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USING LAKE SEDIMENTS TO TRACK ENVIRONMENTAL CHANGE IN A SUBARCTIC, URBAN LAKE SARAH SHENSTONEHARRIS Supervised by Dr. Sarah Finkelstein •Paleolimnology uses lakes sediments as a natural archive to reconstruct past ecological condiMons 4 •sensiMve to ecological changes 4 1. Collect sediment core 2. SecMon and date core Radioisotopic daMng with 210 Pb 3. Isolate biological proxies DIATOMS (algae fossils) METHODS •Cyst:Diatom raMo can measure nutrient levels 5 CHRYSOPHYTE STOMATOCYSTS (algae resMng stage) SUBARCTIC LAKES • SubarcMc lakes are very sensiMve to environmental change, most o[en due to ice cover dynamics • With prolonged ice cover, the biological oxygen demand can increase quickly. As a result, subarcMc lakes are more vulnerable to eutrophicaMon and resulMng anoxia than temperate lakes 1 • Algae communiMes are showing large responses to climate warming in some lakes. For example, there have been widespread diatom community shi[s from benthic taxa to planktonic Cyclotella species, possibly related to decreased ice cover 2 • Urban lakes suffer from many environmental pressures, including nutrient polluMon from surface runoff, toxin influx from industrial and urban waste, shoreline development, etc SUBARCTIC URBAN LAKES SubarcMc lakes in urban areas are unusual, but present a complex, mulMstressor environment Fig 3. Frame Lake straMgraphy showing relaMve abundances of diatom species and the chrysophyte cyst to diatom raMo, with core depth and 210 lead sediment dates on the yaxis. The diatom species are organized by preferred habitat. The benthic category also includes haptobenthics. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Zone 1 Zone 2 Zone 3 0 20 Navicula crptotenella 0 20 Cymbella m icroce p h a l a 0 Cymb e l l a desc r ip t a 0 Cymb e l l a cesa t ii 0 20 Denticu l a kuetzingii 0 20 Ac hananthes minu t i ssim a 0 20 A. mi n u t i s sim a va r . sa p ro p h i l a 0 Nav i cu l a c ry pto c ephala 0 20 Nav i cu l a l ib o n e nsis 0 Navicula pupul a 0 20 Navi cul a sali n arum 0 20 C ycl o te l la m ic h i g a n iana 0 20 C y clot e l l a pseud o stel li g e r a 0 20 40 Fra g i l ar i a pin n a t a 0 20 Fra g i l ar i a b re v i st r ia ta v a r . e l l i p t i ca 0 Fragila r ia c o n s t ru e n s var . vente r 0 20 B ra chysi ra mi c roc e p h a l a 0 Nitzschia d is s ipata 0 Nitzschia f ontic o l a 0 Nitzschia p u ra 0 N i tzschia p a l eace a 0 Ac h a n a n thes cur t i ssim a 4 12 20 28 36 C y st: D i a tom rat i o Epiphytic species Planktonic species Benthic species 1 99 0 19 74 210 Pb dates 19 43 RESULTS FRAME LAKE: • Prior to the 1970s, Frame Lake hosted a healthy fish populaMon and was a prominent swimming area for the community (fig 2) • Frame Lake has experienced a fish populaMon collapse, and suffers from nutrient polluMon, among other problems 6,7 A SMALL SUBARCTIC LAKE WITHIN CITY LIMITS OF YELLOWKNIFE, NWT • What are the major drivers of the observed environmental changes in Frame Lake? • Benthic species replaced epiphyMc species in approximately 1990 (fig 4) DISCUSSION 1. HABITAT CHANGES • This suggests a sudden change in diatom microhabitat— a decline in liforal zone macrophytes and mosses 2. NUTRIENT LEVEL CHANGES • The nutrient enrichments are likely from urban influences. However, since the diatom record ends at the Mme of Yellowknife’s establishment, due to diatom dissoluMon, we cannot analyze the ecology of prehuman seflement. AlternaMvely, Frame Lake may be a subarcMc anomaly and was always high in nutrients • Prior to the 1990s, Frame Lake sMll had a higher trophic status than other lakes in the Yellowknife region (fig 3,5) • According to the chrysophyte cyst to diatom raMo and diatom assemblage, the lake developed this trophic level in the mid to late 1990s (fig 3,5) • Frame Lake is currently eutrophic 7 3. CLIMATE CHANGE • This would suggest that the loss of liforal zone microhabitat is having a greater effect on the diatom assemblage than climate change during this period • Between 1956 and 1992, Frame Lake’s length of ice cover remained relaMvely unchanged 8 (fig 6). Contrarily, Cyclotella and Fragilaria relaMve abundance sMll changed during this period (fig 3,7), species that typically respond to changing ice cover and climate warming 2 • Recent (post 1990s) increase in Cyclotella taxa could be the result of warming, but ice monitoring stopped in 1992, making comparison not currently possible Fig 5. Cyst to diatom raMo Fig 7. RelaMve abundance of planktonic and benthic species. • When did these environmental changes occur? • How are the bioindicators (diatoms) responding? • Is restoraVon possible? CONCLUSIONS AND IMPLICATIONS • Microhabitat availability is the major driver for the diatom assemblage in Frame Lake, although nutrient levels and climate change are also important • Due to diatom dissoluMon, the diatom record predaMng urban seflement was not preserved, making the establishment of baseline for restoraMon difficult • Frame Lake is an unusual, mulMstressor environment Fig 2. Frame Lake beach, 1967 Fig 6. Days of open water, represented as the anomaly from the average 8 . Fig 4. RelaMve abundance of epiphyMc and benthic species. Fig 1. Yellowknife Bay of Great Slave Lake (behind) and Frame Lake (le[ foreground), surrounding City of Yellowknife, NWT Relative Abundance Depth (cm) LITERATURE CITED. 1. Barica, J., Mathias, J.A. 2011. Oxygen DepleMon and Winterkill Risk in Small Prairie Lakes Under Ice Cover. J. Fish. Res. Board. Can. 36: 980986.| 2. Smol, J.P. et al. 2005. Climatedriven regime shi[s in the biological communiMes of arcMc lakes. PNAS 102: 43974402.| 3. Schueler, T., Simpson, J. 2001. Why urban lakes are different. Water ProtecMon Techniques 3: 747 750.| 4.Baferbee, R.W. et al. 2001. Diatoms. In Tracking Environmental Change Using Lake Sediments Volume 3, eds Smol, J.P. and Birks, H.J.B. Kluwer Academic Publishers, Dordrecht, the Netherlands.| 5. Smol, J.P. 1985. The raMo of diatom frustules to chrysophycean statospores: A useful paleolimnological index. Hydrobiologia 123: 199208.| 6.Healey, M.C., and Woodall, W.L. 1973. Limnological surveys of seven lakes near Yellowknife, Northwest Territories. Fish. Res. Board Can. Tech. Rep. No. 407.| 7. Taiga Environmental Laboratory. 2010, 2011. Prepared for the Department of Fisheries and Oceans Canada. Batch No. 100525 and 110117. |8. NaMonal Snow and Ice Data Centre. 2013. Frame Lake, code WRS243. ACKNOWLEDGEMENTS. Dr. Sarah Finkelstein, Dr. Randy Dirszowsky, Magdalena Sobol, Anna Agosta G’Meiner, Maara Packalen, CGCS and Department of Fisheries and Oceans Canada. PHOTO CREDITS. 1. Dave Brosha Photography, 2013. | 2. Grant, T. 1967. Prince of Wales Northern Heritage Centre, Yellowknife, NWT. Frame Lake has a surface area of ~ 1 km and is 6.2 m deep. Obtain ice cover data from NaMonal Snow and Ice Data Centre 8
