Macrophytes organic matter

The second difference between the laboratory tests and exposure under realistic environmental conditions is that in the laboratory exposure concentrations are maintained, or the ecotoxicological endpoints are adjusted to account for any decline. Under natural conditions a combination of the pyrethroids tendency to partition rapidly and extensively to organic matter, coupled with their susceptibility to degradation in aquatic systems where algae and macrophytes are present [13,14], means their overall dissipation rate from the water phase is generally relatively rapid. Water column dissipation half-lives tend to be around 1 day (see Sect. 5). This behavior means that it is unlikely that aquatic organisms will be exposed to pyrethroids in the water phase for prolonged periods in natural water bodies. 

FIGURE 1 Fate and major transformation pathways of phytoplankton- and macrophyte-derived DOM in aquatic systems. Arrows indicate fluxes POC denotes particulate organic matter LMW and HMW DOM refer to the monomeric (low molecular weight) and polymeric (high molecular weight) fractions, respectively. 

FIGURE 3 Proportion of lake area accounted for by littoral zones for the world s lakes (a), and the proportion of extracellular (ER) dissolved organic matter inputs derived from littoral zones (b see text for description of the model). The solid lines illustrate relationships in which lake boundaries are restricted to littoral and pelagic zones and the dotted lines illustrate patterns in which lake boundaries are expanded to include adjacent wetlands. In (b), the two sets of lines illustrate the range in the contribution of littoral zones to total lake ER with variation in rates of primary production for phytoplankton (0.1-2.0 kg organic matter m-2 yr 1) and macrophytes (0.6-3.8 kg organic matter nT2 yr 1). The relationship between littoral zone area and number of lakes is from Wetzel (1983). 

We thank Stuart Findlay and Robert Sinsabaugh for organizing the dissolved organic matter workshop and for comments on an early version of this chapter. Thanks also to Robert Wetzel for discussions and feedback about macrophytes in aquatic ecosystems, and two anonymous reviewers for constructive comments on the manuscript. 

Otsuki, A., and R. G. Wetzel. 1974. Release of dissolved organic matter by autolysis of a submersed macrophyte, Scirpus subterminalis. Limnology and Oceanography 19 842-845. 

Wetzel, R. G. 1969. Factors influencing photosynthesis and excretion of dissolved organic matter by aquatic macrophytes in hard-water lakes. Verhandlungen der Internationale Vereiningung fur Theoretische und Angewandte Limnologie 17 72—85. 

Boschker, H.T.S., de Brower, I.F.C., and Cappenberg, T.E. (1999) The contribution of macrophyte-derived organic matter to microbial biomass in salt-marsh sediments Stable carbon isotope analysis of microbial biomarkers. Limnol. Oceanogr. 44, 309-319. 

Brylinsky, M. (1977). Release of dissolved organic matter by some marine macrophytes. Mar. Biol. 39, 213-220. 

There are other potential sources of organic matter from the coastal zone to the open ocean. However, we know little about the production of organic carbon from these sources. Coastal macrophyte production such as Spartina... 

Estuaries are typically heterotrophic systems, which means that the amount of organic matter respired within the estuary exceeds the amount of organic matter fixed by primary producers (phytoplankton and macrophytes). Since production of carbon dioxide then exceeds biological removal of carbon dioxide, it follows that estuaries are likely to be sources of the gas to the atmosphere. At the same time, since oxidation of organic matter to CO2 requires oxygen, the heterotrophic nature of estuaries suggests that they represent sinks for atmospheric oxygen. In many estuaries, primary productivity is severely... 

Several factors influence the thickness of an oxidized surface layer. These include the oxygen concentration of the floodwater, the soil organic matter content, the amount of reduced compounds in the reduced or anaerobic soil zone, the photosynthetic activity of periphyton and aquatic macrophytes, and the bioturbation by macroorganisms. 

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