Cycling in aquatic ecosystems

The role of aquatic organisms in copper cycling in aquatic ecosystems (Stokes 1979)... 

Arnosti, C. (2003) Microbial extracellular enzymes and their role in dissolved organic matter cycling. In Aquatic Ecosystems Interactivity of Dissolved Organic Matter (Findlay, S.E.G, and Sinsabaugh, R.L., eds.), pp. 316-337, Academic Press, New York. 

Capdeville MJ (2011) Study of the biogeochemical cycles of emerging contaminants in aquatic ecosystems. University of Bordeaux, France... 

Figure 3. General model of bio geo chemical cycles in the Earth s ecosystems. The left part is bio geochemical cycling in terrestrial ecosystems, the right part is aquatic ecosystems and the central part is connected with the atmosphere. The fine solid lines show the biogeochemical food webs (the Latin numbers I-XXI) and directed and reverse relationships between these...

The inherent chemical complexity of DOM presents many challenges to understanding the role of DOM in C and N cycling and other processes in aquatic ecosystems. The measurement of trace organic moieties in major fractions of DOM, such as fulvic acids, can provide valuable data for understanding sources and biogeochemical pathways. In field studies, multiple lines of evidence can be critical for definitive interpretation of results. The tracer approaches outlined in this chapter should be used in conjunction with mass balance and flux measurements, for example. 

There has been a considerable amount of work that has focused on the importance of chemical composition, size, and age in controlling microbial metabolism of DOM. The importance of microbes in DOM cycling was recognized and incorporated into the theory of the microbial loop, which first showed that bacteria are key in controlling the trophic linkages between DOM, POM, and inorganic nutrients in aquatic ecosystems. 

Arsenic can exist in several oxidation states, as both inorganic and organometallic species, and in dissolved and gaseous phases (Table I). Dissolved arsenic species can adsorb to suspended solids and be carried down to the sediments in an aquatic system. Since gaseous arsenic compounds can form, arsenic can be removed from the sediments as dissolved gas or in gas bubbles (e.g. CH ). Thus, arsenic can cycle within aquatic ecosystems and this cyclic behavior has been reviewed by Ferguson and Gavis (1 ) and Woolson 2). In any given system, it is necessary to understand the behavior of a variety of different arsenic compounds as well as a variety of environmental compartments in order to totally characterize the cyclic behavior of this element. 

Despite the complexities of the mechanisms that establish the 5 0 of aqueous sulfate, it is clear that this measurement is a useful additional parameter by which sources of SO and sulfur cychng can be evaluated in aquatic systems. Use of a dual isotope approach to tracing sources of sulfur (i.e., measurement of 5 0 and of sulfate) will often provide better separation of potential sources of sulfur and, under favorable conditions, provide information on the processes responsible for sulfur cycling in the ecosystem. Some examples of studies that have examined the sources of SO4 to groundwater using a dual isotope approach include Yang et al. (1997), Dogramaci et al. (2001), and Berner et al. (2002). 

Discuss the interactions of biogeochemical cycles in microbial mats in aquatic ecosystems. Discuss the peculiarities of individual cycles of C, S, and N, and their interactions in microbial mats. 

Discuss the main links of the biogeochemical food web in aquatic ecosystems. Characterize the interplay between terrestrial and aquatic links of biogeochemical cycles. Give examples. 

Our same research group used tracer to measure the rate of inorganic N-uptake by phytoplankton to evaluate the relative importance of nitrogen cycling mechanisms for phytoplankton productivity in aquatic ecosystems (17), We measured nitrate uptake rates of 54.2 it 14.6 ftg-N/h in an oligotrophic lake. The precision of these measurements as well as the wide range over which they have been effectively used demonstrate the advantages of short-lived radioisotopes for tracer biochemistry. 

In this chapter, we discuss the various approaches that have been used to determine organic phosphorus in the water column and sediments of aquatic ecosystems. We then review the limited number of studies that have examined transformations of organic phosphorus in aquatic ecosystems, and finally assess how organic phosphorus interacts with the aquatic cycles of other nutrients. 

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