A Tropical Freshwater Wetland: II. Production, Decomposition, and Peat Formation

Abstract

As much as 10% of the total carbon stored in peatlands occurs in the tropics. Although tropical peatlands are poorly understood scientifically, they are increasingly exploited for a variety of human uses. Our objective was to measure baseline carbon cycling data in one type of tropical peatland in order to understand better how peat accumulates in these ecosystems. Average plant production for two study sites on the island of Kosrae in the Federated States of Micronesia over 2 year was 1122 g C m À2 year À1 , of which 1058 g C m À2 year À1 was aboveground plant production (bole, buttress and litterfall). Although leaves contributed a high proportion of total plant productivity, their rapid decomposition left little carbon for peat accumulation. In contrast, fine roots only contributed $10% to plant productivity, but their slow decomposition allowed them to accumulate as peat. Wood (branches and stems) probably contributed the most carbon to the formation of peat. Despite being on the soil surface, small branches decomposed more slowly than leaves because of their high C:N and lignin:N ratios. In summary, we suggest that tropical peatlands in Micronesia accumulate peat not because of high plant production but rather because of slow decomposition of roots and wood under anaerobic conditions that result from nearly constant high water levels.

Hydroclimatic shifts in northeast Thailand during the last two millennia – the record of Lake Pa Kho

“…In lake sediments these ratios allow discrimination between aquatic and terrestrial organic matter sources (Meyer and Teranes, 2001;Meyers, 2003). In peatlands, however, C/N ratios may indicate changes in the type of peatforming plants (Kuhry and Vitt, 1996) and/or are an indicator of the degree of peat decomposition (Chimner and Ewel, 2005). δ 13 C org values are reported in parts per thousand (permille, ‰) relative to the Vienna PeeDee Belemnite (VPDB, for C), with an analytical error of ±0.15‰, and are here used as a proxy for the contribution of aquatic versus terrestrial plants (Meyer and Teranes, 2001;Meyers, 2003).…”

“…The overall gradual decrease in the C/N ratio, which starts at 2.93 m (AD 450), may be explained by peat decomposition. This process liberates soluble carbon compounds, whereas nitrogen remains relatively constant, because most of its labile forms have already been consumed or transformed to inorganic forms (Chimner and Ewel, 2005;Ise et al, 2008). Charcoal was observed between 2.98 and 2.73 m (AD 410-650), and the sample analyzed for plant remains between 2.78 and 2.73 m (AD 580-650) is composed of terrestrial-telmatic species (Figure 3).…”

Caracterização de Organossolos em ambientes de várzea do nordeste do Brasil

“…Tal padrão pode ser observado em ambientes onde ocorrem condições anóxicas, provocadas pela saturação por água, baixas temperaturas, ou ainda onde a acidez ou concentração de sais são elevadas (Andriesse, 1988;Driessen, 2001;Chimner & Ewel, 2005). Tais solos têm sido mais identificados nas regiões Sudeste e Sul do Brasil, estando relacionados aos ambientes de várzeas interioranas ou na baixada litorânea, ocorrendo ainda em ambiente altomontano.…”

“…Em virtude da grande fragilidade, esses ecossistemas são muito suscetíveis à degradação (Chimner & Ewel, 2005), resultando em consequências como a alteração do regime hidrológico, o soterramento dos Organossolos pela deposição de sedimentos minerais com o assoreamento das depressões onde ocorrem, a mineralização e a redução dos teores de matéria orgânica e a subsidência (redução de volume e massa). Pode haver diminuição da capacidade de suporte hídrico, do potencial de uso e da ação de filtragem em razão da diminuição da carga hidráulica e da qualidade da água que abastece os aquíferos subterrâneos (Andriesse, 1988;Chimner & Ewel, 2005;Valladares et al, 2008b (Embrapa, 1971(Embrapa, , 1972.…”

“…Pode haver diminuição da capacidade de suporte hídrico, do potencial de uso e da ação de filtragem em razão da diminuição da carga hidráulica e da qualidade da água que abastece os aquíferos subterrâneos (Andriesse, 1988;Chimner & Ewel, 2005;Valladares et al, 2008b (Embrapa, 1971(Embrapa, , 1972. Todos os perfis foram amostrados em várzeas e são muito mal-drenados ou foram drenados artificialmente.…”