Evaluation of simulated strategies for reducing nitrate-nitrogen losses through subsurface drainage systems

The nitrates (NO(3)-N) lost through subsurface drainage in the Midwest often exceed concentrations that cause deleterious effects on the receiving streams and lead to hypoxic conditions in the northern Gulf of Mexico. The use of drainage and water quality models along with observed data analysis may provide new insight into the water and nutrient balance in drained agricultural lands and enable evaluation of appropriate measures for reducing NO(3)-N losses. DRAINMOD-NII, a carbon (C) and nitrogen (N) simulation model, was field tested for the high organic matter Drummer soil in Indiana and used to predict the effects of fertilizer application rate and drainage water management (DWM) on NO-N losses through subsurface drainage. The model was calibrated and validated for continuous corn (Zea mays L.) (CC) and corn-soybean [Glycine max (L.) Merr.] (CS) rotation treatments separately using 7 yr of drain flow and NO(3)-N concentration data. Among the treatments, the Nash-Sutcliffe efficiency of the monthly NO(3)-N loss predictions ranged from 0.30 to 0.86, and the percent error varied from -19 to 9%. The medians of the observed and predicted monthly NO(3)-N losses were not significantly different. When the fertilizer application rate was reduced ~20%, the predicted NO(3)-N losses in drain flow from the CC treatments was reduced 17% (95% confidence interval [CI], 11-25), while losses from the CS treatment were reduced by 10% (95% CI, 1-15). With DWM, the predicted average annual drain flow was reduced by about 56% (95% CI, 49-67), while the average annual NO(3)-N losses through drain flow were reduced by about 46% (95% CI, 32-57) for both tested crop rotations. However, the simulated NO(3)-N losses in surface runoff increased by about 3 to 4 kg ha(-1) with DWM. For the simulated conditions at the study site, implementing DWM along with reduced fertilizer application rates would be the best strategy to achieve the highest NO(3)-N loss reductions to surface water. The suggested best strategies would reduce the NO(3)-N losses to surface water by 38% (95% CI, 29-46) for the CC treatments and by 32% (95% CI, 23-40) for the CS treatments.     

Insecticide residues in cotton soils of Burkina Faso and effects of insecticides on fluctuating asymmetry in honey bees (Apis mellifera Linnaeus)

Four insecticides (acetamiprid, cypermethrin, endosulfan and profenofos) are used quarterly in the cotton-growing areas of Burkina Faso, West Africa. These insecticides were investigated in soils collected from traditionally cultivated and new cotton areas. Also, the effects of insecticide exposure on the developmental instability of honey bees, Apis mellifera, were explored. In soil samples collected three months after insecticide treatments, endosulfan and profenofos concentrations varied in the range of 10-30 μg kg(-1) in the traditionally cultivated zones and 10-80 μg kg(-1) in the new cotton zones, indicating a pollution of agricultural lands. However, only profenofos concentrations were significantly higher in the new cotton zone than the traditionally cultivated zones. In addition, the index of fluctuating asymmetry, FA1, in the length of second tarsus (L(HW)) was increased for bees when exposed to pesticide treated cotton fields for 82d, and their FA levels were significantly higher than those in the control colony in an orchard. The other studied traits of bees exposed to insecticides were not significantly different from controls. Our results indicate that FA may be considered as a biomarker reflecting the stress induced by insecticide treatments. However, the relationship between FA and stressors needs further investigations.     

Uptake and elimination,and effect of estrogen-like contaminants in estuarine copepods: an experimental study

Background, aim, and scope  

In recent years, anthropogenic chemicals which can disrupt the hormonal systems of both humans and wildlife have been raised to a major cause of concern. The aim of the present work was to determine the bioconcentration factors of the two major alkylphenols (AP) of the Seine Estuary [4-nonylphenol (4 NP) and nonylphenol acetic acid (NP1EC)] and of the synthetic estrogen, estrogen ethinylestradiol (EE2), in Eurytemora affinis after exposure in a continuous flow-through system under environmental realistic conditions. Moreover, the elimination of these compounds in copepods from the Seine Estuary has been investigated by measuring concentrations after 1 week in clean water in comparison to background levels.     

Effects of chitosan on oxidative stress and metallothioneins in aquatic worm Tubifex tubifex (Oligochaeta, Tubificidae)

Chitosan is a natural polymer which has the property to elicit the natural defenses mechanism in plant and which can be an interesting biopesticides. It is then necessary to investigate the potential toxicity of chitosan for aquatic animal health. Metallothioneins (MTs) are low molecular weight proteins, mainly implicated in metal ion detoxification. Increase in MTs contents had been considered as a specific biomarker of metal exposure. However recently it has been demonstrated that MTs participate in several cellular functions such as regulation of growth and anti-oxidative defenses. Therefore, the induction of MTs has been investigated in the aquatic worms Tubifex tubifex exposed to chitosan. MTs levels in exposed worm increased significantly (p > 0.05) after 2, 4, and 7 days of exposure to different concentrations of chitosan (maximum + 158.19 +/- 10.2% after 2 days of exposure to 125 mgl(-1) of chitosan). Several antioxidant parameters including glutathione (GSH), glutathione-S-transferase (GST), glutathione reductase (GR), and catalase (CAT) were quantified in T. tubifex after 2, 4, and 7 days of exposure to chitosan. Exposure to chitosan had a negative effect on T. tubifex growth (maximum effect -6.11 +/- 1.6% after 7 days with 125 mgl(-1)) demonstrating the toxic effect of the pesticide. This growth rate decrease was accompanied by a reduction in protein contents. The activity of catalase (CAT), glutathione-S-transferase (GST), and glutathione reductase (GR) increased in response to the chitosan demonstrating an oxidative stress in the worms.     

Is pesticide sorption by constructed wetland sediments governed by water level and water dynamics?

Constructed wetlands (CWs) are used to reduce the pesticide inputs from tile drainage or run-off to surface water. Their effectiveness appears variable and remains to be better characterized and understood. The aim of this study was to assess the influences of two hydraulic parameters (i.e., dynamics and water level) on the sorption process occurring in CWs. Then, two solid/liquid ratios were studied (1/1 and 1/5) to mimic the water level variation in the field, and two agitation speeds were used (none and gentle agitation) to simulate different water dynamics (stagnation and flow pass, respectively). Sorption kinetics and isotherms were obtained for four pesticides with contrasting properties. The pesticide adsorption coefficients were classified as follows: boscalid (BSC) > cyproconazole (CYP) > isoproturon (IPU) ～ dimethachlor (DMT) at any ratio or agitation, in agreement with their water solubilities and K _ow values. The effect of the solid/liquid ratio was evidenced for all conditions. Indeed, the adsorption equilibrium time was reached more quickly for the 1/1 ratio (24–72 h) than for the 1/5 ratio (96–120 h). In addition, the adsorption coefficients (K _f ^ads) were larger for the 1/1 ratio (1.8–11.2 L kg^?1) than for the 1/5 ratio (1.0–5.9 L kg^?1). The agitation effect was ?more evidenced for the 1/5 ratio and for the more hydrophobic molecules, such as BSC and CYP, for which adsorption equilibrium time was never reached with agitation (>120 h), while it was reached at 96 h without agitation. Moreover, the K _f ^ads values were larger with agitation than without agitation for BSC and CYP, whereas they were similar for the two agitations for IPU and DMT. Our results demonstrated that the hydrodynamic function of CWs could influence pesticide sorption with variable effects according to the molecular properties and consequently influence the mitigation effect of CWs throughout the year.     

Numerical Simulation of Gas Injection in Vertical Water Saturated Porous Media

We present numerical simulations of drainage induced by air injection in a vertical water-saturated Hele-Shaw cell filled with glass microbeads. We use the macroscale Subsurface Transport Over Multiple Phases (STOMP) simulator developed by the Pacific Northwest National Laboratory’s Hydrology Group. To trigger fingering, we use random permeability fields consistent to capillary entry pressure fields. We compare the numerical results to our own experimental results shown in a previous study. We analyze the effects of the microheterogeneity degree as well as the macroscopic parameters on the gas saturation results. The main objective of the work is to investigate how microscopic effects could be accounted for by macroscopic variables during drainage.     

Toxicity and removal of pesticides by selected aquatic plants

Pesticides are being detected in water bodies on an increasingly frequent basis. The present study focused on the phytoremediation potential of selected aquatic plants to remove phytosanitary products from contaminated water. We investigated the uptake capacity of Lemna minor (L. minor), Elodea canadensis (E. canadensis) and Cabomba aquatica (C. aquatica) on three pesticides: copper sulphate (fungicide), flazasulfuron (herbicide) and dimethomorph (fungicide). Pesticide toxicity was evaluated by exposing plants to five concentrations (0-1 mg L(-1)) in culture media for 7d using chlorophyll fluorescence as a biomarker. The toxicity of the contaminants was the same for all the aquatic plants studied and occurred in this descending order of toxicity: flazasulfuron>copper>dimethomorph. We found that L. minor had the most efficient uptake capacity, followed by E. canadensis and then C. aquatica. The maximum removal rate (microg g(-1)fresh weight d(-1)) of copper, flazasulfuron and dimethomorph was 30, 27 and 11, respectively.     

Improvement of Vicia-micronucleus test for assessment of soil quality: a proposal for international standardization

The Viciafaba root tip micronucleus test is one of the most employed plant genotoxicity assays, and has been used on various types of contaminated materials. This test has been standardized by AFNOR, the French member organization of ISO. However, this test is usually performed with a water extraction step but soil genotoxicity assessment would be more relevant when performed directly in the soil itself. In order to harmonize these protocols, an ISO standard for the V.faba micronucleus test in both liquid phase (exposure of plants to different liquid matrix, including soil water extracts) and solid phase (direct exposure of plants to the soil) would be very useful. In this context, we compared two exposure durations in the solid phase (48 h and 5 d) for the V.faba micronucleus test with two different well-known genotoxicants, maleic hydrazide and copper sulfate. We concluded that these two durations induced equivalent sensitivity: the micronucleus frequency was significantly increased with 5 μmol maleic hydrazide per kg dry soil and with 2 mmol copper sulfate per kg dry soil with both exposure durations. However, exposing roots to soil during 48 h is more practical. Moreover, organically and conventionally cultured seeds were employed to determine whether the seed provenance influenced the test sensitivity. Organic seeds were less sensitive to copper, possibly because copper-based treatments are permitted, and often applied, in organic farms. Therefore, in the absence of completely non-treated seeds, organically-cultured seeds did not appear to offer any advantages over conventional seeds.     

Influence of papermill sludge on growth of Medicago sativa, Festuca rubra and Agropyron trachycaulum in gold mine tailings: a greenhouse study

A greenhouse study was undertaken to determine the suitability of adding papermill sludge to neutral/alkaline gold mine tailings to improve the establishment of Festuca rubra, Agropyron trachycaulum and Medicago sativa. Festuca rubra root and shoot biomass and A. Trachycaulum shoot biomass were increased with papermill sludge amendment. The addition of papermill sludge and fertilizer drastically increased the shoot and root biomass of M. sativa (20-30 times) while A. trachycaulum and F. rubra showed a more moderate increase in growth. Photosynthetic pigment content of the leaves was higher in papermill sludge treatments than in the treatments without papermill sludge. The organic carbon content, macro-aggregate content and field capacity of the gold mine tailings were increased while the bulk density was decreased by the addition of papermill sludge. This study suggests that addition of papermill sludge and adequate fertilization can alleviate some of the adverse conditions of neutral/alkaline gold mine tailings.     

Impact of metal stress on the production of secondary metabolites in <Emphasis Type="Italic">Pteris vittata</Emphasis> L. and associated rhizosphere bacterial communities

Plants adapt to metal stress by modifying their metabolism including the production of secondary metabolites in plant tissues. Such changes may impact the diversity and functions of plant associated microbial communities. Our study aimed to evaluate the influence of metals on the secondary metabolism of plants and the indirect impact on rhizosphere bacterial communities. We then compared the secondary metabolites of the hyperaccumulator Pteris vittata L. collected from a contaminated mining site to a non-contaminated site in Vietnam and identified the discriminant metabolites. Our data showed a significant increase in chlorogenic acid derivatives and A-type procyanidin in plant roots at the contaminated site. We hypothesized that the intensive production of these compounds could be part of the antioxidant defense mechanism in response to metals. In parallel, the structure and diversity of bulk soil and rhizosphere communities was studied using high-throughput sequencing. The results showed strong differences in bacterial composition, characterized by the dominance of Proteobacteria and Nitrospira in the contaminated bulk soil, and the enrichment of some potential human pathogens, i.e., Acinetobacter, Mycobacterium, and Cupriavidus in P. vittata’s rhizosphere at the mining site. Overall, metal pollution modified the production of P. vittata secondary metabolites and altered the diversity and structure of bacterial communities. Further investigations are needed to understand whether the plant recruits specific bacteria to adapt to metal stress.