Cohen and Neori: Ammonia uptake and nitrogen content of Viva lactuca 475 Botanica Marina Vol. 34, pp. 475-482, 1991 Ulva lactuca Biofilters for Marine Fishpond Effluents I. Ammonia Uptake Kinetics and Nitrogen Content I. Cohen 1 and A. Neori 2 Israel Oceanographic and Limnological Research, National Center for Mariculture, P.O. Box 1212 Eilat 88112, Israel (Accepted 18 July 1991) Abstract The potential of the seaweed Ulva lactuca as a biofilter for effluents of intensive marine fishponds in arid regions has been studied in Eilat, Israel. One kg (wet wt) nor 2 of Ulva in 1 m 2 tanks 60 cm deep, removed, during the day, over 90 percent of the ammonia from the fishpond effluents, at inflow fluxes up to 10 ìéçï1â5 L" 1 h" 1 (0.14 mole m^d" 1 )· At fluxes of 40ìðéïÀ68 L" 1 h~ 3 (0.58 mole m" 2 d" 1 ) 9 nearly 40 percent were removed. Night time ammonia removal remained efficient at low ammonia fluxes. Ammonia uptake rate and percent nitrogen (N) in dry weight (DW) of the seaweed showed hyperbolic correlations with ammonia flux through the tanks. The data fitted the Michaelis-Menten kinetics, with a maximal uptake rate of 28 ìçéïÀâä L" 1 h" 1 (0.4 mole m~ 2 d" 1 ). Pulse ammonia uptake rate was approximately four times that of continuous uptake. Maximal percent N in DW of U. lactuca, when stocked at 1 kg m" 2 , was 4.07. Increased stocking density (2, 4 and 6 kg m" 2 ) did not significantly affect ammonia uptake rate per tank. However, N-content was significantly higher, averaging 5.5 percent of DW. The data indicate that at low ammonia fluxes (below 10 ìéçï1â8 L" 1 h" 1 ) U. lactuca was N-limited and that at higher fluxes the algae became gradually light limited. Our results indicate that 10m 2 of Ulva biofilter can remove from the effluents of our intensive grow-out ponds over 90 percent of the ammonia produced by 1 kg of daily feed ration or by approximately 75 kg of fish. stream eutrophication, which is particularly danger- Intensive culture of marine fishponds is being devel- ous in the highly oligotrophic and enclosed Gulf of oped at the National Center for Mariculture in Eilat, Eilat (Aqaba). Israel. The high densities of fish in the ponds cause Seaweeds have been shown to reduce efficiently the problems of water quality which in turn limit the level of seawater eutrophication in integrated mari- production (Krom et al. 1985 b). Ammonia is a major culture (Ryther et al. 1975). In a series of studies they metabolite produced by the fish and is toxic to them showed some seaweeds to have a high yield and nu- at high levels. It is also a major component in aqua- trient uptake capacity and to be very adequate for culture effluents, contributing to the eutrophication cultivation and harvesting. These advantages could of aquatic environments. Removal of excess ammonia be augmented by the economic potential of many and other inorganic nutrients can improve water qual- seaweeds in various industries. Motivated by these ity in the ponds, and at the same time reduce down- studies, Goldman (unpublished report) suggested the combination of colloid-rich seaweed culture with the fish culture effort in the arid south of Israel. Macroal- gal 'nutrient traps' have thus become a component in of "" e8rattd tert 1Mriculturc in our Corresponding author institute (Gordin 1982). Botanica Marina / Vol. 34 / 1991 / Fasc. 6 Copyright © 1991 Walter de Gruyter · Berlin · New York Brought to you by | Stockholms Universitet Authenticated | 130.237.165.22 Download Date | 9/13/12 9:10 AM