during the initial 6 years of the project. This work is supportedby National Science Foundation grant OPP 92-11773.

ReferencesChinn, T.H. 1979. Hydrologic Research Report, Dry Valleys, Antarctica,

1972-73. Wellington: New Zealand Ministry of Works and Devel-opment.

Chinn, T.H. 1993. Physical hydrology of the dry valley lakes. In W.J.Green and E.I. Friedmann (Eds.), Physical and biogeochemicalprocesses in antarctic lakes (Antarctic Research Series, Vol. 59).Washington, D.C.: American Geophysical Union.

Green, W.J., T.J. Gardner, T.G. Ferdelman, M.P. Angle, L.C. Varner,and P. Nixon. 1989. Geochemical processes in the Lake FryxellBasin (Victorialand, Antarctica). In W.I. Vincent and J.C. Ellis-Evans (Eds.), Hydrobiologia 172. Belgium: Kluwer.

Rantz, S.E., and others. 1982a. Measurement and computation ofstream/low: Volume 1, Measurement of stage and discharge (U.S.Geological Survey Water-Supply Paper 2175). Washington, D.C.:U.S. Government Printing Office.

Rantz, S.E., and others. 1982b. Measurement and computation ofstream/low: Volume 2, Computation of discharge (U.S. GeologicalSurvey Water-Supply Paper 2175). Washington, D.C.: U.S. Govern-ment Printing Office.

McMurdo LTER: Using narrow band spectroradiometry toassess algal and moss communities in a dry valley stream

GAYLE L. DANA, Biological Sciences Center, Desert Research Institute, Reno, Nevada 89506CATHY M. TATE, Water Resources Division, U.S. Geological Survey, Denver, Colorado 80225

SHARON L. DEWEY, Kansas Remote Sensing Program, University of Kansas, Lawrence, Kansas 66045

An objective of the Long-Term Ecological Research (LTER)project in the McMurdo Dry Valleys is to understand

processes regulating productivity, biomass, and distributionof the stream communities using a combination of long-termmonitoring, in situ experiments, and modeling. Algal matand moss communities that grow in and along the margins ofantarctic streams become active during a short period in theaustral summer when temperatures and meltwater are suffi-cient to promote growth. Some streams are known to sup-port high biomass (2-400 milligrams of chlorophyll-a persquare meter), but production rates are at the low range forfreshwater communities (Vincent et al. 1993). Removalprocesses, such as wind, flood scouring, and grazing by pro-tozoans and micrometazoans, may regulate biomass accu-mulations since light and nutrients are not limiting factorsfor algal growth (Howard-Williams and Vincent 1989). Addi-tional controlling factors may include variable streamfiow,freeze-thaw events, and winter desiccation. In turn, the matsare likely to influence downstream soil and lake ecosystemsby removing and transforming nutrients.

Spectroradiometry may be useful in accomplishing sev-eral LTER goals, including assessing distribution, biomass,and nutrient status of the stream communities. The ability ofa plant to reflect or absorb light is dependent on its morpho-logical and chemical characteristics which, in turn, are afunction of plant development, health, and growing condi-tions. The relation between spectral reflectivity and plant sta-tus makes spectroradiometry a potential tool for studyingecological features of plant populations. In this article, weexplore the use of close-range remote-sensing techniques forassessing algal and moss communities of the streams withinthe McMurdo Dry Valleys.

In January 1994, we measured spectral and pigmentcharacteristics of the six dominant algal and moss communi-ties of the Canada Stream in the Lake Fryxell basin, Taylor

Valley. The assemblages are identified here according to theircolor: orange-colored, red-colored, green-colored, or black-colored algae, and green or black moss. Taxonomic identifi-cation is currently in progress; however, previous studiesindicate that the algal mats are dominated by cyanobacteria(Vincent et al. 1993). Spectral-reflectance measurementswere taken from each assemblage by using a handheld spec-troradiometer (Model PSII, Analytical Spectral Devices, Inc.),which measures in 512 bands of about 1.4-nanometer (nm)width between about 350 and 1,000 nm wavelength. Datawere collected between 1000-1400 hours during cloud-freeperiods. Spectra were taken 5 centimeters (cm) above eachsample resulting in a circular field of view of 0.2-cm diame-ter. Algae and mosses were briefly removed from the streamto obtain spectra because flowing water complicated andreduced the spectral signal. Chlorophyll-a and carotenoidswere analyzed using the trichromatic method (Strickland andParsons 1968).

Green-colored moss and red-colored, orange-colored,and green-colored algae exhibited reflectance patterns typi-cal of vegetation; the greatest reflectance occurred in thenear infrared (NIR, 700-800 nm) and absorption in the blue(400-500 nm) and red (600-700 nm) regions of the electro-magnetic spectrum (figure). Absorption in the blue region islikely due to carotenoids, which absorb maximally in the400-550-nm range (Vincent et al. 1993), whereas absorptionin the red region corresponds to the maximum chlorophyll-aabsorption at 680 nm. Chlorophyll-a concentrations in theseassemblages ranged between 5 and 8.8 micrograms persquare centimeter (sg CM-2) and carotenoids between 4.5and 11.2 sg CM-2 (table). Although all phototrophic algaecontain chlorophyll-a, they can be distinctly colored by otherpigments. This range of pigmentation contributes to the vari-ation in spectral signatures observed in the Taylor Valleymats. For example, the red-colored algae are distinguished

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CU0Q)

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by having an additional, smallabsorption feature centered at630 nm, possibly due to the pig-ment phycocyanin, which ab-sorbs maximally at 620 nm (Vin-cent et al. 1993).

Spectral patterns of theblack-colored algae and black-colored moss were markedly dif-

400500600700800900ferent from that of the other fourstream assemblages (figure).Reflectance gradually increasedfrom 400 to 900 nm and despitethe high chlorophyll concentra-tions found in the black-coloredalgae (41.8 .tg cm-2 ; table) theabsorption feature usually asso-ciated with chlorophyll at 680nm is not obvious compared toother algal types (figure). Chlor-

600700800900ophyll-a absorption is maskeddue to the high absorption of allspectral bands by the combined"black" pigments of this assem-blage, leaving no reflectancepeaks (green and NIR) to con-trast with the high red absorp-tion. Black-colored moss, whichwas not as darkly pigmented asthe black-colored algae, reflect -ed higher at all wavelengths than

600700 800 900the black-colored algae and dis-played a slight chlorophyll-aabsorption feature. Chlorophyll-a and carotenoid concentrations

Percentage reflectance of algal and moss assemblages along the Canada Stream, Taylor Valley. Each for black-colored moss were 16.8spectra is the average of 10 samples taken from one position over the assemblage. and 32.3 ULY cm-2 . resnectivelv

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Pigment content and ND VI of Canada Stream algaeNOTE: Samples for pigment analysis were taken 81anuary 1994for all assemblages except black algae, which was collected 13January 1994. Pigment concentrations were not available forgreen moss. NDVI was calculated from spectra taken on 13 Jan-uary 1994 as ND VI=Maximum NIR/Minimum red where NIR isthe near infrared reflectance within the range 700-800 nm, andred is reflectance within 600-700 nm.

Orange-colored algae6.410.2 1.91Red-colored algae5.011.2 1.54Green-colored algae8.84.5 5.16Black-colored algae41.866.9 1.94Green-colored moss- 2.62Black-colored moss16.832.3 1.38

(table).Spectral analysis has been used to estimate biomass and

productivity in aquatic vegetation (e.g., Dewey et al. 1993;Peñuelas et al. 1993). Several indexes have been correlatedwith biomass, including the normalized difference vegetativeindex (NDVI; NDVI=ratio of maximum NIR:minimumreflectance; table), with highly variable results due to vegeta-tive type and influences of background substrate. The use ofa narrow-band NDVI as a biomass predictor of the CanadaStream assemblages was less than satisfactory. No relation-ship between the NDVI and pigment analysis was apparent(table). Variable vegetation type (algae vs. mosses) and three-dimensional structure of the assemblage may be factors con-tributing to the lack of predictive power of the NDVI. Also,the general lack of contrast in spectral reflectance from theblack-colored algae and black-colored mosses makes it diffi -cult to apply classical vegetation indexes, such as the NDVI,which are based on contrast.

The spectral data illustrate the potential for using spec-tral reflectance patterns, spectral biomass indices, and

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changes in the near infrared reflectance as tools for studyingecological features of the algal and moss communities in andalong dry valley streams. The acquisition of ecologicallymeaningful spectral data will require a thorough investiga-tion of the relationships between spectral features and bio-mass, physiological status, pigment content, three-dimen-sional structure of the assemblage, production, and nutrientstatus of dry valley stream communities.

This work was supported by National Science Founda-tion grant OPP 92-11773 and an Institutional Project Assign-ment grant from the Desert Research Institute, Reno, Neva-da. We thank the Desert Research Institute for the use of theASD PSI! Spectrometer, M. Anthony for chlorophyll analysis,and D.M. McKnight for field assistance and advice. Use oftrade names in this article is for identification purposes onlyand does not constitute endorsement by the U.S. GeologicalSurvey.

References

Dewey, S.L., F. deNoyelles, Jr., K. Price, I. Schalles, and A. Clements.1993. Predicting stream periphyton biomass from spectralreflectance using a high-resolution, hand-held spectroradiometer.Bulletin of the Ecology Society ofAmerica, 74, 214.

Howard-Williams, C., and W.F. Vincent. 1989. Microbial communitiesin southern Victoria Land streams (Antarctica). I. Photosynthesis.Hydrobiologia, 172,27-38.

Peñuelas, J., J.A. Gamon, K.L. Griffin, and C.B. Field. 1993. Assessingcommunity type, plant biomass, pigment composition, and pho-tosynthetic efficiency of aquatic vegetation from spectralreflectance. Remote Sensing Environment, 46, 110-118.

Strickland, J.D.H., and T.R. Parsons. 1968. A practical handbook ofseawater analysis (Fisheries Research Board of Canada BulletinNo. 167). Ottawa, Canada: Fisheries Research Board of Canada.

Vincent, W.F., R.W. Castenholz, M.T. Downes, and C. Howard-Williams. 1993. Antarctic cyanobacteria: Light, nutrients, and pho-tosynthesis in the microbial mat environment. Journal of Phycolo-gy, 29, 745-755.

McMurdo LTER: Paleolimnology of Taylor Valley, AntarcticaPETER T. DORAN and ROBERT A. WHARTON, JR., Biological Sciences Center, Desert Research Institute, Reno, Nevada 89506

SARAH A. SPAULDING, U.S. Geological Survey, Boulder, Colorado 80303JAMIE S. FOSTER, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0371

A lthough much information has been gathered on the cli-..CImatological and glaciological histories of the dry valleys(e.g., Stuiver et al. 1981, pp. 319-436; Denton et al. 1989), rel-atively little is known about the physicochemical and biologi-cal state of past lakes in the region. For a recent review ofpaleolimnology in the McMurdo Dry Valleys, see Doran,Wharton, and Lyons (1994). The main objectives of thisresearch are• to put the present lake environments into historical per-

spective,• to trace environmental change (e.g., changes in lake pro-

ductivity, chemistry, sedimentology, and so forth) throughrecent time using lake-bottom sediments,

• to confirm and extend this record by using paleolake sedi-ments left by high lake stands (e.g., perched deltas left byGlacial Lake Washburn between approximately 12,000 to24,000 years ago), and

• to investigate new dating techniques to overcome carbonreservoir effects.

Short cores [less than 35 centimeters (cm)] collectedfrom Lake Hoare in Taylor Valley (figure 1) have been ana-lyzed for character and amount of carbonates and organicmatter, siliceous algal remains, geochemistry, mineralogy,and texture. Carbonates in the short cores are sporadic, usu-ally occurring in the fine-grained strata (figure 2; table), andso far have all been determined to be calcite with varying cal-cium-to-magnesium ratios. For the 31 oxic samples meas-ured to date (strata from cores taken from DH1 and DH2),

carbonates range from 0.3%o to 8.4%o isotopic carbon-13(ô'C), with a mean value of 5.6%o. This is remarkably closeto the 5.4%o value that Aharon (1988) predicts for antarcticlakes precipitating calcite in equilibrium with atmosphericcarbon dioxide (CO2) at 0°C. Lake Hoare sediment 813C val-ues reported here are heavier than those of its nearest neigh-bor, Lake Fryxell (Lawrence and Hendy 1989), by approxi-mately 507oo.

According to Green, Angle, and Chave (1988), LakeHoare surface waters are supersaturated with respect to cal-cite whereas waters below 20 meters depth are undersaturat-ed. Mass-balance calculations further showed that calciumcarbonate (CaCO3) is precipitated in the shallow regions ofthe lake, the area from which our core was extracted. This,coupled with the relatively heavy Lake Hoare dissolved inor-ganic carbon values resulting from the lack of surface waterinflow and mixing (Wharton, Lyons, and Des Marais 1993),helps to explain the isotopically heavy sedimentary carbon-ate. Sedimentary carbonate 813C increases with core depth toapproximately 30 cm in the core depicted in figure 2, sug-gesting a change in lake hydrology and/or productivity overrecent time.

Organic matter 8 13C is relatively light. This may be relat-ed to the findings of Rau, Takahashi, and Des Marais (1989),who suggest that increased solubility of CO2 in colder waterfavors isotopic discrimination by phytoplankton. The rela-tively heavy organic 8 13 C values in the coarser materialreflect an allogenic source for the material.

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