Chlorophyll a concentrations in Otsego Lake, summer 2014

Transcription

1 Chlorophyll a concentrations in Otsego Lake, summer 2014 Morgan Freehafer 1 INTRODUCTION Chlorophyll a concentrations are monitored annually in Otsego Lake in order to estimate algal mass, an important part of evaluating the lake s trophic status. Chlorophyll a, the light-sensitive pigment that enables photosynthesis, is found in the dominant algae of Otsego Lake (APHA 2012). Chlorophyll a concentrations can therefore be used to estimate the relative algal biomass in Otsego Lake (Harman et. al 2002). Due to Otsego Lake s meso-oligotrophic characteristics, such as low nutrients and low algal standing crops (Godfrey 1977), chlorophyll a concentrations in Otsego Lake are expected to be relatively low. Various factors affect chlorophyll a concentrations in Otsego Lake; a primary influence in algal growth are within the lake s food web interactions. In 1986, alewives (Alosa pseudoharengus) were first documented in Otsego Lake (Foster 1990). These planktivorous fish reduced zooplankton population densities, leading to a significant reduction in algal grazing (Harman et al. 2002). Their predation yielded higher algal standing crops, while reducing transparency and concentrations of hypolimnetic dissolved oxygen. Alewives have not been documented in Otsego Lake in recent years, though the historical impact of alewife on algal standing crops remains relevant (i.e., Best 2015). Walleye (Sander vitreus), a popular gamefish, were introduced to Otsego Lake in 2000 (Cornwell 2007) and effectively reduced the alewife population, thereby allowing for the rebound of the zooplankton community (Albright and Best 2015). Zebra mussels (Dreissena polymorpha) are exotic, bi-valve, filter feeders that were first documented in Otsego Lake in 2007 (Waterfield 2009). Widespread by 2010 (Albright and Zaengle 2012), these mussels reduced algal standing crops as a result of their high filtering rate. Both a decrease in chlorophyll a concentrations and a marked increase in water transparency coincided with the introduction of zebra mussels to Otsego Lake (Waterfield and Albright 2013). The purpose of this work is to gain a deeper understanding of concentrations of chlorophyll a throughout the lake. The annual monitoring of chlorophyll a concentrations in Otsego Lake is part of a continued effort to evaluate its trophic parameters related to nutrient concentrations and food web dynamics. 1 F.H.V. Mecklenburg Conservation Fellow, summer Present affiliation: Emma Willard School. Funding provided by the Otsego County Conservation Association.

2 METHODS Chlorophyll a samples were collected every other week from Otsego Lake at sites TR3-C, TR4-C, and TR5-C (see Figure 1). Composite samples from surface to 20 meters were taken at all three sites using a weighted garden hose. At site TR4-C, the deepest point in the lake, discrete samples from surface to 20 meters were collected at 1 meter intervals using a Kemmerer Sampler. Samples were stored in 125 ml Nalgene bottles and kept in a cooler to prevent the chlorophyll a from degrading. Figure 1. Bathymetric map showing sample collection sites for chlorophyll a analysis in Otsego Lake, summer The samples were filtered through a 47mm Whatman GF/A Glass Micro Fiber filter using a low-pressure vacuum pump. The filters were then folded in half, patted dry to remove excess water, and placed in a petri dish. Samples were stored in a freezer until further processing.

3 Each filter was then cut into small pieces in a 15mL grinding tube with approximately 4mL of buffered acetone (90% acetone, 10% MgCO 3 ). Using a drill with a Teflon pestle drill bit, the filter and solution were ground together and transferred to a 15mL centrifuge tube. More buffered acetone was added to bring each sample to 10mL in volume. After g into centrifuge for 10 minutes at 10,000 X G, the samples were analyzed for chlorophyll a in a Turner Designs TD-700 fluorometer. Chlorophyll a concentrations were then ascertained using the methods of Arar and Collins (1997). RESULTS & DISCUSSION Figure 2 shows the average chlorophyll a concentrations for site TR4-C from years 2002 to 2014 (excluding 2008 and 2009). Chlorophyll a concentrations for this summer were lower than last year s concentrations from the surface to 10 meters. From 10 to 20 meters, concentrations of chlorophyll a were higher than last year s. Figure 3 illustrates chlorophyll a concentrations throughout the water column from 18 June, 2 July, 14 July, and 29 July 2014 at site TR4-C. Results from composite sampling done on the aforementioned dates at sites TR3-C, TR4-C, and TR5-C can be seen in Figure 4.

4 Average Chlorophyll a Concentrations in Otsego Lake at TR4-C 0 Concentration (ppb) Depth (m) Figure 2. Mean chlorophyll a concentrations per depth at sample site TR4-C from 2002 to 2014, excluding 2008 and Data were retrieved from 2002 (Wayman 2003), 2003 (Schmitt 2004), 2004 (Murray 2005), 2005 (Zurmuhlen 2006), 2006 (Stevens 2007), 2007 (Ottley 2008), 2010 (Bauer 2011), 2011 (Levenstein 2012), 2012 (Slater 2013), 2013(Bianchine and Tanner 2013) and 2014.

5 Chlorophyll a Concentrations Otsego Lake at TR4-C Concentration (ppb) Depth (m) Jun-14 2-Jul Jul Jul Figure 3. Chlorophyll a concentrations throughout the water column at TR4-C on 18 June, 2 July, 14 July, and 29 July 2014.

6 3 2.5 Concentration (ppb) TR3-C comp TR4-C comp TR5-C comp Figure 4. Mean chlorophyll a concentrations in composite samples from sites TR3-C, TR4-C, and TR5-C from 18 June, 2 July, 14 July, and 29 July CONCLUSION Data collected in summer 2014 continue to indicate that Otsego Lake displays characteristics of an oligotrophic lake. Chlorophyll a concentrations from composite samples at all three sites averaged ~2μg/L, a relatively low concentration that is consistent with results from recent years. REFERENCES Albright, M.F. and M.J. Best A survey of Otsego Lake s zooplankton community, summer In 47 th Annual Report (2014). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Albright, M.F. and O. Zaengle A survey of Otsego Lake s zooplankton community, summer In 44th Annual Report (2011). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. APHA, AWWA, WPCF Standard methods for the examination of water and wastewater, 17th ed. American Public Health Association. Washington, DC.

7 Arar, E.J. and G.B. Collins Method 445.0, In Vitro Determination of Chlorophyll a and Pheophytin a in Marine and Freshwater Algae by Fluorescence. In Methods for the Determination of Chemical Substances in Marine and Estuarine Environmental Matrices, 2nd Edition. National Exposure Research Laboratory, Office of Research and Development, USEPA., Cincinnati, Ohio. EPA/600/R- 97/072. Bauer, H Chlorophyll a analysis of Otsego Lake, summer In 43rd Annual Report (2010). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Best, M.J Summer 2014 trap net monitoring of the fish communities in the weedy littoral zone atrat Cove and the rocky littoral zone at Brookwood Point, Otsego Lake. In 47 th Annual Report (2014). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Bianchine, T. and Tanner, C Chlorophyll a concentrations in Otsego Lake, summer In 46 th Annual Report (2013). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Cornwell, M Walleye re-introduction update and characterization of walleye spawners: In 39th Annual Report (2006). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Foster, J.R Introduction of the alewife (Alosa pseudoharengus) in Otsego Lake. In 22nd Annual Report (1989). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Harman, W.N., M.F. Albright, and D.M. Warner Trophic changes in Otsego Lake, NY following the introduction of the alewife (Alosa Pseudoharengus). Lake and Reservoir Management. 18(3): Levenstein, A Chlorophyll a concentrations in Otsego Lake, summer In 44th Annual Report (2011). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Murray, K Chlorophyll a concentrations in Otsego Lake, summer In 37th Annual Report (2004). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Ottley, S.G Chlorophyll a concentrations in Otsego Lake, summer In 39th Annual Report (2007). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Schmitt, R Chlorophyll a concentrations in Otsego Lake, summer In 36th Annual Report (2003). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Stevens, K Chlorophyll a analysis of Otsego Lake, summer In 39th Annual Report (2006). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta.

8 Waterfield, H.A Update on zebra mussel (Dreissena Polymorpha) invasion and establishment in Otsego Lake, In 41st Annual Report. (2008). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Waterfield, H.A. and M.F. Albright Otsego lake limnological monitoring, summer In 45th Annual Report (2012). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Wayman, K Chlorophyll a concentrations in Otsego Lake, summer In 35th Annual Report (2002). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Welschmeyer, N.A Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnol. Oceanogr. 39: Zurmuhlen, S Chlorophyll a analysis of Otsego Lake, summer In 38th Annual Report (2005). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta.