Freshwater ecosystems

Revenga C, Brunner J, Henninger N, Kassem K, Payne R (2000) Pilot analysis of global ecosystems - Freshwater systems. WRI, Washington DC... 

Thomas, J. D. 1997. The role of dissolved organic matter, particularly free amino acids and humic substances, in freshwater ecosystems. Freshwater Biology 38 1—36. 

Wetzel, R. G. 1995. Death, detritus, and energy flow in aquatic ecosystems. Freshwater Biology 33 83-89. 

The general objective, principle, and scope of application of the pT-method are succinctly described in Section 1 and also reported elsewhere in this book (see Chapter 3 of this volume, Section 5.1), where readers will appreciate that this hazard assessment scheme is adaptable to both liquid and solid media. Briefly recalled here in the context of solid-media samples such as dredged material, the pT-value, which relates to a single bioassay, and the pT-index, derived from the most sensitive organism in a test battery, permit a numerical classification of environmental samples on the basis of ecotoxicological principles. Sediment from any aquatic ecosystem (freshwater, brackish, marine) and from any of its phases (whole sediment, porewaters, elutriates or organic extracts) can be appraised provided that the proper standardized toxicity tests are available. There are whole-sediment test protocols standardized for many agencies (e.g., Environment Canada, ASTM). 

The most evident damage from acid depositions is to freshwater lake and stream ecosystems. Acid depositions can lower the pH of the water, with potentially serious consequences for fish, other animal, and plant life. Lakes in areas with soils containing only small amounts of calcium or magnesium carbonates that could help neutralize acidified rain are especially at risk. Few fish species can survive the sudden shifts in pH (and the effects of soluble... 

Environmental chemists funded by the Department of Energy have studied these sources to learn as much as they can about the chemistry of plutonium dispersed in freshwater and marine ecosystems. Much of the early work determined the concentrations in various water bodies and the distribution between water and sediment. Table I shows results of various freshwater and marine surveys(10). 

Acid precipitation, or acid rain, can causes significant impacts on freshwater, coastal, and forested ecosystems (e.g.. Likens et ai, 1996). Both NOi", from NO emissions, and SO from SO2 emissions contribute significantly to acid rain. The relative ratio of SO /NOf in precipitation will be substantially determined by the regional emissions of SO2/NO3. In developed countries, uncontrolled combustion of coal and high-sulfur fuel oil led to significant emissions of SO2, relative to NO Due to strict control of smokestack SO2 emissions in some regions and increasing NO emissions from automobiles, the relative contribution of NOi is expected to increase (Sirois, 1993 Mayewski et ai, 1990). 

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. 

Consequences of Climate Variability and Human Water Demand on Freshwater Ecosystems A Mediterranean Perspective from the United States... 

The water supply to the Delta comes predominantly from the Sacramento River ( 80%) with lesser amounts from the San Joaquin River ( 15%) and rivers on the east side of the Delta ( 5%). Year-to-year variability in water supply is large. Combined average annual unimpaired runoff (an estimate of flows without upstream dams or diversions) for the Sacramento and San Joaquin rivers for the past century ranges from 6.2 km in 1977 to 68 km in 1983 [2]. The percentage of freshwater flows that go to San Francisco Bay are estimated to be 87% in wet years, 69% in average years, and 51% in dry years. Climate variability associated with the Mediterranean chmate of the region is an essential component of the Delta ecosystem. 

Gibson CA, Meyer JL, Poff NL, Hayc LE, Georgakakos A (2005) Plow regime alterations under changing climate in two river basins implications for freshwater ecosystems. River Res Appl 21 849-864... 

Rudd JWM. 1995. Sources of methyl mercury to freshwater ecosystems a review. Water Air Soil Pollut 80 697-713. 

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

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