Abstract: To explore the source and spatiotemporal distribution of organic matter and its influencing factors in the Pearl River Estuary and adjacent sea areas, we collected suspended particulate organic matters (SPOM) in June (summer) and December (winter) in 2015, and analyzed δ¹³C and δ¹⁵N of SPOM. The results showed that the distributions of SPOM in the Pearl River Delta region had obvious seasonal differences (P<0.01). The coupling effect of the Pearl River diluted water and outer seawater played an important role in controlling the temporal and spatial distribution of SPOM. In summer, the Pearl River Estuary and its adjacent waters were mainly affected by the Pearl River diluted water, brachish mixed water, and outer seawater. The SPOM of the inner sea area was characterized by higher organic matter content, lower δ¹³C value and higher δ¹⁵N value, indicating that organic matter was mainly affected by the terrigenous matter carried by the Pearl River runoff, freshwater algae and anthropogenic discharge. In winter, the δ¹³C and δ¹⁵N distributions of SPOM were consistent with the thermohaline distribution, showing higher δ¹⁵N and lower δ¹³C, indicating that the freshwater algae carried by the Pearl River runoff may be the important source of organic matter in this region. On the whole, the contribution of phytoplankton to organic matter increased gradually from the inner part of the Pearl River estuary to the outer part of the sea.

Key words: suspended particulate matter, stable isotope, source of organic matter, Pearl River Estuary