Major Water Loss Research Articles

Study on Osmotic Consolidation and Hydraulic Conductivity Behavior of an Expansive Soil Inundated with Sodium Chloride Solution

Canals are a very imperative source of irrigation for the agricultural sector in India. Seepage causes major water loss in canals, and hence, the installation of liners becomes necessary. Compacted clay soils are commonly used as liners in the canals. This structure will most probably be subjected to salinization and desalinization cycles throughout its life. Because of the interaction between the pore liquid and clay particles, physico-chemical influences considerably impact the behavior of clay barriers. In this paper, the effect of interacting fluid on volume change, consolidation parameters, and hydraulic conductivity of compacted clay soil is investigated with the help of a one-dimensional consolidation test. The compacted clay specimens were immersed alternatively with distilled water (DW) and sodium chloride (NaCl) solutions (SW) at constant loading of 10 kPa, which replicates the load conditions in the field canal due to 1 m head of water and incremental loading as per IS 2720 part 15 standards. The experimental results proved that there is a percentage volume change increase of about two times for each stage inundated with 4M NaCl solution than its preceding stages inundated with distilled water at constant loading of 10 kPa. The consolidation rate was accelerated with 4M NaCl solution than the normal consolidation at incremental loading. The permeability coefficient in the salt water-induced sample increased by 217% more than the distilled water-induced sample at incremental loading. Therefore, the soil specimen subjected to alternate salinization and desalinization cycles significantly affects the volumetric and consolidation behavior, leading to decreased life of clay barrier structures.

Forecasting the seepage loss for lined and un-lined canals using artificial neural network and gene expression programming

Canal lining is customarily used to raise water-use effectiveness and reduce seepage loss. The major water losses in an irrigation channel are due to leakage and evaporation. The Egyptian General Integrated Management for Water Resources and Irrigation introduced a proposal for lining the Al-Hagar canal based on these losses. This study investigates the effect of lining in the Al-Hagar canal on flow characteristics, and compares the canal before and after introducing the lining. Additionally, it discusses the most common type of water loss, namely, losses due to seepage. Fieldwork was conducted on the Al-Hagar canal, Al-Saff Center, South of Helwan city, Egypt. The result revealed that the discharge of the canal after the lining is approximately 1.362–1.573 times greater than that of the un-lined section. Water losses in the Al-Hagar canal were 38.736% when un-lined but decreased to 29.253% when lined. The conveyance effectiveness in the un-lined canal, which is approximately 61.26%, increased to 70.75% when the entire canal is lined, which means a 9.483% improvement of conveyance. New relations were introduced using Artificial Neural Network and Gene Expression Programming to forecast the seepage loss in the lined and the un-lined canal as a function of Manning’s coefficient, Froude number and hydraulic radius. The consequences were better using the GEP program than using ANN for the lined and the un-lined canals. The value of the determination coefficient was 0.98, Correlation factor was 0.99, and the RMSE was 0.0017 for lined canals and the value of determination coefficient was 1, Correlation factor was 1, and the RMSE was 0.0003 for un-lined canals.

Leakage and evapotranspiration act as two major water losses for the largest lake on North China Plain during water diversion period

Leakage and evapotranspiration act as two major water losses for the largest lake on North China Plain during water diversion period

A comparison between model-based and data-driven leak localization methods*

Water networks are crucial infrastructures for the sustainability of modern cities, and hence their proper operation is of great importance. This includes the fast detection, localization and repair of leaks, which may produce major water losses. This paper presents a comparison between two leak localization methods, which belong to opposite categories: model-based and data-driven. To this end, their main characteristics are reviewed, highlighting their differences and advantages/drawbacks, to finally display several results whose discussion allows to draw important conclusions for the future of the research field.

Decrease in the Water Level of Lake Prespa (North Macedonia) Studied by Remote Sensing Methodology: Relation with Hydrology and Agriculture

The Ohrid-Prespa lake system is the oldest and most diverse permanent lake system in Europe, dating from the Pliocene era and aged at over 4Ma. Its smaller component is Lake Macro Prespa (thereafter called Prespa), shared by North Macedonia, Albania, and Greece. Lake Prespa’s depth was reported as 14 m mean and 48 m maximum before its major water level decline. The lake is highly sensitive to external impacts, including climate change, and has been suffering major water loss for decades. A lake-level decline of almost 10 m was documented between 1950 and 2009 due to restricted precipitation and increased water abstraction for irrigation. This study describes the changes in the surface size of Prespa Lake and the vegetation/land use in the surrounding area in the period 1984–2020 using satellite images (remote sensing, Landsat 5 & 8 images by United States Geological Survey). The lake lost 18.87 km2 of surface in this period (6.9% of its size, dropping from 273.38 km2 to 254.51 km2). Water loss was greater in the period 1987–1993 and 1998–2004. The Analysis of Normalized Difference Vegetation Index (NDVI) in the area (app. 4950 km2) surrounding Lake Prespa revealed an increase in the mean NDVI values over the period studied (1984–2020), pointing to a general increase in vegetation. Areas with NDVI > 0.13 increased from 78% in 1984 to 86% in 2020, while those with the highest vegetation intensity (NDVI > 0.45) increased by 40%. These changes in vegetation may be related to the water loss of the lake.

Determination of the energy expenditure, sources, and loss of water among young adults

BackgroundFew studies on measuring human energy expenditure with the doubly labeled water method has been conducted in China. The sources and loss of water among human body have never been systematically evaluated. Less data can be available for the development of the recommendation on energy expenditure and water intake. The objective of this study was to determine the energy expenditure, water sources, and loss among young adults.MethodsIn this cross-sectional study, 25 participants were recruited. Double-labeled water was used to determine their energy expenditure. Water loss through skin evaporation and respiration of the lungs and water sources from metabolic water were calculated using corresponding formula, respectively. Water loss through excretion of urine was recorded and evaluated using “3-day, 24-h, real-time urine excretion record” method. All urine samples were collected and weighed in the 3 days. Water loss through excretion of feces was evaluated using “3-day, 24-h, real-time fecal-excretion record” method. All fecal samples were collected and tested by the direct drying method. Water sources from fluid intake were recorded by “7-day, 24-h, real-time fluid intake record” method. Water intake from food was calculated and tested by the weighing method combined with the duplicate portion method and the direct drying method in the 3 days.ResultsThe energy expenditure of males was 2187 kcal/d, and that of females was 1987 kcal/d. The median fluid intake, water intake from food, and metabolic water were 887, 1173 and 246 mL, respectively, which accounted for 38.8%, 50.3%, and 11.2% of total water sources. There was a gender difference in the percentage of metabolic water (Z = − 2.135, P = 0.033). The water loss through urine excretion, skin evaporation, respiration, and feces excretion was 1295, 172, 149 and 64 mL, respectively, which accounted for 76.5%, 10.3%, 9.5%, and 3.6% of the total water losses. Gender differences in the amount of water loss through respiration and skin evaporation were found (Z = − 4.125, P < 0.001; Z = − 3.723, P < 0.001).ConclusionsEnergy expenditure of male was higher than that of female. The first major water sources was water intake from food in this study, and the first major water loss was urine excretion.Trial registration The study was registered on the website of Chinese clinical trial registry, and the code of identification is ChiCTR1900028746.

Characteristics of Pore Structure in the Evaporated Stage of Wood-Derived Carbon

Major water loss in the first stage of wood-derived carbon preparation had a direct impact on pore structure during the subsequent pyrolysis of biochar materials. To explore the changes in pore space at this stage, poplar was used as the subject of this study. The pore morphology before and after water evaporation was quantitatively characterized by scanning electron microscope, nitrogen adsorption method, and mercury injection method. Both the fractal dimensions of the multistage pores were obtained by the Frenkel-Halsey-Hill model and the thermodynamic relationship model. The results showed as follows: the adsorption isotherms were presented the mixed type of II and IV after supercritical drying, indicating the mesopores and macropores of wood. The adsorption isotherms after conventional drying were characterized a type II, which was inferred to the reduced mesopores compared to supercritical drying. The hysteresis loops of all wood samples were examined for the H3 type, which was deduced from the presence of slit-like pores. After treatment at 103±2 °C, the porosity and its connectivity properties are reduced by the mercury pressure data. For &lt;50 nm the pore size distribution of the samples shows a shoulder peak at around 6.5 nm. Simultaneously, the pore structure is significantly deformed and the pore size distribution produces smaller peaks at 3014 and 12510 nm. The pore fractal dimension increases in the &lt;50 nm stage. The fractal dimension of pores decreases when the pore size is 50 nm~5 μm. Stability of the pore fractal dimension in the pore size &gt;50 nm stage. This indicates that the conventional drying treatment made the micropore complexity increase, and leads to a reduced or invariable pore structure complexity for the &gt;50 nm. The fractal analysis could assist in better analyzing the changes of pore structure and provide a new perspective for studying the pore structure in the carbonation stage.

Review of factors affecting canal water losses based on a meta‐analysis of worldwide data

AbstractIrrigation water conveyance relies heavily on canal networks because they transport the water cheaply. However, water losses are high, which is a major concern in the face of soaring demand and dwindling new water sources. While researchers have investigated canal water losses and water loss types at irrigation scheme level, their variability and the main factors of influence at a global scale are still not clear. Thus, this study aims to elucidate the effects of canal water flow and soil characteristics on water losses globally. Data for 1388 canal reaches from 45 published articles are used. The results confirm that evaporation is so negligibly smaller than seepage and other water loss types that it can safely be ignored when analysing major water losses from canals. The study results also confirm that canal water losses decrease with soil clay content, due to decreasing permeability. The methods used for assessing water losses show significant influence on water losses; for example, the inflow–outflow method exhibits significantly higher water losses than the ponding technique. The current study results also show that canal shape, wetted perimeter and wetted area have a significant influence on water losses. It can be concluded from the study results that consideration of the physical mechanisms of water losses and different water loss types involved is important in future studies. It is recommended that future canal water loss studies, especially those focusing on losses via evaporation, also assess the effects of factors such as canal embankment height and depth of freeboard on the losses. These results are important for water scientists, engineers and practitioners.

Climate change and cover crop effects on water use efficiency of a corn-soybean rotation system

Climate change led to increased temperature and variable rainfall, which may pose great threats to both agricultural productions and environmental impacts. In this study, we aim to explore how changing climate and its extremes in the 20th and 21st-century influence system water use efficiency (sWUE) of a corn-soybean cropping rotation in a humid sub-tropic environment, and how much can cover crops mitigate these impacts. Different from the traditional yield-focused water use efficiency (WUE), sWUE addresses both production and environmental quality goals by considering grain yields and all major system water losses (evapotranspiration, runoff, and drainage). A calibrated crop simulation model, Root Zone Water Quality Model version 2 (RZWQM2), was applied to simulate grain yields and all major system water losses. The model was forced by daily climate data from in situ observations during 1956–2015 and 10 downscaled and bias corrected General Circulation Model (GCMs) projections under the representative concentration pathways (RCP) 4.5 and 8.5 scenarios during 2020–2079. The results showed that, under the historical baseline and the future RCP4.5 and RCP8.5 scenarios, due to the growth of cover crops, the sWUE for corn were improved by 1.7%, 2.6% and 2.3%, respectively (p-value < 0.001), and for soybean by 0.7% (p = 0.06), 1.0% (p-value < 0.001) and 0.9% (p-value < 0.001). Soil evaporation, as the largest source of water loss from the cropping system, was significantly decreased by 1.7%, 2.6% and 2.3% during the corn growing season, and by 0.7%, 1.0% and 0.9% during the soybean growing season. The annual drainage was decreased by 38 mm, 53 mm and 67 mm, under the baseline, RCP4.5 and RCP8.5, respectively. With the incorporation of wheat cover crops, the correlations of temperature or precipitation extremes with grain yields and major water losses were mostly decreased, suggesting that growing cover crop is an effective means to mitigate the impact of climate extremes on sWUE of a corn-soybean cropping.

Water loss associated with food loss and waste in Brazil

This article aimed to estimate the loss of water associated with food loss and waste in Brazil in 2013. Data from the Food and Agriculture Organization (FAO) of the United Nations (UN) on food balance and waste, as well as the Water Footprint (WF) of agricultural products available at Water Footprint Network (WFN) were used. Results show that food waste reaches 49 million metric tons per year, compromising a total of 87 billion cubic meters of water, which is higher than the average annual flow of the river São Francisco. Major water loss is associated with the agricultural production stage (32%), followed by consumption (19%). Amongst food groups, major water loss is associated with meat (49%), followed by cereals (19%). Roughly 96% of water loss is attributed to the green water component, which highlights that attention must be paid to rainfed agriculture to ensure food and water for everyone. The loss of blue water was more than half of the volume consumed in the urban sector, and the grey component (polluted water) was equivalent to 80% of this consumption. Measures such as improving agricultural practices, logistics, irrigation, expanding and improving rainfed agriculture, developing campaigns and policies to reduce exportation of primary products, as well as consumption of products from animal origin, can contribute to managing the food supply chain more sustainably when the focus is water. Reducing food loss and waste means preserving water.

A study on water seepage losses for ponds and reservoirs

Irrigation is main factor for agricultural production. Our aim is to increase agricultural yield by increasing area under irrigation. It is very important to see that more water available for irrigation is completely used as far as possible to avoid water loss during conveyance through canal. Seepage loss is major water loss during transit. Rainwater harvesting is the artificial collection, storage and use of runoff or rain water. The water harvesting with tanks and ponds is one option to increase water availability and agricultural production at the household level. Rain fed agriculture can be protected by adopting farm ponds. The harvested runoff water in a farm pond creates salinization / water logging problems so; it has to be lined to control the seepage losses. The article presents a review on the type of lining materials viable and to explore for a cost effective sealant which can be adapted. In comparison to clay lining, Bentonite, polymers like HDPE, LDPE, Silpoulin, LLDPE in combination with concrete increases the durability along with the 100% seepage control with benefit cost ratio for HDPE lining in combination with concrete showed highest value of 10.4:1. Bentonite, though costly has shown significant results by reducing the seepage losses by 72% to 96% respectively, depending on the thickness of application. In vertisols, lining did not show any significant variation. Whereas alfisols, luvisols of arid and semi-arid regions require lining materials with diversified crops and conservative irrigation practices.

Holocene peatland water regulation response to ~1000-year solar cycle indicated by phytoliths in central China

Peatland ecosystem processes are strongly influenced by hydrology linked to climate change. However, how transpiration, as major water loss pathway in closed peatland, responds to climate change and then regulates ecosystem water balance that remains poorly understood. Here, we reported an 18,000-year fossil phytolith record from an herbaceous community-dominated mountain peatland in central China to reconstruct climate changes and vegetation evolution and reveal the interactions between regional climate changes and peatland ecosystem. The abundance of bulliform phytoliths—a silicified type of cells that regulate the movements of plant leaves to reduce light exposure and transpiration rate—shows close correlations with the Holocene climate variations with higher bulliform abundance in response to warm-dry climate (11,500–9600 cal yr BP; 7500–3000 cal yr BP) and lower values associated with cold-wet climate (13,000–11,500 cal yr BP; 3000 cal yr BP-present). Spectral analysis reveals that bulliform abundance andreconstructed climate vary with a major ~1000-year periodicity during the Holocene, suggesting a possible causal relationship to solar activity. A high bulliform abundance and warm-dry climate correspond with enhanced solar activity, and vice versa. We interpret that the resultant leaf water deficit resulted from greater light interception, high temperature anddrought promoted the production of bulliform cells to fold leaf for water conservation, which is an effective protective mechanism of peatland grasses from the environmental stress. These results expand our understanding of how grass-dominated peatland plant water regulation recorded by bulliform phytoliths responds to solar radiation and local hydroclimate during geological period.

Altitudinal and temporal evapotranspiration dynamics via remote sensing and vegetation index-based modelling over a scarce-monitored, high-altitudinal Andean páramo ecosystem of Southern Ecuador

In the tropical Andes, the paramo ecosystem is known as water towers and the main water supplier for the cities of the Andean region. Nevertheless, considering that evapotranspiration (ET) is the major water loss and the lack of in situ evapotranspiration measurements in high altitudinal paramo ecosystems, ET dynamics on the hydrological regulation remains largely unexplored. Therefore, to close this gap, we focused on a remote sensing approach. This study addressed the altitudinal and temporal dynamics of actual evapotranspiration using a crop coefficient based on a Vegetation Index (VI) model. Enhanced Vegetation Index (EVI), Normalized Difference Vegetation Index (NDVI) and Soil-Adjusted Vegetation Index (SAVI) retrieved from Landsat imagery were evaluated. Four remote sensing images and ground-level meteorological data for a 10-month period were used to create ET maps from each VI. A cubic spline interpolation was used to obtain daily ET time series between two satellite overpass dates. Aggregated monthly values were used to validate against ET calculated from water balance. Results revealed that EVI-based ET outperformed the other VI-based ET. The results showed 30% of subestimation (Pbias%) in relation to the water balance. For upgraded results, an extended satellite images time series and a fine calibration are needed. Regarding the altitudinal variability, ET exhibited a strong dependence on land cover characteristics. Our work provides a plausible method to estimate ET in paramo ecosystems in the absence of ET measurements and with a scarcity of clear sky images, further evaluation is necessary to improve ET estimations using remote sensing in the future.

Understanding Fundamental Phenomena Affecting the Water Conservation Technology Adoption of Residential Consumers Using Agent-Based Modeling

More than one billion people will face water scarcity within the next ten years due to climate change and unsustainable water usage, and this number is only expected to grow exponentially in the future. At current water use rates, supply-side demand management is no longer an effective way to combat water scarcity. Instead, many municipalities and water agencies are looking to demand-side solutions to prevent major water loss. While changing conservation behavior is one demand-based strategy, there is a growing movement toward the adoption of water conservation technology as a way to solve water resource depletion. Installing technology into one’s household requires additional costs and motivation, creating a gap between the overall potential households that could adopt this technology, and how many actually do. This study identified and modeled a variety of demographic and household characteristics, social network influence, and external factors such as water price and rebate policy to see their effect on residential water conservation technology adoption. Using Agent-based Modeling and data obtained from the City of Miami Beach, the coupled effects of these factors were evaluated to examine the effectiveness of different pathways towards the adoption of more water conservation technologies. The results showed that income growth and water pricing structure, more so than any of the demographic or building characteristics, impacted household adoption of water conservation technologies. The results also revealed that the effectiveness of rebate programs depends on conservation technology cost and the affluence of the community. Rebate allocation did influence expensive technology adoption, with the potential to increase the adoption rate by 50%. Additionally, social network connections were shown to have an impact on the rate of adoption independent of price strategy or rebate status. These findings will lead the way for municipalities and other water agencies to more strategically implement interventions to encourage household technology adoption based on the characteristics of their communities.

Geomechanical and hydrogeological characteristics of Quaternary in karst

AbstractKarst is a terrain with special hydrogeology and relief forms, and it develops in rocks that are relatively soluble in water. Quaternary deposits in karst areas of the Dinarides occupy relatively smaller areas, in poljes and beds of a small number of karst rivers. The subject of the study is the Quaternary formations in the Trebižat riverbed. Although the river has carved its bed through Quaternary limestones, occurrences of major water losses or sinking are not registered due to relatively thick, fine‐grained and clayey alluvium that has been deposited in the canyon. Their depth is relatively large and in places it is over 20 m. Tufa in the form fragments of different sizes is very often present. It has a high holey porosity that is partly due to the decomposition of water plant tissues, and partly due to the dissolution or releasing of organic tissue. Despite the high porosity, tufa does not have a high permeability because the pores are not well interconnected and are often filled with fine‐grained particles. The subject of the paper is geomechanical and hydrogeological properties of these sediments.

Behavior of fiber reinforced concrete for controlling the rate of cracking in canal-lining

Seepage is a major water loss (20–30%) from the canal as compared to the other forms of water losses. Concrete is commonly used for canal-lining to reduce the seepage loss. Considerable seepage (15–20%) has been observed even in the cement–concrete conventional sections. The performance of canals decreases with an increase in the rate of cracking in concrete canal-lining. The rate of cracking in canal-lining can be reduced by improving the flexure, compressive, and splitting-tensile strengths of concrete. Out of these, splitting-tensile strength of concrete plays a vital role in controlling cracks. The use of fibers for characteristics improvement of concrete is very ancient. Natural fibers include many benefits, like low cost due to its abundance, least health hazards, and flexibility. The use of synthetic fibers as reinforcement in matrix has also attained intentness by reasons of its high strength, less water absorption, and low density in nature. The overall aim of the research program is to explore materials for better performance of canal-lining in terms of reduced water losses by controlling its rate of cracking due to alternate wetting and drying, and due to differential settlement, etc. The purpose of this work is to examine experimental behaviors of jute fiber reinforced concrete (JFRC), nylon fiber reinforced concrete (NFRC), and polypropylene fiber reinforced concrete (PPFRC) for controlling the rate of cracking in canal-lining. For this purpose, the mechanical properties (compressive, splitting-tensile, and flexure strengths, energies, and toughness indices), water absorption, and linear shrinkage of JFRC, NFRC, and PPFRC are determined experimentally as per ASTM standards. The properties of plain concrete (PC) are used as reference. The proportion of 1:3:1.5:0.7 (cement: sand: aggregate: water) is used for PC mix. The mixes of JFRC, NFRC, and PPFRC are manufactured by adding the jute fibers, nylon fibers, and polypropylene fibers, respectively, in the same mix design as that of PC. For production of each type of fiber reinforced composite (FRC), fibers having length of 50mm are added in concrete by an amount of 5% (by mass of cement). A reduction in compressive properties, and an improvement in splitting-tensile and flexural strengths, water absorption and linear shrinkage is exhibited by FRCs over that of PC. Among the tested FRCs, PPFRC shows better performance. This may ensure to control the rate of cracking in canal-lining, ultimately improving its performance.

Field Evaluation of Irrigation Scheduling Strategies using a Mechanistic Crop Growth Model

AbstractIn a field experiment with white cabbage (Brassica oleracea L. var. capitata (L.) alef.) in Germany, three irrigation scheduling approaches were tested: (i) three sprinkler irrigation schedules based on soil water balance calculations using different development‐dependent crop coefficients; (ii) automatic drip irrigation based on soil water tension thresholds; (iii) irrigation scheduling by real‐time application of a partially calibrated mechanistic crop growth model. Multi‐objective calibration was applied to derive a fully calibrated model as a diagnostic tool to identify the water loss terms of the individual irrigation strategies.The results of the experiment showed that: (i) high yields can be achieved with relatively low amounts of irrigation water (~100 mm), provided the optimal irrigation strategy and technique are applied; (ii) automated tension threshold‐based drip irrigation outperformed soil water balance or crop growth model‐based strategies; (iii) the soil water balance calculation approach relying on recommended Kc factors led to an enormous overirrigation; (iv) the application of a partially calibrated crop growth model led to an underestimation of the crop water requirements in conjunction with an incorrect timing of irrigation events and therefore resulted in the lowest yields. The diagnostic model identified percolation, for the wet sprinkler irrigation treatments, and canopy evaporation, for the dry and model‐based treatments, as major water loss sources; only minimal additional water was lost in the tension‐controlled treatment. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Biophysical controls on canopy transpiration in a black locust (Robinia pseudoacacia) plantation on the semi‐arid Loess Plateau, China

AbstractIn the semi‐arid Loess Plateau of China, black locust (Robinia pseudoacacia) was widely planted for soil conservation and afforestation purposes during the past three decades. Investigating biophysical controls on canopy transpiration (Ec) of the plantations is essential to understanding the effects of afforestation on watershed hydrology and regional water resources. In addition to monitoring of micrometeorology and soil water content, sap flux densities (Fd) of six representative trees in a 27‐year stand were continuously measured using thermal dissipation probes during the growing seasons in 2013 and 2014. Ec was derived by multiplying stand total sapwood area (AST) with Fd. The daily mean Ec in the growing season was 0.14 and 0.23 mm day−1 in 2013 and 2014, respectively. The responses of daily Ec to Rs and vapour pressure deficit were explained with an exponential threshold model. The variability of monthly Ec was mainly explained by leaf area index (LAI) (R2 = 0.92). The inter‐annual variability of Ec was influenced by LAI that fluctuated dramatically during 2013 and 2014. We found that the status of soil water content at the beginning of the growing season had large impacts on LAI and Ec during the growing season. Contrary to common beliefs that the plantation uses a large amount of water, we found that the black locust plantation had rather low transpiration rates (5.3% of precipitation and 4.6% of ET0). This study suggests that the black locust plantation has adapted to local soil water condition by reducing transpiration, and the major water loss from the plantation was not transpiration. Copyright © 2015 John Wiley &amp; Sons, Ltd.

How efficiently do corn‐ and soybean‐based cropping systems use water? A systems modeling analysis

Agricultural systems are being challenged to decrease water use and increase production while climate becomes more variable and the world's population grows. Low water use efficiency is traditionally characterized by high water use relative to low grain production and usually occurs under dry conditions. However, when a cropping system fails to take advantage of available water during wet conditions, this is also an inefficiency and is often detrimental to the environment. Here, we provide a systems-level definition of water use efficiency (sWUE) that addresses both production and environmental quality goals through incorporating all major system water losses (evapotranspiration, drainage, and runoff). We extensively calibrated and tested the Agricultural Production Systems sIMulator (APSIM) using 6 years of continuous crop and soil measurements in corn- and soybean-based cropping systems in central Iowa, USA. We then used the model to determine water use, loss, and grain production in each system and calculated sWUE in years that experienced drought, flood, or historically average precipitation. Systems water use efficiency was found to be greatest during years with average precipitation. Simulation analysis using 28 years of historical precipitation data, plus the same dataset with ± 15% variation in daily precipitation, showed that in this region, 430 mm of seasonal (planting to harvesting) rainfall resulted in the optimum sWUE for corn, and 317 mm for soybean. Above these precipitation levels, the corn and soybean yields did not increase further, but the water loss from the system via runoff and drainage increased substantially, leading to a high likelihood of soil, nutrient, and pesticide movement from the field to waterways. As the Midwestern United States is predicted to experience more frequent drought and flood, inefficiency of cropping systems water use will also increase. This work provides a framework to concurrently evaluate production and environmental performance of cropping systems.

Effects of permethrin and amitraz on gas exchange and water loss in unfed adult females of Amblyomma americanum (Acari: Ixodidae)

Effects of two acaricides, permethrin and amitraz, with different modes of action, on gas exchange and water balance of the lone star tick, Amblyomma americanum, were examined using a flow-through carbon dioxide (CO2) and water vapor analyzer. Untreated adult female ticks exhibited a distinct discontinuous gas exchange pattern (DGEP) with no measurable water loss. Similarly, ticks with acetone (a solvent) showed little change in gas exchange and water loss. Topical treatment of ticks with a lethal dose of permethrin caused immediate major water loss and long-lasting high frequency DGEP, with increased amplitude of CO2 release. A small water loss spike was observed for each CO2 release. Treatment of ticks with amitraz abolished the DGEP and elicited a long-lasting continuous gas exchange pattern, indicating significantly increased tick metabolism. No detectable water loss was observed during amitraz-elicited continuous gas exchange. Treatment of ticks with a mixture of sub-lethal doses of permethrin and amitraz caused a similar initial major water loss, as in permethrin-treated ticks, followed by a second period of water loss activity at 10–14h after treatment. Mixture of the two acaricides caused immediate onset of major chaotic CO2 release activities with a significantly elevated baseline CO2 emission level. The standard metabolism rate (SMR, VCO2) of acetone-treated ticks (0.452μlh−1) was similar to that of the untreated ticks (0.461μlh−1). Compared to untreated control ticks, permethrin-, amitraz-, and the acaricide mixture-treated ticks exhibited significantly increased SMR (1.054, 1.392 and 1.520μlh−1 respectively (P<0.05). Results obtained from this study clearly demonstrated the detrimental effects of permethrin and amitraz on CO2 gas exchange and water balance in A. americanum ticks. The data also revealed subtle differences between permethrin and amitraz in their effects on tick metabolism, specifically gas exchange and water loss. In addition, the study may provide insight into the modes of action of these two acaricides in tick physiology. The results may also help understand the mechanism of synergism between permethrin and amitraz that was reported previously in other ticks and insects.