- Email: [email protected]
Evaluation of Eutrophication Control Through Hypolimnetic Oxygenation
Available online at www.sciencedirect.com
ScienceDirect Procedia Earth and Planetary Science 17 (2017) 598 – 601
15th Water-Rock Interaction International Symposium, WRI-15
Evaluation of Eutrophication Control Through Hypolimnetic Oxygenation Anne M. Hansena,1, Claudia Hernández-Martínezb, Axel Falcón-Rojasa a
Mexican Institute of Water Technology. Paseo Cuauhnahuac 8532, Jiutepec, Morelos, 62550 Mexico. [email protected]. b National Water Commission-OCAVM, Rio Churubusco 650, Mexico City, 08040 Mexico.
Abstract The accumulation of nutrients in water bodies occur due to excessive phosphorus and nitrogen loads from the catchments and other external sources, causing buildup of nutrients in sediments. Often, water bodies that present thermal stratification, experience depletion of dissolved oxygen (DO) in the hypolimnion, thereby causing anoxic conditions, favoring the release of nutrients and leading to eutrophic conditions. The use of hypolimnetic oxygenation systems (HOS), which can supply over 50 mg/L of DO in the hypolimnion of deeper water bodies, has demonstrated to reverse these conditions in lakes and reservoirs in North America, Europe, and Australia. The objective of this study was to develop a model for forecasting the remediation progress of a eutrophied reservoir using HOS. For this purpose, a mass-balance model was developed that calculates the oxygen accumulation in water bodies, using experimentally obtained oxygen demand (OD) of water and sediment from the reservoir, the extracted OD, the external load of OD, DO provided by natural sources such as photosynthesis and interaction with the atmosphere, and DO supplied by the HOS. The model was applied to forecast DO concentrations in the hypolimnion of a Mexican reservoir under different scenarios of external load of OD and hypolimnetic oxygenation. © 2017 2017The TheAuthors. Authors. Published by Elsevier Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of WRI-15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 Keywords: Hypolimnetic oxygenation; Eutrophication control; Internal load; Oxygen demand; Water and sediment respiration.
1. Introduction The growth of population and productive activities has deteriorated the water quality of lakes and reservoirs. This behavior has been observed in water bodies around the World where lakes and reservoirs are increasingly vulnerable to the pollution caused by anthropogenic activities and the degradation of water quality1. An effect of this
* Corresponding author. Tel.: +52-777-329-3600-Ext.610; fax: +52-777-329-3682. E-mail address: [email protected]
1878-5220 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.159
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Anne M. Hansen et al. / Procedia Earth and Planetary Science 17 (2017) 598 – 601
deterioration of water quality is the acceleration in the eutrophication process of lakes and reservoirs, caused mainly by external nutrient loads of nitrogen and phosphorus from wastewater and runoff due to productive activities such as agriculture, livestock and fish farming, which stimulate the growth of phytoplankton in surface waters2. As phytoplankton die off and sink as organic matter to the bottom of lakes and reservoirs, it is consumed by bacteria that require oxygen for their degradation, contributing to oxygen demand and causing anaerobic conditions that promote the release of phosphate and ammonium from the sediments3. Temperature differences as well as winddriven mixing of water in lakes and reservoirs, promote the distribution of these nutrients released from sediments to surface waters, stimulating phytoplankton growth, and reinforcing anaerobic conditions and release of nutrients4. These nutrients may partially be redeposited in sediments as aerobic conditions occur during periods of water mixing or during hypolimnetic injection of oxygen. Redeposited nutrients may remain accumulated in sediments until anaerobic conditions in the hypolimnium cause their release 5. Hypolimnetic Oxygenation Systems (HOS) are designed to supply Dissolved Oxygen (DO) to the hypolimnion of lakes and reservoirs 3, where anoxic conditions are reversed when DO content is increased in the hypolimnion, thereby reducing or even eliminating internal nutrient loads. Although this technology has been successfully applied in various reservoirs in North America, Europe and Australia3,6, design parameters must be obtained for each case due to the variable climatic and biogeographic characteristics. The objective of this study was to develop a model that allows evaluating the progress of remediation of lakes and reservoirs where installation and operation of HOS is being planned. This model is based on the mass balance of DO and oxygen demand (OD) in water bodies. We describe how we obtained the mass balance parameters and we apply the model with different amounts of HOS and external load (EL) reductions of OD. 2. Methods To predict the accumulation of DO in water of lakes and reservoirs, where it is planned to install and operate HOS, a mass balance model was determined, which considers the inputs and outputs of OD and natural contributions as well as HOS supplied DO (1). ܱܦ ൌ ܱܦ௪௧ ܱܦ௦ௗ ܱܦா െ ܱܦ௫௧ െ ܱܦ௧ െ ܱܦுைௌ
Where ODfin ODwat ODext ODsed ODEL DOnat DOHOS
(1)
OD of water in the hypolimnion after a specified period (e.g. one year) OD of water in the hypolimnion at the beginning of the period OD extracted during the period OD of sediment in the period EL of OD in the period DO provided by external sources, photosynthesis and interaction with the atmosphere in the period DO provided by HOS in the period
The study area is the eutrophied reservoir of the Valle de Bravo dam that is part of the Cutzamala system, which supplies 15 m3/s of water to Mexico City7. The OD of water and sediment from the reservoir were determined through respirometry. For ODwat, 2 L of hypolimnetic water from the reservoir were incubated at 25 + 2 °C. For ODsed, 124 g of dry sediment from the 2-cm upper sections of isotope dated (137Cs and 210Pb) sediment cores, corresponding to an age of 0.3 yr, were suspended in 1.5 L of hypolimnetic water from the reservoir. These sections were established since it is observed as the sediment depths where degradation of organic matter mainly occurs. Both samples were incubated in agitated reactors (100 rpm) with a continuous flow of 0.5 L/min of CO 2-free O2 (Praxair 99.9% purity). The output of gas in the reactors were connected to a solution of Ba(OH) 2, where CO2 produced in the reactor reacts forming BaCO 3 and changing the electrical conductivity (EC). Changes in EC was measured conductimetrically (Condumax CLS21), and temperatures of the solution were monitored with temperature sensor (Ankora type K) and recorded continuously, according to the method described by 8. To
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determinate ODwat and ODsed, the uptake of O2 was obtained by stoichiometrical analysis of the CO2 produced in the reactors. To determine ODwat before initiating the operation of HOS, we multiplied the consumption of O 2 in the period with the volume of water in the hypolimnion. For subsequent periods, ODwat was the DOfin, for the previous period. To determine ODsed, OD of the water was substracted from the consumption of O2 in the reactor, and the result was multiplied with the area of the reservoir. The ODEL was estimated through an inventory of emissions, considering diffuse and point sources in the watershed. These include discharges from untreated municipal wastewater and from municipal sewage treatment plants. Diffuse sources include discharges from fish farming and runoff from soils with different land uses. For the first simulation period, ODext was determined as the product of average Chemical Oxygen Demand (COD) in the period and the volume of extracted water. For subsequent periods, the decrease of the COD, reduced this OD and the new COD concentration in extracted water was obtained by weighting the previous COD with the initial ODwat in the previous and subsequent period. DOnat is O2 contributed by photosynthesis and interaction with atmosphere. Since the reservoir is in steady state with respect to COD, ODfin - ODwat = 0, and DOnat was obtained reorganizing (1). Finally, according to the HOS fabricant 8, an HOS located in the bottom of the reservoir, may typically supply 6 t/d of DO i.e. 2.190 t/yr, considering the average temperature and atmospheric pressure in the study area and water depth of the reservoir. 3. Results DO and OD inputs and outputs that contribute to the DO concentration in the reservoir were identified and characterized as described above, and analyzed in the mass balance (1) to predict annual DOfin. The results of respirometry of water from the reservoir (Fig. 1a) were extrapolated to a one-year period and to the water volume in the hypolimnion (150 Mm3), obtaining ODwat of 19.800 t/yr.
Fig. 1. (a) Results of OD obtained by respirometry of samples of hypolimnion water of eutrophied reservoir; (b) Results of OD obtained by respirometry of 2-cm section of sediment cores obtained in the eutrophied reservoir. 25+2 °C, 0.5 L O2/min, stirring velocity 100 rp
The results of respirometry of sediment from the reservoir (Fig. 1b) were extrapolated to a one-year period and to the water volume, the amount of sediment in the upper 2-cm layer and to the area of the reservoir (1.8 x 10 9 cm2), obtaining ODsed of 174 t/yr. The contribution of diffuse sources of ODEL was 1.946 t/yr and of point sources, 1.254 t/yr, resulting in ODEL of 3.200 t/yr. DOext was calculated in 1.892 t/yr, and ODnat was estimated in 1.482 t/yr. These data were fed into the mass balance equation (1) for different scenarios: one, two, and three HOS, without control of ODEL, and considering a reduction 36 % of OD EL. The results of these simulations (Fig. 2) show that if one HOS is installed and operated during 20 years, DO fin in excess could be attained in the hypolimion. Likewise, with two HOS operating during six years, excess DOfin would be reached, and for three HOS, excess DOfin would occur in four years. With 36 % reduction in OD EL, the remediation times were significantly lower, especially for the case of one HOS.
Anne M. Hansen et al. / Procedia Earth and Planetary Science 17 (2017) 598 – 601
Fig. 2. Results of predicted DOfin using model simulation.
4. Summary A mass-balance modeling approach was developed and applied to predict DO fin in a eutrophied reservoir. Model input parameters were determined by experimental evaluation, and analysis of information on water quality, precipitation and land use in the watershed9. Different scenarios (number of HOS and reduction of OD EL) were evaluated, prediction time intervals for obtaining positive DO fin in the hypolimnion. References 1. Peters NE, Meybeck M. Water quality degradation effects on freshwater availability: impacts of human activities. Water Internat 2000:25:185–193. 2. Horne AJ, Goldman CR. Limnology. 2 ed. McGraw-Hill, Inc. New York. 1994 3. Beutel MW, Horne AJ. A review of the effects of hypolimnetic oxygenation on lake and reservoir water quality. Lake Reserv Manage 1999:15:285–297. 4. Marsden MW. Lake restoration by reducing external phosphorus loading: the influence of sediment phosphorus release. Freshwater Biology 1999:21:139–162. 5. Sondergaard M, Jeppesen E, Lauridsen T, Skov C, van Nes EH, Roijackers R, Lammens E, Portielje R. Lake restoration: successes, failures and long-term effects. J App Ecol 2007:44:1095-1105. 6. Gerling AB, Browne RG, Gantzer PA, Mobley MH, Little JC, Carey CC. First report of the successful operation of a side stream supersaturation hypolimnetic oxygenation system in a eutrophic, shallow reservoir. Wat Res 2015:67:129-143. 7. World Bank, Conagua. Diagnóstico integral del Sistema Cutzamala (Comprehensive disgnosis of Cutzamala system). Technical report. 2015. Available on http://www.conagua.gob.mx/CONAGUA07/Noticias/WB_Cutzamala_LowRes.pdf. 8. van Afferden M, Hansen AM, Kaiser C. Laboratory test system to measure microbial respiration rate. Int. J. Enviro and Poll 2006:26:220-233 9. ECO2 Technology. Hypolimnetic oxygenation system for water quality improvements. Available on http://www.eco2tech.com/ (Consulted April 2016.
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ScienceDirect Procedia Earth and Planetary Science 17 (2017) 598 – 601
15th Water-Rock Interaction International Symposium, WRI-15
Evaluation of Eutrophication Control Through Hypolimnetic Oxygenation Anne M. Hansena,1, Claudia Hernández-Martínezb, Axel Falcón-Rojasa a
Mexican Institute of Water Technology. Paseo Cuauhnahuac 8532, Jiutepec, Morelos, 62550 Mexico. [email protected]. b National Water Commission-OCAVM, Rio Churubusco 650, Mexico City, 08040 Mexico.
Abstract The accumulation of nutrients in water bodies occur due to excessive phosphorus and nitrogen loads from the catchments and other external sources, causing buildup of nutrients in sediments. Often, water bodies that present thermal stratification, experience depletion of dissolved oxygen (DO) in the hypolimnion, thereby causing anoxic conditions, favoring the release of nutrients and leading to eutrophic conditions. The use of hypolimnetic oxygenation systems (HOS), which can supply over 50 mg/L of DO in the hypolimnion of deeper water bodies, has demonstrated to reverse these conditions in lakes and reservoirs in North America, Europe, and Australia. The objective of this study was to develop a model for forecasting the remediation progress of a eutrophied reservoir using HOS. For this purpose, a mass-balance model was developed that calculates the oxygen accumulation in water bodies, using experimentally obtained oxygen demand (OD) of water and sediment from the reservoir, the extracted OD, the external load of OD, DO provided by natural sources such as photosynthesis and interaction with the atmosphere, and DO supplied by the HOS. The model was applied to forecast DO concentrations in the hypolimnion of a Mexican reservoir under different scenarios of external load of OD and hypolimnetic oxygenation. © 2017 2017The TheAuthors. Authors. Published by Elsevier Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of WRI-15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 Keywords: Hypolimnetic oxygenation; Eutrophication control; Internal load; Oxygen demand; Water and sediment respiration.
1. Introduction The growth of population and productive activities has deteriorated the water quality of lakes and reservoirs. This behavior has been observed in water bodies around the World where lakes and reservoirs are increasingly vulnerable to the pollution caused by anthropogenic activities and the degradation of water quality1. An effect of this
* Corresponding author. Tel.: +52-777-329-3600-Ext.610; fax: +52-777-329-3682. E-mail address: [email protected]
1878-5220 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.159
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Anne M. Hansen et al. / Procedia Earth and Planetary Science 17 (2017) 598 – 601
deterioration of water quality is the acceleration in the eutrophication process of lakes and reservoirs, caused mainly by external nutrient loads of nitrogen and phosphorus from wastewater and runoff due to productive activities such as agriculture, livestock and fish farming, which stimulate the growth of phytoplankton in surface waters2. As phytoplankton die off and sink as organic matter to the bottom of lakes and reservoirs, it is consumed by bacteria that require oxygen for their degradation, contributing to oxygen demand and causing anaerobic conditions that promote the release of phosphate and ammonium from the sediments3. Temperature differences as well as winddriven mixing of water in lakes and reservoirs, promote the distribution of these nutrients released from sediments to surface waters, stimulating phytoplankton growth, and reinforcing anaerobic conditions and release of nutrients4. These nutrients may partially be redeposited in sediments as aerobic conditions occur during periods of water mixing or during hypolimnetic injection of oxygen. Redeposited nutrients may remain accumulated in sediments until anaerobic conditions in the hypolimnium cause their release 5. Hypolimnetic Oxygenation Systems (HOS) are designed to supply Dissolved Oxygen (DO) to the hypolimnion of lakes and reservoirs 3, where anoxic conditions are reversed when DO content is increased in the hypolimnion, thereby reducing or even eliminating internal nutrient loads. Although this technology has been successfully applied in various reservoirs in North America, Europe and Australia3,6, design parameters must be obtained for each case due to the variable climatic and biogeographic characteristics. The objective of this study was to develop a model that allows evaluating the progress of remediation of lakes and reservoirs where installation and operation of HOS is being planned. This model is based on the mass balance of DO and oxygen demand (OD) in water bodies. We describe how we obtained the mass balance parameters and we apply the model with different amounts of HOS and external load (EL) reductions of OD. 2. Methods To predict the accumulation of DO in water of lakes and reservoirs, where it is planned to install and operate HOS, a mass balance model was determined, which considers the inputs and outputs of OD and natural contributions as well as HOS supplied DO (1). ܱܦ ൌ ܱܦ௪௧ ܱܦ௦ௗ ܱܦா െ ܱܦ௫௧ െ ܱܦ௧ െ ܱܦுைௌ
Where ODfin ODwat ODext ODsed ODEL DOnat DOHOS
(1)
OD of water in the hypolimnion after a specified period (e.g. one year) OD of water in the hypolimnion at the beginning of the period OD extracted during the period OD of sediment in the period EL of OD in the period DO provided by external sources, photosynthesis and interaction with the atmosphere in the period DO provided by HOS in the period
The study area is the eutrophied reservoir of the Valle de Bravo dam that is part of the Cutzamala system, which supplies 15 m3/s of water to Mexico City7. The OD of water and sediment from the reservoir were determined through respirometry. For ODwat, 2 L of hypolimnetic water from the reservoir were incubated at 25 + 2 °C. For ODsed, 124 g of dry sediment from the 2-cm upper sections of isotope dated (137Cs and 210Pb) sediment cores, corresponding to an age of 0.3 yr, were suspended in 1.5 L of hypolimnetic water from the reservoir. These sections were established since it is observed as the sediment depths where degradation of organic matter mainly occurs. Both samples were incubated in agitated reactors (100 rpm) with a continuous flow of 0.5 L/min of CO 2-free O2 (Praxair 99.9% purity). The output of gas in the reactors were connected to a solution of Ba(OH) 2, where CO2 produced in the reactor reacts forming BaCO 3 and changing the electrical conductivity (EC). Changes in EC was measured conductimetrically (Condumax CLS21), and temperatures of the solution were monitored with temperature sensor (Ankora type K) and recorded continuously, according to the method described by 8. To
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Anne M. Hansen et al. / Procedia Earth and Planetary Science 17 (2017) 598 – 601
determinate ODwat and ODsed, the uptake of O2 was obtained by stoichiometrical analysis of the CO2 produced in the reactors. To determine ODwat before initiating the operation of HOS, we multiplied the consumption of O 2 in the period with the volume of water in the hypolimnion. For subsequent periods, ODwat was the DOfin, for the previous period. To determine ODsed, OD of the water was substracted from the consumption of O2 in the reactor, and the result was multiplied with the area of the reservoir. The ODEL was estimated through an inventory of emissions, considering diffuse and point sources in the watershed. These include discharges from untreated municipal wastewater and from municipal sewage treatment plants. Diffuse sources include discharges from fish farming and runoff from soils with different land uses. For the first simulation period, ODext was determined as the product of average Chemical Oxygen Demand (COD) in the period and the volume of extracted water. For subsequent periods, the decrease of the COD, reduced this OD and the new COD concentration in extracted water was obtained by weighting the previous COD with the initial ODwat in the previous and subsequent period. DOnat is O2 contributed by photosynthesis and interaction with atmosphere. Since the reservoir is in steady state with respect to COD, ODfin - ODwat = 0, and DOnat was obtained reorganizing (1). Finally, according to the HOS fabricant 8, an HOS located in the bottom of the reservoir, may typically supply 6 t/d of DO i.e. 2.190 t/yr, considering the average temperature and atmospheric pressure in the study area and water depth of the reservoir. 3. Results DO and OD inputs and outputs that contribute to the DO concentration in the reservoir were identified and characterized as described above, and analyzed in the mass balance (1) to predict annual DOfin. The results of respirometry of water from the reservoir (Fig. 1a) were extrapolated to a one-year period and to the water volume in the hypolimnion (150 Mm3), obtaining ODwat of 19.800 t/yr.
Fig. 1. (a) Results of OD obtained by respirometry of samples of hypolimnion water of eutrophied reservoir; (b) Results of OD obtained by respirometry of 2-cm section of sediment cores obtained in the eutrophied reservoir. 25+2 °C, 0.5 L O2/min, stirring velocity 100 rp
The results of respirometry of sediment from the reservoir (Fig. 1b) were extrapolated to a one-year period and to the water volume, the amount of sediment in the upper 2-cm layer and to the area of the reservoir (1.8 x 10 9 cm2), obtaining ODsed of 174 t/yr. The contribution of diffuse sources of ODEL was 1.946 t/yr and of point sources, 1.254 t/yr, resulting in ODEL of 3.200 t/yr. DOext was calculated in 1.892 t/yr, and ODnat was estimated in 1.482 t/yr. These data were fed into the mass balance equation (1) for different scenarios: one, two, and three HOS, without control of ODEL, and considering a reduction 36 % of OD EL. The results of these simulations (Fig. 2) show that if one HOS is installed and operated during 20 years, DO fin in excess could be attained in the hypolimion. Likewise, with two HOS operating during six years, excess DOfin would be reached, and for three HOS, excess DOfin would occur in four years. With 36 % reduction in OD EL, the remediation times were significantly lower, especially for the case of one HOS.
Anne M. Hansen et al. / Procedia Earth and Planetary Science 17 (2017) 598 – 601
Fig. 2. Results of predicted DOfin using model simulation.
4. Summary A mass-balance modeling approach was developed and applied to predict DO fin in a eutrophied reservoir. Model input parameters were determined by experimental evaluation, and analysis of information on water quality, precipitation and land use in the watershed9. Different scenarios (number of HOS and reduction of OD EL) were evaluated, prediction time intervals for obtaining positive DO fin in the hypolimnion. References 1. Peters NE, Meybeck M. Water quality degradation effects on freshwater availability: impacts of human activities. Water Internat 2000:25:185–193. 2. Horne AJ, Goldman CR. Limnology. 2 ed. McGraw-Hill, Inc. New York. 1994 3. Beutel MW, Horne AJ. A review of the effects of hypolimnetic oxygenation on lake and reservoir water quality. Lake Reserv Manage 1999:15:285–297. 4. Marsden MW. Lake restoration by reducing external phosphorus loading: the influence of sediment phosphorus release. Freshwater Biology 1999:21:139–162. 5. Sondergaard M, Jeppesen E, Lauridsen T, Skov C, van Nes EH, Roijackers R, Lammens E, Portielje R. Lake restoration: successes, failures and long-term effects. J App Ecol 2007:44:1095-1105. 6. Gerling AB, Browne RG, Gantzer PA, Mobley MH, Little JC, Carey CC. First report of the successful operation of a side stream supersaturation hypolimnetic oxygenation system in a eutrophic, shallow reservoir. Wat Res 2015:67:129-143. 7. World Bank, Conagua. Diagnóstico integral del Sistema Cutzamala (Comprehensive disgnosis of Cutzamala system). Technical report. 2015. Available on http://www.conagua.gob.mx/CONAGUA07/Noticias/WB_Cutzamala_LowRes.pdf. 8. van Afferden M, Hansen AM, Kaiser C. Laboratory test system to measure microbial respiration rate. Int. J. Enviro and Poll 2006:26:220-233 9. ECO2 Technology. Hypolimnetic oxygenation system for water quality improvements. Available on http://www.eco2tech.com/ (Consulted April 2016.
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