Role of Seasons in the Fate of Dissolved Organic Carbon and Nutrients in a Large-Scale Surface Flow Constructed Wetland

Abstract

The role of seasons in the removal of dissolved organic carbon (DOC), nutrients and in changes in the spectral properties of dissolved organic matter (DOM) in a large-scale surface flow constructed wetland (SF-CW) receiving reclaimed water and composed of three basins with different vegetation patterns was studied. Dissolved nitrogen removal efficiencies within the three basins in summer (>50%) and winter (<30%) were significantly different. SF-CW water is enriched in DOC in spring and summer with average outlet concentrations above 8 mg×L−1. UV-visible indices, such as the specific absorbance at 254 nm or the spectral slope between 275 and 295 nm, did not vary over the seasons; thus, the basins did not change DOM aromaticity and average molecular weight. Synchronous fluorescence spectra showed variations in terms of protein-like and humic-like substances, the latter being more sensitive to photodegradation. A lab-scale photodegradation experiment confirmed that radiation from the sun was responsible for this decrease, showing this process could alter the composition of DOM at full-scale. DOM variations result from a seasonal competition between release by vegetation and photodegradation. These results validate the necessity for long-term monitoring of SF-CWs, and the utility of rapid optical methods to monitor DOC.

Investigation of the Distribution and Binding Affinity of Copper to Size-Fractioned Dissolved Organic Matter (DOM) in a Constructed Wetland

“…Constructed wetlands (CW) are effective in improving water quality by reducing organic pollutants, nutrients, and heavy metals (HMs) [1][2][3][4][5][6][7]. The water in CW contains different types of dissolved organic matter (DOM), originating from the inflow and also produced within the wetland itself [6][7][8][9].…”

“…Constructed wetlands (CW) are effective in improving water quality by reducing organic pollutants, nutrients, and heavy metals (HMs) [1][2][3][4][5][6][7]. The water in CW contains different types of dissolved organic matter (DOM), originating from the inflow and also produced within the wetland itself [6][7][8][9]. DOM levels in the wetland can be reduced by natural processes like plant uptake, colloidal aggradation and deposition, biodegradation, and photodegradation, with biodegradation and photodegradation being the main processes [6,[10][11][12][13][14][15][16][17].…”

“…The water in CW contains different types of dissolved organic matter (DOM), originating from the inflow and also produced within the wetland itself [6][7][8][9]. DOM levels in the wetland can be reduced by natural processes like plant uptake, colloidal aggradation and deposition, biodegradation, and photodegradation, with biodegradation and photodegradation being the main processes [6,[10][11][12][13][14][15][16][17]. However, the growth of wetland plants, especially during spring and summer, can lead to an increase in the amount of DOM present [6,7], subsequently raising the concentration of dissolved organic carbon (DOC) in the wetland [6][7][8][9][10][11].…”

“…DOM levels in the wetland can be reduced by natural processes like plant uptake, colloidal aggradation and deposition, biodegradation, and photodegradation, with biodegradation and photodegradation being the main processes [6,[10][11][12][13][14][15][16][17]. However, the growth of wetland plants, especially during spring and summer, can lead to an increase in the amount of DOM present [6,7], subsequently raising the concentration of dissolved organic carbon (DOC) in the wetland [6][7][8][9][10][11]. These transformations result in dynamic changes in the abundance, molecular size, and chemical composition of DOM in aquatic systems, leading to significant impacts on their environmental behavior and ecological function.…”

“…To assess the chemical composition and structure of DOM, optical indicators are used as they are rapid, cost-effective and sensitive tools [6][7][8][9][10][11]30,[35][36][37][38]. One such indicator is SUVA 254 , which is the ratio of ultraviolet absorbance at 254 nm to DOC concentration [39].…”