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Proceeding Paper

Evaluation of Surface Area Dynamics of Manta and Beleu Lakes †

by
Ana Jeleapov
Institute of Ecology and Geography, Moldova State University, MD-2028 Chisinau, Moldova
†
Presented at the 8th International Electronic Conference on Water Sciences, 14–16 October 2024; Available online: https://sciforum.net/event/ECWS-8.
Environ. Earth Sci. Proc. 2025, 32(1), 19; https://doi.org/10.3390/eesp2025032019
Published: 3 June 2025
(This article belongs to the Proceedings of The 8th International Electronic Conference on Water Sciences)
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Versions Notes

Abstract

:
This study evaluated the surface area and volume dynamics of the largest and most important natural lakes in the Republic of Moldova: Manta and Beleu. Lakes and surrounding areas represent the main natural ecosystem of the country, are a shelter to thousands of animals and plant species, and are included in the protected areas network. The lakes are situated in the Lower Prut floodplain, with the main water sources being the Prut River through channels, as well as groundwater, surface runoff and precipitation. Regulations of the Prut River flow, climate change, and the increasing frequency of droughts and floods have a certain impact on lake extension and volume dynamics. The main methods used to evaluate surface area variation are the analysis of satellite images (Landsats, from 1975 to 2024) and the application of the NDWI index. As a result, it was identified that the extent of Beleu Lake varied from 0 to 19 km2, and that of Manta Lake from 5 to 27 km2. The actual average surface area is 7–11 km2 for Beleu and 15–19 km2 for Manta. The last catastrophic drought in 2022 decreased the surface area of Beleu by up to 3.7 km2 and that of Manta by up to 5 km2, while the most recent floods in 2020 extended the area of Beleu by up to 12 km2 and that of Manta by up to 27.3 km2. The volumes of Beleu vary from 0 to 40 mil.m3, with an average of 6.5–9 mil.m3, and of Manta from 4.5 mil.m3 to 55 mil.m3, with an average of 15–22 mil.m3. The shoreline lengths corresponding to the average water surface areas are 14–20 km for Beleu and 35–40 km for Manta.

1. Introduction

Lakes represent continental water resources accumulated in large basins with or without connections to rivers or streams. Lakes and reservoirs are key components of the global water cycle, contributing to land–atmosphere exchanges, river–floodplain dynamics, and groundwater systems [1]. These water bodies play a significant role in human well-being, are important sources of water for the economy (water supply, irrigation, recreation, and fishery), and are habitats for aquatic and semi-aquatic ecosystems. Human activity and climate change have a significant impact on lakes, influencing different characteristics such as surface area (S), temperature, quantity and quality, sediments, nutrients and biodiversity, recreational and transportation opportunities [1,2,3,4,5]. Increased air temperature, changes in precipitation patterns, and rising frequency of natural disasters, including floods and droughts, cause the modification and alteration of lakes’ characteristics, leading to the decrease of these important water resources.
In the Republic of Moldova, lakes of natural origin are only a few dozen, many of which are very small and have not yet been mapped [6,7,8]. The most well-known and largest lakes are Old Dniester (oxbow of the Dniester River), situated in the lower part of the Dniester River Basin, and Manta and Beleu (floodplain lakes), situated in the lower part of the Prut River Basin. These are the only natural lakes delineated as water bodies in the national river basin management plans [7,8]. Representing important regions of natural ecosystems, lakes were included in the protected areas network [9] in order to increase the level of water and biodiversity protection and conservation. However, despite the large number of studies on the water quality, fauna, and flora composition of the lakes and surrounding areas [10,11,12,13,14,15,16,17] and the development of management plans [18,19], their main features such as lakes’ surface area and volume have not been analyzed to date.
According to the literature, the main water sources of Beleu and Manta lakes are the Prut River [13,18]. The main water supply season is spring and summer, when floods pass through the Prut River−floodplain [13]. Beleu and Manta are connected with the Prut River through many inflow and outflow channels, however, no clear link between river flow and lakes’ characteristics could be identified in the literature. Some authors have mentioned that channels’ siltation processes lead to the loss of connection between lakes and the Prut River, fact which contributes to their degradation [13,16,17]. At the same time, the main concern is the decreasing trend of lakes’ areas due to the increasing impact of climate change, especially droughts [13,16,18]. In this regard, within the management plans of the Danube–Prut and Black Sea Basin district [7] and Frumoasa−Crihana Sub-basin [18], some of the measures are dedicated to the state of the lakes. These are focused on channels unclogging and lakes’ ecological rehabilitation. In this regard, limnological studies should be conducted. Thus, the present research is dedicated to the evaluation of the water surface, shoreline length, development index, and volume dynamics of Manta and Beleu lakes. In addition, the correlation between the lakes’ characteristics with the Prut River flow is considered for evaluation.

2. Study Area

The present research focused on the evaluation of the morphological characteristics of the Manta and Beleu lakes. These lakes and surrounding areas represent the main natural ecosystem of the Republic of Moldova and shelter to thousands of animals and plant species. The lakes are situated in the Lower Prut River floodplain, in the Frumoasa−Crihana Sub-basin. Both lakes are part of Ramsar zone Nr. 1029 “Lower Prut lakes” (Lacurile Prutului de Jos), are wetlands of international importance since 2000 [18] as well as part of UNESCO Biosphere reservation “Lower Prut” (Prutul de Jos) from 2018 [18,20,21]. In addition, Beleu Lake has been part of the State Reserve network since 1991, named “Lower Prut”, whose status was changed to Scientific and later to Natural Reserve “Lower Prut” [13,18,21].
Manta and Beleu are formed in the Lower Prut River floodplain, being lateral and very close to the riverbed (minimum about 200–300 m from the lake shore to the river’s left bank). Manta Lake is situated to the north of Beleu by about 23 km. The distances to the Danube River are about 37 km from Manta and 15 km from Beleu. The lake water quality corresponds to quality classes II —good and III—moderately polluted [18]. In addition to the Prut river, the water source of the lakes is the Danube backwater that inflow into the Prut floodplain during floods, small streams, groundwater, direct precipitation, and slope runoff. Regulation of the Prut River, climate change, and the increasing frequency of droughts and floods have a certain impact on the water surface area dynamics of the lakes, mainly by decreasing its morphological features and water resources. The Prut River is regulated by the Costesti–Stinca reservoir situated on the middle course of the river, in the northern part of the Republic of Moldova, which is also the border with Romania. The reservoir was built in the late 1970s, with the aim of flood protection, production of electricity, water supply, fishery, and recreation. Thus, after reservoir construction, the Prut River flood peaks changed from an average of 1119 m3/s in natural regimes to about 360 m3/s in the regulated regime [22], decreasing the capacity of the Prut River to supply the lakes with water. Additionally to the Prut regulation, the impact of climate change modified river water resources, natural flow being reduced, on average, by 12% for the last three decades. An average flow decrease was observed mainly in spring and summer, the main seasons for flow generation. Thus, flow diminished by 30% for April and by 9–23% for May–July for 1991–2020 in comparison with 1961–1977 [23]. The main challenges for lakes are rapid siltation, pollution from point and diffuse sources, and oil extraction in the case of Beleu Lake [13,17,18].
Beleu is a floodplain lake approximately 5000–6000 years old [13]. The connection between the Prut River and the lake is formed through two inflow channels: Manolescu and Popovici, and two outflow channels, Rotaru and Năvodului [18]. Some channels were artificially dug. During this time, they grew from small streams to larger ones till the ’90 of the last century, and then gradually, the siltation process modified their morphology, many sediments being deposited at their mouth near the lake [13]. Manolescu channel is the longest in length; its natural course was artificially modified after 1968, with the aim of bringing as much water with fish from the river as possible [13]. According to some sources, the Manolescu channel is of artificial origin, being built in the ’40 of the last century [17]. Different authors mention that the lake’s average depth used to be 4 m, at present, being 0.5–1.5 m with a maximum of 2.5–2.8 m [13,18].
The Manta lakes network was formed in the Holocene [18], consisted of small lakes: Dracele, Rotunda, Fontan, Surda, Listva, Badelnic, Mărioara, and Coada Vulpei, with a depth of up to 7–8 m or even 10 m, the water being of high clarity and transparency [13,18]. In the ’60 of the last century, the Prut floodplain was subject to change, and the natural ecosystem was heavily modified and converted into agricultural land. Many natural lakes have been transformed into fishery ponds. The other lakes were combined to form the present configuration of the Manta Lake, as a result of the impact of the great floods of the Prut River from 1979 [13]. At present, the connection between the Prut River and the lake is formed through two inflow channels coming from the north and west of the lake and two outflow channels situated in the southern part of the lake. The actual average water depth is estimated to be 50–60 cm, with a maximum of 1 m [18], highlighting the rapid siltation process.

3. Materials and Methods

The main materials used for the evaluation of the dynamics of the surface area of the Manta and Beleu lakes were topographic maps presented in the National Geospatial Fund [24] and Landsat satellite images extracted from the USGS Earth Explorer portal [25]. In total, for 1975–2024, 45 Landsat images were chosen, with no clouds, mainly for spring–summer periods, when floods and droughts occur, in order to estimate also the minimum and maximum water extent. The open water areas of the Manta and Beleu regions were calculated using the QGIS software 3.28 [26] and the NDWI index. A comprehensive list of NDWI indexes used for water extent estimation was provided by Li et al. [27]. Some of the indexes used in the present study are listed in the Table 1.
In order to identify the link between the open water area and Prut River flow, time series for flow were analyzed using the Hydrological Database of the Moldova State Hydrometeorological Service [32]. The nearest hydrological station to the lakes, managed by the Republic of Moldova representatives, is Ungheni [32], which is situated about 335 km upstream of Manta Lake. However, hydrological monitoring of the Prut River is also performed by Romania [33]. The nearest hydrological station is Oancea, which is 20 km upstream of Manta Lake. Nevertheless, access to the Oancea time series is possible only by reading daily forecasts on the Romanian National Institute of Hydrology and Water Management website [33] or daily hydrological bulletins on the Moldova State Hydrometeorological Service website [34]. Using these sources of data, information on the Prut River’s daily flow at Ungheni was identified from 1960 to the present and at Oancea from 2022 to the present. Even with a short time series for Oancea, it was possible to evaluate the flow travel time from Ungheni to Oancea. On average, this value is about 5–7 days. Thus, to identify a link between lake extent and Prut River flow, the main hydrological data were used from the Ungheni station but with a delay of 5, 7, and 10 days from the date of the satellite images used for lake open water mapping.
To evaluate volume dynamics, the Raster surface volume function in QGIS was used [26]. Initially, the digital elevation model (DEM) was constructed. Information on topography, mainly contour lines and elevation points, was digitized from topographic maps at a scale of 1:5000 and 1:10,000 provided by the National Fund of Geospatial Data of the Republic of Moldova [24]. These maps are old, constructed in the ’40–60s of the last century. Information on batimetry is present only as depth points but at a low density. Batimetry was improved using descriptions in the literature [13,18] and discussions with the local population. Finally, the DEM was created using the TIN interpolation function in QGIS with a pixel size of 1 m. Even so, DEM is considered of a medium accuracy; new techniques and approaches are needed to be used in order to develop high-accuracy DEM, which would also include detailed batimetry of the lakes.

4. Results and Discussions

4.1. Dynamics in Surface Area Estimated Basing on Topographic Maps

Topographic maps are important sources of spatial data, especially those constructed before the launch of artificial satellites. Topographic maps with representations of pilot-lakes open water extents were obtained for 1942 and 1963 at scales of 1:5000 and 1:10,000, and for 1982 and 2013 at a scale of 1:50,000 [24]. Not all topographic sheets produced for 1942 and 1963 contained lake extent; therefore, lakes surface areas were mapped only based on their combination. The maps of 1982 and 2013 were developed and detailed at a scale of 1:50,000 and are suitable for comparison. Thus, the extent of Beleu Lake in the middle of the last century was about 8.99 km2, and a small lake was identified in the north of Beleu with an area of 0.5 km2 and 14 smaller lakes in the south with areas between 0.003 and 0.26 km2. The Beleu Lake shoreline (perimeter P) was estimated to be 46 km, being highly sinuous. The 1982 maps allowed the evaluation of a lake surface area of 8.50 km2 and a perimeter of 18 km with a shoreline of much lower sinuosity. Beleu is represented as merged with the northern lake. No other water accumulation was identified. The maps of 2013 showed a smaller Beleu Lake, with a surface area of 6.86 km2 and a perimeter of 14.7 km. The northern lake is represented separately, also addition 4 small lakes appeared in the north-eastern part of the lake, with areas varying from 0.04 km2 to 0.15 km2. All maps show wetlands around Beleu Lake, as well as a large network of irrigation channels in addition to those of natural origin. Thus, analysis of topographic maps for the last 70 years shows a decreasing tendency of the lake’s extent: its area diminished by 24% and its shoreline by 68%, losing its sinuosity. In addition, small water accumulations dry out in the southern part of the lake and appear in the north-eastern part (Figure 1).
The old topographic maps of the Manta Lake region show the presence of a network of over 20 lakes, of which nine are the largest, namely Carasu (S = 0.037 km2, P = 0.85 km), Vadul lui Topor (S = 0.047 km2, P = 0.89 km), Motran (S = 0.048 km2, P= 0.94 km), Bribare (S = 0.11 km2, P= 1.36 km), Listva (S = 0.47 km2, P= 5.4 km), Foltan (S = 1.35 km2, P = 6.54 km), Badelnic (S = 1.37 km2, P = 11.43 km), Rotunda (S = 1.97 km2, P = 12 km), Dracele (S = 2.57 km2, P = 9.29 km). In addition, a large network of channels that assured connection between the Prut River and lakes can be easily identified. The largest channels are Balacea, Surda, and Ciortu. Many of the listed lakes can also be identified on the 1982 maps. The surface area of Rotunda Lake is larger by 0.37 km2, and the shoreline is the same; Dracele Lake is large by 0.23 km2, and the shoreline is smaller by 0.75 km; Badelnic Lake is large by 0.08 km2, and the perimeter is smaller by 5 km, while the surface area of Listva Lake decreased to 0.25 km2 and the perimeter to 4.97 km. It should be mentioned that according to the literature [13], the largest lakes, Dracele, Badelnic, and Rotunda, were merged into one water body as a result of a Prut River flood in 1979. Analysis of topographic maps does not confirm this fact, as the lakes are still separated. In 1975, a fish farm was constructed in the northern part of the Manta region. It is formed from eight small reservoirs and 12 ponds. The volume of the reservoirs was 1.54–2.58 mil.m3 and a surface area of 1.18–2.15 km2 [6]. Overall, the area covered by the fish farm lakes was 14.4 km2. The natural lakes Foltan, Motran, Carasu, and Vadul lui Topor were modified and included in the fish farm reservoir network. Topographic maps of 2013 represent a different extent of lakes compared to the older maps. Only one natural water accumulation was observed: Manta Lake. The fish farm is also visible on the maps. The total area of Manta is 16 km2, with a shoreline of 32.3 km. Manta Lake includes Rotunda Badelnic and Listva lakes as well as Surda, Balacea, and Ciortu channels. A small part of Dracele is also a part of Manta; however, the northern part of it dried out, and only some channels flow through this area. Bribane Lake was not identified, and its region was dry. Overall, the configuration of Manta Lake changed, being one consolidated water body with an area larger by about 10 km2 in comparison with the previous period. The Manta Lake area is characterized by greater dynamics than the Beleu Lake area. From a network of 20 small lakes, it was consolidated into one natural water body, some lakes also were transformed and included in the fish farm reservoir network (Figure 2).

4.2. Dynamics in Surface Area Estimated Basing on Satellite Images

The surface areas of Manta and Beleu lakes were evaluated using freely available Landsat images [25] from 1975 to 2024. From the hundreds of satellite images, those for May to October and those with no clouds and snow coverage were mainly considered. Satellite images were selected in combination with an analysis of the Prut River flow time series, in order to identify those that represent the surface area for different discharges in order to estimate relationships between flow and lake areas. Thus, a total of 45 Landsat images were selected. Delineation of open water was performed using NDWI indexes, and the best and relatively equal results were obtained by applying equations 2 and 4 from Table 1. The analysis was performed only for open water, which was clearly visible in the images. The overlay of all extracted extents of the Beleu and Manta lakes is shown in Figure 3, while the surface area dynamics are presented in Figure 4 and Figure 5.
As a result of satellite image analysis, it was identified that the Beleu Lake surface area varies from 0 to 19 km2. Dry Beleu Lake was observed for the summer–autumn period in 1990 when a catastrophic drought took place. During the droughts of 2007 and 2009 the water extent was about 6–7 km2. The most recent drought, from the summer of 2022, decreased the water extent to about 3–4 km2, which is twice as low as the average.
The largest Beleu extent was observed mainly during the high flows of the Prut River. The maximum water extent was evaluated to be 17–19 km2 for the floods of 1975. Floods from 1991 caused water extensions of about 14.8 km2, and those from 1998 lead to a surface area of about 12.5 km2. 2008 flood increased the water extent only to 9.31 km2 and the one form 2020 to 11.9 km2. It was observed that the surface area of Beleu Lake during the Prut floods was characterized by a decreasing tendency. The reduction in the maximum extent during recent floods is considered to be caused by the regulation of Prut River flow, changes in flood characteristics, and the siltation of the connection channels. For the last two decades, a certain amount of flood water has accumulated in the northern part of Beleu Lake, a region that was not flooded in the previous decades and is characterized by a high density of artificial channels. In addition, high waters accumulated in the southern part of the lake, on the other side of the lake dike, in the region of outflow channels. The average Beleu surface area is estimated to be 10 km2, with a variation of 7–11 km2. A slow decreasing tendency of the average area is also observed, with the surface area being smaller in recent years than in previous decades.
In the case of Manta Lake, all satellite images show a consolidated water body, and not divided lakes, as shown on the topographic maps of 1982. Lakes merging, most probably, occurred after the great floods of 1969 on the Prut River and not in 1979, as stated in the literature [13]. Although no images or maps for 1962–1974 were identified, to appreciate the time of Manta Lake consolidation more specifically. According to satellite images, the Manta surface area varies from 5 to 27 km2. The smallest surface areas were caused by recent droughts. Thus, in 2023, the surface area was about 5 km2, while in 2022, it was 6.3 km2. During the droughts of 2007, 2009, and 2015, the surface area was about 12–14 km2. Interestingly, the catastrophic drought of 1990 did not cause a dramatic decrease of the lake area, which was about 19 km2. The same area was evaluated for 1984. In this regard, the serious decrease in the surface area during recent droughts compared to those from the ’80–90 of the last century can be explained by a lower or even lost connection of the lake with the Prut River, high siltation processes, loss of local sources of water supply, and longer and more intense droughts. The recent smallest area of Manta does not cover the area of the former Dracele Lake at all. Only Badelnic Lake, half of Rotunda Lake, and the Ciortu and Balacea channel areas configured Manta Lake during the drought of 2022 and 2023. Thus, the intensification of the frequency and intensity of drought caused by climate change can lead to the total disappearance of Manta Lake, and urgent measures are needed to avoid this situation.
The maximal surface area of Manta Lake was evaluated to be 27.3 km2 during the floods of 2020. The other floods caused an increase in the area to 22–26 km2. Thus, during the floods of 1975, 1978, 1989, and 1998, the flooded areas were 24–26 km2, while during the flood of 2008, it was only 20.3 km2. No significant changes were identified in the areas formed by floods over the whole time period. The average surface area of Manta Lake is 15–19 km2. As in the case of Beleu Lake, higher values were specific for the last decades of the last century, and the lowest values were observed in recent years.
In addition to the lakes’ surface area calculation, the other two parameters, shoreline length and shoreline development index [35], were determined. These parameters correlated with each other and with the lakes’ surface area (Figure 6). In the case of Beleu Lake, the shoreline length varies from 0 to 76 km, and in the condition of the most recent drought, this characteristic was about 9–11 km. Recent floods have increased the shoreline by about 30–50 km, while the floods of the late 70s and 80s—up to 70–76 km. The length of the shoreline corresponding to the average surface area is 14–20 km. The shoreline development index is, on average, 3, varying from 1.45 to 5.8, depending on the lake’s area. The relationships between the characteristics of Beleu Lake, including surface area, shoreline length, and shoreline development index, showed a high correlation, with the coefficient of determination reaching a value of 0.42–0.9.
The Manta Lake shoreline length varies between 25 and 76 km. Floods caused an increase beyond 50 km, while droughts caused a decrease below 30 km. The average length of the shoreline is 35–40 km long. The shoreline development index is, on average, 2.3, varying from 1.4 to 5.6. Increasing changes in lake surface area over the last 50 years have led to lower coefficients of determination that are formed after the evaluation of the three characteristic relationships. Even a negative coefficient of determination was estimated for the shoreline development index and lake surface area relationship, which shows a large change in the lake area in conditions of floods and droughts, and significant modifications during the last seven decades.

4.3. Relationships Between the Prut River Flow and Lakes’ Surface Area

Manta and Beleu lakes are dependent on the Prut River flow, which is their main water supplier. Thus, in order to estimate the relationship between river flow and lakes’ area, hydrological time series and lake surface area data obtained from satellite images were compared (Figure 7). In order to identify the link between two variables, a correlation was performed between the lakes’ area and Prut River flow from the Ungheni station, with a 5, 7, and 10 days delay from the date of satellite images, considering that the station is upstream of the lakes by about 335 km. The best coefficient of determination was obtained as a result of the correlation between the 5 days delay of flow and surface area of both lakes (Figure 8).
Based on the constructed correlations and comparison of the Prut River flows and lakes surface area (Figure 7 and Figure 8), the following was established: during low Prut River flow, ≤30 m3/s, lakes areas decrease to 6–8 km2 in the case of Manta and 0–5 km2 in the case of Beleu. Flows of 30–50 m3/s increase the lakes’ surface area to 8–15 km2 (Manta) and 5–8 km2 (Beleu). Flows of 50–70 m3/s cause an expansion of lakes to 15–18 km2 (Manta) and 8–11 km2 (Beleu). The extent of Manta and Beleu lakes of 18–21 km2 and 11–13 km2 is caused by flows of 70–100 m3/s. An increase in surface area to 21–23 km2 for Manta and 13–14 km2 for Beleu occurs with discharges of 100–200 m3/s. When the Prut River exceeds 200 m3/s, the lakes expand beyond 23 km2 for Manta and 14 km2 for Beleu.

4.4. Relationships Between Lakes Surface Area and Volume

The most important morphological parameter of a lake is its water volume. In order to estimate the pilot-lakes volumes and their variation, a DEM was constructed using old topographic maps and actual descriptions of lakes taken from the literature [13,18] and discussions with the local population. In general, lakes are shallow, with an average depth of up to 1.5 m. In addition, aquatic vegetation is abundant, especially in Manta Lake, which increases the lake’s secondary pollution and siltation. Based on the modeled DEM, volumes were extracted using QGIS functions, and correlations with the lakes’ surface areas were performed (Figure 9).
Volume validation was difficult to perform due to the absence of any information about lakes’ volumes in the literature. For Beleu Lake, only one volume value was found, which was equal to 8.39 mil.m3 [18]. Modeled volume results are in line with this value; for example, for an average area of 8.5 km2, the estimated volume is 8.6 mil.m3. Thus, the volume of Beleu Lake varies from 0 to 40 mil.m3 for an extent of 0 to 25 km2, with an average of about 6.5–9 mil.m3. In the case of Manta, the estimated water volume varies from 4.5 mil.m3 to 55 mil.m3 for an extent of 5 to 30 km2. The average volume is 15–22 mil.m3.

5. Conclusions

This study represents the first attempt to evaluate the main morphological characteristics of Beleu and Manta lakes, including surface areas, shoreline length, shoreline development index, and also volumes. Topographic maps and satellite images were analyzed to establish their variation. As a result, it was identified that the Beleu Lake surface area varies from 0 to 19 km2, and the Manta Lake extent from 5 to 27 km2. The minimum and maximum surface areas depended on the Prut River flow. During low flows, Beleu’s area decreases to 0–7 km2, while Manta’s shrinks to 5–14 km2. In contrast, high flows expanded Beleu to 15–19 km2 and Manta to 22–28 km2. The average water surface area ranges from 7 to 11 km2 for Beleu and from 15 to 19 km2 for Manta. The length of the shoreline corresponding to the average surface area is 14–20 km for Beleu and 35–40 km for Manta. The shoreline development index is over 2, indicating the complex shape of the lakes. For the last seven decades, the shapes have been changing: significant for Manta Lake, less for Beleu Lake, and this trend will continue in the future.
The correlation of lakes surface area and Prut River flow showed that during the Prut low flow, ≤30 m3/s, Manta Lake area is 6–8 km2, and Beleu surface area is 0–5 km2, during flows of 30–50 m3/s water extent is 8–15 km2 and 5–8 km2, for the flows of 50–70 m3/s, this characteristic is 15–18 km2 and 8–11 km2, for the 70–100 m3/s, extent of Manta and Beleu lakes is about 18–21 km2 and 11–13 km2, for the 100–200 m3/s it is of 21–23 km2 and 13–14 km2. A flow ≥ 200 m3/s generates an extension of over 23 km2 for Manta and 14 km2 for Beleu Lake.
The attempt to evaluate the water volumes of the pilot lakes was based on the development of DEM and extraction of the volumes for certain surface areas. This approach resulted in estimated volumes for Beleu of 0 to 40 mil.m3 for the extent of 0 to 25 km2, with an average of about 6.5–9 mil.m3, and for Manta of 4.5 mil.m3 to 55 mil.m3 for the extent of 5–30 km2, with an average volume of 15–22 mil.m3.
The increasing frequency and intensity of droughts, as well as flow regulations through reservoirs, cause long-term low flow in the Prut River and low volumes in lakes, which negatively influences the aquatic ecosystems of the natural protected areas. The decreasing tendency of water extent shows that these lakes can obtain intermittent characteristics or even completely dry out in the near future. In-depth research is needed for the complex evaluation of both lakes and the development and application of measures in order to rehabilitate and protect them and their valuable ecosystems. Unclogging the lakes and channels, improving the connection between lakes and the Prut, rethinking Prut River flow regulation, installing monitoring stations, and encouraging research in the area are only several steps that can be taken in the near future to improve the state of Manta and Beleu lakes.

Funding

Present research was financed by the Republic of Moldova State budget within project implemented by the Institute of Ecology and Geography of Moldova State University.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are available in this manuscript.

Conflicts of Interest

The author declares no conflicts of interest.

References

  1. Hou, J.; Van Dijk, A.I.J.M.; Renzullo, L.J.; Larraondo, P.R. GloLakes: Water storage dynamics for 27,000 lakes globally from 1984 to present derived from satellite altimetry and optical imaging. Earth Syst. Sci. Data 2024, 16, 201–218. [Google Scholar] [CrossRef]
  2. Noges, T.; Noges, P.; Jolma, A.; Kaitaranta, J. Impacts of Climate Change on Physical Characteristics of Lakes in Europe; EUR 24064 EN; Office for Official Publications of the European Communities: Luxembourg, 2009; p. JRC54650. Available online: https://publications.jrc.ec.europa.eu/repository/handle/JRC54650 (accessed on 18 September 2024).
  3. Adrian, R.; O’Reilly, C.M.; Zagarese, H.; Baines, S.B.; Hessen, D.O.; Keller, W.; Livingstone, D.M.; Sommaruga, R.; Straile, D.; Van Donk, E.; et al. Lakes as sentinels of climate change. Limnol Oceanogr. 2009, 54, 2283–2297. Available online: https://pmc.ncbi.nlm.nih.gov/articles/PMC2854826/ (accessed on 16 September 2024).
  4. Vincent, W. Effects of Climate Change on Lakes. Encycl. Inland Waters 2009, 3, 55–60. Available online: https://www.academia.edu/30167457/Effects_of_Climate_Change_on_Lakes (accessed on 20 September 2024).
  5. Woolway, R.I.; Kraemer, B.M.; Lenters, J.D.; Merchant, C.J.; O’reilly, C.M.; Sharma, S. Global lake responses to climate change. Nat. Rev. Earth Environ. 2020, 1, 388–403. [Google Scholar] [CrossRef]
  6. Cazac, V.; Mihailescu, C.; Bejenaru, G.; Gilca, G. Water resources of the Republic of Moldova. In Surface Waters; Stiinta: Chisinau, Moldova, 2007; p. 248. (In Romanian) [Google Scholar]
  7. The Republic of Moldova Governmental Decision nr. 444 from 29-06-2022 Regarding the Approval of the Management Program of the Danube—Prut and Black Sea Basin District, Cycle II (2023–2028). Available online: https://www.legis.md/cautare/getResults?doc_id=132734&lang=ro (accessed on 17 September 2024). (In Romanian).
  8. The Republic of Moldova Governmental Decision nr. 70 from 19-02-2025 Regarding the Approval of the Dniester Basin District Management Plan, Cycle II (2025–2030). Available online: https://www.legis.md/cautare/getResults?doc_id=147587&lang=ro (accessed on 14 March 2025). (In Romanian).
  9. The Republic of Moldova Parliament Law Nr. 1538 from 25-02-1998 Regarding the Fund of Natural Areas Protected by State. Available online: https://www.legis.md/cautare/getResults?doc_id=141074&lang=ro# (accessed on 16 September 2024). (In Romanian).
  10. Biosphere Reserve Prutul de Jos. Available online: https://prutuldejos.md/despre-noi/ (accessed on 20 September 2024). (In Romanian).
  11. The Lower Dniester National Park. Available online: https://lower-dniester.org/aboutthearea (accessed on 2 September 2024). (In Romanian).
  12. The Natural Heritage of Core Areas of International Importance from the National Ecological Network of the Republic of Moldova: Illustrative Atlas. Available online: https://www.bioticamoldova.org/storage/files/Patrimoniul%20%20natural%20al%20zonelor%20nucleu%20REN.pdf (accessed on 22 September 2024). (In Romanian).
  13. Paladi, V. Ornithofauna of the “Lacurile Prutului de Jos” Ramsar Site. Ph.D. Thesis, Universitatea de Stat Din Moldova, Chisinau, Moldova, 2024; p. 182. Available online: https://www.anacec.md/files/Paladi-teza.pdf (accessed on 15 October 2024). (In Romanian).
  14. Paladi, V. Contribution to the study of water and semiaquatic birds in the Ramsar Wetland, Lower Prut Lakes. Sustainable use and protection of animal word in the context of climate change. In Proceedings of the X-Th International Conference of Zoologists, Chisinau, Moldova, 16–17 September 2021; pp. 348–357. [Google Scholar]
  15. Cojan, C.; Munteanu, A. Population dynamics and behavioral migration characteristics of aquatic and semi-aquatic birds from the Lower Prut basin. Bull. Acad. Sci. Life Sci. 2009, 3, 102–111. (In Romanian) [Google Scholar]
  16. Postolache, G.; Munteanu, A.; Postolache, D.; Cojan, C. Reserve “Prutul de Jos”; Tipografia Centrală: Chisinau, Moldova, 2012; p. 152. (In Romanian) [Google Scholar]
  17. Postolache, G. The integrated protected area of the Lower Prutul de Jos reserve. Mediu. Ambiant 2012, 2, 21–26. (In Romanian) [Google Scholar]
  18. Odainic, V.; Marin, I.; Cazacu, A.; Melnicenco, E. The Management Plan of the Frumoasa-Crihana Sub-Basin Cycle I (2021–2026); EcoContact, Centrul de Consultanţă Ecologică Cahul; Bons Offices SRL: Chişinău, Moldova, 2023; p. 132. (In Romanian) [Google Scholar]
  19. The Management Plan for the “Lower Dniester” Ramsar Zone, Approved by Minister’s Order no. 93 of December 1. 2014; p. 231. Available online: https://am.gov.md/sites/default/files/document/attachments/MAN-PLAN%20Nistru%20de%20Jos.pdf (accessed on 30 September 2024). (In Romanian)
  20. The Republic of Moldova Parliament Law Nr. 132 of 13-07-2018 Regarding the Establishment of the “Prutul de Jos” Biosphere Reserve. Published in Official Monitor Nr. 321–332 art. 515, on 24-08-2018. Available online: https://www.legis.md/cautare/getResults?doc_id=105493&lang=ro (accessed on 25 September 2024). (In Romanian).
  21. The Republic of Moldova Government Decision Nr. 122 from 12-08-2021 Regarding the approval of the Operating Regulations of the “Prutul de Jos” Biosphere Reserve. Available online: https://www.legis.md/cautare/getResults?doc_id=127440&lang=ro (accessed on 20 March 2025). (In Romanian).
  22. Jeleapov, A. The Study on Pluvial Floods in the Context of Human Impact on Environment; Tipografia Impressum: Chişinău, Moldova, 2020; p. 254. (In Romanian) [Google Scholar]
  23. Bulimaga, C.; Bacal, P.; Tugulea, A.; Certan, C. (Eds.) Complex Assessment of Urban and Rural Ecosystems in the Northern Development Region; Impressum: Chişinău, Moldova, 2023; p. 220. Available online: https://www.adrnord.md/public/files/2023WEBMonografie-Aprecierea-complexa-RD-Nord49e6e.pdf (accessed on 1 September 2024). (In Romanian)
  24. National Fund of Geospatial Data of the Republic of Moldova. Available online: https://geoportal.md (accessed on 2 May 2024).
  25. USGS. Earth Explorer, Landsat Images for 1975–2024. Available online: https://earthexplorer.usgs.gov/ (accessed on 2 May 2024).
  26. Quantum GIS. Available online: https://qgis.org/en/site/ (accessed on 12 January 2024).
  27. Li, Y.; Gong, X.; Guo, Z.; Xu, K.; Hu, D.; Zhou, H. An index and approach for water extraction using Landsat–OLI data. Int. J. Remote Sens. 2016, 37, 3611–3635. [Google Scholar] [CrossRef]
  28. Gao, B.-C. A Normalized Difference Water Index for Remote Sensing of Vegetation Liquid Water from Space. Remote Sens. Environ. 1996, 58, 257–266. [Google Scholar] [CrossRef]
  29. McFeeters, S.K. The Use of the Normalized Difference Water Index (NDWI) in the Delineation of Open Water Features. Int. J. Remote Sens. 1996, 17, 1425–1432. [Google Scholar] [CrossRef]
  30. Rogers, A.S.; Kearney, M.S. Reducing Signature Variability in Unmixing Coastal Marsh Thematic Mapper Scenes Using Spectral Indices. Int. J. Remote Sens. 2004, 25, 2317–2335. [Google Scholar] [CrossRef]
  31. Xu, H. A Study on Information Extraction of Water Body with the Modified Normalized Difference Water Index (MNDWI). J. Remote Sens. 2005, 9, 589–595. Available online: https://www.researchgate.net/publication/284418225_A_study_on_information_extraction_of_water_body_with_the_modified_normalized_difference_water_index_MNDWI (accessed on 16 July 2024).
  32. Hydrological Database of the Moldova State Hydrometeorological Service 2024.
  33. Hydrological Forecast. Available online: https://www.hidro.ro/bulletin_type/buletin-hidrologic-zilnic/ (accessed on 12 July 2024). (In Romanian).
  34. Hydrological Forecast. Hidrologic Bulletin. Available online: http://www.meteo.md/index.php/hidrologie/prognoze (accessed on 12 July 2024). (In Romanian).
  35. Hutchinson, G.E. A treatise on limnology. In Geography, Physics and Chemistry; Wiley: New York, NY, USA, 1957; Volume 1, p. 1015. [Google Scholar]
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Figure 1. The Beleu Lake, surface area of 1942–1960 (left), 1982 (center), and 2013 (right).
Figure 1. The Beleu Lake, surface area of 1942–1960 (left), 1982 (center), and 2013 (right).
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Figure 2. The Manta Lake, surface area of 1942–1960 (left), 1982 (center), and 2013 (right).
Figure 2. The Manta Lake, surface area of 1942–1960 (left), 1982 (center), and 2013 (right).
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Figure 3. Overlay of all extracted extents of Beleu (left) and Manta (right) for 1975–2024.
Figure 3. Overlay of all extracted extents of Beleu (left) and Manta (right) for 1975–2024.
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Figure 4. Dynamics of Beleu Lake extent (source: extracted from Landsat images, https://earthexplorer.usgs.gov/, accessed on 2 May 2024).
Figure 4. Dynamics of Beleu Lake extent (source: extracted from Landsat images, https://earthexplorer.usgs.gov/, accessed on 2 May 2024).
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Figure 5. Dynamics of Manta Lake extent (source: extracted from Landsat images, https://earthexplorer.usgs.gov/, accessed on 2 May 2024).
Figure 5. Dynamics of Manta Lake extent (source: extracted from Landsat images, https://earthexplorer.usgs.gov/, accessed on 2 May 2024).
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Figure 6. Relationships between lakes’ surface area, shoreline length, and shoreline development index.
Figure 6. Relationships between lakes’ surface area, shoreline length, and shoreline development index.
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Figure 7. Dynamics of the Beleu and Mata lakes surface area and Prut River flow at Ungheni st. (with 5 days delay).
Figure 7. Dynamics of the Beleu and Mata lakes surface area and Prut River flow at Ungheni st. (with 5 days delay).
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Figure 8. Relationship between the Beleu Lake surface area (left), Manta Lake surface area (right), and Prut River flow at Ungheni (with 5 days delay).
Figure 8. Relationship between the Beleu Lake surface area (left), Manta Lake surface area (right), and Prut River flow at Ungheni (with 5 days delay).
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Figure 9. Correlation between the surface area and volume of Beleu Lake (left) and the surface area and volume of Manta Lake (right).
Figure 9. Correlation between the surface area and volume of Beleu Lake (left) and the surface area and volume of Manta Lake (right).
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Table 1. Indexes used for water extraction from satellite images [27,28,29,30,31].
Table 1. Indexes used for water extraction from satellite images [27,28,29,30,31].
Nr.IndexFormulaReference
1NDWI(BNIR − BSWIR)/(BNIR + BSWIR)Gao 1995 [28]
2NDWI(BG − BNIR )/(BG + BNIR)McFeeters 1996 [29]
3NDWI(BR − BSWIR)/(BR + BSWIR)Rogers and Kearney 2004 [30]
4MNDWI(BG − BSWIR)/(BG + BSWIR)Xu 2005 [31]
BNIR—near-infrared band, BSWIR—shortwave infrared band, BG—green band, BR—red band.
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Jeleapov, A. Evaluation of Surface Area Dynamics of Manta and Beleu Lakes. Environ. Earth Sci. Proc. 2025, 32, 19. https://doi.org/10.3390/eesp2025032019

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Jeleapov A. Evaluation of Surface Area Dynamics of Manta and Beleu Lakes. Environmental and Earth Sciences Proceedings. 2025; 32(1):19. https://doi.org/10.3390/eesp2025032019

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Jeleapov, Ana. 2025. "Evaluation of Surface Area Dynamics of Manta and Beleu Lakes" Environmental and Earth Sciences Proceedings 32, no. 1: 19. https://doi.org/10.3390/eesp2025032019

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Jeleapov, A. (2025). Evaluation of Surface Area Dynamics of Manta and Beleu Lakes. Environmental and Earth Sciences Proceedings, 32(1), 19. https://doi.org/10.3390/eesp2025032019

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