Entire Lake Research Articles

Remote Sensing of Chlorophyll-a in Clear vs. Turbid Waters in Lakes

Chlorophyll-a (Chl-a), a proxy for phytoplankton biomass, is one of the few biological water quality indices detectable using satellite observations. However, models for estimating Chl-a from satellite signals are currently unavailable for many lakes. The application of Chl-a prediction algorithms may be affected by the variance in optical complexity within lakes. Using Lake Winnipeg in Canada as a case study, we demonstrated that separating models by the lake’s basins [north basin (NB) and south basin (SB)] can improve Chl-a predictions. By calibrating more than 40 commonly used Chl-a estimation models using Landsat data for Lake Winnipeg, we achieved higher correlations between in situ and predicted Chl-a when building models with separate Landsat-to-in situ matchups from NB and SB (R2 = 0.85 and 0.76, respectively; p < 0.05), compared to using matchups from the entire lake (R2 = 0.38, p < 0.05). In the deeper, more transparent waters of the NB, a green-to-blue band ratio provided better Chl-a predictions, while in the shallower, highly turbid SB, a red-to-green band ratio was more effective. Our approach can be used for rapid Chl-a modeling in large lakes using cloud-based platforms like Google Earth Engine with any available satellite or time series length.

Health Risk of Heavy Metals in Drinking Water Sources of Water-Carrying Lakes Affected by Retreating Polder: A Case Study of Luoma Lake

Heavy metal pollution is a critical issue affecting the safety of drinking water sources. However, the impact of human activities on heavy metal risk levels in water-carrying lakes remains unclear. This study aims to explore the risk mechanisms of heavy metals in Luoma Lake, an important water-carrying lake for the South-to-North Water Diversion Project. We explored the spatial and temporal differences in the distribution of heavy metals in Lake Luoma using methods such as the heavy metal pollution index (HPI) and assessed the risk variations using a health assessment model. The results indicated that heavy metal concentrations in water-carrying lakes generally decreased during the dry season, with Mn and Zn levels decreasing by 89.3% and 56.2%, respectively. The comprehensive score of HPI decreased by 13.16% following the retreating polder compared to the control area (Non-retreating polder area). Furthermore, the HPI at the drinking water intake was lower, which is closely associated with the elevated dissolved oxygen (DO) and oxidation–reduction potential (ORP) resulting from water diversion. The annual average health risk across the entire lake was not significant, with higher levels observed in the control area. The annual non-carcinogenic risk levels of Mn, Ni, Cu, Zn, and Pb range from 10−13 to 10−9, which are considered negligible risk levels. Notably, the carcinogenic risk posed by arsenic (As) through the drinking pathway reached 10−5 a−1, exceeding the maximum levels recommended by certain organizations. These findings provide a critical foundation for managing heavy metals in water-carrying drinking water sources.

Unveiling the determinants of the spatial variability of nitrogen sources use in the Lake Victoria basin, East Africa

As nitrogen pollution increasingly threatens water quality in the Lake Victoria Basin, it is essential to investigate the spatial factors influencing nitrogen source use. Understanding these determinants is crucial to inform effective strategies to combat eutrophication, enhance nutrient management, ensure food security and promote sustainable ecological development. This study investigated spatial variation of N sources, the farmers' socio-demographic and farm characteristics factors influencing farmers' choice of nitrogen sources. Data was collected from 1500 farmers between October and December 2020. The farmers were randomly selected in Kenya, Rwanda, Uganda, Burundi and Tanzania country sub-basins within the Lake Victoria basin (LVB). Spatial autocorrelation was used to evaluate the spatial variation of the nitrogen sources while the Optimized Parameter Geographical Detector (OPGD) model was used to identify the factors influencing the choice or use of N sources. The OPDG results indicate that the country of residence and livestock ownership are the primary factors accounting for 31.9% and 22.1% of the variation in nitrogen sources across the entire Lake Victoria Basin, respectively. The major sub-basin factors influencing the use of N sources were both farm characteristics (types of crops grown and farm size) and social socio-demographic factors of the farmer (education). These findings highlight the need for tailored strategies, accounting for geographical variations, farm characteristics and socio-demographic factors are essential when formulating nitrogen management strategies and policies at local and regional scales within the LVB.

Interspecies differences and lake‐specificity in the δ13C and δ18O signatures of charophyte carbonate encrustations

Abstract This study identifies the relationships between the δ13C and δ18O signatures of extant charophyte carbonates (δ13CCARB and δ18OCARB) and the δ13C of dissolved inorganic carbon and δ18O of water (δ13CDIC and δ18OWATER), respectively, and the structure of charophyte beds and the physico‐chemical properties of the ambient water. Inter‐ and intra‐specific differences and lake‐related variability are assessed. Four morphologically different charophyte species (Nitellopsis obtusa, Chara tomentosa, Chara rudis, Chara contraria) were studied in four charophyte‐dominated lakes (Chara‐lakes) in Central Europe. A wide distribution of the species in calcium‐rich freshwater lakes, where they form extensive underwater beds and contribute to the deposition of calcareous sediments, makes the study representative of Chara‐lakes. Charophytes and water above them were sampled monthly (June–September 2008) at permanent study sites. Additionally, three comparative macrophyte‐free pelagic sites were sampled in each lake. For all the charophytes studied, there was a greater variation in the δ13C and δ18O values of the encrustations than of the ambient and pelagic waters. Except for N. obtusa and C. tomentosa, the species differed significantly in the δ13CCARB values. The encrustations were enriched in 13C compared to water DIC. Chara tomentosa encrustations were significantly depleted in 18O compared to N. obtusa and C. contraria. In contrast to Chara species, N. obtusa encrustation was 18O‐enriched compared to surrounding water. The largest isotope differences between carbonate encrustations and surrounding water were found for C. rudis. Considering the δ13CCARB versus δ13CDIC values, only slender species (i.e. N. obtusa and C. contraria) precipitated encrustations close to isotopic equilibrium with water DIC. Based on theoretical δ18OCALCULATED and measured δ18OCARB values, only C. tomentosa precipitated encrustation in equilibrium with the δ18OWATER. Using redundancy analysis, the δ13CCARB values positively correlated with the δ13CDIC and δ18OWATER values and the percent volume of water inhabited by plants. The depth of sites, water mineralisation, alkalinity and fertility were inversely correlated with the δ13CCARB. The redundancy analysis revealed a clear division of samples into species and lakes; lakes were especially distinct. We postulate that the stable C and O isotope compositions of charophyte encrustations are lake‐ rather than species‐specific and that the isotopic signatures of charophyte carbonates are representative of the entire lake epilimnion, not just the vegetated littoral zone. Furthermore, the isotopic signal of bulk sediment can provide environmental information that is as useful as species‐specific isotope values.

Remote Sensing Assessment of Water Resources, Vegetation, and Land Surface Temperature in Eastern Saudi Arabia: Identification, Variability, and Trends

Saudi Arabia has one of the biggest water shortages and the least vegetation in the world, which is presumed to provoke this problem further due to climate change. Therefore, the present study investigates the water, vegetation, and temperature over Al-Asfar Lake region, Al Ahsa, Eastern province of Saudi Arabia using the Normalized Difference Water Index (NDWI), Normalized Difference Vegetation Index (NDVI), and Land Surface Temperature (LST: °C) from Landsat-8 based operational land imager (OLI) measurements for the period 2013 to 2023. This study presented annual and seasonal (dry months: June–September and wet months: December–April) spatiotemporal distribution and variations, calculated their absolute change and trends, and examined their relationship. Results showed positive NDWI values over Al-Asfar Lake, indicating waterbodies; while positive NDVI values on the lake's bank, signifying vegetation. Notably, there were significant temporal variations in water and vegetation observed on annual, seasonal, and monthly scales. The study also found an overall decrease in vegetation areas of 5.36 km2 in 2023 compared to 2013, while waterbodies increased by 8.83 km2. The trend analysis using area-averaged data demonstrated that NDWI increased on annual (0.0075/year) and seasonal (dry: 0.0083/year and wet: 0.0049/year) scales, while NDVI decreased (annual: 0.0066/year, dry: 0.0083/year, and wet: 0.0009/year). Moreover, LST was recorded least amount over waterbodies (28.23 °C) and vegetation (32.45 °C) covered areas compared to the entire lake region (38.43 °C), respectively. Remark, LST displayed decreasing trends over waterbodies (−0.05/year), followed by vegetation (−0.17/year), and the entire lake region (−0.0001/year), signifying that water and vegetation are vital components to controlling land surface temperature in this region. Finally, the LST showed a positive correlation with NDVI and negative correlation with NDWI. There may be a direct and indirect impact of climate change upon NDVI, LST, and NDWI as shown by the decreases in NDVI and LST and an increase in NDWI. This study can be considered as a base document to monitor waterbodies, vegetation cover, and temperature changes using remote sensing measurements of NDWI, NDVI, and LST, which will assist policymakers in developing water resource management, irrigation planning, and environmental monitoring strategies.

Long-term climate warming and extreme cold events driving ecological shifts in a deep oligo-mesotrophic lake.

Deep lakes are critical for freshwater storage, yet they are struggling against major ecological issues from climate change and nutrient pollution. A comprehensive understanding of internal feedback mechanisms is crucial for regulating nutrients in these lakes. A five-year study was conducted on the diatom community and environment in Lake Fuxian, China's largest deep freshwater lake, which is becoming eutrophic. The results indicate a shift in the diatom community from a stable state dominated by a single species to a rapid seasonal fluctuation, and there is a significant increase in diatom biomass. Specifically, stable stratification and low nutrient concentrations are limiting the growth of diatom biomass and maintaining the dominance of Cyclotella. Nutrients in the hypolimnion were replenished in the epilimnion during the extreme cold of winter, triggering a shift in the diatom community. This shift may imply that future climate change will exacerbate the positive feedback of hypoxia-nutrient release of algal blooms, potentially triggering a regime shift in the ecosystem of the entire lake. This study underscores the fact that climate change alters the internal feedback mechanisms of deep lakes, reducing ecosystem stability, and provides a scientific basis for further clarification of protection measures for deep lakes.

Landscape Pattern Changes of Aquatic Vegetation Communities and Their Response to Hydrological Processes in Poyang Lake, China

Hydrology is an important environmental factor for the evolution of wetland landscape patterns. In the past 20 years, Poyang Lake, the largest freshwater lake in China, has experienced significant inundation shrinkage and water level decrease, posing a significant threat to the local vegetation community. To explore the potential relationship between aquatic vegetation and hydrological processes in the recent hydrological situation, in this study, the landscape patterns of aquatic vegetation communities in Poyang Lake were studied using time-series Landsat remote sensing images and a support vector machine classifier. The stepwise regression analysis method was adopted to analyze the relationship between the vegetation area and hydrological factors. The results indicated that the area of submerged and emergent vegetation in the entire lake decreased significantly from 2001 to 2017, whereas the area of moist vegetation showed a remarkably increasing trend. The average distribution elevation of the submerged vegetation increased by 0.06 m per year. The corresponding landscape patterns showed that the degree of fragmentation of aquatic vegetation communities in Poyang Lake increased. Several hydrological factors were selected to quantify the potential impact of water level fluctuations. The correlation analysis results indicated that hydrological conditions during the rising- and high-water periods may be the key factors affecting the area of aquatic vegetation. This study systematically investigated the evolution of vegetation communities in Poyang Lake wetlands over the past two decades, which contributes to the protection and management of this unique ecosystem.

An Ecological Study of the Vegetation of the Kolleru Lake

Kolleru lake is a large fresh water body extending over 850 sq. km in the Krishna and West Godavari districts of Andhra Pradesh, between 81°40' and 80°20' E and 17°25' and 1.6°28' N. The entire lake being shallow, has only littoral vegetation with practically no limnetic and profoundal zones. As the lake receives rich nutrients as effluents from the several drains that empty into it, the vegetation is luxuriant. About nineteen species of hydrophytes belonging to thirteen angiosperm families are recorded. Data on the distribution of these hydrophytes in the lake and their frequency, relative frequency and abundance from different regions of the lake at different periods of the year, are presented.

Hypersalinity in Coastal Wetlands and Potential Restoration Solutions, Lake Austin and East Matagorda Bay, Texas, USA

When droughts occur, freshwater inputs to coastal wetlands can become scarce and hypersalinity can become a problem. In 2023, a severe drought negatively affected a Texas watershed known as Lake Austin that fed a large expanse of wetlands on East Matagorda Bay. To study the hypersalinity problem in these wetlands, we identified freshwater inflows and mapped vegetation changes over time. We found that from 1943 to 2023, the upper portion of the Lake Austin watershed lost freshwater wetlands to agricultural conversion, and ranged from fresh to brackish, with salinity rapidly rising to a maximum of 31 mS during the summer drought of 2023. The lower portion of the watershed gained saltwater wetlands due to sea level rise, and marshes became hypersaline (64–96 mS) during the 2023 drought, endangering its biota. But after large precipitation events, the entire Lake Austin basin rapidly freshened but then returned to its normal salinities within a week as the tides re-delivered saltwater into its basin. Given current climatic trends, we expect that freshwater inflow will continue to slightly increase for the Lake Austin watershed but also that there will be more extreme periods of episodic drought that negatively affect its wetlands. Accordingly, we assessed several potential restoration actions that would improve freshwater flow and delivery to the Lake Austin coastal wetlands.

Regime shift in microalgal dynamics: Impact of water level changes on planktonic and benthic algal biomass

Whole-lake microalgal biomass surveys were carried out in Lake Balaton to investigate the seasonal, spatial, and temporal changes of benthic algae, as well as to identify the drivers of the phytobenthos. Phytobenthos was controlled mainly by light: the highest benthic algal biomass was in the shallow littoral region characterized by large grain size (sand) with good light availability but lower nutrient content in the sediment. During the investigated period, phytoplankton biomass showed a significant decrease in almost the entire lake. At the same time, the biomass of benthic algae increased significantly in the eastern areas, increasing the contribution of total lake microalgae biomass (from 20 % to 27 %). Benthic algal biomass increase can be explained by the better light supply, owing to the artificially maintained high water level which greatly mitigates water mixing. The decrease in planktonic algal biomass could be attributed to increased zooplankton grazing, which is otherwise negatively affected by mixing. As a result of the high water level, the trophic structure of the lake has been rearranged in recent decades with a shift from the planktonic life form to the benthic one while the nutrient supply has largely remained unchanged.

The effect of pollutants on the ichthyofauna of Lake Ladoga and preventive measures

Lake Ladoga is the largest body of water in Europe with huge reserves of drinking water, and has a particularly important sanitary and hygienic significance for the Northwestern region of Russia. The lake has significant fishery importance – annual catches reached 6000 tons. per year. However, over the past few decades, the fishery status of the reservoir has changed significantly. Stocks and catches of the most valuable fish species have sharply decreased as a result of anthropogenic impact – pollution and eutrophication.Chemical-analytical studies of samples of water, bottom sediments, atmospheric precipitation and fish for metals were carried out in the laboratory of fishery ecology of the St. Petersburg branch of the Federal State Budgetary Institution "VNIRO" ("GosNIORH" named after L.S. Berg) on an atomic absorption spectrophotometer AA - 7000 (Shimadzu) according to approved methods (PNDF., 2010; M02-2406., 2013 and M02-902-125, 2005), and in the research laboratory of food and natural objects "ANALECT" of the Institute of the Ministry of Health of the Russian Federation, using the method of atomic absorption spectrometry according to approved methods. Hydrochemical and hydrological parameters were determined using an automatic multiparameter probe Aqua TROLL 500.The southern water area of the lake, which is the most valuable in terms of fisheries, turned out to be the most vulnerable to toxicological effects. Pollution of spawning grounds, toxicosis of fish, violation of natural reproduction in combination with the hydrological features of the reservoir have led to irreversible transformations in the structure of the ichthyofauna as a whole for the entire lake. Pronounced consequences for the ichthyofauna of the reservoir are associated with the sensitivity of fish to pollutants, their ability to accumulate pathological information over a long-life cycle. The hydrological features of the southern water area of Lake Ladoga, combined with the location of pollution sources and the routes of pollutants, make it difficult to carry out preventive measures in this most important fishery area.

Obtaining accurate population estimates with reduced workload and lower fish mortality in multi-mesh gillnet sampling of a large pre-alpine lake.

The EU Water Framework Directive requires monitoring of the ecological status of lakes, with fish as a relevant class of biotic quality indicator, but monitoring fish populations in large lakes is demanding. This study evaluated use in Lake Constance of a novel multi-mesh gillnet modified to reduce catch numbers. In direct comparison with conventional European Committee for Standardization (CEN) nets we achieved 48% reduction in fish mortality with 38% less labour for tasks directly influenced by fish catch numbers, while maintaining comparable species composition and catch per unit effort. Comparison of mesh sizes indicated no significant reduction in species detection in area-reduced panels of the small mesh sizes, while total observed species richness was greater when using the modified nets. Differences in benthic species communities among depth strata were common, while those of pelagic zones were more homogeneous and did not differ significantly with depth. Catches of different net types from the same depth stratum did not exhibit significant differences. The dominance structure of the most common species, relevant to lake assessment, was similar in catches of both net types, suggesting overall superiority of the modified nets in Lake Constance. Sampling conducted according to standard European CEN protocol, while deploying 60% fewer nets, yielded sufficiently precise abundance estimates for monitoring shallow areas of the benthic zone. A 50% difference in the abundance of dominant species was detected among sampling events with a certainty of 95%. The sample did not provide comparable accuracy in deep benthic strata or the pelagic zone, but was adequate to record complete inventories of species present. Based on this trial data, a new stratified sampling design is proposed for monitoring large lake fish communities for ecological assessment. Depth-dependent fish communities were used to calculate the required number of nets, which resulted in a 69% reduction for the entire lake compared to the CEN calculation method. Using the modified nets increases the feasibility of performing WFD surveys, by reducing effort and cost, while the simultaneous halving of fish mortality minimises the negative impact of fish surveys.

Shifts in phytoplankton and zooplankton communities in three cyanobacteria-dominated lakes after treatment with hydrogen peroxide

Cyanobacteria can reach high densities in eutrophic lakes, which may cause problems due to their potential toxin production. Several methods are in use to prevent, control or mitigate harmful cyanobacterial blooms. Treatment of blooms with low concentrations of hydrogen peroxide (H2O2) is a promising emergency method. However, effects of H2O2 on cyanobacteria, eukaryotic phytoplankton and zooplankton have mainly been studied in controlled cultures and mesocosm experiments, while much less is known about the effectiveness and potential side effects of H2O2 treatments on entire lake ecosystems. In this study, we report on three different lakes in the Netherlands that were treated with average H2O2 concentrations ranging from 2 to 5 mg L−1 to suppress cyanobacterial blooms. Effects on phytoplankton and zooplankton communities, on cyanotoxin concentrations, and on nutrient availability in the lakes were assessed. After every H2O2 treatment, cyanobacteria drastically declined, sometimes by more than 99%, although blooms of Dolichospermum sp., Aphanizomenon sp., and Planktothrix rubescens were more strongly suppressed than a Planktothrix agardhii bloom. Eukaryotic phytoplankton were not significantly affected by the H2O2 additions and had an initial advantage over cyanobacteria after the treatment, when ample nutrients and light were available. In all three lakes, a new cyanobacterial bloom developed within several weeks after the first H2O2 treatment, and in two lakes a second H2O2 treatment was therefore applied to again suppress the cyanobacterial population. Rotifers strongly declined after most H2O2 treatments except when the H2O2 concentration was ≤ 2 mg L−1, whereas cladocerans were only mildly affected and copepods were least impacted by the added H2O2. In response to the treatments, the cyanotoxins microcystins and anabaenopeptins were released from the cells into the water column, but disappeared after a few days. We conclude that lake treatments with low concentrations of H2O2 can be a successful tool to suppress harmful cyanobacterial blooms, but may negatively affect some of the zooplankton taxa in lakes. We advise pre-tests prior to the treatment of lakes to define optimal treatment concentrations that kill the majority of the cyanobacteria and to minimize potential side effects on non-target organisms. In some cases, the pre-tests may discourage treatment of the lake.

A method for extracting the spatial distribution of submerged vegetation in lakes based on topography measurements

Aquatic vegetation in lakes provides various ecosystem services, identification of its spatial distribution has great importance in lake ecosystem management and conservation. Monitoring of submerged aquatic vegetation is limited due to plants being under the water surface. Based on topography measurements, a new method was proposed to identify the distribution of submerged vegetation. With submerged vegetation occurred in lakes, water depth measured by an echo sounder could be influenced by vegetation and differ from its true value. Vegetation distribution can be extracted by comparing the topographic maps measured with and without vegetation presence. In present study, identification for Potamogeton crispus distribution in Dongping Lake (China) was taken as an example to show the procedures. Errors and accuracy of this method were analyzed, and a discussion was provided about the usefulness and limitations of the proposed method. In this study, measurements were conducted in March (with P. crispus occurrence) and September (without P. crispus occurrence), 2021. Five interpolation methods with ten resampling intervals were used and compared for each measurement, and the minimal mean absolute errors (MAEs) for interpolated topographies in Mar. and Sep. measurements were 0.63 m and 0.46 m, respectively. MAE for the subtraction of raster data between two topographic maps over the entire lake was 0.59 m. Besides, accuracy of this method was validated by comparing the extracted distribution of P. crispus with its distribution of biomass. Taking the P. crispus distribution with dry biomass density larger than 26 g/m2 as reference, the identification accuracy of this method reached its maximum (78%). In regions with P. crispus sparsely distributed, the measured water depth was seldom influenced by vegetation, leading to the differences between two maps ignorable in these regions.

Spatio-temporal dynamics of nutrients at the water-sediment interface: case of the Nokoue lagoon in Southern Benin.

Lake Nokoué, a major component of the hydrographic system of the Ouémé delta, is the largest lagoon-estuarine ecosystem in Benin. Recent studies have shown that benthic processes would actively participate in the maintenance of the eutrophication and biogeochemical cycle of this ecosystem. In order to understand the implication of the bottom on the quality of the waters of the lake, a monthly follow-up of ten (10) parameters of quality of the waters of the bottom was undertaken from July 2020 to December 2021 on a network of nineteen (19) stations distributed on the whole lake. Univariate and multivariate analysis techniques were used to assess the spatial and temporal dynamics of these waters. The Kruskal-Wallis test, PCA, correlation analysis and discriminant analysis all showed a very marked influence of the hydrological regime on the concentration of nutrients compared to the influence of anthropogenic activities around the lake and an influence of climatic conditions on internal processes. Indeed, water inflows from the Ouémé watershed are the main contributors of phosphorus in the lake while benthic processes are the most important contributors of nitrogen. Cluster analysis defined three significantly different areas in Lake Nokoué: the channel, the centre of the lake and the river mouth. A single station in each cluster could be used for a spatial assessment of water quality over the entire lake.

The Holocene silicon biogeochemistry of Yellowstone Lake, USA

Silicon (Si) is an essential macronutrient for diatoms, an important component of lacustrine primary productivity that represents a link between the carbon and silicon cycles. Reconstructions of lake silicon cycling thus provide an underexploited window onto lake and catchment biogeochemistry. Silicon isotope geochemistry has potential to provide these reconstructions, given the competing source and process controls can be deconvolved. The silica-rich volcanic and hydrothermal systems in Yellowstone National Park are a great source of dissolved silicon into Yellowstone Lake, a system with high silicon, and thus carbon, export rates and the formation of diatom–rich sediment. Yellowstone Lake sediments should be an archive of past silicon biogeochemistry, although the effect of sublacustrine hydrothermal activity or hydrothermal explosion events is unclear.Here, we analysed lake water, tributaries, and hydrothermal vent fluids from Yellowstone Lake for their dissolved Si concentrations, isotope composition (δ30Si) and Ge/Si ratios to evaluate the sources of variability in the lake's Si cycle. Bulk elemental composition and biogenic SiO2 (bSiO2) content, together with δ30Si and Ge/Si ratios from a single diatom species, Stephanodiscus yellowstonensis, were analysed in two sediment cores spanning the last 9880 cal. yr BP. We investigate these datasets to identify long term Holocene changes in hydrothermal activity and effects of large and short-term events i.e., hydrothermal and a volcanic eruption.Combinations of bSiO2, δ30Si and Ge/Si with XRF and lithology data revealed that Yellowstone Lake has a resilient biogeochemical system: hydrothermal explosions are visible in the lithology but have no identifiable impact on bSiO2 accumulation or on the δ30Si signature. Both cores show similarities that suggest a stable and homogeneous dSi source across the entire lake. A narrow range of δ30Si and Ge/Si values suggests that the productive layer of the lake was well mixed and biogeochemically stable, with consistently high hydrothermal inputs of Si throughout the Holocene to buffer against the disturbance events. Variation in bSiO2 concentration through time is weakly correlated with an increase towards younger sediment in the δ30Si fossil diatom record in both cores. This increase mirrors that seen in ocean records, and follows changes known in summer insolation, summer temperatures and lake water-column mixing since the deglaciation. This suggests that climate forcing, and soil formation ultimately govern the silicon isotope record, which we suggest is via a combination of changes in weathering stoichiometry, diatom production, and relative proportion of dSi sources.

Spatial distribution prediction model for lake water quality parameters from ultra-sparse sampling data with recent satellite data

ABSTRACT Daily spatial distributions of water quality parameters (WQPs) are a crucial indicator in delicacy management of lake water environment in China. However, because of the high cost of construction and maintenance, there are a few automatic monitoring stations (AMSs) for continuous water sampling with only ultra-sparse spatial sampling data can be obtained. Meanwhile, although WQPs from satellite inversion are spatially continuous, they are missing on most days due to severe affected by weather and satellite revisit cycle, besides the high purchase cost. Thus, the model called MLP-GPR is formulated in this study to address the issue of predicting the spatial distribution of WQPs from ultra-sparse sampling data of AMSs combined with the spatial correlation information based on ultra-sparse satellite inversion data. This model includes the multilayer perceptron model (MLP) and Gaussian process regression model (GPR). MLP is trained to learn the interaction factors of WQPs between different locations through the satellite inversion data for predicting WQPs at more locations based on the data measured by AMSs. Then, GPR regresses the spatial distribution of WQPs at all locations on the entire lake from the predicted data by MLP. Based on the above model, we applied the satellite inversion, AMSs and artificial sampling data to predict the WQP spatial distribution of Shahu Lake in Wuhan, China. The experiment results show that the spatial resolution of WQP distribution predicted by MLP-GPR trained by satellite inversion data can reach 15 m by sampling data from artificial stations on the lake with 3.197 km2. Moreover, for each of these WQPs, compared with the satellite inversion data, the average MRE, R, and NSE of prediction results are below 3.95%, above 0.85, and above 0.69, respectively.

What is hiding below the surface – MPs including TWP in an urban lake

Inland lakes play an important role as habitats for local species and are often essential drinking water reservoirs. However, there is limited information about the presence of microplastics (MPs) in these water bodies. Thirteen sediment samples were collected across a Danish urban lake to map MPs, including tyre wear particles (TWP). The lower size detection limit was 10 µm. MPs were quantified as counts, size, and polymer type by Fourier-transform infrared microspectroscopy (µFTIR) and mass estimated from the 2D projections of the MPs. As TWP cannot be determined by µFTIR, counts and sizes could not be quantified by this technique. Instead, TWP mass was determined by pyrolysis gas chromatography mass spectrometry (Py-GC/MS). The average MP abundance was 279 mg kg−1 (µFTIR), of which 19 mg kg−1 (Py-GC/MS) were TWP. For MPs other than tyre wear, the average MP count concentration was 11,312 counts kg−1. Urban runoff from combined sewer overflows and separate stormwater outlets combined with outflow from a wastewater treatment plant were potential point sources. The spatial variation was substantial, with concentrations varying several orders of magnitude. There was no pattern in concentration across the lake, and the distribution of high and low values seemed random. This indicates that large sampling campaigns encompassing the entire lake are key to an accurate quantification. No preferential spatial trend in polymer characteristics was identified. For MPs other than TWP, the size of buoyant and non-buoyant polymers showed no significant difference across the lake, suggesting that the same processes brought them to the sediment, regardless of their density. Moreover, MP abundance was not correlated to sediment properties, further indicating a random occurrence of MPs in the lake sediments. These findings shed light on the occurrence and distribution of MPs, including TWP, in an inland lake, improving the basis for making mitigation decisions.

STRUCTURE AND ORIGIN OF THE BOTTOM RELIEF OF LAKE CHUKHLOMSKOE (KOSTROMA REGION)<a href="#FN1"><sup>1</sup></a>

The article discusses the first results of studying the structure of the bottom topography and bottom sediments of Chukhlomskoe Lake (Kostroma Region, Chukhlomsky District). We analyzed the lake bottom topography based on the results of our bathymetric survey and discovered two hollows with maximum depths diverging from the lake’s center towards the city of Chukhloma. The maximum depth inside the hollows (and for the entire lake) reaches 5.4 m, and the average lake depth is 2.2 m. There are two steps seen in the bottom topography; 2.0–2.4 m and 1.5–1.8 m. The bottom sediment structure of Chukhlomskoe Lake was revealed by drilling from the ice with two boreholes (with lengths of 9.45 and 7.45 m, located in the area of background depths and inside the hollow, respectively). Five radiocarbon AMS dates were obtained for the core from the hollow’s bottom. The sedimentary sequences of the pre-Holocene part of both cores show high similarity in structure and depths of the marker horizons identified by a set of lithological analyses. The structure and thickness of Holocene sediments differ significantly. In the area of background depths, the Holocene organo-mineralogenic silt is 3.8 m, and inside the hollow, the thickness of this layer is only 1.45 m. Moreover, hiatuses in sedimentation were documented in the structure of the Holocene sediment inside the hollow. The age of hiatuses, based on the sedimentary model, was estimated as 10.6–5.3 and 4.9–0.06 thousand years ago. A probable mechanism for the origin of hollows is localized erosion caused by wind currents in a highly shallow lake. An additional erosion factor can be the degassing of bottom sediments, which leads to the loosening of the bottom layer of sediments, which makes them susceptible to erosion. The cutoff of sediment erosion inside the hollow coincided in time with the construction of a dam on the Veksa River and a rise in the lake level by 1.0–1.5 m in the 1960s.

Spatially Intensive Patterns of Water Clarity in Reservoirs Determined Rapidly With Sensor‐Equipped Boats and Satellites

AbstractOptical water quality affects the quantity and spectral composition of underwater light available to photoautotrophs along with light reflected off the water surface. In reservoirs, prominent gradients for optical water quality and clarity measures occur between inlets and outlets, allowing rapid surveys of ecosystem structure across diverse conditions along with tests of relationships between in situ and remotely sensed water indices. We used a sensor‐equipped boat in a clay‐rich subtropical drinking water reservoir to examine continuous spatial patterns of water clarity and the relationship between in‐lake turbidity and normalized difference turbidity index (ndti) from Sentinel 2 imagery acquired on the same date. Over the 62.3 km boat path, surface turbidity varied between 14 and 85 NTU (mean = 30), with highest values in shallower water near the main inlet. Results indicated a strong linear relationship between sensor turbidity and lab‐determined turbidity. A positive relationship between the satellite turbidity index and in‐lake turbidity, combined with a negative exponential relationship between Secchi depth and turbidity, provided a basis for predicting water clarity metrics continuously over the entire lake surface. In this turbid water body, predicted Secchi depth and turbidity over the whole lake had means of 0.22 m and 54 NTU, with 75% of the lake area <0.29 m and >26 NTU. Pursuit of general relationships involving optical properties of water from high‐speed, data‐intensive spatial surveys and remotely sensed surface reflectance facilitates further development of spatially explicit models of aquatic systems.