Environmental risks of applying sewage sludge compost to vineyards: carbon,heavy metals,nitrogen, and phosphorus accumulation

Biosolids are applied to vineyards to supply organic matter. However, there is concern that this practice can increase the concentration of macronutrients and heavy metals in the soil, some of which can leach. We evaluated the environmental hazard of sewage sludge compost applied in March 1999 at 10, 30, and 90 Mg ha-1 fresh weight in a vineyard in southeastern France. Soil organic matter increased in all plots by 3 g kg-1 18 mo after the amendment. Neither total nor available heavy metal concentrations increased in the soil. Mineral nitrogen (N) in the topsoil of amended plots of 10, 30, and 90 Mg ha-1 increased by 5, 14, and 26 kg (NO3(-)-N + NH4(+)-N) ha-1, respectively, the first summer and by 2, 5, and 10 kg (NO3(-)-N + NH4(+)-N) ha-1, respectively, the second summer compared with controls. At the recommended rate, risks of N leaching is very low, but phosphorus (P) appeared to be the limiting factor. Phosphorus significantly increased only in plots amended with the highest rate in the topsoil and subsoil. At lower rates, although no significant differences were observed, P added was greater than the quantities absorbed by vines. In the long run, P will accumulate in the soil and may reach concentrations that will pose a risk to surface waters and ground water. Therefore, although the current recommended rate (10 Mg ha-1) increased soil organic matter without the risk of N leaching, total sewage sludge loading rates on vineyards should be based on P concentrations.     

Using a fire propagation model to assess the efficiency of prescribed burning in reducing the fire hazard

We examined how fire hazard was affected by prescribed burning and fuel recovery over the first six years following treatment. Eight common Mediterranean fuel complexes managed by means of prescribed burning in limestone Provence (South-Eastern France) were studied, illustrating forest and woodland, garrigue and grassland situations. The coupled atmosphere-wildfire behaviour model FIRETEC was used to simulate fire behaviour (ROS, intensity) in these complex vegetations. The temporal threshold related to the effectiveness of prescribed burning in reducing the fire hazard was assessed from derivated fuel dynamics after treatment. The study showed that prescribed burning treatment was effective for the first two years in most of the Mediterranean plant communities analysed. Thereafter, all forests and shrublands were highly combustible with a fire line intensity of more than 5000 kW/m except for pine stands with or without oak (medium intensity of 2000 kW m⁻¹ 3 years after treatment). Low fire line intensity (900 kW m⁻¹) was obtained for grassland which was entirely treatment-independent since the resprouter hemicryptophyte, Brachypodium retusum, is highly resilient to fire. Fire behaviour was greatly affected by fuel load accumulation of Quercus ilex in woodland, and by standing necromass of Rosmarinus officinalis in treated garrigue. Pure pine stands with shrub strata similar to garrigue showed a lower fire intensity due to wind speed decrease at ground level under tree canopy, underlining the advantage of maintaining a proportion of canopy cover in strategic fuel-break zones.     

Wetland drainage in the Canadian prairies: Nutrient, salt and bacteria characteristics

Intensification of agriculture has led to renewed efforts to drain wetlands throughout North American prairies. It is perceived to threaten downstream ecosystem health through enhancing nutrient, bacteria and salt loading. An experiment was conducted to determine temporal variations in wetland solute storage and export upon drainage. Water quality along seven ditches and five natural spills that form between wetlands was also compared. The experimental wetland acted as a solute storage zone prior to its drainage. Variations in salts and DOC were influenced by hydrological processes, whereas variations in nutrients and bacteria were also influenced by biotic and/or sorption processes. Wetland water quality was an important control of drainage water quality as the wetland ditch acted as a simple conduit. Concentrations of TDN, DOC, HCO₃⁻, K⁺, and Ca²⁺ were higher in ditches than spills. Minimal changes in water quality along ditches and spills occurred, likely due to low spring temperatures that can restrict biotic processing and sorption. Since ditches connect wetlands to streams, they have a greater potential to contribute to downstream solute loading than spills. Wetland drainage efficiency and wetland water quality were deemed the factors critical to determining solute exports via ditches.     

Influence of pore size and membrane surface properties on arsenic removal by nanofiltration membranes

Four NF membranes were compared regarding arsenate rejection and their properties. Rejection of arsenate had no relationship with membrane pore size. A more negative surface charge was favorable for arsenate rejection at neutral pH. A severe membrane fouling could lead to a great reduction of arsenic rejection. Nanofiltration (NF) has a great potential in removing arsenate from contaminated water. The performance including arsenate rejection, water permeability and resistance to fouling could however differ substantially among NF membranes. This study was conducted to investigate the influence of membrane pore size and surface properties on these aspects of membrane performance. Four fully-aromatic NF membranes with different physicochemical properties were adopted for this study. The results showed that surface charge, hydrophobicity, roughness and pore size could affect water permeability and/or arsenate rejection considerably. A more negative surface charge was desirable to enhance arsenate rejection rates. NF90 and a non-commercialized membrane (M#1) demonstrated the best performance in terms of arsenate rejection and water permeability. The M#1 membrane showed less membrane fouling than NF90 when used for filtration of real arsenic-containing groundwater. This was mainly due to its distinct chemical composition and surface properties. A severe membrane fouling could lead to a substantial reduction of arsenic rejection. The M#1 membrane showed the best performance, which indicated that membrane modification could indeed enhance the overall membrane performance for water treatment.     

Eliciting preferences for wetland services: a way to manage conflicting land uses

A choice experiment was used to analyse the preferences of residents neighbouring the Erstein polder (Alsace, France) for the different services that it provides. The heterogeneous nature of these preferences was shown through the use of a latent class model. Whilst the population as a whole values the improvement in water quality and the contribution, even partial, to flood protection, preferences differ when it comes to biodiversity and public access to the site. This study shows the potential conflicts between the different uses of the Erstein polder. These conflicts represent different communication themes for the site managers.