified zooplankton fauna with great potential to support rich aquatic community and fishery production. The reservoir can be classified as fairly clean based on the abundance of the rotifer group. However, the lake should be subjected to regular proper monitoring because of the presence of some pollution tolerant copepod species identified among the zooplankton fauna.

Spatiotemporal distribution of rift valley fever and malaria vectors in Baringo County, Kenya: Implications on vector control

Rift Valley Fever and malaria are zoonotic and human diseases respectively that pose major production and health challenges to pastoralists. This study aimed to determine the spatiotemporal distribution of mosquito vectors of these two diseases in Baringo County, Kenya. A longitudinal study design was used to collect mosquitoes from twenty four sites. Rainfall seasonality was determined using rainfall data from the WorldClim database. Negative binomial and zero-inflated negative binomial regression models were used to determine the effect of rainfall seasonality and ecogeographical conditions on vector distribution. Spatio-temporal maps showing vector distribution were made using the sf package in R. Four Rift Valley Fever vector species and four malaria vector species were collected and were predominantly found in the lowland and riverine zones. Vector control interventions against the two diseases should therefore target these two zones. The study also recommends integrated vector management methods targeting both larval and adult stages.

Variations in water quality parameters and their correlation with fish catch per unit effort of Bhini Stream, a tributary of River Ravi, Jammu and Kashmir, India

The quality of water is very critical for fish survival and growth in a water body. However, little is known about the state of the Bhini Stream’s water quality and its relationship to fish catch. The focus of this study was to evaluate water quality parameters in the Bhini Stream and see if there was a correlation between them and fish catch per unit effort. Monthly samples were gathered using a three-level stratified sampling method. Temperature, depth, transparency, pH, TDS, EC, DO, alkalinity, hardness, chloride, sulphate, phosphate, nitrate, and fish catch (CPUE) were all monitored simultaneously in each of the three strata of the stream. The water quality characteristics were within the permissible range for fish production. There were no significant differences in water quality parameter concentrations between the riverine, transitional, and lacustrine zones (p&gt;0.05). TDS and nitrates from fertilisers used on nearby fields and brought to the stream by runoff or floods were significantly and negatively correlated with CPUE (r=0.84, p&lt;0.05; r=0.71, p&lt;0.05). 13 fish species all belonging to order Cypriniformes were reported from the stream with Schistura denisoni being reported for the first time from the River Ravi.

Long-Term Water Quality Patterns in an Estuarine Reservoir and the Functional Changes in Relations of Trophic State Variables Depending on the Construction of Serial Weirs in Upstream Reaches.

Water quality degradation is one of the major problems with artificial lakes in estuaries. Long-term spatiotemporal patterns of water quality in a South Korean estuarine reservoir were analyzed using seasonal datasets from 2002 to 2020, and some functional changes in relations of trophic state variables due to the construction of serial weirs in the upper river were also investigated. A total of 19 water quality parameters were used for the study, including indicators of organic matter, nutrients, suspended solids, water clarity, and fecal pollution. In addition, chlorophyll-a (CHL-a) was used to assess algal biomass. An empirical regression model, trophic state index deviation (TSID), and principal component analysis (PCA) were applied. Longitudinal fluctuations in nutrients, organic matter, sestonic CHL-a, and suspended solids were found along the axis of the riverine (Rz), transition (Tz), and lacustrine zones (Lz). The degradation of water quality was seasonally caused by resuspension of sediments, monsoon input due to rainfall inflow, and intensity of Asian monsoon, and was also related to intensive anthropic activities within the catchment. The empirical model and PCA showed that light availability was directly controlled by non-algal turbidity, which was a more important regulator of CHL-a than total nitrogen (TN) and total phosphorus (TP). The TSID supported our hypothesis on the non-algal turbidity. We also found that the construction of serial upper weirs influenced nutrient regime, TSS, CHL-a level, and trophic state in the estuarine reservoir, resulting in lower TP and TN but high CHL-a and high TN/TP ratios. The proportions of both dissolved color clay particles and blue-green algae in the TSID additionally increased. Overall, the long-term patterns of nutrients, suspended solids, and algal biomass changed due to seasonal runoff, turnover time, and reservoir zones along with anthropic impacts of the upper weir constructions, resulting in changes in trophic state variables and their mutual relations in the estuarine reservoir.