Ostroumov S. A. Aquatic ecosystem as a bioreactor: water purification and some other functions. - Rivista di Biologia / Biology Forum. 2004. vol. 97. p. 39-50.
Abstract (short). A fundamental concept is proposed of aquatic ecosystem as a bioreactor that carries out the function of water purifi...
Ostroumov S. A. Aquatic ecosystem as a bioreactor: water purification and some other functions. - Rivista di Biologia / Biology Forum. 2004. vol. 97. p. 39-50.
Abstract (short). A fundamental concept is proposed of aquatic ecosystem as a bioreactor that carries out the function of water purification in natural water bodies and streams. The ecosystem as a bioreactor has the following characteristic attributes: (1) it is a large-scale (large-volume) bioreactor; (2) it is a diversified (in terms of the number of taxa and the scope of functional activities) bioreactor; (3) it possesses a broad range of biocatalytic (chemical-transforming and degrading) capabilities. New experimental data on xenobiotics -induced inhibition of the water filtration performed by the molluscs Unio tumidus, U. pictorum, M. galloprovincialis and inhibition of feeding by Limnaea stagnalis emphasized the potential ecological hazard from sublethal concentrations of pollutants (including those exemplified by synthetic surfactants and detergents).
Keywords: environmental hazards, man-made impacts, anthropogenic effects, pollutants, xenobiotics, aquatic ecosystems, water purification, water filtration, bivalves, surfactants, detergents, biosphere, water quality;
SDS, sodium dodecylsulfate; TX100, Triton X-100;
TDTMA, tetradecyltrimethylammonium bromide;
ABSTRACT (EXTENDED, with fragments of the text of the paper):
Ostroumov S. A. Aquatic ecosystem as a bioreactor: water purification and some other functions. Rivista di Biologia / Biology Forum. 2004. vol. 97. p. 39-50.
1 Introduction
2 Methods
3 Role of the main groups of organisms in the biological processes of water purification
4 Aquatic ecosystem as a bioreactor with some features
5. Man-made effects and the effects of some xenobiotics
6. Aquatic ecosystems as part of the apparatus of the biosphere
7. Conclusions.
Abbreviations: SDS, sodium dodecylsulfate; TX100, Triton X-100;
TDTMA, tetradecyltrimethylammonium bromide;
1. INTRODUCTION
Priorities of ecological research include the further studies of ecosystem functioning (Ostroumov et al., [2003]) that include functioning towards water purification (the self-purification of water) in natural water bodies and streams.
The self-purification of water in natural ecosystems is a complex group of processes which includes physical, chemical, and biological components (Sushchenya, [1975]; Alimov [ 1981], [2000]; Skurlatov, [1988]; Uhlmann, [1988]; Izrael, and Tsyban, [1989]; Ostroumov [1998], [2001], [2002b]; Wetzel [2001]). Although biological aspects of water self-purification are generally attributed to heterotrophic microorganisms, the other groups of organisms are also known to play a significant role in this process (Sushchenya, [1975]; Konstantinov [1979], Alimov [ 1981], [2000], Wallace, and Starkweather, [1985]; Vymazal, [1988]; Walz, [1995]; Monakov[1998]; Wetzel [2001]; also, Vinberg, [1973]; Bul'on, Nikulina, [1976]; Ivanova,[1976]; Khlebovich, [1976]; - cit. in Ostroumov, [2001]).
The goal of this work was to analyze some data from the literature and our own experimental data on water self-purification under natural conditions and to formulate a fundamental concept of the aquatic ecosystem as an analog of a bioreactor (in a broad sense) that contributes to water self-purification mediated by main groups of aquatic organisms.
This paper is based on some previous publications of the author (Ostroumov [2000c], [2001], [2002a]).
2. METHODS.
The rate of water purification by macrozoobenthic filter feeders was measured experimentally as described earlier (Ostroumov [2001]). After the water sample had been kept with filter feeders for a certain time, the water filtration efficiency was monitored by the measuring the optical density of the suspension of unfiltered single - cell organisms that remained in the water column. The control samples of water were subjected to the same procedure of filtration, but without the contaminant (chemical) tested. Some other methods of the studies of the effects of contaminants on aquatic organisms are described in (Waterbury & Ostroumov [1994] , Ostroumov et al. [1997]).
3. ROLE OF THE MAIN GROUPS OF ORGANISMS IN THE BIOLOGICAL PROCESSES OF WATER PURIFICATION.
Self-purification of water includes the following biological processes: (1) biodegradation of contaminants; (2) accumulation and sequestration of toxicants in aquatic organisms and the resultant removal of the toxicants from the water column (e.g. Vymazal, [1988]); (3) generation and emission of oxygen required for oxidative degradation of contaminants; (4) uptake of biogenic substances (including N and P) and organic substances from the aquatic environment; (5) production of exometabolites; (6) water filtration (Sushchenya, [1975]; Alimov [1981]; Wallace, and Starkweather, [1985]; Monakov [1998]); and (7) formation of pellet and detritus particles (e.g., Wotton et al. [1998]); and their sedimentation to the bottom (for review, see e.g., Konstantinov,[ 1979]; Ostroumov [1986], [1998], [2001], [2002b]; Skurlatov, [ 1988]). This list is far from complete, and some other biological phenomena simultaneously contribute to several processes listed above. Analysis of the relative contributions of individual groups of aquatic organisms to water self-purification as an integral function of an ecosystem (Table 1) shows that the main groups of organisms simultaneously contribute to several processes of the system of water self-purification. None of the main groups of aquatic organisms can be regarded as being insignificant in terms of water purification. The role of each group of aquatic organisms in these processes can be summarized as an integral ecological rating, which is calculated as the sum of the number of pluses in the corresponding row of Table 1. It is seen from Table 1 that this rating is sufficiently high in all groups of organisms.
Thus, the whole range of biological diversity of aquatic organisms is an important factor in water self-purification (Sushchenya, [1975]; Alimov [1981, 2000], Wallace, and Starkweather, [1985]; Wotton et al. [1998]; Ostroumov [2001], Wetzel [2001]). The biota representatives of the water column, the entire ecosystem volume, the boundary regions of the ecosystem, and zones of contact between the ecosystem and its environment are involved in water purification. Activities of unicellular organisms (including those freely suspended in water, immobilized, and attached to various particles, surfaces, and substrates) (e.g., Inkina, [1988]) as well as of other aquatic organisms (e.g., Ostroumov [2001], Wetzel [2001]) suggest that an aquatic ecosystem may be regarded as a bioreactor (in a metaphorically broad sense; i.e., including biological, physical, and chemical aspects). However, unlike industrial bioreactors, such a broad-sense bioreactor has the following important features.
4. AQUATIC ECOSYSTEM AS A BIOREACTOR WITH SOME FEATURES.
The first feature is a fundamental difference in the bioreactor size. The volume of technological bioreactors does not exceed a few hundred cubic meters, whereas the volume of natural ecosystems is significantly larger. For example, the volumes of lake and estuary ecosystems reach thousands of cubic kilometers: Lake Baikal, 22995 km 3 ; Lake Superior, 12221 km 3 ; Lake Michigan, 4871 km 3 ; Lake Issyk-Kul, 1730 km 3 ; Lake Ladoga, 908 km 3 ; Lake Onega, 280 km 3 ; Lake Balkhash, 112 km 3 ; and Lake Sevan, 38 km 3 ; (1 km 3 = 10 9 m 3 ). This increases the biospheric role of ecological, biochemical, and biofiltration processes in these systems. Therefore, the physical size and volume of the system within which water self-purification take place should be taken into consideration. Thus, natural ecosystems can be regarded as large-size (large-scale) analogues of bioreactors.
The second feature is the differences (in terms of size and diversity) between the gene-pool of organisms inhabiting natural ecosystems and the genetic pool of organizms grown in technological bioreactors. This difference leads to a significantly larger diversity of functional activities of organisms in natural ecosystems. Technological bioreactors are usually inoculated with monocultures or, less frequently, mixed cultures with a small number of constituting species. In contrast to technological bioreactors, the biological diversity of natural ecosystems is substantially broader. According to some incomplete estimates, the number of species in natural ecosystems is as many as several hundred to several thousand (e.g., Konstantinov, [1979]). These estimates were obtained without regard to the number of strains of individual microbial species. If the prokaryote strains are taken into account, the quantitative estimates of the biological diversity of taxa in natural ecosystems may increase by several orders of magnitude.
Third, an aquatic ecosystem is characterized by a higher degree of autonomy (including energy autonomy) than technological bioreactors. This autonomy is based on the presence of autotrophic organisms. Thus we suggest that natural ecosystems should be regarded as multispecies and diversified (i.e., based on the diversity of organisms and their functions) analogs of bioreactors, implementing a broad spectrum of catalytic functions (including transformation and degradation of contaminants).
5. MAN-MADE EFFECTS AND THE EFFECTS OF SOME XENOBIOTICS.
Anthropogenic sublethal effects (including the inhibition of physiological activities) and behavioral changes in virtually any group or taxon of aquatic organisms may decrease the bioreactor efficiency. Some sublethal effects should be regarded as a potential hazard to the purification function (Ostroumov [1998], [2000a ], [2000b], [2002a]; Ostroumov et al. [1997], [1999 ] ). Because the main groups of macroorganisms and microorganisms play a substantial role in self-purification of ecosystems, it is very important to compare the sensitivities of the organisms to various contaminants. In some cases, macroorganisms are at least as sensitive (or even more sensitive) to contaminants as microorganisms (Table 2).
According to the presently adopted regulation of ecological monitoring and bioassaying, the ability of chemical compounds to damage the self-purification potential of ecosystems is being tested using heterotrophic bacteria alone. However, it follows from Table 2 that this approach may result in an underestimation of the effects of contaminants on more sensitive biological components of self-purified ecosystems (e.g., some macroorganisms).
We obtained new data on the ability of xenobiotics to inhibit water filtration by marine and freshwater organisms and on the hygienic function of pulmonary mollusks associated with elimination of organic matter (the removal of phytomass) from the water column in aquatic ecosystems (Table 3).
Some sublethal concentrations of contaminants may inhibit vital activities of other organisms involved in the functioning of the ecosystem as an analog of a bioreactor (e.g., Ostroumov [2001], [2002a], Ostroumov et al. [1999]).
6. AQUATIC ECOSYSTEMS AS PART OF THE APPARATUS OF THE BIOSPHERE.
V.I. Vernadsky considered the biota as the apparatus of the biosphere (Vernadsky, [2001]). To continue and develop his thought, we could consider aquatic ecosystems and aquatic biota as a key part of that apparatus. In that capacity, aquatic ecosystem carries a number of functions, not only the one function discussed above (water purification). Among those biospherically important functions are the following: (1) production of organic matter; (2) removing the excess organic matter; ( 3 ) mediating, catalyzing, and regulating biogeochemical flows and cycles; ( 4) harboring biodiversity and by doing so harboring the genetic pool of biodiversity; (5) providing links among various parts of the biosphere; ( 6) contributing to stability of the biosphere.
7. CONCLUSIONS. The fundamental concept put forward in this work emphasizes that both the biological diversity of aquatic organisms and their normal level of physiological activities are required to provide the effective functioning of an ecosystem as an analog of a bioreactor. That bioreactor carries a number of biospherically important functions and processes (we call them 'microbiospheric processes') including those of water purification (environmental remediation, ecological repair). This may lead to a deeper insight into the mechanisms of aquatic ecosystems and to better understanding of hazards of the anthropogenic impact on the biosphere (Yablokov, Ostroumov [1983], [1985], [1991]; Ostroumov [1986]; [Wetzel, 2001]).
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LIST OF TABLES:
Table 1. Contribution of aquatic organisms to some processes important for water self-purification in ecosystem (some examples; a simplified model).
Table 2. Effect of Triton X-100 (TX) and tetradecyltrimethylammonium bromide (TDTMA) on biological organisms.
Table 3. Inhibition of some functions of molluscs important for water self-purification under exposure to sublethal concentrations of contaminants (new data). Note: SDS, sodium dodecylsulfate; TX100, Triton X-100; TDTMA, tetradecyltrimethylammonium bromide;
ADDENDUM (written in 2010):
After preparing this paper for publication, a number of other articles and some books were published, which supported the main conclusions of this paper. Among those more recent publications were the following:
Ostroumov S. A. Biological Effects of Surfactants. CRC Press. Taylor & Francis. Boca Raton, London, New York. 2006. 279 p. ISBN 0-8493-2526-9 [new facts and concepts on assessment of hazards from chemicals, new look on the factors important to water quality, to sustainability; new priorities in environmental safety]; and other publications.
Ostroumov S. A. Aquatic ecosystem as a bioreactor: water purification and some other functions. - Rivista di Biologia / Biology Forum. 2004. vol. 97. p. 39-50.
