Application of para-nitrophenol (pNP) enzyme assays in degraded tropical soils

Enzyme activities have been used as indicators of soil quality and changes in biogeochemical function due to management or perturbations. The objective of this study was to answer a number of methodological questions regarding sampling schemes, sample handling recommendations, and assay procedures to facilitate the use of enzyme assays in the tropical highlands of East Africa. We used para-nitrophenol (pNP) based substrates for five enzymes: β-glucosidase, cellobiohydrolase, chitinase, acid phosphatase, and alkaline phosphatase. In the first experiment, we examined sampling procedures and compared the results of determining enzyme activities on a plot using composite or discrete samples. Composite samples usually had higher activities than the means of individual cores (P<0.05), but relative ranking of sites was the same if analyses were based on composite or discrete samples. In the second experiment, we examined the effects of storage time and conditions on enzyme activity. Enzyme activity degraded rapidly in frozen samples, but was better maintained in samples stored at 4 °C. Phosphatase and cellobiohydrolase activity declined after 14 days of storage, while the activity of the other enzymes remained close to the values of fresh samples for 28 or more days. In the third experiment, we examined the effect of the addition of an antiseptic, toluene, to prevent bacterial growth during the assay. We found no consistent toluene effect (P>0.4), probably because the assays were of short duration and microbial growth was minimized. Finally, we looked at the incubation time necessary to produce reliable results. Phosphatases, with relatively high activities could reliably be determined in 2 h incubations, but the other enzymes had much lower activities and required longer incubation times for reliable determination. For the enzymes we looked at, 4 h was a good standard time for determining the activity of even the lowest activity enzymes. The results of this study provide practical guidelines for applying these enzyme assays in the degraded tropical soils.     

Impact on Water Quality of High and Low Density Applications of Spent Mushroom Substrate to Agricultural Lands

We studied the influence of spent mushroom substrate (SMS) land application on water resources. Four study sites, including mushroom farms with low or high density land applications of SMS, and two controls, an alfalfa field and a woodland, were instrumented with soilwater lysimeters and groundwater monitoring wells. Water samples were collected during the dormant season (winter) and growing season (spring). Samples were analyzed for a number of water quality parameters, including dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonia, chloride, nitrate, nitrite, phosphate, sulfate, aluminum, cadmium, calcium, chromium, copper, iron, lead, magnesium, manganese, mercury, nickel, potassium, silicon, sodium, and zinc. Additional analyses were performed for pesticides commonly used in the cultivation of alfalfa or corn, or for insect control, including methomyl, dimethoate, hexazinone, atrazine, diuron and permethrin.

All agricultural sites had elevated salt concentrations relative to the woodland site. The mushroom farm where SMS was applied in high concentrations had salt concentrations in the soilwater that were 10 to 100 times higher than the other agricultural sites. Of particular note were ammonium, nitrate, chloride, sulfate, calcium, magnesium, sodium, and potassium. Each of these were also elevated in the groundwater. The high salt concentrations were reflected in measurements of electrical conductivity. DOC and DON concentrations were also elevated in the soilwater and groundwater. Groundwater from each agricultural site, including the agricultural control, exceeded the primary drinking water standard for nitrate.

No pesticide residues were detected in well or lysimeter water collected at either site amended with SMS. Water samples collected from the woodland and at the alfalfa field not receiving SMS contained part per trillion quantities of a few pesticides.     

Consequences of adult and juvenile movement for marine protected areas

Adult and juvenile mobility has a considerable influence on the functioning of marine protected areas. It is recognized that adult and juvenile movement reduces the core benefits of protected areas, namely protecting the full age–structure of marine populations, while at the same time perhaps improving fisheries yield over the no-reserve situation through export of individuals from protected areas. Nevertheless, the study of the consequences of movement on protected area functioning is unbalanced. Significant attention has been paid to the influence of certain movement patterns, such as diffusive movement and home ranges, while the impacts of others, such as density-dependent movements and ontogenetic migrations, have been relatively ignored. Here we review the diversity of density-independent and density-dependent movement patterns, as well as what is currently known about their consequences for the conservation and fisheries effects of marine protected areas. We highlight a number of ‘partially addressed’ issues in marine protected area research, such as the effects of reserves targeting specific life phases, and a number of essentially unstudied issues, such as density-dependent movements, nomadism, ontogenetic migrations, behavioral polymorphism and ‘dynamic’ reserves that adjust location as a realtime response to habitat changes. Assessing these issues will be essential to creating effective marine protected area networks for mobile species and accurately assessing reserve impacts on these species.     

Thermal decomposition of specifically phosphorylated D-glucoses and their role in the control of the Maillard reaction

One of the main shortcomings of the information available on the Maillard reaction is the lack of knowledge to control the different pathways, especially when it is desired to direct the reaction away from the formation of carcinogenic and other toxic substances to more aroma and color generation. The use of specifically phosphorylated sugars may impart some elements of control over the aroma profile generated by the Maillard reaction. Thermal decomposition of 1- and 6-phosphorylated glucoses was studied in the presence and absence of ammonia and selected amino acids through pyrolysis/gas chromatography/mass spectrometry using nonpolar PLOT and medium polar DB-1 columns. The analysis of the data has indicated that glucose-1-phosphate relative to glucose undergoes more extensive phosphate-catalyzed ring opening followed by formation of sugar-derived reactive intermediates as was indicated by a 9-fold increase in the amount of trimethylpyrazine and a 5-fold increase in the amount of 2,3-dimethylpyrazine, when pyrolyzed in the presence of glycine. In addition, glucose-1-phosphate alone generated a 6-fold excess of acetol as compared to glucose. On the other hand, glucose-6-phosphate enhanced retro-aldol reactions initiated from a C-6 hydroxyl group and increased the subsequent formation of furfural and 4-cyclopentene-1,3-dione. Furthermore, it also stabilized 1- and 3-deoxyglucosone intermediates and enhanced the formation of six carbon atom-containing Maillard products derived directly from them through elimination reactions such as 1,6-dimethyl-2,4-dihydroxy-3-(2H)-furanone (acetylformoin), 2-acetylpyrrole, 5-methylfurfural, 5-hydroxymethylfurfural, and 4-hydroxy-2,5-dimethyl-3-(2H)-furanone (Furaneol), due to the enhanced leaving group ability of the phosphate moiety at the C-6 carbon. However, Maillard products generated through the nucleophilic action of the C-6 hydroxyl group such as 2-acetylfuran and 2,3-dihydro-3,5-dihydroxy-4H-pyran-4-one were retarded, due to the blocked nucleophilic atom at C-6.     

Volatile emissions of navel oranges as predictors of freeze damage

Volatile emissions of navel orange (Citrus sinensis L. Osbeck cv. Washington) fruit were evaluated as a means for predicting and gauging freeze damage. The fruits were subjected to -5 or -7 degrees C treatments in a laboratory freezer for various time periods of 2-9.5 h and stored at 23 degrees C for 1, 2, or 7 days, after which time the emission of volatiles from the fruit was measured. Following the final day of volatile measurements the fruits were stored at 5 degrees C for an additional 2-3 weeks and then evaluated for fruit quality characteristics. Peel injury in the form of brown lesions, drying of the juice vesicles, a decline in acidity, and a loss of flavor were observed to occur as a result of freezing. Corresponding to the loss in fruit quality were large increases in the emissions of ethanol, ethyl butanoate, methyl hexanoate, and ethyl octanoate. With the exception of methyl hexanoate, for which volatile emissions decreased during storage for 7 days at 23 degrees C, all of the other volatiles were relatively unchanged in amount by storage. Treatment at -7 degrees C caused greater injury, quality loss, and more volatile emanation than did freezing at -5 degrees C. The measurement of volatile emissions appears to be a useful approach to identify freeze-damaged navel oranges.     

The mobility of the trace metals copper,zinc, lead,cobalt, and nickel in tropical estuarine sediments,Ebrie Lagoon,Côte d’Ivoire

Journal of Soils and Sediments - Trace metals accumulate in the food web and can pose high risks to human health and aquatic biota. We investigated seasonal and spatial variations of Cu, Zn, Pb,...     

Predicted and observed finger diameters in field soils

Wetting front instability resulting in fingered flow has been found in both wettable and nonwettable soils. Understanding how and when this phenomenon occurs under field conditions is greatly limited. Laboratory research has resulted in a number of expressions for finger diameter. In this paper we test the applicability of one of these equations for three different soils in the Netherlands where detailed soil sampling of moisture content was done earlier. In addition, information needed for finger prediction, such as the main wetting and drying loops of the soil moisture characteristic curves and the unsaturated and saturated soil conductivities, were measured in the laboratory. Results show that predicted finger diameters for the two sandy soils agreed well with the observed moisture patterns, while for the loess soil the wetting front was flat as predicted. The finger diameters in dry soil were based on the main wetting loop and in the wet soils were dependent on the main drying loop.     

Seasonal soil nitrogen dynamics affect yields of lowland rice in the savanna zone of West Africa

Background : Rice production in low‐input systems of West Africa relies largely on nitrogen supply from the soil. Especially in the dry savanna agro‐ecological zone, soil organic N is mineralized during the transition period between the dry and the wet seasons. In addition, in the inland valley landscape, soil N that is mineralized on slopes may be translocated as nitrate into the lowlands. There, both in‐situ mineralized as well as the laterally translocated nitrate‐N will be exposed to anaerobic conditions and is thus prone to losses. Aim : We determined the dynamics of soil NO₃‐N along a valley toposequence during the dry‐to‐wet season transition period and the effects of soil N‐conserving production strategies on the grain yield of rainfed lowland rice grown during the subsequent wet season. Methods : Field experiments in Dano (Burkina Faso) assessed during two consecutive years the temporal dynamics and spatial fluxes of soil nitrate along a toposequence. We applied sequential and depth‐stratified soil nitrate analysis and nitrate absorption in ion exchange resin capsules in lowlands that were open to subsurface interflow and in those where the interflow from the was intercepted. During one year only we also assessed the effect of pre‐rice vegetation on conserving this NO₃‐N as well as on N addition by biological N₂ fixation in legumes using δ¹⁵N isotope dilution. Finally, we determined the impact of soil N fluxes and their differential management during the transition season on growth, yield and N use of rainfed lowland rice. Results : Following the first rainfall event of the season, soil NO₃‐N initially accumulated and subsequently decreased gradually in the soil of the valley slope. Much of this nitrate N was translocated by lateral sub‐surface flow into the valley bottom wetland. There, pre‐rice vegetation was able to absorb much of the in‐situ mineralized and the laterally‐translocated soil NO₃‐N, reducing its accumulation in the soil from 40–43 kg N ha^?1 under a bare fallow to 1–23 kg N ha^?1 in soils covered by vegetation. Nitrogen accumulation in the biomass of the transition season crops ranged from 44 to 79 kg N ha^?1 with a 36–39% contribution from biological N₂ fixation in the case of legumes. Rice agronomic performance improved following the incorporation as green manure of this “nitrate catching” vegetation, with yields increasing up to 3.5 t ha^?1 with N₂‐fixing transition seasons crops. Conclusion : Thus, integrating transition season legumes during the pre‐rice cropping niche in the prevailing low‐input systems in inland valleys of the dry savanna zone of West Africa can temporarily conserve substantial amounts of soil NO₃‐N. It can also add biologically‐fixed N, thus contributing to increase rice yields in the short‐term and, in the long‐term, possibly maintaining or improving soil fertility in the lowland.     

Contribution of technic materials to the mobile fraction of metals in urban soils in Marrakech (Morocco)

Background, Aim and Scope  In urban areas, soils are often dramatically altered by anthropogenic activity and these modifications distinguish these soils (Anthrosols, Technosols) from those in natural systems. In urban environments, they receive considerable pollution from industry, traffic and refuse. Since contaminated soil particles can be easily inhaled or ingested, there is a potential transfer of toxic pollutants to humans. Risk assessment is essentially based on the determination of the total or mobile contents of pollutants in soils using chemical extractions. This approach could be improved by taking into consideration the bioavailable fractions of these toxic elements as measured by biotests. The coarse soil fraction usually neglected in analyses can nevertheless have an effect on the concentration of metals in the soil solution. This coarse fraction is made up of the natural materials and of technic materials constituting anthropogenic soils (plastic, paper, fabric, wood, bones, metallic elements and building materials). These materials have variable capacities to release or adsorb trace elements. Samples representative of different technic fraction components of Marrakech urban soils permit one to quantify their contribution to the enrichment of the soluble metal concentrations. Works are carried out to achieve partial extractions of metals from the three fractions (less than 2 mm, coarse natural and coarse technic) of selected urban soils in order to determine their contribution to the metal contamination of soils. Materials and Methods  Selected soils were collected from 9 sites according to a gradient of increasing anthropogenic influence from suburban to urban zones. Soils were air-dried, homogenized, and sieved (2 mm). The coarse fraction was sorted to separate the different technic materials and natural materials. Water extractions were run, on the natural, coarse fraction, on the complete technic fraction of the 9 soils and on average samples made of technic materials sorted out of 58 topsoils sampled from different sites in the city of Marrakech. Results  Results show that the percentage of the technic fraction increases while approaching the historic city center. It represented about 14% in the most anthropogenically disturbed soils. Along this gradient, soils changed progressively from Anthrosols to Technosols according to the WRB classification of urban and industrial soils. Analyses of metal contents showed that the fine fraction (<2 mm) mainly contributed to the metallic contamination of the water soluble fraction. The natural coarse fraction had the highest contribution to the copper release and was responsible for the release of all water-extractable copper in some soils. Concerning the technic fraction, it has a significant contribution essentially in the most anthropogenically disturbed soils as characterized by an elevated percentage of anthropogenic elements. The water extractable metal contents of average samples of these anthropogenic elements shows that elevated metal concentrations were released by bones, wood, plastic and fabric/paper. Discussion  This study concerns soils in urban areas, which are strongly impacted by human activities. Part of the soils can be classified as Anthrosols, profoundly impacted through the addition of organic materials from household wastes, irrigation, or cultivation. Other soils strongly impacted by human activities are Technosols dominated or strongly influenced by man-made materials. Technosols appear mostly in urban and industrial areas and are more likely to be contaminated than Anthrosols. The composition and heterogeneity of urban soils lead to modifications of the mobility and availability of pollutants depending on successive land-uses and on the composition of technic materials. The fine fraction offers a high transferring surface capacity, leading to a high mobilization of metals. The technic fraction contributes significantly to the metal release in the Technosols. This property can be explained by a reversible adsorption of metals on the organic matter. Conclusions  Results confirm that anthropogenic activity causes a wide spatial diversity of soil quality in the urban and suburban area. It introduces large amounts of technic materials in soils that could have an impact on the metal availability. It therefore acts on the metal bioavailability in the urban Technosols. Recommendations and Perspectives  These results show that it is necessary, in addition to the characterization of the fine particles, to take into account the contribution of the coarse fraction of the Technosols in the evaluation of risks of transfer of metals to the food chain.