Detritus, organic

In the leaching phase, soluble compounds are rapidly lost from fresh detritus over a scale of minutes to weeks (figure 8.15 Wilson et al., 1986). In the case of the marsh plant 5. altemiflora, as much as 20 to 60% of the original material can be lost during this phase (Wilson et al., 1986). These soluble DOM compounds released from detrital particles are rapidly used by a high abundance of free bacteria in the surrounding water column (Aneiso et al., 2003). Much of this leached material likely consists of short-chain carbohydrates, proteins, and fatty acids (Dunstan et al., 1994 Harvey et al., 1995). 

There has also been considerable debate about the rate of decay of these labile leached substrates in oxic versus anaerobic conditions, with some studies showing faster decay under oxic conditions (Bianchi et al., 1991 Lee, 1992 Sun et al., 1994 Harvey et al., 

1995) and others showing no effects of redox (Henrichs and Reeburgh, 1987 Andersen, 

Wilson et al., 1986). The source of detritus will clearly affect the period of refractory decay. For example, the refractory phase of phytodetritus may last for only a few weeks compared to vascular plant detritus which may last for months to years (Valiela, 1995 Opsahl and Benner, 1999). Finally, temperature and size of the decomposing detrital particles also represent parameters affecting decay rate. Early work by Hodson et al. (1983) showed that lignocellulose remineralization rates were enhanced with decreasing particle size due to the higher relative abundance of microbes with an increasing surface-to-volume ratio. To no surprise, litter bag experiments indicate that increases in temperature also increase decay rates due to enhanced microbial activity (Wilson et al., 1986). 

Berner (1980) first introduced the following concept of a one-G model for determining first-order decay constants (k) of organic matter decomposition  

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Organically bound matter (OM). Heavy metals/trace elements may be bound in living organisms, detritus, and organic matter of the soil. The organically bound trace elements or heavy metals are affected by the production and decomposition of organic matter. 

In addition to the dissolved elements and compounds in the oceanic water column, a wide variety of water column chemicals are found in marine organisms and organic detritus. For example, a milliliter of surface seawater can contain on the order of 10 million viruses, 1 million bacteria, 100,000 phytoplankton, and 10,000 zooplankton [9]. With the advent of soft ionization processes for mass spectrometry systems, scientists have been able to study these marine organisms at molecular level. The use of electrospray ionization (ESI see Section 2.1.15), atmospheric pressure chemical ionization... 

Another aspect to be described by example is hydrothermal petroleum and the related high temperature alteration of natural products in aqueous medium. In such cases immature organic detritus with natural products is altered mainly to hydrocarbons by rapid reductive hydrous pyrolysis. 

Detenbeck (37) and Detenbeck and Brezonik (38, 39) examined the effect of pH on phosphorus sorption for LRL sediments. Their results suggested that the flux of inorganic P from sediments could be diminished by as much as 90% if the pH of sediments decreased from 6.0 to 4.5. However, there was no observed treatment effect for TP and an apparent increase in SRP summer averages at pH 4.7 (Figure 4). Therefore, chemical sorption-desorption processes probably do not control phosphorus levels in LRL. The direction of response at lower pH implies that the balance between biotic uptake, deposition to sediments, and release from organic detritus by decomposition most likely controls SRP levels in the water column. 

Fenchel, T., 1970. Studies on decomposition of organic detritus derived from the turtle grass Thalassia testudinum. Limnol. Oceanogr., 15 14-20. 

The decay of aquatic organic detritus is generally divided into (1) leaching, (2) decompositon, and (3) refractory phases. 

Decomposition rates of organic detritus in wetlands is relatively slow compared with algal material. The generally slower rates of decay have been attributed to (1) anaerobic conditions, (2) acidity of the water, and (3) inhibition of decomposition by dissolved humic substances and secondary compounds. 

Darnell, R.M. (1967) The organic detritus problem in estuaries. American Association for the Advancement of Science, Publication No. 83, 374—375. 

Odum, E. P., and de la Cruz, A.A. (1967) Particulate organic detritus in a Georgia salt marsh-estuarine ecosystem In Estuaries (Lauff, GH., ed.), pp. 383-388, American Association for the Advancement of Science, Washington, DC. 

The most likely sources of metal ions for marine organisms are the colloidal or particulate moieties such as plankton, organic detritus, and clay minerals. The latter may be coated with iron or manganese oxides which are efficient scavengers of metals in slightly alkaline media. 

Fig. 4.4. Lucifer yellow carbohydrazide dye indicating water flow applied to a deep-root chamber, and detected in mycorrhizal hyphae in a hyphal chamber after crossing airgaps that restrict diffusion. Panel A is an AM hypha that transported the dye during the night (hydraulic lift). Panel B shows a mycorrhizal fungus hydrophilic tip, with hydraulically lifted water exuding out the tip onto a piece of organic detritus. Photographs by Louise Egerton-Warburton and details of the experiment can be found in Querejeta et al. (2003).

The affect of physicochemical form on uptake from solids has been more carefully studied where sediments are the source of food to animals. When deposit-feeding clams -were fed various types of sedimentary substrates (oxides of iron and manganese organic detritus inorganic and biogenic carbonates) labelled with Cd, Co and Zn, uptake of the nuclides varied... 

The differences between the quantities accumulated in oysters held in filtered vs. nonfiltered water suggest that particles play an important role in the accumulation" of elements. Particles in the water may be living microorganisms, organic detritus, inorganic material, or any combination of the three and may vary in quantity, both with time and location. The role of particles in radionuclide accumulation differed with each radionuclide. In oysters, Co appears to be accumulated primarily from the suspended particulate fraction, whereas appears to be... 

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