Environmental Engineering Reference
In-Depth Information
organic matter. The basic principles governing decomposition rates and processes apply
across different ecosystems and I would argue there are more similarities than differences.
After describing a generalized model of decomposition, this chapter will discuss the
organisms responsible for transforming the organic materials and then consider the factors
that control decay rates. As organic matter decays, energy is made available for a wide
array of heterotrophs via several pathways and inorganic nutrients may be either released
or immobilized over several timescales. Lastly, gaps in our knowledge will be highlighted
along with viable research approaches.
DECOMPOSITION OF PLANT-DERIVED
PARTICULATE MATTER
Studies of the disappearance of plant litter have been overwhelmingly dominated by
measurements of mass loss from litter bags (
Figure 4.2
). Despite some concern about con-
tainment effects (
Boulton and Boon 1991
) this is a fairly standardized and straightforward
way to quantify differences in decomposition among types of litter or ecosystems. In such
studies, bags containing a known quantity of litter are placed in the environment and
retrieved over a series of time points to determine how much mass remains. The general
pattern to such data is a convex-up curve showing rapid mass loss early in the sequence
with rates declining over time (
Figure 4.3
). There may or may not be some residual
organic matter apparently resistant to decay during the study interval.
The shape of the curve is often represented by a negative exponential model (
Figure 4.3
)
although there is no inherent reason that rate of mass loss from a complex mixture of organic
compounds under varying environmental conditions should be described by such a model.
The model is “first-order,” meaning the rate of mass loss is proportional to the mass still
FIGURE 4.2
Photo of litter bag containing
Vallisneria americana
litter undergoing decomposition on the shore
of the Hudson River.
(Photo Cornelia Harris.)
