Carmen Aguilar

Ecosystem Transformations of the Laurentian Great Lake Michigan by Nonindigenous Biological Invaders

Lake Michigan, a 58,000-km(2) freshwater inland sea, is large enough to have persistent basin-scale circulation yet small enough to enable development of approximately balanced budgets for water, energy, and elements including carbon and silicon. Introduction of nonindigenous species-whether through invasion, intentional stocking, or accidental transplantation-has transformed the lakes ecosystem function and habitat structure. Of the 79 nonindigenous species known to have established reproductive populations in the lake, only a few have brought considerable ecological pressure to bear. Four of these were chosen for this review to exemplify top-down (sea lamprey, Petromyzon marinus), middle-out (alewife, Alosa pseudoharengus), and bottom-up (the dreissenid zebra and quagga mussels, Dreissena polymorpha and Dreissena rostriformis bugensis, respectively) transformations of Lake Michigan ecology, habitability, and ultimately physical environment. Lampreys attacked and extirpated indigenous lake trout, the top predator. Alewives outcompeted native planktivorous fish and curtailed invertebrate populations. Dreissenid mussels-especially quagga mussels, which have had a much greater impact than the preceding zebra mussels-moved ecosystem metabolism basin-wide from water column to bottom dominance and engineered structures throughout the lake. Each of these non indigenous species exerted devastating effects on commercial and sport fisheries through ecosystem structure modification.

The role of biomineralization in microbiologically influenced corrosion

Synthetic iron oxides (goethite, α-FeO·OH; hematite, Fe2O3; and ferrihydrite, Fe(OH)3) were used as model compounds to simulate the mineralogy of surface films on carbon steel. Dissolution of these oxides exposed to pure cultures of the metal-reducing bacterium, Shewanella putrefaciens, was followed by direct atomic absorption spectroscopy measurement of ferrous iron coupled with microscopic analyses using confocal laser scanning and environmental scanning electron microscopies. During an 8-day exposure the organism colonized mineral surfaces and reduced solid ferric oxides to soluble ferrous ions. Elemental composition, as monitored by energy dispersive x-ray spectroscopy, indicated mineral replacement reactions with both ferrihydrite and goethite as iron reduction occurred. When carbon steel electrodes were exposed to S. putrefaciens, microbiologically influenced corrosion was demonstrated electrochemically and microscopically.

Biogeochemical Cycling of Manganese in Oneida Lake, New York: Whole Lake Studies of Manganese

Oneida Lake, New York is a eutrophic freshwater lake known for its abundant manganese nodules and a dynamic manganese cycle. Temporal and spatial distribution of soluble and particulate manganese in the water column of the lake were analyzed over a 3-year period and correlated with other variables such as oxygen, pH, and temperature. Only data from 1988 are shown. Manganese is removed from the water column in the spring via conversion to particulate form and deposited in the bottom sediments. This removal is due to biological factors, as the lake Eh/pH conditions alone can not account for the oxidation of the soluble manganese Mn(II). During the summer months the manganese from microbial reduction moves from the sediments to the water column. In periods of stratification the soluble Mn(II) builds up to concentrations of 20 micromoles or more in the bottom waters. When mixing occurs, the soluble Mn(II) is rapidly removed via oxidation. This cycle occurs more than once during the summer, with each manganese atom probably being used several times for the oxidation of organic carbon. At the end of the fall, whole lake concentrations of manganese stabilize, and remain at about 1 micromole until the following summer, when the cycle begins again. Inputs and outflows from the lake indicate that the active Mn cycle is primarily internal, with a small accumulation each year into ferromanganese nodules located in the oxic zones of the lake.

Microbial Communities and Chemosynthesis in Yellowstone Lake Sublacustrine Hydrothermal Vent Waters

Five sublacustrine thermal spring locations from 1 to 109 m water depth in Yellowstone Lake were surveyed by 16S ribosomal RNA gene sequencing in relation to their chemical composition and dark CO2 fixation rates. They harbor distinct chemosynthetic bacterial communities, depending on temperature (16–110°C) and electron donor supply (H2S <1 to >100 μM; NH3 <0.5 to >10 μM). Members of the Aquificales, most closely affiliated with the genus Sulfurihydrogenibium, are the most frequently recovered bacterial 16S rRNA gene phylotypes in the hottest samples; the detection of these thermophilic sulfur-oxidizing autotrophs coincided with maximal dark CO2 fixation rates reaching near 9 μM C h−1 at temperatures of 50–60°C. Vents at lower temperatures yielded mostly phylotypes related to the mesophilic gammaproteobacterial sulfur oxidizer Thiovirga. In contrast, cool vent water with low chemosynthetic activity yielded predominantly phylotypes related to freshwater Actinobacterial clusters with a cosmopolitan distribution.

Microbiogeochemical Ecophysiology of Freshwater Hydrothermal Vents in Mary Bay Canyon, Yellowstone Lake, Yellowstone National Park WY

Geothermally derived energy was shown to be definitively involved in elemental cycling and microbiogeochemical ecophysiology of a confined canyon in the caldera portion of Yellowstone Lake. Visual and olfactory evidence from small boats indicated efflux of volatile, redox-labile sulfur compounds on any calm morning. Bulk chemical composition of lakewater was found to be enriched in common geothermal constituents, ΣCO2, Cl−, SiO2, and the oxidized end-product SO4=. Lakewater chemosynthesis in the canyon was not necessarily high, but persistent presence of active chemosynthetic microbial populations was demonstrated in enrichment incubations. Admixtures of lakewater and hydrothermal emanations collected at the orifice of hot vents under this water column contained variable, often substantial enrichment in energy substrates, but samples collected simultaneously only 50 cm above the vent orifice had already become nearly indistinguishable chemically from deep lake water. Ventwaters supported aerobic chemosynthetic activity (dark CO2 fixation) at receiving water temperatures that could be several times the rate of light-saturated surface water photosynthesis on a volumetric basis. Some vents had little activity at 15 °C but sprung into action at 50 °C, indicating populations of obligately thermophilic chemolithoautotrophs. Below the sediment-water interface, pore water chemistry of a >60 °C gravity core displayed strong influence of geothermally altered fluids. Geochemicals ΣCO2, SiO2, and H2S were present at levels far above those attainable through organic matter diagenesis, punctuated by conservative Cl− concentrations of >9 mM, over 60 times that of overlying lakewater. Apparently geothermally altered water was transported through semipermeable subsurface conduits to sediment surface orifices, where emanations were biogeochemically altered to support microbial productivity and mineral encrustation processes. Deep waters of the confined canyon supported stable microbial populations poised to use reduced mineral energy for growth. Chemolithoautotrophic metabolism, either active or potential, was evident throughout the Mary Bay Canyon ecosystem.