Nitrogen cycling in the sediments of a tidal freshwater marsh
Raleigh, NC, North Carolina State Univ., Diss., 1982
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Tag hinzufügen | Zusammenfassung: | Raleigh, NC, North Carolina State Univ., Diss., 1982 The purpose of this research was to describe the nitrogen cycle in a tidal, freshwater marsh (the North River, Massachusetts, USA) by studying the physical and chemical characteristics of the marsh sediments, the rates of microbial ammonium production and consumption in these sediments, and some variables that control these rates. Sediment water content (88% of fresh weight), total nitrogen content (1.7% of dry weight), and organic content (60% of dry weight) are relatively constant over depth and time. In contrast, the total phosphorus content declines markedly from 0.3% of dry weight at the surface to 0.1% at 30 cm. Ammonium is the dominant form of inorganic nitrogen and declines from 3.7 mg NH(,4)-N(.)liter('-1) pore water at the surface to 0.92 mg NH(,4)-N(.)liter('-1) at 30 cm. This distribution of ammonium is different from the distribution observed in subtidal sediments and is probably maintained by pore water displacement and root effects. Ammonium-('15)N and isotope dilution techniques were used to measure ammonium production and consumption rates in the sediments. These rates correlate well with E(,h) and vary as a function of temperature (Q(,10) = 2.6) and substrate quality and availability. Gross ammonium production is about 53.5 g N(.)m('-2)(.)yr('-1), gross ammonium consumption is about 29.5 g N(.)m('-2)(.)yr('-1) and the difference, or net production, is about 24 g N(.)m('-2)(.)yr('-1). Gross ammonium production in the sediments is sufficient to support plant growth (22.3 g N(.)m('-2)(.)yr('-1)), nitrification (1.6 g N(.)m('-2)(.)yr('-1)), and microbial immobilization of free ammonium (17.9 g N(.)m('-2)(.)yr('-1)). The nitrogen required to support gross ammonium production is balanced by inputs of plant litter, allochthonous matter from the river and possibly nitrate assimilation. Assimilatory nitrate reduction (9.4 g N(.)m('-2)(.)yr('-1)) and microbial immobilization of ammonium on plant litter (5.0 g N(.)m('-2)(.)yr('-1)) are important because they conserve nitrogen within the marsh. In addition, both processes actively remove inorganic nitrogen from the adjacent river and therefore are important new sources of nitrogen for biological production. These observations lead to the important conclusion that nitrogen uptake by plants appears to be independent of nitrogen acquisition by the marsh as a whole. This provides flexibility to the ecosystem since the marsh can acquire nitrogen from the adjacent river by microbial immobilization at times other than times of maximum plant demand. |
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| Beschreibung: | 158 S. |