Surface Water Volume Research Articles

Improving surface water quality of the Yellow River Basin due to anthropogenic changes.

Understanding of how changes in diverse human activities and climate contribute to water quality dynamics is crucial for sustainable water environment management especially in the arid and semi-arid regions. This study conducted a comprehensive estimation of the surface water quality change in the Yellow River basin during 2003-2017 and its responses to varied pollution sources and water volumes under socioeconomic and environmental influences. Basin-wide measurements of chemical oxygen demand (COD), ammonium nitrogen (NH+4-N) and dissolved oxygen (DO) concentrations were used in trend detection. Annual anthropogenic (covering six sectors) and natural (sediment-induced, flow-in from the upstream and stored last year) pollution sources and water components (inflow, natural runoff, water consumption, reservoir storage and evaporation) were compiled for each sub-basin. Bottom-up hierarchical analysis was then performed to differentiate individual contributions. Results showed significant decreasing trends in COD and NH+4-N concentrations and increasing trends in DO concentrations. The middle reaches that traverse the Loess Plateau however remained severely polluted with 11.3-39.0% inferior to level III in 2017. The pollutant load played major positive contributions that gradually increased from upper to lower reaches. Declines in urban, rural and industrial pollution discharges following environmental investments and rural depopulation contributed the most: 78-96% for COD and 55-100% for NH+4-N. The total surface water volume had dilution effects in the upper and middle reaches (3-28%) and condensing effects in the lower reaches (2-37%). Precipitation and vegetation dynamics contributed slightly. The primary unfavorable factors were the growing agricultural pollution discharges and water consumption in the upper and middle reaches that also threatened the lower reaches. This study is expected to provide in-depth insights for the systematic response of regional water quality to combined human interventions and references for water quality management in other arid and semi-arid river basins worldwide.

The Uses and evaluation of water resources in the Zalm river basin

This study deals with the subject of a geographical assessment of the use of water resources in the Zalam River Basin. The aim of this study is to highlight the reality of the current uses of water resources for various purposes in the study area. And to achieve a balance between the volume of incoming, surface and underground water in the study area, and to find the amount of consumption of water by the population in the various activities. It appeared through this study that the total water needed for domestic use of the population of the study area was (2.486) million / m3 annually, in the year (2016). The amount of water required for agricultural crops and orchards is estimated at (36.109) million/m3 annually, and this is where the most is consumed compared to other uses in the area, The amount of water used by the livestock in the area is (146) million/liter annually, and the total water consumption of chicken fields and poultry birds is (7.16) million/liter annually. The estimated amount of water used in the food industry is (0.014) million m3/year. The amount of surface and ground water is estimated at (171.698) million/m3 in the study area, and surface water represents (65.45%), while groundwater represents (34.55%), and the amount that is consumed is estimated at (38.762) million/m3 for all uses, and it is clear from the above that there is a surplus of water, said surplus is estimated to be at (132.936) million/m3.

Tracking the source direction of surface mass loads using vertical and horizontal displacements from satellite geodesy: A case study of the inter-annual fluctuations in the water level in the Great Lakes

Climate oscillations with seasonal and longer periods drive surface water cycles and quasi-cycles at regional and global scales. Changes in terrestrial water storage produce responses in the Earth's gravitational field and crustal deformation. Here, we use techniques from the Global Positioning System (GPS) and the Gravity Recovery and Climate Experiment (GRACE) to reveal a normal pattern of inter-annual fluctuations in the water level in the North American Great Lakes (GL). The GRACE-estimated time series was in good agreement with in situ water level measurements from 2002 to 2018, especially in terms of phases. The amplitude of 3–4 inter-annual signals in water thickness was 4–6 cm, which is equivalent to a 50–75 km3 oscillation in surface water volume within the entire GL. The slightly larger annual and inter-annual fluctuation amplitudes estimated using GRACE data indicate that the aquifer system of the GL and its surroundings also contributes to seasonal mass changes. After 2013, water levels in the GL region rose abruptly, and the water mass increased by nearly 270 km3 until the end of 2018. We also used GPS- and GRACE-derived three-component displacements (vertical, northward, and eastward) to identify load patterns. GPS- and GRACE-estimated maximum probability source directions based on multi-channel singular spectrum analysis showed that most of the selected GPS sites point to the GL region, although the direction deviations of GPS results at a few sites are mainly caused by the combined effect of the local load and superposition of the distant GL. Our findings indicate that inter-annual displacement changes at different frequencies (1- to 8-year cycle) are primarily due to water volume fluctuations in the GL. The amplitudes estimated by GPS are greater than the GRACE-based and GL-modeled results at most stations, which reflects sensitivity differences between these geodetic solutions to the surface load, as hydrological processes in the local area around a station are difficult to identify using GRACE data with a resolution of ~300 km.

Granular activated carbon adsorption of perfluoroalkyl acids from ground and surface water

AbstractAdsorption of perfluoroalkyl acids (PFAAs) by granular activated carbon (GAC) was evaluated in bench‐, pilot‐, and full‐scale studies to determine effects of PFAA characteristics and background organic matter on carbon use rates. Rapid small‐scale column tests (RSSCTs) were conducted according to the proportional diffusivity (PD) design to assess their suitability to predict full‐ or pilot‐scale GAC performance. PFAA removal from groundwater (GW) and coagulated surface water (SW) was studied with two sub‐bituminous coal‐based GACs. In batch tests conducted with pulverized GAC, the GACs performed similarly in GW, but the GAC with the larger mesopore volume was more effective for PFAA removal from SW. In column tests, carbon use rates decreased with increasing PFAA chain length and were lower for GW (total organic carbon [TOC] = 0.7 mg/L) than for SW (TOC = 2.0–2.7 mg/L). The volume of SW that could be treated to 10% or 50% PFAA breakthrough was about 50–60% of the volume of GW that could be treated when comparing pilot‐scale data for SW with full‐scale data for GW. Consistent differences in PFAA adsorption capacity were not observed for empty bed contact times of 13 and 26 min in full‐scale adsorbers treating GW. The PD‐RSSCT simulating PFAA removal from GW consistently overpredicted full‐scale adsorption capacity, on average by ~70%. Using a carbon use rate of <25 mgGAC/Lwater treated) as a criterion for the feasibility of GAC treatment, full‐ and pilot‐scale GAC adsorber data suggest that GAC is a viable treatment option (carbon use rate < 25 mgGAC/Lwater treated) for perfluoroalkylcarboxylic acids with six or more carbon atoms in SW and five or more carbon atoms in GW. For perfluoroalkyl sulfonic acids, GAC treatment is viable for compounds containing four or more carbons based on results obtained with both SW and GW.

Nature based solutions: an example from San Salvador city

San Salvador, capital of El Salvador, is an intermediate city located in a mountain area. It has a limited drainage system in unplanned settlements on slopes and streams, which results in floods and landslides, due to intense rains in short periods, which are increasingly frequent. One of the areas with the highest incidence of urban floods in this city is the Arenal Monserrat micro-watershed; For this reason, it was selected for the implementation of pilot interventions of Nature-based Solutions (NbS), under the City Adapt project, executed by the United Nations Environment Program. The implementation began with the elaboration of a mapping of actors, the development of a vulnerability assessment of the micro-watershed, consultations with focus groups to know the perception of risk, valuation of the ecosystems present and their link with the livelihoods used by the population, the selection of the NbS measures to be implemented at the basin, landscape and local community levels and the identification with the ecosystem services that it enhances; until its start-up and monitoring and follow-up. The main results presented are: i) an intervened surface of 451 hectares, between different ecosystems such as coffee plantations, riparian forest and urban area used for planting fruit trees; b) an infiltrated volume of surface water of 284,984 m3 in one year, coming from the water collected in the infiltration ditches and in the absorption wells, built in the upper part of the micro-watershed; iii) a total number of trees planted of 54,529, among coffee, fruit trees and native species. With these results, the next step is the incorporation of NbS measures in urban planning processes in the medium and long term.

Effect of rearing density on nervous necrosis virus infection in Senegalese sole (Solea senegalensis).

Intensive fish farming at high densities results in a wide range of adverse consequences on fish welfare, including pathogen spreading, stress and increased mortality rates. In this work, we have assessed whether the survival of Senegalese sole infected with the nervous necrosis virus (NNV), a pathogen responsible for severe disease outbreaks, is affected by rearing density. Based on the different fish ratios per surface area (gcm-2 ) and water volume (gL-1 ), our research showed an earlier mortality onset in the tanks containing NNV-infected fish reared at medium density (MD: 0.071gcm-2 /5gL-1 ) and high density (HD: 0.142gcm-2 /10gL-1 ), as well as higher cumulative mortality values. However, transcription analysis of hsp70, gr1 and pepck genes, well-known stress biomarkers, seems to indicate that none of the challenged fish were under high stress conditions. NNV load was slightly higher both in dead and in sampled fish from MD and HD groups, and especially in the rearing water from these groups, where peaks in mortality seemed to correlate with increasing NNV load in the water. In conclusion, our results suggest that rearing NNV-infected Senegalese sole at high densities resulted in an earlier mortality onset and higher cumulative values and viral load.

Rapid Population Growth as Foremost Cause of Land Degradation in Ethiopia: A Review

Ethiopia is the second most populous country in Sub-Saharan Africa countries. The rapid population growth in country leads to land degradation; it includes soil degradation, vegetation degradation and water degradation, and natural resources degradation as whole. Diverse scholars indicated, decreasing tendency of forest cover in Ethiopia over time with the population increment. In Ethiopia, the high population growth leads to soil erosion and soil fertility loss; it accelerates soil erosion due to foot path, overgrazing and others, which is meanly estimated 12 tons/ ha/ yr. and, People are using animal dung and crop residue for household fuel rather than being added to the soil to improve soil fertility, which leads to soil quality declination. And, the population pressure leads the water courses to dry up, reduced the volumes of surface water, depletion of aquifers and pollution. If this rapid population growth of Ethiopia continues like the current situation, the land degradation problem is likely to be even more challengeable in the future. Therefore, this paper aims to explore rapid population growth as foremost cause land degradation in Ethiopia by taking typical evidence from different parts of the country and to suggest solutions. Keywords: Rapid Population Growth, Foremost Cause, Land Degradation DOI: 10.7176/JEES/11-8-02 Publication date: August 31 st 2021

Rethinking water and crop management in the irrigated district of Diyar-Al-Hujjej (Tunisia).

In Diyar-Al-Hujjej irrigated area, the aquifer's over-exploitation, sea intrusion, and abandonment of irrigated areas and wells took place. A yield decrease for all crops was observed. Average aquifer water electrical conductivity (EC) jumps from 4 to 6.6 dS/m between 1969 and 2017. A fresh surface water transfer over more than 100 km was launched in 1998 to safeguard this irrigated area but this fresh water supply is not stable; it varies from 1 year to another (about 1,900,000 m3 in 2015 and only 60.000 m3 in 2018) while annual crop water requirement of the perimeter is about 2,500,000 m3. An adaptation by farmers to this new situation of saline and water stress was observed. The follow-up surveys of the farmer's practices showed that (i) new crops with high added value grown during the rainy season were introduced in association with dry season crops (strawberry-pepper association), (ii) rainfed crops, fallow, and water blending are common practices; and (iii) growing of rainy season crops in the aim to reduce water supply. The instability of fresh surface water volume transferred constitutes the main threat for this perimeter. The use of aquifer salt water must be stopped; it is the cause of the large quantities of salts supplied (over 13,000 kg/ha) and also of the low annual net income achieved. Net revenue was less than 2000 US $/ha under salt water and reached even 8000 US $/ha when sufficient surface water is available. An agrarian reform policy must be applied for this perimeter; only crops whose water requirements are partially met by rain should be grown. The introduction of another more sustainable water source should be initiated (as desalination) even at the private farm level.

Economic Analysis of Irrigation Water under Different Water Use Regimes in Godavari Command Area

A study was undertaken in Karimnagar and Warangal districts falling under the Godavari command area of Telangana to analyze the economics of irrigation among the farm households across surface water (SW), groundwater (GW) and conjunctive use (CU) regimes. Data was analyzed using descriptive statistics and natural resource economics tools. The farms under CU realized higher net returns per acre (` 11792) followed by GW farms (` 8229) and SW farms (` 7516). There was also an enhanced savings to the extent of ` 10900 per acre due to reduction in the expenditure on human labour, machine labour, marketing and irrigation cost under CU regime when compared to GW regime. The per annum volume of surface water used in the case of SW farms and CU farms was 263 acre inches and 182 acre inches, respectively. Volume of water used in case of CU is less when compared to SW regimes. Annual cost of irrigation water per acre was found to be highest in GW farms (` 6916) when compared to SW (` 1284) and CU (` 4063) farms. This study has shown the potential benefits of CU regime over SW and GW regime.

RECOG RL01: correcting GRACE total water storage estimates for global lakes/reservoirs and earthquakes

Abstract. Observations of changes in terrestrial water storage (TWS) obtained from the satellite mission GRACE (Gravity Recovery and Climate Experiment) have frequently been used for water cycle studies and for the improvement of hydrological models by means of calibration and data assimilation. However, due to a low spatial resolution of the gravity field models, spatially localized water storage changes, such as those occurring in lakes and reservoirs, cannot properly be represented in the GRACE estimates. As surface storage changes can represent a large part of total water storage, this leads to leakage effects and results in surface water signals becoming erroneously assimilated into other water storage compartments of neighbouring model grid cells. As a consequence, a simple mass balance at grid/regional scale is not sufficient to deconvolve the impact of surface water on TWS. Furthermore, non-hydrology-related phenomena contained in the GRACE time series, such as the mass redistribution caused by major earthquakes, hamper the use of GRACE for hydrological studies in affected regions. In this paper, we present the first release (RL01) of the global correction product RECOG (REgional COrrections for GRACE), which accounts for both the surface water (lakes and reservoirs, RECOG-LR) and earthquake effects (RECOG-EQ). RECOG-LR is computed from forward-modelling surface water volume estimates derived from satellite altimetry and (optical) remote sensing and allows both a removal of these signals from GRACE and a relocation of the mass change to its origin within the outline of the lakes/reservoirs. The earthquake correction, RECOG-EQ, includes both the co-seismic and post-seismic signals of two major earthquakes with magnitudes above Mw9. We discuss that applying the correction dataset (1) reduces the GRACE signal variability by up to 75 % around major lakes and explains a large part of GRACE seasonal variations and trends, (2) avoids the introduction of spurious trends caused by leakage signals of nearby lakes when calibrating/assimilating hydrological models with GRACE, and (3) enables a clearer detection of hydrological droughts in areas affected by earthquakes. A first validation of the corrected GRACE time series using GPS-derived vertical station displacements shows a consistent improvement of the fit between GRACE and GNSS after applying the correction. Data are made available on an open-access basis via the Pangaea database (RECOG-LR: Deggim et al., 2020a, https://doi.org/10.1594/PANGAEA.921851; RECOG-EQ: Gerdener et al., 2020b, https://doi.org/10.1594/PANGAEA.921923).

Mapping regional surface water volume variation in reservoirs in northeastern Brazil during 2009–2017 using high-resolution satellite images

The multiple-year drought that started in 2011 and reached climax in 2015 was the most severe and prolonged one in the semiarid northeastern (NE) Brazil in recent decades. This study aimed to investigate the reservoir surface water volume (SWV) variation in NE Brazil from 2009 to 2017 in four representative regions covering a total area of approximately 10,000 km2 there and encompassing 2,140 reservoirs (areas range from 0.003 to 21 km2). High-resolution (10 m) digital elevation models (DEMs) were generated from the TanDEM-X data acquired during October–December 2015 to represent the reservoirs' bathymetric maps. The water extents in the reservoirs were delineated from high-resolution (6.5 m) RapidEye images acquired during 2009–2017. The combination of the aforementioned two variables yielded reservoir SWV with an accuracy of 0.64 × 106–1.06 × 106 m3, corresponding to 3.1%–5.6% of the maximum SWV in the reservoirs. The results showed that: 1) 81%–99% of the reservoirs in the four regions were from the groups with maximum water extent <50 ha and contributed 2%–59% of the regional reservoir SWV. In contrast, 0.6%–20% of the reservoirs were from the group of >50 ha and contributed 40%–98% to the regional SWV; 2) From 2009 to 2017, reservoir SWV in the four regions decreased at the rates of 2.3 × 106–17.8 × 106 m3/year; and 3) The SWV in the reservoirs responded differently to the regional terrestrial water budget, i.e. the differences between precipitation and evapotranspiration (P-ET). This study filled the data gap of bathymetric maps for the 2140 reservoirs, regardless of their sizes and macrophyte coverage. The SWV variations derived in those reservoirs over a period covering the recent drought can support better preparedness for drought in NE Brazil and better understanding of the regional hydrology in semi-arid regions.

Quantified Exposures from Potential Deepwater Releases for Comparative Risk Assessment of Oil Spill Response Options Including Dispersant Use

ABSTRACT The goal of oil spill response is to mitigate the overall impacts of spilled oil on ecological and socioeconomic resources. Surface and subsea dispersant applications are effective tools that remain controversial after decades of research and discussion. The tradeoff that dispersants potentially increase effects on water column and benthic communities while reducing floating and nearshore/shoreline oil exposure is recognized, but inevitably are qualitatively considered when subjectivity and stakeholder interests prevail. To be objective and transparent, we developed a quantitative approach using oil spill modeling to evaluate response alternatives in a Comparative Risk Assessment (CRA) framework where the fractions of resources potentially exposed are compared, along with their recovery potential. The model quantifies exposure as water surface area, shoreline area and water volume exposed above thresholds of concern, multiplied by duration of exposure, in each environmental compartment. These exposure metrics (i.e., area-days or volume-days) are multiplied by relative densities across the environmental compartments to evaluate the fractions of the resources exposed in each modeled scenario. The fractions of resources exposed, along with their recovery potential, inform decisionmakers using a Spill Impact Mitigation Assessment (SIMA) approach with quantitative estimates of potential consequences, which they may consider along with stakeholder values. Previously, we evaluated a deepwater blowout in the Gulf of Mexico, assuming no intervention or various response options (mechanical recovery, in-situ burning, surface dispersant application, and subsea dispersant injection [SSDI]). The findings were that inclusion of SSDI reduced human and wildlife exposure to volatile organic compounds; dispersed oil into a large water volume at depth; enhanced biodegradation; and reduced surface water, nearshore and shoreline exposure to floating oil and entrained/dissolved oil in the upper water column. Tradeoffs included increased exposures at depth. However, since organisms are less abundant at depth, overall exposure of valued ecosystem components was minimized by use of SSDI. Follow-up modeling shows the benefits of SSDI are due to reduction of the oil droplet sizes released to the water column. Droplet sizes are sensitive to oil and gas release rates, release depth, orifice size and dispersant-to-oil ratio. The exposure metrics resulting from a matrix of scenarios varying these inputs and response actions are expected to be generally representative of the fate and behavior of oil and gas blowouts in the offshore areas of the Gulf of Mexico, as well as other regions with similar oceanographic conditions.

Rainfall And Drought Tendencies In Rajshahi Division, Bangladesh

Insufficient rainfall results in water shortage and eventually leads to drought. This research has investigated drought by utilizing standardize precipitation index in monthly mean rainfall data for 30 years from 1988 to 2017 in Rajshahi division, a region in the northwestern part of Bangladesh. Estimated indices have identified that the years 1992, 1994, 2006, and 2012 experienced moderate to severe droughts, and the year 2010 suffered from extreme drought. Non-parametric and linear trend analyses have shown that the number of draughts in the study area has been growing. The study area is thus judged as moving forward to experience more droughts from lack of water due to rainfall deficit, especially during monsoon. This region has already started to experience a shortage of rainwater, approximately 18%, in the monsoon season. This shortage is likely to affect the volume of surface water and thus the groundwater recharging, which would distort irrigation for agriculture in the region. This work would therefore assist in policy-making addressing the watering system of the region to ensure smooth agricultural production.

Amagmatic hydrothermal systems on Mars from radiogenic heat

Long-lived hydrothermal systems are prime targets for astrobiological exploration on Mars. Unlike magmatic or impact settings, radiogenic hydrothermal systems can survive for >100 million years because of the Ga half-lives of key radioactive elements (e.g., U, Th, and K), but remain unknown on Mars. Here, we use geochemistry, gravity, topography data, and numerical models to find potential radiogenic hydrothermal systems on Mars. We show that the Eridania region, which once contained a vast inland sea, possibly exceeding the combined volume of all other Martian surface water, could have readily hosted a radiogenic hydrothermal system. Thus, radiogenic hydrothermalism in Eridania could have sustained clement conditions for life far longer than most other habitable sites on Mars. Water radiolysis by radiogenic heat could have produced H2, a key electron donor for microbial life. Furthermore, hydrothermal circulation may help explain the region’s high crustal magnetic field and gravity anomaly.

Rise of Great Lakes Surface Water, Sinking of the Upper Midwest of the United States, and Viscous Collapse of the Forebulge of the Former Laurentide Ice Sheet

AbstractGreat Lakes water levels rose 0.7–1.5 m from 2013 to 2019, increasing surface water volume by 285 km3. Solid Earth's elastic response to the increased mass load is nearly known: The Great Lakes floor fell 8–23 mm, and the adjacent land fell 3–14 mm. Correcting GPS measurements for this predicted elastic loading (1) straightens position‐time series, making the evolution of position more nearly a constant velocity and (2) reduces estimates of subsidence rate in Wisconsin, Michigan, and southern Ontario by 0.5–2 mm/yr, improving constraints on postglacial rebound. GPS records Wisconsin and Michigan to have subsided at 1–4 mm/yr. We find this sinking to be produced primarily by viscous collapse of the former Laurentide ice sheet forebulge and secondarily by elastic Great Lakes loading. We infer water on land in the Great Lakes watershed to be total water change observed by GRACE minus Great Lakes surface water smeared by a Gaussian distribution. Water stored on land each year reaches a maximum in March, 6 months before Great Lakes water levels peak in September. The seasonal oscillation of water on land in the Great Lakes basin, 100 km3 (0.20 m water thickness), is twice that in a hydrology model. In the seasons, groundwater in the Great Lakes watershed increases by 60 km3 (0.12 m) each autumn and winter and decreases by roughly an equivalent amount each spring and summer. In the long term, groundwater volume remained constant from 2004 to 2012 but increased by 50 km3 (0.10 m) from 2013 to 2019.

Simulating the interactions between the water and the socio-economic system in a stressed endorheic basin

ABSTRACT The endorheic basin of Zayandehrud in Iran suffers from environmental problems, social tensions, and economic instability. Lack of understanding how the water system and the socio-economic system interact may explain these challenges. A system dynamics model, being a holistic simulation tool, was developed for the Zayandehrud basin and used to evaluate several policy scenarios. The indices of employment, gross regional product, the volume of groundwater and surface water stored, flow into the basin’s end lake, and the water flow in the river were used to evaluate the scenarios. The findings demonstrate that focusing on supply-based activities or water demand management cannot solely improve the condition of the Zayandehrud basin. It is required to reconsider the development policies of the region in a broader context. Reducing the irrigated area by 15% and developing new industries up to a certain limit may make the combined water and socio-economic system sustainable.

Lateral meltwater transfer across an Antarctic ice shelf

Abstract. Surface meltwater on ice shelves can exist as slush, it can pond in lakes or crevasses, or it can flow in surface streams and rivers. The collapse of the Larsen B Ice Shelf in 2002 has been attributed to the sudden drainage of ∼3000 surface lakes and has highlighted the potential for surface water to cause ice-shelf instability. Surface meltwater systems have been identified across numerous Antarctic ice shelves, although the extent to which these systems impact ice-shelf instability is poorly constrained. To better understand the role of surface meltwater systems on ice shelves, it is important to track their seasonal development, monitoring the fluctuations in surface water volume and the transfer of water across ice-shelf surfaces. Here, we use Landsat 8 and Sentinel-2 imagery to track surface meltwater across the Nivlisen Ice Shelf in the 2016–2017 melt season. We develop the Fully Automated Supraglacial-Water Tracking algorithm for Ice Shelves (FASTISh) and use it to identify and track the development of 1598 water bodies, which we classify as either circular or linear. The total volume of surface meltwater peaks on 26 January 2017 at 5.5×107 m3. At this time, 63 % of the total volume is held within two linear surface meltwater systems, which are up to 27 km long, are orientated along the ice shelf's north–south axis, and follow the surface slope. Over the course of the melt season, they appear to migrate away from the grounding line, while growing in size and enveloping smaller water bodies. This suggests there is large-scale lateral water transfer through the surface meltwater system and the firn pack towards the ice-shelf front during the summer.

The impact of climate change and human activities on the Aral Sea Basin over the past 50 years

The destruction of the Aral Sea area constitutes one of the world's most infamous ecological disaster. However, the retreat of the Aral Sea has slowed down in recent years and the underlying reasons are not reported. In this work, based on the extreme-point symmetric mode decomposition (ESMD) method and the multiple linear regression model, we analyzed the changing of the Aral Sea from 1960 to 2018, and detected the time for slowdown of retreat, then explored the driving forces. The results show that the Aral Sea retreated rapidly from 1960 to 2004, and the shrinking rates of water surface area, water volume and water level were 1087.00 km2/year, 25.07 km3/year, and 0.56 m/year, respectively; the retreat has slowed since 2005, with the shrinking rates being 760.00 km2/year, 2.86 km3/year, and 0.38 m/year, respectively. At the same time, the area of water bodies surrounding the Aral Sea increased due to the agricultural drainage water. The oscillation periods of water level in the Aral Sea are 2.1a, 7.6a and 29.5a, of which 29.5a is the main period of oscillation. The trend residual RES indicates that water level shows a non-linear downward trend, and the degree of fluctuation has decreased significantly after 2005. The impact of human activities on the Aral Sea is more significant than that of climate change. Overall, the increased upstream runoff, reduced water withdrawal, and rise in water delivery to the Aral Sea has led to a slowing down of the sea's notorious shrinkage. The findings provide a scientific reference for the management and protection of the Aral Sea.

The Lake Chad hydrology under current climate change

Lake Chad, in the Sahelian zone of west-central Africa, provides food and water to ~50 million people and supports unique ecosystems and biodiversity. In the past decades, it became a symbol of current climate change, held up by its dramatic shrinkage in the 1980s. Despites a partial recovery in response to increased Sahelian precipitation in the 1990s, Lake Chad is still facing major threats and its contemporary variability under climate change remains highly uncertain. Here, using a new multi-satellite approach, we show that Lake Chad extent has remained stable during the last two decades, despite a slight decrease of its northern pool. Moreover, since the 2000s, groundwater, which contributes to ~70% of Lake Chad’s annual water storage change, is increasing due to water supply provided by its two main tributaries. Our results indicate that in tandem with groundwater and tropical origin of water supply, over the last two decades, Lake Chad is not shrinking and recovers seasonally its surface water extent and volume. This study provides a robust regional understanding of current hydrology and changes in the Lake Chad region, giving a basis for developing future climate adaptation strategies.

Effects of Sunlight on the Formation Potential of Dichloroacetonitrile and Bromochloroacetonitrile from Wastewater Effluents

Sunlight plays an important role in transforming effluent organic matter as wastewater effluents travel downstream, but the corresponding effects on the formation of haloacetonitriles (HANs), a group of toxic disinfection byproducts, in wastewater-impacted surface water has not been thoroughly investigated. In this study, we observed that sunlight preferentially attenuated the formation potential of bromochloroacetonitrile (BCAN-FP) over that of dichloroacetonitrile (DCAN-FP) in chlorine- and UV-disinfected secondary effluents. For four effluent samples from different plants, 36 h irradiation by simulated sunlight removed 28%-33% of DCAN-FP and 41%-48% of BCAN-FP. Across a larger set of effluent samples (n = 18), 8 h irradiation (equivalent to 2-3 d of natural sunlight) decreased the calculated cytotoxicity contributed by dihaloacetonitrile-FP in most samples. Similar behavior was observed for a mixture of wastewater and surface water (volume ratio 1:1). For UV-disinfected effluents, the higher the UV dose, the more likely was there a reduction in DCAN-FP and BCAN-FP in the subsequent sunlight irradiation. Experiments with model compounds showed that fulvic acid and UV photoproducts of tryptophan yield excited triplet state organic matters during sunlight irradiation and play an important role in promoting the attenuation of HAN precursors.