Seasonal and spatial variation in biodegradability of organic carbon along the Red River, Vietnam

Abstract

The biodegradability of organic carbon in aquatic ecosystems has been broadly attributed to a variety of interacting physical, chemical and biological factors and processes. The Red River is the second largest river in Vietnam. It also constitutes the main source of water for a large percentage of the population of North Vietnam, however, little has been published on the variation in biodegradability of organic matter in this ecosystem, despite its importance in terms of carbon export to the adjacent coastal ocean. Here, we present the results of an investigation into seasonal and spatial variations of the biodegradability of organic carbon in the Red River basin, North Viet Nam. Biodegradability of DOC (BDOC) and POC (BPOC) seasonally differed at the four stations investigated. BDOC concentrations ranged from 0.2 − 2.84 mgCl−1 and BPOC concentrations fluctuated from 0.02 − 2.6 mgCl−1. In the biphasic degradation, the degradation constant for the labile fraction of DOC (k1) varied between 0.0036 and 0.6357, with values being significantly higher (p < 0.014) during the rainy season than during the dry season. In contrast, no significant difference (p = 0.352) in the biodegradability of the POC labile fraction was observed. In general, the average observed in our study values of the biodegradable fraction of particulate was lower than BDOC, BPOC ranged from 16% to 39%, with biodegradability of total organic carbon (BTOC) ranging from 33% to 44%. The higher rainy %BDOC (49%) than dry season (29%) in watersheds dominated by wetlands.

Keywords

• doc
• poc
• biodegradation
• tropical rivers