Sediment‐bound nutrient export from micro‐dam catchments in Northern Ethiopia

Abstract

The losses in soil nutrients (nitrogen (N), available phosphorus (P av ), organic carbon (OC), potassium (K), calcium (Ca) and magnesium (Mg)) in the catchment and the storage in the reservoir as a result of sediment delivery were assessed in 13 catchments/reservoirs in Tigray, Northern Ethiopia. This specifically dealt with factors controlling the losses, the fertility status of the deposited sediment, the nutrient export (NE) rates and associated costs.Enrichment ratio (ER) values >1 were observed for the plant nutrients and the finer soil fractions. The high ER is associated with the preferential transport of nutrients bound to finer soil fractions and the parent material dissolution and its transport via runoff. However, the fertility status of the deposited sediment is not sufficient by itself to support a sustainable crop growth and hence external addition is necessary, mainly for N and P av fertilizer.Generally, rates of NE were high. The high OC export on the other hand dictates the potential of reservoir sediments for OC sequestration. The cost price of loss of only N and P av , eroded from the catchment slopes, was estimated at s34Á2 million (Euros) in March 2006 for the Tigray. Pity enough, policy makers and beneficiaries do not realize the magnitude of the problem, which forms a major threat for the crop production in the country. Therefore, it is important not only to make the public aware of the problem but also of implementing integrated soil fertility management practices.

Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands – towards a sediment budget

“…This is within the range of sediment yields measured in other catchments in the Tigray highlands (1·9 -18·2 t ha −1 y −1 ), using reservoir sedimentation rates (Nigussie et al, 2007). The sediment delivery ratio…”

Sediment yield as a desertification risk indicator

“…Fonseca et al (1998) investigated the trapped sediments of two reservoirs in Portugal and found that sediments of both reservoirs had high nutrient levels, with values exceeding those of the original soils. Haregeweyn et al (2008) report similar results for 13 reservoirs in the semi-arid northern Ethiopian highlands, where sediments from the reservoirs were richer in nutrients than the original soils from where they eroded. This enrichment in nutrients is associated with the preferential transport of nutrients bound to finer soil fractions and the dissolution of parent material and its transport via runoff ).…”

“…Furthermore, the nutrient-rich sediments in reservoirs can cause eutrophication and water quality problems, particularly in drinking water reservoirs (Lahlou 1996;Fonseca et al 1998). Dredging the sediments and using it as fertilizer could provide a solution, if this is economically feasible (Fonseca et al 1998;Haregeweyn et al 2008) yet only if concentrations of pesticides and herbicides are within acceptable ranges! !.…”

Calibración y aplicación de un modelo de erosión y dinámica del carbono (SPEROS-C) a doce pequeñas cuencas del sureste español

“…los flujos laterales de C. Jacinthe et al, 2004;Moorman et al, 2004;Haregeweyn et al, 2008;Starr et al, 2008;Boix-Fayos et al, 2009;Juárez et al, 2011).…”