Distribution patterns of mesopelagic fishes with special reference to Vinciguerria lucetia Garman 1899 (Phosichthyidae: Pisces) in the Humboldt Current Region off Peru

The horizontal and vertical distributions of adult mesopelagic fishes are described from acoustic and trawl surveys over the full-depth of 500 m at 169 stations on a longitudinal transect crossing the Humboldt Current (03°45′S, 81°76′W and 18°23′S, 71°13′W) at 50–200 nautical miles off Peru during austral spring (October–November) of 2001, 2002 and 2003. A total of 2,952 kg of fishes was collected, which included 13 families, 23 genera and 28 species. The mesopelagic community is dominated by the families Phosichthyidae (Vinciguerria lucetia), Myctophidae (Diogenichthys laternatus and Lampanyctus idostigma) and Bathylagidae (Leuroglossus urotranus), accounting for 60.4, 12.8 and 3.7%, respectively, of the total catch. Based on horizontal distribution patterns these species were categorized into three groups, i.e. northern-central upwelling front group (L. urotranus, Nemichthys fronto and Scopelarchoides nicholsi), Southern upwelling front group (Hygophum reinhardti, Myctophum nitidulum, Paralepis sp and Scopeloberyx sp.) and pan-Humboldt Current group (V. lucetia, D. laternatus, L. (Nannobrachium) idostigma, L. omostigma, M. aurolaternatum, Triphoturus oculeus, Bathylagus (Melanolagus) berycoides, Leuroglossus stilbius, Argyropelecus affinis, Sternoptyx obscura, Melamphaes sp., Stomias sp. and Scopelosaurus sp.). Nighttime vertical distribution was characterized by a single abundance peak in the upper 50 m. Daytime patterns showed three peaks of abundance: an upper peak, in the upper 100 m, a midwater peak between 200 and 400 m, coinciding with an oxygen minimum zone, and a deeper peak between 400 and 500 m. V. lucetia was dominant in the upper and midwater peaks while myctophids, other planctivorous and piscivorous fishes were distributed in the midwater. Acoustic back-scattered energy (S _a) was ubiquitous in the region. Maximum S _a was mainly located between 11° and 18°S during day and night. V. lucetia is a significant component of the sound-scattering layers in the Humboldt Current Region off Peru.     

Hexazinone and simazine dissipation in forestry field nurseries

Hexazinone and simazine field dissipation was studied in two different soils from Spain (Toledo and Burgos), devoted to forest nurseries for Pinus nigra. Laboratory experiments (adsorption-desorption isotherms, leaching experiment and degradation study) were carried out to determine possible mechanisms of dissipation. Higher adsorption was observed for hexazinone in Toledo (KfT = 0.69) compare to in Burgos soil (KfB = 0.20) probably due to the higher organic matter (OM) content of Toledo soil. No differences in adsorption were obtained for simazine in both soils (KfT = 1.27; KfB = 1.34). In every case, adsorption was higher for simazine than for hexazinone, in both soils. The total recovery of hexazinone in the leachates from handpacked soil columns was higher in Burgos (100%) than in Toledo (80%), because of the larger adsorption of hexazinone in this last soil. No differences in simazine leaching between both soils were found, although the total amount of pesticide recovered in leachates (40% in the two soils) was lower for simazine than for hexazinone. Finally, lower degradation was found in Burgos (t1/2 = 91 d) vs Toledo (t1/2 = 47 d), directly related with the high OM content of Toledo. No half-life was calculated for simazine in Toledo because no changes in herbicide soil content were observed during the period of time studied. In the case of Burgos, the half-life for simazine was 50 days. The field residues study showed larger persistence of simazine than hexazinone mainly due to the higher adsorption and lower mobility of simazine in the two soils. The lower persistence of hexazinone in Toledo soil than in Burgos soil is related to the larger rainfall occurred in this soil besides the higher degradation of this herbicide observed in Toledo soil. The much lower temperature in Burgos than in Toledo soil during winter contribute to the higher persistence of the two herbicides in Burgos soil.     

Fenuron sorption on homoionic natural and modified smectites

Abstract

The adsorption isotherms of fenuron (l, l‐dimethyl‐3‐phenylurea) on three smectites (SWy and SAz montmorillonites and SH hectorite) differing in their layer charge (SH<SWy<SAz) and saturated with several inorganic and organic cations were determined. The isotherms and sorption parameters from Freundlich equation indicate low adsorptivity on inorganic clays, but medium sorption in organoclays (OCls). Fenuron adsorption on homoionic smectites increases with decreasing layer charge and hydratation power of the inorganic exchangeable cation (except Fe³⁺), indicating that fenuron adsorbs as neutral molecule on uncharged siloxane surface by hydrophobic bonding, with some contribution of polar bond (fenuron C=O group and water associated to exchangeable cation). In the case of Fe³⁺‐saturated smectite fenuron protonation, provided by the interlayer acidic environment, promotes further sorption of fenuron as cationic form. The sorption on organoclays is enhanced via hydrophobic interaction with organocations, which is favoured for high layer charge and basal spacing and organocation saturation close to CEC. Quaternary alkylamonium is more efficient in high layer charge smectite, whereas primary alkylammonium is more efficient in medium charge smectite. The low values of the maximum sorption obtained with homoionic inorganic and organic smectites (100 and 5000 μmol/Kg) represent one fenuron molecule for each 2000–200 exchange sites and indicate that fenuron sorption is mainly associated to the outer exchange sites. This low adsorptivity of fenuron, as consequence of its high water affinity (high water solubility) would suggest high mobility of fenuron in natural soil and water systems.     

Terbuthylazine persistence in an organic amended soil

The aim of this work was to study the effect of the application of a solid waste from olive oil production (alperujo) on the movement and persistence of the herbicide terbuthylazine (N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine). An experimental olive grove was divided in two plots: (i) Plot without organic amendment (blank) and (ii) Plot treated with alperujo during 3 years at a rate of 17920 kg of alperujo ha(- 1). Terbuthylazine was applied to both plots at a rate of 2 kg ha(- 1) a.i. Triplicates from each plot were sampled at 3 depths (0-10, 10-20 and 20-30 cm), air-dried, remains of olive leaves, grass roots, and stones removed and sieved through a 5 mm mesh sieve. Terbuthylazine was extracted with methanol 1:2 weight:volume ratio, the extracts were evaporated to dryness, resuspended in 2 mL of methanol, filtered and anylized by high performance liquid chromatography (HPLC). Higher amounts of terbuthylazine were detected at each sampling depth in plots treated with alperujo. The increase in soil organic matter content upon amendment with alperujo slightly increased sorption, suggesting that other factors beside sorption affect terbuthylazine degradation rate in organic amended soils.     

Global distribution of a key trophic guild contrasts with common latitudinal diversity patterns

Most hypotheses explaining the general gradient of higher diversity toward the equator are implicit or explicit about greater species packing in the tropics. However, global patterns of diversity within guilds, including trophic guilds (i.e., groups of organisms that use similar food resources), are poorly known. We explored global diversity patterns of a key trophic guild in stream ecosystems, the detritivore shredders. This was motivated by the fundamental ecological role of shredders as decomposers of leaf litter and by some records pointing to low shredder diversity and abundance in the tropics, which contrasts with diversity patterns of most major taxa for which broad-scale latitudinal patterns haven been examined. Given this evidence, we hypothesized that shredders are more abundant and diverse in temperate than in tropical streams, and that this pattern is related to the higher temperatures and lower availability of high-quality leaf litter in the tropics. Our comprehensive global survey (129 stream sites from 14 regions on six continents) corroborated the expected latitudinal pattern and showed that shredder distribution (abundance, diversity and assemblage composition) was explained by a combination of factors, including water temperature (some taxa were restricted to cool waters) and biogeography (some taxa were more diverse in particular biogeographic realms). In contrast to our hypothesis, shredder diversity was unrelated to leaf toughness, but it was inversely related to litter diversity. Our findings markedly contrast with global trends of diversity for most taxa, and with the general rule of higher consumer diversity at higher levels of resource diversity. Moreover, they highlight the emerging role of temperature in understanding global patterns of diversity, which is of great relevance in the face of projected global warming.     

Terbuthylazine persistence in an organic amended soil

The aim of this work was to study the effect of the application of a solid waste from olive oil production (alperujo) on the movement and persistence of the herbicide terbuthylazine (N²-tert-butyl-6-chloro-N⁴-ethyl-1,3,5-triazine-2,4-diamine). An experimental olive grove was divided in two plots: (i) Plot without organic amendment (blank) and (ii) Plot treated with alperujo during 3 years at a rate of 17920 kg of alperujo ha^{? 1}. Terbuthylazine was applied to both plots at a rate of 2 kg ha^{? 1} a.i. Triplicates from each plot were sampled at 3 depths (0–10, 10–20 and 20–30 cm), air-dried, remains of olive leaves, grass roots, and stones removed and sieved through a 5 mm mesh sieve. Terbuthylazine was extracted with methanol 1:2 weight:volume ratio, the extracts were evaporated to dryness, resuspended in 2 mL of methanol, filtered and anylized by high performance liquid chromatography (HPLC). Higher amounts of terbuthylazine were detected at each sampling depth in plots treated with alperujo. The increase in soil organic matter content upon amendment with alperujo slightly increased sorption, suggesting that other factors beside sorption affect terbuthylazine degradation rate in organic amended soils.     

Breeding systems and seed size in a neotropical flora: testing evolutionary hypotheses

A well-known, but largely untested, prediction in plant reproductive ecology is that dioecious taxa should produce larger, more, higher-quality, or better-defended seeds than cosexual taxa. Using a data set composed of 972 species in 104 families, representing the flora of the Tambopata Wildlife Reserve (Madre de Dios, Peru), we evaluated the first component of this prediction, examining ecological and evolutionary relationships between breeding system and mean seed size with two kinds of tests. First, we conducted cross-species analyses to determine whether species with different breeding systems differed significantly with respect to mean individual seed size. Second, we used a hypothesized phylogeny to identify pairs of the most closely related taxa or clades within the Tambopata community that differed with respect to breeding system. Comparing pair members allowed us to determine whether evolutionary divergence in breeding system (between taxa with unisexual vs. cosexual individuals) was consistently associated with evolutionary change in seed size. In both analyses, we controlled for potentially confounding effects of growth form by examining these relationships within woody and nonwoody taxa. Cross-species analyses revealed that dioecious species produced larger seeds than cosexual species among woody species, shrubs, lianas (each growth form analyzed separately), and all species pooled, but not among trees. Phylogenetically independent contrasts upheld the significant association between breeding system and seed size among woody taxa, lianas, and all taxa pooled, but not among shrubs. We discuss the implications of our findings for evolutionary hypotheses regarding associations between dioecy and seed size.     

Sorption and photolysis studies in soil and sediment of the herbicide napropamide

Abstract

The influence of soil and sediment composition on sorption and photodegradation of the herbicide napropamide [N, N‐diethyl‐2‐(1‐naphthyloxy)propionamide] was investigated. Five soils and one sediment were selected for this study and the clay fractions were obtained by sedimentation. Sorption‐desorption was studied by batch equilibration technique and photolysis in a photoreactor emitting within 300–450 nm wavelenght with a maximum at 365 nm. Sorption increased with clay content and was not related to organic matter *content. High irreversibility of sorption was related to the greater montmorillonite content. The presence of soil or sediment reduced photolysis rate due to screen effect and this process did not depend on solid composition but on particle size distribution.     

Behaviour of simazine in soil amended with the final residue of the olive-oil extraction process

Addition of organic wastes to agricultural soils is becoming a common practice as a disposal strategy and to improve the physical and chemical soil properties. However, in order to optimise the use of organic wastes as soil amendments, their effect on the behaviour of other compounds that are also used in agriculture, such as pesticides, needs to be assessed. In this work, we have investigated the effects of the addition of the final solid residue of the new technology of olive-oil extraction (extracted alperujo or solid olive-mill waste, SOMW2) on the sorption, degradation and leaching of the herbicide simazine in a sandy loam soil. The results are compared with those of a previous study, where the intermediary by-product of the olive-oil processing technology (unextracted alperujo or SOMW1) was applied to the same soil. The soil was amended in the laboratory with SOMW2 at two different rates (5% and 10% w/w). Simazine sorption isotherms showed a great increase in herbicide sorption after SOMW2 addition to soil. SOMW2 addition also increased sorption irreversibility. Incubation studies revealed reduced biodegradation of simazine in the soil amended with SOMW2 compared to the unamended soil. Breakthrough curves of simazine in handpacked soil columns showed that SOMW2 addition retarded the vertical movement of the herbicide through the soil and greatly reduced the amount of herbicide available for leaching. Interestingly, the results were quantitatively different from those obtained for the intermediary by-product SOMW1, illustrating the importance of the specific characteristics of the organic amendment in determining its effect on pesticide behaviour.