Characterization of sedimentary humic matter by alkaline hydrolysis

Humic matter fractions from modern sediments of Lake Huron and Lake Michigan have been compared. Large yields of saccharinic acids from alkaline hydrolysis suggest that these fractions contain large portions of carbohydrate materials. Evidence for contributions of aquatic lipid (C-16 fatty acids) and of liginin (phenolic acids) to these sediments is also present in the hydrolysis products. Qualitative differences among fulvic acid, humic acid and humin from the same lake are minor, suggesting common (or similar) organic sources for these fractions. The lability of sedimentary humic matter to alkaline hydrolysis is inversely related to its degree of exposure to oxidative weathering. Lability may also be related to diagenetic state as fulvic acids generally yield greater quantities of hydrolysis components than humic acids which in turn yield more than humin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25370/1/0000819.pd

Hydrocarbons and fatty acids in two cores of Lake Huron sediments

Compositions of aliphatic hydrocarbons and of fatty acids were analyzed in two half-meter cores of postglacial Lake Huron sediment. One core represents a continuous record of the past 450 yr of sediment accumulation; the other consists of a surficial layer of modern sediment overlying 40 cm of 11,000-12,000 yr-old sediment. Concentrations of hydrocarbons are higher in the younger core than in the older one. Based upon n-alkane distributions, this reflects a smaller input of terrigenous material to Lake Huron 11,000 yr ago rather than diagenetic losses. Most of the hydrocarbons present in the 450 yr-old core are allochthonous while half are autochthonous in the older core. Fatty acids are primarily of aquatic character in both cores, and their concentrations decrease rapidly with depth. Unsaturated acids disappear more quickly than do their saturated analogs. Fatty acid degradation occurs mostly in the biologically active zone of these sediments, and little further alteration of fatty acids appears to happen over times as long as 12,000 yr.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23193/1/0000120.pd

Plasticity of Total and Intracellular Phosphorus Quotas in Microcystis aeruginosa Cultures and Lake Erie Algal Assemblages

Blooms of the potentially toxic cyanobacterium Microcystis are common events globally, and as a result significant resources continue to be dedicated to monitoring and controlling these events. Recent studies have shown that a significant proportion of total cell-associated phosphorus (P) in marine phytoplankton can be surface adsorbed; as a result studies completed to date do not accurately report the P demands of these organisms. In this study we measure the total cell-associated and intracellular P as well as growth rates of two toxic strains of Microcystis aeruginosa Kütz grown under a range of P concentrations. The results show that the intracellular P pool in Microcystis represents a percentage of total cell-associated P (50–90%) similar to what has been reported for actively growing algae in marine systems. Intracellular P concentrations (39–147 fg cell−1) generally increased with increasing P concentrations in the growth medium, but growth rate and the ratio of total cell-associated to intracellular P remained generally stable. Intracellular P quotas and growth rates in cells grown under the different P treatments illustrate the ability of this organism to successfully respond to changes in ambient P loads, and thus have implications for ecosystem scale productivity models employing P concentrations to predict algal bloom events

Seasonal changes in microbial community structure and activity imply winter production is linked to summer hypoxia in a large lake

Carbon and nutrient cycles in large temperate lakes such as Lake Erie are primarily driven by phototrophic and heterotrophic microorganisms, although our understanding of these is often constrained to late spring through summer due to logistical constraints. During periods of \u3e 90% ice cover in February of 2008, 2009, and 2010, we collected samples from an icebreaker for an examination of bacterial production as well as microbial community structure. In comparison with summer months (August 2002 and 2010), we tested hypotheses concerning seasonal changes in microbial community diversity and production. Bacterial production estimates were c. 2 orders of magnitude higher (volume normalized) in summer relative to winter. Our observations further demonstrate that the microbial community, including single-celled phototrophs, varied in composition between August and February. Sediment traps deployed and collected over a 3 year period (2008-2011) confirmed that carbon export was ongoing and not limiting winter production. The results support the notion that active primary producers in winter months export carbon to the sediments that is not consumed until the warmer seasons. The establishment of this linkage is a critical observation in efforts to understand the extent and severity of annual summertime formations of a zone of regional hypoxia in Lake Erie. Seasonal changes in microbial community productivity and diversity suggest primary production in winter months may exacerbate summer hypoxia in Lake Eri. © 2014 Federation of European Microbiological Societies

Effect of Phosphorus Amendments on Present Day Plankton Communities in Pelagic Lake Erie

To address questions regarding the potential impact of elevated total phosphorus (TP) inputs (due to relaxed regulations of TP loading), a series of TP enrichment experiments were conducted at pelagic stations in the 3 hydrologically distinct basins of Lake Erie. Results of nutrient assimilation measurements and assays for nutrient bioavailability suggest that the chemical speciation, and not concentration, of nitrogenous compounds may influence phytoplankton community structure; this in turn may lead to the selective proliferation of cyanobacteria in the eastern basin of the lake. Assays with cyanobacterial bioluminescent reporter systems for P and N availability as well as N-tot:P-tot assimilation ratios from on-deck incubation experiments support this work. Considered in the context of a microbial food web relative to a grazing food web, the results imply that alterations in current TP loading controls may lead to alterations in the phytoplankton community structure in the different basins of the Lake Erie system

Sedimentary geolipid records of historical changes in the watersheds and productivities of Lakes Ontario and Erie

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110611/1/lno19964120352.pd

Anthropogenic influences on hydrocarbon contents of sediments deposited in eastern Lake Ontario since 1800

 The amounts and types of extractable hydrocarbon components in sediment cores from the Rochester Basin of eastern Lake Ontario provide a record of environmental changes that have accompanied the settlement and population growth of the surrounding land areas. Sediments deposited prior to the mid-1800s contain low concentrations of hydrocarbons that are dominated by land-plant wax components. Concentrations begin to rise in the late 1800s as erosion of soil and nutrients from watershed areas accelerated. This pattern continues into modern times. Episodes of enhanced aquatic productivity are sometimes recorded in twentieth-century sediments by the dominance of algal hydrocarbons, but land-plant components typically predominate. Petroleum residues begin to appear in sediments deposited in the late 1800's but remain minor constituents of the hydrocarbon contents of modern sediments in the Rochester Basin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42067/1/254-28-1-22_60280022.pd

Alkane and alkanoic acid variations with depth in modern sediments of Pyramid Lake

Pyramid Lake, a salt lake in Nevada, has undergone a 30% reduction in volume over the past 100 yr due to diversion of river inflow for irrigation of farmland. This has altered the depositional-benthic environment and possibly has changed the overall aquatic environment of Pyramid Lake as indicated by changes in the hydrocarbon and monocarboxylic acid content in a sediment core. In the top 30 cm, total organic carbon levels decrease from 2.5 to 1.8% dry weight but change little over the next 100 cm. A decrease in n-alkane concentrations also occurs in the top 30 cm, although no change in chain-length distributions is found. Most significantly, a 6-fold increase in n-alkanoic acid concentrations exists between the sediment surface and a core depth of 20-30 cm and is due primarily to high amounts of C28 and C30 acids. At all depths below 40 cm, as well as at the surface, C16 and C18 acids dominate the distributions, and overall concentrations are much lower than at 20-23 cm. These changes in concentration and in n-alkanoic acid chain-length distributions appear to coincide with the beginning of lake volume reduction and may demonstrate the effect of increased sedimentation rate upon organic matter preservation. In addition, changes in n-alkane distribution throughout this 135 cm sediment thickness indicate fluctuations in the relative contributions of lake-derived and land-derived organic materials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23408/1/0000354.pd

Seasonal Si:C ratios in Lake Erie diatoms - Evidence of an active winter diatom community

Recent investigations of Lake Erie in the winter have demonstrated the occurrence of substantial phytoplankton communities largely consisting of the diatom Aulacoseira islandica (O. Müller) Simonsen. To assess the activity of this diatom community, multiple measures of production, both general and diatom-specific, were undertaken. We measured oxygen (O 2) evolution as proxy for carbon (C)-fixation and 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl) methoxy)-phenyl)oxazole (PDMPO) incorporation as a measure of silica (Si) deposition. The latter demonstrated conclusively that diatoms were active during winter months and confirmed that diatoms are the primary drivers of winter productivity. The stoichiometric relationship between carbon and silica in the winter Lake Erie phytoplankton assemblage was further compared to the activity of the summer community. Although the winter phytoplankton community was observed to be active, it was less active than the summer community, with lower measured rates of O 2 evolution and Si deposition. These findings provide a new and expanded understanding of the biological carbon production in Lake Erie. © 2012 Elsevier B.V

Field investigations of trace metal effects on lake erie phytoplankton productivity

Responses of phytoplankton to trace metal and phosphate enrichments were made in pelagic Lake Erie surface waters over the time period of 1999-2003. All experiments employed trace metal clean sampling protocols. Bioassays were incubated over a 0.75-4 d period. Response was evaluated by measures of biomass (chlorophyll-a; chl-a), photosynthesis (using the carbon-14 technique), and dilution assays used to measure chl-a specific growth and grazing rates. Metals assayed were Cd, Co, Zn (5-50 nM) and Fe over the range of (20-100 nM). Phosphorus was added singly (0.1-1 μM) or in addition with Zn or Fe. The principle finding from this study was that the frequency of observed trace metal limitation in pelagic Lake Erie phytoplankton was low. Picoplankton (0.2-2 μm) responded most frequently to the metal enrichment; metals were as frequently toxic as they were stimulatory. Nanoplankton (2-20 μm) were nearly insensitive to metal enrichment as were the microplankton (20-210 μm). An EDTA chelated mixture of Fe, Cu, Zn, Co, Mn, and Mo did stimulate picoplankton chl-a production over 3 days and the growth and grazing rate of this important size fraction. Toxicity of Zn at 50 nM was observed; the presence of phosphate reduced inhibition by Zn at this concentration. The results suggest that trace metals are not as important over the short term as the availability of phosphorus in controlling phytoplankton productivity; however, trace metal enrichment can periodically have a stimulatory effect, particularly on the picoplankton size class