Water humus

Since the average concentration of organic C, estimated by the dry combustion method, in the water layer from 0 to 100 m equals about 1.8 mg T and at depths of more than 2000 m from 1.2 to 1.4 mg T for three oceans (Skopintsev et al., 1976), the fraction of carbon from identified labile organic compounds in the deep oceanic waters will be less than 10%. The remaining 90% are probably made up of refractory (stable) organic complexes — the water humus. 

The analysis of the results of the experiments on decomposition of OM in dead plankton presents a view of the time-related changes of particulate and dissolved organic C, N and P, and some components of OM. The processes occurring are responsible not only for oxidation of the initial OM, but also in soils (Kononova, 1963) for the polymerisation (condensation of the more biochemically resistant dissolved and particulate fractions of OM. 

Synchronically, new forms of OM are synthesised by bacteria. The combined processes lead to the formation of the refractory organic substance — water humus — in particulate and dissolved state. This surely occurred initially in the Precambrian period with blue-green algae and bacteria in water reservoirs under anoxic conditions (Rutten, 1971). As shown by experiments, the degree of decomposition of the OM of dead hydrobionts under such conditions was less. That is why more organic residues settled on the bottom of the reservoir. Naturally this influenced the further transformation of OM in sediments and the accumulation of oil precursors their concentration in the anaerobic conditions of the Precambrian must have been 

Berzelius (1833) appears to have pioneered a serious study of OM in natural waters. He discovered the dissolved organic compounds with acidic properties in the mineral spring Porla (Sweden). These compounds were called crenic and apocrenic acids. Berzelius assumed that their salts were washed out from soil humus intact . Oden (1919) found the common term for these acids — fulvic acids (fulvus = yellow). Aschan (1932) attributed them to the water humus group, being typical for peat, river and lake waters. 

fulvic acids may originate from continental plants, and when carried by rivers and streams to the reservoirs, seas and oceans, they constitute the major part of the allochthonous water humus. Kalle (1966) suggested they were only partly responsible for the yellow substance (Gelbstoffe) present in oceanic waters, the concentration of which in the water decreases with the increase of salinity. He considered that a part of the yellow substance was of autochthonous origin. It seems probable, that its existence in water is due to transformed products of excretion of dissolved and thinly dispersed OM which was discovered in littoral algae during studies conducted by Khailov (1962), Sieburth and Jensen (1969) and Sieburth (1969). 

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These observations later stimulated the general belief that prevailed through the earlier decades of the 19th century—namely, that humus is the only or the major soil product supplying nutrients to plants. The direct utilization of humus by plants was fully developed by Thaer (1808,1846), who stated that humus comprises a more or less considerable portion of soil fertility of the soil depends largely upon it since, besides water, humus is the only material that supplies nutrients to plants. This concept was referred to as the humus theory. 

Aschan, O. (1932). Water humus and its role in the formation of marine iron ore. Ark. Kemi Mineral. Geol. lOA, No. 15, 1-143. 

Conclusions. The processes and the rates of decomposition of OM of marine and fresh phytoplankton in the sea and in fresh water are virtually identical. Temperature changes considerably influence the rate of decomposition. The amount of the dissolved OM in water tends to increase towards the end of the experiment. This is, probably, a refractory OM or water humus of planktonic origin. The remaining non-degradable particulate OM (detritus) also shows a relatively h h stability. 

It thus appears that the content of dissolved OM in the experiments with phytoplankton was, after 160 days, twice that in the control experiments. The accumulation of this refractory OM — the water humus — constituted 2—3% of the organic mass of plankton. In the fresh-water control the content of organic C showed no evidence of changing. The decomposition d ee of OM thus evaluated by C equalled 93 and 82%. 

The analysed data on carbon content and also on content of organic N and P in dissolved and particulate state at the end of all the experiments illustrate the stability of OM. The experiments simulate accumulation of resistant insoluble and soluble organic compounds in reservoirs and soils. These compounds appear as the result of decomposition of dead living matter and its living excretions. The processes are not only responsible for transformation of initial OM (oxidation, polymerisation, condensation), but also for synthetic processes, caused by bacterial activity (Kononova, 1963), and this is the water humus of planktonic origin. 

Of all the dissolved oi anic components present at the beginning of the experiment, organic C and carbohydrates constituted the major part (39 and 16 mg r ). This is due to the considerable amount of coloured humus compounds, found in the initial water. The experimental evidence (Bikbulatov and Skopintsev, 1974) strongly su ested that the addition of phenol-sulphuric reagent to such water caused a considerable increase in light absorption in the 480—490 nm sector. This is evidently caused by (a) the conversion of organic components of the high sulphuric acid medium into more coloured forms, and (b) the hydrolysis of carbohydrate compounds of the coloured water humus. 

During the next days, the content of dissolved organic C and carbohydrates varied considerably, probably due to additions from the products of particle decomposition. On the 56th day their content was 27 and 24 mg r, respectively (i.e. an increase of carbohydrate C with respect to total organic C). At the end of the experiment the content of dissolved organic C decreased to 12 mg r — this could be the remaining water humus of the fresh water and the produced water humus of planktonic or in. Organic N and P (which were measured by the difference between total emd mineral N and P) were almost below the limits of detection on the seventh day. 

As the water humus is the dominating component of OM in ocean waters, the formulations below concern the humus in the first place ... 

According to Bii e and Juday (1934), the refractory OM appears in the process of decomposition of dead plankton in lakes. This is the vrater humus of autochthonous origin. Krogh (1934) considered that in the deep waters of the ocean OM consists partly of humus , which is resistant even for bacteria. Waksman (1936), studying the question of the formation of OM in reservoirs, distinguished three types of humus river, lake and sea humus. Besides this natural water humus, there may enter and be formed a humus from sewage of domestic origin. It was Odum (1975) who considered humic substance (humus), the most stable product of OM decomposition in nature, to be a necessary component of the ecosystem. 

Thus, it appears that water humus is the indispensable resistant product resulting from transformation, decomposition and synthesis of OM of excretions and dead remains of plankton in the ocean its final structure is largely determined by the activity of micro-organisms (Skopintsev, 1950). 

The annual input and formation of water humus in the waters of the world ocean and its chemical characteristics... 

Table VIII summarises data to allow an approximate budget of water humus in the ocean. It is assumed that the annual decrease as a result of oxidation, aggregation and adsorption on the surface of particles with their subsequent sedimentation, equals its input.

Bordovsky (1974) is right in his belief that HA of marine deposits is of autochthonous and allochthonous origin, the latter playing a minor role. Based on chemical investigations and isotope determinations of C in HA isolated from ocean sediments, Nissenbaum smd Kaplan (1972) do not seree with this point of view. The allochthonous HA in the bottom sediments of the ocean is evidently at the limits of detection of the analyticsil methods employed. According to Table IX the total annual input of water humus to the ocean constitutes 1.5 X 10 g C, provided the distribution is proportional, this amounts to 1 pg C T . 

Approximate annual budget of water humus in the world ocean (in carbon)... 

Number in brackets in mg I annual input of water humus in the oceans equals <0.1% of its total content in ocean water. 

There are, however, other factors which determine the water humus decrease partial loss of colour in the surface layers, sorption onto particles, aggregation followed by partial consumption by deep-sea inhabitants and sedimentation possibly also by chemical oxidation. 

A dynamic equilibrium can be said to exist between the annual input and decrease of water humus in the world ocean (Skopintsev, 1950). Its annual average input equals 1 pg C T (see Table IX). In reality, according to the vertical distribution of phytoplankton, zooplankton (Yashnov, 1962) and bacteria (Sorokin, 1962), its input should be highest in the euphotic zone and zones adjacent to it. The trophic factors determine the regularity of the vertical distribution of zooplankton (Vinogradov, 1968) and bacteria. Thus,... 

The upper layers of ocean water have the most intensive biochemical decay of organic remains and have also the most intensive decomposition of water humus and nutrient formation, especially in upwelling areas. This phenomenon is usually ascribed to microbial metabolism (co-metabolism), which causes the decomposition of stable organic compounds (Horwath, 1972). 

As a result of a reduced input of labile OM, processes leading to formation of water humus decreased with depth, and hence the concentration of humus also decreased, although at the lower water temperature the rate of decomposition is lower. The observed decrease of organic C (Skopintsev et al., 1966 Starikova, 1970 Menzel and Ryther, 1970 Williams, 1975) content in the ocean with depth, is in agreement with the above-mentioned opinion. 

The mechanism of its input to the ocean (specifically, to the deeper layers) is the sinking process of highly productive cold water masses in the areas of the North and South Polar fronts (Skopintsev, 1950 Szekielda, 1968b). This follows the conception of Redfield (1942) that these waters supply the deep ocean with dissolved oxygen and biogenic elements. It seems therefore logical that water humus should also reach the deeper waters. 

The question arises, as to how the decomposition of water humus in the ocean proceeds. The method of estimation of oxygen decrease in water, incubated in the dark at specific temperature, is commonly applied as a qualitative index of OM decomposition. The biochemical oxygen demand (BOD) method was suggested to estimate the degree of purification of waste waters... 

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