Integrated outdoor culture of two estuarine macroalgae as biofilters for dissolved nutrients from <Emphasis Type="Italic">Sparus auratus</Emphasis> waste waters |
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Authors: | Email author" target="_blank">Ignacio?HernándezEmail author M?Angeles?Fernández-Engo J?Lucas?Pérez-Lloréns Juan?J?Vergara |
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Institution: | (1) Area de Ecología, Universidad de Cádiz, Facultad de Ciencias del Mar y Ambientales, 11510 Puerto Real, Cádiz, Spain |
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Abstract: | An integrated outdoor cultivation of two macroalgal species: Ulva rotundata (Chlorophyta) and Gracilariopsis longissima (Rhodophyta) was designed. The macroalgae were cultured in effluents from an intensive marine culture (growout phase) of
gilthead seabream Sparus aurata. The biomass evolution of the algal tanks followed a logistic curve, where the approach to the maximum stocking density of
seaweeds was governed by thalli self-shading, as nutrient limitation in the cultivation tank was unlikely. The maximum stocking
density of the system was approximately 27.8 g U. rotundata L−1 (16.7 Kg m−2) and 11.9 g G. longissima L−1 (7.12 Kg m−2). Yield was more than 3 times higher in U. rotundata than in G. longissima. Overall, U. rotundata removed a greater percentage of phosphate (8.9%) and total dissolved inorganic nitrogen (54%) flowing into the algal tanks
than G. longissima. The latter species biofiltered approximately 3.2% of phosphate and 17% of the total dissolved inorganic nitrogen input.
However, mean nutrient uptake rates on wet weight basis were usually higher in G. longissima than in U. rotundata. The production of total oxidised nitrogen in the algal tanks, considered as being the nitrification rate occurring on the
algal fronds by nitrifying bacteria, was less than half of the ammonium uptake by the macroalgae, suggesting that seaweeds
competed efficiently for ammonia against the nitrifyers. The biofiltration during a diel cycle showed that mean phosphate
biofiltration was lower than 4.5% in the two species whereas ammonium was biofiltered efficiently (up to 67%), especially
in U. rotundata. The metal and heavy metal content in the algal tissue at the end of the monitoring period suggested no metal contamination
of tissues so that both macroalgal species could be used in the food industry. The study reveals the value of ecological engineering
techniques in reducing the dissolved nutrient content in effluents from the fish farm, with the prospect of a better management
practises, based on integrated mariculture designs, being developed by the local farmers. |
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Keywords: | ecological engineering environmental impact Gracilariopsis nitrogen phosphorus Ulva |
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