The in situ nitrogen (ammonium and nitrate) uptake kinetics of Macrocystis pyrifera (L.) C. Agardh: applications for integrated multi-trophic aquaculture (IMTA) in Big Glory Bay, Stewart Island, New Zealand

Macrocystis pyrifera;nitrogen;ammonium;nitrate;kelp;aquaculture;New Zealand;IMTA;multi-trophic;integrated;Macrocystis;uptake;kinetics

Stewart, Cohen John ; Hepburn, Christopher

University of Otago

关键词: Macrocystis pyrifera;    nitrogen;    ammonium;    nitrate;    kelp;    aquaculture;    New Zealand;    IMTA;    multi-trophic;    integrated;    Macrocystis;    uptake;    kinetics;   

Others  :  https://ourarchive.otago.ac.nz/bitstream/10523/5925/1/CohenStewartJ2015MSc.pdf

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来源: Otago University Research Archive

【 摘 要 】

The in situ nitrogen (ammonium and nitrate) uptake kinetics of Macrocystis pyrifera and the potential for M. pyrifera to be used in an integrated multi-trophic aquaculture (IMTA) approach with salmon (Oncorhynchus tshawytscha) and mussels (Perna canaliculus) was investigated in Paterson Inlet, Stewart Island, New Zealand.The in situ nitrogen uptake kinetics of M. pyrifera were determined using transparent polyethylene bags that were wrapped around in situ M. pyrifera blades or blade pieces and spiked with either ammonium or nitrate of varying concentrations. Experiments were conducted with both intact blades and blade pieces to assess the effect of tissue excision on macroalgal nutrient uptake. After being exposed to the nutrient solution, nutrient uptake rates were determined for each tissue type. M. pyrifera displayed rate-unsaturable uptake for ammonium at the studied concentrations (~80 µM) and uptake discontinuity for nitrate with uptake initially saturating (Vmax = 31.67 μmol gdw-1h-1, Ks = 61.00 µM) and then displaying rate-unsaturable uptake thereafter. Tissue excision did not significantly affect M. pyrifera ammonium uptake and this was attributed to the long tissue recovery period (eighteen hours) allocated to the cut blades and the short incubation period which meant the loss of the capacity for translocation did not significantly affect uptake. The effect of tissue excision on M. pyrifera nitrate uptake could not be determined due to insufficient data. To assess the suitability of M. pyrifera as an IMTA species, juvenile M. pyrifera were grown outside a salmon farm, a mussel farm and at a control site in both summer and autumn in Big Glory Bay or Glory Cove, Stewart Island, New Zealand. After the growing period (26-28 days), the M. pyrifera was harvested and growth rates, carbon and nitrogen status, nitrogen isotope (δ15N) signatures and pigment concentrations were determined and compared. In summer there was some evidence of improved M. pyrifera growth at the salmon farm site and the M. pyrifera percentage nitrogen content and soluble ammonium concentration were higher at the salmon farm site compared to M. pyrifera that were grown at the mussel and control sites. Analysis of δ15N signatures suggested that on average 68% of assimilated nitrogen was derived from the nitrogen in salmon pellets. However, in autumn, evidence indicated that salmon farm-derived nitrogen was a less important source of nitrogen as naturally occurring seawater nitrogen concentration was increasing. Analysis of δ15N signatures suggested that on average only 26% of assimilated nitrogen was derived from the nitrogen in salmon pellets during autumn. Results demonstrate that M. pyrifera can take up nitrogen derived from the salmon farm but seasonal differences in nitrogen demand by M. pyrifera suggest that nitrogen sequestration by this species will be greatest during the summer period.The results from the in situ uptake experiments were combined with seawater chemistry and M. pyrifera nitrogen status data from the IMTA trials to answer two questions: (1) how long will it take for M. pyrifera to reach maximum tissue nitrogen content given the salmon farm nitrogen input rate and M. pyrifera ammonium uptake rate? and (2) how much M. pyrifera would need to be cultivated in summer and autumn to make a significant contribution to reducing nitrogen waste from the Kiwa 1 salmon farm, Big Glory Bay which produces 2,400 tonnes of salmon annually? By addressing these questions, insight was gained in terms of the short-term nitrogen enrichment buffering capacity of M. pyrifera as well as the amount of standing crop of M. pyrifera that would need to be cultivated in order to sequester the nitrogen inputs coming from the salmon farm. M. pyrifera takes approximately 63 hours to reach three percent nitrogen content (the maximum tissue nitrogen content for M. pyrifera) given the ammonium uptake rate of M. pyrifera and the rate of nitrogen input from the Kiwa 1 salmon farm. After accounting for nitrogen input from the Kiwa 1 salmon farm and the percentage nitrogen content of M. pyrifera from the salmon site, between 0.5 km2 and 5.96 km2 of M. pyrifera would be required to sequester all of the nitrogen inputs coming from the salmon farm depending on cultivation biomass and the season in which the M. pyrifera is grown. Such space requirements would be a significant area of Big Glory Bay and would require the closure of mussel and oyster farms and therefore total sequestration of Kiwa 1 salmon farm nitrogen inputs is not feasible. However, it was concluded that even if only a portion of the salmon farm-derived nitrogen could be sequestered by M. pyrifera cultivation, the IMTA approach could still be worthwhile. The co-cultured M. pyrifera could buffer against eutrophication and associated harmful algal blooms and provide oxygen, habitat, the potential for economic diversification and a point of difference in the market place.