ELOISE Nutrient Dynamics-Role of vegetation in nutrient cycling (1)

Nutrient Dynamics in European Water Systems
Synthesis Results

3. Fate of nutrients in coastal areas (3 of 4)

Autotrophy
The production of organic compounds from inorganic compounds by plants and bacteria.
See Glossary for a complete list of all terms.

3.2 Role of Vegetation in Nutrient Cycling

Until recently and mostly based on theoretical considerations, it was assumed that the oxygen release into the sediments by benthic plants created favourable conditions for coupled nitrification-denitrification. Ammonia produced by ammonification in the sediment can be oxidised to nitrate in oxic sediment layers and can diffuse into the anoxic zone and be denitrified.

Microsensor studies
The use of a miniature electronic device that detects information about a specific variable such as temperature or light.
See Glossary from complete list of terms.

Risgaard-Petersen (2003) convincingly showed for studies of sediments inhabited by microalgae, supported with microsensor studies, that this anticipated effect is overruled by ammonium (and nitrate) uptake by the algae. The diurnal integrated coupled nitrification–denitrification rates in alga-colonized sediments were between 4 and 51% of the activity measured in heterotrophic sediment (Figure 3.2(a)). Competition for the nitrogen substrate decreases the amount of inorganic nitrogen available to nitrifying bacteria for coupled nitrification-denitrification.

At a community level, the autotrophy-heterotrophy status of sediment communities will determine whether the sediment as a whole acts as a sink or source of nutrients. When the sediment is net heterotrophic a fraction of the dissolved inorganic nitrogen released by diagenetic processes may become available for denitrification In autotrophic sediments, the released nitrogen is efficiently incorporated by primary producers (Risgaard-Petersen, 2003).

Diagenetic processes
Processes involving physical and chemical changes in a sediment after deposition that convert it to a rock. The processes include compaction, squeezing out of excess water, cementation, and sometimes recrystallisation (especially in limestones). These are processes brought about by water percolating through the sediment and by the low pressures of new sediment being deposited on top.
See Glossary for a complete list of terms.

Primary producer
Organisms that occupy the first trophic level in the grazing food chain.
See Glossary for a complete list of all terms.

Heterotrophy
Literally, other-feeding; the condition of an organism that is not able to obtain nutrients by synthesizing non organic materials from the environment, and that therefore must consume other life forms to obtain the organic products necessary for life e.g., animals, fungi, most bacteria.
See Glossary for a complete list of all terms.

Figure 3.2(a). Production profile of NO₃^- in the alga-free sediment and in the alga-inoculated sediment. In both light and darkness, the NO₃^- profiles indicated only consumption. In contrast, the alga-inoculated sediment displayed significant NO₃^- production in the entire oxic zone. (Risgaard-Petersen, 2003).

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