Decaying biomass

The influence of toxic substances on nutrient cycles can also be important. One of the more important nutrient cycles is the carbon cycle carbon from atmospheric carbon dioxide is fixed as organic carbon in plant biomass, biomass is consumed by organisms, and carbon in decaying biomass is released back to the atmosphere as carbon dioxide, with a concurrent release of phosphate, nitrogen, and other nutrients. Toxic substances may cause perturbations in such a cycle, as has been observed when toxic heavy metals in soil have killed populations of earthworms, which are important in biomass recycling. 

Other significant biogenic sources of VOCs that have been investigated by PTR-MS are the emissions from plants initiated by wounding , from decaying biomass, and from biomass burning. 

The Monod equation differs from the Michaelis-Menten equation in that it includes as a factor biomass concentration [X], which can change with time. A microbe as it catalyzes a redox reaction harvests some of the energy liberated, which it uses to grow and reproduce, increasing [X], At the same time, some microbes in the population decay or are lost to predation. The time rate of change in biomass... 

It is difficult to estimate the decay constant D from the results of laboratory experiments, since microbes in the natural environment are more likely to die from predation (e.g., Jurkevitch, 2007) than spontaneous decay. Instead, we figure a value from Equation 33.7, setting d[X]/dt = 0 to reflect the steady state. In this case, we see the molal reaction rate, expressed per unit biomass,... 

FIGURE 5.4. The flow of substrate and biomass according to the activated sludge concept for aerobic, heterotrophic transformations. The three major pathways of the flow, biomass growth, hydrolysis and biomass decay, were included in the first attempt to describe the corresponding processes in the sewer. The components are defined in Section 3.2.6. 

Based on this modified activated sludge concept, it was possible to produce acceptable model simulation results for the water-phase processes of the heterotrophic carbon transformations in sewers. However, problems were identified for the description of the heterotrophic biomass decay. A major problem was the magnitude of the 1-order decay rate constant with respect to the biomass concentration. Henze et al. (1987) and Kappeler and Gujer (1992)... 

The Rothamsted Carbon Model (RothC) uses a five pool structure, decomposable plant material (DPM), resistant plant materials (RPM), microbial biomass, humified organic matter, and inert organic matter to assess carbon turnover (Coleman and Jenkinson 1996 Guo et al. 2007). The first four pools decompose by first-order kinetics. The decay rate constants are modified by temperature, soil moisture, and indirectly by clay content. RothC does not include a plant growth sub-module, and therefore NHC inputs must be known, estimated, or calculated by inverse modeling. Skjemstad et al. (2004) tested an approach for populating the different pools based on measured values. 

Oxygen is assumed to be present only in the liquid phase. The biomass is assumed to follow Monod growth kinetics, depending on both the oxygen and substrate concentrations in the liquid phase and to decline according to a first order decay term, where... 

The rate of growth of the trees slows as the forest reaches maturity and canopy closure occurs. In addition, the forest eventually establishes equilibrium with the environment, where the rate of carbon sequestration is exactly balanced by the loss of carbon dioxide to the atmosphere due to decay of dead trees and other biomass. 

The ability of a degradable plastic to decay depends on the structure of its polymer chain. Biodegradable plastics are often manufactured from natural polymers, such as cornstarch and wheat gluten. Micro-organisms in the soil can break down these natural polymers. Ideally, a biodegradable plastic would break down completely into carbon dioxide, water, and biomass within six months, just like a natural material. 

Soil Biomass Soil Organic Matter Soluble Organic P Decaying Plant Residues... 

Our consumption of food and the burning of biomass (such as wood) are part of the natural cycles of the earth (and because they are consumed food and fuel do not need to be durable). So too, in a more extended way, is our use of natural materials to build the world. Materials such as cotton and wool, wood and metal are liable to decay or corrode, even if they are part of artefacts. When we stop actively protecting these materials by keeping them dry or cleaning, natural processes take hold and the materials are returned to natural cycles. 

---