Food webs trophic transfer

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. 

Importance in trophic transfer of MeHg. Preference should be given to bioindieator organisms that have an important role in the trophic transfer of MeHg within food webs. 

Although the entry of MeHg into the base of the food web and its subsequent transfer in the lowest trophic levels are poorly understood, it is evident that the concentration of MeHg in all trophic levels is strongly correlated with its supply from methylating environments. In fish, for example, much of the modem spatial variation in mercury concentrations (within a given trophic level) can be attributed to variation in factors and processes that affect the microbial production of MeHg and its entry into oxic waters. 

In summaiy, prey fish are present in most surface waters, require moderate sampling effort, are important in the trophic transfer of MeHg in aquatic food webs, and probably indicate annual changes in exposure to MeHg. Given these attributes. 

Zooplankton are small, often microscopic crustaceans that live in the water colunm. They are widely distributed, common, and important in pelagic food webs. Zooplankton are eaten by marty fish and by early life stages of some fish that become piscivorous as juverriles or adrrlts. Zooplankton are not eaten by httmans but are an appropriate and relevant candidate indicator because of their importance in the trophic transfer of MeHg to fish. Sampling would not significantly affect populations or assemblages of zooplankton, even in small lakes. 

Food-web and trophic dynamics. Organisms at the base of aquatic food webs play a key role in the transfer of MeHg to npper trophic levels (Jackson and Harvey 1993 Plomde etal. 1997 Tremblay and Lucotte 1997 Bodaly and Fudge 1999). Within a given water body, interarmual... 

Bioaccumulation is generally referred to as a process in which the chemical concentration in an organism achieves a level that exceeds that in the respiratory medium (e.g., water for a fish or air for a mammal), the diet, or both. The extent to which chemicals bioaccumulate is expressed by several quantities, including the bioconcentration factor (BCF), bioaccumulation factor (BAF), biomagnification factor (BMF), and trophic or food web magnification factor (TMF) [6]. The ecological, biological and chemical parameters involved in the transfer and accumulation of contaminants in food webs are complex. 

Borga, K., Fisk, A.T., Hoekstra, P.F. and Muir, D.C.G. (2004) Biological and chemical factors of importance in the bioaccumulation and trophic transfer of persistent organochlorine contaminants in Arctic marine food webs. Environ Toxicol Chem, 23, 2367-2385. 

The length of the food chain has the largest effect on the observed accumulation of PCBs in top predators [268]. However, one of the more sensitive aspects of trophic transfer in food webs is the initial uptake of PCBs into the primary trophic level, phytoplankton [263]. The BCF from water to phytoplankton is approximately 105 -106, and subsequent BMFs to higher trophic levels are on the order of two to five. Due to the life cycle of most phytoplankton, their rate of growth is on the same order as their rate of uptake of PCBs, thus making their uptake very time-dependent [227,269-271]. Bioaccumulation into top predators will be greater if phytoplankton have a chance... 

At the ecosystem scale, the significance of microbial community organization is that it determines the magnitude and efficiency of carbon transfer to other portions of the food web. High density communities like biofilms and floes can be directly grazed by metazoans, which divert microbial and detrital carbon out of the microbial loop (Wotton, 1994). In dilute planktonic systems, much of the carbon reaches metazoans through a microbial food-web after two to three trophic transfers, only a small fraction of microbial production remains. 

Twiss, M.R., Campbell, P.G.C. and Auclair, J.-C. (1996) Regeneration, recycling, and trophic transfer of trace metals by microbial food-web organisms in the pelagic surface waters of Lake Erie, Limnology and Oceanography 41, 1425-1437. 

Pinnipeds (e.g., seals, walruses) are a key link in many marine food webs, in that they are commonly found, predate on fish, and are hunted in turn by sharks, polar bears, and Arctic Inuit peoples as part of their traditional diet. In these roles, pinnipeds play a significant role in bioaccumulating POPs and in transferring these contaminant burdens to higher trophic levels. Thus, an understanding of POP dynamics in pinnipeds is important in exposure and risk assessment, and an enantiomer-specific understanding is vital given that pinnipeds bioprocess POPs enantioselectively. 

Law, K. HaUdorson, T. Danell, R. Stem, G. Gewurtz, S. Alaee, M. Marvin, C. Whittle, M. Tomy, G., Bioaccumulation and trophic transfer of some brominated flame retardants in a Lake Winnipeg (Canada) food web Environ. Toxicol. Chem. 2006, 25, 2177-2186. 

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