Net Water Balance Research Articles

Cropping calendar, agroclimatic and agroecological zoning for rainfed maize (Zea mays L.) under different rainfall scenarios in a semi-arid region of Brazil

Context The productivity of crops is influenced by the available net water balance, which relies on a complex interplay of edaphic and climatic factors. In this sense, rainfall is the leading water input for crop growth and yield, especially in water-scarce regions under semi-arid climates worldwide. Aims This study aimed to define the optimum cropping calendar and the agroclimatic and agroecological zones for rainfed maize in the state of Ceará, which is predominantly located within the Brazilian semi-arid region, assuming different rainfall scenarios. Methods We considered the subdivision of the study area into eight homogeneous precipitation regions according to the regional rainfall pattern. The climatic water balance for each region over two decades was calculated from historical weather data series, assuming three rainy scenarios: dry, regular, and rainy. The agroclimatic zoning was defined through the crop water balance results, soil classification, land use and occupation, slope and temperature, weighted through a multi-criteria decision analysis based on the Analytic Hierarchy Process. Key results The recommended planting period was broader in rainy conditions. However, there may be some dry spells between two 10-day intervals of the calendar, which impair plant growth depending on their intensity. For the dry scenario, the agroclimatic zoning showed that the marginal water deficiency covered 96.55% of the study area. Conclusions Rainfed maize cultivated under the semi-arid climate of Ceará state is viable in rainy conditions, partially restricted in regular years, and not recommended in dry years. Implications This study emphasises the importance of climate monitoring in effective planning for rainfed maize cultivation in semi-arid regions.

Modeling the water security in a watershed using the water footprint concept and water scarcity indicators

AbstractWater scarcity has received global attention in the last decade as it challenges food security in arid and semi-arid regions. This study employs water scarcity indices to assess water resources in the agricultural sector of Iran's Jazmourian watershed. Overall, we find that the watershed is experiencing a “very high stress” water situation. This is primarily due to intensive water usage for diverse crops, which has resulted in a negative net virtual water balance and contributed to a rise in water stress and poverty levels. The water stress index is 0.88, and the agricultural water stress is 1.25. The agricultural water footprint is 2,018.53 million cubic meters (MCM), with the share of blue, green and gray water footprints being 80.21, 6.08, and 13.72%, respectively. The region possesses 3,210 MCM of available water for crops, with 17.1% sourced from green waters and 82.9% from blue waters. Despite low annual rainfall and limited water resources, the region excessively exploits water for diverse crops. The net virtual water balance is negative, indicating high virtual water export (1,112–1,605 MCM) compared to imports (58–265 MCM). With declining water availability and increasing crop production, the region experiences rising water stress. The spatial analysis of sub-watersheds reveals diverse patterns of water stress and poverty, as detailed in the study.

Recognizing Low-Inflow Estuaries as a Common Estuary Paradigm

It has become clear that estuaries with low rates of freshwater inflow are an important but overlooked sphere of estuarine science. Low-inflow estuaries (LIEs) represent a major class of estuary long downplayed because observations do not fit well in the dominant estuary paradigm, which was developed in perennially wet climates. Rather than being rare and unusual, it is now evident that LIEs are common globally and an alternate estuary paradigm within the idea of an estuary as the place where a river meets the sea. They are found mostly in areas with arid, semi-arid, or seasonally arid climates, but LIE phenomena are also found in estuaries along mountainous coasts with small watersheds and short-tailed hydrographs. Inflows can be defined as “low” relative to basin volume, tidal mixing, evaporative losses, or wave forcing at the mouth. The focus here is on common physical phenomena that emerge in low-inflow estuaries—how low river flow is expressed in estuaries. The most common is hypersalinity (and the associated potential for inverse conditions), which develops where there is a net negative water balance. However, in small microtidal estuaries, low inflow results in mouth closure even as a positive water balance may persist, accounting for extreme stratification. Attention is also given to the longitudinal density gradient and the occurrence of thermal estuaries and inverse estuaries. Finally, ocean-driven estuaries are highlighted where marine subsidies (nutrients, particulates) dominate watershed subsidies. While climate change is altering freshwater inflow to estuaries, locally driven changes are generally more important and this presents an opportunity to restore estuaries through restoring estuarine hydrology.

A statistical analysis of tropical salinity and its relationship to SST, highlighting two contrasting areas

Tropical air-sea interactions, near-surface salinity (Ss), and sea surface temperature (SST) fluctuations are studied via ocean reanalysis products in the period 1980–2020. The statistical work considers how the net heat and water balance affects mixed layer depth (MLD) and coupling between the upper ocean and atmosphere. Field correlations of Ss – SST exhibit significant negative values in tropical latitudes 10S-15 N, between the semi-permanent marine anticyclones and the equatorial trough. Highlighting contrasts in two areas: the tropical east Atlantic and subtropical southwest Indian Ocean, annual cycles, inter-annual fluctuations of 6 – 8 yr, and long-term downward trends of Ss emerge. The SW Indian Ocean exhibits large swings of net heat and water balance as the monsoon reverses, and steady running-correlations of Ss and SST. The E Atlantic has a subdued annual cycle, and running-correlations are weak and unsteady. In both areas the Ss lags SST by a month. A fresh minus salty composite analysis reveals that the two contrasting areas respond to opposing phases of the Southern Oscillation: E Atlantic (La Nina) and SW Indian (El Nino). Projected long-term trends for increased tropical marine rainfall could be neutralized by declining runoff from continental monsoons. Statistical outcomes infer that a 0.1 ppt reduction of near-surface salinity leads to a 5 m reduction of MLD and a 0.4 C increase of tropical SST, contributing to deeper atmospheric convection. Limitations of the study derive from inferences based on infrequent salinity measurements.

Coupled modeling of peatlands carbon cycle and carbon dioxide emission from their peat deposits

COmplex Model of BOg LAndscapes (COMBOLA) is a set of dynamic models of carbon and nitrogen turnover, net ecosystem exchange, water balance, heat and water transport, generation and transfer of CO2 and CH4 in a peat deposit on a number of time scales. Combined modeling of carbon turnover and carbon dioxide emission from peat deposits on an annual time scale is carried out as part of COMBOLA for several bog landscapes in Western-Siberian south taiga. One-dimensional vertical reaction-diffusion model for carbon dioxide emission from peat deposit is combined with compartment carbon cycle model allowing estimate both bog type vegetation changes and greenhouse gases balance under probable climate change or perturbations initiated by human activities. Water table level (WTL) separating aerobic peat layer from the anaerobic one is calculated by means of the whole peat layer depth and its water balance relations. Minimal statistical information is used for calibrating temperature dependencies together with coefficients of heat and water transfer equations. The stationary states of carbon cycle are accompanied by steady average profiles of carbon dioxide concentration and can loose stability under human or climatic perturbations. The model dynamics is simulated with several climatic projections of the IPSL atmospheric circulation model for 21st century with anthropogenic scenarios RCP-2.6 and RCP-8.5.

Intensified microbial sulfate reduction in the deep Dead Sea during the early Holocene Mediterranean sapropel 1 deposition.

The hypersaline Dead Sea and its sediments are natural laboratories for studying extremophile microorganism habitat response to environmental change. In modern times, increased freshwater runoff to the lake surface waters resulted in stratification and dilution of the upper water column followed by microbial blooms. However, whether these events facilitated a microbial response in the deep lake and sediments is obscure. Here we investigate archived evidence of microbial processes and changing regional hydroclimate conditions by reconstructing deep Dead Sea chemical compositions from pore fluid major ion concentration and stable S, O, and C isotopes, together with lipid biomarkers preserved in the hypersaline deep Dead Sea ICDP‐drilled core sediments dating to the early Holocene (ca. 10,000 years BP). Following a significant negative lake water balance resulting in salt layer deposits at the start of the Holocene, there was a general period of positive net water balance at 9500–8300 years BP. The pore fluid isotopic composition of sulfate exhibit evidence of intensified microbial sulfate reduction, where both δ34S and δ18O of sulfate show a sharp increase from estimated base values of 15.0‰ and 13.9‰ to 40.2‰ and 20.4‰, respectively, and a δ34S vs. δ18O slope of 0.26. The presence of the n‐C17 alkane biomarker in the sediments suggests an increase of cyanobacteria or phytoplankton contribution to the bulk organic matter that reached the deepest parts of the Dead Sea. Although hydrologically disconnected, both the Mediterranean Sea and the Dead Sea microbial ecosystems responded to increased freshwater runoff during the early Holocene, with the former depositing the organic‐rich sapropel 1 layer due to anoxic water column conditions. In the Dead Sea prolonged positive net water balance facilitated primary production and algal blooms in the upper waters and intensified microbial sulfate reduction in the hypolimnion and/or at the sediment–brine interface.

Future Changes in the Surface Water Balance over Western Canada Using the CanESM5 (CMIP6) Ensemble for the Shared Socioeconomic Pathways 5 Scenario

The Prairie provinces of Canada have about 80% of Canada’s agricultural land and contribute to more than 90% of the nation’s wheat and canola production. A future change in the surface water balance over this region could seriously affect Canada’s agro-economy. In this study, we examined 25 ensemble members of historical (1975 to 2005), near future (2021–2050), far future (2050–2080), and end of the century (2080–2100) simulations of the Canadian Earth System Model version 5 (CanESM5) from the Coupled Model Intercomparison Project Phase 6 (CMIP6). A comprehensive analysis of a new Net Water Balance Index (NWBI) indicates an increased growing season dryness despite increased total precipitation over the Prairie provinces. Evapotranspiration increases by 100–300 mm with a 10–20% increase in moisture loss due to transpiration. Total evaporation decreases by 15–20% as the fractional contribution of evaporation from soil decreases by 20–25%. Total evaporation from vegetation increases by 10–15%. These changes in the surface water balance suggest enhanced plant productivity when soil moisture is sufficient, but evaporative water loss that exceeds precipitation in most years.

Evaluation of hydration status during the COVID-19 pandemic: a study of Turkish young adults.

Adequate hydration is an essential component of health at every stage of life. Although many factors such as age, gender, physical activity, drug use, and illness affect hydration status, it is vital to maintain water balance, especially in infectious diseases. This study was conducted to estimate the hydration status of young adults living in Turkey during the COVID-19 pandemic. The total water intake (TWI) and total water loss of the individuals were determined using the Water Balance Questionnaire (WBQ), which consists of questions about physical activity status, frequency of food and beverage consumption, water consumption, and water loss with urine and feces. The TWI of men and women was found to be 4,776.1 and 4,777.3 mL/day, respectively (p > 0.05). It was determined that 29% of the total water was obtained from drinking water, 49% from other beverages, and 22% from food. A positive net water balance was found in all body mass index (BMI) groups, men, and women. The net water balance was statistically lower in men (2,230.6 mL) than women (2,783.8 mL) (p < 0.05). As the COVID-19 pandemic continues, studies should be done on hydration status in the more balanced populations in terms of BMI and age groups.

Inverse Modeling of the Net Water Balance of the Black Sea From the Last Glacial Maximum to the Present

AbstractThe net freshwater balance plays a central role in the biological, chemical, geological and physical changes in the Black Sea since the Late Glacial Maximum (LGM), that is, 18–24,000 years BP. Past estimates of this balance vary widely. Here we solve inversely a water balance model coupled to two previously published Bosporus flow models, that is, flow rates controlled either by hydraulics with a critical height or by channel friction. We drive both models with two previously proposed Black Sea water‐level histories, that is, a smooth transition to saltwater entry and the “flood” scenario. First, we find that flow control by channel friction is far more likely than control by critical‐height hydraulics, as the latter does not allow Marmara Sea water to enter the Bosporus at any time in the past and predicts present‐day outflows that are far greater than observed. Prior to intense glacial melting (12–14,000 years BP), all models retrodict net freshwater inflow far less than previously assumed, that is, on the order of −1 to +10 km3 yr−1, rather than +100 s km3 yr−1. Thus, our results explain the ease by which the Black Sea could switch from evaporative to water gain conditions, as implied by water‐level records for that period. In addition, the channel friction model hindcasts glacial meltwater spikes during the transition from the LGM to the Holocene that are much smaller, that is, 100–250 km3 yr−1, than retrodicted by the hydraulic model or reported in the literature, that is, &gt;1,000 km3 yr−1.

Combining Remote Sensing and Crop Models to Assess the Sustainability of Stakeholder‐Driven Groundwater Management in the US High Plains Aquifer

AbstractNonrenewable groundwater contributes ∼20% of global irrigation water. As a result, key agricultural regions around the world are on unsustainable trajectories due to aquifer depletion, threatening food production and local economies. With increasing resource scarcity in the central High Plains Aquifer in the United States, an innovative stakeholder‐driven groundwater management framework emerged in Kansas referred to as the Local Enhanced Management Area (LEMA) program. This framework enables groups of irrigators to join together to implement measures to conserve groundwater. Here, we assessed the efficacy of the first LEMA to move the region toward sustainability with a process‐based crop model driven by well records and satellite‐derived annual land use. We found increased irrigation efficiency under the LEMA program reduced groundwater extraction by 25% (40 million m3). However, only 22% of pumping reductions benefitted the net water balance (9 million m3) due to decreased irrigation return flow resulting from increased irrigation efficiency. We then estimated economic impacts using simulated crop yields, commodity prices, and estimated energy saved from reduced groundwater pumping. Cost savings from reduced pumping were about 4.5 times greater than the income lost from minor yield penalties. This suggests that the program promotes both economic and water sustainability, but water targets may need to be more strict to stabilize groundwater levels. As aquifer depletion threatens crop production in many parts of the world, approaches that integrate dynamic process‐based models with in situ and satellite data can inform economically and hydrologically sustainable management strategies. Our work highlights the need to consider both economic factors and root zone processes when evaluating irrigation conservation programs.

DynACof: A process-based model to study growth, yield and ecosystem services of coffee agroforestry systems

The DynACof model was designed to model coffee agroforestry systems and study the trade-offs to e.g. optimize the system facing climate changes. The model simulates net primary productivity (NPP), growth, yield, mortality, energy and water balance of coffee agroforestry systems according to shade tree species and management. Several plot-scale ecosystem services are simulated by the model, such as production, canopy cooling effect, or potential C sequestration. DynACof uses metamodels derived from a detailed 3D process-based model (MAESPA) to account for complex spatial effects, while running fast. It also includes a coffee flower bud and fruit cohort module to better distribute fruit carbon demand over the year, a key feature to obtain a realistic competition between sinks.The model was parameterized and evaluated using a highly comprehensive database on a coffee agroforestry experimental site in Costa Rica. The fluxes simulated by the model were close to the measurements over a 5-year period (nRMSE = 26.27 for gross primary productivity; 28.22 for actual evapo-transpiration, 53.91 for sensible heat flux and 15.26 for net radiation), and DynACof satisfactorily simulated the yield, NPP, mortality and carbon stock for each coffee organ type over a 35-year rotation.

THE IMPACT OF IRRIGATION IMPROVEMENT ACTIVITIES ON WATER AND SALT BALANCE FOR THE IRRIGATED LAND IN NEKLA CANAL (EL-BEHIRA GOVERNORATE)

Three representative mesqas, i.e. Arfa Mousa at the head, Elafeer2 at the middle and Elbanna at the tail of Nekla canal.Elbehara Gov were selected to evaluate the impact of the implementation of activities and processes of field irrigation system development on crop yield, water saving, water productivity, water and salt balance. Results indicated slight increases in yield of the tested crops either irrigated from head - Arfa Mouse, middle - Elafeer2 or Tail - Elbanna mesqas. The average increases were about 6.98, 5.99 and 7.19% respectively. The average increases in crop water productivity were about 19.9, 19.5 and 20.0 % for crops irrigated from the three mesqas respectively. The average increases in crop water productivity for wheat, rice, Egyptian clover, cantaloupe and watermelon pulp as affected by field irrigation system development were about 15.3, 21.5, 22.9, 18.5 and 20.6% respectively. The average increases in water saving were about 10.8, 11.2 and 10.6 % for crops irrigated from the three tested meqas respectively. The average increases in water saving for wheat, rice, Egyptian clover, cantaloupe and watermelon pulp as affected by field irrigation system development were about 7.36, 12.9, 13.7, 10.6 and 9.88% respectively. Results revealed that the net water balance (NWB) values decreased to about 87.6, 76.7 and 85.5% as affected by field irrigation system development relatve to values before development equal to 100 for wheat, rice and Egyptian clover respectively under irrigation from Arfa Mousa mesqa at the head of Nekla canal. Similar results were also observed for wheat, rice and Egyptian clover irrigated from Elafeer2 at middle, and Elbanna mesqa at tail of Nekla canal. The average amount of salts added into soil cultivated with wheat, rice, Egyptian clover, cantaloupe and watermelon pulp were 800, 2350, 1255, 848 and 454 kg/Fad respectively before and 702, 1939, 1026, 719 and 388 kg/Fad after field irrigation system development. The average amount of salts removed from soil cultivated with wheat, rice, Egyptian clover, cantaloupe and watermelon pulp were 722, 2456, 1337, 802 and 454 kg/Fad respectively before development and 567, 2887, 591, 598 and 309 kg/Fad after field irrigation system development. It could be concluded that field irrigation system development has a positive effect on water saving, crop yield, water productivity and reducing salt accumulation in crop growth medium because field irrigation system development prevent seepage and weed growth increases in the developed mesqas and made water available all the time in the mesqa.

Hunting for a Larger Diversity of Urban Trees in Western Europe—A Case Study from the Southern Caucasus

The primary aim of this study was to communicate a method for locating natural habitats where trees grows under conditions that are comparable to those in urban environments in terms of water stress. This is presented by analyzing five different forest reserves in the southern Caucasus (Republic of Georgia) where calculation of net water balance over the period of a year was conducted. This provided an insight into the drought at the sites during the growing season. The data were thereafter compared with similar calculations for five different cities in Western Europe in order to see if there were any matches in drought stress between the cities and the forest reserves. To extend the analysis, conditions in the five cities were assessed for high density and low density areas, and for the current climate and a future climate scenario. The comparisons revealed some matches between conditions in the forest reserves and those in different scenarios/areas in the cities. A secondary aim was to identify specific ecotypes in the wild demonstrating great potential to handle growing conditions similar to those in urban environments based on inventories of woody plants in the forest reserves. A total of 44 woody species were found in the forest reserve systems with a random distribution throughout the five study sites. Based on the commitments presented above a preliminary screening can be done where future tree selection focus can be directed towards highly promising species and ecotypes, which would undoubtedly limit the time lag before proper plant material can be released.

The water footprint from hydroelectricity: a case study for a hydropower plant in Romania

In Romania, the hydropower is the main form of renewable source with an important share in energy mix. Despite their valuable advantages on supplying energy and balancing the energy system, public acceptance, environmental, social and economic impact has become a common challenge in development of hydropower projects. Increasing of water consumption and raising awareness regarding available water resources leads to an integrated management approach of them. In this paper the water footprint is estimated for one of the largest Romanian hydropower project, namely Hydropower Plant Vidraru. The water footprint from hydroelectricity is evaluated considering electricity production of the hydropower plant, water footprint of dam construction and three different approaches to quantify water footprint of the reservoir: gross water consumption, net water consumption and water balance. Also, water footprint is assessed based on economic value of the reservoir using allocation coefficients for various purposes of the reservoir. It is estimated that economic benefit of the reservoir is 81.92·106 €/y, with hydroelectricity major contributor.

The osmorespiratory compromise in the euryhaline killifish: water regulation during hypoxia.

Freshwater- and seawater-acclimated Fundulus heteroclitus were exposed to acute hypoxia (10% air saturation, 3 h), followed by normoxic recovery (3 h). In both salinities, ventilation increased and heart rate fell in the classic manner, while ṀO2 initially declined by ∼50%, with partial restoration by 3 h of hypoxia, and no O2 debt repayment during recovery. Gill paracellular permeability (measured with [14C] PEG-4000) was 1.4-fold higher in seawater, and declined by 50% during hypoxia with post-exposure overshoot to 188%. A similar pattern with smaller changes occurred in freshwater. Drinking rate (also measured with [14C] PEG-4000) was 8-fold higher in seawater fish, but declined by ∼90% during hypoxia in both groups, with post-exposure overshoots to ∼270%. Gill diffusive water flux (measured with 3H2O) was 1.9-fold higher in freshwater fish, and exhibited a ∼35% decrease during hypoxia, which persisted throughout recovery, but was unchanged during hypoxia in seawater fish. Nevertheless, freshwater killifish gained mass while seawater fish lost mass during hypoxia, and these changes were not corrected during normoxic recovery. We conclude that this hypoxia-tolerant teleost beneficially reduces gill water permeability in a salinity-dependent fashion during hypoxia, despite attempting to simultaneously improve ṀO2 , but nevertheless incurs a net water balance penalty in both freshwater and seawater.

Complex bog landscape model (COMBOLA) as an integrated tool for modeling of biotic turnover and peat deposit processes

Biotic cycling in ecosystems consists of live organic matter production and dead organic matter destruction. The latter is accompanied by the emission of greenhouse gases into the atmosphere. In peatland landscapes, additional conditions are imposed due to the presence of a water table depth (WTD), under which the destruction is anaerobic with methane generation, while above the WTD it is aerobic, and part of the diffusing methane is consumed by the methanotrophic bacteria. Hence, due to the complexity of heat and water transfer processes in the peat deposit and the nonlinearity of biological turnover, it is necessary to make a combination of their models. The COmplex Model of BOg LAndscapes (COMBOLA) is a set of dynamic models of carbon and nitrogen turnover, net ecosystem exchange, water balance, heat and water transport, generation and transfer of CO2 and CH4 in a peat deposit on annual, seasonal, and daily time scales. The main component includes a series of biotic turnover models – from a mass-balance equation on an annual time scale to a NEE dynamics model on a daily one. Biotic turnover can be represented by a single carbon cycle, a single nitrogen cycle or both. Another important component of the COMBOLA system is a one-dimensional vertical model of heat-water-gas exchange in a peat deposit. Thus, a number of interconnected modules constitute an integrated mathematical model of peatland landscapes adapted to any given initial information.

Environmental globalization

PurposeThe purpose of this paper is to present an alternative viewpoint to better manage the global natural resources using the case of soybean international market as a baseline and water as the natural resource, although the product and natural resource could be any other.Design/methodology/approachThe case of Brazilian soya production and the international soybean market was used to illustrate the commodities and agricultural use of water, a global and finite natural resource. The water footprint analysis was applied to balance the international water trade associated to soybean exportation.FindingsThe net water balance indicates that Brazil is more efficient in the water use to soybean production considering water origin (types of water) and availability. That implies a benefit for soybean importers from Brazil who does not internalize this natural input in the cost of their products.Research limitations/implicationsThe alternatives proposed and discussed in this essay are far from being complete and definitive. The details of their implications are beyond the scope and purpose of this essay. However, it may be the starting point for a wider academic and political debate.Practical implicationsThere are externalities in the soybean market that are generating environmental and social costs. Those costs could be minimized by a fair international market that internalizes the costs of using finite natural resources. For that, adequate public policies should be designed, implemented and maintained. The monetary funds obtained from internalization of costs in water use could be addressed to research devoted to enlarge the water saving practices.Originality/valueFrom a discussion about the fundamental role of natural resources in the maintenance of mankind life and the implications of its irrational use, a global governance of natural resources is being proposed. As practical actions for global governance, a green soybean, marketed under a water seal, has been discussed.

Mine Water Management – A study at Edikan Gold Mine (EGM)

Water is an essential part of all mining activities and the availability of quality water year round is critical to mining operations.Mine water is largely employed in drilling, dust suppression, mineral processing and other in-pit operations. Shortage of water ina mine results in poor drilling control, dust pollution, and mill shutdowns, hence a critical need to optimize the use of water invarious mining processes. This paper seeks to establish an effective mine water management system at Edikan Gold Mine (EGM)to have enough water in store for drought conditions. A site water balance was established primarily taking into accounts theinflows and outflows of water at the mine. Results show that rainfall and the Asuafa River are the principal sources of water forEGM mining operations, while the processing plant was the main water user on the mine site. Annual net water balance is alsoestimated to help determine the required capacities of future water storage facilities.

Pore fluids in Dead Sea sediment core reveal linear response of lake chemistry to global climate changes

Abstract Pore fluids extracted from a 456 m sediment core, recovered within the framework of a multinational and International Continental Scientific Drilling Program (ICDP) co-sponsored effort at the bottom of the terminal Dead Sea, recorded the chemical variations in the deep lake over the past 220 k.y. Mg2+ and Br– were shown to be conservative in the pore fluids, increasing in concentration during interglacial periods, diluting during glacials, and providing excellent proxies for deep lake net water balance changes. Furthermore, the Na/Cl ratio recorded the process of halite precipitation and dissolution induced by these hydrological changes. Mg2+ and Br– records follow a glacial-interglacial pattern, such as observed in atmospheric CO2 concentrations and global sea-surface temperatures, albeit with a phase offset. At the end of the last interglacial (ca. 116 ka), there is a delay in onset of dilution of the deep lake, most likely due to the limnological transition from holomictic to meromictic conditions. The increase in deep lake concentrations at Last Glacial Termination I is delayed as a result of freshwater input into the deep lake during the cooler Younger Dryas period. There is a persistent relationship between precipitation in the watershed and North Atlantic sea-surface temperatures, similar to conditions observed over the past instrumental record. Deviations from the long-term trends occurred during interglacial periods, Marine Isotope Stages MIS 5e and MIS 1, when the deep Dead Sea was significantly diluted, and coincided with Mediterranean sapropel layers S5 and S1.

Comparison of the water footprint of two hydropower plants in the Tocantins River Basin of Brazil

The purpose of this study was to characterize the water footprint of the Tucuruí and Lajeado hydropower plants (HPPs), located in the Tocantins River Basin, Brazil. The water footprint of hydropower was evaluated by three different methods based on the electricity production of the HPP and the monthly and annual evaporation rates estimated according to Penman's method. The first water footprint method (WF-1) considers only the gross water consumption by the HPPs; the second method (WF-2) considers the net water consumption, discounting what would be lost by evapotranspiration in the area previous to the construction of the reservoir; and the third method (WF-3) accounts for the net water balance. The results demonstrated that the estimates of average annual water footprint for the Tucuruí reservoir, using the WF-1, WF-2 and WF-3 methods, were, respectively, 49 m3/GJ, 26 m3/GJ and −21 m3/GJ, while for Lajeado, these estimates were 95 m3/GJ, 48 m3/GJ and 21 m3/GJ. The flooded area of the reservoir per unit of installed capacity of Tucuruí HPP is 34 ha/MW, while for Lajeado, this value reaches 70 ha/MW, which explains Tucuruí's greater water efficiency. Confirming this result, the normalized WFs based on the reservoir area and the installed capacity were approximately 100% higher for the Lajeado HPP than for the Tucuruí HPP through all water footprint methods analyzed. The WF-2 method is the most appropriate to account for the consumption of water directly related to hydroelectric energy generation since it considers the change in evaporation caused by the construction of the reservoir.