Autochthonous organic matter

Most of the organic matter in seawater was created in situ by marine processes and is, hence, classified as autochthonous. Organic matter of nonmarine origin is classified as allochthonous and is primarily terrestrial detritus, transported by rivers or winds. The input of organic matter from rivers is small (0.4 Pg C/y) compared to primary productivity (40 to 50 Pg C/y). The aeolian input is unknown but thought to be significant. 

Allochthonous vs. autochthonous organic matter - key UV-VIS mediated processes regulate heterotrophic utilization... 

Murphy, K.R., Stedmon, C.A., Waite, T.D., and Ruiz, G.M. (2008). Distinguishing between terrestrial and autochthonous organic matter sources in marine environments using fluorescence spectroscopy. Mar. Chem., 108,40-58. 

Recent investigations provide new insight on the structural chemistry of dissolved organic matter (DOM) in freshwater environments and the role of these structures in contaminant binding. Molecular models of DOM derived from allochthonous and autochthonous sources show that short-chain, branched, and alicyclic structures are terminated by carboxyl or methyl groups in DOM from both sources. Allochthonous DOM, however, had aromatic structures indicative of tannin and lignin residues, whereas the autochthonous DOM was characterized by aliphatic alicyclic structures indicative of lipid hydrocarbons as the source. DOM isolated from different morphoclimatic regions had minor structural differences. 

Mixture complexity must be minimized before structural studies can begin. One approach is fractionation of the mixture to concentrate and isolate the property of interest (5-7). An alternative is to study DOM found in environmental end-member systems. End-member environments are water bodies for which inputs of organic matter (allochthonous versus autochthonous) and climate (polar versus tropic) are homogeneous compared to those of most water bodies. The following research presents a fractionation of DOM isolated from end-member systems moderately definitive molecular models were derived. 

Supply of Dissolved Organic Matter to Aquatic Ecosystems Autochthonous Sources... 

At whole lake scales, littoral zones are a major component of autochthonous DOM production and important sources of labile organic matter for aquatic bacteria. Of the approximately one billion lakes in the world, the littoral zone accounts for more than 95% of lake surface area in nearly 99.8% of all lakes (Wetzel, 1983 Fig. 3a). The importance of shallow waters is even more marked when the bounds of lakes are expanded to include wetlands. With such an expanded view, the littoral zone and wetlands comprise more than 95% of the area in 99.999% of all lakes (Fig. 3a). Clearly, shallow waters are a dominant feature of lentic ecosystems. 

We hypothesized that the input of terrestrial organic matter relative to the input of autochthonous carbon would be a good predictor of the relative importance of heterotrophic organic N formation in different aquatic systems. Following a flow path from streams to lakes to rivers to estuaries to oceans, this hypothesis would suggest that microbial organic N formation would be highest in wooded streams and rivers, moderate in lakes and estuaries, and lowest in open-water marine systems. 

Functional processes are essentially the same in both freshwater and marine systems, the differences become apparent when the emphasis is placed on the source of the organic matter (OM). The source of this OM affects the rate at which it is used not the overall process of use (Wetzel, 2000). These rates differ because of the greater influx of humic or recalcitrant materials in inland systems versus the dominating inputs of autochthonous OM in marine systems. These studies show that bacterial populations do respond to differences in the DOM pool. The challenge now lies in increasing the scope of these studies to find patterns in the spatiotemporal distribution... 

Bertilsson, S., and Jones, J. B., Jr. (2003). Supply of dissolved organic matter to aquatic ecosystems Autochthonous sources. In Aquatic Ecosystems—Interactivity of Dissolved Organic Matter, Findlay, S. E. G., and Sinsabaugh, R. L., eds., Academic Press, Amsterdam, pp. 3-24. 

---