Abstract
Abstract. Dissolved organic carbon (DOC) is a significant component of carbon and nutrient cycling in fluvial ecosystems. Natural wetlands, as important DOC sources for river and ocean ecosystems, have experienced extensive natural and anthropogenic disturbances such as climate change, hydrological variations and land use change in recent years. The DOC characteristics in surface ponds from contrasting wetlands in the Sanjiang Plain, Northeastern China were investigated. Surface ponds at seven sites (two natural phialiform wetlands, three natural riparian wetlands, one degraded wetland and one artificial wetland, i.e., rice paddy) were monitored during the growing seasons of 2009 and 2010. The results show that the surface ponds at the five natural wetland sites exhibited a wide range of DOC concentrations (10.06–48.73 mg L−1) during the study period. The DOC concentrations showed no annual differences (P > 0.05) at all the wetland sites, except one of the phialiform wetland sites. The two phialiform wetlands exhibited higher DOC concentrations than the three riparian wetlands (P < 0.05). The DOC concentration in the surface pond at the artificial wetland site was relatively low (P < 0.05) compared to that at the degraded wetland site. The C/C ratios (the color per carbon unit ratio, Abs400/DOC concentration) showed inconsistent variations among these seven wetland sites, while the E4/E6 ratio (Abs465/Abs665, fulvic acid/humic acid) from the surface pond in the rice paddy land exerted 42.07–55.36% reductions (P < 0.05), compared to those at the five natural wetland sites. Furthermore, the E4/E6 ratio in the surface pond at the rice paddy site was significantly lower compared to that at the degraded wetland site (P < 0.05), which indicated that disturbance to wetland DOC in surface ponds might be stronger when natural wetlands were converted to rice paddies in comparison with wetland degradation. This study could not only provide insightful points for understanding the aquatic DOC dynamics from different wetland ecosystems, but also support data information for incorporating the aquatic DOC into the model for regional carbon budgets in the future.
Highlights
Dissolved organic carbon (DOC) is a collective term for dissolved and colloidal organic compounds in various stages of decomposition, defined as the organic fractions that pass through a 0.45 μm filter (Roulet and Moore, 2006; Clay et al, 2009)
Our previous study found that the DOC concentration from the surface pond decreased from the natural phialiform wetlands to rice paddy lands (Wang et al, 2010), while there was no significant difference between the riparian wetland and degraded wetland (Song et al, 2011)
In this study we determined that the averaged DOC48v5alue was 23.25 mg L−1 for the surface ponds at the five n4a86tural 4.2 DOC characteristics from different natural wetland wetland sites in the Sanjiang Plain during the two-year samecosystems plings
Summary
Dissolved organic carbon (DOC) is a collective term for dissolved and colloidal organic compounds in various stages of decomposition, defined as the organic fractions that pass through a 0.45 μm filter (Roulet and Moore, 2006; Clay et al, 2009). It consists of a variety of molecules that range in size and structure from simple acids and sugars to complex humic substances (Thurman, 1985; Wallage et al, 2006). The specific UV light absorption at 254 nm (SUVA254) has been suggested as an index of the aromaticity of DOC (Weishaar et al, 2003; Fellman et al, 2008)
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