Insights into dissolved organic carbon biodegradation process and influencing factors in shallow lakes in a metropolitan, China

Lakes perform a pivotal role in both regional and global carbon cycles. However, seasonal variations and drivers of dissolved organic carbon (DOC) biodegradability are poorly understood in shallow urban lakes. To address this knowledge gap, a 28-day incubation experiment in urban shallow lakes was carried out to quantify proportion of biodegradable DOC (%BDOC) and temperature sensitivity (Q10 value). %BDOC and Q10 value were significantly higher in the wet season (%BDOC20: 14.48% ± 7.92%, %BDOC30: 17.61% ± 8.98%, Q10:1.32 ± 0.62) over the dry season (%BDOC20: 10.35% ± 6.98%, %BDOC30: 11.59% ± 7.36%, Q10: 1.20 ± 0.65). The absorbance at 350nm (a350) followed a decreasing-increasing-decreasing trend, while a250 / a365 (E2:E3) had a contrasting trend to a350 during the incubation. Three (dry season) and five (wet season) fluorescent components were captured by parallel factor analysis (PARAFAC). The components C2 (terrestrial humic-like) and C3 (tryptophan-like) were largely biodegraded on day 28 in the wet season. The %BDOC was positively related to total dissolved nitrogen (TDN), total dissolved phosphorus (TDP) and fluorescence index (FI), but negatively related to humification index (HIX) during the dry season. However, in the wet season, the %BDOC was positively related to TDN, TDP and DOC. The results show that the controls of DOC biodegradation shift from the combined DOC quality and nutrients (dry season) to DOC quantity (wet season). The study sheds light on the drivers of BDOC seasonality, and underscores the significance of both nutrients and DOC in understanding carbon-geochemistry within lake ecosystems.