Water Surface Area Research Articles

THE BOTTOM RELIEF OF VYZYRKA POND (ODESSA REGION, ODESSA DISTRICT)

Problem Statement and Purpose. For arid conditions of southern Ukraine, the problem of preservation and use of the local water resources has been relevant for a long time. One of the types of adaptation of economic activity to the natural conditions of the area is artificial water bodies’ creation. Operation of ponds without repair work led to reduction of the water surface area of most of them, siltation, reduction of depths, overgrowth, as a result of which the ponds from water accumulators turned into evaporators. The publications review devoted to ponds and artificial reservoirs showed that their hydrochemical, hydrobiological regime, hydrological elements and ecological condition are mainly studying. The purpose of the research is to establish the regularities of the relief structure of the bottom of the pond in the village of Vyzyrka. Data & Methods. Field research was conducted in July 2021–2022. From two reservoirs, located within the village of Vyzyrka, the larger one was investigated. Work in the water area was carried out from the rowing boat Kolibri. The depths were determined with a Garmin Echo 200 echo sounder a geodetic rail. The use of the echo sounder made it possible to visually trace the relief of the bottom changes on the tacks and choose typical underwater points during relief measurements (ND31– 7.002.-2005). The depths were determined at 60 points, located evenly across the water area. The coordinates of measurement points were determined using a Garmin GPS72H GPS receiver. The journal of points was exported to Garmin Base Camp software. Results. Vyzyrska Pond has existed as an artificial reservoir since 1923. The relief has a trough-like shape inherited from the beam relief. Three areas are distinguished in the structure of the bottom relief: flat bottom of the northern part; underwater continuation of concave coastal slopes; the central depression stretches along the axis of the reservoir from southeast to northwest. The creation and use of artificial reservoirs leads to the development of geomorphological processes associated with the interaction of the native relief, which was formed in other physical and geographical conditions, with the water environment. Further studies of the pond are aimed at establishing the spatial distribution of hydrological elements in the water area of the pond in order to establish patterns of their change, which are important for the aquatic biota development.

Passive Microwave Radiometry at Different Frequency Bands for River Discharge Retrievals

AbstractThe present era of climate change and expanding population requires major improvements in sustained observation of global river discharge. Floods and droughts are affecting food supplies, and suspected long‐term trends require appropriate data for evaluation. Orbital remote sensing can address this observational need. Here we use satellite Ka‐ (36.5 GHz) and L‐band (1–2 GHz) passive microwave radiometry (PMR) to monitor river discharge changes and determine what size rivers can be measured and the frequencies and polarization configurations that yield the most robust results. Selected satellite gauging reaches (SGRs) can be measured at near‐daily intervals from 1998 to present (Ka‐band) and 2010 to present (L‐band). The SGRs are 10–36 km in length; the dynamic proportion of water surface area within each varies with river discharge. Due to contrasting dielectric properties, water and land emit different intensities of microwave radiation; thus emission from a mixed water/land pixel decreases as the proportion of water within the pixel increases. Depending on the river and floodplain morphology, water flow area can be a robust indicator of discharge and the microwave sensors can retrieve daily discharge to ±20%. Instead of spatial resolution, it is the sensor measurement precision, geolocation accuracy, and channel and floodplain morphology that most strongly affect accuracy. Calibration of flow area signals to discharge can be performed using nearby ground stations (even if now discontinued) or by comparison to hydrologic modeling.

Suitable water surface area of the tail lake under the constraint of water diversion scheme in arid areas based on emergy theory

Study regionThe East Juyan Sea (Inner Mongolia, China) Study focusMaintaining a certain water surface area in the East Juyan Sea is the main sign of the success of the Heihe River water diversion. However, under the realistic constraint of limited water resources, the maintenance of the lake's water surface area and the oasis ecological water are in conflict. Through comprehensively considering various factors such as ecology, economy, and water resources, this study focused on the relationship between the East Juyan Sea's ecological service value and water surface area, which was investigated with emergy theory. Meanwhile, based on the status of local water resources and the principle of water diversion, the suitable water surface area of the East Juyan Sea's was given. New hydrological insights for the regionThe results indicated the optimal water surface area of the East Juyan Sea is approximately 40 km2. In addition, we can observe that the value of ecological services of a specified area increases infinitely with the expansion of its water surface area. But, within a certain threshold value, the amount of its value will become stabilize. Below or beyond this threshold, the value of regional ecological services will increase at a faster rate. However, the larger is not always better. The larger the water surface area, the easier it is to create competition for water with the oasis vegetation, which will be detrimental to the ecological health and stability of this region. Thus, the appropriate water surface area needs to be determined comprehensively by considering various factors such as ecology, economy, and water resources.

Status of aquatic organisms resources and their environments in Yangtze River system (2017–2021)

The Yangtze River is the mother river of China. To promote the aquatic ecosystem protection of the great river, the Project of Yangtze Fisheries Resources and Environment Investigation (2017–2021) supported by the Ministry of Agriculture and Rural Affairs, P. R. China carried out by 24 institutes and universities that located in the Yangtze River basin surveys the status of (1) fish species composition and spatial distribution, (2) current fish abundance, (3) endangered fishes, (4) Yangtze finless porpoise, (5) aquatic eco-environments, (6) water-level fluctuation areas, (7) capture fisheries and recreational fisheries of the Yangtze River mainstream and 10 of its main tributaries, including Yalong River, Heng River, Min River (including Dadu River), Chishui River, Tuo River, Jialing River, Wu River, Han River, Dongting Lake and Poyang Lake. The results showed that there were 443 fish species (belonging to 163 genus, 37 families, and 18 orders) before 2017, but only 323 fish species (including 15 new recorded exotic species) were recorded in the project of 2017–2021. Among them, Cyprinus carpio, Carassius auratus, Hypophthalmichthys molitrix, Pelteobagrus fulvidraco, Coilia brachygnathus, Silurus asotus, Saurogobio dabryi, Ctenopharyngodon idellus, Pelteobagrus nitidus, Hemiculter leucisculus, Siniperca chuatsi, Coreius heterodon, Culter alburnus, Parabramis pekinensis, and Aristichthys nobilis were the dominant species across the whole Yangtze River system. It is estimated that there were 886 million individuals weighing 124.8 million kg, merely equivalent to 27.3% of the resources in 1950s, 30.9% of the resources in 1960s, or 58.7% of the resources in 1980s. In the new list of protected fishes that recorded in the Yangtze River system, only 15 of 29 were collected in this project of 2017–2021. Psephurus gladius has been affirmed to be Extinct by International Union for Conservation of Nature (IUCN). The wild individuals of Tenualosa reevesii and Luciobrama macrocephalus have disappeared for many years and maybe have been extinct already. Acipenser dabryanus has been affirmed to be Extinct in the Wild by IUCN. The natural propagations of A. sinensis, Myxocyprinus asiaticus and Trachidermus fasciatus have been interrupted for many years. The populations of Yangtze finless porpoise in the Yangtze River mainstream, Dongting Lake and Poyang Lake have steadily rising sizes and expanding distributions in 2017–2021. Parts of them migrate from one region to another with the seasons, which would result in the fluctuation of Yangtze finless porpoise population within some regions. The conventional indicators of water quality in the Yangtze River system were good and conformed to the water quality criteria of fishery in 2017–2021. In the last 40 years, the maximum surface water area in the Yangtze River basin extended to approximately 63,360 km2, the minimum surface water area covered approximately 26,396 km2, and the seasonal water-level fluctuation areas occupied approximately 36,964 km2. Compared with 1984–2000 period, the 2001–2020 period witnessed an overall decreasing trend in the frequency of surface water occurrence within about 25,869 km2 of aquatic areas. From 1984 to 2000 period to 2001–2020 period, permanent surface water has decreased by nearly 8,750 km2. In 2017, the fishermen were mainly 40–60 years old and their educational levels were mainly lower than junior high school. In 2017, most anglers were older than 40 and used hand rod and/or sea rod. Their average catch of each time was mainly less than 1 kg. Results suggested that the fishing ban in key waters of the Yangtze River basin is not only an ecological project of aquatic ecosystem conservation, but also a livelihood project for the fisherman to embrace industrial transformation and improve their living conditions. After the implementation of the fishing ban, the fisheries resources would gradually recover, and the Yangtze finless porpoise population size would also see a steady increase. However, the endangered species would remain threatened for a long time. The degraded waterbodies and water-level fluctuation areas would be the key restrictive factors for future aquatic ecosystem recovery in the Yangtze River basin. Since this survey was carried out before the fishing ban, the current results could provide a baseline for future evaluation of the effect of the Yangtze River fishing ban.

Abating eutrophication on urban lakes: a case study of Kabaka's Lake, Uganda

Abstract Eutrophication of water bodies is a challenge in many urban areas. This study measured and modelled quantitatively the pollutant nutrient load of an urban lake (80,596 m2), and assessed both external (constructed wetland) and internal (dredging) eutrophication extenuation measures. For the past 25 years, there has been redistribution (p < 0.005) of the lake's catchment land use, with built-up area increasing by 78.5%, and a reduction in vegetated (37.2%) and water surface (1.8%) areas. A 92.2% reduction in the lakes receiving wetland footprint (p = 0.000003) was noted, with increased nutrient load. The lake's light attenuation was found to be dominated by algae, limited by nitrogen and classified under the oligotrophic class (Trophic State Index < 40), with a threat of eutrophication in an estimated 25 years. Scenario analyses show that the construction of a wetland in the remaining 0.54 hectares of natural wetland will reduce total phosphorus by 35% and total nitrate by 45% (p = 0.05), whereas dredging the lake could reduce them by 80% each (p = 0.0005). Watershed management is the only sustainable solution to control nutrient flow into the lake and enable self-cleansing, factoring in the design of the receiving wetland and groundwater sources.

Su Kalitesi Durum Değerlendirmesi- Salda Gölü, Türkiye

Inland water bodies, either flowing or non-flowing all around the world, are under the adverse effect of both the climate change and anthropogenic activities. The water surface areas of lakes and wetlands diminish over time and thus, this global reality brings together the deterioration of water quality especially if such water bodies confront with a variety of human activities exerting pollutants. An example of such a vulnerable ecosystem is the Lake Salda located in the southwestern part of Turkey. This lake has gained the attention of international public due to its similarities with Mars. Over a long period of time, many researches have been conducted in this lake by different disciplines and scientists to better understand its unique features. In this study, water samples from the three selected stations on the lake at three different depths were collected and analyzed on physico-chemical parameters, organic matter content, nutrients, metals and semi metals according to national legislation and Water Framework Directive (WFD) of EU. The results are tabulated and analyzed in detail considering the potential pollution sources arising from the lake’s basin. The pollutants are linked with the experimental measurements, and those parameters that exceeded the Environmental Quality Standards (EQS) are underlined. It is for sure that the lake necessitates utmost care and attention according to the results achieved.

Multi-source satellite reveals the heterogeneity in water storage change over northwestern China in recent decades

The northwestern China (NWC) generally suffers from severe water shortages. To improve the management and utilization of the limited water storage in NWC, it is crucial to explore the distribution and variation of water storage. Here, we obtained the variations of terrestrial water storage (TWS), surface water area (SWA), and groundwater storage (GWS) in NWC (which refers to Xinjiang Uyghur Autonomous Region in the study) from 2002 to 2018 based on multi-source satellite data, and analyzed the factors influencing water storage changes. The results indicated that (1) SWA exhibited an increasing trend with 40.90 km2/year from 2002 to 2018 based on main lakes/reservoirs and rivers water area in NWC, due to the increase of precipitation and glacier melting. TWS and GWS showed a decreasing trend with a mean rate of −1.25 mm/year and −1.08 mm/year from 2002 to 2018 in NWC, respectively, due to the increase of arable land area and water consumption. (2) SWA in northern and southern NWC showed a decrease (-0.72 km2/year) and an increase (51.14 km2/year) from 2002 to 2018, respectively. The different rates are due to regional precipitation and temperature variations. TWS in northern and southern NWC showed a declining of −0.14 mm/year and −1.94 mm/year, respectively. GWS in northern and southern NWC showed a declining of −0.55 mm/year and −1.72 mm/year, respectively. The differences are related to the greater evapotranspiration and irrigation water consumption in southern than northern NWC. This study enriches the information on water storage in NWC and provides useful guidance for local water resource management and protection.

The Impacts of Land Use Changes on Water Yield and Water Conservation Services in Zhangjiakou, Beijing’s Upstream Watershed, China

The Water Conservation Functional Zone and Ecological Environmental Supporting Zone (the Capital Two Zones in China), Zhangjiakou (ZJK) City, situated in China, has played a key role in mitigating water scarcity pressure on Beijing via delivering sustainable and high-quality water yield, as well as water conservation services aimed at maintaining the ecological functions of the Capital Two Zones. However, the changing mechanism for both water yield and water conservation services instigated by the combined impacts of human activities and climate change remains poorly understood. In this study, we used the Integrated Valuation of Ecosystem Services and Trade-offs Tools (InVEST) model to analyze the changes in water yield and water conservation services, revealing the impacts of different land use scenarios. The results showed significant forest and impervious land area increment, while the water surface area decreased sharply from 1990 to 2020, with obvious urbanization expansion in ZJK during the period. Average annual water yield and water conservation from 1990 to 2020 were recorded at 48.98 mm and 2.35 mm, respectively. Precipitation emerged as the primary driver of water yield and conservation service changes, while the south of ZJK generally exhibited higher water yield and conservation service than the north of ZJK. Results also indicate that grassland had the highest water yield, with an average of 56.60 mm, followed by forest (55.66 mm) and shrub (55.07 mm). Further, the forest had the highest water conservation value (3.73 mm), followed by shrub (2.56 mm), and grassland (2.37 mm), respectively. The return of cropland to forest scenario had the most substantial decrease in water yield. Findings suggest that precipitation has a direct impact on water yield and conservation services via the amount of atmospheric water input, while land use alteration contributes to changes in regional-scale water.

A sustainable water vortex-based air purification for indoor air quality

High-efficiency particulate air (HEPA) filters are widely used in air purifiers to trap particular matter. However, from an environmental and economic standpoint, HEPA filters have a low cumulative clean mass and consume many resources for replacement or disposal after use. Herein, we present a water-vortex-based air purification method. The water vortex generated by a rotating impeller can efficiently capture particular matter of any size, owing to the increased surface area and circulation of water. Furthermore, the captured particular matters settle to the bottom due to the centrifugal force, enabling the water vortex-based air purifier to maintain 90% of its air purifying performance even after trapping 7.0 g of particular matters. On the other hand, a HEPA filter decreased its performance to less than 50% after trapping 3.5 g of particular matters because the HEPA filter captures particular matters by a deep-bed filtration mechanism.

Spatial spillover effects of urban decline in Southeast Michigan

This paper uses an effective means to explore spatial processes and extents of urban decline using Detroit as a case study. We examined spatial lag of X (SLX) model and its variations, using vacant urban land as a proxy for urban decline. Fourth-order of queen contiguity provided an optimal spatial extent of spillover effects, and SLX was the better-fit model. Multi-unit housing structures, female-headed households, recently moved-in household heads, water surface area, and urban land use area showed negative spillover effects whereas manufacturing employee population, old building structures, low-income population, and agricultural land area exhibited positive spillover effects. Additionally, agricultural, urban, and water surface area, property value, and education level showed significant direct effects. The maximum spatial extent clustered 131 census tracts, suggesting a collaboration of all cities/townships, communities, and private sectors to avert urban decline's spillover effects.

Res-CN (Reservoir dataset in China): hydrometeorological time series and landscape attributes across 3254 Chinese reservoirs

Abstract. Dams and reservoirs are human-made infrastructures that have attracted increasing attention because of their societal and environmental significance. Towards better management and conservation of reservoirs, a dataset of reservoir-catchment characteristics is needed, considering that the amount of water and material flowing into and out of reservoirs depends on their locations on the river network and the properties of the upstream catchment. To date, no dataset exists for reservoir-catchment characteristics. The aim of this study is to develop the first database featuring reservoir-catchment characteristics for 3254 reservoirs with storage capacity totaling 682 595 km3 (73.2 % of reservoir water storage capacity in China) to support the management and conservation of reservoirs in the context of catchment level. To ensure a more representative and accurate mapping of local variables of large reservoirs, reservoir catchments are delineated into full catchments (their full upstream contributing areas) and intermediate catchments (subtracting the area contributed by upstream reservoirs from the full upstream part of the current reservoir). Using both full catchments and intermediate catchments, characteristics of reservoir catchments were extracted, with a total of 512 attributes in six categories (i.e., reservoir and catchment body characteristics, topography, climate, soil and geology, land cover and use, and anthropogenic activity characteristics). Besides these static attributes, time series of 15 meteorological variables of catchments were extracted to support hydrological simulations for a better understanding of drivers of reservoir environment change. Moreover, we provide a comprehensive and extensive reservoir dataset on water level (data available for 20 % of 3254 reservoirs), water surface area (99 %), storage anomaly (92 %), and evaporation (98 %) from multisource satellites such as radar and laser altimeters and images from Landsat and Sentinel satellites. These products significantly enhance spatial and temporal coverage in comparison to existing similar products (e.g., 67 % increase in spatial resolution of water level and 225 % increase in storage anomaly) and contribute to our understanding of reservoir properties and functions within the Earth system by incorporated national or global hydrological modeling. In situ data of 138 reservoirs are employed in this study as a valuable reference for evaluation, thus enhancing our confidence in the data quality and enhancing our understanding of the accuracy of current satellite datasets. Along with its extensive attributes, the Reservoir dataset in China (Res-CN) can support a broad range of applications such as water resources, hydrologic/hydrodynamic modeling, and energy planning. Res-CN is on Zenodo through https://doi.org/10.5281/zenodo.7664489 (Shen et al., 2022c).

Numerical Analysis of Wave Load Characteristics on Jack-Up Production Platform Structure Using Modified k-ω SST Turbulence Model

One of the important stages in the offshore structure design process is the evaluation of the marine hydrodynamic load in which the structure operates, this is to ensure an appropriate design and improve the safety of the structure. Therefore, accurate modeling of the marine environment is needed to produce good evaluation data, one of the methods that can accurately model the marine environment is through the Computational Fluid Dynamic (CFD) method. This research aims to analyze the ocean wave load of pressure and force characteristics on the jack-up production platform hull structure using the (CFD) method. The foam-extend 4.0 (the fork of the OpenFOAM) software with waveFoam solver is utilized to predict the free surface flow phenomena as its capability to predict with accurate results. The Reynold Averaged Navier Stokes (RANS) turbulence model of k-ω SST is applied to predict the turbulence effect in the flow field. Five variations of incident wave direction type are carried out to examine its effect on the pressure and force characteristics on the jack-up production platform hull. The wave model shows inaccurate results with the decrease in wave height caused by excessive turbulence in the water surface area. Excessive turbulence levels can be overcome by incorporating density variable and buoyancy terms based on the Standard Gradient Diffusion Hypothesis (SGDH) into the turbulent kinetic energy equation. The k-ω SST Buoyancy turbulence model shows accurate results when verified to predict wave run-up and horizontal force loads on monopile structures. Furthermore, test results of the wave load on the jack-up production platform hull structure shows that the most significant wave load is obtained in variations with the wave arrival direction relatively opposite to the platform wall. Especially in the direction of 90° because it also has the most expansive impact surface area. Meanwhile, the lower wave load is obtained in variations 45° and 135°, which have the relatively oblique direction of wave arrival to the surface.

GRACE Data Quantify Water Storage Changes in the Shiyang River Basin, an Inland River in the Arid Zone

Global changes and human activities have significantly altered water cycle processes and water resource patterns in inland river basins in arid zones. New tools are needed to conduct more comprehensive and scientific assessments of basin water cycle processes and water resource patterns. Based on GRACE satellite and Landsat data, this study investigated terrestrial water storage changes and surface water area in the Shiyang River Drainage Basin from 2002 to 2021. It explored the effects of climate change and water conservancy construction on terrestrial water storage changes in the basin. The results of the study show that, although the surface water quantity in the Shiyang River basin has increased in the past 20 years, the overall decreasing trend of terrestrial water storage in the basin of the Shiyang River has an interannual decreasing rate of 0.01 cm/a. The decreasing trend of water storage in the midstream and downstream areas is more prominent. The change in precipitation controls the change in water storage in the Shiyang River Drainage Basin. Artificial water transfer has changed the spatial distribution of water resources in the basin of the Shiyang River. However, it still has not completely reversed the trend of decreasing water storage in the middle and lower reaches of the Shiyang River.

Piping hot science: Coffee or tea?

A fine grind Americans drink more than 491 million cups of coffee per day, according to a 2023 report from the National Coffee Association, including the many cups of joe that scientists consume before beginning their daily research grind. One popular coffee-brewing technique is known as espresso, in which water at a near-boiling temperature is pushed through a bed of ground coffee beans at multiple atmospheres of pressure to produce a piping hot drink. Viewed through a scientific lens, the water acts as a solvent in this method to extract the molecules responsible for espresso’s popular bitter flavor. Conventional coffee-brewing wisdom holds that the finer the grind of the coffee beans, the richer the flavor—and science seems to find that line of thinking sensible, as a finer grind provides more surface area for water to dissolve coffee chemicals to make your espresso extra tasty. Not so fast, say leading coffee

A statistical approach on distribution and seasonal habitat use of waterfowl and shorebirds in Çıldır Lake (Ardahan, Türkiye).

Wetlands are crucial habitats for both migrant and resident bird assemblages. The distribution and habitat preferences of birds in aquatic ecosystems are significantly influenced by environmental and ecological factors that critically impact the relevant habitats. In order to reveal the distribution and habitat preferences of the birds, many statistical models and methodologies are employed in ecology and conservation biology. Herein, we investigated the effects of year, season, habitat, and species variables on the distribution and population dynamics of waterfowls and shorebirds associated with the wetland. In this regard, field surveys were carried out in and around Çıldır Lake (Ardahan, Türkiye) between April 2017 and September 2018 to examine the distribution of waterfowls and shorebirds and variations in population sizes. As an experimental design, a stratified random sampling design was used to assess bird fauna in the four dominant habitat types (open water surface, reeds, grasslands, and agricultural areas) in the study area. Accordingly, a total of 51 waterfowl and shorebird species were identified during the study period. Of the identified families, Anatidae (n = 18), Scolopacidae (n = 8), and Ardeidae (n = 8) were the most common families. Considering bird species, common coot Fulica atra and mallard Anas platyrhynchos were the most abundant species. The dependent variable (bird populations) was compared with the independent variables (year, season, habitat, and species). The population in 2018 decreased by 13% in comparison to the population in 2017 (p < 0.05). Once the reed area was considered as the reference, the population density in the water surface habitat increased by 65% (p < 0.001). In relation to seasonal reference, a 65% increase in population growth in spring was recorded in comparison to the growth in fall (p < 0.001). On the other hand, no statistical differences were noted in population growth in winter and summer ((p > 0.05). With respect to the reference species (Anas crecca), critical differences in species fluctuation were observed among species (p < 0.001). Consequently, the findings of the present study suggest that seasonal factor might be of the substantial factors linked to the habitat composition. However, more descriptive and predictive analytical methods are needed beyond classical regression approaches in habitat use and selection studies at bird ecology.

Landsat Satellite Image-Derived Area Evolution and the Driving Factors Affecting Hulun Lake from 1986 to 2020

The area fluctuation of lakes directly affects the stability of the surrounding ecological environment. Research on the area evolution of lakes and the driving factors affecting it plays an important role in sustainable water resource management. In this study, Hulun Lake, located in the Hulunbuir grassland, was taken as the research object. Based on remote sensing images of the Hulun Lake area from 1986 to 2020, MNDWI interpretation was used to obtain the change law of lake surface area over a long time frame. Combined with natural factors and anthropogenic factors, Pearson correlation analysis and principal component analysis were used to analyze the driving force. The results showed that (1) in the past 35 years, the water surface area of Hulun Lake has decreased significantly. The dynamic change in water area could be divided into four stages. The areas with dramatic changes in water area are distributed mainly in the northeast and south of Hulun Lake. (2) In terms of natural factors, the meteorological factors based on evaporation and relative humidity, the runoff of rivers entering the lake, and the vegetation with medium-high coverage and medium-low coverage had significant effects. In terms of anthropogenic factors, the population had the most significant impact. The artificial water diversion project had different degrees of influence on the response of the Hulun Lake area change to natural factors. (3) Anthropogenic factors were the main driving force causing the rapid change in the Hulun Lake area from 2000 to 2016, explaining 48% of the change in the Hulun Lake area. These research results can provide a scientific basis for the development and utilization of water resources and sustainable development in the Hulun Lake area.

Improved UNet-Based Shoreline Detection Method in Real Time for Unmanned Surface Vehicle

Accurate and real-time monitoring of the shoreline through cameras is an invaluable guarantee for the safety of near-shore navigation and berthing of unmanned surface vehicles; existing shoreline detection methods cannot meet both these requirements. Therefore, we propose an improved shoreline detection method to detect shorelines accurately and in real time. We define shoreline detection as the combination of water surface area segmentation and edge detection, the key to which is segmentation. To detect shorelines accurately and in real time, we propose an improved U-Net for water segmentation. This network is based on U-Net, using ResNet-34 as the backbone to enhance the feature extraction capability, with a concise decoder integrated attention mechanism to improve the processing speed while ensuring the accuracy of water surface segmentation. We also introduce transfer learning to improve training efficiency and solve the problem of insufficient data. When obtaining the segmentation result, the Laplace edge detection algorithm is applied to detect the shoreline. Experiments show that our network achieves 97.05% MIoU and 40 FPS with the fewest parameters, which is better than mainstream segmentation networks, and also demonstrate that our shoreline detection method can effectively detect shorelines in real time in various environments.

Lowland artificial watersheds with unique nutrient transport: Response to natural and anthropogenic drivers

Excess nitrogen (N) and phosphorus (P) from watersheds is a key factor causing eutrophication and water quality deterioration in downstream lakes/rivers. However, tracking N & P loss and transport at a watershed scale is challenging especially in lowland artificial watersheds (polders) with complex hydrological processes. To address this challenge, this study selected 171 polders in lower reach of Yangtze River in China as the study area, and investigated the response of N & P loss to both natural and anthropogenic drivers using two process-based models (PDP & NDP) specifically developed for polders. Our modelling practices revealed that these polders had a high N & P loss intensity of 38.37 and 1.75 kg/ha/yr, respectively. Rainy-season precipitation and TN & TP concentrations in connected-rivers were characterized as sensitive factors determining polder N & P loss with a threshold value of 950 mm/yr, 0.2 and 0.02 mg/L, respectively. Compared with annual precipitation, rainy-season precipitation more highly (P < 0.001, R2 >0.8) determined polder N & P loss, with a loss-intensity increase of 6.05 and 0.28 kg/ha/yr for 100 mm increase of rainy-season precipitation. Polder N & P loss was highly related (P < 0.001) to the area of farmland and surface water within these polders. This study can potentially improve our understanding of N & P cycling for lowland polders, and can thus support N & P control in water management practices.

Temporal and Spatial Variation Analysis of Lake Area Based on the ESTARFM Model: A Case Study of Qilu Lake in Yunnan Province, China

Qilu Lake is one of the nine plateau lakes in Yunnan Province, China. In recent years, under the influence of extreme climate and human activities, the area of Qilu Lake has shrunk significantly, the water level has dropped, and the problem of water shortage has become increasingly serious. Based on the Landsat and MODIS image data from 2000 to 2020, this study applied the ESTARFM spatiotemporal fusion model to unify the data images used in the study to February, used three kinds of water body indexes, selected the water body index most suitable for the study area to extract relevant information, and analyzed the spatiotemporal change characteristics of Qilu Lake area in the last 20 years. The results showed that: (1) Based on the ESTARFM model, the Landsat and MODIS data on 18 January 2020, the Landsat and MODIS data on 9 May 2020, and the MODIS data on the date to be predicted (February 13) were fused to obtain the Landsat image data of the predicted date, which met the accuracy requirements; (2) Taking 2005 as an example, the NDWI, MNDWI, and AWEIsh indexes were used to extract the water body with the precisions of 99.0%, 99.6% and 98.6%, respectively, and then the MNDWI water body index was selected to extract the lake area; (3) In the past 20 years, the overall area of Qilu Lake has shown a downward trend, with the area reduced by 0.7132 km2. From 2000 to 2010, the lake area was relatively stable, fluctuating up and down around 36 km2. From 2010 to 2015, the lake area decreased sharply, with a change rate of −40%. After 2015, the lake area gradually increased; (4) The spatial change of Qilu Lake area mainly occurred in the southwest and west, which decreased by 0.44 km2 and 0.49 km2, respectively, and there were small fluctuations in other directions. In the past two decades, the shape index of Qilu Lake has shown a downward trend as a whole; the contour of the lake tends to be simplified, the contour is complex and stable from 2000 to 2010, and the shape index decreases from 2.17 to 1.74 from 2010 to 2020; (5) The change in the Qilu Lake area is positively correlated with the change in the water level. Polynomial models with different times were selected as the model for retrieving water level elevation from the Qilu Lake water surface area, with a highest correlation coefficient of 0.9259. The temporal and spatial changes of the Qilu Lake area in the last 20 years are the result of the joint action of natural factors and socio-economic factors. According to the analysis, the annual average temperature, annual precipitation, annual average sunshine hours, and population density are the main driving forces leading to the change. In the future, the government and relevant researchers should strengthen real-time monitoring and regular research, formulate and optimize emergency plans to deal with changes in the ecological environment of lakes, and promote the sustainable development of the ecological environment and social economy of the basin.

Impacts of climatic variability on surface water area observed by remotely sensed imageries in the Red River Basin

Recent wetting in the Northern Great Plain (NGP) exerted strong influences on lakes and wetlands. However, the influence of recent increase in precipitation on spatiotemporal variation of surface water area is poorly understood in the Red River Basin (RRB, northern United States and southern Canada). Here, we used a high-resolution global surface water dataset to understand spatiotemporal dynamics of the annual, total, permanent, and seasonal water extent in RRB. Monthly surface water area is investigated to detect the change in seasonal surface water extent. We found four distinct phases of variation in surface water: Phase 1 (1990–2001, wetting); Phase 2 (2002- 2005, dry); Phase 3 (2006–2013, recent wetting); and Phase 4 (2014–2019, recent drying). A bare land to a permanent and seasonal water area switch is observed during Phase 1, while the other phases have experienced relatively little fluctuation. Findings have implications for nutrient concentration assessment in lakes and wetlands.