Entire Lake Research Articles

Introduction of a new method of measuring the water level when creating a digital monitoring system of the Baikal water area

In this article, the solution of the tasks of monitoring the Baikal natural water area is supplemented by the introduction of a new method of measuring the water level. This method is aimed at solving current problems and tasks that arose earlier in the development of a digital monitoring system.[1-2] The transition to a new measurement method will improve the accuracy of measurements, calculate both the average level of the entire Lake Baikal and the local level in certain regions of the lake. The possibility of radio-channel data transmission makes it possible to capture data in remote areas of Lake Baikal. Our own innovative method of measuring the water level is characterized by a simple setup and calibration of the sensitive elements of the device, which allows you to set the required number of monitoring points throughout Lake Baikal. The introduction of a new measurement method will create a budget monitoring system that is not inferior to foreign analogues.

Spatial Risk Assessment and Source Identification of Heavy Metals in Riverine Sediments of Lake Chaohu Basin, China

In recent decades, the rivers in Lake Chaohu Basin have been subjected to intensive anthropogenic disturbance. However, previous studies have mainly focused on Lake Chaohu, and the inflowing and outflowing rivers have not been well examined. To characterize the pollution status of heavy metals in the entire Lake Chaohu Basin, 8 heavy metals (Cu, Zn, Pb, Cr, Cd, As, Hg, and Ni) in riverine surface sediments were measured at 131 sampling sites in 7 subbasins. Spatial patterns and pollution characteristics were evaluated based on the potential ecological risk, geoaccumulation, and pollution load indexes. The results showed that Cr and Hg were the 2 main heavy metal pollutants in the surface sediments, with mean contents exceeding background values by a factor of 4.12 and 2.64, respectively. The Nanfei River (NF), which flows through Hefei city (a metropolis of the capital of Anhui Province), is characterized by large amounts of domestic and industrial waste discharged into the water body due to human activities; this waste caused serious heavy metal pollution, and NF substantially contributed to heavy metal pollution inputs to Lake Chaohu. Several subbasins in the southern part of Lake Chaohu Basin exhibited high concentrations of Cu in surface sediments, mainly from mining and agriculture. This study identified the main contamination areas, revealed the possible sources of each heavy metal, and can serve as a reference for the remediation and management of Lake Chaohu Basin to ensure the water safety of Lake Chaohu.

A novel remote sensing index for brine shrimp (Artemia) slick detection in salt lakes

Artemia (brine shrimp) are a widely distributed zooplankton in inland salt lakes and artificial ponds throughout the tropical, subtropical, and temperate zones. Notably, they are of great importance to fishery production and salt lake ecosystem health. Recently, Artemia resources have been threatened by habitat deterioration and overfishing, which mandate adequate monitoring; however, advanced methods for detecting Artemia from remote sensing images have rarely been discussed. Accordingly, this study explored the possibility of detecting the adult Artemia (Artemia) slicks using multispectral optical sensors by analyzing their unique aggregation patterns and consistent optical properties. After measuring Artemia spectra in the field, reflectance troughs were observed at ∼431 nm and ∼ 560 nm, which were deemed likely related to the absorption of β-carotene and heme, respectively, resulting in their reddish color. These characteristics could also be used to differentiate Artemia from other confounding features, including clean water and chlorophyll-a (Chl-a)- or suspended particulate matter (SPM)- dominated water. Based on these spectral signatures, a brine shrimp index (BSI) was developed using the difference between the reflectance at NIR band and a linear baseline between green and SWIR1 bands of Landsat-8 Operational Land Imager (OLI) imagery. Further, a BSI-based Artemia slick pixel extraction method was proposed. Using observation geometry information in conjunction with the BSI value of entire lakes, the BSI thresholds for the Artemia-containing pixels were automatically determined, and > 80% overall accuracy was achieved. The index performance was affected by the presence of residual cloud shadows, high water turbidity, and mixed pixels with low Artemia density. Moreover, BSI values were found to be relatively insensitive to atmospheric signals. It was shown here that the BSI detection limit was >0.53% Artemia subpixel coverage under clean water conditions; whereas a higher coverage was required to separate Artemia from Chl-a- or SPM- dominated water. The mean absolute percentage difference of BSI values calculated from Rayleigh-corrected and top-of-atmosphere (TOA) reflectance was <4% compared with surface reflectance derived BSI, and the relative difference in coverage area was < ±10%. Lastly, time series analyses of Lake Aibi in northwest China and the Great Salt Lake in North America revealed that the annual areal coverage estimation of Artemia slicks based on BSI was a positive indicator of Artemia harvesting, which can facilitate the Artemia resource management.

Heavy metal (Cr, Cu, Ni, Pb, and Zn) contents of endemic Salvia halophila plants around Lake Tuz

Heavy metals occur naturally in ecosystems at varying concentrations. However, heavy metal sources that have emerged in present-day mainly due to human influence, i.e. industrial activities, agricultural waste, pesticides, use of fossil fuels and traffic, have included a part of heavy metals in the ecosystem. Lake Tuz, together with the entire lake surroundings, water beds and important steppe areas, was declared Turkey’s Specially Protected Area (SPA) in 2001. Our aim in this investigation was to determine the levels of heavy metals such as Chrome (Cr), Copper (Cu), Nickel (Ni), Lead (Pb) and Zinc (Zn) in endemic Salvia halophila grown in different areas of Lake Tuz. The results of the heavy metal contents analyzed at the plant were compared with the international standard levels of heavy metals. The consequences displayed that differing extents of heavy metals are accumulated in S. halophila. The results obtained differed in accordance with the collection time and localities. When the outcomes are appraised, it is achievable to say that Pb is higher than the standard values. The findings of this investigation are the first reported results for this endemic S. halophila species that grows naturally at Lake Tuz and are important as they are newly discovered results.

Improving the digital elevation model of topographic maps in GIS (applied study on Al-Tharthar Lake)

The research aims to be an attempt by the researchers to apply improving the model of the digital rise, thus opening the way for researchers who are interested in developing and expanding this idea in the future. The development of the improved digital elevation model within the boundaries of Al-Tharthar Lake its elevation levels means the unimproved digital elevation model within the lake boundaries of Mozaic topographic maps, in order to avoid the limitations of the unimproved digital elevation model that shows the entire lake at a level of 44 meters above sea level, so the improved digital elevation model shows its morphological, hydrological, topographic and topographic properties within the lake's various elevations within the lake's various elevations within the boundaries of the lake. These proposed steps in the research have proven to be efficient in improving digital elevation models, and the improved digital elevation model has proven to be highly effective in giving a high-level geo-reality perception of the lake greater credibility than it does: the unimproved digital elevation model as well as the old topographic maps. One of the recommendations of the research, recommends the Ministry of Water Resources and General directorate of Survey do accurate field survey principally hydrographic survey for lakes and rivers of the country through the marine area devices which are the best way to represent the topography of the lake with very high accuracy on two levels: horizontal topographic morphometric, vertical interval and elevation levels from both local and national geodesic reference. Consequently, the possibility of updating topographic maps which belong to 20th century

Horizontal and vertical distribution of microplastics in Gehu Lake, China

Abstract Microplastics (MPs) widely exist in the aquatic environment. In this study, the horizontal and vertical distribution of MPs in different depths of Gehu Lake was analyzed. The study found that MPs were detected in water bodies at different depths. The Gehu Lake Basin's MP abundance throughout the entire lake region ranged from 1.40 to 5.53 n/L. Microplastic abundance in surface water (3.13 ± 0.32 n/L) was highest, and the average abundance of MPs in the middle water (2.28 ± 0.24 n/L) and bottom water (1.03 ± 0.14 n/L) was appreciably reduced (p &amp;lt; 0.05). The microplastics observed in water samples were analyzed, and it was found that the particle size of most of the obtained microplastic particles was between 100 and 500 microns, the main shape was fibrous MP, and the MP content of transparent color was highest, and the four most common MPs was polyethylene (PE), polystyrene, polyester (PES), and polypropylene (PP). In this article, we emphasize the importance of comprehending the specific distribution characteristics of MPs in Gehu Lake. It provides a data foundation for future monitoring of MPs present in Gehu Lake, provides scientific and technological support for the assessment and prevention of microplastic pollution in this area, and offers some assistance for future lake water quality regulation.

Trace Element Compositions and Water Quality Assessment in the Angara River Source (Baikal Region, Russia)

The relevance of studying the spatial-temporal dynamics in the trace element composition of the water at the Angara River source is associated not only with determining the degree of anthropogenic load on the local area of the water body but also with the use of the water chemical composition of the Angara River source as an integral indicator of the hydrochemical state of the entire Lake Baikal. The current work is based on monthly monitoring studies conducted from March 2021 to February 2022 along the left shore, middle part, and right shore of the Angara River source. In water samples, the concentrations of Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Sn, Cs, Tl, Pb, Th, and U were measured by inductively coupled plasma mass spectrometry. The results indicated that the concentrations of the trace elements lie within mean + 1SD: Cd in 97% of samples; U in 94% of samples; Tl in 92%; Al, Cr, Co, Ni, Cu, Zn, Sn, Pb, and Cs in over 80%; Fe in 78% of samples; and Mn and Th in over 60% of samples. Such results show a high degree of consistency in the water trace element composition at the source of the Angara River. The major factors responsible for the water hydrochemistry at the Angara River source include the runoff of Lake Baikal, the anthropogenic effect of Listvyanka and Port Baikal settlements, and water transport activity. The concentrations of all trace elements in the water of the Angara River source are substantially below the standards for drinking water. At the same time, the single-factor pollution index revealed water samples with considerable contamination by Fe, Zn, Sn, Al, Cs, Mn, Cu, Tl, Cd, Pb, and Th and very high contamination by Cr, Fe, Co, Cs, Tl, Pb, and Th. The pollution load index has classified most of the water samples as having baseline levels of pollutants. Three samples taken from the left shore, four from the middle part, and seven from the right shore were classified as polluted. This means that the ongoing anthropogenic impact may worsen the water quality and have a negative impact on living organisms. The obtained results make a clear case for strengthening environmental protection measures to minimize the anthropogenic effect on the ecosystems of Lake Baikal and Angara River.

Primary productivity of phytoplankton and its influencing factors in cold and arid regions: A case study of Wuliangsuhai Lake, China

This study measured the primary productivity (PPeu) of phytoplankton in Wuliangsuhai Lake from April 2014 to January 2019 based on the monitoring and on-site exploration of 20 sampling points in the entire lake using a vertically generalized production model (VGPM). The relationship between the spatiotemporal variation in PPeu and environmental factors was also analyzed. Our findings indicated that the temporal heterogeneity of PPeu was strong, and the average annual PPeu of the four seasons was significantly different (P < 0.05, F = 54.74), exhibiting the following descending order: summer (1279.89 ± 111.04 mg C∙m−2∙d−1) > spring (782.42 ± 59.34 mg C∙m−2∙d−1) > autumn (465.03 ± 49.30 mg C∙m−2∙d−1) > winter (96.34 ± 10.36 mg C∙m−2∙d−1). Even in winter with harsh environmental conditions, PPeu under the ice sheet can reach 8 % of that in summer. The spatial heterogeneity was weak, and only the average annual PPeu in spring exhibited a significant spatial difference (P < 0.05, F = 5.18): north > central > south. However, there were no significant differences in other seasons. Redundancy analysis (RDA) and multiple linear regression (MLR) results showed that in addition to directly participating in the calculation of the environmental factors of PPeu, PPeu in spring was mainly affected by total nitrogen (TN), total phosphorus (TP), and dissolved oxygen (DO). PPeu in summer was mainly affected by dissolved inorganic phosphorus (DIP), dissolved oxygen (DO), salinity (S), electrical conductivity (EC), and water temperature (WT). PPeu in autumn was mainly affected by pH, electrical conductivity (EC), suspended solids (SS), and water temperature (WT). PPeu in winter was mainly affected by water temperature (WT) and ice thickness (IT). The mechanisms through which environmental factors affect primary productivity are complex and dynamic. Therefore, long-term monitoring and research of PPeu in Wuliangsuhai Lake are necessary to explore the adaptation strategies of phytoplankton in ice and ice-free periods and understand the operation of natural life support systems under the alternation of ice generation and extinction. In turn, this would facilitate the development of strategies to maintain phytoplankton biodiversity and prevent algal blooms.

Lake Victoria Thunderstorms: Radar-Observed Initiation and Storm Evolution Modes

Abstract The enhanced observation period during the HIGHWAY field campaign in East Africa provided the opportunity to obtain continuous ground-based radar observations over the Lake Victoria basin. This provided insight into thunderstorm initiation processes and thunderstorm evolution. This insight is significant for it can lead to nowcasting thunderstorms over Lake Victoria, which is particularly important because of the &gt;200 000 fishers using the lake daily and the extremely high number of drownings resulting from capsized boats caused by large waves and high winds from thunderstorms. Radar data from the south shoreline of Lake Victoria made it possible to observe thunderstorm activity over the entire lake. Unexpectedly the radar returns from high concentration of insects over the lake made it possible for the radar to observe boundary layer convergence lines. With this information a radar-trained forecaster could provide nowcasts of severe storm locations and by using extrapolation techniques provide nowcasts of their future location. In addition, rules for forecasting the timing and extent of nighttime thunderstorm activity over the lake based on radar monitoring of earlier activity along the northeast land/lake region are provided. While there are many obstacles to overcome, it is hoped that in the near future this possible life-saving information can be provided to Lake Victoria boaters. Significance Statement Radar data from the south shore of Lake Victoria has enabled new understanding of thunderstorm initiation and evolution over the lake. This understanding provides the potential to nowcast thunderstorms over Lake Victoria. This is particularly important because of the extremely high number of drownings that occur over the lake that result from capsized boats caused by large waves and high winds from thunderstorms. Radar-based rules are provided for forecasting and nowcasting the timing and severity of Lake Victoria thunderstorms.

Characteristics and source analysis of water pollution in dry season (November to March) of Dongping Lake (China)

In this study, factor analysis, principal component analysis (PCA) and correlation analysis were used to analyze the water quality in dry season of Dongping Lake, which is the only natural lake in the lower Yellow River and an important hub of South-North Water Diversion Project (SNWDP) of China. The nutritional status of the lake was evaluated by trophic level index, and the spatial heterogeneity and aggregation status of the eutrophication level were studied by spatial autocorrelation analysis. Moreover, the pollution-discharge-coefficient method was carried out to clarify the potential pollutant sources. Results showed that the lake was in the light eutropher state with the water quality of V and poor V. Nitrogen pollutants were the primary driving factor of water quality, and water depth was the main environmental factor affecting the spatial distribution of nitrogen pollutants. The eutrophication level of the entire lake showed significant positive spatial autocorrelation. Due to the influence of regional eutrophication levels, the spatial heterogeneity of eutrophication level was low. Two hotspots (High-High concentration) of eutrophication were present in the southeast (P < 0.01) and the north (P < 0.05) of the lake. However, causes for the formation of these two hotspots were different, which mainly resulted from the non-point source discharge of surrounding towns along the southeastern lake and the weak hydrodynamic conditions in the northern lake, respectively. Therefore, it is necessary to pay more attention to control the non-point source discharge into Dongping Lake, especially for regions around the southeast of the lake, in the future management.

Assessment and source analysis of heavy metal contamination in water and surface sediment in Dongping Lake, China

Dongping Lake is the only natural lake in the lower Yellow River and an important hub of South-North Water Diversion Project, its water quality is of vital importance to the environmental protection and the security of water supply. To assess the heavy metal (HM) contamination in Dongping Lake, samples in water and surface sediment were taken from 59 sampling sites over the entire lake. The statistical characteristics, pollution conditions, and source identifications were analyzed using coupling methods of entropy water quality index (EWQI), modified pollution index (mCd), enrichment coefficient (EF), geo-accumulation index (Igeo), potential ecological risk index (PERI), and positive matrix factorization (PMF). In present study, the averaged concentrations of all studied HMs in water body of Dongping Lake were below the limit of drinking water quality standard recommended by WHO, and the EWQI and mCd of HM concentrations were identified to be in good and excellent conditions. The concentrations of almost all studied HMs in surface sediment of Dongping Lake exceeded the background values in the soil of Shandong Province, and Cd (cadmium) was the dominant pollutant. With EF > 2, Igeo > 1, and Er > 80, Cd in sediment was under moderate pollution. The outcomes of source analysis revealed that the HMs in surface sediment were mainly derived from the primary and secondary industries. Specifically, manufacturing industries contributed the most to the HM contaminations in sediment of Dongping Lake.

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

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

Transition of a small Himalayan glacier lake outburst flood to a giant transborder flood and debris flow

Glacial lake outburst floods (GLOFs) are a great concern for the Himalaya, as they can severely damage downstream populations and infrastructures. These floods originate at high altitudes and can flow down with enormous energy and change the terrain’s existing morphology. One such devastating event occurred on the night of 5 July 2016, from the inconspicuous Gongbatongsha Lake, located in the Poiqu basin, Eastern Himalaya. The Poiqu basin in the Tibetan Autonomous Region currently contains numerous big glacial lakes; however, this event originated from a small lake. The GLOF was triggered following heavy precipitation that led to a slope failure above the lake and deposition of debris into the lake, which breached the moraine dam and rapidly drained the entire lake. The flood damaged several downstream infrastructures, including the Arniko highway, the Upper Bhotekoshi hydropower plant, and several buildings as it made its way into the Bhotekoshi basin in Nepal. This study adopts a multi-model approach to reconstruct the GLOF trigger and the flood’s transformation into a severe debris flow. Proxies including flow discharge, flow velocity, runout distances were used to calibrate the model and validate the results. Results reveal that a debris flow of volume ranging between 3000 and 6000 m3 from the headwall must have led to lake overfill, eventually leading to the GLOF event. The GLOF showed a significant increase in peak discharge from 618 to 4123 m3 s−1 at the Zhangzangbo-Bhotekoshi confluence. The average velocity of the flow is calculated to be ~ 5.5 m s−1. Reconstruction of the erosion and deposition dynamics show that maximum erosion occurred in the first 6.5 km, with maximum deposition occurring near the Upper Bhotekoshi hydropower station. The modeling indicates that the availability of the entrainable debris along the channel, likely from the previous landslides, amplified the event by three orders of magnitude-additional water ingested from the river. Overall, we demonstrate how the small-scale Gongbatongsha GLOF amplified downstream by incorporating pre-existing sediment in the valley and triggered damaging secondary landslides leading to an economic loss of > 70 million USD.

Variation of satellite-derived total suspended matter in large lakes with four types of water storage across the Tibetan Plateau, China

Total suspended matter (TSM), as an indicator of the concentration of fine materials in the water column including particulate nutrients, pollutants, and heavy metals, is widely used to monitor aquatic ecosystems. However, the long-term spatiotemporal variations of TSM in lakes across the Tibetan Plateau (TP) and their response to environmental factors are rarely explored. Accordingly, taking advantage of the Landsat top-of-atmosphere reflectance and in-situ data, an empirical model (R2 = 0.83, RMSE = 1.08 mg/L, and MAPE = 19.49 %) was developed to estimate the average autumnal TSM in large TP lakes (≥50 km2) during the 1990–2020 period. For analyzing the spatiotemporal variability in TP lakes TSM, the examined lakes were classified into four types (Type A-D) based on their water storage changing in different periods. The results showed that the lakes in the southern and some northeastern parts of the TP exhibited lower TSM values than those situated in other regions. The assessment of TSM in each of these four lake types showed that more than half of them had a TSM value of <20 mg/L. Apart from Type D, the lakes with the TSM showing significantly decreasing trends were dominantly Types A-C. A relative contribution analysis involving five driving factors indicated that they contributed by >50 % to lake TSM interannual variation in 73 out of 114 watersheds, and the lakes area change demonstrated the greatest contribution (82.2 %), followed by wind speed (11.0 %). Further comparison between the entire lake and the non-expansive regions suggested that the expansive region played an indispensable role in determining the TSM value of the whole lake. This study can help to better understand the water quality condition and provide valuable information for policy-makers to maintain sustainable development in the TP region.

Regional-scale investigation of the molecular weight distribution and metal-binding behavior of dissolved organic matter from a shallow macrophytic lake using multispectral techniques

In this work, based on excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-FARAFAC) and two-dimensional correlation analysis of synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy, and combination of two spectra (2D-SF-COS, 2D-FTIR-COS, and Hetero-2D-COS), the characteristics and metal-binding behaviors of DOM in Dongping Lake were explored for molecular weight (MW), fluorescence components, and functional groups. The results showed that the entire lake was governed by protein-like materials with low MW(< 1 kDa). The complexation occurred preferentially in protein-like materials for bulk DOM after adding copper (Cu2+) and lead (Pb2+), which were changed by fractionation for MW. The active points were aliphatic C－OH for DOM-Cu and phenol －OH or polysaccharide for DOM-Pb from 2D-FTIR-COS. The protein-like components possessed higher LogK than humic-like component during binding to Cu2+ or Pb2+. Moreover, the complexing affinities of DOM-Cu (LogKCu: 3.26 ± 0.87–4.04 ± 0.49) were higher than those of DOM-Pb (LogKPb: 2.66 ± 0.52–3.78 ± 0.36). On a spatial scale, high LogKCu and LogKPb were found in the center and entrance of the lake, respectively. Humic-like component C2 in the LMW fraction possessed a stronger binding capacity with Cu2+. This study affords new insights into the migration and conversion of HMs in lakes.

Direct and indirect effects of climate change on distribution and community composition of macrophytes in lentic systems.

ABSTRACTMacrophytes are an important part of freshwater ecosystems and they have direct and indirect roles in keeping the water clear and providing structure and habitats for other aquatic organisms. Currently, climate change is posing a major threat to macrophyte communities by altering the many drivers that determine macrophyte abundance and composition. We synthesise current literature to examine the direct effects of climate change (i.e. changes in CO2, temperature, and precipitation patterns) on aquatic macrophytes in lakes as well as indirect effects via invasive species and nutrient dynamics. The combined effects of climate change are likely to lead to an increased abundance and distribution of emergent and floating species, and a decreased abundance and distribution of submerged macrophytes. In small shallow lakes, these processes are likely to be faster than in deep temperate lakes; with lower light levels, water level fluctuations and increases in temperature, the systems will become dominated by algae. In general, specialized macrophyte species in high‐latitude and high‐altitude areas will decrease in number while more competitive invasive species are likely to outcompete native species. Given that the majority of endemic species reside in tropical lakes, climate change, together with other anthropogenic pressures, might cause the extinction of a large number of endemic species. Lakes at higher altitudes in tropical areas could therefore potentially be a hotspot for future conservation efforts for protecting endemic macrophyte species. In response to a combination of climate‐change induced threats, the macrophyte community might collapse, which will change the status of lakes and may initiate a negative feedback loop that will affect entire lake ecosystems.

Utilization of Pollution Indices, Hyperspectral Reflectance Indices, and Data-Driven Multivariate Modelling to Assess the Bottom Sediment Quality of Lake Qaroun, Egypt

Assessing the environmental hazard of potentially toxic elements in bottom sediments has always been based entirely on ground samples and laboratory tests. This approach is remarkably accurate, but it is slow, expensive, damaging, and spatially constrained, making it unsuitable for monitoring these parameters effectively. The main goal of the present study was to assess the quality of sediment samples collected from Lake Qaroun by using different groups of spectral reflectance indices (SRIs), integrating data-driven (Artificial Neural Networks; ANN) and multivariate analysis such as multiple linear regression (MLR) and partial least square regression (PLSR). Jetty cruises were carried out to collect sediment samples at 22 distinct sites over the entire Lake Qaroun, and subsequently 21 metals were analysed. Potential ecological risk index (RI), organic matter (OM), and pollution load index (PLI) of lake’s bottom sediments were subjected to evaluation. The results demonstrated that PLI showed that roughly 59% of lake sediments are polluted (PLI &gt; 1), especially samples of eastern and southern sides of the lake’s central section, while 41% were unpolluted (PLI &lt; 1), which composed samples of the western and western northern regions. The RI’s findings were that all the examined sediments pose a very high ecological risk (RI &gt; 600). It is obvious that the three band spectral indices are more efficient in quantifying different investigated parameters. The results showed the efficiency of the three tested models to predict OM, PLI, and RI, revealing that the ANN is the best model to predict these parameters. For instance, the determination coefficient values of the ANN model of calibration datasets for predicting OM, PLI, and RI were 0.999, 0.999, and 0.999, while they were 0.960, 0.897, and 0.853, respectively, for the validation dataset. The validation dataset of the PLSR produced R2 values higher than with MLR for predicting PLI and RI. Finally, the study’s main conclusion is that combining ANN, PLSR, and MLR with proximal remote sensing could be a very effective tool for the detection of OM and pollution indices. Based on our findings, we suggest the created models are easy tools for forecasting these measured parameters.

The spatiotemporal characteristics of water quality and phytoplankton community in a shallow eutrophic lake: Implications for submerged vegetation restoration

One of the most serious consequences of eutrophication in shallow lakes is deterioration of water quality, proliferation of phytoplankton and disappearance of submerged macrophytes. After removing herbivorous and plankti-benthivorous fish, submerged macrophyte restoration was utilized at the entire lake (82.7 km2) to combat eutrophication and improve water quality in the shallow subtropical aquaculture of Lake Datong. We conducted two years of monitoring, from March 2018 to February 2020. During the first year of restoration, 80% of the area of Lake Datong (approximately 60 km2) was successfully recovered by submerged vegetation, and the water quality was improved. For example, the phosphorous (P) content (including total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP)) and turbidity decreased, and the Secchi depth (SD) increased. However, the submerged vegetation disappeared from autumn 2019 in the intermittent recovery area (MN), while the continuous recovery area (DX) continued to recover with an abundance of submerged vegetation. During the second year, the water quality continued to improve significantly in the DX area, with high biomass and coverage of submerged vegetation. In the MN area, although turbidity and ammonia nitrogen (NH4+-N) increased significantly and SD decreased significantly, the P content (TP, TDP, and DRP) still continued to decrease. The restoration of submerged macrophytes could significantly decrease the density of phytoplankton. Over time, there was a regime shift in Lake Datong. The structural equation model (SEM) results illustrated that the water level and submerged plant coverage were the primary drivers that triggered changes in the state of the lake ecosystem. Our results highlight the potential of restoring submerged vegetation to control water eutrophication at the whole-lake scale. However, the water level in spring was the primary driver that triggered changes in the state of the lake ecosystem. Water level management should be emphasized during the early stages of recovery of submerged plants.

Joint Spatial Modeling of Nutrients and Their Ratio in the Sediments of Lake Balaton (Hungary): A Multivariate Geostatistical Approach

Eutrophication, water quality, and environmental status of lakes is a global issue that depends not only on external loadings from industrial, agricultural, and municipal sources but often also on internal loadings from lake sediments. In the latter case, in addition to the quality and quantity of nutrients stored in sediments, their relative content may be an important factor. In the example of Lake Balaton, we jointly modeled the spatial distribution of the nutrients nitrogen (N) and phosphorus (P) and their ratio (i.e., N:P) in the sediments of the lake and then provided spatial predictions at different scales (i.e., point, basin, and entire lake) with the associated uncertainty. Our aim was to illustrate the merits of applying multivariate geostatistics when spatial modeling of more than one variable is targeted at various scales in water ecosystems. Variography confirmed that there is a spatial interdependence between the nutrients. The results revealed that multivariate geostatistics allows this interdependence to be taken into account and exploited to provide coherent and accurate spatial models. Additionally, stochastic realizations, reproducing the joint spatial variability, can be generated that allow providing spatially aggregated predictions with the associated uncertainty at various scales. Our study highlighted that it is worthy of applying multivariate geostatistics in case spatial modeling of two or more variables, which jointly vary in space, is targeted in water ecosystems.

Исследования влияния расхода воды на протяжённость нерестовой миграции байкальского омуля Coregonus migratorius (Coregonidae) в реке Селенге на базе многолетних данных

The Selenga River, the main tributary of Lake Baikal, is 1,453 km long and accounts for 50 % of its surface runoff. It is a large foothill, free-flowing, unregulated watercourse flowing through Mongolia (2/3 of the length) and Russia (1/3). Global climatic changes in recent decades have been particularly evident in the Baikal region: since the mid-1990s, there has been a significant decrease in water and sediment runoff in the Selenga basin. Omul spends most of its life cycle in the lake; spawning takes place in the river system. In total, there are 22 spawning rivers of Baikal omul in the Lake Baikal basin, among which 47 % of its spawning grounds are concentrated in Selenga. Omul spawns in the Selenga channel within 20–580 km upstream of the lake, and in some years it crosses the border between Russia and Mongolia. Based on long-term (1936–2018) data of the Baikal omul spawning migration in the Selenga River, the relationship between the average migration distance of the spawning herd core and the water discharge at the beginning of the spawning migration (September) was analyzed. Statistical analysis has established an approximate threshold for water discharge, which marks the shortening of the spawning path in «high-water» years and a noticeable extension of it upstream in “low-water” years. The role of other cumulative factors affecting the spawning distance of omul is discussed. Under conditions of a long subglacial period, omul eggs are successfully incubated in large areas for five to six months (November–April). Stability of habitat characteristics in such a shelter is ensured by a significant decrease in flow velocity and temperature, as well as increased water transparency and a relatively favorable oxygen regime. Ice cover formation can also be attributed to protective factors: it reliably shelters eggs from external atmospheric impact: average ice thickness on the river during the study period was 0,5 m (0,1–1,5 m, maximum by spring it often reaches 2 m near the shores). Hydraulic construction in the upper Selenga Watershed in Mongolia could have a significant negative impact on the spawning grounds of the Baikal omul, reducing the survival of its eggs during the winter months. Such impacts, combined with global warming and other anthropogenic disturbances, may even lead to the extinction of this cold-loving endemic of the Selenga Basin, which will undoubtedly affect the entire lake ecosystem.