Water Level Decline Research Articles

Effect of water depth and waterway obstructions on the divergence and confluence areas of Dongting Lake and the Yangtze River after the operation of the Three Gorges Project

AbstractClimate change and human activities have profoundly changed the evolutionary processes and developmental trends of the hydrology and geomorphology of rivers and lakes. Such changes have affected the evolution of bars and channels at the intersections of rivers and lakes and the utilization of water depth resources in waterways, which, in turn, have affected the sustainable development of waterways, such as the “Golden Waterway” of the Yangtze River. Considering the confluence of Dongting Lake and the Yangtze River as the present study area, we analyzed the effect of the hydrology of Dongting Lake and the evolution of bars and channels in the Jingjiang reach of the Yangtze River on the depth of the waterways. Our results indicated that from before the operation of the Three Gorges Project (1960–2002) to after its operation (2003–2021), the flow and sediment volume of the three inlets of Dongting Lake demonstrated a continuous decreasing trend. Furthermore, the relative increase in the runoff of the Jingjiang reach increased channel erosion. Channel erosion at the river–lake confluence from 2003 to 2021 created favorable conditions for increasing the dimensions of the waterways. The total length of the river–lake confluence that did not meet the requirements for safe navigation [4.5 × 200 m (water depth × width)] was 12.6 km, accounting for 68.35% of the total length of the Jingjiang reach with obstructed navigation. We observed that a decrease in the low‐water level and “steep slope and rapid flow” were the major factors hindering the navigation of the reach (from Zhicheng to Dabujie) affected by the Songzikou diversion of Dongting Lake. This was mostly reflected by the width of the 4.5 m waterway being less than 200 m. A declining water level, shrinking sandbanks and tidal flats, and alternating branches that destabilize the low‐water route were the major factors hindering navigation in the reach (from Taipingkou) affected by the Taipingkou diversion of Dongting Lake. Consequently, alternative waterways were implemented during low‐water periods with the water depth decreasing below 4.5 m. The obvious collapse of sandbanks and tidal flats and their erosion and migration were the major factors hindering navigation of the Ouchikou diversion of Dongting Lake. In addition, the scattered submerged shoals in the navigation channel restricted the width of the 4.5 m channel to less than 200 m. The reach affected by the Dongting Lake confluence (from Xiongjiazhou–Chenglingji reach) was subject to the erosion and silting of bends and the jacking effect of lake outflow, causing shoals with a water depth of less than 4.5 m in the channel. However, the jacking effect slowed the current, thereby assisting in improving channel conditions.

Enhancing spatial resolution of GRACE-derived groundwater storage anomalies in Urmia catchment using machine learning downscaling methods

The Urmia lake in north-west Iran has dried up to perilously low levels in the past two decades. In this study, we investigate the drivers behind the decline in lake water level with the help of in-situ and remote sensing data. We use total water storage (TWS) changes from the gravity recovery and climate experiment (GRACE) satellite mission. TWS from GRACE includes all the water storage compartments in a column and is the only remote sensing product that can help in estimating groundwater storage (GWS) changes. The coarse spatial (approx. 300 km) resolution of GRACE does not allow us to identify local changes that may have led to the Urmia lake disaster. In this study, we tackle the poor resolution of the GRACE data by employing three machine learning (ML) methods including random forest (RF), support vector regression (SVR) and multi-layer perceptron (MLP). The methods predict the groundwater storage anomaly (GWSA), derived from GRACE, as a function of hydro-climatic variables such as precipitation, evapotranspiration, land surface temperature (LST) and normalized difference vegetation index (NDVI) on a finer scale of 0.25° × 0.25°. We found that i) The RF model exhibited highest R (0.98), highest NSE (0.96) and lowest RMSE (18.36 mm) values. ii) The RF downscaled data indicated that the exploitation of groundwater resources in the aquifers is the main driver of groundwater storage and changes in the regional ecosystem, which has been corroborated by few other studies as well. The impact of precipitation and evapotranspiration on the GWSA was found to be rather weak, indicating that the anthropogenic derivers had the most significant impact on the GWSA changes. iii) We generally observed a significant negative trend in GWSA, having also significant positive correlations with the well data. However, over regions with dam construction significant negative correlations were found.

Monitoring Climate Change and Air Quality Project Initiative: A Case Study of the Collaboration between ECSTAR and TeroSpace in Thailand

In Thailand, the alteration of weather patterns has resulted in an increase in instances of irregular rainfall, contributing to the occurrence of droughts. The decline of water levels in dams, due to the combined effects of climate change and prolonged droughts, has had a significant impact on agricultural productivity. Drought has a profound effect on the terrestrial biosphere and the atmospheric water cycle and can also contribute to air pollution. Researchers have found a strong correlation between air pollution and drought severity. In response to this pressing issue, the Excellence Center of Space Technology and Research (ECSTAR) at King Mongkut’s Institute of Technology Ladkrabang has joined forces with TeroSpace company to launch an initiative aimed at promoting sustainable growth in Chiang Rai, a province in Thailand known for its rich biodiversity. ECSTAR and TeroSpace’s partnership on the sustainable growth initiative in Thailand’s Chiang Rai province focuses on expanding their collaboration to include international organizations such as the Centre National d’Etudes Spatiales (CNES), which will provide access to satellite imagery and climate and weather information to improve decision-making in various areas of development. CNES is a French organization in charge of space-related activities in France. The collaboration between France and Thailand for this project, in the context of the France-Thailand Year of Innovation 2023, will be crucial for the successful initiation and execution of this research project. The project aims to explore the relationship between air pollution and climate change through the deployment of air quality monitoring devices in designated locations, connected to a global data-sharing network. The results of this research will be valuable to policymakers as they consider the interplay between air pollution and climate change and make efforts to address these challenges.

Variations of plant communities in diversity and composition along the western coast of Lake Khanka caused by high water level

Lake Khanka is the largest freshwater body of water in northeast Asia, with a basin of about 25 000 km2. The hydrological regime of the lake is cyclical in nature due to various factors affecting water inflow and outflow. The last increase of water level in the lake began in the 2000s and by 2015 reached the maximum value of 416 cm (with the average annual level of 293 cm). A steady decline in water level has been observed since 2021. To assess the diversity and structure of coastal plant communities on the sandy-pebbly substrate along the western shore of Lake Khanka and their dynamics under the influence of flooding, we laid 20 transects and performed descriptions at seven sites, including two sites in the protected area of the Cluster Sosnovy of the Khanka Nature Reserve. Using the diversity and similarity/difference indices, plant communities were compared across the sites. It was shown that their heterogeneity is due to the diversity of both aboriginal and adventive species. In protected areas, the role of adventive species is significantly lower than in recreational areas. The five dominant species in the communities account for 50 % or more of the total abundance. Vegetation groupings in the three identified zones, which have been inundated for different periods of time, have a similar diversity, with differences due only to the native fraction of species. The second zone, characterized by the greatest influx of species of different ecological and cenotic groups during water recession, differs in species richness. The obtained data show for the first time the diversity and structure of coastal plant communities of the sandy-pebble beech of the western coast of Lake Khanka and reflect some processes of its dynamics in connection with the long-term standing water. For more successful coverage of the issues raised, long-term monitoring on the laid transects, at least covering one 20–30-year cycle of the dynamics of the hydrological regime of Lake Khanka, is necessary.

Палеогеография, археология и античная топонимика и терминология Крымского Приазовья

The article was prepared within the framework of the project "Black Sea and Central Asian periphery of the ancient world and nomadic communities of Eurasia: at the crossroads of cultures and civilizations" № НИОКТР 122011200269-4. The article discusses ancient toponyms, terminology and relevant archeological realities of the Sea of Azov, but mostly their relevancy with paleogeology and paleogeography of the region in antiquity. The attention is mostly paid to the level changes of the Sea of Azov and the Chokrak Lake. The author uses the results of the latest archeological excavations and of some natural-scientific investigations. He analyzes both differences and similarities of the three groups of the sources. In the first “case” the author uses the results of the long-term excavations of the academic expedition led by him. The expedition investigates on the significant area and extent not only multi-temporal and multi-cultural sites of the Sea of Azov, but also relevant natural landscapes. Particularly, several periods of water level decline and rises of local bodies of water have been determined and chronologically confirmed, first and foremost those of the Sea of Azov and neighboring lakes and rivers, as well as of subsoil waters. There processes’ having had impact on the origin, location and state of conservation of settlement structures, demography and features of economic activities of the local population in the 6th century BCE to the 6th century ACE have been analyzed. These results serve to determine two or three periods which show either desolation or (vice-versa) prosperity of the lands in question. But it is important that the results have confirmed that a lot of our written sources are well informed and even objective. Sometimes they permit to better understand the sources or even to correct the former translations and, moreover, relevant comments. Thus, they emphasize again great degree of information in the works by Herodotus, Diodorus Siculus, Scylax, Polybius, Strabo, Pomponius Mela, Plinius Major, Claudius Ptolemaeus and in the less degree of other authors of various historical and geographical works, first and foremost, peripli, on the size and depth of the Sea of Azov, the quantity of settlements on its coasts, the direction of trade routes (proceeding from the main streams), local climate and its changes through centuries, historical events etc. In a number of cases archeology served to significantly clarify the chronology and scope of some changes, and (last but not least) to emphasize the importance of the complex approach for general and specific research of the ancient geographical legacy.

Tracking of sea level impact on Caspian Ramsar sites and potential restoration of the Gorgan Bay on the southeast Caspian coast.

The situation of Ramsar sites along the Caspian Sea coast has deteriorated over the past decades, and this is more noticeable in the narrow coastal strip of the south Caspian Sea. In this study we investigate how the Caspian Sea level changes affect the coastal Ramsar sites. Particularly, we focus on the Gorgan Bay in the southeast corner of the Caspian Sea, which is experiencing extensive water level decline, even desiccation. We used satellite images from three periods corresponding to periods of two sea level falls and one sea level rise, in order to decipher spatio-temporal changes of the wetlands. We conducted field campaign in the Gorgan Bay for sampling and measurement of physical, chemical and biological parameters. We simulated water circulation for the past, current and future conditions of the Gorgan Bay, which is essential to sustain better water exchange between the Bay and the Caspian Sea. We applied dust simulation in the case of a total desiccation of the Gorgan Bay. The result shows that the total area of the Caspian coastal Ramsar sites during the two periods of the sea level fall is almost the same; however, the aerial changes in the southern wetlands are more visible. Nutrient and plankton analysis of the Gorgan Bay display mainly mesotrophic conditions, in some areas close to eutrophic ones. The average current velocity in the main inlet is 2.5 cms-1. Dust simulation indicates that in case of the Gorgan Bay desiccation, it will become a dust source for the surrounding area up to 60 km. Simulation of the water circulation with dredging of inlets (future scenario), indicates that the water exchange velocity doubles compared to the current scenario. A recommended inlet maintenance would accelerate water circulation and reduce residence time, which will lead to better trophy and prevent bay desiccation.

Simulation of Groundwater Flow Dynamics under Different Stresses Using MODFLOW in Rechna Doab, Pakistan

Groundwater is a primary source of freshwater provisions all around the world. Due to its limited availability, water has become a precious entity nowadays. The future accessibility of groundwater is endangered due to its massive exploitation, particularly in the irrigation sector. Therefore, the current study was conducted to assess the declining groundwater levels in Rechna Doab, Punjab, Pakistan, where the aquifer has been reported to be highly stressed. A groundwater flow model was developed using the MODFLOW code of the USGS, and the steady-state model was calibrated for the year 2006, followed by a transient calibration for the years 2006–2010. Finally, the model was validated for 2011–2013, and a new scenario-based approach was used. Multiple future scenarios were developed to simulate the future response of the aquifer under changed recharge and pumping. The hydrodynamics of the groundwater flow was studied for two decades, i.e., up to 2033. The results under the business-as-usual scenario revealed a net gain in water levels in the upper parts of the study area. In contrast, a lowering of water levels was predicted in the central and lower parts. A maximum drop in the water level was anticipated to be 5.17 m, with a maximum gain of 5 m. For Scenario II, which followed the historical trend of pumping, an overall decline in water levels was observed, with a maximum expected drawdown of 15.68 m. However, the proposed water management Scenario III showed a general decrease in the upper study region, with the highest drop being 10.7 m, whereas an overall recovery of 6.87 m in the lower regions was observed. The simulations also suggested that the unconfined aquifer actively responded to the different scenario-based interventions. It was concluded that the region’s aquifer needs immediate action regarding pumping and recharge patterns to avoid a potential increase in pumping costs and to preserve the sustainability of endangered groundwater resources. Moreover, proper groundwater pumping and its policy legislation for its management should be implemented in order to protect this precious resource.

Assessing nitrogen dynamics model and the role of artificial lagoon in effluent loading of shrimp farms in Gomishan wetland, southern Caspian Sea

Shrimp farming increases the nutrients, especially nitrogen in the water resources reducing water quality. This study was conducted to evaluate the nitrogen dynamics in white shrimp (Litopenaeus vannamei) farms and the role of artificial lagoon (24 ha) in reducing nitrogen levels in Gomishan coastal wetland, the eastern Caspian Sea. The results indicated that at the end of the 4-month breeding period, the amounts of nitrogen and phosphorus introduced into Gomishan wetland were calculated as to 220.157 and 39 tons, respectively in a breeding area covering 830 hectares. Nitrogen values (based on nitrate) calculated based on the relationship between the basin and the discharge of the outlet channel of the site at the time of complete emptying of the farms, were calculated to be approximately 121.8 tons per breeding time that it had an important role in eliminating about 45% of nutrient pollution and reducing the concentration of dissolved nitrogen. Moreover, nitrogen isotopic trace was observed in shrimp samples, in similar levels in the samples of both shrimp pond and lagoon, which emphasizes the role of feeding from natural food, especially benthic fauna. Overall, due to the decline of Caspian Sea water level, Gomishan coastal wetland is drying, and the output of shrimp farms is currenly the only source supplying water for the wetland. Hence, appropriate management strategies could minimize the amounts of nutrients into the natural water whilst aiding wetland’s survaival.

Row spacing and irrigation management affect soybean yield, water use efficiency and economics

Declining water levels in the Mississippi River Valley Alluvial Aquifer necessitates research on the management practices that can reduce irrigation water use and improve irrigation water use efficiency. A three-year field study from 2019 to 2021 evaluated the effects of row spacing and irrigation management on soybean seed yield and quality, irrigation water use efficiency (IWUE), water productivity (WP), and profitability. Soybean was planted in two row spacings [single- (SR) and twin-row (TR)] and irrigated with three different methods [every row irrigated (ERI), alternate row irrigated (ARI), non-irrigated (NI)]. Soybean yields were increased with application of irrigation either as ERI or ARI as compared to NI in all three years ranging from 20% to 79%. The ERI had 20% increase in yield over ARI in 2021, whereas no significant differences were found between ERI and ARI in 2019 and 2020. Averaged over row spacing, IWUE was 66–91% greater with ARI compared to ERI. Only 2021 showed an increase (34%) in WP with irrigation applied as ARI than NI. Differences in rainfall amount among years and amount of irrigation applied under different treatments affected the soybean yields. Soybean yield showed reduction by 0.37–1.2 kg ha−1 with each unit increase in cumulative stress (kPa-days) for soil moisture potential drier than the −40 kPa on very fine sandy loam soils. Twin-row soybean had higher expected returns in all cases except for the NI and ERI in 2021. The TR soybean produced the greatest average risk-return than other treatments. The ARI with TR had the second highest overall risk-return trade-off. The ARI resulted in an equivalent risk-return production system as ERI for SR soybeans. Alterations in furrow irrigation methods could be more beneficial than row spacing to improve soybean productivity and IWUE.

Genotoxic risk assessment of solar UV radiation in tadpoles from Brazilian wetlands

Solar ultraviolet (UV) radiation is an environmental genotoxic factor linked to amphibian decline. Here we assessed the genotoxic risk of UVB and UVA exposure for tadpoles from open ponds in southern Brazil, a mid-latitude region influenced by stratospheric ozone depletion. Daily UV doses were measured on the surface of a pond in Taim Ecological Station (TAIM; 32°49’24’’S; 52°38’31’’W) on a cloudless summer day to predict the worst-case scenario for UV-induced DNA damage. Pond descriptors were related to the use of microhabitats by Boana pulchella tadpoles in two ponds over the climate seasons of 2013 and 2014. Our results indicate that shaded microhabitats were more frequent than unshaded ones in autumn, winter, and spring but not in summer. Hence, the penetration of UV radiation into the water of unshaded microhabitats was evaluated through laboratory experiments with artificial UV sources and pond water samples. Physical and biological sensors were applied in the experiments to measure the incident UV radiation and its genotoxic action. By integrating field and laboratory data, we demonstrate that low doses of biologically effective UV radiation reached the tadpoles in autumn, winter, spring, and early summer due to a high proportion of shaded microhabitats and a high concentration of solids in unshaded microhabitats. However, the relative reduction of shaded microhabitats jointly with a declining water level in late summer may have exposed tadpoles to high UV doses. Our experiments also indicate that solar UVB radiation, but not UVA, is primarily responsible for the induction of DNA pyrimidine dimers in organisms living under the surface of aquatic ecosystems. The present work highlights the determinant role of wetland descriptors for minimizing the genotoxic potential of UV radiation and its consequences for amphibians.

Temporal changes in limno-morphometric characteristics in a floodplain lake within Cross River ecosystem during low water period

Iyieke Lake is one of the floodplain lakes within the middle reaches of the Cross River, it is a major foraging and breeding site of several fish species. It is not directly connected to any river, so the water level depends on seasonal inundation by the Cross River. With gradual changes in precipitation and consequent alteration in flooding pattern, and increased agricultural activities around the lake, there are indications of steady annual decline in water level and quality, and lake area. In order to understand the effect of these changes on the aquatic biota, the morphology and some limnological parameters of the lake were studied during low water period (March-May) in 2005, 2011 and 2019 at interval of 6.5 years. Water samples were collected from the lake and the limno-morphological parameters measured at the littoral and limnetic zones of the lake following standard procedures. The results showed that monthly rainfall was significantly (p<0.05) lower in 2019 compared to 2005 and 2011, while minimum and maximum temperature trended conversely (p<0.05). The mean total dissolved solids (TDS) increased from 13.00mg/l in 2005 to 39.33mg/l in 2019 and conductivity trended the same. Mean nitrate (0.92mg/l) and phosphate (1.78mg/l) were higher in 2019 compared to 2005 and 2011. Contrarily, transparency decreased from 0.45m in 2005 to 0.19m in 2019. Similarly, mean dissolved oxygen (3.80mg/l), maximum length (443.20m) and width (314.50m) declined significantly toward 2019 (p<0.05). Lake length, transparency, conductivity and TDS that were seemingly good predictors of water deterioration could be useful in modelling, which is vital in conserving the biodiversity of the Cross River floodplain ecosystem.

Study of the impact of reservoir water level decline on the stability treated landslide on reservoir bank

Affected by the reservoir water and rainfall and other factors, the stability of the landslide changes with the different reservoir water level decline rate. Using the Baota landslide in Yunyang County in Three Gorges Reservoir region as an example, and applying the saturated-unsaturated numerical simulation method, the groundwater seepage field is calculated when the reservoir water level rises and declines. The calculated pore water pressure is used for the ultimate equilibrium analysis of landslide, and the effect of reservoir water level drop on landslide stability was discussed. The calculation results show that with the water level falling from 159 m to 145 m, and the increase of the rate of decline in the reservoir water level, the decline in groundwater seepage lines has increased somewhat. The landslide stability coefficient calculated under each working condition is larger than that in the original design, and the decrease rate of reservoir water has a qualitative effect on the stability of the landslide, but the influence is very small. Through the SBAS-InSAR time series monitoring of Sentinel-1 data in the 13th period and field verification, it is found that the cumulative deformation of the slope is small, which prove the stability of the landslide.

Limiting burrowing activity and overland dispersal of the invasive alien red swamp crayfish Procambarus clarkii by sophisticated design of watercourses

Invasive alien crayfish species pose major ecological and hydrological risks globally. The red swamp crayfish (Procambarus clarkii) is one of the most widespread crayfish species worldwide. Its impacts arise from burrowing activities and lead to mobilization of soil nutrients, water safety risks by instability of dikes and erosion of banks. Increased sediment load demands additional dredging of drainage ditches and canals to ensure their water discharge capacity. Sustainable methods for limiting burrowing in banks and dispersal behaviour of crayfish were not yet available. Therefore, a field study was performed to determine whether the number of burrows and overland movement of crayfish were related to a particular bank type. Burrows were counted in three watercourses during a water-level decline. The number of burrows was significantly lower in natural banks than in non-natural and semi-natural banks. The construction of natural-like banks along watercourses may significantly reduce sediment load, erosion and the collapse of banks by burrowing activities of crayfish. An inclination experiment mimicking various types of terrestrial dispersal barriers elucidated that steepness, soil type and vegetation structure of small embankments near watercourses were significant factors for manipulating overland movement of crayfish. Crayfish were taken out of the water for this purpose and placed on small experimental embankments varying in slope and types of vegetation. The lowest frequencies of upward movement were recorded at inclinations of 20° and 30° on bare sandy soil and short and species-poor grassland substrates. This implies that crayfish crawling out of the water will return to the watercourse when encountering such a dispersal barrier. Therefore, a sophisticated design of embankments along watercourses can be a tool to reduce colonization risk of nearby located, hydrologically isolated water bodies with high nature values.

Identification of Suitable Recharge Sites by Integrated Hydrogeophysical Approach for Augmenting Groundwater in Reodar Block, District Sirohi, Rajasthan

Abstract The dependence of human beings on groundwater and ever-increasing demands of growing population, agriculture and industries, has resulted in its over-exploitation. This has led to the decline of groundwater levels and its shortage especially in lean season. The study area, Reodar block of Sirohi district, Rajasthan, is an over-exploited block with the stage of groundwater extraction at 159% and has an average declining water level trend at the rate of 0.24 m/year. Artificial recharge was proposed in the study area through the construction of recharge shafts and injection wells, after delineating the weathered thickness in the submergence area of existing ponds and check dams of the study area by carrying out vertical electrical sounding (VES). In all, VES were conducted at 178 sites and recharge structures were constructed at 76 out of 109 scientifically selected sites with suitable weathered thickness and attempt was made to establish their impact on water levels through pre-monsoon water level monitoring. The comparison of pre-monsoon water level observations spanning over four decades reveals its spatio-temporal decline in the study area. The construction of these recharge structures has resulted in significant increase in area from 38% to 68%, under 0 to 20 m below ground level water level range. This study demonstrates the importance of resistivity surveys in scientifically selecting the suitable sites for construction of recharge structures and significance of long-term water level monitoring in assessing the groundwater scenario and impact assessment, in poorly characterized hydrogeological areas.

Aquifer and Land Subsidence Interaction Assessment Using Sentinel-1 Data and DInSAR Technique

Climate change and overpopulation have led to an increase in water demands worldwide. As a result, land subsidence due to groundwater extraction and water level decline is causing damage to communities in arid and semiarid regions. The agricultural plain of Samalghan in Iran has recently experienced wide areas of land subsidence, which is hypothesized to be caused by groundwater overexploitation. This hypothesis was assessed by estimating the amount of subsidence that occurred in the Samalghan plain using DInSAR based on an analysis of 25 Sentinel-1 descending SAR images over 6 years. To assess the influence of water level changes on this phenomenon, groundwater level maps were produced, and their relationship with land subsidence was evaluated. Results showed that one major cause of the subsidence in the Samalghan plain was groundwater overexploitation, with the highest average land subsidence occurring in 2019 (34 cm) and the lowest in 2015 and 2018 (18 cm). Twelve Sentinel-1 ascending images were used for relative validation of the DInSAR processing. The correlation value varied from 0.69 to 0.89 (an acceptable range). Finally, the aquifer behavior was studied, and changes in cultivation patterns and optimal utilization of groundwater resources were suggested as practical strategies to control the current situation.

Influencing factors, deformation mechanism and failure process prediction for reservoir rock landslides: Tanjiahe landslide, three gorges reservoir area

Compared with terrestrial rock landslides, reservoir rock landslides are also affected by the rise and fall of the reservoir water level, and these landslides are more threatening. High-speed debris flows may form once they lose stability, and once they enter the water a surge is formed. This endangers the safe operation of reservoirs. This study explored the deformation characteristics and influencing factors of the Tanjiahe reservoir rock landslide in the Three Gorges Reservoir using field investigations, GPS surface displacement monitoring, and groundwater level monitoring. The discrete element system MatDEM was used to simulate failure motion, and predict the hazard area affected by the Tanjiahe landslide. The results show that within the reservoir water variation section (145–175 m), the Tanjiahe landslide mass was composed of surface soil (156–175 m) with low permeability and deep cataclastic rock (145–156 m) with high permeability. Due to the difference in permeability between the deep and surface layers, the response of landslide deformation to water level rise is not obvious. The high-level (175 m) operation of the reservoir and the decline in the reservoir water level (175–145 m) are key factors affecting the landslide deformation. Rainfall had a positive effect on landslide deformation. Under their combined action, the stability of the front gentle anti-sliding section of the landslide decreases, and the displacement of the middle and rear steeper sliding section increases under the driving force, which may lead to slope failure. The simulation results show that the upper part of the Tanjiahe landslide slides first and pushes the lower part to move, which is a typical of thrust load-caused failure. The speed of the sliding mass has three stages: rapid rise, rapid decline, and slow decline. The higher the slope angle, the higher the acceleration of the sliding mass in the direction parallel to the slope surface, the higher the speed peak value and the faster the sliding mass speed reaches the peak value. During the failure process, energy is transferred between sliding mass through collisions. Landslides can easily lead to debris flow. The maximum height of the first wave generated when the debris flow entered the water is 5.95 m, and the wave height that propagated to the opposite bank is 3.09 m. The landslide-induced waves propagated along the reservoir area for 30 km.

Impacts of global change on two tropical, high mountain lakes in Central Mexico

High mountain lakes and their catchments are remote ecosystems in areas with low anthropogenic disturbance. High mountain lakes integrate changes in the atmosphere and catchment areas (e.g., acid rain, airborne pollutants, climate change). The present research analyses long-term datasets of meteorological and limnological variables representing two tropical high mountain lakes, El Sol and La Luna, in Central Mexico to identify the impacts of anthropogenic disturbance (i.e., sentinels of global/climate change). The 54-year meteorological analysis showed marked interannual variability with no statistically significant air temperature or rainfall trends. However, from 2000 to 2018, the air temperature increased by 0.5 °C. Accordingly, the lake water temperature increased (Lake El Sol: 0.8 °C, Lake La Luna: 0.6 °C). Although the rainfall displayed no change, the water level decreased in both lakes (1.5 m), most likely associated with increased evapotranspiration. Unexpectedly, the dissolved inorganic nitrogen (DIN) concentration in the lakes decreased. The initial acid pH rose to close neutrality in Lake La Luna and to alkaline values in Lake El Sol. The latter may be a consequence of the lowered SOx and NOx emissions from governmental regulations promulgated to control atmospheric pollution beginning in 2000 and probably resulting in less acidic deposition. An additional explanation for the lakes' deacidification is the increased deposition of alkaline ions derived from activities at the volcano slopes. Since the atmospheric supply is the primary nitrogen source to high mountain lakes, the DIN concentration decline could reflect the reduction in atmospheric HNO3. Thus, Lakes El Sol and La Luna evidenced global change. Both lakes are inside the same crater and are subjected to similar influences; thus, they showed similar responses to global change (increasing lake water temperatures, declining water levels, higher pH value, and lower DIN concentrations). Nevertheless, their differences (e.g., catchment size, surface area, water volume, water depth, trophic status) influenced the magnitude of the impacts, with higher pH increases recorded in Lake El Sol and higher DIN concentrations in Lake La Luna.

Responses of soil enzyme activities and bacterial community structure to different hydrological regimes during peatland restoration in the Changbai Mountain, northeast China.

Appropriate hydrological management is critical for peatland restoration. An important prerequisite for peatland restoration is a recovery of soil biological processes. However, little is known about the effects of different hydrological management practices on soil biological processes during peatland restoration. In this study, the variations in soil properties, enzyme activities, and bacterial communities across different peatlands, namely natural peatland (NP), peatland restored under high water level (HR), peatland restored under alternating high-low water level (HLR), peatland restored under low water level (LR), and degraded peatland (DP), in the Changbai Mountains were investigated. Results showed that soil organic carbon, soil water content, and total nitrogen in NP were significantly higher than those in restored and degraded peatlands, and these soil properties in restored peatlands increased with the water level. The activities of soil hydrolases including β-1, 4-glucosidase, β-1, 4-n-acetylglucosidase, and acid phosphatase in NP were higher than in restored and degraded peatlands, while the activity of polyphenol oxidase in NP was the lowest. In restored peatlands, all measured enzyme activities decreased with the decline in water level. Both bacterial diversity and richness in NP were the lowest, while the highest diversity and richness were observed in HR. Redundancy analysis indicated that soil organic carbon, water level, soil water content, total nitrogen, and pH were the most important factors that affected the soil enzyme activities and bacterial community. Our findings give insight into the effects of different hydrological regimes on soil biological processes during peatland restoration. Maintaining a high water level early in the restoration process is more beneficial to restoring the ecological functions of peatlands than other hydrological regimes.

Analysis of Spatial–Temporal Variations and Driving Factors of Typical Tail-Reach Wetlands in the Ili-Balkhash Basin, Central Asia

The Ili River Delta (IRD) is the largest delta in the arid zone of Central Asia. Since the 1970s, the entire delta system has undergone a series of changes due to climate change and the impoundment of the Kapchagay Reservoir upstream of the delta, triggering an ecological crisis. Wetlands play a crucial ecological role in biodiversity conservation. Most studies have mainly focused on the response of vegetation and soil microbial to ecological changes in the delta, ignoring the dynamic processes of wetlands changes. Hence, such changes in the IRD and the underlying mechanisms need to be investigated in depth. In this study, wetlands in the IRD from 1975 to 2020 were extracted based on Landsat images using the object-oriented method; changes in the wetland area, wetland landscape pattern, NDVI, and NPP were analyzed; and the contributions of natural and human factors to wetland evolution were quantified. The results indicated the following: (1) From 1975 to 2020, the wetland area of the IRD showed an increasing trend, and changes in the wetland area were mainly found in the middle part of the delta near the Saryesik Peninsula. (2) The wetland landscape pattern in the IRD changed markedly from 1975 to 2020. The dominant patches of the wetland in the middle of the delta continued to expand; the patch aggregation index (AI) increased, and the landscape fragmentation index (LFI) decreased. (3) From 2000 to 2020, the average annual normalized difference vegetation index (NDVI) and net primary productivity (NPP) in the IRD increased, which is consistent with the change in wetland expansion. (4) Inflow to the delta from the Ili River and the water level of Balkhash Lake are significantly correlated with the wetland area, which are the dominant factors driving wetland evolution; and water evaporation from the Kapchagay Reservoir and irrigation water diversion on the left bank of the reservoir obviously intensified the process of lake water level decline and wetland degradation during 1970 to 1985. These results can provide scientific background for making informed ecological protection decisions in the IRD under the impacts of climate change and human activities.

Effects of water level changes on the morphological and physiology of the submerged macrophyte Vallisneria natans

To study the response of the Vallisneria natans morphological and physiology to water level change, seedlings were placed in a submerged condition at depths ranging from 50 cm to 135 cm and set the rising and declining water levels respectively (0.2 cm/d, 0.5 cm/d, 0.8 cm/d, 1.1 cm/d, 1.4 cm/d, 1.7 cm/d). After 50 days of simulation experiment, we observed the effects on plant height, the number of blades, root activity, biomass, chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll (a + b) (Chl a + b), carotenoid (Car), soluble protein (SP) and soluble sugar (SS) of V. natans under different water level change rates. The results showed that (1) plant height and the number of blades showed an overall upward trend under the condition of high-rate water level change, while the low-rate change of water level showed a trend of first rising and then decreasing. (2) the root activity of 0.5–1.7 cm/d groups increased with the test time at rising water level, and the declining water level showed a trend of increasing and then decreasing. The total biomass showed an upward trend with the extension of the test time. (3) Chl a, Chl b, Chl (a + b), and Car showed a multi-peak downward trend with the extension of the test time. (4) the response of SP and SS to the test time showed a trend of first increase and then decrease with water level changes. In conclusion, our study demonstrates that the morphological and physiology of V. natans could adapt to water level changes, but it could be stressed if the water level exceeded the suitable range.