Food-web

The methods available include enhanced fiushing, enhanced vertical mixing, altered mixing frequency, and food-web manipulation. 

A depiction of how food chains become interconnected to form food webs. (Gale Group, Inc.)... 

Sensitive ecosystems that cannot neutralize the unnatural levels of acidity are adversely affected. Soil nutrient systems may be altered with a resulting direct or indirect damage to forest. Aquatic habitats have been chemically altered and many lakes and streams no longer support the traditional life forms. Fish have been lost from many lakes with a resulting affect on other food-web elements. 

Numerous studies have shown that increased levels of UV affect photosynthetic activity (10-23), growth rate (24), nitrogen metabolism (25), and locomotion (26) of phytoplankton. Additionally, increases in UV-B are likely to alter community diversity as well as phytoplankton species composition. Thus, by weakening the base of the food web and altering trophodynamic relationships, UV-induced changes could potentially have far-reaching effects on the entire ecosystem. 

Figure 6. Food web in the Antarctic marine ecosystem showing the key position occupied by krill. (Reproduced with permission from reference 45. Copyright 1962 W. H. Freeman and Company.)...

Lehman, J. T. (1988). Hypolimnetic metabolism in Lake Washington Relative effects of nutrient load and food web structure on lake productivity. Limnol. Oceanogr. 33,1334-1347. 

Pollutants Increase of pollutant concentration and enhanced effects on the biota All groups Complex food web effects Diversity decrease Effects on metabolism Effects on material processing... 

Reid DJ, Quinn GP, Lake PS et al (2008) Terrestrial detritus supports the food webs in lowland intermittent streams of south-eastern Australia a stable isotope study. Freshw Biol 53 2036-2050... 

The first case is based on a hypothetical stream receiving a metal-poUuted source (for instance the outlet of a metal factory). In this case, metal concentration is expected to be driven by dilution, being higher under low-flow than under base-flow conditions and minimum during floods. Metal accumulation is expected to be maximum under low-flow conditions and proportional to the duration of this water scarcity situation. Chronic exposure will lead to community adaptation, which is often related to changes in species composition. Metals will therefore be bioaccumulated in fluvial biofihns and transferred to higher trophic levels in the fluvial food web. 

In Europe the situation is radically different. Isotopic variations at the bottom end of the food web, brought about by differences in plant metabolism (C3, versus C4 and CAM), and origin of the fixed COj, (causing a systematic discrepancy between terrestrial and marine ecosystems) are generally absent. This leads to relatively small variations in ratios at the beginning of... 

Fry, B. 1991 Stable isotope diagrams of freshwater food webs. Ecology 72 2293-2297. 

Schoeller, D.A., Minagawa, M., Slater, R. and Kaplan, I.R. 1986 Stable isotopes of carbon, nitrogen and hydrogen in the contemporary North American human food web. Ecology ofPood andNutrition 18 159-170. 

BIOGENIC ISOTOPIC SIGNALS USED TO ASSESS THE PRESERVATION OF ISOTOPIC SIGNALS IN FOSSIL SAMPLES FROM C3 PLANT FOOD WEBS... 

Bocherens, H., Fizet, M., Mariotti, A., Lange-Badre, B., Vandermeersch, B., Borel, J.P and Bellon, G. 1991a Isotopic biogeochemistry ( C, N) of fossil vertebrate collagen implications for the study of fossil food web including Neandertal Man. Journal of Human Evolution 20 481 92. 

Kay SH. 1984. Potential for biomagnification of contaminants within marine and freshwater food webs. Vicksburg, MS Department of the Army, Waterways Experiment Station, Corps of Engineers. D-84-7. 

Kucklick JR, HR Harvey, PH Ostrom, NE Ostrom, JE Baker (1996) Organochlorine dynamics in the pelagic food web of Lake Baikal. Anal Chim Acta 15 1388-1400. 

White GF, NJ Russell, EC Tidswell (1996) Bacterial scission of ether bonds. Microbiol Rev 60 216-232. Yoch D (2002) Dimethylsulfoniopropionate its sources, role in the marine food web, and biological degradation to dimethylsulfide. Appl Environ Microbiol 68 5804-5815. 

While methylmercury occurs naturally in tlie environment, it is reasonable to expect that methylmercury levels have increased in modem times as a result of increased inorganic mercury concentrations. Whether methylmercmy concentrations have increased to a similar extent as inoiganic mercuiy is not known. It is clear, however, that elevated fish mercuiy concentrations can currently be found in remote lakes, rivers, reservoirs, estuaries, and marine conditions, typically in predators such as sportfish at the top of food webs. As of 2003, 45 states had fish consumption advisories related to mercuiy, and 76% of all fish consumption advisories in the United States were at least partly related to mercury (USEPA 2004a). The number of advisories is increasing with time, although this is due at least partly to more sites being sampled (Wiener et al. 2003). 

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