Limnological and marine geochemical opinion favors phosphorus limitation of organic production in aquatic environments, while marine biological opinion favors nitrogen limitation. Clues in the literature and nutrient budgets for selected marine ecosystems suggest that phosphorus vs. nitrogen limitation is a function of the relative rates of water exchange and internal biochemical processes acting to adjust the ratio of ecosystem N:P availability.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1984.29.6.1149

Phosphorus versus nitrogen limitation in the marine environment1

Basin-scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind-mixed layer. Thus, correct modeling of lake mixing and transport requires accurate modeling of basin- scale internal waves: examining this capability with a hydrostatic, z-coordinate three-dimensional (3D) numerical model at coarse grid resolutions is the focus of this paper. It is demonstrated that capturing the correct thermocline forcing with a 3D mixed-layer model for surface dynamics results in a good representation of low-frequency internal wave dynamics. The 3D estuary and lake computer model ELCOM is applied to modeling Lake Kinneret, Israel, and is compared with field data under summer stratification conditions to identify and illustrate the spatial structure of the lowest-mode basin-scale Kelvin and Poincarewaves that provide the largest two peaks in the internal wave energy spectra. The model solves the unsteady Reynolds-averaged Navier-Stokes equations using a semi-implicit method similar to the momentum solution in the TRIM code with the addition of quadratic Euler-Lagrange dis- cretization, scalar (e.g., temperature) transport using a conservative flux-limited approach, and elimination of vertical diffusion terms in the governing equations. A detailed description is provided of turbulence closure for the vertical Reynolds stress terms and vertical turbulent transport using a 3D mixed-layer model parameterized on wind and shear energy fluxes instead of the convential eddy viscosity/diffusivity assumption. This approach gives a good representation of the depth of the mixed-layer at coarse vertical grid resolutions that allows the internal waves to be energized correctly at the basin scale. Wind stresses, surface heating, and density currents form the driving energy fluxes of a stratified lake. The basin-scale energy flux from the wind is of particular interest because of its dominant role in setting the thermocline in motion, which, in the absence of inflows and outflows, is the primary energy store for transport and mixing below the wind-mixed layer. Thus, modeling the basin-scale internal wave behavior is an a priori requirement to modeling and quantifying the flux paths of nutrients in a stratified lake (Imberger 1994). This paper takes a first step in this direction by analyzing our ability to model basin-scale internal waves that are seen in Lake Kinneret, Israel. Energy flux path in a stratified lake —Energy flux through a stratified lake has a fundamental dependence on forced and free baroclinic motions. The wind imparts both momentum and turbulent kinetic energy (TKE) to the water in the sur- face layer. The TKE distributes momentum vertically in the

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2000.45.7.1603

Modeling basin-scale internal waves in a stratified lake

The energetic demand of microorganisms in natural waters and the flux of energy between microorganisms and metazoans has been evaluated by empirical measurements in nature, in microcosms and mesocosms, and by simulation models. Microorganisms in temperate and tropical waters often use half or more of the energy fixed by photosynthesis. Most simulations and some experimental results suggest significant energy transfer to metazoans, but empirical evidence is mixed. Considerations of the range of growth yields of microorganisms and the number of trophic transfers among them indicate major energy losses within microbial food webs. Our ability to verify and quantify these processes is limited by the variability of assimilation efficiency and uncertainty about the structure of microbial food webs. However, even a two-step microbial chain is a major energy sink.

Energetics of microbial food webs

We estimated In si tu grazing rates of heterotrophic nanoplankton (HNAN) on bactenoplankton in a salt marsh estuary using a select~ve metabolic inhibitor technique. Seasonal experiments with prokaryohc inhibitors showed a significant, positive relation between bacterial abundance and HNAN grazing rates. On average, only 40 to 4 5 '/o of bacterioplankton produchon in the estuary appeared to be consumed by phagogrophic Protozoa <20 pm in size. Eukaryotic inhibitor experiments suggested that protozoan grazlng can have a positive feedback effect on bacterioplankton production, and that nitrogen regeneration by Protozoa may be of particular importance to bacterial growth. Although eukaryotic inhibitors did not prove to be rouhnely useful to estimate protozoan grazing rates on bacterioplankton, they may contribute to understanding qualitahve control mechanisms in the microbial food web.

/pdf/trophic-interactions-between-heterotrophic-protozoa-and-3wqv4sz8ld.pdf

Trophic interactions between heterotrophic Protozoa and bacterioplankton in estuarine water analyzed with selective metabolic inhibitors

We have studied the net and gross metabolism of Tomales Bay, a temperate climate estuary in northern California. Tomales Bay has proved to be heterotrophic, implying that the bay oxidizes a subsidy of organic carbon from outside the system, in excess of inorganic nutrients supplied to it from outside and in addition to material cycling within it. Net organic oxidation releases dissolved inorganic nutrients, and the system exports these dissolved inorganic products. Dissolved inorganic phosphorus is exported to the ocean via mixing and constitutes the most direct record of net ecosystem production (NEP). Excess dissolved inorganic nitrogen is lost to denitrification. Excess dissolved inorganic carbon largely results in alkalinity elevation and hydrographic export of alkalinity due to sulfate reduction. The negative NEP of this system results in little release of CO2 to the atmosphere, because of this alkalinity elevation. A major purpose of the study was to ascertain the relative importance of various sour...

Annual cycle and interannual variability of ecosystem metabolism in a temperate climate embayment

Abstruct A formal approach is presented of ordering the time scales of the dominant fluxes of material in an estuary and then accordingly choosing the spatial and temporal resolution of the sampling program. In this way bounds can be derived for the internal turnover times, boundary exchange rates, and import or export fluxes of a particular substance purely from measurements of the standing stock values in the estuary water. Application of this methodology to an experiment in the Duplin River, Georgia, showed that if the effects of the water motion and mixing are extracted from the variation of a biological component, then the variability of the residual can be successfully interpreted. For a typical summer condition it was shown that ammonium was cycled rapidly within the marsh water, its distribution was very patchy, and only its decomposition products left the marsh; that the refractory dissolved organic carbon (DOC) component was steadily exported by longitudinal mixing while labile DOC was rapidly recycled in the water; that silicate was produced in large amounts in the marsh and exported by longitudinal mixing; that particulate organic carbon (POC) concentrations were almost completely determined by the turbulence intensity in the water; and that compared to this internal cycling, export was of minor significance.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1983.28.2.0201

R. R. Christian

Papers

The influence of water motion on the distribution and transport of materials in a salt marsh estuary1