Evaluation of Seston in Otsego Lake, summer William A. Hahn Jr.! INTRODUCTION

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1 138 Evaluation of Seston in Otsego Lake, summer 1998 William A. Hahn Jr.! INTRODUCTION There have been an abundance of studies performed on Otsego Lake, reviewing many aspects of its integrity, and factors that may affect it (Albright, 1998). One important factor of the lake's biological system is its trophic state. The trophic state of a lake is, fundamentally, a measure of the biological activity in a lake, which is largely influenced by the available nutrition. Most organic matter which is generated in a lake through primary production will eventually decay, and in doing so, consume oxygen dissolved in the water. An ultimate consequence of increasing eutrophy is the loss of oxygen in a lake's deeper thermal strata. If severe, this results in the Joss of deep water fauna, including cold-water fish, and promotes the liberation of phosphorus from lake sediments, compounding the problem and making remediation difficult (Wheat et al., 1998). One indicator ofa lake's trophic condition is an analysis of the amount ofseston, or particulate matter suspended in free water (Hutchinson, 1967). Seston includes both non-living matter (tripton) and living matter (plankton), such as algae and zooplankton. The current seston study applies methods utilized in an Otsego Lake seston analysis during the summer of 1997 (Wheat et al., 1998). The study evaluates site TR4-C, and includes preliminary data on North Site and South Site (Figure 1). METHODOLOGY Preparation for seston analysis was accomplished by rinsing (23) 4.7 em diameter GF/A glass microfibre filters by passing three 20 ml aliquots of distilled water under vacuum. Filters were transferred to stainless steel planchets and dried at 105 C until constant weight was obtained (about one hour). Filters were stored in a sealed desicator and were weighed to the nearest 0.1 mg immediately before sample processing. The samples taken from TR4-C were acquired on 12 August 98 using a 4-liter Van Dorn sampler. They were collected at 4-meter intervals from the surface to 20 meters with duplicate samples taken at 16 meters and 20 meters. Samples from North Site and South Site were collected on 13 August 98. Due to shallower depths, North Site samples were collected at 4-meter intervals from the surface to 12 meters, and South Site at 4-meter intervals from the surface to 16 meters with a duplicate at the surface. I Bassett Healthcare Science Research Training Program, Summer Present affiliation: Worster High School

2 139 CRIPPLE CREEK CLARKE POND 01$(GO uo.k~ (GlIMMERGlASSJ eou-rrv. Ift'W..,... ~-- THREEMILE POINT LEATHERSTOCKING CREEK POINT JUDITH KINGFISHER TOWER BLACKBIRD BAY WILLOW BROOK SUSQUEHANNA RIVER Figure 1. Map of Otsego Lake with site TR4-C, North Site, and South Site labeled (King, 1998).

3 140 After collection, the samples were processed by passing them through the prepared fl1ters under vacuum at 15 PSI. The apparatus consisted of a 1/6 horse power vacuum pump, a 6-place manifold fit with #9 stoppers, 1000 ml filter flasks fit with #8 stoppers, and 400 ml funnel cups. The procedure was continued until either the entire sample had passed through the filter, or until the filter became clogged. In either event, the volume of water that was passed through the filter was recorded, and the f!lter was returned to its planchet. After all of the samples were processed, they were placed in an oven for one hour at 105 C. They were then reweighed and returned to the desicator. The difference between this weight and the filter weight prior to sample processing provides the seston dry weight. For quality control, five blank filters were also processed. This involved passing 100 ml of distilled water through prepared filters and processing as usual. To acquire ash weight, the filters were combusted in a mufi1e furnace at 550 C for one hour, cooled in the decicator, and reweighed. The difference between this weight and filter weight previous to processing yielded ash weight. weight is the difference between dry weight and ash weight. RESULTS Table 1 contains the results of the analysis of site TR4-C, taken on 12 August 98. It displays profiles of dry weight, organic seston weight, and ash weight, all displayed in milligrams/liter. Table 2 similarly summarizes the results of the analysis ofnmth Site and Table 3 the South Site on 13 August, 98. Table 4 contains the results of the analysis of the blank filters. Depth m Drywt. mgll mgll (%) mgll (85) (55) (55) (48) (10) (89) (32) (75) 0.38 Table 1. Profiles of dry weight (mg/l), organic seston weight (mg/l and as a % of dry weight), and weight (mg/i), TR4-C, 12 August, 1998.

4 141 Depth m Dry wt. mg/i mg/i (%) mg/i (40) (27) (38) (38) 1.56 Table 2. Profiles of dry weight (mg/i), organic seston weight (mg/i and as a % of dry weight), and weight (mg/i), North Site, 13 August, Depth m Dry wt. mg/j mg/j (%) mg/j a (87) (24) (60) (59) (60) 0.73 Table 3. Profiles of dry weight (mg/i), organic seston weight (mg/i and as a % of dry weight), and weight (mg/i), South Site, 13 August, S am pie Dry wt. mg mg mg Table 4. Profiles of dry weight (mg), organic seston weight (mg), and weight (mg), blank filters. These involved passing 100 ml of distilled water through prepared filters and processing as usual.

5 142 DISCUSSION Generally, the changes in trophic indices that have been documented over the past several decades in Otsego Lake imply increasing eutrophy of this water body (Wheat el ai., 1998). However, the results of this year's study exemplify concentrations of organic seston most comparable with those found in the study done in 1997, and much lower then those of the 1975 study (Figure 2). There are several possible reasons for these apparent discrepancies. The original seston study in 1935 (Tessler and Bere, 1936), as well as the studies done in 1971 (Sohacki, 1972) and 1975 (Doremus, 1976), used a continuous-flow centrifuge rather then the vacuum filter method. Comparing the current work with the studies up until 1997 may be difficult due to the differing methodologies. Secondly, all of the studies examined seston on only one occasion (with respect to the individual site). Seasonal fluctuations in algal standing crop are considerable, as are temporal trends among years (Albright, 1998). Another methodological problem was that the filters would become clogged with sestonic matter, limiting the volume of seston that could be filtered to the point of being near the limit of accurate weighing. The effects of experimental error are magnified when working with such relatively small sample quantities. Despite the fact that the results offered by this study do not coincide with the trophic trends such as oxygen depletion rates, transparency, and clorophylla, the study was, perhaps, valuable for its evaluation of the technique. The study provided insight as to possible improvements for its theoretically sound methodology. One conceivable improvement would be to sample regularly throughout the summer. This would help to reduce the affect that seasonal algal variations and benthic organisms have on the results. Use of larger filters is another potential improvement. This would allow less filter obstruction and, when combined with increased sample quantities, may increase accuracy.

6 143 Organic Seston (mg/i) , e l1j OJ E. 10.c Q. l1j /35 _7123/71 --,!,- 8115/75 --*-8/11/97 --*-8/12/ Figure 2. concentrations at TR4-C, Otsego Lake, on 7/23/3 5 (Tressler and Bere 1935), 7/23/71 (Sohacki, 1972), 8/15/75 (Doremus, 1976) 8/11/97 (Wheat et ai" 1998), and 8/12/98. (Modified from Wheat et ai" 1997). REFERENCES Albright, M.F Personal communication. SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Albright, M.F Otsego Lake limnological monitoring, summer In 30 th Annual Report (1997). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Doremus, C Ecological factors affecting phytoplankton grow1h during summer stratification in Otsego Lake including comments on the Lake's trophic stutus. In

7 144 8 th Annual Report (1975). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Hutchinson, G.E A treatise on limnology, Vo!. II. lntrouction to lake biology and the limnolplankton. John Wiley and Sons, Inc. New York. King, D.A Analysis of chlorophylla in Otsego Lake, summer In 30 til Annual Report (1997). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Sohacki,L.P Limnologicalinvestigations.ln4 1ll AnnualReport (1961). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Pp Tressler,W.L and R. Bere A limnological study of some of the lakes in the Delaware and Susquehanna water sheds. In A biological survey of the Delaware and Susquehanna watersheds. Pp Wheat ef al A preliminary investigation of the seston of Otsego Lake, summer In 30 til Annual Report (1997). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta