Nitrogen Transformations and Fluxes in Fish Ponds: a Modelling Approach

Nitrogen transformations andfluxe s infis hponds : a modelling approach Ricardo A. Jimenez-Montealegre Promotoren: Prof.Dr . E.A. Huisman Prof.Dr .J.A.J . Verreth Hoogleraar ind eVisteel t en Visserij Wageningen Universiteit Co-promotor: Dr.M.C.J . Verdegem Universitair docent aand e Leerstoelgroep Visteelt en Visserij Wageningen Universiteit Samenstelling promotiecommissie: Prof.Dr .Ir . H.Va n Keulen Wageningen Universiteit Prof.Dr .M . Scheffer Wageningen Universiteit Prof.Dr .R . Piedrahita University of California Prof.Dr .Y . Avnimelech Technion, Israel Institute of Technology Nitrogen transformations andfluxes i n fish ponds: a modelling approach Ricardo A. Jimenez-Montealegre Proefschrift ter verkrijging van degraa d van doctor opgeza gva n derecto r magnificus van deWageninge n Universiteit, Prof.dr.ir. L. Speelman, inhe t openbaar te verdedigen opwoensda g 18apri l 2001 des namiddagst e twee uur in de Aula. ISBN 90-5808-401-9 Stellingen It is evident that aquaculturists should feed their fish rather than their pond. This thesis In aquacultureenterprises , the wholenitroge n cycle must be optimized to minimize nitrogen discharges into the environment. This thesis Rate differences between the variouspart s of thenitroge n cycle result from environmental differences between aquaculture systems. Theconcept s in the mindso f scientists areeasie r to discuss and improve when they are presented asmathematica l models. Fish driven resuspension increases pond productivity. In spite of growing computing power, computers will remain only tools to understand our environment better. "Data become information ifw ekno w the processes involved inth e system. Information becomes knowledge ifw eunderstan d how the system is operating. But knowledge becomes wisdom only when we seeho w the system must change and deal with reality" (Peter Allen: Coherence, Chaos and Evolution inth e Social Context. Futures 26:597 , 1994). "A man with one watch knows what time it is.A ma n with two watches isneve r sure" (Segal's law). Stellingen belonging to the thesis "Nitrogen transformation andfluxes i nfis h ponds:a modelling approach" Ricardo A.Jimenez-Montealegr e Wageningen, April 18,200 1 Table of Contents General Introduction Chapter 1 Nitrogen budget and fluxes in Colossoma macropomum ponds 25 Chapter 2 Conceptualization an validation of adynami c model for the simulation ofnitroge n transformations and fluxes in fishpond s 43 Chapter3 The effects oforgani c nitrogen and carbon mineralization and sediment-water inorganic nitrogen fluxes on bottom organic matter accumulation infish pond s 83 Chapter 4 Organic matter sedimentation andresuspensio n in Tilapia {Oreochromis niloticus)fish pond s during agrowin g cycle 111 Chapter 5 Therol e of sedimentation and resupension in the nitrogen dynamics infish ponds :a modellin g approach 131 Chapter 6 Conclusions and Recommendations 157 Summary 167 Samenvatting 171 Resumen 177 Acknowledgements 181 Curriculum Vitae 183 General Introduction General Introduction Background Aquaculture represents one of the fastest growing food producing sectors. By 1998, the total production of cultured finfish, shellfish and aquatic plants reached 39.43 million tons (FAO 2000). World food production will have to increase to satisfy the increasing demands of the growing world population, which will have grown to 8 billion people by 2025.Fisherie s production can not increase further, and therefore, any future growth in fish protein supply will have to come from aquaculture. The potential of aquaculture to meet the challenges of food security is clearly demonstrated by the rapid expansion ofthi s sector, whichha s grown at an average annual rate of almost 10% since 1984compare d to 3%fo r livestock meat and 1.6% for capture fisheries production (FAO 1997). Aquaculture uses natural resources like water, land, fertilisers and feed. Ground and surface freshwater resources are finite, while societal demands for these resources are growing. Considering the explosive growth of aquaculture and the limited availability ofit sresources ,ther ei sa nee d formor e efficient resourceuse . Aquaculture production systems can be characterised based on input/management levels, from extensive (low level of input/management) to intensive (high level of input/management). Growth in land-based aquatic production since 1984 was partly the result of intensification combining the use of high quality feeds, with increased stocking densities and water use. The high nutrient input levels applied in intensive culture may surpass the carrying capacity of the culture environment, and lead to water quality problems. By replacing the nutrient rich water with clean, nutrient poor water, culture problems due to bad water quality are avoided. However, the large amounts of water needed to maintain good water quality are not always available, and shortage leads to eutrophication of pond ecosystems. Dominance or frequent blooms of blue green algae (Sevrin-Reyssac and Pletikosic 1990), higher daily fluctuations inp H ordissolve d oxygen concentrations (Smith 1985) and highly unbalanced C:N ratios (Avnimelech et al. 1992) are some of theproblem s related to eutrophication. In addition, discharging large amounts of nutrient rich water leads to eutrophication of the surrounding surface waters,wher e the above mentioned problems will also occur. With high levels of eutrophication, diseases occurmor efrequently, a sreporte d for shrimp farms (Lightner etal. 1992).I nregion s with a high farm density, diseases easily spread among farms through the surrounding surface Nitrogen Transformation and Fluxes in fish ponds waters. In all cases disease outbreaks leads to significant losses of farmed stocks and diminishedfinancial returns . Nitrogen and aquaculture Nitrogen is an essential element in aquaculture. It is mainly present as protein, which is found in all life organisms. However, many inorganic forms of nitrogen are also present, and some forms canb e toxict o aquatic organisms.Nitroge n inputs in the form of feeds/fertilisers enhanceth eaquati cproductio nbu t simultaneouslyincreas e thepotentia lo f pollution of the surrounding environment. Control of nitrogen transformation processes in the pond combined with optimal feed utilisation in aquaculture systems are needed. On average, 30%o f the nitrogen added to ponds as feed or fertiliser is recovered by the target organism, which means that 70% of the nitrogen input is excreted in a dissolved or particulate form (Edwards 1993). Nitrogen loading rates of aquaculture ponds are often limited by the capacity of the pond to assimilate nitrogenous excretion (Hargreaves 1998). Theprincipa l endproduc t ofprotei n metabolism infish i s ammonia. After oxygen, ammonia is the second most common limiting factor for fish stocking density (Robinette 1976;Col t and Tchobanoglous 1978;Tomass oet al. 1979;Tomass oet al. 1980;Shil oan d Rimon 1982; Schwedler and Tucker 1983; Palachek and Tomasso 1984; Meade 1985). Not all the effects of sub-lethal ammonia levels on growth are known, but ammonia may lead toproliferatio n ofth e gill epithelium, thusreducin g theoxyge n uptake capacity ofth e gills and affecting growth (Burrows 1964;Larmoyeu x and Piper 1973).Productio n losses maybe substantial (Meade 1985). Just as in any other (intensive) agricultural practice, nitrogen discharge is one of theprincipa l sourceso fpollutio ndu et oaquacultur e (Jorgensenan dRasmusse n 1991).Th e amount of nitrogen discharged from aquaculture farms is influenced by several factors sucha sth eamoun t offeeds/fertiliser s applied andthei refficienc y ofus ewithi nth e system. Animportan t goaltoda yi st omaintai n goodwate rqualit ywhil e improvingth eretentio no f the nutrient inputs into harvestable products. As a result, less nutrients will be discharged orlost . The nitrogen cycle in ponds is a mixture of various biotic and abiotic processes. The complexity of the nitrogen cycle, with many different forms of nitrogen existing side General Introduction by side, and the numerous transformation processes are shown in Figure 1. Although the basic processes of the nitrogen cycle were described in detail, it remains difficult to understand thecomplexit yo fth ewhol enitroge ncycle . NHj Nitrification Nitrification OrganicN • • (fish, algae) OrganicN (dissolved) Degradation Ammonificatio n OrganicN (fish, algae) Resuspension JSEDIMENTS ,OXYDIZE D I OrganicN NR, Particulate Ammonification OrganicN i' Nitrate reduction Particulate Ammonification N03" SEDIMENTS, REDUCED | Assimilation OrganicN Particulate Ammonification OrganicN Refractory Figure 1. Principal nitrogen forms and processes within the nitrogen cycle Nitrogen Transformation and Fluxes in fish ponds Most of the literature on nitrogen cycling in shallow aquatic systems has been directly applied to aquaculture ponds. Management strategies to control the deleterious effects of nitrogen accumulation in the system have been proposed, but their effectiveness is limited by our present understanding of the nitrogen cycle in aquaculture ponds. Studies of nitrogen cycling under the particular circumstances prevailing in earthen aquaculture ponds are scarce. Abette r understanding of the fluxes andtransformation s ofnitroge n in aquaculture production systems is,therefore , needed. Modelling of the nitrogen cycle Modellingo fth enitroge n cycleallow st oexplore ,t ounderstand , andt o re-evaluate relationshipsbetwee nN-specie s inth e system. In aquaculture, theus e of computer models botht ounderstan

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