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

The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

/pdf/the-ecology-of-phytoplankton-4ev70n3jsq.pdf

The Ecology of Phytoplankton

Human population growth, economic development, climate change, and the need to close the electricity access gap have stimulated the search for new sources of renewable energy. In response to this need, major new initiatives in hydropower development are now under way. At least 3,700 major dams, each with a capacity of more than 1 MW, are either planned or under construction, primarily in countries with emerging economies. These dams are predicted to increase the present global hydroelectricity capacity by 73 % to about 1,700 GW. Even such a dramatic expansion in hydropower capacity will be insufficient to compensate for the increasing electricity demand. Furthermore, it will only partially close the electricity gap, may not substantially reduce greenhouse gas emission (carbon dioxide and methane), and may not erase interdependencies and social conflicts. At the same time, it is certain to reduce the number of our planet’s remaining free-flowing large rivers by about 21 %. Clearly, there is an urgent need to evaluate and to mitigate the social, economic, and ecological ramifications of the current boom in global dam construction.

A global boom in hydropower dam construction

▪ AbstractThe coexistence in the deep ocean of a finite, stable stratification, a strong meridional overturning circulation, and mesoscale eddies raises complex questions concerning the circulation energetics. In particular, small-scale mixing processes are necessary to resupply the potential energy removed in the interior by the overturning and eddy-generating process. A number of lines of evidence, none complete, suggest that the oceanic general circulation, far from being a heat engine, is almost wholly governed by the forcing of the wind field and secondarily by deep water tides. In detail however, the budget of mechanical energy input into the ocean is poorly constrained. The now inescapable conclusion that over most of the ocean significant “vertical” mixing is confined to topographically complex boundary areas implies a potentially radically different interior circulation than is possible with uniform mixing. Whether ocean circulation models, either simple box or full numerical ones, neither explic...

/pdf/vertical-mixing-energy-and-the-general-circulation-of-the-530xn4nnsb.pdf

Vertical mixing, energy, and the general circulation of the oceans

Vertical mixing in the thermocline of lakes is poorly understood and most of the current knowledge is based on ex situ methods like laboratory measurements and simulations. Here, we used the eddy correlation technique (EC) to directly measure oxygen and buoyancy fluxes in the thermocline of two lakes (Lake Scharmutzelsee and Lake Arendsee in 2012 and 2013, respectively). Additionally, sets of temperature microstructure profiles (SCAMP) were measured during the EC deployments. We used these data to quantify the mixing efficiency as well as the turbulent diffusivity. The derived turbulent diffusivities from EC for the Prandtl number of DO were one order of magnitude higher than predicted by commonly applied parameterization, while the diffusivities for the Prandtl number of heat confirmed the parameterization. The results from EC and SCAMP showed strong differences which we attribute to the fact that SCAMP measurements reflect snapshots of the instantaneous turbulence field while EC provides a temporal average of the prevailing turbulence. Finally, we discuss problems of the EC and the inertial dissipation method in a strongly stratified environment and propose how they could be improved to resolve the full temporal variability of mixing in thermoclines. This article is protected by copyright. All rights reserved.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016JC012188

Mixing efficiency in the thermocline of lakes observed from eddy correlation flux measurements

Hydraulic and biological controls of biofilm nitrogen uptake in gravel-bed streams

Triangulation hand‐held laser‐scanning (TriHaLaS) for micro‐ and meso‐habitat surveys in streams

The effect of stream shading on the inflow characteristics in a downstream reservoir

As methane has 21 times the global warming potential as the same mass of carbon dioxide, it is important to determine the physical processes which contribute to the upward flux to the atmosphere from methane-containing submarine seeps. The Black Sea’s contribution to the global methane flux is a growing concern, it is important to properly understand the relevant transport mechanisms in the water column. Subsurface methane is released into the water column in the Black Sea from destabilizing methane hydrates and active seep areas. Vertical methane transport can occur due to bubble transport, methane-induced bubble plumes and turbulent diffusion. The combination of modeling and analysis reveals that advective methane transport to the surface from plumes and gas bubbles is very low, and only occurs in very shallow sites (<200 m). Furthermore, the low turbulent diffusion coefficient and the relatively high methane oxidation rates are important processes that hinder high methane contributions to the atmosphere.

Andreas Lorke

Papers

Mixing efficiency in the thermocline of lakes observed from eddy correlation flux measurements

Hydraulic and biological controls of biofilm nitrogen uptake in gravel-bed streams

Triangulation hand‐held laser‐scanning (TriHaLaS) for micro‐ and meso‐habitat surveys in streams

The effect of stream shading on the inflow characteristics in a downstream reservoir

Upward flux of methane in the Black Sea: does it reach the atmosphere?