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Organic Matter Types (organic + matter_type)
Selected AbstractsBeneficial links for the control of aphids: the effects of compost applications on predators and preyJOURNAL OF APPLIED ECOLOGY, Issue 4 2008James R. Bell Summary 1Polyphagous predators, such as spiders and beetles, perform a fundamental ecosystem service as regulators of agricultural pests, particularly aphids. They are most effective when they colonize the crop before the pest has reached its exponential growth phase. However, this is also when predators find themselves in a state of near-starvation. 2Predator numbers can be enhanced by applications of different types of organic matter, but the mechanism is not clearly understood. One hypothesis is that compost applied to the field may introduce a new detrital food chain to maintain predators until the pest arrives, but this may also be detrimental to effective pest control, fostering a surplus of alternative prey and causing a switch away from the pest. To elucidate these possible outcomes, we report on the use of within-field compost applications on aphids and their predators, presenting 4 years of field-scale manipulations. 3We found both direct and indirect links between compost, aphids and predators. In years when compost-treated plots had significantly higher numbers of predators, aphids were in significantly lower numbers than in plots without compost. Conversely, when there was a lack of response by predators, aphid numbers showed similar trends in all treatments. 4In all years, alternative prey responded strongly to compost application and did not fluctuate at the level shown by predators, suggesting that these two prey groups were decoupled. Instead, the predicted positive feedback of compost on predators numbers was either weak or absent. 5Synthesis and applications. The effect of compost on aphids clearly requires further practical refinement if it is to provide constant pest suppression, making it difficult to provide specific management recommendations at this stage. In the short term, compost application may not always confer immediate benefits in terms of pest control alone but this must be set against other better known benefits (moisture retention, nutrients). In the long term, experiments measuring the full trophic pathway are needed to unravel the effects of organic matter type, application time and the siting of compost relative to the crop in order to optimise pest suppression potential. [source] Reach-scale geomorphology affects organic matter and consumer ,13C in a forested Piedmont streamFRESHWATER BIOLOGY, Issue 6 2007D. M. WALTERS Summary 1. We investigated the spatial (longitudinal position and reach geomorphology) and seasonal (spring and autumn) influences on the variation of ,13C among organic matter sources and consumers in a forested Piedmont river, South Carolina, U.S.A. 2. Six sites were sampled along a continuum and varied in basin area from approximately 30 to 300 km2. Sites fell into two geomorphic categories (i) high-gradient, rock bed (,rock') or (ii) low-gradient, sand bed (,sand') sites. 3. Variation in ,13C was more strongly related to reach geomorphology than longitudinal position. ,13C of biofilm and consumers was consistently enriched at rock sites. Leaf litter (i.e. coarse particulate organic matter, CPOM) ,13C did not vary with bed type. There was significant ,13C enrichment at rock sites for biofilm, seston, fine benthic organic matter (FBOM), and eight of nine consumer trophic guilds (e.g. grazing invertebrates, insectivorous fishes). ,13C of biofilm and four trophic guilds was also positively correlated with drainage area, but the magnitude of enrichment was less than between bed types. 4. ,13C was generally enriched in spring, but this varied among organic matter types, consumers, and by bed type. CPOM and seston were enriched in spring, FBOM was enriched in autumn, and biofilm showed no trend. Five consumer guilds were enriched in spring, and only one fish guild, generalised carnivores, showed enrichment of muscle tissue in autumn. 5. Consumer ,13C enrichment at rock sites suggests greater reliance on algal carbon than for consumers at sand sites, but we also found ,13C enrichment of biofilm at rock sites. Thus, differences in consumer ,13C between bed types could be related to (i) increased consumption of biofilm at rock compared with sand sites, or (ii) consumption of biofilm at rock sites that is enriched relative to biofilm at sand sites or (iii) both mechanisms. 6. ,13C signatures in local food webs appear to respond to processes operating at multiple spatial scales. Overall downstream enrichment of biofilm and consumers was disrupted by strong local effects related to bed morphology. These results suggest that human alteration of channel habitat will have corresponding effects on stream food webs, as assessed by changes in ,13C. [source] Characteristics of Oil Sources from the Chepaizi Swell, Junggar Basin, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010LIU Luofu Abstract: So far there has been no common opinion on oil source of the Chepaizi swell in the Junggar Basin. Therefore, it is difficult to determine the pathway system and trend of hydrocarbon migration, and this resulted in difficulties in study of oil-gas accumulation patterns. In this paper, study of nitrogen compounds distribution in oils from Chepaizi was carried out in order to classify source rocks of oils stored in different reservoirs in the study area. Then, migration characteristics of oils from the same source were investigated by using nitrogen compounds parameters. The results of nitrogen compounds in a group of oil/oil sand samples from the same source indicate that the oils trapped in the Chepaizi swell experienced an obvious vertical migration. With increasing migration distance, amounts and indices of carbazoles have a regular changing pattern (in a fine linear relationship). By using nitrogen compounds techniques, the analyzed oil/oil sand samples of Chepaizi can be classified into two groups. One is the samples stored in reservoir beds of the Cretaceous and Tertiary, and these oils came from mainly Jurassic source rock with a small amount of Cretaceous rock; the other is those stored in the Jurassic, Permian and Carboniferous beds, and they originated from the Permian source. In addition, a sample of oil from an upper Jurassic reservoir (Well Ka 6), which was generated from Jurassic coal source rock, has a totally different nitrogen compound distribution from those of the above-mentioned two groups of samples, which were generated from mudstone sources. Because of influence from fractionation of oil migration, amounts and ratios of nitrogen compounds with different structures and polarities change regularly with increasing migrating distance, and as a result the samples with the same source follow a good linear relationship in content and ratio, while the oil samples of different sources have obviously different nitrogen compound distribution owing to different organic matter types of their source rocks. These conclusions of oil source study are identical with those obtained by other geochemical bio-markers. Therefore, nitrogen compounds are of great significance in oil type classification and oil/source correlation. [source] Geochemical Signatures of Early Paleogene Source Rocks in the Sanshui Basin, South ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2010Chunlian LIU Abstract: The Honggang member of the early Paleogene Buxin Formation is the main source rock in the Sanshui Basin, characterized by organic-rich black shales with the cyclic recurrence of organic-poor sediments. The geochemical characteristics of the Honggang member have been documented to determine the organic matter types and depositional environments in this paper. The organic matter of the black shales mainly consists of a mixture of land plant-derived and phytoplankton-derived organic matter. Total organic carbon content (TOC)-sulfur-iron (Fe) relationships suggest that the organic-rich black shales were deposited under dysoxic-to-euxinic water conditions. The time that iron minerals remained in contact with H2S in anoxic waters possibly influenced the formation of syngenetic pyrite, and organic carbon controlled the formation of diagenetic pyrite. Organic-poor intervals usually show pyrite sulfur enrichment and higher degree of pyritization values relative to low organic carbon contents. This resulted from HS, diffusing downward from overlying organic-rich sediments and formed Fe sulfides through reactions with sufficient Fe. Trace elements generally exhibit low concentrations and little TOC dependence, suggesting some degree of depletion in these elements in the early Paleogene sediments of the Sanshui Basin. This probably resulted from cyclic recurrences of oxic benthic conditions, which promoted the remobilization of trace elements and caused the low concentration of trace elements. [source] | ||||||||||