Detrital matter

Distribution of241 Am in a dialysis system containing sediment, phytoplankton, and detrital matter established that a substantial amount of americium accumulated in all three phases both in fresh and marine waters (NRC 1981). The adsorption process was not reversible and the longer the americium was adsorbed, the more difficult the chemical was to desorb. Appreciable amounts of americium have been shown to adsorb to bacterial cells such as those found in the Waste Isolation Pilot Plant in New Mexico (Francis et al. 1998). There is a potential that americium attached to biocolloids may facilitate its transport from the waste site. 

Note These (maceral) constituents can be identified and quantitatively measured by examining thin sections or polished surfaces under a microscope, and reflect the nature of the primordial source material as well as the conditions under which it was deposited. Vitrinites derive from humic gels, wood, bark and cortical tissues eoi lnites are the remains of fungal spores, leaf cuticles, algae, resins and waxes and inertinites comprise unspecified detrital matter, "carbonized" woody tissues and fungal sclerotia and mycelia. 

Analcime occurs only in the upper lagoonal complex in beds 150-300 m thick. It is most widespread in the cement of sandstones and fills the pores of many chemogenic rocks associated with them. The widespread occurrence of analcime in the upper complex and its absence in the. lower complex (despite the similar composition of detrital matter and the identical conditions of formation) would have been unaccountable were it not for one peculiar feature of the heavy mineral fraction. The heavy mineral content of rocks of the upper complex varies from fractions of a percent to 2 or 2.5%. Up ot 50% of the heavy mineral fraction consists of fresh, monoclinic pyroxene and amphibole. 

Hodson, R.E, Christian, R.R., and Maccubbin, A.E. (1983) Lignocellulose and lignin in the salt marsh grass Spartina altemiflora initial concentration and short-term, post-depositional changes in detrital matter. Mar. Biol. 81, 1-7. 

The continental slope represents a transit zone of the sediment fluxes supplied in the form of detrital matter from the rivers and the products of abrasion, as well as the sediments carried by turbidity flows. The continental slope is covered with compacted clayey oozes (grain-size fractions of 0.001-0.01 mm). At selected places on steeper parts of the slope, remains of mollusk fauna such as shells of Dreissena rostriformis have been encountered. At sites with gentle sloping, they are overlain by the Holocene and recent sediments [11]. 

The sediments of the Caucasian region are formed under the influence of the solid runoff of mountain rivers and due to the intensive development of the processes of abrasion and denudation. Waves and coastal currents significantly affect the distribution of the terrigenous-detrital matter over the underwater slope, concentrating largest particles of the matter of boulders, pebbles, and sands close to the coastline and on the beach. Beyond the zone of the wave action, fine-grained sands and silty oozes are accumulated. Often, bedrocks are exposed at abrasive surfaces of the underwater slope at depths down to 60 m. 

Atmospheric carbon dioxide is fixed during photosynthesis, and organic carbon is produced. As plants age, older tissue is converted into detrital tissue and is subjected to fragmentation, leaching, and decomposition while attached to living plants. Some of this detrital matter may be above the floodwater surface. 

The relative proportion of these constituents varies with the type and source of detrital matter, the degree of decomposition, and the age of the material. Approximate measures of these constituents in plant material, peat, and soil organic matter are shown in Table 5.7. 

A majority of the extracellular enzymes released by the microbes are bound to the solid surface (such as particulate detrital matter or soil organic matter in clays), but a small fraction remains in the soil pore water (Eigure 5.17). Those free in soil pore water are most susceptible to microbial degradation and chemical alteration. Surface-bound enzymes may not be as effective as free enzymes because of a slow rate of substrate diffusion to the sites where enzymes are present. 

Similar interactions (described above) can occur in the water column of wetlands dominated by periphyton or microbial mat communities, and detrital matter prodnced from emergent macrophytes. 

Abiotic decomposition can be referred to as physical processes attacking the detrital matter, which may include... 

In wetland soils, organic matter decomposition is frequently limited by electron acceptor availability, rather than carbon availability as in upland ecosystems. The concentration and type of electron acceptors available in soils determine the types of microbial communities involved and the rate of decomposition process. Much of the detrital matter produced in wetlands is deposited on the soil surface. It is unlikely that there is enough oxygen in this matrix to decompose this material. Therefore, the decomposition of detrital matter is also dependent on the activity of anaerobic microorganisms using alternate electron acceptors. Similarly, the rate of organic matter decomposition in soils is dependent on the availability of electron acceptors (see for discussion in Chapters 3 and 4). 

Some extracellular enzymes are involved in catalyzing the breakdown polymers. Detrital matter is broken down into complex polymers (cellulose, proteins, lipids, lignin). Enzymes break these polymers into simple monomers (sugars, amino acids, fatty acids) that bacteria can consume. 

Let us assume that 100 units (dry weight basis) of plant detritus is undergoing decomposition in a wetland. The carbon content of detrital matter is 40 units assuming 40% carbon content (dry weight basis). Carbon and nitrogen use efficiency is set at approximately 40% for aerobes and 10% for anaerobes. Based on the above assumptions, 16 units of carbon are assimilated by aerobes and 4 units of carbon by anaerobes. To maintain C N ratio of 10 in their biomass, aerobic microbes and anaerobes would require 1.6 units and 0.4 units of nitrogen, respectively. 

The C N ratio is important because during the decomposition of plant detrital matter, carbonaceous substances provide energy source for microbes and nitrogen is assimilated and metabolized as proteins in the synthesis of cellular materials. 

As discussed earlier, most of the phosphorus entering wetlands accumulates within the system. Surface soils in nutrient-impacted wetlands are often enriched as a result of recent accumulation, decomposition processes, and remobilization of phosphorus from subsurface soils to surface through plant uptake and deposition as detritus material. Thus, total phosphorus content of surface soils is higher than that of subsurface soils. Similar total phosphorus profiles have been seen for many wetlands and aquatic systems. In the impacted site, subsurface total phosphorus content can also represent the background levels of phosphorus for these soils, assuming that the surface material is the result of recent accumulation. Much of this phosphorus accumulation is due to organic matter accretion (detrital matter deposition) associated with phosphorus sorption to particulate matter. 

Organic PP is associated with detrital matter from dead and decomposing bacteria, phytoplankton, zooplankton cells, and periphyton, as well as from vascular plants, and organic phosphorus associated with particulate matter is termed as POP. POP is estimated as follows ... 

Microorganisms also can play a major role in retaining phosphorus in wetlands with organic matter inputs or those producing large quantities of detrital matter internally as a result of high primary productivity. Microorganisms incorporate dissolved phosphorus into cellular constituents. 

DOM and associated DOP produced from POM (detrital matter and soil organic matter) are the major components transported from wetlands to adjacent aquatic systems. Within wetlands, DOM and associated DOP can have significant influence on heterotrophic production and nutrient cycling. DOP can be produced and mineralized by the following abiotic processes ... 

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