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The Groundwater Ubiquity Score (GUS) is widely used to indicate the relative leachability of pesticides based on the soil half-life and the adsorption partition coefficient. In this manuscript, we derive mathematically the Theoretical Groundwater Ubiquity Score (TGUS) that, based on considerations of the preferential movement of pesticides to groundwater and a first-order pesticide degradation model, leads to a similar function as the GUS model. In the preferential flow model, movement to groundwater is fast, and the adsorption partition coefficient is thus not used for calculating the travel time to the groundwater (as it is in the advective-dispersive equation) but rather only determines the distribution of the pesticide between the water and soil phases. Both the GUS and TGUS models well predict the groundwater contamination of the originally studied pesticides for rainfall event(s) that caused pesticide leaching from 30 days after application. The theoretically derived Groundwater Ubiquity Score (TGUS) shows, in accordance with experimental evidence, that for leaching events shortly after spraying, the mass lost to (and resulting concentration in) groundwater is inversely related to the adsorption partition coefficient and not necessarily to the GUS index.

The highlands serve as water towers for the blue water in the surrounding area, with often insufficient rainfall for rainfed crops. The population is growing in the highlands, changing the hydrology and blue and green water availability. One of the changes that affect the highlands of Ethiopia is the rapidly expanding areas of small patches of eucalyptus on farmers fields. This manuscript aims to sort through the limited available literature and develop a water balance model as a starting point to discuss how hydrology is affected by increased acreage of eucalyptus in the highlands. We find some evidence in the literature that patches of eucalyptus during the dry phase may withdraw water from the subsoil up to twice the rate of evapotranspiration when the soil water is not limited. Since saturation excess generates surface runoff in the subhumid and humid highlands, water withdrawn during the dry phase should be made up before the area with eucalyptus becomes hydraulically active. The amount of water that can be removed from storage by eucalyptus is greater in areas with a long dry monsoon phase than in temperate climates for the same increase in trees. We also found, as expected, that the eucalyptus water balance model, as developed in this paper, was not valid for areas in semi-arid and arid regions. Soil crusting and water repellency might induce infiltration excess runoff. A tentative implication is that since most blue water is produced in the areas with the highest rainfall, eucalyptus in subhumid and humid monsoon regions will affect the blue water supply downstream but not the plant available green water although shading will decrease yield in the immediate surroundings of the eucalyptus trees.

Finding effective ecosystem services (ESS) management practices to counteract land degradation and poverty is becoming increasingly urgent in the Ethiopian highlands, where livelihood security is strongly dependent on local ESS, particularly those provided by water and soil. In this paper, we test the effects of widely implemented soil and water conservation (SWC) interventions on storm flow and sediment concentration in the Debre Mawi watershed (representative of watersheds in the upper Blue Nile basin and Ethiopian highlands). The SWC interventions were tested with a Parameter Efficient Distributed (PED) model. The PED model simulates saturation excess runoff from degraded and saturated valley bottoms, and base and interflow from hillsides. The model was calibrated with observed runoff and sediment data in a 95-ha subcatchment. We found that the PED model simulated the discharge and soil loss well by decreasing the proportion of degraded lands due to installing SWC practices. The results show that four years after the implementation of SWC practices, the infiltration of rainwater was improved in 53% of the degraded lands. Thus, installing SWC practices on hillsides where infiltration is limited is most beneficial and will result in greater water availability during the dry phase, especially in locations where volcanic dikes block the lateral flow. [ABSTRACT FROM AUTHOR]

The absence of a basin-wide apportionment agreement on using the Nile River equitably has been a long-standing source of disagreement among Nile riparian states. This study introduces a new approach that the riparian states can consider that quantifies the Nile River's apportionment. The approach includes (1) developing a basin-wide database of indicators representative of the United Nations Watercourse Convention (UNWC) relevant factors and circumstances, (2) developing an ensemble of indicator weighting scenarios using various weighting methods, and (3) developing six water-sharing methods to obtain a range of apportionments for Egypt, Sudan, Ethiopia and the group of the White Nile Equatorial States for each weighting scenarios. The results illustrate a relatively narrow range of country-level water apportionments, even though some individual factor weights vary from 3% to 26%. Considering the entire Nile River, the water apportionment for Ethiopia ranges from 32% to 38%, Sudan and South Sudan from 25% to 33%, Egypt from 26% to 35%, and the Equatorial States from 5% to 7%. We trust that the six proposed equitable water-sharing methods may aid in fostering basin-wide negotiations toward a mutual agreement and address the dispute over water sharing. [ABSTRACT FROM AUTHOR]

The importance of soils to society has gained increasing recognition over the past decade, with the potential to contribute to most of the United Nations' Sustainable Development Goals (SDGs). With unprecedented and growing demands for food, water and energy, there is an urgent need for a global effort to address the challenges of climate change and land degradation, whilst protecting soil as a natural resource. In this paper, we identify the contribution of soil science over the past decade to addressing gaps in our knowledge regarding major environmental challenges: climate change, food security, water security, urban development, and ecosystem functioning and biodiversity. Continuing to address knowledge gaps in soil science is essential for the achievement of the SDGs. However, with limited time and budget, it is also pertinent to identify effective methods of working that ensure the research carried out leads to real‐world impact. Here, we suggest three strategies for the next decade of soil science, comprising a greater implementation of research into policy, interdisciplinary partnerships to evaluate function trade‐offs and synergies between soils and other environmental domains, and integrating monitoring and modelling methods to ensure soil‐based policies can withstand the uncertainties of the future. Highlights: We highlight the contributions of soil science to five major environmental challenges since 2010.Researchers have contributed to recommendation reports, but work is rarely translated into policy.Interdisciplinary work should assess trade‐offs and synergies between soils and other domains.Integrating monitoring and modelling is key for robust and sustainable soils‐based policymaking. [ABSTRACT FROM AUTHOR]

Earth's water resources are critical for supporting livelihoods and food security but are being increasingly overexploited to support global agriculture. Diversifying cropping systems could potentially resolve unsustainable water use but trade‐offs with other aspects of sustainability and food security have not yet been assessed. We performed a detailed analysis of 31 different field crop rotations conducted during 1990–2019 in the North China Plain, to assess the potential impact of crop diversification on actual evapotranspiration (ETa), changes in regional groundwater table, grain yield, economic output, and water use efficiency (WUE) and to identify configurations that can achieve co‐benefits across multiple dimensions. We found that a combination of lowering the cropping index (i.e., harvest frequency), incorporating fallow periods, and introducing higher‐value crops into the currently dominant winter wheat–summer maize double cropping system can reduce growing season ETa by as much as 31%, mitigate groundwater decline by 19% or more, and increased economic output and economic WUE by more than 11% and 3%, respectively. We also found that multiple diversified wheat‐maize–based rotations—all with rotation lengths greater than 2 years—achieve co‐benefits across all evaluated dimensions. This study provides new empirical evidence of the opportunities for diversified crop rotations to balance the multiple objectives of food production, sustainable groundwater use, and farmer profitability. Extending this solution to other water‐stressed agricultural regions could be an effective strategy in achieving more sustainable food production system globally. [ABSTRACT FROM AUTHOR]

Agricultural production in the North China Plain with rainfall of less than 500 mm$yr-1 has been steadily increasing over the past 40 years, with the groundwater levels decreasing at a rate of over 1 m$yr-1. In this paper, it is demonstrated theoretically that the water level in the aquifer can be expressed as a function of agricultural production and the sum of water added as rainfall and imported from outside the basin. Therefore, the most effective measures to halt groundwater depletion are importing water, decreasing cropping intensity and growing less thirsty crops. Irrigation improvements, mulching and agronomic measures that could increase the yield per unit area have less of an impact on solving the declining groundwater levels. [ABSTRACT FROM AUTHOR]