McMurdo LTER: Phytoplankton nutrient deficiency in ...
tively high rates of sulfate reduction and methane production occur close to the sediment-water interface in Lake Fryxell (Howes and Smith 1990). All these data indicate that Lake Fryxell, and perhaps the west lobe of Lake Bonney, will have CaCO3 dynamics dominated by biological activity, whereas the other two lakes, especially Lake Hoare, may not. Our aim is, in part, to compare and contrast the affects of high biological vs. low biological activities on the dynamics (i.e., production and dissolution) of CaCO3 in these lake systems. This research was supported by National Science Foundation grant OPP 92-11773. Special thanks are given to L. Mastro, A. Butt, G. Dana, and P. Doran for help with sample collection.
References Bird, M.I., A.R. Chivas, C.J. Randell, and H.R. Burton. 1991. Sedimentological and stable-isotope evolution of lakes in the Vestfold Hills, Antarctica. Palaeogeography, Palaeoclimatology, and Palaeoecology, 84, 109-130. DeMora, S.J., R.F. Whitehead, and M. Gregory. 1991. Aqueous geochemistry of major constituents in the Mph River and its tributaries in Walcott Bay, Victoria Land, Antarctica. Antarctic Science, 3, 73-86. Green, W.J., M.P. Angle, and K.E. Chave. 1988. The geochemistry of antarctic streams and their role in the evolution of four lakes in
the McMurdo Dry Valleys. Geochimica et Cosmochimica Acta, 52, 1265-1274. Green, W.J., and D.E. Canfield. 1984. Geochemistry of the Onyx River and its role in the chemical evolution of Lake Vanda. Geochimica et CosmochimicaActa, 48, 2457-2467. Howes, B.L., and R.L. Smith. 1990. Sulfur cycling in a permanently ice-covered amictic antarctic lake, Lake Fryxell. Antarctic Journal of the U.S., 25(5), 230-232. Keys, J.R., and K. Williams. 1981. Origin of crystalline, cold desert salts in the McMurdo region, Antarctica. Geochimica et Cosmochimica Acta, 45, 2299-2309. Lawrence, M.J.F., and C.H. Hendy. 1989. Carbonate deposition and Ross Sea ice advance, Fryxell Basin, Taylor Valley, Antarctica. New Zealand Journal of Geology and Geophysics, 32, 267-277. Priscu, J.C. 1994. McMurdo LTER: Phytoplankton nutrient deficiency in lakes of the Taylor Valley, Antarctica. Antarctic Journal of the U.S., 29(5). Vincent, W.F. 1988. Microbial ecosystems of Antarctica. Cambridge: Cambridge University Press. Welch, K.A., P.A. Mayewski, J.E. Dibb, M.S. Twickler, and S.I. Whitlow. In preparation. Marine and polar continental air mass influence in glaciochemical records from the Dry Valley region of Antarctica. Atmospheric Environment. Wharton, R.A., Jr., W.B. Lyons, and D.J. Des Marais. 1993. Stable isotope biogeochemistry of carbon and nitrogen in a perennially icecovered antarctic lake. Chemical Geology, 107, 159-172. Wharton, R.A., Jr., B.C. Parker, and G.M. Simmons, Jr. 1983. Distribution, species composition and morphology of algal mats in antarctic dry valley lakes. Phycologia, 22, 355-365.
McMurdo LTER: Phytoplankton nutrient deficiency in lakes of the Taylor Valley, Antarctica JOHN C. PRISCu, Department
of Biology, Montana State University, Bozeman, Montana 59717
revious reports on nutrient deficiencies in antarctic lakes p have been based on indirect evidence such as nitrogento-phosphorus ratios in the water column (Vincent 1981; Priscu et al. 1989), nutrient ratios in streams entering the lakes (Canfield and Green 1985), and direct measurement of nitrogen uptake using nitrogen-15 labeled compounds (Priscu 1989, pp. 173-182; Priscu et al. 1989). With the inception of studies focusing on photosynthesis (Priscu et al. 1990), nitrogen transformations (e.g., Priscu, Ward, and Downes 1993), and long-term ecological research (Wharton, Antarctic Journal, in this issue) in the lakes of the dry valley region of McMurdo Sound, knowledge of nutrient regulation of primary productivity in these systems is imperative. This article presents results from experimental nutrient (nitrogen and phosphorus) bioassays conducted on Lakes Bonney (east and west lobes), Hoare, Fryxell, and Vanda. Experiments were conducted on phytoplankton populations at 5, 13, and 18 meters and 5 and 13 meters in the east and west lobes of Lake Bonney, respectively, and at 5 meters in Lakes Hoare, Fryxell, and Vanda. The depths selected for Lake Bonney were from phytoplankton biomass and productivity maxima; those for the other lakes represent the phytoplankton
populations immediately beneath the permanent ice covers. All experiments were conducted at the Lake Bonney field camp during November and December 1993. A 4-liter sample was enriched with carbon-14 bicarbonate (0.1 to 0.2 microcuries per milliliter (mL) final concentration), and 500 mL was decanted into each of eight acid-washed high-density polyethylene bottles. Two bottles each were then enriched with 20 micromolar (!IM) ammonium, 2 tM phosphorus, and 20 iM ammonium plus 2 tM phosphorus; 2 nonamended bottles served as controls. All bottles were placed in an environmental chamber that simulated light and temperature conditions from which the samples were collected. Subsamples (80 mL) were removed from each bottle at 24-hour intervals (for 144 hours) and filtered through Whatman GF/F filters. The filters were acidified with 0.5 mL of 3 normal hydrochloric acid and dried at 50°C to remove unincorporated isotope. Radioactivity on the filters (which represents photosynthetic activity) was determined by standard liquid scintillation spectrometry at McMurdo Station. Nutrient chemistry was measured using methods described by Sharp and Priscu (1990). Photosynthesis in all phytoplankton populations sampled from Lake Bonney was stimulated strongly, relative to the non-
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1000000 amended controls, by phosBONNEY, E30, 13m AIBONNEY, E30, 18m phorus enrichment alone (fig- BONNEY, E30, 5m 7500 ure 1). Simultaneous enrich- 750000 ment with phosphorus plus H MD ^D 500000 nitrogen enhanced photosynthesis over that of phosphorus MiO alone at 5 meters in both 250000 lobes. Photosynthesis in Lake Bonney was never stimulated ^4 150 50 100 150 0 50 by the addition of nitrogen TIME (hours) alone. Simultaneous addition Cl) of phosphorus and nitrogen also resulted in the greatest increase in photosynthesis in < 200000 BONNEY, W20, 13m Lakes Hoare and Fryxell (figure BONNEY, W20, 5m o CONTROL 2). Single addition of phospho+ • +20 AM NH rus elevated photosynthetic H -3 rate significantly over the con+2 AM PO4 trol in Lake Hoare whereas ni- cr N+P trogen addition alone showed a stronger stimulatory effect 0•• than phosphorus in Lake Fryx- 00 0 50 100 150 ell. Photosynthesis in nutrient IME (hours) amended treatments were all below the control in Lake Figure 1. Results from nutrient bioassay experiments conducted between November and December 1993 in Lake Bonney. Disintegrations per minute represents the amount of carbon-14 bicarbonate incorporated into Vanda (figure 2). Results from these time- phytoplankton via photosynthesis. course bioassay experiments indicate that all phytoplankton populations in Lake Bonney are strongly deficient in phosphorus. That simultaneous nitrogen and phosphorus addition resulted in even higher stimulation in the 5-meter populations implies a possible colimitation by these nutrients (Dodds, Johnson, and Priscu 1989). Nutrient stimulation relative to control samples Edecreased in the deeper samples indicating a lower degree of nutrient deficiency with depth. Dissolved inorganic nitrogen (DIN=nitrate plus nitrite plus ammonium) to soluble reactive L. FRYXELL 5m phosphorous (SRP) ratios in Lake Bonney were all greater than that required for balanced growth in algae (16 by atoms; 5000 Redfield, Ketchum, and Richards 1963, pp. 26-77) supporting U) the bioassay experiments that indicate a phosphorus defiZ ciency system. '-5 DIN:SRP ratios in Lakes Hoare and Fryxell were below that required for balanced algal growth (table) implying potentially nitrogen-deficient systems. Nitrogen deficiency is r 11 supported in part by the Lake Fryxell bioassay experiments, which showed that nitrogen addition alone stimulated photoz synthesis more than phosphorus addition. The low DIN:SRP Cl) ratio at 5 meters in Lake Hoare is not supported by the nutrient bioassays. Because little is known about temporal dynamics (i.e., turnover times) of phosphorus vs. nitrogen pools in these lakes, implications regarding nutrient deficiencies based on pool sizes can be misleading and remain equivocal. Bioassay results from Lake Vanda show that nutrient additions actually lowered photosynthetic activity relative to TIME (hours) the control. The time-course profile also shows no net photoFigure 2. As in figure 1 except data from Lakes, Hoare, Fryxell, and synthetic activity in the sample from the time of the first Vanda.
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Chlorophyll concentration (Chl, micrograms per liter), nutrient concentration (MM), and nutrient ratios (by atoms) from lakes and depths (meters) where nutrient bioassay experiments were conducted
References
Canfield, D.E., and W.J. Green. 1985. The cycling of nutrients in a closed-basin antarctic lake: Lake Biogeochemistry, 1, Ii:l']Ii:i i Dodds, W.K., K.R. Johnson, and J.C.
Bonney 5 1.42 4.74 0.06 0.65 5. 45 0.10 54.50 Priscu. 1989. Simultaneous nitro(east) gen and phosphorus deficiency in 13 1.20 21.54 0.19 0.86 22. so 0.19 118.90 natural phytoplankton assem18 0.33 55.94 0.94 14.37 71. 25 0.10 712.50 blages: Theory, empirical evidence, Bonney 5 1.42 7.69 0.13 0.82 8. 4 0.18 48.00 and implications for lake management. Lake and Reservoir Manage(west) 13 6.23 30.13 0.21 0.71 31.()5 0.14 221.79
ment, 1, 21-26.
Hoare 5 1.63 0.01 0.01 0.00 0.1)2 0.54 0.04 Priscu, J.C. 1989. Photon dependence
Fryxell 5 5.79 0.01 0.02 0.08 0:11 0.64 0.17 of inorganic nitrogen transport by
measurement (24 hours) to 120 hours. It should be noted that, owing to helicopter logistics, the sample collected at Lake Vanda remained in the dark for more than 10 hours in the collection carboy before processing. Together, these facts imply that the phytoplankton suffered physiological damage during sample storage. Consequently, bioassay results from Lake Vanda should be treated as suspect. The DIN:SRP ratios (table), however, indicate that Lake Vanda was phosphorus deficient, at least to the extent that one can assume that the nitrogen and phosphorus pools have similar turnover times. These nutrient bioassay experiments are the first to address directly nutrient deficiency miakes of the McMurdo Dry Valleys. To obtain a more thorough view of nutrient deficiency in these lakes, temporal experiments should be conducted over the phytoplankton growing season and should include samples from the phytoplankton maxima within each lake. I thank Richard Bartlett, Cristopher Woolston, Vann Kalbach, and Rob Edwards for field and laboratory assistance. This research was supported by National Science Foundation grants OPP 91-17907 and OPP 92-11773 to J.C. Priscu.
phytoplankton in antarctic lakes. In W.F. Vincent and E. Ellis-Evans (Eds.), High latitude limnology (Hydrobiology 172). The Netherlands: Kiewer Press. Priscu, J.C., T.R. Sharp, M.P. Lizotte, and P.J. Neale. 1990. Photoadaptation by phytoplankton in permanently ice-covered antarctic lakes: Response to a nonturbulent environment. Antarctic Journal of the U.S., 25(5), 221-222. Priscu, J.C., W.F. Vincent, and C. Howard-Williams. 1989. Inorganic nitrogen uptake and regeneration in perennially ice-covered Lakes Fryxell and Vanda, Antarctica. Journal of Plankton Research, 11(2),335-351. Priscu, J.C., B.B. Ward, and M.T. Downes. 1993. Water column transformations of nitrogen in Lake Bonney, a perennially ice-covered antarctic lake. Antarctic Journal of the U.S., 26(5), 237-239. Redfield, A.C., B.H. Ketchum, and F.A. Richards. 1963. The influence of organisms on the composition of seawater. In M.N. Hill (Ed.), The Sea (Vol. 2). New York: Wiley Interscience. Sharp, T.R., and J.C. Priscu. 1990. Ambient nutrient levels and the effects of nutrient enrichment on primary productivity in Lake Bonney. Antarctic Journal of the U.S., 25(5), 226-227. Vincent, W.F. 1981. Production strategies in antarctic inland waters: Phytoplanklon eco-physiology in a permanent ice-covered lake. Ecology, 62(5), 1215-1224. Wharton, R.A., Jr. 1994. McMurdo Dry Valleys Long-Term Ecological Research (LTER): An overview of 1993-1994 activities. Antarctic Journal of the U.S., 29(5).
McMurdo LTER: Primary production model of benthic microbial mats in Lake Hoare, Antarctica DARYL L. MOORHEAD, Ecology
Program, Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409-3131 Desert Research Institute, Reno, Nevada 89506
ROBERT A. WHARTON, JR.,
icrobial mats are found throughout much of the benthM ic regions of antarctic lakes and streams and are composed primarily of cyanobacteria (e.g., Phormidium, Oscillatoria, and Lyngbya), pennate diatoms, and eubacteria (Vincent 1988). The perennially ice-covered lakes of Taylor Valley, southern Victoria Land, Antarctica, have well-developed benthic microbial communities (Wharton, Parker, and Sim-
mons 1983). In places, portions of these mats tear loose (liftoff) from the sediments and float to the surface, where they are frozen within the overlying ice. This material is transferred through the ice by ablation and distributed by wind throughout the valley (Parker et al. 1982). The extremely low productivities of terrestrial ecosystems in this region suggest that allochthonous inputs of microbial mat may be
ANTARCTIC JOURNAL - REVIEW 1994 241
References Bird, M.I., A.R. Chivas, C.J. Randell, and H.R. Burton. 1991. Sedimentological and stable-isotope evolution of lakes in the Vestfold Hills, Antarctica. Palaeogeography, Palaeoclimatology, and Palaeoecology, 84, 109-130. DeMora, S.J., R.F. Whitehead, and M. Gregory. 1991. Aqueous geochemistry of major constituents in the Mph River and its tributaries in Walcott Bay, Victoria Land, Antarctica. Antarctic Science, 3, 73-86. Green, W.J., M.P. Angle, and K.E. Chave. 1988. The geochemistry of antarctic streams and their role in the evolution of four lakes in
the McMurdo Dry Valleys. Geochimica et Cosmochimica Acta, 52, 1265-1274. Green, W.J., and D.E. Canfield. 1984. Geochemistry of the Onyx River and its role in the chemical evolution of Lake Vanda. Geochimica et CosmochimicaActa, 48, 2457-2467. Howes, B.L., and R.L. Smith. 1990. Sulfur cycling in a permanently ice-covered amictic antarctic lake, Lake Fryxell. Antarctic Journal of the U.S., 25(5), 230-232. Keys, J.R., and K. Williams. 1981. Origin of crystalline, cold desert salts in the McMurdo region, Antarctica. Geochimica et Cosmochimica Acta, 45, 2299-2309. Lawrence, M.J.F., and C.H. Hendy. 1989. Carbonate deposition and Ross Sea ice advance, Fryxell Basin, Taylor Valley, Antarctica. New Zealand Journal of Geology and Geophysics, 32, 267-277. Priscu, J.C. 1994. McMurdo LTER: Phytoplankton nutrient deficiency in lakes of the Taylor Valley, Antarctica. Antarctic Journal of the U.S., 29(5). Vincent, W.F. 1988. Microbial ecosystems of Antarctica. Cambridge: Cambridge University Press. Welch, K.A., P.A. Mayewski, J.E. Dibb, M.S. Twickler, and S.I. Whitlow. In preparation. Marine and polar continental air mass influence in glaciochemical records from the Dry Valley region of Antarctica. Atmospheric Environment. Wharton, R.A., Jr., W.B. Lyons, and D.J. Des Marais. 1993. Stable isotope biogeochemistry of carbon and nitrogen in a perennially icecovered antarctic lake. Chemical Geology, 107, 159-172. Wharton, R.A., Jr., B.C. Parker, and G.M. Simmons, Jr. 1983. Distribution, species composition and morphology of algal mats in antarctic dry valley lakes. Phycologia, 22, 355-365.
McMurdo LTER: Phytoplankton nutrient deficiency in lakes of the Taylor Valley, Antarctica JOHN C. PRISCu, Department
of Biology, Montana State University, Bozeman, Montana 59717
revious reports on nutrient deficiencies in antarctic lakes p have been based on indirect evidence such as nitrogento-phosphorus ratios in the water column (Vincent 1981; Priscu et al. 1989), nutrient ratios in streams entering the lakes (Canfield and Green 1985), and direct measurement of nitrogen uptake using nitrogen-15 labeled compounds (Priscu 1989, pp. 173-182; Priscu et al. 1989). With the inception of studies focusing on photosynthesis (Priscu et al. 1990), nitrogen transformations (e.g., Priscu, Ward, and Downes 1993), and long-term ecological research (Wharton, Antarctic Journal, in this issue) in the lakes of the dry valley region of McMurdo Sound, knowledge of nutrient regulation of primary productivity in these systems is imperative. This article presents results from experimental nutrient (nitrogen and phosphorus) bioassays conducted on Lakes Bonney (east and west lobes), Hoare, Fryxell, and Vanda. Experiments were conducted on phytoplankton populations at 5, 13, and 18 meters and 5 and 13 meters in the east and west lobes of Lake Bonney, respectively, and at 5 meters in Lakes Hoare, Fryxell, and Vanda. The depths selected for Lake Bonney were from phytoplankton biomass and productivity maxima; those for the other lakes represent the phytoplankton
populations immediately beneath the permanent ice covers. All experiments were conducted at the Lake Bonney field camp during November and December 1993. A 4-liter sample was enriched with carbon-14 bicarbonate (0.1 to 0.2 microcuries per milliliter (mL) final concentration), and 500 mL was decanted into each of eight acid-washed high-density polyethylene bottles. Two bottles each were then enriched with 20 micromolar (!IM) ammonium, 2 tM phosphorus, and 20 iM ammonium plus 2 tM phosphorus; 2 nonamended bottles served as controls. All bottles were placed in an environmental chamber that simulated light and temperature conditions from which the samples were collected. Subsamples (80 mL) were removed from each bottle at 24-hour intervals (for 144 hours) and filtered through Whatman GF/F filters. The filters were acidified with 0.5 mL of 3 normal hydrochloric acid and dried at 50°C to remove unincorporated isotope. Radioactivity on the filters (which represents photosynthetic activity) was determined by standard liquid scintillation spectrometry at McMurdo Station. Nutrient chemistry was measured using methods described by Sharp and Priscu (1990). Photosynthesis in all phytoplankton populations sampled from Lake Bonney was stimulated strongly, relative to the non-
ANTARCTIC JOURNAL - REVIEW 1994
239
1000000 amended controls, by phosBONNEY, E30, 13m AIBONNEY, E30, 18m phorus enrichment alone (fig- BONNEY, E30, 5m 7500 ure 1). Simultaneous enrich- 750000 ment with phosphorus plus H MD ^D 500000 nitrogen enhanced photosynthesis over that of phosphorus MiO alone at 5 meters in both 250000 lobes. Photosynthesis in Lake Bonney was never stimulated ^4 150 50 100 150 0 50 by the addition of nitrogen TIME (hours) alone. Simultaneous addition Cl) of phosphorus and nitrogen also resulted in the greatest increase in photosynthesis in < 200000 BONNEY, W20, 13m Lakes Hoare and Fryxell (figure BONNEY, W20, 5m o CONTROL 2). Single addition of phospho+ • +20 AM NH rus elevated photosynthetic H -3 rate significantly over the con+2 AM PO4 trol in Lake Hoare whereas ni- cr N+P trogen addition alone showed a stronger stimulatory effect 0•• than phosphorus in Lake Fryx- 00 0 50 100 150 ell. Photosynthesis in nutrient IME (hours) amended treatments were all below the control in Lake Figure 1. Results from nutrient bioassay experiments conducted between November and December 1993 in Lake Bonney. Disintegrations per minute represents the amount of carbon-14 bicarbonate incorporated into Vanda (figure 2). Results from these time- phytoplankton via photosynthesis. course bioassay experiments indicate that all phytoplankton populations in Lake Bonney are strongly deficient in phosphorus. That simultaneous nitrogen and phosphorus addition resulted in even higher stimulation in the 5-meter populations implies a possible colimitation by these nutrients (Dodds, Johnson, and Priscu 1989). Nutrient stimulation relative to control samples Edecreased in the deeper samples indicating a lower degree of nutrient deficiency with depth. Dissolved inorganic nitrogen (DIN=nitrate plus nitrite plus ammonium) to soluble reactive L. FRYXELL 5m phosphorous (SRP) ratios in Lake Bonney were all greater than that required for balanced growth in algae (16 by atoms; 5000 Redfield, Ketchum, and Richards 1963, pp. 26-77) supporting U) the bioassay experiments that indicate a phosphorus defiZ ciency system. '-5 DIN:SRP ratios in Lakes Hoare and Fryxell were below that required for balanced algal growth (table) implying potentially nitrogen-deficient systems. Nitrogen deficiency is r 11 supported in part by the Lake Fryxell bioassay experiments, which showed that nitrogen addition alone stimulated photoz synthesis more than phosphorus addition. The low DIN:SRP Cl) ratio at 5 meters in Lake Hoare is not supported by the nutrient bioassays. Because little is known about temporal dynamics (i.e., turnover times) of phosphorus vs. nitrogen pools in these lakes, implications regarding nutrient deficiencies based on pool sizes can be misleading and remain equivocal. Bioassay results from Lake Vanda show that nutrient additions actually lowered photosynthetic activity relative to TIME (hours) the control. The time-course profile also shows no net photoFigure 2. As in figure 1 except data from Lakes, Hoare, Fryxell, and synthetic activity in the sample from the time of the first Vanda.
oLi
tOO 150
100000
150
50 100
25000
0
50
tOO
750O
2500
2000
1500
D
ANTARCTIC JOURNAL
240
—
REVIEW
1994
50
too
150
Chlorophyll concentration (Chl, micrograms per liter), nutrient concentration (MM), and nutrient ratios (by atoms) from lakes and depths (meters) where nutrient bioassay experiments were conducted
References
Canfield, D.E., and W.J. Green. 1985. The cycling of nutrients in a closed-basin antarctic lake: Lake Biogeochemistry, 1, Ii:l']Ii:i i Dodds, W.K., K.R. Johnson, and J.C.
Bonney 5 1.42 4.74 0.06 0.65 5. 45 0.10 54.50 Priscu. 1989. Simultaneous nitro(east) gen and phosphorus deficiency in 13 1.20 21.54 0.19 0.86 22. so 0.19 118.90 natural phytoplankton assem18 0.33 55.94 0.94 14.37 71. 25 0.10 712.50 blages: Theory, empirical evidence, Bonney 5 1.42 7.69 0.13 0.82 8. 4 0.18 48.00 and implications for lake management. Lake and Reservoir Manage(west) 13 6.23 30.13 0.21 0.71 31.()5 0.14 221.79
ment, 1, 21-26.
Hoare 5 1.63 0.01 0.01 0.00 0.1)2 0.54 0.04 Priscu, J.C. 1989. Photon dependence
Fryxell 5 5.79 0.01 0.02 0.08 0:11 0.64 0.17 of inorganic nitrogen transport by
measurement (24 hours) to 120 hours. It should be noted that, owing to helicopter logistics, the sample collected at Lake Vanda remained in the dark for more than 10 hours in the collection carboy before processing. Together, these facts imply that the phytoplankton suffered physiological damage during sample storage. Consequently, bioassay results from Lake Vanda should be treated as suspect. The DIN:SRP ratios (table), however, indicate that Lake Vanda was phosphorus deficient, at least to the extent that one can assume that the nitrogen and phosphorus pools have similar turnover times. These nutrient bioassay experiments are the first to address directly nutrient deficiency miakes of the McMurdo Dry Valleys. To obtain a more thorough view of nutrient deficiency in these lakes, temporal experiments should be conducted over the phytoplankton growing season and should include samples from the phytoplankton maxima within each lake. I thank Richard Bartlett, Cristopher Woolston, Vann Kalbach, and Rob Edwards for field and laboratory assistance. This research was supported by National Science Foundation grants OPP 91-17907 and OPP 92-11773 to J.C. Priscu.
phytoplankton in antarctic lakes. In W.F. Vincent and E. Ellis-Evans (Eds.), High latitude limnology (Hydrobiology 172). The Netherlands: Kiewer Press. Priscu, J.C., T.R. Sharp, M.P. Lizotte, and P.J. Neale. 1990. Photoadaptation by phytoplankton in permanently ice-covered antarctic lakes: Response to a nonturbulent environment. Antarctic Journal of the U.S., 25(5), 221-222. Priscu, J.C., W.F. Vincent, and C. Howard-Williams. 1989. Inorganic nitrogen uptake and regeneration in perennially ice-covered Lakes Fryxell and Vanda, Antarctica. Journal of Plankton Research, 11(2),335-351. Priscu, J.C., B.B. Ward, and M.T. Downes. 1993. Water column transformations of nitrogen in Lake Bonney, a perennially ice-covered antarctic lake. Antarctic Journal of the U.S., 26(5), 237-239. Redfield, A.C., B.H. Ketchum, and F.A. Richards. 1963. The influence of organisms on the composition of seawater. In M.N. Hill (Ed.), The Sea (Vol. 2). New York: Wiley Interscience. Sharp, T.R., and J.C. Priscu. 1990. Ambient nutrient levels and the effects of nutrient enrichment on primary productivity in Lake Bonney. Antarctic Journal of the U.S., 25(5), 226-227. Vincent, W.F. 1981. Production strategies in antarctic inland waters: Phytoplanklon eco-physiology in a permanent ice-covered lake. Ecology, 62(5), 1215-1224. Wharton, R.A., Jr. 1994. McMurdo Dry Valleys Long-Term Ecological Research (LTER): An overview of 1993-1994 activities. Antarctic Journal of the U.S., 29(5).
McMurdo LTER: Primary production model of benthic microbial mats in Lake Hoare, Antarctica DARYL L. MOORHEAD, Ecology
Program, Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409-3131 Desert Research Institute, Reno, Nevada 89506
ROBERT A. WHARTON, JR.,
icrobial mats are found throughout much of the benthM ic regions of antarctic lakes and streams and are composed primarily of cyanobacteria (e.g., Phormidium, Oscillatoria, and Lyngbya), pennate diatoms, and eubacteria (Vincent 1988). The perennially ice-covered lakes of Taylor Valley, southern Victoria Land, Antarctica, have well-developed benthic microbial communities (Wharton, Parker, and Sim-
mons 1983). In places, portions of these mats tear loose (liftoff) from the sediments and float to the surface, where they are frozen within the overlying ice. This material is transferred through the ice by ablation and distributed by wind throughout the valley (Parker et al. 1982). The extremely low productivities of terrestrial ecosystems in this region suggest that allochthonous inputs of microbial mat may be
ANTARCTIC JOURNAL - REVIEW 1994 241
