What factors determine trace metal contamination in Lake Tonga (Algeria)?

A study of trace metal (TM) contamination was conducted at Lake Tonga (Algeria), a site surrounded by several indirect contamination point sources such as an abandoned mine and steelworks. Studying two sampling sites over four seasons, we were able to depict the spatial and temporal variability of TM contamination in the lake. Among the seven TM examined (Pb, Cd, Fe, Zn, Ni, Cu, and Cr), only Fe, Pb, and Cd showed concentrations significantly higher than the site's geological background. The contamination index (sediment concentration/background concentration) calculated for these three TM (Cd = 1.9 ± 1.6, Fe = 6.8 ± 1.8, and Pb = 3.3 ± 2.6) clearly indicated anthropogenic contamination. Sediment TM contamination differed both between sampling sites and seasons despite environmental variables (e.g., oxygen and pH) being similar, thus suggesting different TM contamination sources. Fe contamination was high at the two sampling sites and over all studied seasons, possibly indicating general lake-scale Fe contamination, probably related to atmospheric deposition of steelworks emissions both on the lake and within the watershed. Lake tributaries were further suspected of channeling Fe contamination from the watershed into the lake. On the other hand, the sampling site close to the outlet was especially rich in Cd and Pb typically reflecting contamination by mine wastes. The indirect connection between the abandoned mine and the lake indicates that runoff of mine leachates through groundwater was likely a candidate in explaining the specificity of the TM contamination in this part of the lake. This study provides insights for management of TM contamination by addressing both spatial and temporal variability within the lake as well as differences in contamination sources.

Nutri-priming as an efficient means to improve the agronomic performance of molybdenum in common bean (Phaseolus vulgaris L.).

Microelements play important roles in improving crop productivity and quality. Two traditional methods of providing micronutrients are soil and foliar application, yet the cost involved and phytotoxicity risks poses a major challenge in most global agricultural areas. Nutri-priming represents thus a very promising and viable alternative to ensure that the plants' requirements for micronutrients are met. This paper explores the Mo-priming effects on the germination, growth and yield components of common bean (Phaseolus vulgaris L.). In order to accomplish this research objective, our study is divided in two phases. The first phase seeks to determine the effects of two durations (5 and 10 h) of Mo-priming on the germination parameters. Then, a greenhouse pot experiment was conducted with primed seeds showing better germination performance to assess the effects of Mo-priming on certain parameters related to biological nitrogen fixation and crop yield. Five seed pretreatments were studied, namely, 0, 0.025, 0.05, 0.1 and 0.2% of ammonium heptamolybdate ((NH4)6Mo7O24.4H2O). Unprimed seeds treated with or without the recommended dose through a soil application were used as controls. Hydropriming is sufficient to improve seed germination performance. However, 0.1% Mo-priming for 10 h improved the net CO2 assimilation rate, chlorophyll content and biological nitrogen fixation. Six times more nitrogen was fixed (65.8 kg ha-1) in these plants than in the controls. Additionally, grain yield increased by 115% compared to the negative control. Thus, compared to soil intake, nutri-priming was a very efficient experimental method.

Sewage sludge used as organic manure in Moroccan sunflower culture: Effects on certain soil properties, growth and yield components.

The wastewater treatment and sludge production sectors in Morocco are recent. Considered as waste, no management strategy for sewage sludge (SS) has been implemented. Thus, its disposal definitely represents a major environmental problem since sludge is either incinerated, used as landfill or simply deposited near wastewater treatment plants. The objective of this study was to determine the effects of dehydrated SS on certain soil properties (pH, electrical conductivity (EC), Mineral nitrogen, available phosphate P2O5, and soluble potassium K2O), and also on growth and yield components of the sunflower (Helianthus annuus L.). An experiment was conducted using six treatment rates (0; 0 + NPK; 15; 30; 60 and 120 t ha-1). The results showed that soil pH was significantly affected by SS, becoming less alkaline compared to the control, while electrical conductivity increased significantly when the applied doses were above 30 t ha-1. Also, a significant enrichment in mineral N and available phosphorus was detected in amended soil. However, no differences were found between pots having received the mineral fertilization and the SS at 15 t ha-1. Stem height growth of the sunflower seedlings receiving SS increased significantly compared to the two controls. For both the aerial and root parts, significant increases in dry biomass accumulation were observed compared to the unamended plants. Net CO2 assimilation (An) increased, while stomatal conductance (gsw) and transpiration rates (Tr) decreased with increasing SS rates. SS application at 15 t ha-1 presented similar values of the yield components compared to plants fertilized chemically. However, grain yield (in quintals ha-1) was noted to be 2.4, 5 and 8 times higher in treatments receiving SS respectively at the rate of 30, 60 and 120 t ha-1.

Sewage sludge as a soil amendment in a Larix decidua plantation: Effects on tree growth and floristic diversity.

Sewage sludge application in forest plantations is an interesting complementary alternative practice to sewage sludge reutilization and recycling, with a significant and sustainable net effect in climate change mitigation. However, to optimize it a detailed knowledge of its effects on ecosystem components such as plants, soil, water and fauna is needed. We investigated the effects of sewage sludge application on soil, tree growth and floristic diversity in a ten-year-old plantation of European larch (Larix decidua Mill.). Our one-hectare study site, located at Mélisey, Haute-Saône, France (47°753' Lat., 6°580' Long.), was subdivided into six plots. Three plots, alternating with three control plots (no sewage sludge application), were amended in June 2008 with 0.4tDWha-1 obtained from a municipal urban wastewater treatment plant in Mélisey. Within each plot, one subplot was delimited and sludge was again manually applied at 3t of DWha-1 in July 2009 and March 2010 to the soil surface of the amended subplots without incorporation. The results showed no effect on radial and height growth of European larch amended with 0.4tDWha-1. While a significant temporary increase in pH, macro-element contents (N, P and Ca) and the trace metal (Cu and Zn) concentration in the soil was observed, it had no significant effect on needles and sporocarp contents. The number of species in the amended subplots with 3tDWha-1year-1 increased by 80% compared to the control. However, the relative species abundance present only in amended subplots remains <1, except for Hypericum humifusum.

Land spreading of sewage sludge in forest plantations: effects on the growth of the duckweed Lemna minor and trace metal bioaccumulation in the snail Cantareus aspersus.

Wastewater plants generated annually millions of tons of sewage sludge (SS). Large amounts of this organic residue are spread on agricultural lands as a fertilizer, although it is viewed as a major potential source of contamination, presenting a danger to the terrestrial and aquatic environments. This study was undertaken to evaluate the impact of this practice on the duckweed Lemna minor and the snail Cantareus aspersus. Sludge was applied to soil either at six different loading rates equal to 0, 0.4, 3, 10, 30, and 60 tons dry matter (DM) ha(-1) for L. minor test or at three rates equal to 0, 30, and 60 tons DM ha(-1) for C. aspersus test. At the highest rate of SS application (60 tons DM ha(-1)), the eluates showed that an increase in pH (6.1) resulted in a decrease in Al levels. Thus, the high stimulation of L. minor growth observed after this high rate of SS application can be explained by (i) a reduction in Al toxicity after precipitation and (ii) macro- and micronutrient enrichment. At a rate of SS application of only 30 tons DM ha(-1), growth appeared to be slightly significant (p < 0.05), in spite of the significant increase in essential mineral elements. However, it is very difficult to discriminate between Al toxicity and pH effects. For the test with C. aspersus, the snail biomass was not affected by sludge application over the exposure period. Mortality was extremely low, with a rate of less than 4 % at the last sampling date. Yet, Cu, Pb, and Cd accumulated significantly in the soft body of snails exposed to SS application, suggesting that the amount of metals excreted is lower than that absorbed. In contrast, Zn levels remain constant, inferring that absorption and elimination of Zn are balanced at the beginning of the experiment.

What factors drive seasonal variation of phytoplankton, protozoans and metazoans on leaves of Posidonia oceanica and in the water column along the coast of the Kerkennah Islands, Tunisia?

A hierarchical sampling design was used during two seasons (spring (May) and summer (August) 2006). Using this design, three regions of the Kerkennah Islands (Tunisia) were analyzed for the distribution of microalgal, protozoan and metazoan assemblages in two different habitats: (1) the water column; and (2) on Posidonia oceanica (L.) Delile (P. oceanica) leaves in shallow meadows. A total of 85 species were obtained. In particular, the diatom family Naviculacea consistently dominated (both numerically and in their diversity) the micro-algae in all regions for the two seasons of the study and in both habitats. In the Chergui region, which is the closest area to a source of impact, fast growing centric diatoms (such as Thalassionema, Rhizosolenia, Striatella, and Skeletonema) were identified as indicators of high organic matter and nutrient enrichment in water bodies. Protozoan and metazoan species abundance in the different regions indicate a non-random spatial and temporal distribution of the epiphytic organisms on leaves of P. oceanica that correlated with phytoplankton. The results also indicate that (1) the abundance of micro- and macroorganisms in the three regions were higher on P. oceanica leaves than in the water column for the two seasons; (2) environmental factors such as currents and tide influenced assemblages; and (3) the highest abundance was due to direct exposure to the polluted coast of Sfax and the effect of tidal asymmetries generating nutrient-rich inputs from the city.