|BRUNE, DAVID - University Of Missouri|
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 10/27/2014
Publication Date: 2/20/2015
Citation: Brune, D.E., Brown, T.W., Tucker, C.S. 2015. Oxygen and nitrogen dynamics in split ponds vs. conventional catfish production ponds. Aquaculture America Conference. P.80.
Technical Abstract: The Split Pond aquaculture system (SP) has captured the attention of catfish producers across the southern U.S. The SP represents a lower cost adaptation of Clemson University’s Partitioned Aquaculture System (PAS). The original PAS design relied on slowly rotating paddlewheels to move water through a channelized pond, promoting accelerated algal growth rate and removal of ammonia nitrogen from culture water. Target cultured fish (catfish) were confined to high density concrete raceways containing fountain aerators. Tilapia co-culture in the PAS provided control of algal species dominance and algal density. In contrast to the PAS, prototype SPs located at the “National Warmwater Aquaculture Center” in Stoneville Mississippi (NWAC), consist of a ~ 1 acre, 5-6 ft deep earthen fish culture pond (averaging 1.8 million gallons) linked to a ~ 4.6 acre 4-5 ft deep water treatment pond (averaging 6.7 million gallons) by way of cross-levee canals with one containing a paddlewheel delivering 10,000-12,000 gpm water flow providing 4-6 fish culture zone water exchanges per 12 hrs. Field experience with culture of hybrid catfish (Ictalurus punctatus x I. furcatus) at NWAC has demonstrated annual catfish carrying capacity and yields close to PAS maximum of 20,000 lbs/acre-season. However, tilapia co-culture has not been used in the SPs for control of algal biomass or species composition. From July 7-14, 2014 preliminary water quality data and operational details of the performance of two prototype SPs were compared to two conventional catfish production ponds (CC) at NWAC. At the time of observation, SPs were receiving an average 136 lbs/acre-day of 28% protein feed compared to an average 186 lbs/acre-day to CC ponds. Daily light/dark bottle oxygen observations, ammonia measurements, settling rates and water velocity determinations, as well as, microscopic examination of pond algal populations and zooplankton enumerations suggest that the SPs contain three relatively stable volume elements, with approximately 30% of total volume providing a high rate of photosynthetic ammonia removal in the top 14 inches of the fish culture and treatment zones, averaging 8.6 gm-C/m2–day. The SP consists of an aerobic zone ~ 65% of total system volume with an anaerobic zone of ~ 35% of system volume, with a transient anoxic system volume estimated at 15% of volume. A critical stabilizing feature of the SP includes a nitrogen recycle ratio of ammonia-N from the anaerobic zone supplying nitrogen at 75% to 125% of fish nitrogen excretion rate. This nitrogen addition insures an uninterrupted high rate of algal carbon fixation. A second stabilizing feature includes a high population of uniformly sized zooplankton that likely help to control algal species composition insuring dominance of a small-cell cyanobacteria population. The primary algal removal mechanism appears to be algal/bacterial co-flocculation, along with zooplankton and fish culture detritus, with sedimentation and removal to the anaerobic zone. The anaerobic and anoxic zones function to provide ammonification and denitrification of added nitrogen. The transient aerobic zone appears to provide SP nitrification capacity of ~ 30% of the algal ammonia removal rate while no nitrification capacity was detected in CC ponds. Preliminary oxygen mass balances suggest algal primary production is supplying around 50% of fish oxygen demand, this source of oxygen supply stabilized by continuous algal removal to, and anaerobic degradation in, the deeper treatment zone. Pond total nitrogen mass balances suggest the ultimate fate of nitrogen addition to the SP is denitrification occurring in the anoxic interface between the aerobic and anaerobic zones.