Movement Of Organic Material Research Articles

Dual processes for cross-boundary subsidies: incorporation of nutrients from reef-derived kelp into a seagrass ecosystem

Movement of organic material across ecosystem boundaries can be critical for subsidizing production in recipient systems, particularly in systems with low in situ productivity or resource availability. Yet, what happens in highly productive and resource-rich ecosystems? Kelp, which is dislodged in high quantities in temperate regions, can accumulate in seagrass ecosystems where productivity and resource availability are high. Using an experimental approach of adding isotopically-labelled (15N) kelp in laboratory and field experiments, we tested whether allochthonous kelp could be incorporated into seagrass ecosystems via (1) the uptake of leached nutrients by macrophytes and (2) the assimilation of nutrients by consumers. Seagrass and epiphytes assimilated kelp-15N under laboratory and field conditions, with epiphytes showing a greater rate of uptake than the seagrass leaves. Unlabelled kelp leached 1225 and 736 -g N (100 g kelp)-1 d-1 of dissolved organic nitrogen from freshly detached and 2 wk old kelp, respectively. Mesograzers (gastropods) assimilated kelp-15N under laboratory and field conditions, despite the presence of alternative food sources. We conclude that reef-derived kelp can act as an important vector of nutrient and energy transfer to both primary producers and consumers in marine landscapes, regardless of their levels of productivity and resource availability.

Remote Sensing And GIS As Tools For The Hydro-geomorphological Modeling Of Soil Erosion In Semi-arid Mediterranean Regions

2 3 Abstract This contribution highlights the advantages of using a multidisciplinary modelling approach to the characterisation of the environmental dynamics of a typical semi-arid Mediterranean region, the Flumendosa river basin located in central Sardinia (Italy). Here, the widespread presence of geomorphological active processes interacts with the consequences of intense human activities on crop cultivation and forest management to produce a fragile environment the equilibrium of which must be carefully surveyed and maintained. To this end, an hydro-geomorphological soil erosion hazard model was devised and applied using remote sensing and G.I.S. techniques as support tools. Radiometric enhancement and supervised classification processing of multitemporal Landsat TM images were used to derive land cover mformation, allowing to understand the seasonal evolution of the area and to monitor the presence and movement of organic materials. These data were then combined with those derived from ground truth and ground survey campaigns concerning geology and geomorphology. At the same time, rainfall simulations were carried out in order to evaluate the principal parameters involved in the soil erosion processes. On these data a hydro-geomorphological model based on the spatial prevalence of the different erosion processes, was applied. Six main parameters (i.e. soil erosivity, land use, hillslope gradient and curvature, contributing area and soil infiltration capacity) were used and combined with a matrix linear combination. Results show that the model could represent, if routinely applied at a local administrative level, a valuable tool for forecasting the relative risk of soil erosion in the framework of a correct environmental management.

Evaluation of fractionation effects during the early stages of primary migration

A stepwise extraction technique, based on that of Beletskaya (1972), has been aplied to sedimentary rock samples of variable grain size and maturity from a Neogene sequence in the Pannonian Basin (S.E. Hungary). The resulting chloroform extracts, claimed by Beletskaya (1978) to sample “open” and mineralogically “closed” pores, have been analysed by gas chromatography and gas chromatography-mass spectrometry. Differences in the concentrations of the two extracts and the concentrations of their hydrocarbon fractions, and in the distributions of n -alkanes and steroid hydrocarbons suggest that either the “open” pores are impregnated with mature oil which has migrated from depth, or that movement of organic material from the “closed” to “open” pores occurs with considerable fractionation based on both polarity and molecular size. The implications of these differences for source rock-oil correlation studies are discussed and an assessment of mechanisms for primary migration is given.

Stable carbon isotope ratios in Fundulus heteroclitus (L.) muscle tissue and gut contents from a North Carolina spartina marsh

Recent food habit and productivity research on the killifish, Fundulus heteroclitus (L.), suggests that this species is important in the movement of organic material within and out of the salt marsh ecosystem. The stable carbon isotope ratios of Fundulus muscle tissue and gut contents were measured seasonally to determine the carbon source of the killifish. For muscle δ 13C values ranged from -13.9% to -15.8% and -15.8% to -18.4% for gut contents, suggesting differential assimilation of ingested material. Muscle tissue indicate that assimilated carbon probably originated from a mixture of benthic algae and Spartina ingested by major prey species: the filddle: crab, Uca pugnax (Smith): the polychaete, Nereis (Neanthes) succinea Frey and Leuckart; the tanaid, Leptochelia rapax Harger; and other small crustaceans. Small fish (age0–1 yr) showed slightly lower δ 13C values than larger fish (age 1–3 yr), consistent with differences in their feeding habits. The only seasonal pattern was an enrichment in tissue 13C that occurred for both small and large fish in the spring, corresponding to the peak spawning period. The δ 13C determination is a useful tool in identifying and tracing carbon sources through the salt marsh food web, detecting differences in feeding habits between age classes of organisms, and assessing the relative nutritive value of ingested dietary items if differential assimilation is suspected.

Movement of organic materials in plants: a note on a recently suggested mechanism

Movement of organic materials in plants: a note on a recently suggested mechanism