Phosphorus Transport in Intensively Managed Watersheds

An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.Understanding controls of P movement through watersheds are essential for improved landscape management in intensively managed regions. Here, we analyze observational data from 104 gaged river sites and 176 nongaged river sites within agriculturally dominated watersheds of Minnesota, USA, to understand the role of landscape features, land use practices, climate variability, and biogeochemical processes in total, dissolved and particulate P dynamics at daily to annual scales. Our analyses demonstrate that factors mediating P concentration‐discharge relationships varied greatly across watersheds and included near‐channel sediment sources, lake and wetland interception, assimilation by algal P, and artificial land drainage. The majority of gaged sites exhibited mobilizing behavior for all forms of P at event (i.e., daily) timescales and chemostatic behavior at annual timescales. The large majority of watershed P export (>70%, on average) occurred during high flow conditions, suggesting that more frequent large storm events arising from climate change will drive increased P losses from agricultural watersheds without substantial management changes. We found that P export could be dominated by dissolved P, particulate P, or an even mix of the two forms, depending on watershed attributes. Implementation of management practices to control P losses must be guided by understanding of how local landscapes interact with current and future climate conditions. Managing for both dissolved and particulate P is required to reduce overall P load in many agricultural watersheds

Lessons Learned from Flood Management in Iran

Iran has a longstanding challenge in supplying water during prolonged drought periods. This has drawn considerable attention towards the dam industry over the past four decades, leading to the study, construction and operation of several large dams. These dams played a critical role in controlling the massive floods of 2019 and 2020, among others. Nevertheless, due to the increased intensity and frequency of extreme events because of climate change, the downstream regions of these large storage dams still face significant damages. This is mainly attributed to the insufficient dredging of rivers and tributaries, lack of rule curve and operation guideline for some storage dams, inaccurate prediction of flood volume, violation of land-use and water management action plans, promotion of industries with high water need, and floodplain encroachment. In this study, we aim to evaluate the performance of several large dams in the Karkheh and Karoon river basin, located in southwestern Iran, in managing the floods took place in the aforementioned periods. We also discuss the challenges and the lessons learned, with suggestions for improving the flood management in the country

Conflict Resolution of Water Resources Allocations Using the Game Theoretic Approach: The Case of Orumieh River Basin

During recent years, unavoidable consequences of increased demand for, and decreased supply of, various natural resources, especially water, have caused increased conflict over their exploitation and also allocation to different stakeholders. Water allocations merely based on a water rights approach usually do not make efficient use of water for the whole river basin. Thus, there is a need for a comprehensive and stable allocation method that can satisfy all involved interest groups in the best manner. One of these methods is game theory that can be used to allocate the water resources among riparian parties regarding principles of equity, efficiency and sustainability. In this study, first a comprehensive linear programming model has been developed to achieve the optimal allocation pattern based on the initial water rights of stakeholders. Then, by using the results of the water planning model combined with the game theoretical concepts  such as the Core, the Shapely Value, and, the Gately propensity to disrupt index, possible cases of cooperation among riparian parties have been evaluated. Finally, through the case study of the Orumieh River Basin in Iran with scarce water resources and multiple users, effectiveness and potential advantages of this approach have been shown. The results of the optimization model showed that the Kordestan province has the best situation in supplying its demands relative to the other provinces and in contrast, the East Azarbayejan has the most deficiency in supplying its demands in both agriculture and environmental sectors. Moreover, by following the given allocation pattern, the amount of water entering the Lake Orumieh will be more than its environmental demand during the planning. Therefore, the results of this study showed that cooperative game theory can be applied successfully to assess the cases of cooperation in the Orumieh River Basin in conjunction with a comprehensive water planning model

Time-Variant Lagrangian Transport Formulation Reduces Aggregation Bias of Water and Solute Mean Travel Time in Heterogeneous Catchments

AbstractLack of hydro‐bio‐chemical data at subcatchment scales necessitates adopting an aggregated system approach for estimating water and solute transport properties, such as residence and travel time distributions, at the catchment scale. In this work, we show that within‐catchment spatial heterogeneity, as expressed in spatially variable discharge‐storage relationships, can be appropriately encapsulated within a lumped time‐varying stochastic Lagrangian formulation of transport. This time (variability) for space (heterogeneity) substitution yields mean travel times (MTTs) that are not significantly biased to the aggregation of spatial heterogeneity. Despite the significant variability of MTT at small spatial scales, there exists a characteristic scale above which the MTT is not impacted by the aggregation of spatial heterogeneity. Extensive simulations of randomly generated river networks reveal that the ratio between the characteristic scale and the mean incremental area is on average independent of river network topology and the spatial arrangement of incremental areas

Power of a Remote Hydrogen Bond Donor: Anion Recognition and Structural Consequences Revealed by IR Spectroscopy

Natural and synthetic anion receptors are extensively employed, but the structures of their bound complexes are difficult to determine in the liquid phase. Infrared spectroscopy is used in this work to characterize the solution structures of bound anion receptors for the first time, and surprisingly only two of three hydroxyl groups of the neutral aliphatic triols are found to directly interact with Cl^–. The binding constants of these triols with zero to three CF₃ groups were measured in a polar environment, and <i>K</i>_CD₃CN(Cl^–) = 1.1 × 10⁶ M^–1 for the tris­(trifluoromethyl) derivative. This is a remarkably large value, and high selectivity with respect to interfering anions such as, Br^–, NO₃^– and NCS^– is also displayed. The effects of the third “noninteracting” hydroxyl groups on the structures and binding constants were also explored, and surprisingly they are as large or larger than the OH substituents that hydrogen bond to Cl^–. That is, a remote hydroxyl group can play a larger role in binding than two OH substituents that directly interact with an anionic center