Patch-occupancy models indicate human activity as major determinant of forest elephant Loxodonta cyclotis seasonal distribution in an industrial corridor in Gabon

The importance of human activity and ecological features in influencing African forest elephant ranging behaviour was investigated in the Rabi-Ndogo corridor of the Gamba Complex of Protected Areas in southwest Gabon. Locations in a wide geographical area with a range of environmental variables were selected for patch-occupancy surveys using elephant dung to assess seasonal presence and absence of elephants. Patch-occupancy procedures allowed for covariate modelling evaluating hypotheses for both occupancy in relation to human activity and ecological features, and detection probability in relation to vegetation density. The best fitting models for old and fresh dung data sets indicate that (1) detection probability for elephant dung is negatively related to the relative density of the vegetation, and (2) human activity, such as presence and infrastructure, are more closely associated with elephant distribution patterns than are ecological features, such as the presence of wetlands and preferred fresh fruit. Our findings emphasize the sensitivity of elephants to human disturbance, in this case infrastructure development associated with gas and oil production. Patch-occupancy methodology offers a viable alternative to current transect protocols for monitoring programs with multiple covariates.     

The influence of neighbouring grassland plants on each others'' endomycorrhizas and root-surface microorganisms

In three glasshouse experiments the grassland plants Anthoxanthum odorattum. Lolium perenne, Plantayo lanceolata and Trifolium repens were grown in pots of grassland soil, in monocultures and various two-species mixtures. Mixed-species and single-species swards were also sown in a garden bed; and in a permanent pasture P. lanceolata individuals whose surrounding vegetation had been removed were compared with control plants. Abundance of root-surface bacteria and fungi, and of internal mycorrhizal infection were measured by direct observation of randomly-selected root segments.

The abundance of all three microbial groups on a given “host” species was often significantly altered by the presence of other plant species. Bacteria usually changed in the same direction as fungi, but proportionately less. Mycorrhizas usually changed less than the other two groups and not always in the same direction. In the pot experiments, when growth in a mixture resulted in a plant being larger and having higher nutrient concentration than in monoculture, the abundance of fungi on its roots also increased; bacteria and mycorrhizas showed this correlation less clearly. Superimposed on this relationship was a general tendency for fungi, and to a lesser extent bacteria, to be more abundant in mixture than monoculture even when the plants did not change in size. Possible mechanisms involved in these responses are discussed.     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

Development of direct-drilling systems for sandy loam soils in the cool humid climate of Atlantic Canada

This study provides an overview of the adaptation of direct-drilling systems on sandy loam soils under the cool boreal, humid to perhumid soil climate of Prince Edward Island in Atlantic Canada, where the growing season is relatively short (May–October). Direct drilling can overcome the constraints of limited field workdays for seeding of spring cereals, owing to wet soil conditions in early May, or the integration of planting date with optimum soil temperatures for silage corn (Zea mays L.). However, the advantage of timeliness may be offset under sequential direct drilling for these crops, owing to a combination of reduced macroporosity at the soil surface and increased percentage of water-filled pore space, especially in soils with levels of organic carbon below 2% (w/w). In contrast, the presence of standing-crop residue, in pasture-renovation studies, allowed sequential or regular direct drilling of various forage species to occur with no adverse effect on soil structure. Use of direct drilling for spring cereals and silage corn on a rotational basis allowed intermittent soil loosening to prevent increasing surface soil compaction. Overall, direct drilling on perhumid, sandy loam soils proved successful when soil surface compaction was alleviated or circumvented.     

Hydroponic Study of Aluminum Accumulation by Aquatic Plants: Effects of Fluoride and pH

The potential of five common aquatic plant species (Typha latifolia, Myriophyllum exalbescens, Potamogeton epihydrus, Sparganium angustifolium and Sparganium multipedunculatum)to be used for Al phytoremediation was tested. The plants were exposed, for 14 days under hydroponic conditions, to synthetic effluents representing extreme conditions that could occur accidentally at an aluminum refinery site. Tested Al concentrationsranged between 0 and 400 μM, fluoride concentrations between 0 and 900 μM, and the pH varied from 4.5 to 7.5. The results indicate that all the plants tested accumulated aluminum, and as a result induced a decrease of Al in the ambient water. For individual species Al uptake (in mol g^-1 dw d^-1) decreased in the following order: Myriophyllum exalbescens > Sparganium sp. ≌Typha latifolia > Potamogeton epihydrus. M. exalbescens accumulated Al more rapidly in its leaves than in other tissues, whereas T. latifolia and Sparganium sp. accumulated Al essentially in their roots. For P. epihydrus the relative importance of the leaves and roots varied with exposure conditions. For all species, fluoro-Al complexes contributed to Al uptake, contrary to the predictions of the Free-Ion Model, according to which the bioavailability of aluminum should be best predicted by the concentration of the free ion, Al³⁺. The influence of pH on Al uptake varied among the different species and among the parts of the plant: competition between Al and the H⁺-ion was evident for the roots of T. latifolia and the leaves and stem of M. exalbescensand P. epihydrus, whereas the roots of M. exalbescens, P. epihydrus and Sparganium sp. showed an inverse trend (Al uptake increased at low pH). For the leaves of T. latifolia and Sparganium sp., no pH influence could be demonstrated. Overall, the results of this study indicate that aquatic plants have a potential for Al phytoremediation.     

High pressure liquid chromatographic determination of aflatoxins in peanut butter using a silica gel-packed flowcell for fluorescence detection

A high pressure liquid chromatographic method has been developed for determining aflatoxins B1, B2, G1, and G2 in peanut butter. The method is based on extraction with acidified aqueous methanol, partition of the aflatoxin into methylene chloride, and purification of the extract on a 2 g silica gel column. The extracted aflatoxins are resolved on a microparticulate (10 micrometer) porous silica gel column in ca 10 min with a water-washed chloroform-cyclohexane-acetonitrile solvent that contains 2% isopropanol. The fluorescence detection system determines aflatoxins B1, B2, G1, and G2 at low levels, i.e., 0.25 ppb B1, 0.5 ppb G1, and 0.2 ppb B2 and G2. Multiple assays of 5 samples of naturally contaminated peanut butters containing total aflatoxins (B1 + B2 + G1 + G2) at levels of 1, 2, 3, 9, and 17 ppb gave intralaboratory coefficients of variation of 7, 4, 4, 11, and 3%, respectively. Samples spiked at levels of 5, 9, and 17 ppb total aflatoxins showed recoveries of 79, 81, and 81%, respectively.     

On the relationship between incoming solar radiation and daily maximum and minimum temperature

A relationship between atmospheric transmittance and the daily range of air temperature is developed. The relationship is T_t = A[1—exp(—BΔT^c)] where T_t is the daily total atmospheric transmittance, ΔT is the daily range of air temperature, and A, B, and C are empirical coefficients, determined for a particular location from measured solar radiation data. Tests on three data sets indicate that 70–90% of the variation in daily solar radiation can be accounted for by this simple model.     

Possible mechanisms of aluminum toxicity in a dilute,acidic environment to fingerlings and older life stages of salmonids

The respiratory, acid-base, and ionoregulatory responses of juvenile rainbow trout (Salmo gairdneri) were monitored during exposure of the fish in the laboratory to inorganic Al (2.8 μM) over the pH range 4.0 to 6.5. Responses to Al were most severe at pH 6.1 and 4.5, mortality being primarily due to asphyxia at pH 6.1 and to electrolyte loss at pH 4.5. Competition between the H⁺-ion and Al for binding at the gill surface is offered as an explanation for the decreased toxicity of Al at pH 4.0, one which is compatible with the free-ion toxicity model that has been developed for other metals. The physiologically distinct response of S. gairdneri to Al at pH 6.1 is less amenable to unambiguous interpretation. If a mixed ligand hydroxo-Al complex is incorporated in the free-ion model, and if it is assumed that the two Al species, [Al-L-gill] and [HO-Al-L-gill], provoke distinct toxicological responses, then a bimodal toxicological response to Al is indeed predicted. An alternative explanation of the apparent toxic action of Al at pH 6.1, i.e., at pH values close to that of minimum Al solubility, is the precipitation of solid Al(OH)₃ at the gill surface, i.e., a ‘physical’ effect rather than a biochemical one.     

Trends in wet and dry deposition of sulphur in the United Kingdom

UK data on sulphur deposition trends between the 1960's and 1990's are presented. Long term data sets of sulphur dioxide (SO₂) concentrations at two sites have been analysed and dry deposition determined using a resistance model. Wet deposition has been calculated from non-marine sulphate concentration and rainfall fields for 1978–80 and 1989–93. These maps have been interpolated and corrected for seeder feeder enhancement. The wet deposition of sulphur declined by about 43 % between 1979 and 1993 whereas emissions of sulphur declined by about 32 %. An indication of the trends in sulphur dry deposition is provided by data from Eskdalemuir, a site in southern Scotland where wet deposition and SO₂ concentration have been measured since 1979. Dry deposition at Eskdalemuir has decreased by 70 % and wet deposition by 48 %. Hence, while wet deposition has responded approximately linearly with the decline in UK emissions of sulphur dioxide, dry deposition has declined at twice the rate of decline in UK emissions.     

Soil moisture affects the interaction between Gaeumannomyces graminis var. Tritici and antagonistic bacteria

Reduction in the soil moisture from a potential of ?10 to?108 kPa reduced the growth of Gaeumannomyces graminis. The antagonist Bacillus cereus only spread through the soil or sand at potentials between ?10 and ?60 kPa. The spread of B. pumilus was not affected by the water potential within the range tested. Both B. cereus and B. pumilus were less antagonistic in the drier sand and soil. When the bacteria and the fungus were grown together the maximum growth of the fungus occurred at those potentials when bacterial antagonism was reduced but the fungus was still able to grow.