Ultra-oligotrophic

Rellstab CV, Maurer MZ, Biirgi HR, Spaak P (2007) Temporary collapse of the daphnia population in turbid and ultra-oligotrophic Lake Brienz. Aquat Sci 69 257-270... 

Existing data lend mixed support to the hypothesis that sulfate reduction is limited by availability of electron donors. Laboratory studies have shown that sulfate reduction in sediments can be stimulated by addition of carbon substrates or hydrogen (e.g., 85, 86). Increases in storage of reduced sulfur in sediments caused by or associated with addition of organic matter (108, 109) also have been interpreted as an indication that sulfate reduction is carbon-limited. Addition of nutrients to Lake 227 in the Experimental Lakes Area resulted in increased primary production and increased storage of sulfur in sediments (110, 111). Natural eutrophication has been observed to cause the same effect (23, 24, 112). Small or negligible decreases in sulfate concentrations in pore waters of ultra-oligotrophic lakes have been interpreted... 

Urbach, E., K. L. Vergin, L. Young, A. Morse, G. L. Larson, and S. J. Giovannoni. 2001. Unusual bacterioplankton community structure in ultra-oligotrophic Crater Lake. Limnology and Oceanography. 46 557-572. 

Figure 6. Summary results of a simple Michaelis-Menton model of molybdenum uptake by plankton including the effect of sulfate inhibition. Isolines are in units ofpmol Mo p g Chi) h and are shown as a function of the sulfate and molybdate concentrations. The cloud labelled "lakes" represents the range of sulfate and molybdate concentrations for most freshwater lakes. "Low-Mo" refers to molybdenum-deficient, ultra-oligotrophic lakes such as Castle Lake and a variety of New-Zealand lakes. "High-Mo" refers to molybdenum-rich, eutrophic lakes such as Lake Donk. Pyramls Lake is. saline. Data for Baltic. seawater Include points for experimental additions of molybdenum ("Baltic- -Mo") and of sulfate ("Baltic-y.sulfate) (Howarth et al., I9H8).

The concentration of dissolved nutrients in the deep waters of the Eastern Mediterranean is much lower than those in other oceans of the world, and when these are mixed into the surface waters they support very low primary productivity. The basic reason for this ultra-oligotrophic status is that the Mediterranean has an anti-estuarine (reverse thermohaline) circulation in which nutrient-depleted surface waters flow into the western basin at the Straits of Gibraltar and then on into the eastern basin at the Straits of Sicily. The deeper counter current consists of Levantine Intermediate Water (LIW) which contains a significant amount of dissolved nutrients. 

The phytoplankton community in the offshore region is dominated by pico- and nano-plankton, with microplankton and eukaryotes only important in coastal regions and upwelling areas associated with mesoscale features such as the Rhodes Gyre. Heterotrophic bacteria are an important component of this nutrient depleted system. Both depth integrated chlorophyll a and primary productivity levels are extremely low, characteristic of ultra-oligotrophic systems. 

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