Phytoplankton respiration

The loss terms in N-cycle models that transform particulate and dissolved organic nitrogen into other forms can include a variety of processes (e.g., phytoplankton exudation, zooplankton grazing, sloppy feeding, phytoplankton and zooplankton mortality, bacterial remineralization, etc.). Different models may differ substantially in terms of which of these are included and their formulation (Christian and Anderson, 2002). Many N-cycle models now include significant phytoplankton exudation loss terms. This is often parameterized by simply specifying that some fixed fraction of the DIN uptake by phytoplankton is shunted directly to the DON pool (e.g., Anderson and Williams, 1998). Sloppy feeding by zooplankton can be similarly accounted for. Many models also include linear loss terms in the phytoplankton equation that represent either natural mortality or phytoplankton respiration (e.g.. Hood et ai, 2001). 

A certain amount of photosynthetic production is needed to offset phytoplanktonic respiration before... 

Therefore, considering only the phytoplankton respiration and the predation by zooplankton, the death rate of phytoplankton is given by the equation... 

This is not a reversible reaction in the strict sense and does not spontaneously seek equilibrium between products and reactants. The exothermic reverse reaction, respiration, occurs in a different part of phytoplankton cells or is mediated by heterotrophic organisms. 

Oceanic surface waters are efficiently stripped of nutrients by phytoplankton. If phytoplankton biomass was not reconverted into simple dissolved nutrients, the entire marine water column would be depleted in nutrients and growth would stop. But as we saw from the carbon balance presented earlier, more than 90% of the primary productivity is released back to the water column as a reverse RKR equation. This reverse reaction is called remineralization and is due to respiration. An important point is that while production via photosynthesis can only occur in surface waters, the remineralization by heterotrophic organisms can occur over the entire water column and in the underlying sediments. 

Redfield (1934), who analyzed the major elemental content of many samples of mixed plankton (phytoplankton and zooplankton) caught in nets towed through the surface ocean. They compared the carbon, nitrogen, and phosphorus composition of these collections to concentration profiles of dissolved inorganic carbon (DIC), NOs, and P04 throughout the water column. This pioneering research demonstrated that these three elements are continually redistributed in the ocean by selective removal into plankton cells and their remains (i.e., fecal pellets), which are then efficiently respired as they sink through the marine water column. 

The effects of photosynthesis are clearly seen in the low TDIC and nutrient concentrations of the surface water. The O2 concentrations are high because of contact with the sea surfece and production by phytoplankton. The temperature and O2 concentration data have been used to compute the percent saturation with respect to O2. The high degree of supersaturation in the surfece water suggests that the rate of O2 supply via photosynthesis is exceeding its removal via the dual processes of aerobic respiration and degassing across the air-sea interface. 

POPs can be absorbed actively or passively by zooplankton and phytoplankton species, or by higher organisms, such as fish, via ingestion, respiration and diffuse absorption. Some compounds may accumulate in body tissue, while others are transformed into other compounds by the metabolism of the organism or excreted to the water column in its original form [75-77]. As consequence of particle deposition, POPs will eventually end up on the bottom of the lake and be incorporated into the sediment were they are generally well preserved due to the low biological activities in these lakes [50, 51]. 

As nonconservative gases, carbon dioxide and oxygen are closely coupled to the organic carbon pool through autotrophic (e.g., photosynthesis) and heterotrophic (e.g., respiration) processes. The dominant primary producers in estuaries and the coastal ocean are benthic and pelagic microalgae (phytoplankton). The average atomic C-to-N-to-P ratio... 

Caffrey, J.M., Cloem, J.E., and Grenz, C. (1998) Changes in production and respiration during a spring phytoplankton bloom in San Francisco Bay, California, U.S.A implications for net ecosystem metabolism. Mar. Ecol. Prog. Ser. 172, 1-12. 

Kanneworff, E., and Christensen, H. (1986) Benthic community respiration in relation to sedimentation of phytoplankton in the Oresund. Ophelia 26, 269-284. 

Smith EM (1998) Coherence of microbial respiration rate and cell-specific bacterial activity in a coastal planktonic community. Aquat Microb Ecol 16 27-35 Smith WO Jr, Nelson DM, DiTullio GR, Leventer AR (1996) Temporal and spatial patterns in the Ross Sea phytoplankton biomass, elemental composition, productivity and growth rates. J Geophys Res 101 18455-18466 Smith WO Jr, Marra J, Hiscock MR, Barber RT (2000) The seasonal cycle of phytoplankton biomass and primary productivity in the Ross sea, Antarctica. Deep-Sea Res II 47 3119-3140... 

The daily C fluxes (pg C L-1 d-1 ) originate from an ecosystem model by Ruardij et al. (2005) and are averaged values over a period of 36 days. The standard run represents the situation as was observed during the mesocosm experiment, with both P. globosa single cells and colonies present. Viral lysis of phytoplankton is specific for P. globosa. Viral lysis of bacteria is a second order density-dependent mortality. Respiration and high refractory DOC were modeled but are not included in the table... 

The primary engine that drives these ocean interior variations is the photosynthetic fixation of carbon into organic matter by marine phytoplankton in the fight-illuminated upper ocean (euphoric zone) (see Fig. 1.1). Along with carbon, nutrient elements such as nitrogen, phosphorus, iron and many others are taken up and assimilated. Most of the resulting organic matter is either respired or reminerafized... 

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