Application of multi-element isotopes for assessing sedimentary quality within aquaculture systems

The low precision of acid volatile sulfide relative to total sulfur can decrease the sensitivity for estimating sediment qualities along accumulated organic matter (OM) mixtures within natural (lake, estuary, and marine) and aquaculture systems. Therefore, in the current study, we describe a method for effectively diagnosing the sedimentary qualities in different aquaculture systems (fish, shellfish, and seaweed) by analyzing multi-element isotopes (C, N, and S) within sedimentary OM. The isotopic signatures suggest that variations in δ³⁴S_TS values in different aquaculture systems (shellfish: -7.8 ± 5.0 ‰, seaweed: 5.2 ± 6.6 ‰, fish: -17.0 ± 4.0 ‰) are primarily associated with the degree (25-85 %) of sulfate reduction and the accumulation of different aquaculture-derived OM. Together with the C/S ratios indicative of redox conditions (e.g., oxic/sub-oxic status), the isotopic integration criteria using the end-member mixing model may help determine the origin and reactivity of sedimentary OM occurring in different aquaculture systems. Consequently, the isotopic approach may provide important information for classifying the redox status of aquaculture sediments that may interact with benthic biological variables.