The Akaki River, laden with untreated wastes from domestic, industrial, and commercial sources, serves as a source of water for irrigating vegetable farms. The purpose of this study is to identify the impact of waste-water irrigation on the level of heavy metals and to predict their potential mobility and bioavailability. Zn and V had the highest, whereas Hg the lowest, concentrations observed in the soils. The average contents of As, Co, Cr, Cu, Ni, Zn, V, and Hg of both soils; and Pb and Se from Fluvisol surpassed the mean + 2 SD of the corresponding levels reported for their uncontaminated counterparts. Apparently, irrigation with waste water for the last few decades has contributed to the observed higher concentrations of the above elements in the study soils (Vertisol and Fluvisol) when compared to uncontaminated Vertisol and Fluvisol. On the other hand, Vertisol accommodated comparatively higher average levels of Cr, Cu, Ni, Zn, etc V, and Cd, whereas high contents of Pb and Se were observed in Fluvisol. Alternatively, comparable levels of Co and Hg were found in either soil. Except for Ni, Cr, and Cd in contaminated Vertisol, heavy metals in the soils were not significantly affected by the depth (0-20 and 30-50 cm). When the same element from the two soils was compared, the levels of Cr, Cu, Ni, Pb, Se, Zn, V, Cd at 0-20 cm; and Cr, Ni, Cu, Cd, and Zn at 30-50 cm were significantly different. Organic carbon (in both soils), CEC (Fluvisol), and clay (Vertisol) exhibited significant positive correspondences with the total heavy metal levels. Conversely, Se and Hg contents revealed perceptible associations with carbonate and pH. The exchangeable fraction was dominated by Hg and Cd, whereas the carbonate fraction was abounded with Cd, Pb, and Co. conversely, V and Pb displayed strong affinity to reducible fraction, where as Cr, Cu, Zn, and Ni dominated the oxidizable fraction. Cr, Hg, Se, and Zn (in both soils) showed preference to the residual fraction. Generally, a considerable proportion of the total levels of many of the heavy metals resided in non residual fractions. The enhanced lability is generally expected to follow the order: Cd > Co > Pb > Cu > Ni > Se > V and Pb > Cd > Co > Cu > Ni > Zn in Vertisol and Fluvisol, respectively. For the similar wastewater application, the soil variables influence the status and the distribution of the associated heavy metals among the different soil fractions in the study soils. Among heavy metals that presented relatively elevated levels and with potential mobility, Co, Cu, Ni (either soil), V (Vertisol), Pb, and Zn (Fluvisol) could pose health threat through their introduction into the food chain in the wastewater irrigated soils.

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Parthenium weed (Parthenium hysterophorus L.), an invasive alien species, has been spreading at alarming rate in Ethiopia, causing biodiversity degradation, yield losses in field and horticultural crops, health problems to human beings and livestock. A study on the socioeconomic and ecological impacts of P. hysterophorus was conducted in five Kebeles (lowest administrative division) of Boset Woreda (District), Ethiopia. Data was collected using Ecological Survey, Semi Structured Interviews, Focus Group Discussion, and Field Observations. 200 quadrats were employed where every plant species found in each quadrat were counted, recorded and identified. Data on informant's perception about the first appearance, infestation levels, agents of dispersal, impact, and cultural management of the Parthenium weed were analyzed using descriptive statistics. Shannon Diversity Index (H′), Species Richness, Evenness, and Jaccard's Similarity Index were executed to evaluate Parthenium's effect on species diversity of the weed flora. 78 Herbaceous plants belonging to 59 genera and 21 families were collected. Poaceae (28.2%) and Asteraceae (16.7%) were the dominant families of weeds observed in the study Kebeles. Digalu and Merko Kebeles had high infestation of P. hysterophorus represented by high distribution, abundance, and dominance of the weed, but with corresponding low Richness, H′, and evenness of herbaceous plants. Species Richness of herbaceous flora and abundance of Parthenium weed reveled significant negative association (P < 0.01; R 2 = 0.93). Most of the informants believed that Parthenium affected crop and livestock production as well as human health. Farmers employed hand weeding, plowing, and manual clearing to manage the weed. For effective use of the weed, Integrated Weed Management approaches are required to check the spread and reduce the adverse impacts.

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