Low Dissolved Oxygen Concentrations Research Articles

Analysis of chemical variables in the water of the Córrego do Galante Watershed – SP

Population growth accompanied by inefficiencies in the management of sanitary effluents has been triggering adversities in relation to water quality. In view of the above, this work aims to analyze the concentrations of dissolved oxygen and biochemical oxygen demand in the water of the Córrego do Galante Hydrographic Microbasin - SP. Six strategic points were selected to carry out the research, each with its own characteristic, totaling eight collections of water samples, between the months of December/2021 to July/2022. Taking into account the results of the work, it was necessary to carry out an analysis of two chemical variables, which followed specific methodologies. Regarding the Dissolved Oxygen (DO), it was determined by the spectrophotometry methodology of HANNA Instruments, as for the Biochemical Oxygen Demand (BOD), it followed the method described in the Standard Methods for Examination of Water and Wastewater. The lowest DO concentrations obtained were recorded in the Dec/2021 and Jan/2022 periods. In general, over the period studied, the BOD resulted, for the most part, in values ​​outside the limits established by legislation. The period Feb/2022 for point 1 – east – resulted in a concentration of 181 mg.L⁻¹. It is concluded that the Córrego do Galante Watershed is an example of an environment that has been supporting constant anthropogenic impacts, being able to confirm this state through the OD and BOD variables. Among the negative factors, those that most influence the variations in concentrations are the release of sanitary effluent and urban drainage.

Pilot Study of Oxic–Anoxic Process under Low Dissolved Oxygen for Nitrogen Removal from Low COD/N Tropical Wastewater

Conventionally, nitrification in biological nitrogen removal (BNR) requires high dissolved oxygen (DO) concentrations (>2 mg L−1), making the process energy intensive. Recent studies have shown that efficient ammonium removal and energy reduction can be realized by operating the nitrification at low DO concentrations (<1 mg L−1). In this study, the low-DO oxic anoxic (low-DO OA) process was operated in a pilot-scale sequencing batch reactor (SBR) over 218 days to evaluate the feasibility of nitrogen removal from low chemical oxygen demand-to-nitrogen ratio (COD/N) tropical municipal wastewater. The results revealed that the low-DO OA process attained high removal efficiency for ammonium (97%) and total nitrogen (TN) (80%) under an average DO concentration of 0.6 mg L−1. The effective TN removal efficiency is attributed to the occurrence of simultaneous nitrification–denitrification (SND) under low DO conditions. Further batch tests revealed that slowly biodegradable COD (sbCOD) in tropical wastewater can support denitrification in the post-anoxic phase, resulting in a high TN removal rate. Compared with high DO concentrations (2 mg L−1), low DO conditions achieved 10% higher TN removal efficiency, with similar ammonium and COD removal efficiency. This study is crucial in promoting the energy efficiency and sustainability of wastewater treatment plants treating low COD/N wastewater.

Exposure to extremes in multiple global change drivers: Characterizing pH, dissolved oxygen, and temperature variability in a dynamic, upwelling dominated ecosystem

ABSTRACTIn upwelling systems, fluctuations in seawater pH, dissolved oxygen (DO), and temperature can expose species to extremes that differ greatly from the mean conditions. Understanding the nature of this exposure to extremes, including how exposure to low pH, low DO concentrations, and temperature varies spatiotemporally and in the context of other drivers, is critical for informing global change biology. Here, we use a 4‐yr time series of coupled pH, DO, and temperature observations at six nearshore kelp forest sites spanning the coast of California to characterize the variability and covariance among these drivers. We further compare observed properties to those derived from a high‐resolution coupled physical‐biogeochemical simulation for the central California current system. We find the intensity, duration, and severity of exposure to extreme conditions beyond heuristic, biologically relevant pHT (< 7.7), and DO (< 4.6 mg L−1) values were greatest at sites with strong upwelling. In contrast, sites with relatively weaker upwelling had little exposure to pH or DO conditions below these heuristic values but had higher and more variable temperature. The covariance between pH, DO, and temperature was highest in sites with strong upwelling and weakest in sites with limited upwelling. These relationships among pH, DO, and temperature at the observation locations were mirrored in the model, and model output highlighted geographic differences in exposure regimes across the California marine protected area network. Together, these results provide important insight into the conditions marine ecosystems are exposed to relevant to studies of global change biology.

The Impact of Sediment–Water Ratio and Hydraulic Residence Time on the Release of Inorganic Nitrogen from Sediments in the Pearl River Delta

Black-odorous water bodies in the Pearl River Delta have been treated. However, the re-release of nitrogen (N)-containing compounds in sediment can cause a relapse of black-odorous water bodies. Sediment–water ratio (SWR) and hydraulic residence time (HRT) influence pollutant release. Therefore, how to control SWR and HRT during the treatment process has become an urgent problem. This study focuses on the dynamic release of endogenous inorganic N from sediments into overlying water in a river channel of Dongguan City, Guangdong Province. Physicochemical parameters (dissolved inorganic nitrogen (DIN), NH4+-N, NO3−-N, NO2−-N, dissolved oxygen (DO), pH, oxidation-reduction potential (ORP), chemical oxygen demand (COD), Fe and total phosphorus (TP)) of overlying water were monitored under different SWRs (0.71, 0.38, and 0.16) and HRTs (13 days and 6.5 days), and the nitrogen release flux under different conditions was compared. Finally, the correlation and influence pathways among environmental factors were analyzed. The results showed that SWR significantly affected DO, pH, ORP, and sediment N release fluxes while prolonging HRT-promoted denitrification. DIN → NO2−-N → DO pathway had a total effect of 19.6%, and DIN may promote low DO concentration via NO2− oxidation. Maintaining reasonable SWR and HRT can reduce the release of inorganic N from sediment into the overlying water. This study provides a theoretical basis for controlling black-odorous water bodies.

Distribution and interaction characteristics of water quality at the stratified confluence reservoirs

The construction of large-scale dams creates tributary bays between the main and the tributary reservoirs. The water temperature and water quality in the tributary reservoirs are inevitably affected by backflow from the main reservoir. In this study, the spatial-temporal evolutions of water temperature, biochemical oxygen demand (BOD) and dissolved oxygen (DO) in the Baihetan reservoir and its four tributary reservoirs are investigated by building, validating and applying the TBD (temperature, BOD and DO) numerical model. The results show that the influence of the main reservoir on its tributary reservoirs show seasonal patterns. The water quality in the main reservoir is determined by inflow, reaeration and temperature-driven stratification, all of which exhibit seasonal patterns. Stratification determines the fate of inflow after it enters the reservoir, which leads to relatively low DO concentration in the middle layer of the Baihetan reservoir in summer and autumn. For the tributary reservoirs, water quality is also affected by the balancing between the upstream inflow and downstream backflow, which varies both seasonally, and as a function of the reservoir geometry. These results have great significance in analyzing and understanding the environmental impact of large hydraulic projects, which can be used as the basis for enacting hydraulic project plans and preserving the aquatic ecosystem in the reservoir areas.

Hypoxia and Anoxia Tolerance in Diploid and Triploid Eastern Oysters at High Temperature

Increasing reliance on the use of triploid oysters to support aquaculture production relies on their generally superior growth rate and meat quality over that of diploid oysters. Reports of elevated triploid mortality have generated questions about potential trade-offs between growth and tolerance to environmental stressors. These questions are particularly relevant as climate change, coastal activities, and river management impact water salinity, temperature, nutrients, pH, and oxygen levels within key estuarine oyster growing areas. In particular, the co-occurrence of warm water temperatures and low dissolved oxygen concentration (DO) events are increasingly reported in estuaries, with potentially lethal impacts on sessile, oyster resources. To investigate potential differences in DO tolerance, diploid and triploid market-sized or seed oysters were exposed to continuous normoxia (DO > 5.0 mg L–1), hypoxia (DO < 2.0 mg L–1), and anoxia (DO < 0.5 mg L–1) at 28°C and their mortalities were monitored. The hemolymph of the market-sized oysters was collected to measure cellular and biochemical changes in response to hypoxia and anoxia, whereas their valve movements were also measured. In general, about half of market-sized oysters died within about 1 wk under anoxia (LT50: 5.7–8.9 days) and within about 2 wk under hypoxia (LT50: 11.9–19.4 days) with diploid oysters tending to die faster than triploid oysters. Seed oysters took longer to die than market-sized oysters under both anoxia (LT50: 9.5–12.1 days) and hypoxia (LT50: 21.8–25.0 days) with diploid oysters (LT50: 9.5–11.8 days) dying slightly faster than triploid oysters (LT50: 11.8–12.1 days) under anoxia. Hemolymph pH decreased and plasma calcium and glutathione concentrations increased with decreasing DO, with values under anoxia being different than those under normoxia. Hemocyte density was also lower under anoxia than under either normoxia or hypoxia. Overall, few differences in physiological responses to hypoxia and anoxia were found between diploid and triploid oysters suggesting that ploidy (2N versus 3N) had limited effect on the tolerance and response of eastern oysters to low DO.

Dissolved oxygen benefits N-decanoyl-homoserine lactone regulated biological nitrogen removal system to resist acute ZnO nanoparticle exposure

The beneficial effects of N-decanoyl-homoserine lactone (C10-HSL), one of the typical N-acyl-homoserine lactones on biological nitrogen removal (BNR) system to resist the acute exposure of zinc oxide nanoparticles (ZnO NPs) has attracted extensive attentions. Nevertheless, the potential impact of dissolved oxygen (DO) concentration on the regulatory capacity of C10-HSL in the BNR system has yet to be investigated. This study conducted a systematic investigation of the impact of DO concentration on the C10-HSL-regulated BNR system against short-term ZnO NP exposure. Based on the findings, sufficient DO played a crucial role to improve the BNR system's resistance capacity to ZnO NPs. Under the micro-aerobic condition (0.5 mg/L DO), the BNR system was more sensitive to ZnO NPs. The ZnO NPs induced increased intracellular reactive oxygen species (ROS) accumulation, reduced antioxidant enzyme activities, and decreased specific ammonia oxidation rates in the BNR system. Furthermore, the exogenous C10-HSL had a positive effect on the BNR system's resistance to ZnO NP-induced stress, primarily by decreasing ZnO NPs-induced ROS generation and improving ammonia monooxygenase activities, especially under low DO concentrations. The findings contributed to the theoretical foundation for regulation strategy development of wastewater treatment plants under NP shock threat.

Effect of oxygen on pitting corrosion of copper pipe in fire sprinkler system

In this study, pitting corrosion in copper pipe used for sprinkler according to dissolved oxygen (DO) concentration was investigated through failure analyses, flow visualization test, DO consumption rate analysis, electrochemical tests, surface analyses, and corrosion simulation test. As a result of the failure analysis, all 10 leaks were due to pitting corrosion, and 8 leaks occurred in the branch pipe at the end of sprinkler system. As a result of flow visualization test, there were air pockets occupying 20% of the maximum total volume at the end of the branch pipe due to pressure drops. DO consumption rate analysis showed that air pocket acted as the oxygen source to maintain high DO concentration. As a result of electrochemical tests, surface analyses, and corrosion simulation, the corrosion rate of the higher DO concentration is about 10 times higher than that of lower DO concentration due to the increased oxygen reduction reaction. Through these results, it was confirmed that an air pocket was formed at the end of the pipe in the sprinkler system, and this air pocket became an oxygen source and accelerated galvanic corrosion between inside and outside of the pit during pitting propagation. This can be used as a guideline to prevent water leakage for pitting corrosion on copper pipe.

Biodegradation of 1,4-dioxane by a native digestate microbial community under different electron accepting conditions.

The potential of a native digestate microbial community for 1,4-dioxane (DX) biodegradation was evaluated under low dissolved oxygen (DO) concentrations (1-3mg/L) under different conditions in terms of electron acceptors, co-substrates, co-contaminants and temperature. Complete DX biodegradation (detection limit of 0.01mg/L) of initial 25mg/L was achieved in 119days under low DO concentrations, while complete biodegradation happened faster at 91 and 77days, respectively in nitrate-amended and aerated conditions. In addition, conducting biodegradation at 30 ˚C showed that the time required for complete DX biodegradation in unamended flasks reduced from 119days in ambient condition (20-25°C) to 84days. Oxalic acid, which is a common metabolite of DX biodegradation was identified in the flasks under different treatments including unamended, nitrate-amended and aerated conditions. Furthermore, transition of the microbial community was monitored during the DX biodegradation period. While the overall richness and diversity of the microbial community decreased, several families of known DX-degrading bacteria such as Pseudonocardiaceae, Xanthobacteraceae and Chitinophagaceae were able to maintain and grow in different electron-accepting conditions. The results suggested that DX biodegradation under low DO concentrations, where no external aeration was provided, is possible by the digestate microbial community, which can be helpful to the ongoing research for DX bioremediation and natural attenuation.

Regulating the concentration of dissolved oxygen to achieve the directional transformation of reactive oxygen species: A controllable oxidation process for ciprofloxacin degradation by calcined CuCoFe-LDH

Different reactive oxygen species (ROS) tend to attack specific sites on pollutants, leading to the formation of intermediates with different toxic effects. Therefore, regulating the directional transformation of ROS is a new effective approach for safe degradation of refractory organic compounds in wastewater. However, the regulation mechanism and transformation path of ROS remain unclear. In this work, the dissolved oxygen (DO) content was controlled by aeration to generate different ROS through the activation of O2 on the calcined CuCoFe-LDH (CuCoFe-300). ROS quantitative experiments and electron paramagnetic resonance proved that O2 was mainly activated to superoxide radical (•O2−) and singlet oxygen (1O2) under low DO concentration (0.231 mmol/L) (O2 → •O2− → 1O2). With the increasing of DO concentration (0.606 mmol/L), O2 was inclined to convert into hydroxyl radicals (•OH) (O2 → •O2− → H2O2 → •OH). The density functional theory and function model of active sites utilization and DO concentration built a solid proof for ROS conversion mechanism that increasing the DO concentration promotes the increase of active sites utilization on the CuCoFe-300 system. That is, the •O2− was more prone to convert to •OH, not 1O2 in thermodynamics under high active sites utilization condition. Hence, the ROS generation was controlled by regulating DO concentration, and the nontoxic degradation pathway of ciprofloxacin was well-designed. This work is dedicated to the in-depth exploration of the mechanism between DO concentration and ROS conversion, which provides an extremely flexible, low energy consumption, and environmentally friendly wastewater treatment method in a new perspective.

Environmental Sensing in High-Altitude Mountain Ecosystems Powered by Sedimentary Microbial Fuel Cells.

The increasing need for fresh water in a climate change scenario requires remote monitoring of water bodies in high-altitude mountain areas. This study aimed to explore the feasibility of SMFC operation in the presence of low dissolved oxygen concentrations for remote, on-site monitoring of physical environmental parameters in high-altitude mountainous areas. The implemented power management system (PMS) uses a reference SMFC (SMFCRef) to implement a quasi-maximum power point tracking (quasi-MPPT) algorithm to harvest energy stably. As a result, while transmitting in a point-to-point wireless sensor network topology, the system achieves an overall efficiency of 59.6%. Furthermore, the control mechanisms prevent energy waste and maintain a stable voltage despite the microbial fuel cell (MFC)'s high impedance, low time response, and low energy production. Moreover, our system enables a fundamental understanding of environmental systems and their resilience of adaptation strategies by being a low-cost, ecological, and environmentally friendly alternative to power-distributed and dynamic environmental sensing networks in high-altitude mountain ecosystems with anoxic environmental conditions.

Unique bacterial communities and lifestyles in deep ocean blue holes: Insights from the Yongle Blue Hole (South China Sea)

Deep ocean blue holes possess steep physicochemical gradients, especially low dissolved oxygen concentration, which shape the extraordinary microbial communities. However, the environmental responses of microorganisms with different lifestyles and knowledge of culturable microorganisms in the blue holes are still unknown. Here, we investigated the bacterial community structure with different lifestyles of the world’s deepest blue hole - the Yongle Blue Hole (YBH) in the South China Sea using both culture-dependent and -independent methods. YBH can be divided by oxygen content into an oxic zone, a suboxic zone and two anoxic zones. The abundance of bacteria, archaea, genesdsrBandsoxBwere all higher in the free-living (FL) lifestyle than in the particle-associated (PA) lifestyle, yet the diversity and richness of PA bacteria were higher than that of FL bacteria. MoreGammaproteobacteriaand lessAlphaproteobacteria,ChloroflexiandNitrospinaewere observed within the FL fraction than within the PA fraction. The relative abundance of sulfur-oxidizing bacteria (SOB) was dominant between 100-140 m (anoxic zone I) in YBH, with a maximum of 90.0% (140 m FL fraction). The SOB in YBH were mainly colorless sulfur bacteria and purple non-sulfur bacteria, of whichThiomicrorhabdusandSulfurimonaswere the main representatives. In addition, a total of 294 bacterial strains were isolated on a variety of media and culture conditions, and 22.2% (18/81) of anaerobic strains were identified as potential novel species. Our study reveals a distinction between FL and PA bacteria in YBH. It contributes to further understanding of the bacterial community in deep ocean blue holes, and provides bacterial resources for subsequent studies on their adaptation to extreme marine environments.

Antioxidant and cellular immune response to acute hypoxia stress in the ark shell (Anadara broughtonii)

In this work we studied antioxidant status and cellular immunity of ark shells (A. broughtonii) to determine the range of the adaptive potential to hypoxia. For this, the effects of 24 h and 72 h periods of exposure to dissolved oxygen concentration 1.5–1.9 mg O2 L−1 were assessed. Hypoxia was not associated with changes in hemocyte morphology as well as with shifts in hemolymph cellular composition. Intracellular reactive oxygen species (ROS) production by hemocytes decreased following the 24 h exposure period but recovered after 72 h of hypoxia. Hypoxia contributed more to reduced phagocytosis and mitochondrial membrane potential of hemocytes. In gills, the activity of catalase and superoxide dismutase was suppressed upon exposure to hypoxia but the expression levels of the appropriate genes were stable. Metabolic depression state appeared to be the main driver for reduced cellular immune status and the activity of antioxidant enzymes in ark shells. Overall, ark shells demonstrated stability of functional state upon exposure to hypoxia and stabilization of cellular immune parameters under prolonged incubation to low dissolved oxygen concentrations.

Effects of dissolved oxygen (DO) in seawater on microbial corrosion of concrete: Morphology, composition, compression analysis and transportation evaluation

This paper experimentally investigates the impact of dissolved oxygen (DO) in seawater on the degree of microbiologically induced concrete corrosion (MICC). The bacterial growth, microstructure of biofilm, hydration products, mechanical and transport performance of concrete are explored in both sufficient and low DO groups. The results show that DO has a positive effect on the reproduction of sulfur oxidizing bacteria (SOB), colonization of biofilm, reaction with cementitious hydration products and enhancement in compression in the early stage. The migration of Cl− erosion is reduced in rich DO environment compared with low DO content due to the inhibition in both biofilm and interior structures.

Effect of low dissolved oxygen concentration on the defects and composition of regenerated passive film of Ti-6Al-4V alloy under continuous wear.

Tribocorrosion is one of the most common forms of failure of biomedical titanium alloys. As the passive film of titanium alloys is highly dependent on oxygen conditions, the passivation behavior and the microstructure of the passive film of Ti-6Al-4V under tribocorrosion in 1 M HCl with a low dissolved oxygen concentration (DOC) were studied by means of electron probe microanalysis (EPMA), Ar-ion etched X-ray photoelectron spectroscopy (XPS), focused ion beam (FIB) milling and high resolution transmission electron microscopy (HRTEM). The results showed that the protective ability of the regenerated passive film decreased sharply under low DOC. Al and V ions dissolved in excess, and a large number of oxygen atoms entered the matrix, leading to internal oxidation. Structural characterization indicated that Ti atoms occupied more metal lattice points in the regenerated passive film and that the high dislocation density in the deformed layer caused by wear facilitated the diffusion of Al and V. Finally, the first-principles calculation showed that Al had the minimum vacancy formation energy.

Water quality fluctuations in small intermittently closed and open lakes and lagoons (ICOLLs) after natural and artificial openings

Water quality fluctuations are influenced by natural and artificial openings of ICOLLs. In this study artificial opening resulted in a greater degradation of water quality than natural openings. Artificial openings are commonly undertaken in response to flood risk to human assets but often cause fish kills. We assessed water quality (parameters: temperature, dissolved oxygen, pH, salinity) within two ICOLLs before and after natural openings and two ICOLLS before and after artificial openings. Natural openings caused only a slight decline in water quality and no fish kills, whereas the artificial openings triggered poor water quality and fish kills. Decline of dissolved oxygen concentrations were observed following two artificial opening events associated with fish kills. We conclude that there are multiple drivers and sources contributing to low dissolved oxygen concentrations that are unique to individual ICOLLs and the type of opening.

Predicted Episode of Submarine Groundwater Discharge Onto the South Carolina, USA, Continental Shelf and Its Effect on Dissolved Oxygen

AbstractSubmarine groundwater discharge (SGD) may directly influence the dissolved oxygen (DO) content of coastal bottom waters. Here, we report a predicted episode of enhanced SGD that caused low DO concentrations on the South Carolina continental shelf. The prediction model linked episodes of SGD to upwelling‐favorable winds. The data revealed these waters were a factor of 2–6 higher in 226Ra and 228Ra compared to typical bottom water values and were significantly depleted in DO (&lt;130 μM). The tight 228Ra:226Ra correlation of these data was similar to values during a strong hypoxic event off SC in 2012. Water ages from 224Ra and 223Ra indicated the event occurred 2–9 days before sampling. The success of the prediction lends added credence to the correlation of upwelling‐favorable winds—but not necessarily accompanied by upwelling—to episodic SGD events. This prediction from wind data represents a major advance for quantifying SGD in the region.

Mathematical simulation and experimental verification of a novel control strategy for a single stage PN/A (partial nitrification/Anammox) SBR (sequencing batch reactor)

The single reactor PN-A process offers a cost-effective solution for nitrogen removal. The successful startup and operation of the PN/A reactor requires the enrichment and balanced growth of AOB (Ammonium oxidizing bacteria) and AMX (AMAMMOX bacteria). The precise aeration supply or DO (dissolved oxygen) control was regarded to be the key for successful operation of the PN/A reactor. However, due to the low DO concentration requirement for the PN/A reactor, it is not practical to apply the precise aeration or DO concentration control. In this study, a new control strategy for the rapid startup and operation of the single stage PN/A (partial nitrification) SBR (sequencing batch reactor) was put forward. The control strategy relies on the periodic measurement of effluent NH4+, NO2-, and NO3- concentration to determine the nitrogen loading rate and aeration pump speed (i.e., not exact air supply volume). It does not require precise oxygen supply or DO (dissolved oxygen) control. This feature makes the control strategy easily applicable for practical application. A calibrated mathematical model was used to evaluate the control strategy, which was shown to be effective in achieving satisfactory nitrogen removal and NOB suppression. The control strategy was tested in a lab PN/A batch reactor, in which TN removal efficiency of 80% was achieved under low influent NH4+ concentration of 100 mg N/L and nitrogen loading rate of 0.12 Kg N/(m3•d) within 60 days of the experiment.

Evaluating the eutrophication risk of artificial lagoons–case study El Gouna, Egypt

Eutrophication problem in El Gouna shallow artificial coastal lagoons in Egypt was investigated using 2D TELEMAC-EUTRO-WAQTEL module. Eight reactive components were presented, among them dissolved oxygen (DO), phosphorus, nitrogen, and phytoplankton biomass (PHY). The effect of warmer surface water on the eutrophication problem was investigated. Also, the spatial and temporal variability of the eutrophication was analyzed considering different weather conditions: tide wave, different wind speeds and directions. Moreover, effect of pollution from a nearby desalination plant was discussed considering different pollution degrees of brine discharge, different discharge quantities and different weather conditions. Finally, new precautions for better water quality were discussed. The results show that tide wave created fluctuations in DO concentrations, while other water quality components were not highly influenced by tide’s fluctuations. Also, it was found that high water temperatures and low wind speeds highly decreased water quality producing low DO concentrations and high nutrients rates. High water quality was produced beside inflow boundaries when compared to outflow boundaries in case of mean wind. Moreover, the results show that the average water quality was not highly deteriorated by the nearby desalination operation, while the area just beside the desalination inflow showed relatively strong effects. Different weather conditions controlled the brine’s propagation inside the lagoons. Moreover, increasing the width of the inflow boundaries and injecting tracer during tide and mean wind condition are new precautions which may help to preserve the water quality in a future warmer world. This study is one of the first simulations for eutrophication in manmade lagoons.

Changing water quality and thermocline depth along an aquaculture gradient in six tropical crater lakes

Understanding how lakes respond to changes in nutrient loading along a productivity gradient can help identify key drivers of aquatic change, thereby allowing appropriate mitigation strategies to be developed. Physical, chemical and biological water column measurements combined with long-term water monitoring data for six closely located crater lakes, in Southeast Asia, were compared to assess the response of lakes along a productivity gradient equating to a transect of increasing aquaculture intensity. Increasing chlorophyll a (phytoplankton biomass) in the upper waters appeared to modify the thermocline depth and light availability causing a shift from a deep chlorophyll maximum at low aquaculture intensity to the emergence of algal dead zones lower in the water column with high aquaculture intensity. High phosphorus loading and light limitation from enhanced algal biomass, associated with high aquaculture intensity, exacerbated nitrogen drawdown, leading to the prevalence of potentially nitrogen-fixing cyanobacteria. Seasonal overturn during the cooler season resulted in low dissolved oxygen concentrations in the epilimnion, potential harmful algal blooms, a reduction in the habitable depth for fish and ultimately increased mortality amongst farmed fish.