Agricultural Returns Research Articles

Will there be water? Climate change, housing needs, and future water demand in California

Climate change in California is expected to alter future water availability, impacting water supplies needed to support future housing growth and agriculture demand. In groundwater-dependent regions like California's Central Coast, new land-use related water demand and decreasing recharge is already stressing depleted groundwater basins. We developed a spatially explicit state-and-transition simulation model that integrates climate, land-use change, water demand, and groundwater gain-loss to examine the impact of future climate and land use change on groundwater balance and water demand in five counties along the Central Coast from 2010 to 2060. The model incorporated downscaled groundwater recharge projections based on a Warm/Wet and a Hot/Dry climate future from a spatially explicit hydrological process-based model. Two urbanization projections from a parcel-based, regional urban growth model representing 1) recent historical and 2) state-mandated housing growth projections were used as alternative spatial targets for future urban growth. Agricultural projections were based on recent historical trends from remote sensing data. Annual projected changes in groundwater balance were calculated as the difference between land-use related water demand, based on historical estimates, and climate-driven recharge plus agriculture return flows. Results indicate that future changes in climate-driven groundwater recharge, coupled with cumulative increases in agricultural water demand, result in overall declines in future groundwater balance, with a Hot/Dry future resulting in cumulative groundwater decline in all but Santa Cruz County. Cumulative declines by 2060 are especially prominent in San Luis Obispo (−2.9 to −5.1 Bm3) and Monterey counties (−6.5 to −8.7 Bm3), despite limited changes in agricultural water demand over the model period. These two counties show declining groundwater reserves in a Warm/Wet future as well, while San Benito and Santa Barbara County barely reach equilibrium. These results suggest future groundwater supplies may not be able to keep pace with regional demand and declining climate-driven recharge, resulting in a potential reduction in water security in the region. However, our county-scale projections showed new housing and associated water demand does not conflict with California's groundwater sustainability goals. Rather, future climate coupled with increasing agricultural groundwater demand may reduce water security in some counties, potentially limiting available groundwater supplies for new housing.

Hydrogeologic and hydrochemical inputs to emerging wetlands on the shores of the receding Salton Sea, California

AbstractThe Salton Sea has experienced significant recession over the past two decades due to changes in the diversion of Colorado River water to the Salton Trough for agricultural irrigation. As a result, wetlands have emerged in some exposed playa areas along the Salton Sea, primarily in regions with extensive agricultural return flows and agricultural drainage. One notable wetland system, known as the Bombay Beach Wetlands, has formed on the north shore of the Salton Sea, in an area devoid of agriculture. In many other areas with limited or no agriculture, wetlands have failed to develop, leaving exposed playa surfaces as the Salton Sea recedes. These dry playa surfaces pose a significant threat to the health of local residents due to the presence of toxins contained in windblown dust associated with playa deposits. In this study, stable water isotope data, combined with other hydrological information, led to identification of two potential water sources for the Bombay Beach Wetlands. The first possibility proposes that thermal artesian waters alone contribute to the wetlands' water source, while the second hypothesis involves a combination of drainage from Salton Sea bank storage water mixing with the thermal artesian water. The thermal artesian water discharges into drainage channels that flow towards the Bombay Beach Wetlands, initially devoid of possible groundwater baseflow until reaching the wetlands. Studies were subsequently done along the full reach of the drainage channels receiving thermal artesian water. Dissolved solids content, P and N nutrients, arsenic, and stable water isotopes were tested synoptically along the drainage channels. Channel investigations led to the development of a novel model of salinization, which is linked to channel discharge, channel morphometrics, and channel incision.

Evaluation of the Effect of Agricultural Return Flow on Water Quality, Water Quantity and Aquatic Ecology in Downstream Rivers

Agricultural water serves various functions, including public interest purposes, beyond its primary role in agricultural production. In order to evaluate the various public interest purposes of agricultural water, a quantified study of the effect of agricultural water on river flow, water quality, and aquatic ecosystems is needed. Therefore, this study quantified the impact of agricultural water on the environmental and ecological maintenance function of downstream rivers, taking into account the return flow of agricultural water in rural areas. To this end, first, the effect of agricultural return flow on river maintenance function was evaluated by comparing the return flow quantity calculated using the reservoir supply data with the simulated river flow rate through the SWAT model. Second, the effect of the agricultural return flow on the downstream river environmental ecological function was analyzed using the optimal flow rate results calculated through the PHABSIM model. The lastly, the effect of agricultural water by farming period on the water quality of downstream rivers was analyzed. As a result of the analysis, it was found that the return flow of agricultural water had a large effect on the river flow rate in the case of the non-rainy season, but the optimal ecological flow rate was not satisfied. In the case of river water quality, it was confirmed that the effect of agricultural water (mainly considered as a pollutant) was not significant, except for the drainage duration of rice paddies. Therefore, it can be understood that agricultural water is not only used for the purpose of production but can also have a positive impact on the aquatic ecology of downstream rivers.

Analyzing the effect of severe weather on farmers' fertilizer usage and input investment amidst decreasing productivity in single-season agroecosystems

IntroductionIn Ghana and comparable developing countries, advancing farm investments and adopting innovative rice farming techniques encounters obstacles because of climate change. Smallholder farming households, affected by climate events, confront substantial risks that affect both agricultural returns and investment decisions.MethodsThis research evaluates the enduring impact of fluctuating weather patterns in a single-cropping agroecological region on rice yields, examining the consequent influence on the utilization of inorganic fertilizers and agricultural input investment among rain-fed households, investigating disparities, reasons, and underlying mechanisms. The research used panel data from 60 communities, employing regression analysis and probability models. It integrated monthly cropping season weather data across the study zone's grid cells for community-level time series analysis.Results and discussionThe results suggest that while weather shocks have a minimal impact on farmers abandoning inorganic fertilizers altogether, they do significantly decrease the overall amount of fertilizer used, agricultural investments, and rice crop yields. Floods and severe shocks exert a more pronounced influence compared to droughts and moderate shocks. Off-farm employment aids households in recovering from these shocks and maintaining agricultural investments. Climate shocks impact agricultural investment by reducing farm household income via altering crop yield and revenue. Consequently, this disrupts their ability to save, resulting in financial constraints. Encouraging and sustaining farm investments in vulnerable agrosystems involves diversifying income sources through combined crop and livestock farming, supplemented by off-farm activities. This strategy is fortified by climate-resilient farming practices, including resilient crop varieties supported by irrigation, weather insurance, and risk-oriented credit.

Distribution of Groundwater Hydrochemistry and Quality Assessment in Hutuo River Drinking Water Source Area of Shijiazhuang (North China Plain)

The Hutuo River Drinking Water Source Area is an important water source of Shijiazhuang (North China Plain). Knowing the characteristics of groundwater chemistry/quality is essential for the protection and management of water resources. However, there are few studies focused on the groundwater chemistry evolution over the drinking water area. In this study, total of 160 groundwater samples were collected in November 2021, and the spatial distribution of groundwater chemistry and related controlling factors were analyzed using hydrological and multivariate analysis. The entropy-weighted water quality index (EWQI) was introduced to assess the groundwater quality. The results show that the hydrogeochemical types of groundwater are Ca-HCO3 (78.1%), mixed Ca-Mg-Cl (20%), and Ca-Cl (1.9%) in the area. Graphical and binary diagrams indicate that groundwater hydrochemistry is mainly controlled by water–rock interaction (i.e., rock weathering, mineral dissolution, and ion exchange). Five principal components separated from the principal component analysis represent the rock–water interaction and agricultural return, redox environment, geogenic sources, the utilization of agricultural fertilizer, the weathering of aluminum silicates, and dissolution of carbonates, respectively. More than 70% of the samples are not recommended for irrigation due to the presence of high salt content in groundwater. EWQI assessment demonstrates that the quality of the groundwater is good. The outcomes of this study are significant for understanding the geochemical status of the groundwater in the Hutuo River Drinking Water Source Area, and helping policymakers to protect and manage the groundwater.

Novel Fe/Ca oxide co-embedded coconut shell biochar for phosphorus recovery from agricultural return flows.

Efficient elimination and recovery of phosphorus from agricultural return flows are crucial for effective eutrophication management and phosphorus reuse. In this study, a neutral Fe/Ca oxide co-embedded biochar (FCBC) was synthesized using calcium peroxide and ferrous chloride as precursors for phosphate recovery from agricultural return flows. FCBC possesses a highly intricate pore structure and an abundance of surface-active groups. Fe/Ca oxides were loaded onto the biochar in the form of Ca2Fe2O5, Fe2O3, and CaCO3. FCBC demonstrated a broad pH tolerance range (pH = 6-12) in the aquatic environment. The maximum saturation adsorption capacity was 53.31 mg g-1. Phosphorus removal is influenced by Ca3(PO4)2 generation, intra-particle diffusion, and electrostatic attraction. The produced FCBC showed exceptional phosphorus removal efficiency in the presence of various anions, except for wastewater with high concentrations of SO4 2-, CO3 2-, HCO3 -, and F- (>500 mg L-1). FCBC can effectively remove phosphorus from agricultural return flows and reduce the risk of the water environment. Returning it to the field can also mitigate the depletion of phosphorus resources, effectively reduce carbon emissions from farmland, improve soil fertility, and realize multiple benefits.

Extreme heat and rural household adaptation: Evidence from Northeast China

More extreme heat events are expected under climate change, posing threats to food production as well as the lives of agriculture-dependent rural households. Using a detailed panel of rural households in an agricultural region of China, we find extreme heat substantially decreases crop production and lowers households’ agricultural returns. Nevertheless, the households successfully smooth their consumption contemporaneously by utilizing precautionarily saved buffers (liquid financial assets and crop stocks), especially among those who regularly hold these buffers. Their future expenditures are also largely unaffected. This adaptability of consumption smoothing discourages within-season adjustments in variable inputs and productive assets. Still, extreme heat guides impacted households toward a more diverse but less risky crop portfolio in later years.

Analyzing spatial patterns and driving factors of cropland change in China's National Protected Areas for sustainable management

Farming in protected areas frequently challenges ecological conservation goals while supporting local livelihoods. To balance protection and agriculture, a comprehensive understanding of cropland dynamics in protected areas is of paramount importance. However, studies addressing this trade-off are relatively scarce, especially considering explicit Chinese government regulations on population relocation and cropland retirement in National Protected Areas (NPAs). Our study examined the spatial and temporal pattern of cropland in NPAs and explored the covariance between cropland density and species richness. Concurrently, the driving factors of cropland development in NPAs were analyzed using Multiple Linear Regression. The results indicate that the cropland area in NPAs continued to expand, growing from 1.93 to 2.34 million hectares in 2000–2020, with a cropland density of approximately 0.4. Cropland expansion in the northern NPAs, particularly in the resource-rich Northeast (28.12 %) and the Northwest with high marginal agricultural returns (38.26 %), have encroached upon species habitats and aggravated biodiversity loss. Moreover, cities with higher cropland densities in NPAs are usually located at borders, possibly due to decentralized management. The Multiple Linear Regression results show that high cropland density is usually associated with a high population density (β = 0.156) and lower levels of rural education (β = −0.101) and income (β = −0.122). To mitigate the issue of cropland development in NPAs, it is crucial to avoid one-size-fits-all management strategies, strengthen regional legal supervision, adjust fiscal incentives, and promote eco-friendly agriculture. In the north regions, the expansion of cropland in NPAs should be strictly controlled. For the southwest, the positive role of preserving cropland in NPAs for alleviating human-nature conflict and maintaining social stability should be emphasized. This study provides research support for China's exploration of geographically suitable strategies for controlling cropland in NPAs. Moreover, the findings could serve as a reference for the governance of NPAs in other countries.

Water quality mitigation strategy analysis of the Salton Sea, California, using the Delft-3D modeling suite

The Salton Sea is the largest lake in California and is a shallow, hypersaline lake. The endorheic lake has been significantly maintained by agricultural return flows from Imperial Valley farming and two rivers- the New River and Alamo River- which originate in Mexicali, Mexico. The current salinity is at 74 ppt and is expected to increase due to the Quantification Settlement Agreement signed in 2003, stipulating the transfer of nearly 0.616 km3 per year of Colorado River water to urban areas for up to 75 years. This has resulted in inflows reduction, and the dust storms created by the dried-up playa have become a prominent risk to public health in the region. Massive fish and bird kills began in the 1980s and continued to occur periodically. In this study, the Delft3D numerical modeling suite- FLOW, WAVE, and WAQ- was utilized to investigate the transport and cycling of nutrients under the influence of wind-induced sediment resuspension activity. The three-dimensional hydrodynamic and water quality combined model was applied to simulate mitigation scenarios to assess long-term effects on salinity and water quality of (1) emerged islands as a nature-based solution, (2) seawater import/export, and (3) seawater import/export in addition to treating tributary rivers to remove nutrients. Overall, this study supported the findings from previous studies and showed that sediment resuspension is the driving force for nutrients cycling in the water column and that emerged islands have long-term potential to enhance burial activity for pollutants removal in the Salton Sea. Furthermore, the seawater import/export scenario showed promising results of reducing salinity level from 46 ppt to 38–39 ppt in 2 years. The 3D numerical hydrodynamic/water quality model developed in this work is the first and latest integrated modeling approach tailored to the Salton Sea's system and has the capacity to improve understanding of the complicated water quality dynamics changes in various restoration concepts. This study demonstrated that being able to explore the full potentials of restoration designs using a comprehensive 3D water quality modeling framework is critical in achieving wholesome planning that will create environmental, social, and economic benefits in the long term for the Salton Sea.

Assessment of the current state of the hydrochemical regime and water-environmental problems of the basin of the Gavaraget River flowing into Lake Sevan

The results of studies of the current hydro-chemical state and water-ecological problems of the Gavaraget River basin, which flows into Lake Sevan from the north-west, are presented. Extreme water discharge, ten-day flow, ecological output have been determined, water-ecological features have been identified, long-term dynamics of the main indicators characterizing the ecological state of the Gavaraget River, spatial-temporal changes in winter and summer-autumn ten-day flow have been shown, the hydro-chemical state has been presented, the main water-ecological problems of this basin and ways to solve them were proposed, the physical and chemical state of Gavaraget water was clarified in accordance with the standards and requirements for water quality, and the level of risk was indicated. It has been clarified that the annual runoff in the basin basically follows the general features of the annual precipitation regime: the minimum amount falls in winter, and the maximum in spring. It is shown that Gavaraget is one of the most polluted rivers in the Lake Sevan basin. It was revealed that it is mainly contaminated with untreated domestic wastewater and agricultural return water. It was found that as the impact of anthropogenic load increases, river water pollution increases from the source to the mouth of the river. The water quality in the upper part of Gavaraget (0.5 km upstream from the village of Tsaghkashen) is excellently characterized as “excellent” (I) and “good” (II), in the lower part (at the river mouth) with “moderate” (III) and “unsatisfactory” (IV) class. The research results can be useful in solving geo-ecological problems, managing aquatic ecosystems, determining ecological flow, assessing risks, predicting water disasters, protecting river ecosystems from degradation, etc.

Research on the Influence of the Law of Diminishing Marginal Returns in Agriculture

Agriculture is the primary industry in China and plays a vital role in the country's economic construction. In the process of developing agriculture, there are many scientific methods and laws that need to be followed in order to increase crop yield, reduce costs, and thus obtain more profits. The law of diminishing marginal returns is a widely used theory in the agricultural field. This paper studies the embodiment and influence of the law of diminishing marginal returns on some important factors in agricultural production. The research method adopted is empirical research. The study concluded that the planting density, the number of labor and the amount of fertilizer applied in agriculture largely follow the law of diminishing marginal returnsblindly increasing the above factors will not maximize the benefit, but will make the total profit negative growth. Therefore, it must be combined with the actual production situation, control its use in agricultural production, so as to maximize the profit, that is, the marginal revenue brought by the input is equal to its marginal cost.

Development of a portable DNA extraction and cross-priming amplification (CPA) tool for rapid in-situ visual diagnosis of plant diseases

Plant pathogens cause severe losses to crop yields and economic returns in agriculture. Despite plant tissue DNA extraction of typically constituting a preliminary step in nucleic acid-based molecular diagnostics, such lab-based methods can be time-consuming and arduous to complete many samples. To mitigate these challenges, we developed an inexpensive portable DNA extraction technique that is lightweight and suitable for deployment in sampling locations, such as fields. It includes a DNA extraction device fabricated with a Steel Microneedle Array (SMA) and a simple high-efficiency DNA extraction buffer. As a result, DNA extraction times can be reduced to within ~ 1 min, and the eluted DNA is demonstrated to be suitable for subsequent molecular biological analyses without requiring additional purification. Cross-priming amplification (CPA) technology was first established to detect Phytophthora infestans, which achieves sensitivity attainment of 10–7 ng/µL. The detection result can be conveniently estimated with naked-eye visual inspection using fluorescent dsDNA binding dye. CPA was demonstrated to be more feasible than PCR-based approaches and performed well in species-specific and practicability tests. This study elucidates a novel integrated pathogen detection technique coupled with SMA-Device extraction and a modified visual CPA assay to establish and verify various field-based samples infected with multiple pathogens. Altogether, the total sample-to-answer time for pathogen detection was reduced to ~ 1.5 h, making field-based analysis affordable and achievable for farmers or extension workers inside and outside the laboratory.

Application of the practical salinity scale to the waters of San Francisco estuary

The Practical Salinity Scale 1978 (PSS-78)—developed using samples of standard seawater—is widely used as a conductivity-based measure of salinity in oceans and estuaries. Here we evaluate the application of the scale across San Francisco Estuary where salinity reflects a mixture of seawater, riverine inflows, and agricultural return flows from islands within the estuary. We employ an extensive salinity data set that includes measurements of specific electrical conductance (EC) and major ion concentrations to demonstrate the scale's applicability in this estuary. We find the scale to be valid in waters dominated by seawater intrusion as well as in waters dominated by the largest riverine input to the estuary, i.e. the Sacramento River. In these waters, we further find that the scale to be valid well below its recommended lower-bound value of 2.0. However, the scale under-estimates salinity in waters dominated by the San Joaquin River, the second largest riverine input to the estuary. Similarly, the scale under-estimates salinity in agricultural return flows to the estuary. This work shows that a singular PSS-78 relationship cannot be used to accurately compute salinity across the entire estuary from EC measurements—a finding of considerable importance for salinity monitoring and modeling applications. Using data from the estuary, we propose appropriate corrections to the scale for these drainage-influenced waters. We recommend further research into how these modified PSS-78 formulations can be used to more accurately estimate salinity and ionic constituent concentrations in this and other estuaries.

Unraveling the paleo-marine signature in saline thermal waters of Cambay rift basin, Western India: Insights from geochemistry and multi isotopic (B, O and H) analysis

Cambay rift basin is the only geothermal province in India that hosts several saline thermal water manifestations having EC values varying from 525 to 10,860 μS/cm. Various ionic ratios (Na/Cl, Br/Cl, Ca/(SO4 + HCO3), SO4/Cl) as well as boron isotopic composition (δ11B = 40.5 to 46 ‰) clearly ascribes the presence of fossil (relics of evaporated seawater) seawater as origin of increased salinity in the majority of thermal waters. Depleted isotopic (δ18O, δ2H) composition of these thermal waters also substantiates the presence of paleowater in these systems. In rest of the thermal waters, agricultural return flow is found to be source of dissolved solutes as confirmed from different bivariate plots such as B/Cl vs. Br/Cl and δ11B vs. B/Cl as well as from ionic ratios. This study thus provides the diagnostic tools to elucidate the source of variable salinity in the thermal waters circulating in the Cambay rift basin, India.

The Impact of Climate Change on Risk and Return in Indian Agriculture

We investigate the extent to which climate change will result in insurable and uninsurable losses for farmers in India. Changes in temperature and precipitation patterns may increase the volatility of farmers’ yields, leading to rising but insurable risk. These changes may also reduce the expected yield in an ‘average year’, causing uninsurable reductions in the returns to farming. We use a multi-run climate model to predict the future distribution of potential yields at the district level for sixteen major crops. For the average district, we project a sharp decline in expected agricultural revenue, but small shifts in volatility. This is because weather draws resulting in extremely low agricultural returns—what had once been 1-in-100-year events—are predicted to become the norm by the end of the century. Our projections therefore imply substantial uninsurable losses from the changing climate for Indian farmers.

Evolution of salinity in the Gaza Strip over the last five decades deduced from field data

Gaza coastal aquifer has been exposed to severe overexploitation to meet the human needs for water supply. This exploitation has resulted in lowering of the groundwater level to by more than 15 m below mean sea level in the south and around 5 m in the north. Groundwater level drop has exposed the aquifer to seawater intrusion and inland saline upconing in the central south and south-east of the Gaza Strip.We developed five cross sections based on wells drilled over the past five decades representing aquifer stratigraphy in the five governorates (North, Gaza, Deir El Balah, Khan Younis and Rafah) of the Gaza Strip. Those cross sections have been used to map the chloride concentration over the past five decades (years 1972, 1980, 1990, 2000, 2010, 2017 and 2021).The results show three main sources of aquifer salinity: (1) seawater intrusion, (2) lateral inflow from Eocene rocks in the east and/or from agricultural return flow as a result of using treated wastewater for irrigation in Israel close to the eastern border and (3) upconing due to fossil marine salt water trapped at the bottom of the aquifer. The clay layers which are subdividing the aquifer have caused a difference in sub-aquifer level chloride difference. Before the year 2000, the public water supply wells were placed far away from the sea and no seawater intrusion was noticed especially in the south of Gaza Strip (Khan Younis and Rafah governorates), while afterwards public water supply wells appeared within 2 km from the Mediterranean Sea. From then on, seawater intrusion has been taking place due to heavy groundwater abstraction. Also, lateral inflow with chloride concentrations of more than 1,000 mg/l is well noticed during the different years, related to eastern inflow from Eocene rock formation where the coastal aquifer rests directly on it, 10–15 km from the coast. Inland areas with high chloride contents were observed as a result of upconing from deep saline groundwater. Cumulative Distribution Function (CDF) curves were created for all wells in each cross section and showed a remarkable shrinkage of freshwater percentage in the aquifer.

Water quality stress to Amirkalayeh Wetland, Northern Iran

Amirkalayeh Wetland, listed aswetlands of International Importancein the Ramsar Convention, exposes to severe water quality stress resulted from increase in dissolved ions and nutrients concentrations. In addition to in situ measurements of physicochemical parameters (electrical conductivity, pH, and temperature), a total number of 28 water samples were collected from Amirkalayeh Wetland and surrounding surface and groundwater resources to investigate the most important factors increasing trophic state and decreasing the water quality of the wetland. Water samples were analyzed for major ions and dissolved plant nutrients (nitrate, nitrite, ammonium, and phosphate). Up to three-time increase in salinity and dramatic rising in nutrients level was observed in Amirkalayeh Wetland from 2017 to 2021. The excessive nutrients intake resulted in hyper-eutrophication trophic status of Amirkalayeh Wetland. Our hydrological, hydrochemical, and statistical studies investigating the role of a variety of possible water quality degrading factors show that surface and subsurface drainage of agricultural return water into the Amirkalayeh Wetland are the major cause of increase in trophic level and decreasing water quality. Results of this work indicate that Amirkalayeh Wetland is exposed to severe water quality stress that threatens the aquatic life and ecosystem of this wetland. Therefore, preventing the inflow of surface and subsurface agricultural drains to the wetland and providing a sustainable water management plan are vital to improve water quality of the wetland.

Is wealth found in the soil or in the brain? Investing in farm people in Malawi

AbstractShould a typical developing country invest more in agriculture or education? At what stage of development is it optimal to invest more in each of these sectors? These are important questions that governments of developing countries grapple with when designing investment plans. In this paper, I propose a soil–human capital conceptual framework of development and use it to explain estimates of agricultural returns to schooling in Malawi. I use panel survey data for Malawi and rely on the exogenous education policy changes and spatial variation in access to schooling to identify effects of schooling on agricultural incomes. In addition, I correct for selection into income activities within a panel data and instrumental variables estimation framework. I find annual agricultural returns to schooling in Malawi of 3%–4% after correcting for selection and unobserved heterogeneity and 7% in the uncorrected specifications. I also find consistently higher returns to schooling in the nonagricultural sector for those not living in the village of birth and higher returns in the agricultural sector for those living in the village of birth. Given the size of the farm sector, wealth in Malawi is still in the soil, but that future growth in wealth depends on human capital investments.

Featured Collection Introduction: Severe Sustained Drought Revisited: Managing the Colorado River System in Times of Water Shortage 25 Years Later — Part I

Featured Collection Introduction: Severe Sustained Drought Revisited: Managing the Colorado River System in Times of Water Shortage 25 Years Later — Part I

Quantity–quality-based water allocation programming in a reservoir–river system

Abstract Simulation–optimization approaches are useful methods for the assessment of water resource engineering plans and finding the best management policy at the watershed scale. In this study, to find the optimum operation for a reservoir with the purpose of satisfying water demands while meeting the water quantity and quality criteria, a generic reservoir and river basin simulation model (MODSIM) is coupled with the particle swarm optimization (PSO) algorithm leading to construct the PSO–MODSIM model. With the decision variables of the reservoir's monthly releases, the objective function is to maximize the supply for downstream demands while keeping the electrical conductivity (EC) in the river flow lower than a predefined level at the downstream checkpoint, which is a function of the EC in the agricultural return flows. Moreover, a safe flow rate is defined in which the streamflow should not exceed at the checkpoint resulting in mitigation of the submerging lands damage. Results obtained by the PSO–MODSIM model indicate the ability of the proposed simulation–optimization approach for solving the problem of optimal quantity–quality-based water allocation in a reservoir–river system. For instance, the EC at the checkpoint is decreased by 61% in the optimum reservoir operation state comparing the present situation, whereas the municipal and environmental demands are fully met and the agricultural demands are supplied with a desirable reliability satisfaction level.