Autochthonous inputs

Variation among Sampling Sites. Dissolved humic substance samples from seven end-member environments were isolated for study. Autochthonous inputs to DOM were expected to dominate in Big Soda Lake and in Island Lake, which is a groundwater-sustained eutrophic lake in the sandhills of western Nebraska. Allochthonous inputs to DOM from a swamp environment predominate in the Suwannee River. They also dominate in the Calcasieu River in western Louisiana, but the proportion of swampland is much lower there. The Temi River is a tropical blackwater tributary of the Orinoco River in Venezuela, where allochthonous inputs dominate. The entire Sagavanirktok River basin is located north of the tree line on the North Slope of Alaska a mixture of allochthonous and autochthonous inputs was expected for the various rivers and lakes in this basin. Lastly, Hidden Lake Creek, which is the outlet of Hidden Lake on the Kenai Peninsula of Alaska, was sampled to determine if nutrient inputs from decaying salmon were contributing to primary production and autochthonous inputs to DOM. 

The Sagavanirktok River is intermediate in aromatic carbon content. This river drains the bogs on the Arctic tundra (allochthonous inputs) and several lakes (autochthonous inputs). Samples from the Suwannee and Calcasieu rivers are very similar in peak-height ratios with the exception of peak 2 1 ratio, which is much lower for the Calcasieu River sample. The data in Table II indicate that the Calcasieu River fulvic acid has a greater ring content... 

Rounick, J. S., M. J. Winterbourn, and G. L. Lyon. 1982. Differential utilization of allochthonous and autochthonous inputs by aquatic invertebrates in some New Zealand streams A stable carbon isotope study. Oikos 39 191—198. 

Dystrophic. Subject to a high loading of allochthonous organic matter, but with a low level of autochthonous input. Dystrophic lakes are heavily stained ( brown water ) and have a high content of humic substances. 

The examination of DOM fluorescence in freshwater ecosystems with respect to tanporal variability has been undertaken at a range of time scales from diurnal to seasonal. Seasonal variation in humic-like and protein-like fluorescence has been used to show increasing autochthonous inputs (i.e peak in protein-like fluorescence), increasing allocthonous inputs (i.e., peak in humic-like fluorescence), and thus the dominance of biological or hydrological controls on the ecosystem (Jaffe et al., 2008 Miller and McKnight, 2010). Simple DOM measurements such as the fluorescence index (ratio of Aem 470 to 520 nm at a... 

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. 

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. 

In this chapter, we review and discuss the role of autochthonous sources of DOM in surface waters. Our focus is on the input of DOM from algae and macrophytes within aquatic ecosystems and largely confined to the major pools of DOM potentially available for use as substrates by heterotrophic bacteria. Hence, we will not consider phytoplankton/macrophyte release of specific volatile organics, vitamins, antibiotics, toxic compounds, or enzymes, unless they fall within the scope stated above. 

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... 

Stable carbon isotopes have been commonly used to distinguish between allochthonous versus autochthonous organic carbon inputs to estuaries. One of the most important pieces of information that can be gathered from this information is the delineation between C3 and C4 plant inputs. 

Figure 8.6 Major sources of dissolved organic matter (DOM) to estuaries, primarily composed of riverine inputs, autochthonous production from algal and vascular plant sources, benthic fluxes, groundwater inputs, and exchange with adjacent coastal systems. (Modified from Hansell and Carlson, 2002.)...

The dominant allochthonous inputs are from riverine, marine/estuarine plankton, and bordering terrestrial wetland sources. Autochthonous sources typically include plankton, benthic and epiphytic micro- and macroalgae, emergent and submergent (e.g., seagrasses) aquatic vegetation (EAV and SAV) within the estuary proper, and secondary production. 

Sources of autochthonous DON to estuaries may be derived from actively growing phytoplankton communities, where small molecules such as DFAA are released, which are highly available to bacteria. Allochthonous DON sources from terrestrial runoff, plant detritus leaching, soil leaching, sediments, and atmospheric deposition may also represent important inputs to estuaries. 

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