Water Quality In Aquaculture Ponds Research Articles

Factor affecting the willingness to adopt good aquaculture practices (GAPs) in traditional shrimp farming in Pinrang Regency, South Sulawesi Province, Indonesia

This study explores the factors influencing shrimp farmers’ adoption of Good Aquaculture Practices (GAPs) in traditionally managed aquaculture ponds cluster in Pinrang Regency, South Sulawesi Province, Indonesia. The factors influencing shrimp farmers’ decision to apply GAPs to traditional ponds in Pinrang Regency were analyzed using the Theory of Planned Behavior (TPB) with structural equation modeling (SEM). The analysis results showed that shrimp farmers’ willingness to adopt GAPs was strongly influenced by their attitude that GAPs can increase their production or income, improve a positive reputation in society, and contribute to improving the aquaculture environment. Meanwhile, the main impetus for adopting GAPs came from exporters or local entrepreneurs and directives and assistance from the relevant government, universities, and academics. The shrimp farmers believe that to maximize the level of application and the adoption of GAPs, improving pond engineering and managing environmental limiting factors are of high priority. The decline in aquaculture pond water quality is closely related to the condition of ponds with problems exchanging water, particularly disposing of aquaculture waste after the operation.

Seagrass meadows improve inflowing water quality in aquaculture ponds

Water quality is critical for fish health in aquaculture production. In flow-through systems, the inflowing water normally requires quality controls and treatments for being supplied from coastal water bodies that can be polluted by nutrients, suspended solids, and microorganisms. Here we assess how seagrass meadows benefit aquaculture systems through the provision of ecosystem services (water filtration, biological control, and regulation of dissolved gasses) in the water reservoir that supplies earthen ponds in an aquaculture system in southern Portugal. In the 1.45-ha reservoir, seagrasses retained daily an estimate of 0.8–1.8 kg d−1 of nitrogen, 0.04–0.07 kg d−1 of phosphorus in their biomass, and 0.7–1.1 kg dw d−1 of suspended total particulate matter, bringing benefits in terms of nutrient and particle removal from the water column. Diel and spatial variation in faecal coliforms levels (Escherichia coli) in the reservoir suggested that seagrasses, in combination with light exposure, may reduce the levels of this pathogen. Furthermore, the seagrass-dominated system oxygenated the water through photosynthesis at a faster rate than the respiratory oxygen consumption, maintaining the system above the aquaculture minimum oxygen. This study demonstrates that seagrasses can be used as a nature-based solution to overcome water quality challenges in flow-through aquaculture ponds.

Immobilization of Rhodopseudomonas palustris P1 on glass pumice to improve the removal of NH 4 + ‐N and NO 2 − ‐N from aquaculture pond water

We conducted this research in order to investigate the potential of a new material called glass pumice for use as a microorganism immobilization carrier to improve aquaculture pond water quality. The pH adjustment capacity and the Rhodopseudomonas palustris P1 cell adsorption capacity of glass pumice were measured. The immobilized Rps. palustris P1 and the free sample were compared to determine which had an enhanced NH4 + -N and NO2 - -N removal efficiency. The results showed that glass pumice significantly affected the pH of the acid solution (P<0.05); the pH increased from 3.0±0.08 to 7.21±0.13 in 12H. Rps. palustris P1 adsorption to glass pumice was rapid and reached equilibrium within 60Min. The Langmuir adsorption parameter data showed that glass pumice had a higher affinity for Rps. palustris P1 than SiO2 powder, with an adsorption capacity of 4.02×108 cellsg-1 . The maximum NH4 + -N and NO2 - -N removal rates by immobilized Rps. palustris P1 were 134.82±0.67% and 93.68±0.14% higher than those of nonimmobilized P1, respectively. Based on the above results, we propose that glass pumice is potential as a microorganism carrier material in aquaculture water treatment.

Effect of intermittent aeration mode on nitrogen concentration in the water column and sediment pore water of aquaculture ponds

Nitrogen in pond sediments is a major water quality concern and can impact the productivity of aquaculture. Dissolved oxygen is an important factor for improving water quality and boosting fish growth in aquaculture ponds, and plays an important role in the conversion of ammonium-nitrogen (NH4+-N) to nitrite-nitrogen (NO2−-N) and eventually nitrate-nitrogen (NO3−-N). A central goal of the study was to identify the best aeration method and strategy for improving water quality in aquaculture ponds. We conducted an experiment with six tanks, each with a different aeration mode to simulate the behavior of aquaculture ponds. The results show that a 36 hr aeration interval (Tc = 36 hr: 36 hr) and no aeration resulted in high concentrations of NH4+-N in the water column. Using a 12 hr interval time (Tc = 12 hr: 12 hr) resulted in higher NO2−-N and NO3−-N concentrations than any other aeration mode. Results from an 8 hr interval time (Tc = 8 hr: 8 hr) and 24 hr interval time (Tc = 24 hr: 24 hr) were comparable with those of continuous aeration, and had the benefit of being in use for only half of the time, consequently reducing energy consumption.

Bioremediation of nitrogen- and phosphorus-polluted aquaculture sediment by utilizing combined immobilized effective microorganisms and

The endogenous release of nitrogen and phosphorus from aquaculture sediment can continuously pollute the water quality in aquaculture ponds. In this study, an integrated bioremediation approach that combined effective microorganisms (EM) with aeration techniques was designed to restore contaminated aquaculture sediment. Initially, a set of laboratory-scale experiments was designed to evaluate the feasibility of the technology for the bioremediation of nitrogen and phosphorus. The removal and transformation efficiency indexes of both the overlying water and sediment were measured. From the obtained results, the combination of sediment aeration and immobilized EM significantly improved the nitrogen and phosphorus removal rate from the overlying water and sediment when compared to other methods. Subsequently, a series of field-scale experiments was further implemented to assess the integrated technique in practical applications. In field experiments, the variation in the comprehensive trophic level index (TLI) and sediment biodegradation activities (G value) was used to assess the effect of sediment bioremediation. In pond II which promotes sediment biodegradation, the values of TLI varied from 70.13 to 54.16, and the classification level changed from Hypereutrophic to a Light eutrophic. In addition, the G value increased from 0.98 kg/(kg·h) to 2.12 kg/(kg·h). The organic matter (OM) and sediment thickness (ST) decreased by 17.4 g/kg and 2.3 cm, respectively. The obtained results indicated that the combination of EM and sediment aeration might be feasible and effective for the remediation of nitrogen- and phosphorus-polluted aquaculture sediment. Keywords: effective microorganisms, immobilization technology, aeration, aquaculture sediment, bioremediation DOI: 10.25165/j.ijabe.20191206.4904 Citation: Wang L K, Shao X H, Xu M, Chen S. Bioremediation of nitrogen- and phosphorus-polluted aquaculture sediment by utilizing combined immobilized effective microorganisms and sediment aeration technology. Int J Agric & Biol Eng, 2019; 12(6): 192–201.

Annual Variation of Water Quality in Aquaculture Ponds for Apostichopus japonicus

Annual Variation of Water Quality in Aquaculture Ponds for Apostichopus japonicus

Bioremediation of nitrogen- and phosphorus-polluted aquaculture sediment by utilizing combined immobilized effective microorganisms and sediment aeration technology

The endogenous release of nitrogen and phosphorus from aquaculture sediment can continuously pollute the water quality in aquaculture ponds. In this study, an integrated bioremediation approach that combined effective microorganisms (EM) with aeration techniques was designed to restore contaminated aquaculture sediment. Initially, a set of laboratory-scale experiments was designed to evaluate the feasibility of the technology for the bioremediation of nitrogen and phosphorus. The removal and transformation efficiency indexes of both the overlying water and sediment were measured. From the obtained results, the combination of sediment aeration and immobilized EM significantly improved the nitrogen and phosphorus removal rate from the overlying water and sediment when compared to other methods. Subsequently, a series of field-scale experiments was further implemented to assess the integrated technique in practical applications. In field experiments, the variation in the comprehensive trophic level index (TLI) and sediment biodegradation activities (G value) was used to assess the effect of sediment bioremediation. In pond II which promotes sediment biodegradation, the values of TLI varied from 70.13 to 54.16, and the classification level changed from Hypereutrophic to a Light eutrophic. In addition, the G value increased from 0.98 kg/(kg·h) to 2.12 kg/(kg·h). The organic matter (OM) and sediment thickness (ST) decreased by 17.4 g/kg and 2.3 cm, respectively. The obtained results indicated that the combination of EM and sediment aeration might be feasible and effective for the remediation of nitrogen- and phosphorus-polluted aquaculture sediment. Keywords: effective microorganisms, immobilization technology, aeration, aquaculture sediment, bioremediation DOI: 10.25165/j.ijabe.20191206.4904 Citation: Wang L K, Shao X H, Xu M, Chen S. Bioremediation of nitrogen- and phosphorus-polluted aquaculture sediment by utilizing combined immobilized effective microorganisms and sediment aeration technology. Int J Agric & Biol Eng, 2019; 12(6): 192–201.

Review of ammonia-oxidizing bacteria and archaea in freshwater ponds

Aquaculture ponds are simple and unique ecosystems, which are affected intensively by human activities. In this mini-review, we focus our attention on the distribution and community diversity of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in pond water and sediments, as well as the possible ecological mechanisms involved. Moreover, we discuss the possibility of increasing the activity of ammonia-oxidizing organisms in order to improve the water quality in aquaculture ponds. Compared with eutrophic lakes, the significantly higher ammonia concentration in pond water does not lead to significantly higher AOB levels, and the abundance of AOA is too low to quantify accurately. Similar to eutrophic lakes, high abundances of AOA and AOB are present in the surface sediments at the same time, where the oxidation of ammonia is performed mainly by AOB. AOB and AOA exhibit significant seasonal variations in aquaculture ponds, which are affected by the temperature, pH, and dissolved oxygen. The dominant AOB species are Nitrosomonas and the Nitrosospira lineage in pond environments. Nitrososphaera or members of the Nitrososphaera-like cluster dominate the AOA species in surface sediments, whereas the Nitrosopumilus cluster dominates the deeper sediments. AOB and AOA can be enriched on artificial substrates suspended in the pond water, thereby potentially improving the water quality.

An Analysis on Hemocytes Profile in Kijing Taiwan (Anodonta woodiana) and Water Quality in Freshwater Aquaculture Ponds

Kijing Taiwan ( Anodonta woodiana ) is found in water with muddy substrate. Kijing Taiwan lives in bottom waters and is relatively settled. Kijing Taiwan is a filter feeder organism that can filter water and is able to survive in polluted environment, so it can be used as a bio-indicator of a water body. The study was conducted in the Public Hatchery Unit (UPR) Sumber Mina Lestari. Profile hemocytes in Taiwan Kijing influenced by environment pollution inducer among others. Hemocytes were observed consisting of Total Haemocyte Count (THC) and Differential Haemocyte Count (DHC). The results show that the profile of hemocytes (THC and DHC) of Kijing Taiwan is not polluted. Results from aquaculture pond water quality measurements indicate that the indicators of the water quality i.e. temperature, pH, dissolved oxygen, and ammonia are still within normal limits. However, in TOM test, BOD and soil organic matter has exceeded the normal limits. The existence of organic matter became the medium of life for Kijing Taiwan, due to its role as a biofilter among other organic materials. Keywords: Hemocytes Profile, Kijing Taiwan, Water Quality.

Microbial succession in biofilms growing on artificial substratum in subtropical freshwater aquaculture ponds.

Biofilms can be used to improve the water quality in aquaculture ponds, and elucidating the process of microbial succession in biofilms would allow the characterization of metabolic processes and permit optimization. In the present study, microbial succession of a biofilm growing on artificial substrata in a subtropical freshwater pond was investigated by high-throughput sequencing. Providing artificial substrata effectively reduced the concentrations of total nitrogen and total phosphorus in the pond. Relatively stable microbiota were formed after approximately 1 week. The dominant phyla in the mature biofilm were Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria. The relative abundances of denitrifiers and phosphorus-removing bacteria, such as those in Comamonadaceae and Neisseriaceae, were significantly increased. The use of avermectin B1 changed the community structure of the microbiota; the microbiota were more similar to those at Week 0 than to those at Week 3. However, the microbial community structure recovered after approximately 1 week. Our results indicate that using artificial substrata can create a habitat for denitrifiers and phosphorus-removing bacteria, and thereby improve pond water quality. This study provided insight into how the use of artificial substrata could improve water quality and elucidated the environment-biofilm relationship in a subtropical freshwater pond.

Community characteristics of the macrozoobenthos and bioassessment of water quality in aquaculture ponds of the Pearl River Delta

珠江三角洲是我国主要的水产养殖区域之一. 为了解珠江三角洲鱼类养殖池塘底栖动物群落结构，进而评价养殖水体水质状况，于2016年7-8月对6种养殖模式30口池塘底栖动物及其环境因子进行调查. 结果表明：1）共采集底栖动物18种，隶属于3门14属，其中寡毛类和水生昆虫均为7种，软体动物为4种. 优势种为克拉泊水丝蚓（Limnodrilus claparedeianus）、水丝蚓属一种（Limnodrilus sp.）和摇蚊属一种（Chironomus sp.）等耐污种类. 2）6种养殖模式池塘底栖动物平均种类数无显著差异，但其密度和生物量却存在显著差异，杂交鳢Y（杂交鳢幼鱼）和杂交鳢C（杂交鳢成鱼）养殖池塘均显著高于其他4种养殖模式池塘. 3）皮尔逊相关分析结果表明，影响珠江三角洲池塘底栖动物密度和生物量的主要因素是总氮（TN）和总磷（TP）. 两个主要分类群中，寡毛类密度和生物量仅与TN浓度呈显著正相关，而摇蚊幼虫却与TN和TP浓度均呈显著正相关. 4）采用Shannon-Wiener多样性指数、Margalef多样性指数和Biotic Index生物指数对6种养殖模式30口池塘水质进行评价，结果表明Shannon-Wiener多样性指数不宜应用于珠江三角洲池塘的水质评价，Margalef多样性指数和Biotic Index生物指数的评价结果均表明杂交鳢Y、杂交鳢C以及草鱼池塘全部处于重度污染，而大口黑鲈S（投喂饲料）、大口黑鲈S+B（投喂饲料+冰鲜鱼类）和罗非鱼池塘大部分处于重度污染，少数处于中度污染.;Pearl River Delta is one of the main aquaculture areas in China. In order to understand the community structures of macrozoobenthos and further assess the water quality in aquaculture ponds, a field investigation of macrozoobenthos and environmental parameters was conducted in 30 ponds with six aquaculture models during July to August 2016. The results showed that a total of 18 species belonging to 14 genera and 3 phyla were identified, and the species number of oligochaeta, aquatic insect, and mollusca was 7, 7, and 4, respectively. The dominant taxa of macrozoobenthos were the Limnodrilus claparedeianus, Limnodrilus sp., and Chironomus sp., which have strong tolerances to pollution. The average species number among the six model ponds had no significant differences. However, the density and biomass were significantly different, and which were significant higher in two models (juvenile and adult fish, respectively) of hybrid snakehead (Channa maculate♀×Channa arguss♂) than the other four model ponds. Pearson correlation analyses showed that the TN and TP were the main factors influencing the density and biomass of macrozoobenthos in aquaculture ponds of Pearl River Delta. The density and biomass of oligochaeta were only positively correlated with TN, while which of chironomids were significantly affected by TN and TP. The water quality of 30 aquaculture ponds were assessed using Shannon-Wiener index, Margalef index, and Biotic index. It suggested that the Shannon-Wiener index was not appropriate for the assessment of water quality in aquaculture ponds of Pearl River Delta. The assessment results by Margalef and Biotic index showed that all the ponds of grass carp (Ctenopharyngodon idellus) and hybrid snakehead were heavily polluted, while most ponds of large mouth bass (Micropterus salmoides) and tilapia (Oreochromis mossambicus) were heavily polluted and a few ponds were moderately polluted.

Effects of Nonaerated Circulation Water Velocity on Nutrient Release from Aquaculture Pond Sediments

Sustaining good water quality in aquaculture ponds is vital. Without an aerator, the dissolved oxygen in ponds comes primarily from mass transfer at the water-ambient atmosphere interface. As sediment can seriously affect water quality, this study used indoor experiments to examine the nutrient (nitrogen and phosphorus) release mechanisms and fluxes from sediment in aquaculture ponds with moving water but no aeration. The results showed that the ammonia nitrogen (NH3-N) concentration in the overlying water was inversely proportional to flow velocity and that a higher flow velocity tended to result in a lower concentration in the overlying water, a steeper vertical gradient of concentration within the bed sediments, and a faster release rate from the sediments. The sediment disturbed by flowing water released more nitrate nitrogen (NO3-N) and nitrite nitrogen (NO2-N) into the overlying water and NO2-N could become oxidized into NO3-N. In still water, NO3-N was released gradually and some anaerobic NO3-N was nitrified into NO2-N. Phosphorus release from the sediments was controlled by the adsorption–desorption balance, with the phosphorus concentration in the overlying water dropping gradually to a steady value from its initial maximum. The relationship between NH3-N release flux and flow rate is described by a cubic function.

Application of sediment microbial fuel cell for in situ reclamation of aquaculture pond water quality

Performance of sediment microbial fuel cell (SMFC) with external resistance (SMFC-1) as well as short-circuited mode (SMFC-2) was evaluated at different operating temperatures (28–30°C and 21–25°C) and in presence and absence of aeration at the cathode. The performance was evaluated in terms of chemical oxygen demand (COD) removal and total kjeldahl nitrogen (TKN) removal for offering in situ treatment of aquaculture pond water. SMFC-2 demonstrated maximum COD and TKN removal efficiencies both in the absence and presence of aeration near cathode as compared to SMFC-1. With aeration at cathode, the COD and TKN removal efficiencies were 79.4% and 92.6% in SMFC-1 and 84.4% and 95.3% in SMFC-2, respectively. Without aeration and at lower operating temperature, the COD and TKN removals were slightly lower, yet satisfying aquaculture quality norms. SMFCs demonstrated effective in situ remediation of aquaculture water and can drastically save the operating cost of aquaculture.

Prototype of an Aquacultural Information System Based on Internet of Things E-Nose

Abstract Aquaculture is the fastest growing food-producing sector in the World, especially, in P. R. China. In the ongoing process of Internet growth, a new development is on its way, namely the evolution from a network of interconnected computers to a network of interconnected objects that is called the Internet of Things (IoT). Constructing an affordable, easy-to-use, aquaculture information system based on IoT is the future trend for modern aquaculture. The prototype IoT of aquaculture information system is developed with following functions: (1) Sense in real time the water quality in aquaculture ponds and send water quality data in time to remote IoT Platform with wireless sensor network and mobile internet; (2) Forecast the change trend of water quality based real-time data and operating suggestion will be created for special aquaculture application automatically; (3) Real-time and efficient exchange with special users and common users with WEB, WAP and SMS; (4) Some control devices may be operated ...

Organic flocculants for the removal of phytoplankton biomass

The formation of noxious phytoplankton blooms causes deterioration of water quality in aquaculture ponds and reservoirs, but also in swimming pools and aquaria. We have studied the effects of selected cationic polyacrylamides on natural phytoplankton community, which was investigated by a decrease of chlorophyll a content in the water column and photosynthetic activity of phytoplankton floccules. Results indicate that cationic polyacrylamides are able to remove more than 80% of phytoplankton biomass. Moreover, no cell damage or lysis was observed by microscopic observation after flocculation. To our knowledge, this is the first report suggesting the removal of cyanobacterial blooms by organic flocculants. Cationic polyacrylamides are biodegradable organic flocculants with low toxicity to aquatic organisms, and seem to be a prospective tool with a possibility for algal or cyanobacterial bloom management in aquaculture.

Viability of a Freshwater Mussel (Elliptio complanata) as a Biomechanical Filter for Aquaculture Ponds II: Effects on Aquaculture Pond Water Quality

Bivalves have been proven to be an inexpensive method for removing suspended solids, dissolved nutrients, and controlling algal growth through suspension feeding. The freshwater mussel, Elliptio complanata, is one of the most abundant species in Delaware, and it is additionally favorable for this experiment because of its hardiness against environmental stress and its filtration efficiency. This study examines the possibility that biomechanical filters such as E. complanata can supplement existing chemical and mechanical filtration regiments in aquaculture pond management. Twelve earthen aquaculture ponds located at the Delaware State University were stocked at a density of 4,000 catfish (Ictalurus punctatus) per hectare. Four different concentrations (0, 75, 150, and 300) of E. complanata were placed in trays within the ponds with three replicates of each concentration. The trays were suspended 15 cm below the surface of the water for a period of five months. Fish were fed a 32% protein diet twice daily at a rate of 1% of their body weight. Water quality was analyzed weekly while fish and mussel growths were measured biweekly. Results from water quality parameters varied significantly and were not conclusive based on the data obtained in this study. Water quality did not improve within the mussel treatment ponds during the course of this study and was found to be significantly below that of control ponds for all of the water chemistry parameters measured, with the exception of ammonia. Catfish in the 150 mussel treatment ponds grew the fastest; the 75 mussel treatment provided the most growth in mussels; and the 300 mussel group maintained the highest mussel survivorship. Although there were differences between ponds, fish growth and survivorship were not significantly different between treatments. While our mussel densities may have not been sufficient, their placement within the water column may have added additional stress. Being removed from the sediment can result in a decreased clearance rate in a benthic species such as E. complanata. This study may not have been conclusive in proving that mussels can be used to maintain water quality in aquaculture ponds, but we did see positive growth and survivorship of mussels and fish that indicated that the mussels were thriving in the aquaculture pond setting. This study may show that aquaculture ponds provide a suitable habitat in which propagated mussels may be held until their release into native areas.

Formation of periphyton biofilm and subsequent biofouling on different substrates in nutrient enriched brackishwater shrimp ponds

Periphyton grown on substrates is known to improve water quality in aquaculture ponds. Five different substrates, (i) bamboo pipe (ii) plastic sheet (iii) polyvinylchloride (PVC) pipe (iv) fibrous scrubber, and, (v) ceramic tile were evaluated for the formation of biofilm in this experiment. The substrates were suspended 25 cm below the water surface. Each type of substrate was collected fortnightly to analyze the abundance and biomass of different periphytic algae and of the biofouling organism. The study was terminated after 60 days due to severe fouling by polychaete. Results showed that pond water nutrients were high on day 60 with mean total ammonia-N, nitrite-N and soluble reactive phosphorus concentrations of 309.6±8.6 μg L−1, 26.0±2.7 μg L−1 and 87.2±7.1 μg L−1 respectively. During the first two weeks the substrates were colonized by 19 periphytic algae. The most abundant family was Bacillariophyta (8 genera) followed by Chlorophyta (7 genera) and Cyanophyta (4 genera). Periphyton colonization on bamboo pipe showed the highest (p < 0.05) biomass in terms of chlorophyll a amongst all the substrates used. The biomass varied from 179 to 1137 μg m−2 with mean values of 1137.2±0.6, 929.6±0.6, 684.2±1.2, 179.1±0.6 and 657.0±0.6 μg m−2 on bamboo pipe, PVC pipe, plastic sheet, fibrous scrubber and ceramic tile respectively for the first 15 days. From 3rd week, polychaetes began to form tubes on the substrate. By day 60, the whole surface of all substrates was covered with tightly packed polychaete tubes with mean densities of 168.0±15.4, 121.0±13.5, 72.8±9.8, 72.4±7.4 and 56.0±6.8 polychaete tubes cm−2 for bamboo, PVC, plastic, fibrous scrubber and ceramic tile respectively. This study illustrated the invasive nature of attached polychaete thus hampering the formation of periphyton biofilm on substrates which could have been used for improving water quality in enriched brackishwater shrimp ponds.

Ecological niche modeling as a predictive tool: silver and bighead carps in North America

The silver carp and bighead carp (Cyprinidae), native to eastern Asia, have been introduced into the United States in attempts to improve water quality in aquaculture ponds, reservoirs, and sewage pools. Escaped or released specimens from fish farms have been reported in many states, and both species are already locally established and spreading further. We used the Genetic Algorithm for Rule-set Prediction (GARP) to model the niches of these two carps in their native ranges using hydrologic and general environmental parameters in concert with native distributional data. The results accurately predicted native occurrence data withheld from the modeling process (P < 0.01). We then projected the niche models onto the North American landscape. Native niche range models significantly predicted known occurrence data from North American introductions (P < 0.001). Further, the models suggest that both species have the potential of spreading throughout the eastern U.S. and selected areas of the West Coast.

Calibration and validation of TAP, and aquaculture pond water quality model

A computer model of water quality in aquaculture ponds (The Aquaculture Pond model, TAP) has been run for data obtained from five research sites around the world. The procedures followed for data manipulation, and the assumptions made to complete the data requirements are described. Agreement between simulated and measured dissolved oxygen values was used as an indicator of the quality of the simulations. The quality of the simulations varied between sites and in some cases between pond treatments at a given site. Possible reasons for the variations in quality of fit are discussed.