Freshwater cycle

The freshwater cycle is an important link in the carbon cycle as an agent of erosion and as a necessary condition for terrestrial life. Although the amount of carbon stored in freshwater systems is insignificant as a carbon reservoir (De Vooys, 1979 Kempe, 1979a), about 90% of the material transported from land to oceans is carried by streams and rivers. 

Kempe, S. (1979a). Carbon in the freshwater cycle. In "The Global Carbon Cycle" (B. Bolin, E. T. Degens, S. Kempe and P. Ketner, eds), pp. 317-342. Wiley, New York. 

As emphasized by Postel and co-workers (9), only freshwater flowing through the solar-powered hydrological cycle is renewable (Fig. 7). 

The oceans hold about 97% of the earth s water. More than 2% of the total water and over 75% of the freshwater of the world is locked up as ice ia the polar caps. Of the remaining 1% of total water that is both Hquid and fresh, some is groundwater at depths of > 300 m and therefore impractical to obtain, and only the very small difference, possibly 0.06% of the total water of this planet, is available for human use as it cycles from sea to atmosphere to land to sea. Only recently have humans been able to regulate that cycle to their advantage, and even now (ca 1997), only infinitesimally, ia some few isolated places. 

Fig. 14-4 Schematic representation of the transport of P through the terrestrial system. The dominant processes indicated are (1) mechanical and chemical weathering of rocks, (2) incorporation of P into terrestrial biomass and its return to the soil system through decomposition, (3) exchange reactions between soil interstitial waters and soil particles, (4) cycling in freshwater lakes, and (5) transport through the estuaries to the oceans of both particulate and dissolved P.

Lerman et al. (1975) considered several cases in which mankind s activities perturbed the natural cycle. If we assume that all mined P is supplied to the land as fertilizer and that all of this P is incorporated into land biota, the mass of the land biota will increase by 20%. This amount is small relative to the P stored in the land reservoir. Since P incorporated into land biota must first decompose and be returned to the land reservoir before being transported further, there is essentially no change in the other reservoirs. Thus, although such inputs would significantly alter the freshwater-terrestrial ecosystem locally where the P release is concentrated, the global cycle would be essentially unaffected. 

Zillioux EJ, Porcella DB, Benoit JM. 1993. Mercury cycling and effects in freshwater wetland ecosystems. Environ Toxicol Chem 12 2245-2264. 

Rosenbaum R, Bachmann TM, Gold LS, Huijbregts MAJ, Jolliet O, Juraske R, Koehler A, Larsen HF, MacLeod M, Margni M, McKone TE, Payet J, Schuhmacher M, van de Meent D, Hauschild MZ (2008) USEtox the UNEP-SETAC toxicity model recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment. Int J Life Cycle Assess 13 532-546... 

Based on the previous studies and the above discussions, it is required to achieve environmentally sustainable development in textile industry since closing of water cycle is highly recommended [29]. It can often be done by the application of the combined membrane-biological processes, especially by the implementation of NF-biological and RO-biological processes, which enables the water reuse process, thereby the minimization of freshwater consumption. 

Stokes, P.M. 1979. Copper accumulations in freshwater biota. Pages 357-381 in J.O. Nriagu (ed.). Copper in the Environment. Part 1 Ecological Cycling. John Wiley, NY. 

A freshwater sponge (Ephydatia fluviatilis) grew normally at a concentration of 0.65 pg Zn/L, but growth was reduced at lower concentrations tested (Francis and Harrison 1988). Daphnids (Daphnia pulex, Daphnia magna) reared for six brood cycles in zinc-free water showed reduced survival, inhibited reproduction, and cuticle damage (Keating and Caffrey 1989). Zinc is important... 

Toxaphene is extremely toxic to freshwater and marine biota. In laboratory tests of 96-h duration, 50% mortality was recorded for the most sensitive species of freshwater and marine teleosts, marine crustaceans, and freshwater insects at nominal water concentrations of less than 10 pg/L of toxaphene, and, in several cases, less than 1 pg/L (Table 27.2). Bioassays of longer duration, based on exposure of aquatic organisms for the entire or most of the life cycle, produced significant adverse effects on growth, survival, and reproduction at toxaphene concentrations between 0.025 and 1.0 pg/L (Table 27.3). Toxaphene was most toxic to freshwater fishes in soft water at elevated temperatures (Saleh 1991). Based on its high toxicity and extensive use, it is not surprising that toxaphene was considered a major cause of nationwide fish kills in 1977 (USEPA 1980b). 

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