Papers by Claire Schelske
Limnology and Oceanography, 2010
Controversy exists about the historic shift of primary producer community structure (PPCS) in Lak... more Controversy exists about the historic shift of primary producer community structure (PPCS) in Lake Apopka, a shallow, 125-km 2 lake in central Florida, U.S.A. The controversial questions are: was a lake-wide shift from macrophyte to phytoplankton dominance triggered by a 1947 hurricane or tornadoes spawned by the hurricane within a few weeks or months, or was the shift forced by progressive cultural eutrophication over several years? In 1947, fringing wetlands (35 km 2 ) were being diked and drained for agricultural purposes changing their function from nutrient sinks to nutrient point sources to the lake. We examined whether anthropogenic darkening of the water column induced the PPCS shift during a 0.6-m lake-stage rise. Darkening was defined as lake-bottom photosynthetically available radiation (PAR) # 1.0% of incident PAR. We simulated darkening from changes in the light extinction coefficient (K d ) due to water color, chlorophyll a, and rising lake stage. Simulations predicted that darkening was restricted to 80% of the lake deeper than 2.16 m, a finding consistent with persistence of shallow-water submersed macrophytes after 1947. Anthropogenic wetland draining increased water color, lake stage, and phytoplankton blooms stimulated by phosphorus enrichment, causing a progressive shift to lake-wide phytoplankton dominance over at least several years. The relationship between the 1947 hurricane and the PPCS shift was not causal, but only a temporal coincidence. Our darkening model can be applied to other systems with known bathymetry to predict submersed aquatic vegetation (SAV) coverage from SAV light requirements and water-column light attenuation.
Environmental Science Technology, 2004
J Paleolimnol, 1996
We examine sediment distribution patterns in seven Florida lakes and discuss implications for pal... more We examine sediment distribution patterns in seven Florida lakes and discuss implications for paleolimnological studies of shallow, subtropical lakes. The study lakes are highly productive and should exhibit thick organic sediment deposits, but organic sediments are ...
Hydrobiologia, 1978
A natural phytoplankton assemblage from Grand Traverse Bay, Lake Michigan, was treated with facto... more A natural phytoplankton assemblage from Grand Traverse Bay, Lake Michigan, was treated with factorial enrichments of nitrate and phosphorus, with maintained nutrient concentrations ranging from 5 to 60 pg total soluble phosphorus liter? and 0.225 to I. 12 mg nitrate-nitrogen liter-'Dne container wasspiked with added vitamins, a chelator, and trace metals. The assemblage response was monitored at the species level. Significant differences in growth rates as a function of nutrient enrichment were detected at both the division and the species levels. Growth rates associated with the various levels of enrichment are reported for several diatom taxa. Many of the diatom taxa exhibited highly significant (P < 0.01) increases in growth rate after phosphorus enrichment, with the largest effects occurring between 5 and 15 pg total soluble phosphorus liter-'. Significant (P < 0.05) N effects were also observed, and the nature of these effects was found to be taxon-specific. Taxa also showed significant changes in percent composition, due both to time and to nutrient enrichment, indicating a substantial heterogeneity in response at the species level. Experimentally induced population changes were qualitatively similar to those observed in regions of the Great Lakes which have undergone anthropogenic eutrophication
Can J Fisheries Aquat Sci, 1985
Ambio a Journal of the Human Environment, Jun 1, 2005
Limnol Oceanogr, 1998
Organic matter and its carbon and nitrogen isotopic composition were measured in sequential sedim... more Organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the Rochester Basin of Lake Ontario to evaluate their usefulness in reconstructing historic changes in lake productivity. The greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events, indicating that calcite precipitation is an effective mechanism for sedimenting organic matter. Carbon isotopes of organic matter were low prior to the onset of stratification, increased to maximum values in late summer, and then decreased following fall overturn. This pattern is controlled mainly by the timing of stratification and primary productivity, which preferentially removes "COZ from the epilimnion. The physiological effect of decreased carbon isotopic fractionation with decreasing supplies of [CO,],,, may have also contributed to increased PC orgc' Nitrogen isotopes showed a seasonal pattern opposite to that of carbon, whereby S"N values were low during the summer stratified period and high for the remainder of the year. Seasonal variability in S'INorgN probably reflects changes in the source of sedimented organic particles, which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period. A comparison of organic carbon accumulation rates and 6'&, between sediment cores collected in 1987 and 1993-1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters, but will not change the S"C,,,,,. values. All cores analyzed for PC,,,, display the reproducible pattern of a progressive increase in the 19OOs, peaking in the early to mid-1970s, and then decreasing to the present. This pattern matches the historical trends of phosphorus loading to the basin, suggesting that 613C of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column. The 6"N of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0.3%0 per decade, and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment. The increase in @N,,,,, reflects a combination of factors, including early forest clearance by Europeans, increased sewering by municipalities after 1940, and increased nitrate utilization as productivity increased in the lower Great Lakes. Increased rates of denitrification in the central basin of upstream Lake Erie from the 1930s to the early 1970s may have also contributed to the rise in P5N,,,, values.
Limnol Oceanogr, 1995
Lacustrine productivity in Lake Erie was reconstructed using measurements of V3C of sedimented or... more Lacustrine productivity in Lake Erie was reconstructed using measurements of V3C of sedimented organic C (S13C,,,) and non-apatite inorganic P (NAIP) in three cores. Inferred changes in lacustrine productivity were related to historic changes in phosphorus loading. P loading increased slowly after forest clearance and early settlement in the late 18OOs, then increased exponentially from the late 1940s to early 197Os, and finally decreased after the mid-1970s in response to management practices implemented to improve water quality. Similarly, the sediment accumulation rate of NAIP increased rapidly during the 1940s and 195Os, peaked during the late 1960s and early 197Os, and then decreased after the mid-1970s. The signal of 613C,, normalized to account for the historic 1.4o/oo depletion in V3C of atmospheric CO, mirrors that for accumulation of NAIP in sediments. Our results show that paleoproductivity peaked in the lower Great Lakes during the mid-1970s but has since declined as a result of P abatement programs. Inferred trends for NAIP and 613C Orgc are those predicted in P-limited lacustrine systems and demonstrate that the carbon isotopic ratio of organic C can be used as a proxy for paleoproductivity in large, deep lakes. Francis, Gary Fahnenstiel, Jason Kahne, William Kenney, Arthur Peplow, Eugene Stoermer, BobLuke Wejinya, and Julie Wolin. We also acknowledge the invaluable services provided by the marine superintendent, captain and crew of the RV Laurentian, and support staff of the University of Michigan, Center for Great Lakes and Aquatic Sciences. We thank Martha Love and Marilyn Bachmann for assistance with manuscript prepa-
Organic matter and its carbon and nitrogen isotopic composition were measured in sequential sedim... more Organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the Rochester Basin of Lake Ontario to evaluate their usefulness in reconstructing historic changes in lake productivity. The greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events, indicating that calcite precipitation is an effective mechanism for sedimenting organic matter. Carbon isotopes of organic matter were low prior to the onset of stratification, increased to maximum values in late summer, and then decreased following fall overturn. This pattern is controlled mainly by the timing of stratification and primary productivity, which preferentially removes "COZ from the epilimnion. The physiological effect of decreased carbon isotopic fractionation with decreasing supplies of [CO,],,, may have also contributed to increased PC orgc' Nitrogen isotopes showed a seasonal pattern opposite to that of carbon, whereby S"N values were low during the summer stratified period and high for the remainder of the year. Seasonal variability in S'INorgN probably reflects changes in the source of sedimented organic particles, which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period. A comparison of organic carbon accumulation rates and 6'&, between sediment cores collected in 1987 and 1993-1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters, but will not change the S"C,,,,,. values. All cores analyzed for PC,,,, display the reproducible pattern of a progressive increase in the 19OOs, peaking in the early to mid-1970s, and then decreasing to the present. This pattern matches the historical trends of phosphorus loading to the basin, suggesting that 613C of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column. The 6"N of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0.3%0 per decade, and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment. The increase in @N,,,,, reflects a combination of factors, including early forest clearance by Europeans, increased sewering by municipalities after 1940, and increased nitrate utilization as productivity increased in the lower Great Lakes. Increased rates of denitrification in the central basin of upstream Lake Erie from the 1930s to the early 1970s may have also contributed to the rise in P5N,,,, values.
An analysis of stable carbon isotope (␦ 13 C) ratios in Lake Apopka, Florida, reveals extreme 13 ... more An analysis of stable carbon isotope (␦ 13 C) ratios in Lake Apopka, Florida, reveals extreme 13 C enrichments of dissolved inorganic carbon (DIC) pools in the water column and sediment pore water of this shallow polymictic and hypereutrophic lake. The sediment pore water had high average ␦ 13 C of DIC (26.4‰), DIC (8.37 mmol L Ϫ1), and methane (CH 4) concentrations (1.23 mmol L Ϫ1). The extreme 13 C enrichment in the sediment pore-water DIC pool is attributed to methanogenesis, which produces 13 C-rich carbon dioxide (CO 2) and 13 C-poor CH 4 during the bacterial fermentation of organic matter. The ␦ 13 C in the water-column DIC pool ranged from 5‰ to 13‰ with an average of 9.0‰. The flux-weighted ␦ 13 C from the DIC due to external loading and sediment respiration was estimated as Ϫ12‰, whereas the ␦ 13
The structure of the planktonic food-web was studied during the spring (April/May) and summer (Au... more The structure of the planktonic food-web was studied during the spring (April/May) and summer (August) periods in 1993 to 1995 at twelve stations located in the offshore region of all five Great Lakes. All components of the planktonic food-web were collected from the same water sample (with the exception of crustaceans), counted microscopically, converted to carbon units, and averaged over the euphotic zone. Due to phosphorus load reductions and the impact of non-indigenous mussels in the lower lakes, physical/chemical characteristics of the lower lakes are becoming similar to those in the upper lakes. Spring total phosphorus and euphotic zone depth were relatively similar among all the stations (except western Lake Erie), ranging from 3 to 7 jig/L and 21 to 26 m, respectively. During the summer, total phosphorus concentrations were more variable, but ranged between 4 tol0 jig/L at all stations except western Lake Erie. Planktonic biomass was correlated with total phosphorus concentration. Within a season, the structure of the planktonic food-web was remarkably similar among all stations across all the lakes. Of the seventeen food-web structure parameters examined, only two exhibited significant differences among stations during the spring isothermal period; only four parameters exhibited significant differences among stations during the summer. Small plankton were very abundant in all the lakes. Picoplankton (0.2 to 2.0 jim) biomass was approximately equal to the combined biomass of nannoand microplankton (2 to 200 jim). For microorganisms (all organisms except crustaceans) autotrophic: heterotrophic ratios averaged 1.3 (spring = 1.1, summer = 1.5). The heterotrophic microorganism community was comprised of bacteria (mean = 65%), protozoans (mean = 32%), and rotifers (3%). Even though zebra mussel veligers were found in all the lakes except Lake Superior, their contribution to microorganism biomass never exceeded 1%. Due to seasonal variation in crustacean abundance, the mean contribution of major functional groups varied by season; producers (autotrophs), decomposers (bacteria), micrograzers (protozoans and rotifers), and mesograzers (crustaceans) constituted 40%,30%, 11%, and 19% of total planktonic carbon, respectively, during the spring, and 32%, 15%, 9%, and 43%, 531 532 Fahnenstiel et al.
Limnology and Oceanography, 1995
Lacustrine productivity in Lake Erie was reconstructed using measurements of V3C of sedimented or... more Lacustrine productivity in Lake Erie was reconstructed using measurements of V3C of sedimented organic C (S13C,,,) and non-apatite inorganic P (NAIP) in three cores. Inferred changes in lacustrine productivity were related to historic changes in phosphorus loading. P loading increased slowly after forest clearance and early settlement in the late 18OOs, then increased exponentially from the late 1940s to early 197Os, and finally decreased after the mid-1970s in response to management practices implemented to improve water quality. Similarly, the sediment accumulation rate of NAIP increased rapidly during the 1940s and 195Os, peaked during the late 1960s and early 197Os, and then decreased after the mid-1970s. The signal of 613C,, normalized to account for the historic 1.4o/oo depletion in V3C of atmospheric CO, mirrors that for accumulation of NAIP in sediments. Our results show that paleoproductivity peaked in the lower Great Lakes during the mid-1970s but has since declined as a result of P abatement programs. Inferred trends for NAIP and 613C Orgc are those predicted in P-limited lacustrine systems and demonstrate that the carbon isotopic ratio of organic C can be used as a proxy for paleoproductivity in large, deep lakes. Francis, Gary Fahnenstiel, Jason Kahne, William Kenney, Arthur Peplow, Eugene Stoermer, BobLuke Wejinya, and Julie Wolin. We also acknowledge the invaluable services provided by the marine superintendent, captain and crew of the RV Laurentian, and support staff of the University of Michigan, Center for Great Lakes and Aquatic Sciences. We thank Martha Love and Marilyn Bachmann for assistance with manuscript prepa-
Limnology and Oceanography, 2004
An analysis of stable carbon isotope (␦ 13 C) ratios in Lake Apopka, Florida, reveals extreme 13 ... more An analysis of stable carbon isotope (␦ 13 C) ratios in Lake Apopka, Florida, reveals extreme 13 C enrichments of dissolved inorganic carbon (DIC) pools in the water column and sediment pore water of this shallow polymictic and hypereutrophic lake. The sediment pore water had high average ␦ 13 C of DIC (26.4‰), DIC (8.37 mmol L Ϫ1 ), and methane (CH 4 ) concentrations (1.23 mmol L Ϫ1 ). The extreme 13 C enrichment in the sediment pore-water DIC pool is attributed to methanogenesis, which produces 13 C-rich carbon dioxide (CO 2 ) and 13 C-poor CH 4 during the bacterial fermentation of organic matter. The ␦ 13 C in the water-column DIC pool ranged from 5‰ to 13‰ with an average of 9.0‰. The flux-weighted ␦ 13 C from the DIC due to external loading and sediment respiration was estimated as Ϫ12‰, whereas the ␦ 13 C from particulate organic carbon (POC) due to water-column production was Ϫ13‰. The 13 C enrichment in the water column is attributed directly to the diffusion and advection of isotopically heavy DIC from the sediment and to the isotopic fractionation by phytoplankton photosynthesis and is attributed indirectly to the removal of isotopically light CH 4 by ebullition and organic matter by sedimentation and outflow. Atmospheric invasion and sedimentation were the most important source and sink, respectively, in the carbon mass balance. CH 4 oxidation, atmospheric invasion, anaerobic respiration, and sedimentation are the important flux terms affecting the isotopic mass balance. A combination of shallow water depth, frequent wind mixing, anoxic sediments with high rates of methanogenesis, high phytoplankton productivity, and lack of external loading dominated by terrestrial carbon led to the 13 C enrichment of the water-column DIC pool in Lake Apopka.
Limnology and Oceanography, 1998
Organic matter and its carbon and nitrogen isotopic composition were measured in sequential sedim... more Organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the Rochester Basin of Lake Ontario to evaluate their usefulness in reconstructing historic changes in lake productivity. The greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events, indicating that calcite precipitation is an effective mechanism for sedimenting organic matter. Carbon isotopes of organic matter were low prior to the onset of stratification, increased to maximum values in late summer, and then decreased following fall overturn. This pattern is controlled mainly by the timing of stratification and primary productivity, which preferentially removes "COZ from the epilimnion. The physiological effect of decreased carbon isotopic fractionation with decreasing supplies of [CO,],,, may have also contributed to increased PC orgc' Nitrogen isotopes showed a seasonal pattern opposite to that of carbon, whereby S"N values were low during the summer stratified period and high for the remainder of the year. Seasonal variability in S'INorgN probably reflects changes in the source of sedimented organic particles, which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period. A comparison of organic carbon accumulation rates and 6'&, between sediment cores collected in 1987 and 1993-1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters, but will not change the S"C,,,,,. values. All cores analyzed for PC,,,, display the reproducible pattern of a progressive increase in the 19OOs, peaking in the early to mid-1970s, and then decreasing to the present. This pattern matches the historical trends of phosphorus loading to the basin, suggesting that 613C of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column. The 6"N of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0.3%0 per decade, and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment. The increase in @N,,,,, reflects a combination of factors, including early forest clearance by Europeans, increased sewering by municipalities after 1940, and increased nitrate utilization as productivity increased in the lower Great Lakes. Increased rates of denitrification in the central basin of upstream Lake Erie from the 1930s to the early 1970s may have also contributed to the rise in P5N,,,, values.
Limnology and Oceanography, 1991
Cores from Lake Ontario provide a record of lake :rcsponses to increased phosphorus loading that ... more Cores from Lake Ontario provide a record of lake :rcsponses to increased phosphorus loading that began after early forest clearance in the mid-1800s. We measured1XY2C ratios of organic and inorganic C (calcite) in the sediments to infer recent .trends in primary production. The 6% of organic C increased in response to historic increases in P enrichment until the mid-1970s and then decreased in response to reduced P loading. The 6°C of calcite increased after 1940 but did not decrease in response to reduced P loading. We conclude that the results differ because 8°C of organic C is determined by primary production early in the seasonal cycle when flux of organic C to the sediments is greatest, whereas 6°C of calcite depends on the isotopic composition of dissolved inorganic C during late summer when calcite is precipitated.
Limnology and Oceanography, 1998
We studied water, sediment trap, and core samples from eastern Lake Ontario to reconstruct the fa... more We studied water, sediment trap, and core samples from eastern Lake Ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so-called whiting events. Calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors, including temperature, primary productivity, and the abundance of pica-cyanobacteria during the stratified period. Calcite precipitation is highly correlated to lake temperature, because physical and biological factors interact to produce conditions favorable for whitings during warm years when the lake stratifies early in the seasonal cycle. Carbonate stratigraphies in multiple cores from eastern Lake Ontario revealed similar patterns of historical variation in percent carbonate. An exponential rise in carbonate accumulation occurred in nine cores after 1930, culminating in peak values in the early 1980s. This rise was related to historic increases in primary productivity resulting from increased phosphorus loading to Lake Ontario. Superimposed upon this rise were four peaks (centered on 1940-1942, 1957-1961, 1971-1977, and 1983) that correlate with maxima in summer air-temperature anomalies from the Great Lakes region and with strong El Niiio events. These peaks are also associated with maxima in S'C values and minima in S180 values of carbonate, lending support to our model that more calcite is precipitated with higher 6'C values during warm years when thermal stratitication occurs early in the seasonal cycle. Beginning in the mid-1980s calcite accumulation and its 6°C ratio began to decrease, suggesting a reduction in primary productivity in surface waters, probably related to lower phosphate concentrations in epilimnetic waters of Lake Ontario during the stratified period. Reduced summer P loading may be explained either by a lagged response to P abatement measures that began in the late 1970s or by decreased P loading from upstream Lake Erie beginning in the late 1980s as a result of the establishment of filter-feeding zebra mussels
Lake and Reservoir Management, 2005
Riedinger-Whitmore, M.A., T.J. Whitmore, J.M. Smoak, M. Brenner, A. Moore, J. Curtis and C.L. Sch... more Riedinger-Whitmore, M.A., T.J. Whitmore, J.M. Smoak, M. Brenner, A. Moore, J. Curtis and C.L. Schelske. 2005. Cyanobacterial proliferation is a recent response to eutrophication in many Florida lakes: A paleolimnological assessment. Lake and Reserv. Manage. 21(4):423-435.
Lake and Reservoir Management, 1995
ABSTRACT Lake Hollingsworth lies in phosphate-rich central Florida. Recent limnological data show... more ABSTRACT Lake Hollingsworth lies in phosphate-rich central Florida. Recent limnological data show the lake has been hypereutrophic for&amp;amp;amp;gt; 25 years, but nothing was known of the lake&amp;amp;amp;#39;s trophic history prior to the late 1960s. A paleolimnological study was undertaken to: ...
Journal of Paleolimnology, 1996
We examine sediment distribution patterns in seven Florida lakes and discuss implications for pal... more We examine sediment distribution patterns in seven Florida lakes and discuss implications for paleolimnological studies of shallow, subtropical lakes. The study lakes are highly productive and should exhibit thick organic sediment deposits, but organic sediments are ...
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Papers by Claire Schelske