Humic lake

Even within the subset of boreal lakes there is probably a direct relationship between external inputs of organic matter and their importance to zooplankton (Meili, M. Fry, B. Kling, G. W. unpublished data). In the case of Lake N2 and other upland arctic lakes, thermokarst processes and active erosion of shoreline peat banks are much less important than they are in coastal plain lakes (62, 75, 103). In addition, DOC made up less of the total organic carbon in Lake N2 than it did in the humic lake studied by Hessen (72) the ratio of DIC DOC.POC in Lake N2 was 25 8 1 (Table II), whereas in the humic lake the ratio was 1.6 21 1. The lower loading rates of particulate carbon and the smaller relative amounts of DOM in Lake N2 may explain the observation that pelagic productivity depended mainly on new algal production. 

VII. Elemental Acquisition in Humic Lakes Implications for Ecosystem Structure and Function 205... 

Given that the Fe and P bound to the DOM in humic lakes are probably not directly available to organisms, the DOM-Fe-P complex would have to undergo some form of transformation to yield bioavailable Fe and P species. In terms of biological uptake, in general it can be said that Fe is preferred in the dissolved free ionic form and P as orthophosphate (P04). Several known processes result in the transformation of Fe and P from the DOM-Fe-P complex into biologically available species. Two of the mechanisms are physical-chemical processes (1) UV-mediated photoreduction and (2) DOM-mediated chemical reduction or dark reduction. Other mechanisms are... 

VII. ELEMENTAL ACQUISITION IN HUMIC LAKES IMPLICATIONS FOR ECOSYSTEM STRUCTURE AND FUNCTION... 

Bacteria are known to outcompete algae for the uptake of available P in P-limited systems (Currie and Kalff, 1984). The greater ability of the bacterial community to acquire P has also been demonstrated in a small humic lake (Salonen et al., 1994). Bacteria tend to dominate in terms of both biomass and production in humic lakes (Tranvik, 1989 Hessen, 1992) and are likely the most important mobilizers of both Fe and P in these systems. 

Given how the DOM-Fe-P complex influences ecosystem structure, it is also likely that the DOM-Fe-P complex influences humic lake ecosystem function in terms of C metabolism. First, the bacterial conversion of dissolved C into biomass it is quite low, with an average of 25 % across a trophic gradient (del Giorgio et al., 1997). And despite the evidence that bacteria may be better equipped to acquire the Fe and P bound to DOM, the added energetic expenditure in acquiring these elements may result in a significant... 

Bergstrom, A., and A. Isaksson. 2001. The importance of mixotrophic flagellates as bacterial grazers in a large humic lake — results from a three-year study in northern Sweden. In American Society of Limnology and Oceanography Meeting, Albuquerque, NM, Abstract, p. 23. 

De Haan, H., and T. de Boer. 1986. Geochemical aspects of aqueous iron, phosphorus and dissolved organic carbon in the humic Lake Tjeukemeer, the Netherlands. Freshwater Biology 16 661—672. 

De Haan, H., R. I. Jones, and K. Salonen. 1990. Abiotic transformations of iron and phosphate in humic lake water revealed by double-isotope labeling and gel filtration. Limnology and Oceanography 35 191 19. ... 

Hessen, D. O. 1992. Dissolved organic carbon in a humic lake effects on bacterial production and respiration. Hydrobiologia 229 115—123. 

Hessen, D. O. 1998. Food webs and carbon cycling in humic lakes. In Aquatic Humic Substances (D. O. Hessen and L. J. Tranvik, Eds.), pp. 285-315. Springer-Verlag, Berlin. 

Jones, R. I., K. Salonen, and H. De Haan. 1988. Phosphorus transformations in the epilimnion of humic lakes Abiotic interactions between dissolved humic materials and phosphate. Freshwater Biology 19 357-369. 

Niirnberg, G. K., and M. Shaw. 1998. Productivity of clear and humic lakes Nutrients, phytoplankton, and bacteria. Hydrobiologia 382 97-112. 

Salonen, K., R. I. Jones, H. De Haan, and M. James. 1994. Radiotracer study of phosphorus uptake by plankton and redistribution in the water column of a small humic lake. Limnology and Oceanography 39 69—83. 

Tulonen, T., K. Salonen, and L. Arvola. 1992. Effects of different molecular weight fractions of dissolved organic matter on the growth of bacteria, algae and protozoa from a highly humic lake. Hydrobiologia 229 239-252. 

Vahatalo, A. V., M. Salkinoja-Salonen, P. Taalas, and K. Salonen. 2000. Spectrum of the quantum yield for photochemical mineralization of dissolved organic carbon in a humic lake. Limnology and Oceanography 45 664-676. 

Sojo, L.E. and de Haan, H. (1991) Multicomponent kinetic analysis of iron speciation in humic lake Tjeukemeer comparison of fulvic acid from the drainage basin and lake water samples. Environ. Sci. Technol., 25, 935-939. 

Hessen, D. O., Andersen, T., andLyche, A. (1990). Carbon metabolism in a humic lake Pool sizes and cycling through zooplankton. Limnol. Oceanogr. 35(1), 84—99. 

The concentration of total hydrolyzable sugars in freshwaters ranges over more than three orders of magnitude, with a median concentration of —2.6 p,mol L. The median percentage of DOC that occurs as sugars is —3%, which agrees well with the estimate of Benner (2003) for rivers and humic lakes, but which is about a factor of 3 lower than the estimates of Thurman (1985) for rivers and lakes. 

Anesio A. M. and GraneU W. (2003) Increased photoreactivity of DOC by acidification implications for the carbon cycle in humic lakes. Lirrmol. Oceanogr. 48, 735-744. 

Gjessing E. T. (1992) The HUMEX project experimental acidification of a catchment and its humic lake. Environ. Int. 18, 535-543. 

A.V. Vahatalo, K. Salonen, U. Munster, M. Jarvinen, R.G. Wetzel (2002). Photochemical transformation of allochthonous organic matter provides bioavailable nutrients in a humic lake. Arch. Hydrobiol, in press. 

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