Nitrogen and phosphorus cycling and transformations in a prototype 'non-polluting' integrated mariculture system, Eilat, Israel

Abstract

An intensive inar~culture system for the growth of sea bream has been developed which uses seaweed Ulva lactuca to remove d~ssolved nutr~ents ( N and P) from the circulating water This allows water to be safely recycled to the fish and results ~n a comparatively 'non-polluting' final effluent As with other marlculture systems, only -25% of the food-N was used for f~s h growth The damnant processes affecting N illthin the system were excietion by flsh of ammonia-N (30%), dissolved organlc mtrogen (DON) (30'X,) and faeces-N (1OU%) rapid transformation of DON to ammonia-N (16%) In the fish tank and uptake of aminonla-N (17 to 3 9 % ) by the seaweed (all percentages e x p~e s s e d relative to food input) N i t r~f~c a t~o n (10%) competed with the seaweed for the available a m m o n~a -N There was only min~mal uptake of mtrate by the seaweed Anoxic condltlons developed in the sedimentation tank Denitiification (5%) and bacterlal ammon~fication, ~ncludlng sulphate reduction, were observed The system showed only m n o r seasonahty, probably because the malor processes (food input and U lactuca uptake) had only a slight dependence on temperature Our quantitative understanding of the processes affecting N within the system was conf~rmed by a parallel study In which a computer simulation model was developed which was able to p r e d~c t well the observed changes In ammonia-N, total oxidised N and U lactuca growth There was a n excess of phosphorus In the food supplied It was removed by the seaweed (9 to 21 %) but to a lesser degree than ammonia-N The residual organlc matter in the s e d~m e n t a t~o n tank was ennched In P, probably because of the presence in the food of bone meal which is resistant to bacterlal decdv The final effluent d~s c h a r g e d contarned 20 to 27 % of the N supplied (and 39 to 47 % of the P) which IS less than half the N d~s c h a r g e d from conventional manculture technology

Nitrogen transformations and factors leading to nitrite accumulation in a hypertrophic marine fish culture system

“…This potential, measured with the addition of ample ammonia, is about 3 times higher then the actual values determined during normal mariculture operation by Krom et al (1995) for this model ecosystem. Therefore, the overall normal ammonia oxidation process was substrate-limited, most probably as a consequence of competition by the seaweed.…”

“…The latter process might occur in the less aerated areas within this tank. Evidence, however, that the observed nitrite buildup resulted also from nitrification and not only from denitrification was provided in a previous study of this experimental system (Krom et al 1995). There, both nitrite and nitrate accumulated in the fish tank.…”

“…Nitrite and nitrate were analyzed as in Glibert & Loder (19771, TAN as in Krom et al (1985). Precision of each method in our laboratory is given in Krom et al (1995). DO was measured with a YSI electrode (Yellow Springs Instrument Co.) after calibration against the Winkler method.…”

“…Nitrification rate was defined for practical considerations as the net accumulation rate of total oxidized nitrogen (ToxN = NO2-+ NO3-). Rates of ToxN production in the tanks were calculated from inflow and outflow concentrations of the nitrogenous species, multiplied by the water exchange rates, as in Krom et al (1995). Potential rates of ToxN production in the tanks were measured by stopping the water exchange, topping up the water with ammonium salt to concentrations between 100 and 150 PM, ToxN production rates were measured in the 3 main compartments comprising the model manculture system: the seaweed tanks, the fish tank and the sedimentation tank.…”

“…The system was characterized by steady input rates of water and nutrients and by the daily discharge of the anaerobic sediments (Neori et al 1993(Neori et al , 1996. Relatively high and persistent production rates of nitrite and nitrate had been found in this system (Krom et al 1995, Neori et al 1996. The physical separation between the autotrophic and heterotrophic compartments and the lack of significant sediment buildup have allowed the detailed characterization of these transformations.…”