Bio- and photo-lability of dissolved organic matter in the Pearl River (Zhujiang) estuary

We investigated the bioand photo-lability of dissolved organic matter (DOM) from the head, mixing zone, and mouth of the Pearl River estuary. At all three sites, bioand photo-refractory dissolved organic carbon (DOC) and biorefractory chromophoric DOM (CDOM) dominated over the corresponding bioand photo-labile constituents, while photolabile CDOM dominated over photo-refractory CDOM. Relative to the mixing-zone and mouth waters, the headwater was enriched with bioand photo-labile DOC and photolabile CDOM and depleted with biolabile CDOM. Biolabile DOC was richer than photolabile DOC in the headwater, while photolabile CDOM was richer than biolabile CDOM at all three sites. Pre-biotransformation inhibited, stimulated, or had little impact on DOM photodegradation, depending on site. Ultra-violet absorption coefficients are indicators of bioand photo refractory DOC. The relative proportions of transparent and chromophoric DOM control the turnover of biolabile DOC and the effect of pre-biotransformation on DOM photodegradation.

Automated summary

This study investigated the bio- and photo-lability of dissolved organic matter (DOM) in different areas of the Pearl River estuary. The headwater had higher levels of bio- and photo-labile DOM compared to the mixing zone and mouth, while the latter two had higher levels of bio- and photo-refractory DOM. The impact of pre-biotransformation on DOM photodegradation varied depending on the specific site. UV absorption coefficients were indicators of bio- and photo-refractory DOC, and the relative proportions of transparent and chromophoric DOM controlled the turnover of biolabile DOC and the effect of pre-biotransformation on DOM photodegradation.