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Utility of Soluble Reactive Phosphorus Measurements in Great Lakes Surveillance Programs: a Summary
J. Great Lakes Res. 14(3):377-379 Internat. Assoc. Great Lakes Res., 1988
REPORT UTILITY OF SOLUBLE REACTIVE PHOSPHORUS MEASUREMENTS IN GREAT LAKES SURVEILLANCE PROGRAMS: A SUMMARY
J. Barica and R. J. Allan Lakes Research Branch National Water Research Institute Canada Centre for Inland Waters Burlington, Ontario L7R 4A6 ABSTRACT. This report summarizes the findings and conclusions ofa special workshop convened by the National Water Research Institute at Burlington, Ontario, to review differences in opinion regarding the utility and continuation of soluble reactive phosphorus (SRP) measurements in the Great Lakes surveillance programs. SRP measurements were discussed taking into account recent developments in understanding the role of phosphorus in bacterial and algal nutrition, phosphorus utilization, and phosphorus turnover times. The workshop concluded that SRP is an acceptable measure of dissolved bioavailable phosphorus when concentrations are significantly above detection limit, and recommended continuation of SRP measurements on surveillance cruises until a better alternative is developed. ADDITIONAL INDEX WORDS: Eutrophication, nutrients, chemical analysis.
The utility of continuing SRP measurements in oligotrophic areas of the Great Lakes, where phosphorus levels are near the detection limit for most of the year, has been questioned. SRP measurements continue to be made in the Great Lakes system and elsewhere despite Rigler's (1966, 1968) demonstration that SRP methodology can overestimate ambient true P04 concentrations by at least an order of magnitude. The rationale for continuing SRP measurements seems to be based on the implicit assumptions that (1) SRP concentrations are proportional to P04 concentrations, and/ or (2) the SRP pool, although composed largely of organic compounds and/or inorganic-organic complexes, is "bioavailable" to microorganisms (algae and bacteria). Tarapchak and Rubitschun (1981) and Tarapchak et al. (1982 a, b, c) suggested that SRP technology and the numbers it produces should be carefully scrutinized before further measurements are made as part of routine Great Lakes monitoring programs in the United States and Canada. Several agencies have discontinued SRP measurements in their monitoring programs because of perceived difficulties in interpreting values at extremely low levels (Department of Fish-
eries and Oceans, Experimental Lakes Area, North-Western Ontario and Arctic Lakes Project; Department of the Environment, Water Quality Branch, Western and Northern Region). Sample storage times and preservation techniques also have presented additional problems (Philbert 1973, EI-Shaarawi and Neilson 1984). Total phosphorus values are usually used to track open lake trends in the Great Lakes, and to demonstrate responses to reduced phosphorus loadings according to the Great Lakes Water Quality Agreement (GLWQA). Total phosphorus reductions have been well documented (Dobson 1984). Only nominal effort, however, has been put forward to determine if equivalent changes have occurred with the soluble reactive, soluble organic, and particular phosphorus fractions, and the significance of these changes. In response to the International Joint Commission's Great Lakes Surveillance Work Group (SWG) and Department of the Environment, Inland Waters/Lands Directorate-Ontario Region, which is responsible for carrying out monitoring programs on the Great Lakes in compliance with GLWQA, the National Water Research Institute 377
378
BARICA and ALLAN
(NWRI) of Canada convened a special workshop on 24-25 March 1987. The workshop integrated recent research findings on P-availability and Pturnover time, which were not available when routine SRP monitoring was first introduced to the Great Lakes surveillance program. Leading scientists from the Great Lakes basin and elsewhere were invited to participate and to provide their opinions on the utility of SRP measurements. The individual statements by the speakers, discussion among Canadian and U.S. participants, full list of references, and graphic documentation were recorded separately (Barica and Allan 1987) and are available upon request. The conclusions of both the discussions and the questionnaire distributed to all participants were summarized as follows: (1) SRP Methodology. Despite the fact that the molybdenum blue method for SRP determination provides varying results in different experimental conditions, as demonstrated by S. Tarapchak (Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan), these differences become less significant when working over a broad range of concentrations and with standardized pretreatment and analytical conditions (internal standards with elimination of salt effect and arsenate interference, standard filter size and filtered volume, constant reaction time, etc.). It was recommended to re-test the method further in view of Dr. Tarapchak's suggestions. (2) Utility of SRP and Continuation of Monitoring. SRP was found to represent a variable mixture of ortho-phosphorus and low molecular weight organic phosphorus, of which the availability of the organic or inorganic-organic fraction was, and could be, very different than ortho-phosphorus. SRP was recognized as a useful parameter for identifying regions of high phosphorus regeneration and upwelling events, hypolimnetic conditions, summer depletion and spatial and temporal trends, and success rate of P-controls. The problems in SRP interpretation arise primarily at extremely low levels, which is a common problem of any water quality parameter. SRP was considered to be an acceptable estimate of the soluble phosphorus fraction and believed to be available to lake biota. All participants were in favor of continuation of SRP measurements on a year-round basis in the lower Great Lakes, but some of them recommended discontinuation in offshore waters of Lakes Superior and Huron because of chronically
low values near the detection limit. Use of SRP in lake management programs was not considered a waste. (3) Alternatives to SRP. 32P-P0 4 turnover time seems to provide the most representative value for assessment of the pathways of P in the cells of aquatic organisms, and a system to track the readily available phosphorus pool (Lean 1973, Lean and Nalewajko 1979). However, it is not practically feasible to introduce this method into a routine operation for economic and work-safety reasons (isotope radioactivity). Developmental work on other alternative approaches (algal and bacterial bioassays, nutrient limitation and demand measurements, Lean and Pick 1981, etc.) should be emphasized and encouraged. SRP should be related more to community response and phosphorus exchange between biologically and chemically significant compartments. In the meantime, SRP data should continue to be gathered in the existing manner and subject to methodological retesting. (4) Kinetic Versus Static Approach. The workshop provided a useful forum to take a new look at SRP, introduced into water quality monitoring during the 1960s, when little was known about phosphorus turnover time, its physiological role, and P kinetics in general (Lean and White 1983, Nalewajko and Voltolina 1986, Nalewajko et al. 1986, and Peters 1978). SRP has been used as a static indicator of ambient concentrations remaining after removal of phosphorus from sewage treatment plant effluents (Nicholls et al. 1986, Robinson 1986). In this context, SRP has been a useful indicator of spatial and temporal trends. The recent findings on P kinetics have changed basic assumptions and have shown that even at undetectable P levels, microorganisms can still intensively utilize phosphorus in the food chain. The 1970s represented a whole new era in understanding the role and pathways of phosphorus (Tarapchak and Nalewajko 1986). It is, therefore, not surprising that there are conflicting interpretations as a result of basic differences between old, static, and new kinetic approach. Finally, despite its drawbacks at low levels, SRP is currently the most utilitarian mean of estimating dissolved phosphorus, although it does not provide full information on quantity and short-term/long-term bioavailability. (5) New Look at the Trophic State Controls in Great Lakes. The workshop provided an update of strategies on nutrient control problems in the Great Lakes basin. It is now true that eutrophica-
SOLUBLE REACTIVE PHOSPHORUS MEASUREMENTS
tion in the open water of the Great Lakes has been stabilized over the past 10 years in the face of continuing population expansion. Eutrophication in this respect is considered to be generally under control as long as the GLWQA's target loads are met. However, new developments must now be considered with equal seriousness. Eutrophication is not completely under control in near-shore areas which are still affected by the growths of Cladophora. Its frequent massive dieoffs still cause aesthetic problems and impairments of drinking water quality. Further, many of the IJC Areas of Concern are to a large degree affected by elevated nutrient inputs. Our nutrients control focus should therefore shift from the open lakes to the near-shore and to IJC Areas of Concern. Further, and perhaps of longer term significance is the analysis of the interactions of nutrients with toxic contaminants. This is a new emerging issue and research projects to address them are already underway. REFERENCES Barica, J., and Allan, R. J. 1987. An analysis of the
utility of SRP measurements in Great Lakes surveillance programs. National Water Research Institute Contribution No. 87-73, Burlington, Ontario. Dobson, H. F. H. 1984. Lake Ontario water chemistry atlas. Inland Waters Directorate, Burlington, Ontario. Scientific Series No. 139. EI-Shaarawi, A. H., and Nielson, M. A. 1984. Changes in nutrient levels of lake waters stored at 4°C. Can. J. Fish. Aquat. Sci. 41:985-988. Lean, D. R. S. 1973. Phosphorus dynamics in lake water. Science 179:678-680. _ _ _ _ , and Nalewajko, C. 1979. Phosphorus turnover time and phosphorus demand in large and small lakes. Arch. Hydrobiol. Beih. 13:120-132. _ _ _ _ , and Pick, F. R. 1981. Photosynthetic response of Lake Plankton to nutrient enrichment: a test for nutrient limitation. Limnol. Oceanogr. 26:1001-1019. _ _ _ _ , and White, E. 1983. Chemical and radiotracer measurements of phosphorus uptake by Lake Plankton. Can. J. Fish. A quat. Sci. 40:147-155. Nalewajko, C., and Voltolina, D. 1986. The effects of environmental variables of growth rates and physiological characteristics of Lake Superior phytoplankton. Can. J. Fish. Aquat. Sci. 43: 1163-1170. _ _ _ _ , Paul, B., Lee, K., and Shear, H. 1986. Light history, phosphorus status, and the occurrence
379
of light stimulation or inhibition of phosphate uptake in Lake Superior phytoplankton and bacteria. Can. J. Fish. Aquat. Sci. 43:329-335. Nicholls, K. H., Heinstch, L., Carney, E., Beaver, J., and Middleton, D. 1986. Some effects of phosphorus loading reductions on phytoplankton in the Bay of Quinte, Lake Ontario. In C. K. Minns, D. A. Hurley, and K. H. Nicholls (Eds.), Project Quinte:
Point-Source Phosphorus Control and Ecosystem Response in the Bay of Quinte, Lake Ontario, pp. 145-158. Can. Spec. Publ. Fish. Aquat. Sci. 86. Peters, R. H. 1978. Concentrations and kinetics of phosphorus fractions in streams entering Lake Memphremagog. J. Fish. Res. Board Can. 35: 315-328. Philbert, F. J. 1973. The effect of sample preservation by freezing prior to chemical analysis of Great Lakes waters. In Proc. 16th Con! Great Lakes Res., pp. 282-293. Internat. Assoc. Great Lakes Res. Rigler, F. H. 1966. Radiobiological analysis of inorganic phosphorus in lake water. Verh. Int. Ver. Theor. Angew. Limnol. 16:465-470. _ _ _ _ . 1968. Further observations inconsistent with the hypothesis that the molybdenum blue method measures orthophosphate in lake water. Limnolo Oceanogr. 13:7-13. Robinson, G. W. 1986. Water quality of the Bay of Quinte, Lake Ontario, before and after reductions in phosphorus loading. In C. K. Minns, D. A. Hurley, and K. H. Nicholls (Eds.), Project QUinte: Point-
Source Phosphorus Control and Ecosystem Response in the Bay of Quinte, Lake Ontario, pp. 50-58. Can. Spec. Pub I. Fish. Aquat. Sci. 86. Tarapchak, S. J., and Nalewajko, C. 1986. Introduction: phosphorus-plankton dynamics symposium. Can. J. Fish. Aquat. Sci. 43:293-301. _ _ _ _ , and Rubitschun, C., 1981. Comparison of soluble reactive phosphorus and orthophosphorus concentrations at an offshore station in southern Lake Michigan. J. Great Lakes Res. 7:290-298. _ _ _ _ , Chambers, R. L., and Bigelow, S. M., 1982a. Soluble reactive phosphorus measurements in Lake Michigan: causes of method-specific differences. J. Great Lakes Res. 8:700-710. _ _ _ _ Chambers, R. L., and Rubitschun, 1982b. Soluble reactive phosphorus measurements in Lake Michigan: filtration artifacts. J. Great Lakes Res. 8:550-557. _ _ _ _ , Bigelow, S. M., and Rubitschun, C. 1982c. Overestimation of ortho-phosphorus concentrations in surface waters of southern Lake Michigan: effects of acid and ammonium molybdate. Can. J. Fish. Aquat. Sci. 39:296-304.
REPORT UTILITY OF SOLUBLE REACTIVE PHOSPHORUS MEASUREMENTS IN GREAT LAKES SURVEILLANCE PROGRAMS: A SUMMARY
J. Barica and R. J. Allan Lakes Research Branch National Water Research Institute Canada Centre for Inland Waters Burlington, Ontario L7R 4A6 ABSTRACT. This report summarizes the findings and conclusions ofa special workshop convened by the National Water Research Institute at Burlington, Ontario, to review differences in opinion regarding the utility and continuation of soluble reactive phosphorus (SRP) measurements in the Great Lakes surveillance programs. SRP measurements were discussed taking into account recent developments in understanding the role of phosphorus in bacterial and algal nutrition, phosphorus utilization, and phosphorus turnover times. The workshop concluded that SRP is an acceptable measure of dissolved bioavailable phosphorus when concentrations are significantly above detection limit, and recommended continuation of SRP measurements on surveillance cruises until a better alternative is developed. ADDITIONAL INDEX WORDS: Eutrophication, nutrients, chemical analysis.
The utility of continuing SRP measurements in oligotrophic areas of the Great Lakes, where phosphorus levels are near the detection limit for most of the year, has been questioned. SRP measurements continue to be made in the Great Lakes system and elsewhere despite Rigler's (1966, 1968) demonstration that SRP methodology can overestimate ambient true P04 concentrations by at least an order of magnitude. The rationale for continuing SRP measurements seems to be based on the implicit assumptions that (1) SRP concentrations are proportional to P04 concentrations, and/ or (2) the SRP pool, although composed largely of organic compounds and/or inorganic-organic complexes, is "bioavailable" to microorganisms (algae and bacteria). Tarapchak and Rubitschun (1981) and Tarapchak et al. (1982 a, b, c) suggested that SRP technology and the numbers it produces should be carefully scrutinized before further measurements are made as part of routine Great Lakes monitoring programs in the United States and Canada. Several agencies have discontinued SRP measurements in their monitoring programs because of perceived difficulties in interpreting values at extremely low levels (Department of Fish-
eries and Oceans, Experimental Lakes Area, North-Western Ontario and Arctic Lakes Project; Department of the Environment, Water Quality Branch, Western and Northern Region). Sample storage times and preservation techniques also have presented additional problems (Philbert 1973, EI-Shaarawi and Neilson 1984). Total phosphorus values are usually used to track open lake trends in the Great Lakes, and to demonstrate responses to reduced phosphorus loadings according to the Great Lakes Water Quality Agreement (GLWQA). Total phosphorus reductions have been well documented (Dobson 1984). Only nominal effort, however, has been put forward to determine if equivalent changes have occurred with the soluble reactive, soluble organic, and particular phosphorus fractions, and the significance of these changes. In response to the International Joint Commission's Great Lakes Surveillance Work Group (SWG) and Department of the Environment, Inland Waters/Lands Directorate-Ontario Region, which is responsible for carrying out monitoring programs on the Great Lakes in compliance with GLWQA, the National Water Research Institute 377
378
BARICA and ALLAN
(NWRI) of Canada convened a special workshop on 24-25 March 1987. The workshop integrated recent research findings on P-availability and Pturnover time, which were not available when routine SRP monitoring was first introduced to the Great Lakes surveillance program. Leading scientists from the Great Lakes basin and elsewhere were invited to participate and to provide their opinions on the utility of SRP measurements. The individual statements by the speakers, discussion among Canadian and U.S. participants, full list of references, and graphic documentation were recorded separately (Barica and Allan 1987) and are available upon request. The conclusions of both the discussions and the questionnaire distributed to all participants were summarized as follows: (1) SRP Methodology. Despite the fact that the molybdenum blue method for SRP determination provides varying results in different experimental conditions, as demonstrated by S. Tarapchak (Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan), these differences become less significant when working over a broad range of concentrations and with standardized pretreatment and analytical conditions (internal standards with elimination of salt effect and arsenate interference, standard filter size and filtered volume, constant reaction time, etc.). It was recommended to re-test the method further in view of Dr. Tarapchak's suggestions. (2) Utility of SRP and Continuation of Monitoring. SRP was found to represent a variable mixture of ortho-phosphorus and low molecular weight organic phosphorus, of which the availability of the organic or inorganic-organic fraction was, and could be, very different than ortho-phosphorus. SRP was recognized as a useful parameter for identifying regions of high phosphorus regeneration and upwelling events, hypolimnetic conditions, summer depletion and spatial and temporal trends, and success rate of P-controls. The problems in SRP interpretation arise primarily at extremely low levels, which is a common problem of any water quality parameter. SRP was considered to be an acceptable estimate of the soluble phosphorus fraction and believed to be available to lake biota. All participants were in favor of continuation of SRP measurements on a year-round basis in the lower Great Lakes, but some of them recommended discontinuation in offshore waters of Lakes Superior and Huron because of chronically
low values near the detection limit. Use of SRP in lake management programs was not considered a waste. (3) Alternatives to SRP. 32P-P0 4 turnover time seems to provide the most representative value for assessment of the pathways of P in the cells of aquatic organisms, and a system to track the readily available phosphorus pool (Lean 1973, Lean and Nalewajko 1979). However, it is not practically feasible to introduce this method into a routine operation for economic and work-safety reasons (isotope radioactivity). Developmental work on other alternative approaches (algal and bacterial bioassays, nutrient limitation and demand measurements, Lean and Pick 1981, etc.) should be emphasized and encouraged. SRP should be related more to community response and phosphorus exchange between biologically and chemically significant compartments. In the meantime, SRP data should continue to be gathered in the existing manner and subject to methodological retesting. (4) Kinetic Versus Static Approach. The workshop provided a useful forum to take a new look at SRP, introduced into water quality monitoring during the 1960s, when little was known about phosphorus turnover time, its physiological role, and P kinetics in general (Lean and White 1983, Nalewajko and Voltolina 1986, Nalewajko et al. 1986, and Peters 1978). SRP has been used as a static indicator of ambient concentrations remaining after removal of phosphorus from sewage treatment plant effluents (Nicholls et al. 1986, Robinson 1986). In this context, SRP has been a useful indicator of spatial and temporal trends. The recent findings on P kinetics have changed basic assumptions and have shown that even at undetectable P levels, microorganisms can still intensively utilize phosphorus in the food chain. The 1970s represented a whole new era in understanding the role and pathways of phosphorus (Tarapchak and Nalewajko 1986). It is, therefore, not surprising that there are conflicting interpretations as a result of basic differences between old, static, and new kinetic approach. Finally, despite its drawbacks at low levels, SRP is currently the most utilitarian mean of estimating dissolved phosphorus, although it does not provide full information on quantity and short-term/long-term bioavailability. (5) New Look at the Trophic State Controls in Great Lakes. The workshop provided an update of strategies on nutrient control problems in the Great Lakes basin. It is now true that eutrophica-
SOLUBLE REACTIVE PHOSPHORUS MEASUREMENTS
tion in the open water of the Great Lakes has been stabilized over the past 10 years in the face of continuing population expansion. Eutrophication in this respect is considered to be generally under control as long as the GLWQA's target loads are met. However, new developments must now be considered with equal seriousness. Eutrophication is not completely under control in near-shore areas which are still affected by the growths of Cladophora. Its frequent massive dieoffs still cause aesthetic problems and impairments of drinking water quality. Further, many of the IJC Areas of Concern are to a large degree affected by elevated nutrient inputs. Our nutrients control focus should therefore shift from the open lakes to the near-shore and to IJC Areas of Concern. Further, and perhaps of longer term significance is the analysis of the interactions of nutrients with toxic contaminants. This is a new emerging issue and research projects to address them are already underway. REFERENCES Barica, J., and Allan, R. J. 1987. An analysis of the
utility of SRP measurements in Great Lakes surveillance programs. National Water Research Institute Contribution No. 87-73, Burlington, Ontario. Dobson, H. F. H. 1984. Lake Ontario water chemistry atlas. Inland Waters Directorate, Burlington, Ontario. Scientific Series No. 139. EI-Shaarawi, A. H., and Nielson, M. A. 1984. Changes in nutrient levels of lake waters stored at 4°C. Can. J. Fish. Aquat. Sci. 41:985-988. Lean, D. R. S. 1973. Phosphorus dynamics in lake water. Science 179:678-680. _ _ _ _ , and Nalewajko, C. 1979. Phosphorus turnover time and phosphorus demand in large and small lakes. Arch. Hydrobiol. Beih. 13:120-132. _ _ _ _ , and Pick, F. R. 1981. Photosynthetic response of Lake Plankton to nutrient enrichment: a test for nutrient limitation. Limnol. Oceanogr. 26:1001-1019. _ _ _ _ , and White, E. 1983. Chemical and radiotracer measurements of phosphorus uptake by Lake Plankton. Can. J. Fish. A quat. Sci. 40:147-155. Nalewajko, C., and Voltolina, D. 1986. The effects of environmental variables of growth rates and physiological characteristics of Lake Superior phytoplankton. Can. J. Fish. Aquat. Sci. 43: 1163-1170. _ _ _ _ , Paul, B., Lee, K., and Shear, H. 1986. Light history, phosphorus status, and the occurrence
379
of light stimulation or inhibition of phosphate uptake in Lake Superior phytoplankton and bacteria. Can. J. Fish. Aquat. Sci. 43:329-335. Nicholls, K. H., Heinstch, L., Carney, E., Beaver, J., and Middleton, D. 1986. Some effects of phosphorus loading reductions on phytoplankton in the Bay of Quinte, Lake Ontario. In C. K. Minns, D. A. Hurley, and K. H. Nicholls (Eds.), Project Quinte:
Point-Source Phosphorus Control and Ecosystem Response in the Bay of Quinte, Lake Ontario, pp. 145-158. Can. Spec. Publ. Fish. Aquat. Sci. 86. Peters, R. H. 1978. Concentrations and kinetics of phosphorus fractions in streams entering Lake Memphremagog. J. Fish. Res. Board Can. 35: 315-328. Philbert, F. J. 1973. The effect of sample preservation by freezing prior to chemical analysis of Great Lakes waters. In Proc. 16th Con! Great Lakes Res., pp. 282-293. Internat. Assoc. Great Lakes Res. Rigler, F. H. 1966. Radiobiological analysis of inorganic phosphorus in lake water. Verh. Int. Ver. Theor. Angew. Limnol. 16:465-470. _ _ _ _ . 1968. Further observations inconsistent with the hypothesis that the molybdenum blue method measures orthophosphate in lake water. Limnolo Oceanogr. 13:7-13. Robinson, G. W. 1986. Water quality of the Bay of Quinte, Lake Ontario, before and after reductions in phosphorus loading. In C. K. Minns, D. A. Hurley, and K. H. Nicholls (Eds.), Project QUinte: Point-
Source Phosphorus Control and Ecosystem Response in the Bay of Quinte, Lake Ontario, pp. 50-58. Can. Spec. Pub I. Fish. Aquat. Sci. 86. Tarapchak, S. J., and Nalewajko, C. 1986. Introduction: phosphorus-plankton dynamics symposium. Can. J. Fish. Aquat. Sci. 43:293-301. _ _ _ _ , and Rubitschun, C., 1981. Comparison of soluble reactive phosphorus and orthophosphorus concentrations at an offshore station in southern Lake Michigan. J. Great Lakes Res. 7:290-298. _ _ _ _ , Chambers, R. L., and Bigelow, S. M., 1982a. Soluble reactive phosphorus measurements in Lake Michigan: causes of method-specific differences. J. Great Lakes Res. 8:700-710. _ _ _ _ Chambers, R. L., and Rubitschun, 1982b. Soluble reactive phosphorus measurements in Lake Michigan: filtration artifacts. J. Great Lakes Res. 8:550-557. _ _ _ _ , Bigelow, S. M., and Rubitschun, C. 1982c. Overestimation of ortho-phosphorus concentrations in surface waters of southern Lake Michigan: effects of acid and ammonium molybdate. Can. J. Fish. Aquat. Sci. 39:296-304.