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Modelling the accumulation of organic matter in the sediments of a newly constructed reservoir
War. Res. Vol. 23. No. 10, pp. 1327-1329, 1989 Printed in Great Britain. All rights reserved
0043-1354/89 $3.00+ 0.00 Copyright © 1989PergamonPress plc
TECHNICAL NOTE MODELLING THE ACCUMULATION OF ORGANIC MATTER IN THE SEDIMENTS OF A NEWLY CONSTRUCTED RESERVOIR YORAM AVNIMELECH Faculty of Agricultural Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel (First received April 1988; accepted in revised form April 1989)
Abstract--Aging of reservoirs is related to the accumulation of organic matter in the sediments. The accumulation is considered to be a function of the sedimentation rate and of a first order decomposition process. The organic matter level approaches a constant level with time. Organic matter concentration in the sediments of the newly constructed Maaleh Hakishon reservoir were measured through a series of sediment corings. The annual sedimentation of organic components was computed from input--output budgets and from sediment trap data. The computed decomposition rate constants for organic carbon and nitrogen are 0.42 and 0.35 yr-t, respectively. Using the proposed model and the derived parameters it is possible to predict the approach of the reservoir's sediments to a steady state and its properties at that point. It is predicted that a 900 achievement of the steady state situation will occur 4 years after the construction of the reservoir. Key words--sediments, reservoir, organic carbon, organic nitrogen, decomposition, eutrophication
INTRODUCTION Newly constructed man-made reservoirs are undergoing a series of processes along the transition from a terrestrial system to an aquatic environment (Gunnison et al., 1985). The major change along that transition is the change of the reservoir bottom layer from a soil into a sediment layer. The bottom layer is changed from an aerobic soil into an oxygen limited sediment (Gunnison et al., 1980, 1985), a change that results in the accumulation of ammonium (Waring and Bremner, 1964; Gunnison et al., 1985; Avnimelech and Wodka, 1988) and the increase in the level of soluble iron and manganese (Gunnison et al., 1985). A sequence of processes is initiated by the accumulation of organic residues and nutrients on the reservoir bottom, a stage followed by a series of decomposition and diagenetic reactions. Maaleh Hakishon reservoir is an artificial lake, dug in the Valley of Jezreel as a storage for reclaimed sewage effluents from the Haifa municipal area. The reservoir and its operation were described elsewhere (Avnimeleh and Wodka, 1988). The main issue regarding the operation of the reservoir is the possibility of its deterioration with time, with regard to nutrient enrichment, to the development of anaerobic conditions and to the development of odour problems. All of these are related to the accumulation of organic matter and other nutrients in the sediments of the reservoir. The monitoring of nutrient accumulation in the sediments of the reservoir and the construction of a
nutrient budget for the period of operation of the reservoir was described (Avnimelech and Wodka, 1988). In this paper we present a simplified model describing the accumulation of organic components in the sediment and predict the approach (to a steady state situation) of the reservoir. THEORY
The accumulation of organic matter in the sediment is a function of the sedimentation of organic materials on the one hand, and the microbial degradation of the organic matter on the other hand. The organic matter sedimentation is assumed to be constant with respect to time (neglecting seasonal effects) and the decomposition of the organic matter is considered to follow first order kinetics (Berner, 1980; Johnson et al., 1982; Avnimelech et al., 1984). This process can be formulated as: dC/dt = 8 - KC
(1)
where C =concentration of the organic component (mg/g or kg/m2); B = rate of the organic component flux onto the sediment (kg/m 2 yr); K - - r e l e v a n t decay constant (yr-I); and t = time (yr). Upon integration and rearrangement we get:
1327
C =
B - e -k' ( B - KCo)
K
(2)
1328
Technical Note CONCLUSIONS REGARDING MAALEH HAK1SHON RESERVOIR
E
.~_~ oX~x~x~ x -x
x.X .x" k = 0 . 1 0 x"x
.,~///
.~' ~ ~
~ / /x ~' x
o
x/ .e~ e " /~/~.'°'°'"
~
2 E
k= 0.25 ~ o
I 2
I 6
-
k --" 0 . 5 0
I 10
I 14
o
o
I 18
Time (yr)
Fig. 1
where Co is the concentration of the given component at t = 0. An important implication of the process described in equation (2) is that the accumulation of the organic matter in the sediment is limited: lim
C =
B/K
(3)
t~0c
The sediment can accumulate, according to equation (3), only a given amount of organic matter. The potential organic matter accumulation increases linearly with B, the rate of organic matter flux onto the sediment, and decreases with the increase of the organic matter decomposition rate constant. A schematic representation of the accumulation of organic matter in sediments, as a function of time, is given in Fig. 1. The amounts accumulated are given in units of B, the annual influx rate and calculated for three rate constants: 0.1, 0.25 and 0.5 yr ~. The solid straight line in the figure represents the accumulated influx, i.e. the potential accumulation if not decomposition had taken place. As can be seen, the accumulation of organic matter is lower for the higher rate constants cases. Moreover, the system reaches a steady state (i.e. degradation equals the influx), at a faster rate with the higher the decomposition rate constant. It takes less than 5 years to get a 90% saturation level for the 0.5 yr-~ constant and about I 0 and 23 years for the 0.25 and the 0.1 yr -~ constants, respectively.
The sediments of Maaleh Hakishon reservoir were sampled before the flooding of the newly constructed reservoir and in August 1986, 2.3 years after its day of operation (Avnimelech and Wodka, 1988). The average concentrations of organic carbon and nitrogen in the top 10 cm layer of the reservoir at t = 0 and at t = 2.3 yr were established (Table 1). The rates of organic carbon and nitrogen addition onto the sediments were calculated from data on the input and output of nutrients, as well as from sediment trap results. The respective data are presented as to the whole reservoir or for the northern basin, the one into which the effluents are introduced and where most sedimentation is taking place. Those data, tabulated in Table 1, were introduced into equation (2) and the respective rate constants, K, solved by successive approximations. The rate constants for the decay of the added organic carbon were found to be 0.42 yr ~ for the whole reservoir, or 0.485 yr-l for the northern basin. The rates of decomposition of the organic nitrogen were found to be 0.35 and 0.65 yr -~, respectively, for the whole reservoir or the northern basin. The rate constants for the decomposition of organic matter in the sediments of the Maaleh Hakishon reservoir are in agreement with other reported findings. Westrich and Berner (1984) reported and cited values in the range of 0.44 yr-~ for the more stable fraction of available organic matter in sediments. Avnimelech (1984) found that the rate constants describing the decomposition of fresh organic matter in fish pond sediments are 0.44 and 0.45 yr- ~, for organic carbon and nitrogen, respectively. The last data are supported by equivalent measurements of sediment oxygen requirement in fish ponds (Schroeder, 1975; Boyd et al., 1978). The rate constant for the organic matter decomposition in reservoirs' sediments could be assumed to be in that order of magnitude. The systems involved are all typified by the presence, or the dominance, of labile organic matter, mostly fresh algal deposits. Both the agreement of the results found here with the systems mentioned above as well as the consistency of the different rate constants found in this work, are supportive as to the reliability of the results. The results obtained here may help to predict the
Table 1. Concentrations*,sedimentationrates and computeddecompositionrate constantsfor the organiccarbonand nitrogen in the Maaleb Hakishon reservoir Whole reservoir Northern basin Organic Total Organic Organic Total Organic carbon nitrogen nitrogen carbon nitrogen nitrogen Parameter 0.308 0.066 Concentrationat t = 0 (kg/m~) 0.578 0.104 Concentrationat t = 2.3 yr (kg/m2) 0.311 0.03 Sedimentationrate (kg/m2 yr) 0.42 0.16 Decomposition rate constant (yr ~) *Concentrations.in kg/m:are givenfor the topmost 10cm layer.
0.033 0.061 0.03 0.35
0.308 0.642 0.387 0.49
0.066 0.112 0.04 0.23
0.033 0.055 0.04 0.65
Technical Note future developments of the Maaleh Hakishon reservoir. According to Fig. 1, or to equation (2), it is expected that the reservoir sediment is close to a steady state. A 90% achievement of the steady state should occur, as predicted from equation (2), 4 years after the operation of the reservoir, i.e. around 1987-1988. The organic matter concentration in the sediment, at the onset of the steady state will be, according to equation (3), equal to B / K or to about 0,75 gC/m 2. The level of organic components in the sediment is an important parameter for the prediction of the processes in the reservoir at large, such as the nutrient flux from the sediment to the water, or the sediment oxygen demand. The sediment oxygen demand at the onset of the steady stage, calculated considering the expected concentration of organic matter and the rate of organic matter decomposition will be, according to the model, about 0.6 kg O J m 2 per year. LIMITATIONS OF THE PROPOSED MODEL
One limitation of the model proposed here is the fact that it assumes a constant rate of the processes involved both temporally and spatially. The assumption regarding the constancy with time disregards seasonal and the assumption of constancy over the reservoir area disregards accumulation of sediments in deep places or up wind. These assumptions are certainly wrong, yet it may be postulated that due to the linearity of both processes involved, the averaging of the processes' rates, over area or time spans will not distort the picture. The model can thus be used for a general prediction of the system behaviour. However, it has to be kept in mind, that since the model considers average data only, it is impossible to use it for predictions as to the situation expected at any given point in the system. Another limitation that has to be kept in mind is related to the fact that the organic components considered are the relatively available ones. Once these are degraded, more stable components are accumulating in the sediments and a slower sequence of reactions begins. The results and predictions presented here pertain only to the first sequence of
1329
reactions taking place in the transition from the terrestrial situation to the aquatic ones. More data are needed to expand our predictions to the slower sets of processes. Acknowledgements--This research was supported by grants
from KFK (Kernforschungszentrum Karlsruhe) and the BARD (U.S.A.-Israel Binational Agricultural Research & Development Foundation). REFERENCES
Avnimelech Y. (1984) Reactions in fish pond sediments as inferred from sediment cores data. In Research on Aquaculture (Edited by Rosenthal H. and Sarig S.), pp. 41-54. Europ. Maricult. Soc. Spec. Publ. No. 8. Avnimelech Y. and Wodka M. (1988) Accumulation of nutrients in the sediments of Maaleh Hakishon reclaimed effluents reservoir. Wat. Res. 22, 1437-1442. Avnimelech Y., McHenry R. J. and Ross J. D. (1984) Decomposition of organic matter in lake sediments. Envir. Sci. Technol. 18, 5 11. Berner R. A. (1980) A rate model for organic matter decomposition during bacterial sulfate reduction in marine sediments. In Biogeochernistry of Organic Matter at the Sediment Water Interface, pp. 35-44. CNRS Int. Colloq. Boyd C. E., Romaire R. P. and Johnston E. (1978) Predicting early morning dissolved oxygen concentrations in channel catfish ponds. Trans. Am. Fish. Soc. 107, 484-492. Gunnison D., Engler R. M. Patrick W. H. Jr (1985) Chemistry and biology of newly flooded soils: Relationship to reservoir water quality. In Microbial Processes In Reservoirs (Edited by Gunnison O.), pp. 3%57. Junk, Dortrecht. Gunnison D., Brannon J. M., Smith I. Jr and Burton G. A. (1980) Changes in respiration and anaerobic nutrient regeneration during the transition phase of reservoir development. In Hypertrophic Ecosystems, Vol. 2, pp. 151-158. SIL workshop on hypertrophic ecosystems. Developments in Hydrobiol. Johnson T. C., Evans J. E. and Eisenreich S. J. (1982) Total organic carbon in Lake Superior sediments: Comparison with hemipelagicand pelagic marine environments. Limnol. Oceanogr. 27, 481-491. Schroeder G. L. (1975) Night time material balance for oxygen in fish ponds receiving organic wastes. Bamidgeh 27, 65-74. Waring S. A. and BremnerJ. M. (1964) Ammonium production in soil under waterlogged conditions as an index of nitrogen availability. Nature 201,951-952. Westrich J. T. and Berner R. A. (1984) The role of sedimentary organic matter in bacterial sulfate reduction: The G model tested. Limnol. Oceanogr. 29, 236--249.
0043-1354/89 $3.00+ 0.00 Copyright © 1989PergamonPress plc
TECHNICAL NOTE MODELLING THE ACCUMULATION OF ORGANIC MATTER IN THE SEDIMENTS OF A NEWLY CONSTRUCTED RESERVOIR YORAM AVNIMELECH Faculty of Agricultural Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel (First received April 1988; accepted in revised form April 1989)
Abstract--Aging of reservoirs is related to the accumulation of organic matter in the sediments. The accumulation is considered to be a function of the sedimentation rate and of a first order decomposition process. The organic matter level approaches a constant level with time. Organic matter concentration in the sediments of the newly constructed Maaleh Hakishon reservoir were measured through a series of sediment corings. The annual sedimentation of organic components was computed from input--output budgets and from sediment trap data. The computed decomposition rate constants for organic carbon and nitrogen are 0.42 and 0.35 yr-t, respectively. Using the proposed model and the derived parameters it is possible to predict the approach of the reservoir's sediments to a steady state and its properties at that point. It is predicted that a 900 achievement of the steady state situation will occur 4 years after the construction of the reservoir. Key words--sediments, reservoir, organic carbon, organic nitrogen, decomposition, eutrophication
INTRODUCTION Newly constructed man-made reservoirs are undergoing a series of processes along the transition from a terrestrial system to an aquatic environment (Gunnison et al., 1985). The major change along that transition is the change of the reservoir bottom layer from a soil into a sediment layer. The bottom layer is changed from an aerobic soil into an oxygen limited sediment (Gunnison et al., 1980, 1985), a change that results in the accumulation of ammonium (Waring and Bremner, 1964; Gunnison et al., 1985; Avnimelech and Wodka, 1988) and the increase in the level of soluble iron and manganese (Gunnison et al., 1985). A sequence of processes is initiated by the accumulation of organic residues and nutrients on the reservoir bottom, a stage followed by a series of decomposition and diagenetic reactions. Maaleh Hakishon reservoir is an artificial lake, dug in the Valley of Jezreel as a storage for reclaimed sewage effluents from the Haifa municipal area. The reservoir and its operation were described elsewhere (Avnimeleh and Wodka, 1988). The main issue regarding the operation of the reservoir is the possibility of its deterioration with time, with regard to nutrient enrichment, to the development of anaerobic conditions and to the development of odour problems. All of these are related to the accumulation of organic matter and other nutrients in the sediments of the reservoir. The monitoring of nutrient accumulation in the sediments of the reservoir and the construction of a
nutrient budget for the period of operation of the reservoir was described (Avnimelech and Wodka, 1988). In this paper we present a simplified model describing the accumulation of organic components in the sediment and predict the approach (to a steady state situation) of the reservoir. THEORY
The accumulation of organic matter in the sediment is a function of the sedimentation of organic materials on the one hand, and the microbial degradation of the organic matter on the other hand. The organic matter sedimentation is assumed to be constant with respect to time (neglecting seasonal effects) and the decomposition of the organic matter is considered to follow first order kinetics (Berner, 1980; Johnson et al., 1982; Avnimelech et al., 1984). This process can be formulated as: dC/dt = 8 - KC
(1)
where C =concentration of the organic component (mg/g or kg/m2); B = rate of the organic component flux onto the sediment (kg/m 2 yr); K - - r e l e v a n t decay constant (yr-I); and t = time (yr). Upon integration and rearrangement we get:
1327
C =
B - e -k' ( B - KCo)
K
(2)
1328
Technical Note CONCLUSIONS REGARDING MAALEH HAK1SHON RESERVOIR
E
.~_~ oX~x~x~ x -x
x.X .x" k = 0 . 1 0 x"x
.,~///
.~' ~ ~
~ / /x ~' x
o
x/ .e~ e " /~/~.'°'°'"
~
2 E
k= 0.25 ~ o
I 2
I 6
-
k --" 0 . 5 0
I 10
I 14
o
o
I 18
Time (yr)
Fig. 1
where Co is the concentration of the given component at t = 0. An important implication of the process described in equation (2) is that the accumulation of the organic matter in the sediment is limited: lim
C =
B/K
(3)
t~0c
The sediment can accumulate, according to equation (3), only a given amount of organic matter. The potential organic matter accumulation increases linearly with B, the rate of organic matter flux onto the sediment, and decreases with the increase of the organic matter decomposition rate constant. A schematic representation of the accumulation of organic matter in sediments, as a function of time, is given in Fig. 1. The amounts accumulated are given in units of B, the annual influx rate and calculated for three rate constants: 0.1, 0.25 and 0.5 yr ~. The solid straight line in the figure represents the accumulated influx, i.e. the potential accumulation if not decomposition had taken place. As can be seen, the accumulation of organic matter is lower for the higher rate constants cases. Moreover, the system reaches a steady state (i.e. degradation equals the influx), at a faster rate with the higher the decomposition rate constant. It takes less than 5 years to get a 90% saturation level for the 0.5 yr-~ constant and about I 0 and 23 years for the 0.25 and the 0.1 yr -~ constants, respectively.
The sediments of Maaleh Hakishon reservoir were sampled before the flooding of the newly constructed reservoir and in August 1986, 2.3 years after its day of operation (Avnimelech and Wodka, 1988). The average concentrations of organic carbon and nitrogen in the top 10 cm layer of the reservoir at t = 0 and at t = 2.3 yr were established (Table 1). The rates of organic carbon and nitrogen addition onto the sediments were calculated from data on the input and output of nutrients, as well as from sediment trap results. The respective data are presented as to the whole reservoir or for the northern basin, the one into which the effluents are introduced and where most sedimentation is taking place. Those data, tabulated in Table 1, were introduced into equation (2) and the respective rate constants, K, solved by successive approximations. The rate constants for the decay of the added organic carbon were found to be 0.42 yr ~ for the whole reservoir, or 0.485 yr-l for the northern basin. The rates of decomposition of the organic nitrogen were found to be 0.35 and 0.65 yr -~, respectively, for the whole reservoir or the northern basin. The rate constants for the decomposition of organic matter in the sediments of the Maaleh Hakishon reservoir are in agreement with other reported findings. Westrich and Berner (1984) reported and cited values in the range of 0.44 yr-~ for the more stable fraction of available organic matter in sediments. Avnimelech (1984) found that the rate constants describing the decomposition of fresh organic matter in fish pond sediments are 0.44 and 0.45 yr- ~, for organic carbon and nitrogen, respectively. The last data are supported by equivalent measurements of sediment oxygen requirement in fish ponds (Schroeder, 1975; Boyd et al., 1978). The rate constant for the organic matter decomposition in reservoirs' sediments could be assumed to be in that order of magnitude. The systems involved are all typified by the presence, or the dominance, of labile organic matter, mostly fresh algal deposits. Both the agreement of the results found here with the systems mentioned above as well as the consistency of the different rate constants found in this work, are supportive as to the reliability of the results. The results obtained here may help to predict the
Table 1. Concentrations*,sedimentationrates and computeddecompositionrate constantsfor the organiccarbonand nitrogen in the Maaleb Hakishon reservoir Whole reservoir Northern basin Organic Total Organic Organic Total Organic carbon nitrogen nitrogen carbon nitrogen nitrogen Parameter 0.308 0.066 Concentrationat t = 0 (kg/m~) 0.578 0.104 Concentrationat t = 2.3 yr (kg/m2) 0.311 0.03 Sedimentationrate (kg/m2 yr) 0.42 0.16 Decomposition rate constant (yr ~) *Concentrations.in kg/m:are givenfor the topmost 10cm layer.
0.033 0.061 0.03 0.35
0.308 0.642 0.387 0.49
0.066 0.112 0.04 0.23
0.033 0.055 0.04 0.65
Technical Note future developments of the Maaleh Hakishon reservoir. According to Fig. 1, or to equation (2), it is expected that the reservoir sediment is close to a steady state. A 90% achievement of the steady state should occur, as predicted from equation (2), 4 years after the operation of the reservoir, i.e. around 1987-1988. The organic matter concentration in the sediment, at the onset of the steady state will be, according to equation (3), equal to B / K or to about 0,75 gC/m 2. The level of organic components in the sediment is an important parameter for the prediction of the processes in the reservoir at large, such as the nutrient flux from the sediment to the water, or the sediment oxygen demand. The sediment oxygen demand at the onset of the steady stage, calculated considering the expected concentration of organic matter and the rate of organic matter decomposition will be, according to the model, about 0.6 kg O J m 2 per year. LIMITATIONS OF THE PROPOSED MODEL
One limitation of the model proposed here is the fact that it assumes a constant rate of the processes involved both temporally and spatially. The assumption regarding the constancy with time disregards seasonal and the assumption of constancy over the reservoir area disregards accumulation of sediments in deep places or up wind. These assumptions are certainly wrong, yet it may be postulated that due to the linearity of both processes involved, the averaging of the processes' rates, over area or time spans will not distort the picture. The model can thus be used for a general prediction of the system behaviour. However, it has to be kept in mind, that since the model considers average data only, it is impossible to use it for predictions as to the situation expected at any given point in the system. Another limitation that has to be kept in mind is related to the fact that the organic components considered are the relatively available ones. Once these are degraded, more stable components are accumulating in the sediments and a slower sequence of reactions begins. The results and predictions presented here pertain only to the first sequence of
1329
reactions taking place in the transition from the terrestrial situation to the aquatic ones. More data are needed to expand our predictions to the slower sets of processes. Acknowledgements--This research was supported by grants
from KFK (Kernforschungszentrum Karlsruhe) and the BARD (U.S.A.-Israel Binational Agricultural Research & Development Foundation). REFERENCES
Avnimelech Y. (1984) Reactions in fish pond sediments as inferred from sediment cores data. In Research on Aquaculture (Edited by Rosenthal H. and Sarig S.), pp. 41-54. Europ. Maricult. Soc. Spec. Publ. No. 8. Avnimelech Y. and Wodka M. (1988) Accumulation of nutrients in the sediments of Maaleh Hakishon reclaimed effluents reservoir. Wat. Res. 22, 1437-1442. Avnimelech Y., McHenry R. J. and Ross J. D. (1984) Decomposition of organic matter in lake sediments. Envir. Sci. Technol. 18, 5 11. Berner R. A. (1980) A rate model for organic matter decomposition during bacterial sulfate reduction in marine sediments. In Biogeochernistry of Organic Matter at the Sediment Water Interface, pp. 35-44. CNRS Int. Colloq. Boyd C. E., Romaire R. P. and Johnston E. (1978) Predicting early morning dissolved oxygen concentrations in channel catfish ponds. Trans. Am. Fish. Soc. 107, 484-492. Gunnison D., Engler R. M. Patrick W. H. Jr (1985) Chemistry and biology of newly flooded soils: Relationship to reservoir water quality. In Microbial Processes In Reservoirs (Edited by Gunnison O.), pp. 3%57. Junk, Dortrecht. Gunnison D., Brannon J. M., Smith I. Jr and Burton G. A. (1980) Changes in respiration and anaerobic nutrient regeneration during the transition phase of reservoir development. In Hypertrophic Ecosystems, Vol. 2, pp. 151-158. SIL workshop on hypertrophic ecosystems. Developments in Hydrobiol. Johnson T. C., Evans J. E. and Eisenreich S. J. (1982) Total organic carbon in Lake Superior sediments: Comparison with hemipelagicand pelagic marine environments. Limnol. Oceanogr. 27, 481-491. Schroeder G. L. (1975) Night time material balance for oxygen in fish ponds receiving organic wastes. Bamidgeh 27, 65-74. Waring S. A. and BremnerJ. M. (1964) Ammonium production in soil under waterlogged conditions as an index of nitrogen availability. Nature 201,951-952. Westrich J. T. and Berner R. A. (1984) The role of sedimentary organic matter in bacterial sulfate reduction: The G model tested. Limnol. Oceanogr. 29, 236--249.