Seasonal distribution, sources and sink of dissolved organic carbon in integrated aquaculture system in coastal waters

Dissolved organic carbon (DOC) concentrations were measured in the Sanggou Bay (SGB) in northern China, in order to investigate the seasonal distribution, sources and sink of DOC in an integrated multi-trophic aquaculture (IMTA) system of fish, shellfish and seaweed. The sampling was conducted during April (spring), August (summer), October (autumn) and January (winter) of 2011-2012. Salinity, Chlorophyll a (Chl a) and DOC showed large spatial and seasonal variation during sampling period. DOC increased with increasing Chl a in spring, summer and autumn and decreased with increasing salinity in summer compared to other seasons. Maximum surface concentration of DOC ranged from 108.0 to 875.2 A mu M and minimum from 134.4 to 184.7 A mu M was found during summer and spring, respectively. Terrestrial input, phytoplankton and seaweed were the main sources of DOC in SGB. Shellfish farming area was enriched in organic matter as well as served to reduce DOC levels in the bay. As it was indicated that average annual removal of 42 % DOC occurred in the shellfish, the lowest occurred at an average 32 % in combined shellfish and seaweed culture area. Additionally, controlled experiment results showed that seaweed produced approximately 64.81 +/- 40.86 A mu M day(-1) and shellfish generated approximately 13.36 +/- 6.07 A mu M day(-1) and assimilated 17.07 +/- 13.12 A mu M day(-1) DOC in SGB. Accumulation of DOC at the bottom could be a result of long-term aquaculture activities in the bay. Integration of sea cucumber into IMTA system could be useful to mitigate the stockpile of organic matter at the bottom.