Characterisation of water quality in effluents of land-based abalone farms in the Western Cape, South Africa

Abstract

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 9:87-102 (2017) - DOI: https://doi.org/10.3354/aei00217 Characterisation of water quality in effluents of land-based abalone farms in the Western Cape, South Africa T. A. Probyn1,*, M. Pretorius2, K. Seanego1, A. Bernatzeder2 1Aquaculture Research and 2Sustainable Aquaculture Management, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Vlaeberg 8018, Cape Town, South Africa *Corresponding author: trevorp@daff.gov.za ABSTRACT: Effluent water quality was measured at 9 abalone (Haliotis midae) farms in 2 regional nodes (west and south) along the South African coastline. For most farms, effluent total suspended solids (TSS) exceeded the background reference level (80th percentile), and 3 did not comply with the 5 mg l-1 standard. Total ammonia nitrogen (NH4+) concentrations were mostly greater than reference levels but well below the 43 µmol N l-1 standard. Inflow-corrected concentrations of nitrate, nitrite and phosphate were low compared to NH4+ and would not pose a significant eutrophication risk. Similarly, the biochemical oxygen demand measured at 3 of the farms was low (median 1.31 mg l-1). Abalone production-specific annual loads of TSS (334 kg per metric tonne [mt]), total N (20.3-38.1 kg N mt-1) and total P (3.2-7.5 kg P mt-1) agree with what has been found for different land-based aquaculture operations. These figures translate to N-based human population equivalents of 5.4-10.6 persons mt-1 for both regions. At the broader ecosystem level, the annual TSS loads calculated from 2013 production data of 43 mt yr-1 (west) and 369 mt yr-1 (south) are, respectively, 0.35 and 2.8% of that estimated for kelp erosion. Similarly, the dissolved inorganic N loads of 1.9 mt N yr-1 (west) and 9.4 mt yr-1 (south) are trivial by comparison with nitrate advected during upwelling. Local abalone farms have a relatively high specific C footprint—conservatively ~44 kg CO2 kg-1 production. Our findings support a relatively low potential impact of farm effluents in this coastal upwelling environment. KEY WORDS: Abalone farm · Effluents · Suspended solids · Nutrients · Haliotis Full text in pdf format PreviousNextCite this article as: Probyn TA, Pretorius M, Seanego K, Bernatzeder A (2017) Characterisation of water quality in effluents of land-based abalone farms in the Western Cape, South Africa. Aquacult Environ Interact 9:87-102. https://doi.org/10.3354/aei00217 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 9. Online publication date: February 21, 2017 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2017 Inter-Research.