Organic matter, dissolved

and DOC represent dissolved organic phosphorus, nitrogen, and carbon, respectively. POP, PON, and POC represent particulate organic phosphorus, nitrogen, and carbon, respectively, ud = undetectable. 

Values are single values, ranges, or means with errors, depending on die source of data. See details of publications for determination of errors. Publications reporting significant uptake or release, but no rates are not listed in this table citations to those publications are in cited literature. ( ) represents data that has been reinterpreted, ns = not significant. 

When ammonium is elevated above ambient, nitrate increases in the water, demonstrating a large potential for nitrification. We have routinely observed that 10% of ammonium uptake is oxidized to nitrate within hours of uptake (Atkinson etal., unpublished data). There is very little work showing rates of nitrification. Denitrification rates in reef sediments are estimated to be 1-4 mmol Nm 2d 1 (see discussion of interstitial geochemistry below). 

There are no published studies of silica on coral reefs. Silica minerals are not abundant on coral reefs, so the biogeochemistry of silica has been ignored. It is evident, however, from the results of our uptake experiments (we measure silica in all our experiments) that silica concentrations in the water sometimes decreases and sometimes increases. This result is probably related to whether benthic diatoms are occupying the reef surfaces. At Biosphere 2 coral reef mesocosm, silica goes through a distinct seasonal cycle related to blooms of benthic diatoms (Atkinson etal., 2001). Concentrations of silica in pore-water can also change seasonally (Falter, 1998). 

DOM is operationally defined by many investigators and represents the material that passes through 

FIGURE 5.6 Relationship between total organic carbon and dissolved organic carbon of the water column. (Data from Wetzel, 2001.) 

Decomposition of organic substrates involves both labile and recalcitrant organic matter, the latter comprising the bulk of the DOC. Turnover of labile pool is very rapid and often may approach a rate of 5-10 times per day thus, actual concentration (storage) of labile DOC is very low (DeBusk and Reddy, 1998). 

---

Studies have appeared where photolysis in natural bodies of water under normal sunlight conditions has been examined. For example, metolachlor was slowly photodegraded by sunlight in lake water, with a half-life of 22 days in summer and 205 days in winter (28). Addition of a 5% solution of dissolved organic matter to the water extended the half-Hves two to three times longer, depending on the season (see PHOTOCHEMICAL TECHNOLOGY, photocatalysis). ... 

The bioavailability, and hence the toxicity, of metal depends on the physical and chemical form of the metal, which in turn depends on the chemical characteristics of the surrounding water. The dissolved form of the metal is generally viewed as more bioavailable and therefore more toxic than the particulate form. Particiilate matter and dissolved organic matter can bind the metal, making it less bioavailable. What is not well known or documented is the various chemical transformations that occur both within the effluent stream and when the effluent reaches and mixes with the receiving water. Metal that is not bioavailable in the effluent may become bioavailable under ambient chemical conditions. 

A great diversity in the concentration of dissolved organic matter also occurs in natural water. Commonly, the concentration ranges from 0.5 to 50 mg/liter. Fresh water and seawater typically have values of 0.5-1.5 mg/liter (18). 

As shown in Fig. 10-13, there is also a flux of O2 produced during net photosynthesis from the ocean to the atmosphere and an export flux of particulate and dissolved organic matter out of the euphotic zone. For a steady-state system, new production should equal the flux of O2 to the atmosphere and the export of organic carbon (Eppley and Peterson, 1979) (when all are expressed in the same units, e.g., moles of carbon). Such an ideal state probably rarely exists because the euphotic zone is a dynamic place. Unfortunately, there have been no studies where all three fluxes were measured at the same time. Part of the difficulty is that each flux needs to be integrated over different time scales. The oxygen flux approach has been applied in the subarctic north Pacific (Emerson et al, 1991) and subtropical Pacific (Emerson et al, 1995, 1997) and Atlantic (Jenkins and Goldman, 1985). The organic carbon export approach has... 

Essentially all the dissolved organic matter in seawater can be assumed to be non-living. However, particulate organic matter can be either living or dead, with the latter often referred to as "detritus."... 

Williams, P. J. LeB. (1975). Biological and chemical aspects of dissolved organic matter in seawater. In "Chemical Oceanography," Vol. 2 (J. P. Riley and G. Skirrow, eds). Academic Press, London. 

F g- 15-15 Schematic representation of Fe and organic matter interactions in an estuary. POM = particulate organic matter DOM = dissolved organic matter PIM = particulate inorganic matter. 

Little is known about MeHg in phytoplankton, particnlarly freshwater phytoplankton (Becker and Bigham 1995). Concentrations of MeHg in freshwater phytoplankton are related to those in water bnt the partitioning of MeHg between water and phytoplankton is strongly affected by concentrations of dissolved organic matter (Watras et al. 1998). 

Spark KM, Swift RS (2002) Effect of soil composition and dissolved organic matter on pesticide sorption. Sci Total Environ 298(1-3) 147-161... 

The degradation of DEHP is directly related to releasable TOCw, perhaps the presence of TOCw improved the solubility and microbial degradability under thermophilic conditions in several studies [61, 62], Bauer and Herrmann [18] revealed that the elution of DEHP from MSW was facilitated by the presence of dissolved organic matter (DOM) even under anaerobic conditions. 

Ohlenbusch G, Kumke MU, Frimmel FH (2000) Sorption of phenols to dissolved organic matter investigated by solid phase microextraction. Sci Total Environ 253 63-74... 

Singlet oxygen o2 Light absorbing dissolved organic matter (humic acids)... 

Dissolved organic matter can be thought of, for simplicity, as soluble organic matter present in soil solution. However, although some workers have measured dissolved organic matter in soil leachates or extracted soil solutions, many use the extract from a 1 2 w/v soil/water extraction... 

Due to the transient nature of dissolved organic matter, seasonal fluctuations in its concentrations are commonly encountered (Sarathchandra et al. 1988 Jensen et al. 1997 Campbell et al. 1999a,b Murphy et al. 

---