Note: Experimental Design has been revised. See First Addendum to the Eighth Work Plan

Objectives
Significance
Anticipated Benefits
Identification of Beneficiaries
Collaborative Arrangements
Experimental Design
Schedule/Time line
References

Objectives

1) To estimate the amounts of N, P and suspended solids discharged from pond waters during draining.

2) To evaluate several management practices to reduce loadings of nutrients and solids in effluent waters.

Significance

Nutrient enrichment of pond waters is an essential management practice in aquaculture (Pillay 1990, Boyd 1990). However, the discharge of such nutrient-rich waters may result in deteriorating water quality in receiving waters, and is the subject of increasing regulation in many countries (Pillay 1992). Means to minimize the environmental impacts of effluents released from ponds would include minimizing the use of nutrients, managing drainage to retain most nutrients in the pond system, and maximizing use of surplus materials in sediments by animals during grow-out. Several of these topics are the subject of current CRSP proposals. Previous research in Thailand has indicated the most efficient nutrient application systems includes combined organic and inorganic materials at loading rates of 70 kg·ha^-1·wk^-1 chicken manure, and sufficient urea and phosphorus to provide 0.5 g·m^-2·d^-1 N and 0.125 g·m^-2·d^-1 P (Knud-Hansen et al. 1993). These loadings provide organic matter to maintain high alkalinity levels, yet optimize loadings of N and P so they are efficiently used in the pond. Such inputs also result in production of about 4800 kg/ha per 150-day grow-out of tilapia (Diana et al. 1994).

Nutrient analyses of source and pond waters in Thailand indicate that such a fertilization system results in minimal increases in concentrations of P and N in pond waters through a grow-out (Diana et al. 1994). While nutrients may be lost with any overflow water, these will not load receiving waters beyond normal levels during rain events. However, at draining the water quality of effluents may be considerably lower, due to accumulation of materials in pond sediments or in the water near the soil-water interface which is discharged at harvest (Pillay 1992). Several strategies could reduce such effects, including more gradual draining of the ponds, holding back of deep water at harvest, and removal of water into settling ponds or other fish ponds. The CRSP project has not monitored the quality of effluent waters, so there is no information available to evaluate the magnitude of this problem.

Anticipated Benefits

This experiment will fulfill several goals of the CRSP experiments. It will include further work on the soil-water interaction, at least during harvest. It will also evaluate the environmental impacts of fish culture, particularly related to effluent discharge. Once these results are available, methods to implement the best management schemes, such as means to discharge the final polluting portion of the water or better methods to harvest fish without draining, can be determined. Such experiments should be guided by effluent studies done above and by other experiments previously conducted on treatment systems.

The environmental impacts of aquaculture could include many characteristics, but certainly major concerns include release of exotic or diseased animals, as well as loading of receiving waters by aquaculture effluents. Research to better understand the effluent conditions will help managers involved in aquaculture regulation. Such work also provides a direct link between the freshwater aquaculture program of the CRSP and brackish water work in Honduras.

Identification of Beneficiaries

Culturists throughout southeast Asia and other tropical countries who experience effluent problems which affect their ability to discharge nutrients into receiving waters.

Collaborative Arrangements

The Asian Institute of Technology will collaborate with these analyses. The facilities for such research ponds are at AIT. This collaboration is included in our Memorandum of Understanding for work in Thailand. The University of Michigan will provide logistic and planning support for this project, and will be involved in the final data analysis and write up as well.

Experimental Design

To achieve objective 1, water samples should be collected throughout the culture period to estimate budgets for organic C, N, and P based on inputs and outflows. This requires additional data collected on nutrient and sediment loads. Such collections do not require specific experiments to be useful, and should be done at several sites if possible and at several loading rates. Measurements would include N, P, total suspended solids, soluble organic compounds and BOD of suspended solids in discharge waters at several stages during draining. If one assumes all ponds are held at 1 m depth during grow-out, then effluent sampling could be done when pond depth reaches 1 m, 0.5 m, 0.25 m, 0.10 m, and 0 m.

To achieve objective 2, experiments will require different draining procedures. The management practices to be first tested include complete drainage, drainage to 0.25 m depth, and drainage to 0.1 m depth. Harvesting in the latter 2 experiments will be done by seine. Once again, discharge water quality will be evaluated as in 1 above. Measurements in this experiment include standard water quality measures, fish yield and harvest, and nutrient discharge at draining. Discharge water will be diverted to a retention pond and characteristics monitored over time to determine removal efficiency of suspended solids, nutrients and BOD. While reduced nutrient loadings would be preferable, it could be done with any other pond experiments.

Sites: Thailand; AIT, as well as other possible sites.

Pond facilities: The first experiments will require at least 4 ponds with similar nutrient loadings. The second experiment requires 9 to 12 ponds, with three treatments: 1. Normal drainage, 2. Drainage to 0.25 m depth, then fish removal by seining, 3. Drainage to 0.1 m, then fish removal by seining.

Culture period: Pond experiments will be done over 150 days.

Stocking rates: Two Nile tilapia per square meter.

Water management: Water will be filled by rainfall and will remain stagnant. Water management will include drainage procedures outlined under pond facilities.

Other inputs: Chicken manure will be added at 70 kg·ha^-1·wk^-1, and sufficient urea and phosphorus will be added to provide 0.5 g·m^-2·d^-1 N and 0.125 g·m^-2·d^-1 P.

Test Species: Nile tilapia

Sampling plan: Measurements of water quality will be taken biweekly including standard PD/A CRSP water quality parameters (Egna et al. 1987). Fish growth will be measured on a monthly basis. Diel analyses will be done monthly. Water quality, particularly P, N, DO, total solids and settleable solids, will be monitored extensively during draining in both particulate and soluble fractions.

Statistical methods and hypotheses: The null hypotheses are that each treatment will not result in appreciable differences in Secchi disk depth, water quality, primary production, and fish growth compared to the control ponds. Significant differences will be tested using ANOVA and multiple regression.

Schedule/Time line

This experiment is planned for the first year of the new work plan. To fit into seasonal schedules, ponds experiments will begin around March and complete in August 1997.

Final Report Submittal: Final reports will be completed with the 1996-97 annual report in Fall 1997.

References

Boyd, C. E. 1990. Water quality in ponds for aquaculture. Agriculture Experiment Station, Auburn University.

Diana, J. S., C. K. Lin, and K. Jaiyen. 1994. Supplemental feeding of tilapia in fertilized ponds. Journal of the World Aquaculture Society 25:497-506.

Egna, H. S., N. Brown, and M. Leslie. 1987. General reference: site descriptions, material and methods for the global experiment. Pond Dynamics/Aquaculture Collaborative Research Data Reports, Volume 1. Oregon State University, Corvallis, Oregon. 84 pp.

Knud-Hansen, C. F., C. D. McNabb, and T. R. Batterson. 1993. The role of chicken manure in the production of Nile tilapia (Oreochromis niloticus). Aquaculture and Fisheries Management 24:483-493.

Pillay, T. V. R. 1990. Aquaculture: principles and practices. Fishing Book News, London.

Pillay, T. V. R. 1992. Aquaculture and the environment. Fishing Book News, London.