Abstract
Stable isotopic signatures of organic carbon (δ 13 C) and total nitrogen (δ 15 N) were measured on suspended particulates and sediments in order to understand the sources of organic matter (OM), water quality and flow of organic carbon and nitrogen among integrated multi- trophic aquaculture (IMTA) species, as well as to evaluate the role of IMTA practice in accumula- tion and assimilation of OM during wet and dry seasons. OM distribution and composition were studied during 2011 in Sanggou Bay (SGB) of northern China, a system that receives terrestrial and oceanic inputs, and which is used for IMTA ventures. Results showed that higher terrestrial input of OM occurs during the wet compared to the dry season in the SGB. OM in suspended par- ticulates (POM) showed marine- and terrestrial-derived signatures during the wet season, as revealed from their ranges in δ 13 C (�27.4 to �20.7‰) and δ 15 N (4.7 to 9.4‰). Sedimentary organic matter (SOM) showed signatures of marine-derived OM during both seasons, with ranges in δ 13 C and δ 15 N of �22.4 to �21.4‰ and 1.7 to 6.4‰, respectively. Shellfish and combined (shellfish, sea- weed) cultures in SGB have the potential to reduce OM received from the fish cages as well as from the seasonal inputs from rivers. Mixing with Yellow Sea water, combined with prevailing circulation, favours the dispersal, dilution and transformation of OM and maintains and improves water quality. Based on our results, and compared with previous studies, the water quality of the SGB is likely to be sustained by IMTA activities.
Highlights
Excess amounts of carbon and nitrogen produced either from land-based or offshore aquaculture activities are considered to be one of the main sources of pollution in coastal environments
In Sanggou Bay (SGB), phytoplankton production is one of the main sources of organic matter (OM) to higher trophic levels during the wet season, as indicated by a positive correlation between δ13C and particulate OM (POM), the latter of which containing a large proportion of phytoplankton
Based on the results of the stable isotope analysis, our conceptual model for the wet season suggested that ~80% of the OM including faecal material and riverine OM in the form of POM is extracted by oyster and scallop
Summary
Excess amounts of carbon and nitrogen produced either from land-based or offshore aquaculture activities are considered to be one of the main sources of pollution in coastal environments. Aquacult Environ Interact 8: 207–219, 2016 additional nutrient and OM enrichment in the coastal marine system (Evgenidou & Valiela 2002) This waste affects the area in close proximity to the sources but can alter a wider coastal zone at various ecosystem levels; reducing the biomass, density and diversity of the benthos, plankton and nekton, and modifying natural food webs and stimulating eutrophication (Gowen et al 1991, Pillay 1991, Vollenweider 1992, Duarte 1995). The aquaculture-derived nutrients can be removed by seaweed biofilters (Buschmann et al 2008) Such a combined species cultivation method, so-called integrated multi-trophic aquaculture (IMTA), is practiced in Chinese coastal zones. The IMTA of shellfish, seaweed and fish is common on the coast of northern China and has been in practice over 3 decades (Fang et al 1996a,b, 2009)
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