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At least 181 records · Page 10Linked to original sources
USGS2003

Methanogenic activity in plankton samples and fish intestines A mechanism for in situ methanogenesis in oceanic surface waters

When plankton samples were incubated anaerobically with a cysteine-sulfide reducing agent, pronounced methane evolution occurred. This activity was inhibited by air, CHCl 3 , C 2 H 2 , and 2-bromoethanesulfonic acid. Adding [ 14 C]CO 3 2− resulted in accumulation of [ 14 C]CH 4 . Portions of the digestive tracts of three fishes were incubated in methanogenic media, and two of the samples showed the presence of methanogenic bacteria.

Limnology and Oceanography↗
USGS2003

High frequency radar measurements of tidal currents flowing through San Pablo Strait, San Francisco Bay

High frequency (HF) radar measurements of the surface current averaged over the upper 0.5 m in San Pablo Strait were compared with current meter measurements of the subsurface current made at 9.4 m below mean lower low water (MLLW) over two 12.4-h tidal cycles. After averaging the radar and current meter data over two tidal cycles, a southerly (ebbing direction) surface current of 32 cm·s −1 was deduced from the radar measurements and a northerly (flooding direction) subsurface current of 7 cm·s −1 from the current meter measurements. This nontidal flow is maintained by freshwater discharge from the Sacramento–San Joaquin Rivers into Suisun and San Pablo Bays. The radar measurement technique provides quantitative estimates of the surface currents that previously were determined only from surface drifter studies.

Limnology and Oceanography↗
USGS2003

The chemical composition of lakes in the north‐central United States

Lake waters of the north‐central U.S.A. are classified into five groups, based on increasing specific conductivity and changes in ionic composition from east to west, from Wisconsin through Minnesota to North and South Dakota. The most dilute group of waters has specific conductivities <29 µ mhos · cm −1 at 25°C; the most concentrated group has specific conductances that range from 7,000 to 73,000 µ mhos. As conductivity increases all major ions increase, but there is a shift in cation dominance from Ca 2 + to Mg 2+ to Na + , and in anion dominance from HCO 3 − to SO 4 2− . This shift partly reflects a westward increase in climatic aridity, and partly a westward sequence of glacial drifts from noncalcareous to calcareous and thence to calcareous with abundant sulfur‐bearing minerals. Levels of pH, K, Cl, F, B, and SiO 2 also show a distinct westward increase. Concentrations of NO 3 − and Mn increase from east to west, but the trend is less distinct. Concentrations of Fe vary widely without any trend over the range of conductivity. Color, mostly from dissolved organic matter, is controlled chiefly by lake depth, except for lakes with extensive peatlands in their drainage basins.

Minnesota, North Dakota, South Dakota, Wisconsin↗
USGS2003

Big Soda Lake (Nevada). 1. Pelagic bacterial heterotrophy and biomass

Bacterial activities and abundance were measured seasonally in the water column of meromictic Big Soda Lake which is divided into three chemically distinct zones: aerobic mixolimnion, anaerobic mixolimnion, and anaerobic monimolimnion. Bacterial abundance ranged between 5 and 52 x 10 6 cells ml &minus;1 , with highest biomass at the interfaces between these zones: 2&ndash;4 mg C liter &minus;1 in the photosynthetic bacterial layer (oxycline) and 0.8&ndash;2.0 mg C liter &minus;1 in the chemocline. Bacterial cell size and morphology also varied with depth: small coccoid cells were dominant in the aerobic mixolimnion, whereas the monimolimnion had a more diverse population that included cocci, rods, and large filaments. Heterotrophic activity was measured by [methyl- 3 H]thymidine incorporation and [ 14 C]glutamate uptake. Highest uptake rates were at or just below the photosynthetic bacterial layer and were attributable to small (<1 &micro; m) heterotrophs rather than the larger photosynthetic bacteria. These high rates of heterotrophic uptake were apparently linked with fermentation; rates of other mineralization processes (e.g. sulfate reduction, methanogenesis, denitrification) in the anoxic mixolimnion were insignificant. Heterotrophic activity in the highly reduced monimolimnion was generally much lower than elsewhere in the water column. Therefore, although the monimolimnion contained most of the bacterial abundance and biomass (&sim;60%), most of the cells there were inactive.

Nevada↗
USGS2003

Big Soda Lake (Nevada). 2. Pelagic sulfate reduction

The epilimnion of hypersaline, alkaline, meromictic Big Soda Lake contains an average 58 mmol sulfate liter &minus;1 and 0.4 &micro; mol dissolved iron liter &minus;1 . The monimolimnion, which is permanently anoxic, has a sulfide concentration ranging seasonally from 4 to 7 mmol liter &minus;1 . Depth profiles of sulfate reduction in the monimolimnion, assayed with a 35 S tracer technique and in situ incubations, demonstrated that sulfate reduction occurs within the water column of this extreme environment. The average rate of reduction in the monimolimnion was 3 &micro; mol sulfate liter &minus;1 d &minus;1 in May compared to 0.9 in October. These values are comparable to rates of sulfate reduction reported for anoxic waters of more moderate environments. Sulfate reduction also occurred in the anoxic zone of the mixolimnion, though at significantly lower rates (0.025&ndash;0.090 &micro; mol liter &minus;1 d &minus;1 at 25 m). Additions of FeS (1.0 mmol liter &minus;1 ) doubled the endogenous rate of sulfate reduction in the monimolimnion, while MnS and kaolinite had no effect. These results suggest that sulfate reduction in Big Soda Lake is iron limited and controlled by seasonal variables other than temperature. Estimates of the organic carbon mineralized by sulfate reduction exceed measured fluxes of particulate organic carbon sinking from the mixolimnion. Thus, additional sources of electron donors (other than those derived from the sinking of pelagic autotrophs) may also fuel monimolimnetic sulfate reduction in the lake.

Nevada↗
USGS2003

Big Soda Lake (Nevada). 3. Pelagic methanogenesis and anaerobic methane oxidation

In situ rates of methanogenesis and methane oxidation were measured in meromictic Big Soda Lake. Methane production was measured by the accumulation of methane in the headspaces of anaerobically sealed water samples; radiotracer was used to follow methane oxidation. Nearly all the methane oxidation occurred in the anoxic zones of the lake. Rates of anaerobic oxidation exceeded production at all depths studied in both the mixolimnion (2–6 vs. 0.1–1 nmol liter −1 d −1 ) and monimolimnion (49–85 vs. 1.6–12 nmol liter −1 d −1 ) of the lake. Thus, a net consumption of methane equivalent to 1.36 mmol m −2 d −1 occurred in the anoxic water column. Anaerobic methane oxidation had a first-order rate constant of 8.1±0.5 × 10 −4 d −1 , and activity was eliminated by filter sterilization. However, in situ methane oxidation was of insufficient magnitude to cause a noticeable decrease of ambient dissolved methane levels over an incubation period of 97 h.

Nevada↗
USGS2003

Big Soda Lake (Nevada). 4. Vertical fluxes of particulate matter: Seasonality and variations across the chemocline

Vertical fluxes of particulate organic matter were measured with sediment traps above and below the chemocline of Big Soda Lake to define the seasonality of sinking losses from the mixolimnion and determine the effectiveness of the chemocline (pycnocline) as a barrier to the sinking of biogenic particles. Seasonality of sedimentation rates reflected seasonal changes in the community of autotrophs. During summer-autumn, when production is dominated by autotrophic bacteria, vertical fluxes were small: 100 mg C m −2 d −1 and ≅0.5 mg Chl a m −2 d −1 . Following the winter diatom bloom, vertical fluxes increased markedly: ≅570 mg C m −2 d −1 and 23 mg Chl a m −2 d −1 . The bulk of the seston (> 80%) and particulate carbon (≅ 65%) sinking to the chemocline passed through it, showing that this very sharp density discontinuity does not effectively retard the sinking of particulate matter. However sinking losses of particulate carbon were generally small (≅10%) relative to previous measures of primary productivity, indicating that the mixolimnion is a zone of efficient carbon cycling. Exceptions occurred following the winter bloom when sinking losses were a larger fraction (≅40%) of productivity.

Nevada↗
USGS2003

The design and use of a hydraulic potentiomanometer for direct measurement of differences in hydraulic head between groundwater and surface water

The hydraulic potentiomanometer described herein consists of a potentiometer connected to a manometer by a flexible tube. The device is used to directly measure the direction of seepage as well as the hydraulic-head difference between groundwater and surface water. The device works most effectively in sandy materials. For accurate measurements the device must be free of air leaks.

Limnology and Oceanography↗
USGS2003

A positive relationship between groundwater velocity and submersed macrophyte biomass in Sparkling Lake, Wisconsin

We measured groundwater velocity and submersed macrophyte biomass at 52 shal- low (0.4-6.6 m) sites in mesotrophic Sparkling Lake, Vilas County, Wisconsin, during May-Au- gust 1985. Seventeen percent of variation in macrophyte biomass was explained by a signifi- cant (P < 0.005) relation with depth [log(biomass + 1) = 0.49 depth - 0.08 (depth)2 + 0.121. Some of the remaining variation in macrophyte bio- mass was explained by a significant rank corre- lation of biomass-on-depth residuals with groundwater velocity (rs = 0.46, P < 0.0 1). These results suggest that water movement through the sediment-water interface may be a determinant of macrophyte abundance and distribution.

Wisconsin↗
USGS2003

A study of model bivalve siphonal currents

We carried out experiments studying the hydrodynamics of bivalve siphonal currents in a laboratory flume. Rather than use living animals, we devised a simple, model siphon pair connected to a pump. Fluorescence-based flow visualization was used to characterize siphon-jet flows for several geometric configurations and flow speeds. These measurements show that the boundary-layer velocity profile, siphon height, siphon pair orientation, and size of siphon structure all affect the vertical distribution of the excurrent flow downstream of the siphon pair and the fraction of excurrent that is refiltered. The observed flows may effect both the clearance rate of an entire population of siphonate bivalves as well as the efficiency of feeding of any individual. Our results imply that field conditions are properly represented in laboratory flume studies of phytoplankton biomass losses to benthic bivalves when the shear velocity and bottom roughness are matched to values found in the field. Numerical models of feeding by a bivalve population should include an effective sink distribution which is created by the combined incurrent-excurrent flow field. Near-bed flows need to be accounted for to properly represent these benthic-pelagic exchanges. We also present velocity measurements made with a laser-Doppler anemometer (LDA) for a single configuration (siphons flush with bed, inlet downstream) that show that the siphonal currents have a significant local effect on the properties of a turbulent boundary layer.

Limnology and Oceanography↗
USGS2003

The cycling of iron and manganese in the water column of Lake Sammamish, Washington

Processes controlling the distribution and mobility of Fe and Mn in Lake Sammamish, Washington, a seasonally anoxic lake, are deduced from a year‐long monthly study of physical, chemical, and biological parameters in the lake. Inventories of dissolved Mn and Fe in the bottom waters increase as the redox potential lowers with dissolved Mn inventories during stagnation being much larger than inventories of dissolved Fe. The shapes of the dissolved metal profiles indicate that dissolved Fe is supplied to the hypolimnion during stratification by diffusion of Fe(II) from the sediments into the overlying anoxic water as well as reduction of Fe oxide particles settling through the anoxic water column, while the dominant source of dissolved Mn to the anoxic bottom waters during most of the stratification period appears to be reduction of settling Mn‐oxide particles. Inventories of particulate Fe in the hypolimnion during the latter stages of stratification are significantly larger than inventories of particulate Mn. Peaks of particulate Fe and Mn occur in the water column from July through November and particulate Mn peaks always occur at shallower depths than peaks of particulate Fe. Flux calculations suggest that there is a sufficient supply of both oxygen and reduced metal to the particulate zones for metal‐oxide precipitation to occur. Thermodynamic calculations suggest that during the sulfidic phase of stagnation dissolved Fe concentrations in the very bottom waters may be controlled by FeS precipitation.

Washington↗
USGS2003

The biogeochemical cycling of trace metals in the water column of Lake Sammamish, Washington: Response to seasonally anoxic conditions

Total acid‐soluble and dissolved Cd, Co, Cr, Cu, Ni, Pb, and Zn concentrations in the water column of a seasonally anoxic lake (Lake Sammamish, Washington) were measured on a monthly basis during the course of a year. These data, in conjunction with Fe, Mn, sulfide, and nutrient data, are used to assess the biochemical processes controlling the distribution of trace metals in the lake and how the importance of these processes varies with time. Thermodynamic calculations are used to examine changes in dissolved metal speciation in the bottom waters during the year and to assess the saturation state of metal‐sulfide phases. Spatial and temporal changes in the redox conditions of the bottom waters result in increases in dissolved Co and Ni concentrations, peaks in particulate Co profiles, decreases in dissolved Cu and Cr concentrations, and significant changes in dissolved metal speciation during stagnation. The redox‐driven cycling of Fe and Mn in the hypolimnion has a dramatic effect on Co distributions, a slight effect on Ni concentrations, and virtually no effect on Cd, Cu, Cr, and Zn concentrations. Biological uptake and regeneration processes result in a correlation between Zn and silicate concentrations throughout the water column, and it appears that biological cycling may also influence the distribution of Cd. During the sulfidic phase of stagnation dissolved Cd concentrations in the bottom waters may be controlled by metal‐sulfide precipitation, Cr(VI) is probably reduced to more particle‐reactive Cr(III) and removed by settling particles, and Cu(II) is most likely reduced to Cu(I) and precipitated as a metal‐sulfide phase.

Washington↗
USGS2003

Landscape linkages between geothermal activity and solute composition and ecological response in surface waters draining the Atlantic slope of Costa Rica

Surface waters draining three different volcanoes in Costa Rica, ranging from dormant to moderately active to explosive, have a wide range of solute compositions that partly reflects the contribution of different types of solute-rich, geothermal waters. Three major physical transport vectors affect flows of geothermally derived solutes: thermally driven convection of volcanic gases and geothermal fluids; lateral and gravity-driven downward transport of geothermal fluids; and wind dispersion of ash, gases, and acid rain. Specific vector combinations interact to determine landscape patterns in solute chemistry and biota: indicator taxa of algae and bacteria reflect factors such as high temperature, wind-driven or hydrologically transported acidity, high concentrations of various solutes, and chemical precipitation reactions. Many streams receiving geothermally derived solutes have high levels of soluble reactive phosphorus (SRP) (up to 400 µ g liter −1 ), a nutrient that is typically not measured in geochemical studies of geothermal waters. Regional differences in levels of SRP and other solutes among volcanoes were typically not significant due to high local variation in solute levels among geothermally modified streams and between geothermally modified and unmodified streams on each volcano. Geothermal activity along the volcanic spine of Costa Rica provides a natural source of phosphorus, silica, and other solutes and plays an important role in determining emergent landscape patterns in the solute chemistry of surface waters and aquatic biota.

Limnology and Oceanography↗
USGS2003

Meromixis in hypersaline Mono Lake, California. 2. Nitrogen fluxes

Vertical fluxes of nitrogen were examined in hypersaline Mono Lake over a 9-yr period which encompassed the onset, persistence, and breakdown of meromixis. Under monomictic conditions, ammonia, which accumulates in the hypolimnion, is mixed into the euphotic region during autumn overturn. Following the onset of meromixis in 1983 and elimination of the winter period of holomixis, ammonia was depleted in the mixolimnion and accumulated beneath the chemocline. The mean rate of particulate nitrogen deposition, as measured by sediment traps over a 2-yr period during meromixis, was 2.0 mmol m −2 d −1 . Until meromixis weakened in 1988, ammonia concentrations in the euphotic zone remained below 5 µ M and increased to ~500 µ M beneath the chemocline. Meromixis ended in November 1988 and a large pulse of ammonia was injected into surface waters, resulting in surface ammonia concentrations of ~45 µ M. Because the pH of Mono Lake is high (9.8) the : ratio is ~5, and elevated surface concentrations of ammonia during the 2 yr following breakdown of meromixis resulted in high losses of nitrogen via ammonia volatilization (mean, ~10 mmol m − 2 d −1 ). High release rates of ammonia from the sediments were estimated from both the ammonia gradients in pore-water profiles (3–10 mmol m −2 d −1 ) and the balance of mixolimnetic nitrogen fluxes (4–10 mmol m −2 d −1 ). The monimolimnetic balance suggested fluxes of ammonia out of the sediments below the chemocline were reduced during meromixis.

California↗
USGS2003

Exopolymer microenvironments of microbial flora: Multiple and interactive effects on trophic relationships

Microbial cells in natural environments are often encased in different types of exopolymer secretions (EPS), ranging from tight capsules surrounding individual cells to the looser slime matrices of biofilms. The different physical and chemical properties of exopolymers could have secondary effects on trophic interactions between microbial cells and consumer animals. Laboratory studies showed that capsule EPS is significantly less digestible to consumers than slime EPS, even when extracted from the same bacterial strain. Bacterial cells with EPS capsules are less efficiently digested than noncapsuled cells, suggesting that capsules protect against digestion. Follow-up experiments determined that polysaccharide-rich fractions of slime EPS are absorbed with very high efficiencies while protein portions, which are more abundant in capsular polymers, are absorbed relatively poorly. Another series of experiments showed that dissolved organic matter (DOM), when adsorbed directly to the mineralogical portions of sediment particles, is available to deposit feeders. However, the further presence of an exopolymer coating on sediments more than doubled the bioavailability of adsorbed DOM to the consumer. Observations using cold-stage scanning electron microscopy indicated that exopolymer microenvironments are a common feature of natural marine sediments. Microbial exopolymers range from easily digestible carbon sources to relatively refractory ones that effectively protect some microbial cells from consumer digestion. Exopolymer microenvironments may also make recently adsorbed DOM highly accessible to particle-ingesting animals.

Limnology and Oceanography↗
USGS2003

Stable isotopes of oxygen and hydrogen in the Truckee River–Pyramid Lake surface‐water system. 2. A predictive model of δ18O and 182H in Pyramid Lake

A physically based model of variations in δ 18 O and δ 2 H in Pyramid Lake is presented. For inputs, the model uses measurements of liquid water inflows and outflows and their associated isotopic compositions and a set of meteorological data (radiative fluxes, air temperature, relative humidity, and windspeed). The model simulates change of lake volume, thermal and isotopic stratification, evaporation, and the isotopic composition of evaporation. A validation of the model for 1987–1989 and 1991 indicates that it can reproduce measured intra‐ and interannual variations of δ 18 O and δ 2 H. Three applications of the model demonstrate its ability to simulate longer term responses of δ 18 O to change in the hydrologic balance and hydrologic characteristics (opening and closing) of the lake.

Nevada↗