To examine the impact of small reservoir irrigation development in Africa, the performance and productivity of two small reservoirs and irrigation schemes in the Upper East Region of Ghana were investigated in this study. Hydrologic data measured included daily irrigation volumes and daily evaporation. Farmer cost inputs, excluding labor, and harvest data were also recorded. There was a strong contrast in water availability between the two systems, the Tanga system having a higher amount of available water than did the Weega system. The concept of relative water supply was used to confirm this disparity; Tanga was an inefficient system with a relative water supply of 5.7, compared to a value of 2.4 for the efficient Weega system. It was also concluded that the dissimilar water availabilities resulted in the evolution of very different irrigation methods and coincided with different management structures. Where there was more water available per unit land (Tanga), management was relaxed and the irrigation inefficient. Where there was less water available per unit land (Weega), management was well structured and irrigation efficient. The productivity of water (US$ m À3 ) of the Tanga system was half that of the Weega system, when analyzed at a high market price for crops grown. In terms of productivity of cultivated land (US$ ha À1 ), however, the Tanga system was 49% more productive than the Weega system. The difference in the productivity of land is primarily a result of increased farmer cash inputs in the Tanga system as compared to the Weega system. The difference in the productivity of water can be attributed to the varying irrigation methods and management structures, and ultimately to the contrasting water availability. Tanga avait un système inefficace avec un taux d'approvisionnement relatif en eau de 5.7 comparé à un taux de 2.4 du système efficace de Weega. Il a été conclu que les différences au niveau de la disponibilité d'eau sont à la base d'une évolution de méthodes et s'accordent avec de concepts de gestion d'irrigation très contrastés. Quand il y avait plus d'eau disponible par unité de surface (Tanga), la gestion était peu organisée et l'irrigation moins efficace. Par contre, quand les ressources en eau étaient limitées (Weega) la gestion était bien structurée et l'irrigation très efficace. En termes d'eau les agriculteurs de Tanga recevaient seulement la moitié du bénéfice économique des agriculteurs de Weega quand le prix du marché était élevé pour les produits récoltés. Par contre, en termes de surface cultivée, les agriculteurs de Tanga faisaient 49% plus de profit par rapport aux agriculteurs de Weega. La différence du bénéfice économique de la terre cultivé est principalement une conséquence des investissements élevés des agriculteurs dans le système de Tanga comparé au système de Weega. La différence du bénéfice économique de l'eau peut être attribuée aux variations des méthodes d'irrigation et des structures de gestion et donc finalement aux disponibilités en eau très contrastées.

Phosphorus flux from agricultural landscapes to surface waters may cause eutrophication. In the northeastern United States, P transport largely depends on P sorption of soils in variable source areas or in land treatment systems. Soil redox fluctuation commonly occurs in these areas. Nevertheless, the effect of soil redox on P sorption has been variable in the literature. This study investigated P sorption of an organic‐rich northeastern glaciated silt loam (Langford) under air‐dried, field‐wet, and reduced conditions using batch P sorption experiments. Additionally, the influence of farm wastewater on soil P sorption was studied. Major results indicated that soil reduction increased the maximum amount of P that can be sorbed (Smax) and decreased the aqueous P concentration at which P sorption and desorption are equal (EPC0), both determined from a modified Langmuir isotherm model. The slightly reduced field‐wet soils had no significant difference in Smax due to limited soil reduction. Using the diluted wastewater as the sorption solution matrices instead of 0.01 mol L−1 KCl solution, the soils generally exhibited greater Smax and lower EPC0 except for the EPC0 of a reduced surface soil, implying more complex P sorption in the field. Identified P sorption mechanisms include phosphate precipitation, ligand exchange with organic matter, and adsorption onto Fe hydroxides. Transformation of Fe compounds during soil reduction is primarily responsible for the changes in soil P sorption.

No abstract

No abstract

Green stormwater infrastructure such as bioretention can reduce stormwater runoff volumes and trap sediments and pollutants. However, bioretention soil media can have limited capacity to retain phosphorus (P) or even be a P source, necessitating addition of P-sorbing materials. We investigated the potential trade-off between P removal by drinking water treatment residuals (DWTRs) and hydraulic conductivity to inform the design of bioretention media. Batch isotherm and flow-through column experiments showed that P removal varied greatly among three DWTRs and across methodologies, which has implications for design requirements. We also conducted a large column experiment to determine the hydraulic and P removal effects of amending bioretention media with solid and mixed layers of DWTRs. When DWTRs were applied to bioretention media, their impact on hydraulic conductivity and P removal depended on the layering strategy. Although DWTR addition in solid and mixed layer designs improved P removal, the solid layer restricted water flow and exhibited incomplete P removal, while the mixed layer had no effect on flow and removed nearly 100% of P inputs. We recommend that DWTRs be mixed with sand in bioretention media to simultaneously achieve stormwater drainage and P reduction goals.