Productivity of sewage fertilized fish ponds

Water Research VoL 9, pp. 269 to 274 Pergamon Press, 1975. Printed in Great Britain.

PRODUCTIVITY OF SEWAGE FERTILIZED FISH PONDS K. P. KRISHNAMOORTHI.M. K. ABDULAPPA.R. SARKARand R. H. SlDDIQI Central Public Health Engineering Research Institute, Nehru Marg, Nagpur, India

Receired 13 October 1973) INTRODUCTION

Necessity of intensive utilization of water resources and increasing food production can not be over emphasized. Addition of plant nutrients to water when used for domestic purposes makes it suitable for agricultural operations when properly managed. Fish ponds fertilized with sewage have been used both in India and other countries in the past [I]. Extent of sewage addition and consequent fertilization depends on the characteristics of the sewage, climatic conditions. physical features of the pond and the type offish being cultured. Because of the numerous influencing factors, which at times cannot be clearly delineated, the practice of fish culture in such ponds has developed largely on the basis of local experience. This paper reports primary productivity, fish yields and other relevant biological and physico-chemical parameters of some experimental fish culture ponds receiving effluent from a stabilization pond treating domestic_ wastewater.

METHODS

The fish culture ponds were located at Nagpur, 21 ° N, in central India. The ponds were 5-5 x 16.5 m in size with a 1 m water depth. These were fertilized with a stabilization pond effluent, Fig. 1. Two sets of data obtained in experiments designated as I and II are presented here. In experiment I the fish ponds receiving effluent differentially diluted with raw water were operated in parallel. Fifty, 33 and 25~o dilutions of the pond effluent were used. The 33;/0 dilution was fed to two ponds. One pond was fed with undiluted effluent. In experiment I1 the ponds were connected in series and were fed undiluted effluent. In both the experiments, one fish pond receiving only raw water was operated as a control. Figure 1 also shows the average characteristics of the stabilization pond influent and effluent. The stabilization pond on an average was loaded at the rate of 435 kg BOD ha- ~ day- 1. This paper was received for the Paris Conference, but together with several more was accepted for Water Research as there was no place for it on the Conference Programme. 269

Throughout the period of study there was considerable amount of seepage. 4000-15,0001. d a y - ' , from each of the fish ponds. Undiluted and diluted effluent and raw water had to be added to make up the loss. The make up flow to the ponds was maintained for 34 h. depending on seepage, during daylight hours and stopped when the ponds attained operational level. Experiment I was conducted from July 1970 to March 1971, experiment II from May 1971 to December 1972. In experiment I the control and the ponds receiving 50 and 33°,/, dilution were stocked with 50 fingerlings each of Cyprimls carpio on 7 July, 1970. On 22 September, 1970, 50 fingerlings of Laheo rohita were also released into each of these ponds and the one receiving 25')o diluted effluent. In experiment II each of the ponds were stocked with 100 fingerlings of Cyprimts carpio on 3 May, 1971. Trial netting of fish was done in each pond approximately once in 2 months and weight of at least 10 random fish specimens were recorded. Primary production was measured using light and dark bottles [2] suspended at every 15 cm intervals of

Experiment I

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depth. Bottles ~ere incubated for 2 h periods. Observations ~ere carried out throughout the da?light hours and in some instances onl~ betv,een IO a.m. and 12 noon. In experiment L observations were carried out only in January and Februar~ 1971. In experiment II. fi,,e observations were conducted covering winter. summer and rainy' seasons. A measured quantity' of water was filtered using 200 mesh bolting silk net for collection of zooplankton. Numerical evaluation was done using Sedgwick Rafter cell. For phytoplankton, surthce samples were collected, preserved in Lugol's iodine and numerical evaluation was done using a haemocytometer. Samples for bottom lituna were collected using Ekman's dredge. Samples for bottom fauna and zooplankton determinations were collected once a month and that lbr phy toplankton every v,eek. Physico-chemical analyses included measurement of temperature, pH, DO. N and P once every week. Samples for DO were collected from the surface and bottom. DO and pH measurements were done at mid-day. post-sunset and predawn hours. Phosphorus determinations were conducted after filtering the sample through Whatman No. 42 filter paper. OBSERVATIONSAND DISCUSSION Out of the determinations described above only those which are considered important tbr operation and control of fish culture are reported and discussed here. During the entire period of the study the temperature of the ponds ranged between 18 and 35°C. There was no appreciable difference from pond to pond in a particular season. The low temperatures occurred during December-January and the high temperatures in May-June. There was no significant temperature gradient in the ponds. T h e ' p H of the ponds ranged between 7.2 and 9"6. Most of the time the extreme values occurred within a day in each pond, the high pH being associated with intense photosynthetic activity in the afternoon hours and the low pH occurring during the pre-dawn hours. During daylight hours there was always an abundance ofdissolved oxygen, going as high as 4 times the saturation value. The critical dissolved oxygen concentrations occurred during the pre-dawn hours. These values are shown in Figs. 2 and 3 for the two experiments. It is seen that in experiment I, the average values were sufficiently high for maintaining fish life {greater than 2 mg 1- ~) except in the case where there was no dilution. The figure also shows the recored minimum surface and bottom dissolved oxygen conccntrations. Even though ponds receiving 33 and 25%

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dilution show an average dissolved oxygen concentration sufficient for maintaining fish life, the recorded minimum value reached critical levels. In experiment lI pre-dawn dissolved oxygen concentrations were much lower. There was, however, a trend of increasing concentrations as the effluent passed from the first to the fifth pond in series. Still on many occasions the ponds showed zero dissolved oxygen concentrations. The consumption of oxygen during night hours is attributed to two main reactions, namely, bacterial oxidation of organic matter and endogenous respiration of zoo- and phytoplankton. It is seen from Figs. 4 and 5 that in experiment II the ponds were harbouring a much larger population of zoo- and phytoplankton as compared to experiment I. The low dissolved oxygen concentrations in experiment II were therefore probably due to endogenous respiration of these organisms. Further, their death and subsequent degradation by bacteria would also lead to a higher oxygen consumption rate. While nitrogen and phosphorus are considered as essential macro-nutrients to support phytoplankton, the starting level of trophic pyramid, a high concentration of ammonia nitrogen may be detrimental to fish life. Figures 2 and 3 show that ammonia nitrogen was well below 2 mg !- t except for the ponds where undilu ted effluent was added, in which case it was in the range of 4-6 mg 1- '. It is well recognised that ammonia toxicity depends, along with other characteristics of the aquatic environment, to a very large extent on its pH

Productivity of sewage fertilized fish ponds

271

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{3]. At high pH ~alues e*.en Io~ concentr:ttions or ammonia become toxic due to presence of the molecular species. The values obser,,ed in these experiments are not considered as toxic. Fish mortality, whene,,er occurred ,,,,as acute and it alwaxs took place during pre-dawn hours when the pH was Io~est. Addition of nitrogen for fertilization of fish ponds is not considered necessary b~ m;mv investigators [-t]. Application of phosphatic fertilizers, on the other hand, has been shown to be of advantage. Data presented in Figs. 2-5 are replotted in Fig. 6 to bring out the relationship between phosphorus and phytoplankton. It is seen that phosphorus concentrations higher than 4 mg I-~ are coincident with excessive algal blooms ranging between 150 x 103 and 310 × l0 s phytoptankton ml- ~. Results of biological anabses were averaged and are shown in Figs. 4 and 5. There were frequent blooms of blue green algae, however, no trend was noticeable from season to season. Throughout the period of study the blue-green algae particularly :~licroc)'stis were predorninant. Among the greens, Chlorello, Carteria and Scenedesmus and Euglemt were observed. The zooplankton consisted mainly ofrotifersand crustaceans in almost equal numbers. There was a significant increase in their number, about I0 times the average value, in the months of November and December. The bottom fauna consisted of both oligochaetes and blood worms. The blood worms which are an ideal fish food were dominant of the two. In all 30 dawn to d u s k primary productivity measurements were carried out during the entire period of stud,v. A constant relationship between the productivity during 10 a.m. and 12 noon and that in the whole day has been reported [5]. In order to establish such a relationship for the experimental ponds described here, the data were analysed accordingly and it was found that 25 per cent (S.D. 874;) of the daily primary productivity occurred during this period. Additional measurements during 10-12 h period were therefore converted to dail~ production rate on this basis. Figures 2 and 3 show the average value of primary productivity of the ponds. In experiment I, productivity studies were carried out only in the winter season while in experiment II in all the three seasons. In experiment I, the primary productivity increased from 2-4 g O_, m-2 day-~ (control pond) to 18.4 g 02 m-~ day-1 (pond receiving 3Y'[, dilution). The productivity decreased to lower values when lesser or higher dilutions were used. The data of experiment II showed that while the productivity during summer and rainy seasons was of the same magnitude, that in the winter season was much lower. There was an increase m primary

producti~ it}, as the effluent passed through the ponds in series. A comparison of p h ~ t o p k m k t o n and primar~ producti~it 5 da[a sho~s that in experiment II even though the p h ~ t o p l a n k t o n ~erc in a much higher concentration, the primary producti~it~ of ~intcr season

was much lo~er as compared to that in experiment [. As observed b,, Hepher [5] and Lund [6] this was due to a shallow euphoric zone resulting from a dense bloom of algae at the surface. The observations on growth of fish are shown in Figs. 7 and S. In experiment 1, Cyprinu.s carpio had a hi~her growth rate than Laheo rohita. In the pond receiving 33 per cent diluted effluent C. carpio attained an individual a,,erage weight of 350 g in 6-5 months which is about 4 times that in control. Growth of Laheo rohit~t levelled off tit about 75 g in 4 months in ponds receiving 33 and 25";) diluted effluent. Cyprhm,~ cw'pio is an omnivorous fish which particularly leeds on )dicrocystis, the dominant algal form present in the ponds. The major carp Labeo rohita, on the other hand, preters diatoms and desmids E7]. It was not able to utilise the food available. This resulted in almost similar growths. 60 and 75 g in the control and the fertilized ponds respectively. On a few occasions there was mortalit? in pre-dav,n hours. Some of the dead specimens showed chokage of gills with Microcysti.v In experiment II only limited data on fish growth could be obtained because of sudden and heavy mortalities. The mortalities are attributed to depletion of dissolved oxygen in pre-dawn hours. The data in Fig. 7 suggest that fish productivity improved as the effluent passed through the ponds in series. In the fifth pond, the fish attained a weight of 800 g in 4 months as compared to 350 g in the third pond. The growth in the control during this period had levelled offat 55 g. The excellent growth of Cyprim~.s carpio in the fertilized

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ponds may again be noted. Ponds which receive only stabilization pond effluent may be used if daily addition of effluent is regulated to a lower level than what was necessary in the present case because of excessive seepage. Daily addition of nutrients through make up effluent causes blooms while seepage through pond sides and bottom acts as a straining mechanism leaving behind the algal mass in surface layers. The trophic levels in the pond can be divided into two major groups, the primary producers or photosynthetic organisms and the consumers or the fish. The other intermediate groups would be the zooplankton. the microbial decomposers and the bottom fauna. On the basis of observations described above, a balance of energy flow through the pond ecosystem may be attempted for the data of experiment I for Cyprim~s carpio. The average winter visible solar radiation at Nagpur is approximately 195 cal cm--' day- t. According to the chemical equation of photosynthesis by algae

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3680 cal are fixed for each g of oxygen liberated. From Fig. 2, the average winter season primary productivity of the pond receiving 33% diluted stabilization pond effluent was 18"4 g O2 "'--' day-'. Therefore the efficiency of fixation of solar radiation was = (3680 x

274

K.P. KRISH',;ANOORTHI,M. K. ABDULAPpA.R. SARI~ARand R. H, SIDDIQI

18.4 x 100)/'(195 x 10~1 or 3-47 per cent. If 100 fish are taken to be stocked per pound and the growth of fish is at the rate of 350 g in 6"5 months on an average individual weight basis, Fig. 7. the yield of fish would be 2 g m - ~ day- ~. Assuming 1000 cal to be fixed per g of fish growth, the et'ficiency of fixation of solar radiationwas(1000 x 2 x 100)/(195 x 10"lor 0"1 percent. The ratio incident energy: gross primary production: net fish yield, therefore was 100:3'47:0.1. Similarly the ratio for the control pond was 100:0.51:0-031. It may be noted that above figures are based on 6'5 month period observation and for Cyprinus carpio.

SUMMARY

Observations were carried out on productivity of fish culture ponds receiving stabilization pond effluent. Suitable environmental conditions for the culture of fish could be maintained where the effluent was diluted with fresh water. In case where no dilution was used. an excessive growth of algae led to depletion of dissolved oxygen leading to fish mortality. Such ponds may be used if daily addition ofeffluent is regulated to a lower level than what was necessary in the present case because of a high rate of seepage. Phosphorus in excess of 4 mg I - t under the conditions of the experiment was coincident with high phytoplankton counts. M icrocystis was the predominant phytoplankton in all the ponds.

Primary productivity of ponds was high when the effluent was dituted. Excessive bloom ofalgae resulted in lowering of primary productivity. Cyprinus carpio could grow well in the fertilized ponds. Its yield was better where diluted effluent was used. A similar trend was noted for primary productivity. An energy balance showed that 3-86 per cent of incident energy was fixed through primary production and 0.1 per cent could be harvested in the form of fish. REFERENCES

I. Allen G. H. {1969) A preliminary bibliography on the utilization of sewage in fish culture. FAO Fisheries Circuhtr ,Vo. 308. FRI/C308. Rome. 2. Vollenwelder R. A. (1969) A Manual on Methods Jor Measuriny Primary Production in Aquatic Environments. Btackwell. Oxford. 3. Doudoroff P. and Katz M. (1950) Critical review of literature on the toxicity of industrial wastes and their components to fish--l. Sew. Ind. Wastes, 22, (I I) 14321458. 4. Hickling C. F. (1968) The Farminy of Fi.sh. Biology in action series, Pergamon Press, London. 5. Hepher B. (1962~ Primary production in fish ponds and its application to fertilization experiments. Limnol. Oceano~lr. 7, t 31-136. 6. Lurid J. W. G. (1969) Phytoplankton. Eutrophication ca,tses, consequences, correctices. Proceedings of the Symposium. National Academy of Sciences, Washington, D.C. 7. Menon M. D.. et al. (1959). Report to the Indian Council of Agricultural Research on the Madras Piscicultural Scheme worked from 1942-1952. Government Press. Madras.