Net community production

N2 fixation can be quantified by measuring the increase in total N in the euphotic layer during periods when other sources of phytoplankton N (deep-water entrainment, additions from sediments, rivers and coastal point-sources) are insignificant or can be quantified. Using this approach Larsson et al. (2001) estimated that N2 fixation in the Baltic Proper was 180—430 kt N year sufficient to sustain 30—90% of the pelagic net community production during summer. 

In an ideal steady-state world the flux of organic carbon from the upper ocean would be equal to net community production, which would be related via a stoichiometric ratio of C N to new production. This relationship was first suggested by Eppley and Peterson (1979) who termed the ratio of new to total production the/-ratio. A schematic picture of the processes that lead to the creation and transport of organic matter from the surface to the deep ocean is presented in Fig. 1.15. Nearly all the reaction rates and reservoir fluxes for N, C and O2 in the figure have been measured. Relating the fluxes of the... 

Hansell, D.A. and C. A. Carlson (1998) Net community production of dissolved organic carbon. Global Biogeochem. Cycles 12, 443-53. 

Williams, P.J. leB. and D.A. Purdie (1991) In vitro and in situ derived rates of gross production, net community production and respiration of oxygen in the oligotrophic subtropical g3rre of the North Pacific Ocean. Deep-Sea Res. 38, 891-910. 

Table 2.2 Gross primary production (P), Community respiration (R), Net Community Production (NCP), and Net Community Calcification (G) in mmol C m 2 day1 for various communities as originally tabulated by Kinsey (1985) with additional data from Gattuso etal. (1993, 1996), Kraines etal. (1996, 1997), Boucher etal. (1998), and Andrefouet and Payri (2000). Means are in bold followed by the range in parentheses...

There have been no studies measuring both carbon and nutrient fluxes in different morphological zones, nor studies relating net carbon sources and sinks to nutrient fluxes. For many reefs, errors in gross production and respiration are too high (10-15%) to get reliable estimates of net community production (Crossland etal, 1991) while changes in nutrient concentrations are nearly undetectable. Such experimental restrictions have limited our ability to understand the relationship between carbon and nutrient cycles in coral reefs. 

Lange BM, Rujan T, Martin W, Croteau R (2000) Isoprenoid biosynthesis The evolution of two ancient and distinct pathways across genomes. Proc NatT Acad Sci 97 13172-13177 Laws EA (1991) Photosynthetic quotients, new production and net community production in the open ocean. Deep-Sea Research 38 143-167... 

Seasonal timescale euphotic zone mass budgets, particularly of oxygen, carbon, and carbon isotopes, which lead to estimates of net community production. 

Table 8.2 Estimates of above- and below-ground net primary production (NPP) of some selected species/community types of salt marsh grasses and mangroves.

Table 13.4 Maximum net primary production in dry weight (NPP) of the most important herbaceous plant populations and communities in the varzea of the Central Amazon.

Other benthic suspension feeders may have increased in abundance to occupy the niche formerly filled by C. virginica. For example, in certain areas of the lower Chesapeake Bay it has been reported that 35—100% of net plankton community production may be transferred from the pelagic to the benthic zone to support production of the polychaete, Chaetopterus c variopedatus and its tubes, given an ecological transfer efficiency of 10% (Thompson and Schaffner, 2001). Tube production by suspension feeders may be a mechanism by which nitrogen is transferred to and retained in sediments. Approximately 12% of the N flux to the benthos in central Long Island Sound, NY, reportedly is necessary to support tube production by the sea anemone Ceriantheopsis americanus (Kristensen et al., 1991). 

Decomposition is a key ecological process that roughly balances net primary production in terrestrial ecosystems and is an essential process in resupplying nutrients to the plant community. 

The salinity of water bodies (Box 3.1) has an effect on the composition of primary producer communities. Fresh water and seawater in typical open marine environments contain the greatest numbers (diversity) of species. However, relatively few organisms can tolerate large fluctuations in salinity (e.g. where fresh water meets seawater in estuaries) and hypersaline conditions. In hypersaline conditions (Box 3.1) phytoplanktonic diversity is much reduced but the species adapted to these environments can produce large amounts of organic material. In addition, herbivore abundance may be low, so much of the net primary production may be available for incorporation into sediments. Cyano-bacterial mat communities tend to be successful in the shallow areas of such environments, and productivity can reach 8-12gCor m-2 day-1 (Schidlowski 1988). °rB... 

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