The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Environmental mercury contamination in China: Sources and impacts☆

Extensive water use may alter stream flows so that areas used by spawning salmonids are dewatered, thus exposing intergravel development phases to suddenly changed physical and chemical conditions. Environmental alteration may result in considerable mortality, particularly of the more vulnerable post-hatch phases. Five documented case histories of redd dewatering are reviewed. The primary conditions in the gravel that influence survival during dewatering are residual flow, moisture retention, temperature, gravel composition, dissolved oxygen, alevin behavior, and species characteristics. These factors are discussed and their complex relationships are evaluated. Considerable variation in intergravel conditions can be expected during dewatering at different locations. Onsite studies are needed to obtain data for assessment of potential impacts in other dewatering situations, and for development of effective mitigation procedures. 4 figs.

Environmental biology of fishes

This paper presents the first application and validation of a 2D hydrodynamic model of the Amazon at a large spatial scale. The simulation results suggest that a significantly higher proportion of total flow is routed through the floodplain than previously thought. We use the hydrodynamic model LISFLOOD-FP with topographic data from the Shuttle Radar Topography Mission to predict floodplain inundation for a 240 × 125 km section of the central Amazon floodplain in Brazil and compare our results to satellite-derived estimates of inundation extent, existing gauged data and satellite altimetry. We find that model accuracy is good at high water (72% spatial fit; 0.99 m root mean square error in water stage heights), while accuracy drops at low water (23%; 3.17 m) due to incomplete drainage of the floodplain resulting from errors in topographic data and omission of floodplain hydrologic processes from this initial model.

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Modeling large-scale inundation of Amazonian seasonally flooded wetlands

Mercury in the Tapajós River basin, Brazilian Amazon: A review

The bioaccumulation of mercury by fish was studied in three natural lakes lining the Tapajos River, Brazilian Amazon. The Hg content variations are also reported between the rainy and the rising water seasons. Position of fish in the food chain and the source of carbon at the base of the food chain were determined using nitrogen and carbon stable isotopes ratios respectively. During the two seasons, the effect of the Hg biomagnification between the non-piscivorous and piscivorous fish of the three lakes is observed. The correlation between the mercury concentrations and the nitrogen isotopic ratios suggests that the fish mercury content variability is connected with the trophic position and size. Aside from classic observations on mercury biomagnification by certain species of fish (i.e. contents increase with size or trophic status), novel results were revealed as well, such as some species decrease of mercury contents with size of fish. Aquatic organisms in the Amazon are adapted to the complexity of trophic webs coupled with changes in environmental variables, depending on the location and/or the season, which results in a wide range of mercurial contamination among the Tapajos ichthyofauna.

Trophic Structure and Bioaccumulation of Mercury in Fish of Three Natural Lakes of the Brazilian Amazon

Foram estudadas as concentracoes de mercurio total (Hg), a bioacumulacao e a biomagnificacao desse metal na ictiofauna de tres lagos do rio Tapajos. Alem disso, uma atencao especial foi dada as possiveis variacoes temporal e espacial dos niveis desse metal na ictiofauna. Os resultados provem de duas amostragens correspondentes a cheia (abril-maio/2000) e a enchente do rio (janeiro/2001). A biomagnificacao do Hg na cadeia trofica dos tres lagos foi identificada durante os dois periodos analisados. No periodo das chuvas, 31% dos peixes predadores apresentaram concentracoes superiores ao valor critico de 500 ng/g, contra 28% durante a enchente. Sao raramente observadas correlacoes do tipo linear ou curvilinear positiva entre as concentracoes de Hg do tecido muscular e o comprimento total dos peixes. Varias especies de importância comercial nao apresentaram nenhuma variacao nas concentracoes de Hg com o aumento do comprimento do peixe. Outras correlacoes, do tipo linear negativa e nao linear positiva e negativa do Hg ao longo do desenvolvimento dos peixes, foram igualmente identificadas. Nossos dados sugerem que as concentracoes de Hg possam variar sazonalmente. Nenhuma variacao espacial das concentracoes de Hg foi observada na maioria das especies estudadas. De acordo com a presente pesquisa, e importante que os diferentes modos de acumulacao do Hg pelos peixes, bem como eventuais variacoes espaco-temporais dos niveis desse metal, sejam considerados no momento em que medidas de intervencao/educacao visando informar as populacoes expostas forem empreendidas

H. Poirier

Papers

Trophic Structure and Bioaccumulation of Mercury in Fish of Three Natural Lakes of the Brazilian Amazon

Mercúrio nos peixes do Rio Tapajós, Amazônia brasileira