Profundal Lake Sediments Research Articles

Quantitative evidence for Arctic continental freezing in a high-CO 2 world: Junggar Basin, NW China

Abstract We show that the Late Triassic–Early Jurassic continental Arctic experienced wintertime freezing conditions, despite the exceptionally high atmospheric CO 2 levels, by quantifying common lake ice-rafted debris (L-IRD) identified in the Junggar Basin of Xinjian, NW China. This L-IRD consists of outsized (0.1–12 mm) lithic clasts ‘floating’ in otherwise fine-grained, profundal lake sediment matrix. Laser-diffraction grain-size analysis demonstrates that the grain-size distribution for lacustrine strata of Junggar Basin is very similar to modern sediments from the seasonally ice-covered Sea of Okhotsk, reflecting a similar depositional mechanism. Three-dimensional computed tomography and two-dimensional thin sections demonstrate that the outsized clasts are dispersed, rather than confined to sand lenses or layers. These results are inconsistent with alternative methods of bimodal sediment deposition such as mud flows, algae rafting or root rafting. The discovery of Triassic–Jurassic continental freezing provides new context for understanding global climate during periods with high-CO 2 conditions and climate and biotic changes in the Mesozoic Era.

Seasonal patterns of methylmercury production, release, and degradation in profundal sediment of a hypereutrophic reservoir

Fuhrmann B, Beutel M, Ganguli P, Zhao L, Brower S, Funk A, Pasek J. 2021. Seasonal patterns of methylmercury production, release, and degradation in profundal sediment of a hypereutrophic reservoir. Lake Reserv Manage. 37:360–377. Profundal lake sediment is an important site of toxic methylmercury (MeHg) production by anaerobic bacteria. This study tracked sediment MeHg cycling in hypereutrophic Hodges Reservoir, in the United States. Sediment-associated MeHg was most elevated in the early spring during moderately reduced conditions. In the late spring, MeHg and iron were released into hypolimnetic water during the progression from iron-reducing to sulfate-reducing conditions at the sediment–water interface. A decrease in porewater sulfate in the early summer indicated enhanced sulfate-reducing bacteria (SRB) activity and was associated with sediment buildup of MeHg, likely due to enhanced sorption to iron sulfides. Depletion of sulfate in the sediment during the fall corresponded with a substantial decrease in both sediment and water-column MeHg, suggesting that methanogenic conditions led to enhanced MeHg degradation. Shortly afterward, MeHg increased in the hypolimnion, indicating an upward shift in the zone of SRB methylation. Our study suggests 2 “hot moments” of MeHg entry into the water column, where it is susceptible to uptake into the pelagic food web: a spring window of mildly reduced conditions that promote MeHg release from sediment, and a fall window where MeHg is produced in the upper hypolimnion. These hot moments may potentially be managed to lower mercury bioaccumulation via redox enhancement of the profundal zone with approaches such as bottom water oxygenation, which began operation in Hodges Reservoir in 2020. However, the complexity of biogeochemical responses to such management perturbations in regard to MeHg cycling makes it difficult to predict the ultimate effect of oxygenation on mercury bioaccumulation. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2021.1940397 .

Effects of chironomid density and dissolved oxygen on mercury efflux from profundal lake sediment

ABSTRACTBeutel MW, Cox SE, Gebremariam S. 2016. Effects of chironomid density and dissolved oxygen on mercury efflux from profundal lake sediment. Lake Reserv Manage. 32:158–167.Benthic macrofauna can dramatically affect the flux of dissolved compounds into and out of lake sediment. In this study, replicate experimental chambers containing profundal sediment from a relatively pristine lake were incubated under low (∼1000/m2) and high (∼3800/m2) chironomid densities and low (∼2.5 mg/L) and medium (∼5.0 mg/L) dissolved oxygen in chamber water. Dissolved methylmercury efflux rates were highest in high chironomid density/low oxygen chambers (0.35 ± 0.06 ng/m2/d, mean ± standard error, n = 4) and lowest in low density/medium oxygen chambers (0.06 ± 0.14 ng/m2/d). In contrast, dissolved total mercury efflux assessed at low dissolved oxygen (∼2.5 mg/L) was higher at low chironomid density (4.6 ± 0.7 ng/m2/d) relative to high chironomid density (2.5 ± 0.8 ng/m2/d, n = 4). Results indicate that oxygen addition, a common lake management practice, may enhance methylmercury efflux from profundal sediment as macrofauna recolonize previously anaerobic sediments. However, benthos-mediated methylmercury efflux rates are lower than hypolimnetic methylmercury accumulation rates under anaerobic conditions; therefore, relative to anaerobic conditions, oxygenation should lower net methylmercury accumulation rates in relatively pristine lakes.

Bacillus stamsii sp. nov., a facultatively anaerobic sugar degrader that is numerically dominant in freshwater lake sediment

A novel type of anaerobic bacteria was previously isolated from profundal lake sediment by direct dilution of the sediment in mineral agar medium containing glucose and a background lawn of Methanospirillum hungatei as a syntrophic partner. The isolated bacteria grouped with aerobic Bacillus spp. according to their 16S rRNA gene sequence, and the most closely related species is Bacillus thioparans. Fermentative growth of the novel strain with glucose was possible only in the presence of syntrophic partners, and cocultures produced acetate and methane, in some cases also lactate and traces of succinate as fermentation products. In contrast, the closely related strains Bacillus jeotgali and Bacillus sp. strain PeC11 are able to grow with glucose axenically by mixed acid fermentation yielding lactate, acetate, formate, succinate, and ethanol as fermentation products. Alternatively, the isolated strain grew anaerobically in pure culture if pyruvate was added to glucose-containing media, and lactate, acetate and formate were the major fermentation products, but the strain never produced ethanol. Aerobic growth was found with a variety of organic substrates in the presence of partly reduced sulfur compounds. In the absence of sulfide and oxygen, nitrate served as an electron acceptor. Strain BoGlc83 was characterized as the type strain of a new species for which the name Bacillus stamsii sp. nov. (DSM 19598=JCM 30025) is proposed.

Linkages between Quaternary climate change and sedimentary processes in Hala Lake, northern Tibetan Plateau, China

Profundal lake sediment cores are often interpreted in line with diverse and detailed sedimentological processes to infer paleoenvironmental conditions. The effects of frozen lake surfaces on terrigenous sediment deposition and how climate changes on the Tibetan Plateau are reflected in these lakes, however, is seldom discussed. A lake sediment core from Hala Lake (590km2), northeastern Tibetan Plateau spanning the time interval from the Last Glacial Maximum to the present was investigated using high-resolution grain-size composition of lacustrine deposits. Seismic analysis along a north–south profile across the lake was used to infer the sedimentary setting within the lake basin. Periods of freezing and melting processes on the lake surface were identified by MODIS (MOD10A1) satellite data. End-member modeling of the grain size distribution allowed the discrimination between lacustrine, eolian and fluvial sediments. The dominant clay sedimentation (slack water type) during the global Last Glacial Maximum (LGM) reflects ice interceptions in long cold periods, in contrast to abundant eolian input during abrupt cold events. Therefore, fluvial and slack water sedimentation processes can indicate changes in the local paleoclimate during periods of the lake being frozen, when eolian input was minor. Inferred warm (i.e., ∼22.7 and 19.5cal.ka BP) and cold (i.e., ∼11–9 and 3–1.5cal.ka BP) spells have significant environmental impacts, not only in the regional realm, but they are also coherent with global-scale climate events. The eolian input generally follows the trend of the mid-latitude westerly wind dynamics in winter, contributing medium-sized sand to the lake center, deposited within the ice cover during icing and melting phases. Enhanced input was dominant during the Younger Dryas, Heinrich Event 1 and at around 8.2ka, equivalent to the well-known events of the North Atlantic realm.

High spatial resolution of distribution and interconnections between Fe- and N-redox processes in profundal lake sediments.

The Fe and N biogeochemical cycles play key roles in freshwater environments. We aimed to determine the spatial positioning and interconnections of the N and Fe cycles in profundal lake sediments. The gradients of O2, NO3(-), NH4(+), pH, Eh, Fe(II) and Fe(III) were determined and the distribution of microorganisms was assessed by most probable numbers and quantitative polymerase chain reaction. The redox zones could be divided into an oxic zone (0-8 mm), where microaerophiles (Gallionellaceae) were most abundant at a depth of 7 mm. This was followed by a denitrification zone (6-12 mm), where NO3(-)-dependent Fe(II) oxidizers and organoheterotrophic denitrifiers both reduce nitrate. Lastly, an iron redox transition zone was identified at 12.5-22.5 mm. Fe(III) was most abundant above this zone while Fe(II) was most abundant beneath. The high abundance of poorly crystalline iron suggested iron cycling. The Fe and N cycles are biologically connected through nitrate-reducing Fe(II) oxidizers and chemically by NOx(-) species formed during denitrification, which can chemically oxidize Fe(II). This study combines high resolution chemical, molecular and microbiological data to pinpoint sedimentary redox zones in which Fe is cycled between Fe(II) and Fe(III) and where Fe and N-redox processes interact.

Response of the methanogenic microbial community of a profundal lake sediment (Lake Kinneret, Israel) to algal deposition

An algal bloom of Peridinium gatunenese generally precedes the annual maximum of methane release from the profundal sediment of Lake Kinneret. Therefore, we investigated the response of the sediment methanogenic microbial community to simulated algal deposition. Addition of algal biomass on top of sediment cores resulted in increased CH4 production rates and concentrations of the fermentation products acetate and propionate in the upper 4‐cm layers with maximum values at 1‐cm depth. Addition of algae to sediment slurries also resulted in increased CH4 production rates and a transient increase of H2, propionate, and acetate concentrations within the first 10 d after addition. The composition of the active microbial community was determined by analysis of terminal restriction fragment polymorphism (T‐RFLP) targeting ribosomal RNA and cloning and sequencing of reverse‐transcribed 16S rRNA. Analysis of the sediment in the presence and absence of algae indicated that among the Bacteria, members of Deltaproteobacteria and Clostridiales responded by synthesis of ribosomes after 1 d of incubation and those of Bacteroidetes after 6 d. Among the Archaea, ribosomal RNA of the Methanosaetaceae (i.e., acetate‐utilizing methanogens) slightly increased after 6 d. Algal deposition apparently stimulated ribosomal synthesis in these sediment microorganisms, thus resulting in increased activity. We conclude that these microorganisms were involved in degradation of the algal biomass resulting in transient release of acetate and other fermentation products and increased production of CH4.

An assessment of toxicity in profundal lake sediment due to deposition of heavy metals and persistent organic pollutants from the atmosphere

A Tier I Sediment Ecological Risk Assessment of profundal lake sediment contaminated by diffuse pollution of heavy metals and POPs deposited from the atmosphere was completed. The concentrations of seven heavy metals and four groups of POPs (OCs, PCBs, PAHs, PBDEs) were determined in the profundal sediment of ten lakes in the United Kingdom and two sediment toxicity tests completed (chironomid survival and emergence and cladoceran survival and reproduction). The results showed that around half the lakes are at least moderately contaminated by Pb, Zn, Cd, As and PAHs deposited from the atmosphere and the toxicity quotient suggests that the contaminants of concern are Pb, As and PAHs, and not the other metals nor OCs and PCBs. There was toxicity in the sediment of four of the lakes. The Probable Effect Concentration Quotient values indicated that metals in the sediments of Scoat Tarn, Agden Reservoir and Llyn Llagi were likely to be responsible for the laboratory toxicity found in these lakes, with PAHs also contributing in Agden Reservoir.

Community structure of Archaea and Bacteria in a profundal lake sediment Lake Kinneret (Israel)

The microbial community structure of an anoxic profundal lake sediment, i.e., subtropical Lake Kinneret, was analysed with respect to its composition by culture-independent molecular methods including terminal restriction fragment length polymorphism (T-RFLP) analysis, comparative sequence analysis, and quantitative real-time PCR. In particular we were interested in the structure, species composition, and relative abundance of the overall microbial community in the methanogenic sediment layer (0–10 cm depth). Pairwise comparison of archaeal and bacterial 16S rRNA gene T-RFLP profiles obtained from three independent samplings indicated stability of the microbial community. The numbers of Archaea and Bacteria, quantified by real-time PCR, amounted to about 10 8 and 10 10 16S rRNA gene copies cm −3 sediment, respectively, suggesting that Archaea may account for only a minor fraction (approximately 1%) of the total prokaryotic community. Hydrogenotrophic Methanomicrobiales and acetoclastic Methanosaeta spp. dominated T-RFLP profiles of the archaeal community. T-RFLP profiles of the bacterial community were dominated by Deltaproteobacteria, sulphate reducers and syntrophs in particular. The second most abundant group was assigned to the Bacteroidetes–Chlorobi-group. Only one bacterial group, which was affiliated with halorespiring bacteria of subphylum II of the Chloroflexi, showed variation in abundance within the sediment samples investigated. Our study gives a comprehensive insight into the structure of the bacterial and archaeal community of a profundal lake sediment, indicating that sulphate reducers, syntrophs, bacteroidetes, halorespirers and methanogens are of particular importance in Lake Kinneret sediment.

Mercury Concentrations in Lake Sediments – Revisiting the Predictive Power of Catchment Morphometry and Organic Matter Composition

Lake sediments are a potential source of mercury (Hg) for aquatic biota. Here, we investigated the predictive power of (a) key parameters for lake catchment morphometry and (b) organic matter composition of sediments in an effort to account for observed variations of total (THg) and methyl (MeHg) mercury concentrations in lake sediments. Using regression models we demonstrate that the morphometric parameters lake depth as well as inclination of catchment soils and lake bottoms can significantly predict variations of THg concentrations, but not MeHg, at profundal lake sediments. Although THg and MeHg concentrations in sediments could not be predicted by specific organic matter sources, as elucidated by atomic C/N ratios, our data suggest that wetland-derived total organic carbon (TOC) contained less THg concentrations than TOC derived from mostly forested watersheds. However, TOC concentrations could significantly predict MeHg concentrations and the proportion of methylated Hg at all sediment stations. Finally, from an ecotoxicological point of view, we propose that concentrations of TOC at surface lake sediments, rather than parameters of catchment morphometry, may predict dietary sources of MeHg for benthic consumers and consequently perhaps for organisms at higher trophic levels.

Dynamics in composition and size-class distribution of humic substances in profundal sediments of Lake Constance

Organic matter from profundal lake sediments was fractionated and analyzed with high depth resolution, and the size-class distribution of humic substances was determined by gel-permeation chromatography. Together with a depth-dependent increase of the thermal stability of the organic matter and an increasing C/N atomic ratio of the humic acids, the size-distribution patterns of different fractions indicated an increasing degree of humification with depth. The main stabilization processes occurred in the surface layer (0–2 cm depth), which is clearly distinguished from the deeper sediment. The depth profiles also indicated that humification in lake sediments consists of simultaneous degradation and polymerization processes.

Lake sediment geochemical methods in the Canadian Shield, Cordillera and Appalachia

Abstract Lake sediment geochemistry has been used in Canada since the 1970s for mineral exploration and resource evaluation in glaciated regions of Appalachia, the Canadian Shield and the western Cordillera which are of low to moderate relief. Geochemical signatures of bedrock and mineralization within a lake’s catchment basin are commonly reflected in the chemical constituents of the organic-rich Holocene sediment which has been transported from source by a combination of mechanical and hydromorphic processes. Lake sediment geochemical surveys have been used successfully to discover base metal, Au, Mo, W, Sb, Sn, U, and REE mineralization. The scale of such surveys determines the size and density of lake sediment sampling. In regional surveys, large lithological targets such as greenstone belts or chemically distinctive intrusives can be identified by low density ( c. 1 per 10–15 km 2 ) sampling of relatively larger lakes. Smaller targets such as mineralized areas require higher density ( c. 1 per 4–5 km 2 ) sampling using a greater number of smaller lakes. Regional surveys are typically helicopter-borne, and employ a tubular grab sampler which permits rapid reconnaissance-scale coverage of large areas. Centre-basin profundal lake sediment, or gyttja, is an ideal sample medium because of its homogeneity and abundance of fine-grained organic matter, which complexes with many trace elements. Multi-element analytical techniques in common use include inductively coupled plasma emission spectrometry (ICP-ES), ICP mass spectrometry (ICP-MS) and instrumental neutron activation analysis (INAA). Reliability of data is assessed by analysis of known standards, site duplicates and sample splits. PC statistical software packages facilitate the interpretation of geochemical data, and desktop GIS packages aid in further interpretation and generation of multi-layer maps.

A comparison of differing lake sediment field sample sizes: application to geochemical exploration for epithermal gold deposits in central British Columbia

Profundal lake sediments are effective sample media for geochemical surveys in the northern Interior Plateau of central British Columbia, where epithermal gold prospects are an important exploration target. The problems posed by sampling of surficial materials for Au analysis are well known, but no field investigations have been made into the most appropriate size of lake sediment samples to collect in this part of the Cordillera. Samples collected with the Hornbrook-type sampler typically weigh 50 to 100 g when dry, and doubling the size of the field samples might be expected to yield more representative and reliable Au concentrations. To test this hypothesis, a comparative study of two field sample sizes was conducted in Clisbako Lake, adjacent to the Clisbako epithermal gold prospect, to ascertain whether or not there are significant differences in Au concentrations with increasing sample size. Clisbako Lake is located about 100 km west of Quesnel in the Fraser Plateau, an area of low to moderate relief and extensive drift cover. Gold occurs in quartz stockwork and silicified breccia zones within a low-sulphidation adularia-sericite epithermal system hosted in Eocene continental volcanics. Two corresponding lake sediment samples were collected at each of 36 sites: a standard sample obtained from a single drop of the sampler, and a second, larger sample obtained by combining sediment from two drops of the sampler. Sediments were dried, disaggregated and pulverized in a ceramic ring mill prior to analysis for Au and additional elements by instrumental neutron activation analysis (INAA). Gold concentrations in the centre of the profundal basin (4–8 ppb) are considerably greater than the regional median of 1 ppb in the Nechako Plateau to the north. Elevated concentrations of Au, As (median: 25.5 ppm) and Sb (median: 3.1 ppm) in lake sediments reflect the geochemistry of adjacent zones of epithermal mineralization and alteration. Median concentrations of 9 ppb Au over the entire lake were obtained for both standard and large-size sample suites, and gold distribution patterns are similar for both sample sizes. Equivalency of population means were tested with a two-sample paired duplicate t-test and single-factor analysis of variance (ANOVA) on 34 sample pairs. Results indicate that there is no significant difference between Au concentrations of the standard and large-size lake sediment samples. There is no evidence to suggest that use of larger, more costly, lake sediment samples are more effective or reliable indicators of epithermal Au mineralization in this region than standard-size samples. The standard samples are satisfactory media for regional and property-scale lake sediment geochemical surveys.

Do aquatic insects avoid cadmium‐contaminated sediments?

AbstractThe long‐term colonization of profundal lake sediments having a range of spiked cadmium (Cd) concentrations (0.007 to 2.7 μol/g dry wt.) was measured in the field. Population densities of two of the most abundant colonizing insects (the chironomids Procladius [Holotanypus] sp., and Sergentia coracina) were unrelated to the Cd gradient, even though both taxa accumulated Cd in direct relation to its concentration in sediment. Cadmium concentrations in these taxa ranged from approximately 0.3 to 5 μg/g, and 1 to 65 μg/g, respectively, along the sediment Cd gradient. Cadmium concentrations in Chironomus (salinarius gp.) sp. larvae also responded positively to the sediment Cd gradient and ranged from 0.2 to 50 μg/g. In contrast with the two other taxa, the abundance of Chironomus (salinarius gp.) sp. larvae was negatively correlated with the sediment Cd gradient. To determine if the abundance pattern of Chironomus (salinarius gp.) sp. was the result of a behavioral or a toxic response, larvae of the three chironomid taxa were given a choice between field]control and Cd‐spiked sediments in the laboratory. None of the taxa avoided the Cd‐spiked sediments, suggesting that the lower abundance of Chironomus (salinarius gp.) sp. at high Cd concentrations in the field was due to Cd toxicity and not to avoidance of the Cd‐rich sediments.

Effects of Deposit-Feeder Activity on Bacterial Production and Abundance in Profundal Lake Sediment

Effects of the amphipod Monoporeia affinis, the oligochaete Tubifex tubifex and the chironomid Chironomus riparius on the production ([³H]-thymidine incorporation) and abundance (acridine orange direct counts) of sediment bacteria were studied in a series of microcosm experiments. Measurements were performed on the visually distinct sediment zonation generated by oxygen penetration and influenced by deposit-feeder activity. All three species at higher densities caused an increase in the depth of the light-colored surficial sediment layer in the microcosms. Bacterial production in surficial sediment increased by factors as high as 3.2× (Monoporeia experiment), 1.4× (Tubifex experiment), and 4.4× (Chironomus experiment) compared with controls. Physical disturbance of sediment through invertebrate activity was concluded to be the main causal mechanism for increases in bacterial production. Changes in bacterial abundance appeared to be zoobenthos species-specific, reflecting differences in feeding and/or foraging behavior of the animals. Bacterial abundance was negatively affected by mechanical stirring and by the activity of Tubifex tubifex, a subsurface deposit-feeder known to gain a large proportion of its energy demand from sediment bacteria. Monoporeia affinis and Chironomus riparius did not affect bacterial abundance; apparently their surficial feeding activity resulted in a compensation of bacterial losses. In subsurface sediment layers neither bacterial abundance nor production was affected by any of the three species.

Mobilization of gold into lake sediments from acid and alkaline mineralized environments in the southern Canadian Shield: Gold in lake sediments and natural waters

To be an effective indicator of mineralization in lake sediment surveys within the Canadian Shield, it is desirable that an element migrate in solution or adsorbed on suspensates. Given the low relief and disorganized drainage patterns of this region, dispersal in clastic form in drainage systems is limited and gives rise to erratic distributions. The purpose of this study was to discover whether Au shows significant hydromorphic mobility, which would justify the increasing use that is being made of this element in lake sediments as an indicator for gold mineralization. Waters and lake sediments were collected from Napier Lake, Ontario; PAP Lake, Saskatchewan; and Foster Lake, Manitoba, all of which contain Au-quartz vein mineralization and lie within the glaciated boreal forest zone of the Canadian Shield. In all three areas, profundal lake sediments down-drainage of mineralization contain Au concentrations higher than regional mean concentrations. Significant dissolution and transport of Au was found under oxidizing conditions associated with waters with pH that varied from acid to alkaline. Waters from drill holes penetrating mineralization contain up to 401 ng L −1 Au (note; 1 ng L −1 is equivalent to 1 part per trillion, 10 −12). Surface waters overlying or near mineralization collected from bogs, seeps, ponds and streams contain up to 13 ng L −1. The content of Au in lake waters is lower, with a maximum of 1.1 ng L −1. There is also a detectable quantity of Au present in suspensates. Two samples of particulates (> 1 μm) filtered from lake water have Au equivalent to 0.17 ng L −1 and 0.039 ng L −1. While the contents of Au present in solution or as suspensates in lake and stream water are relatively small, they are sufficient, if precipitated, to generate anomalies in lake sediments. Thus for Reservoir Lake, in the Foster Lake area, water from the principal stream entering the lake carries 0.3 ng L −1 Au. This provides an annual flux which far exceeds that required to generate the 7.3 ppb Au contained in profundal sediments of this lake; a content that is anomalous relative to the regional median content of < 1 ppb Au for lake sediments. Hydrogeochemical prospecting involving analysis for Au is one method for tracing the source of anomalous Au in lake sediments. Collection of 1 L samples without field treatment, followed by extraction of Au into MIBK, then analysis by graphite-furnace atomic absorption spectrophotometry, permits detection levels for Au of 0.5 ng L −1. This is below the contents of Au found in some waters from mineralized areas. A detection limit of 0.3 ng L −1 was obtained using larger water samples.

Mineralization of glucose and lignocellulose by four arctic freshwater sediments in response to nutrient enrichment.

Microbial biomass and activity were examined in four different arctic sediments: littoral lake sediment and profundal lake sediment from Toolik Lake, Alaska, thaw pond sediment, and eroding river bank peat. The thaw pond sediment had the largest viable microbial biomass, while the profundal sediment had the smallest. Rates of glucose or acetate incorporation into lipids, glucose mineralization, and lignocellulose mineralization (all normalized per unit of biomass) were highest in the river peat sample, however. The kinetics of glucose mineralization in the profundal sediment were very different from those in the other three samples: although the initial rate of mineralization was five times lower than that in the peat and two times lower than that in the littoral and thaw pond sediments, the maximum amount of 14CO2 evolved from [14C]glucose eventually equaled that in the peat and exceeded that in the littoral and thaw pond sediments by 2.0 and 3.5 times, respectively. Carex aquatilis [14C-cellulose]- and [14C-lignin]lignocellulose mineralization rates in the profundal sediment equaled or exceeded those in the littoral sediment after 16 and 46 days, but the pattern of nutrient limitation differed: the profundal sediment was the only one sampled that exhibited nitrogen limitation, while the other three sediments appeared to be limited primarily by phosphorus. The addition of nitrogen and phosphorus together had no cumulative effects on lignocellulose mineralization. When the rates of mineralization or incorporation of glucose are compared with those of lignocellulose, the results of this study indicate that profundal sediment communities may be better able to utilize the more recalcitrant substrates relative to the labile substrates than microbial communities from sediments rich in detritus and standing macrophytes.

Metals in Fish Scales Collected in Lake Opeongo, Canada, from 1939 to 1979

Abstract Time series (1939–1979) of metal concentrations in historical collections of scales from lake trout Salvelinus namaycush and smallmouth bass Micropterus dolomieui from Lake Opeongo, Canada, were compared with temporal trends in metal concentration profiles in core samples of profundal lake sediment. There was no trend for Zn in scales. Elevated Cu and Hg concentrations occurred early in the study period in both species. Elevated Cd was found in the earliest year in smallmouth bass scales. Temporal trends in Hg (and possibly Cd) in smallmouth bass scales probably were attributable to differences in fish weight among years. The data did not support the hypothesis that temporal trends in metal loadings entering lakes are reflected by fish tissue concentrations.

Emission of hydrogen from deep and shallow freshwater environments

In-situ partial pressures of hydrogen in anoxic profundal lake sediments reached values of up to 5 Pa which were more than 5 orders of magnitude lower than the partial pressures of methane. Analysis of gas bubbles collected from anoxic submerged paddy soil showed H2 partial pressures in the range of 1.8 ± 1.3 Pa being ca. 4 orders of magnitude lower than the CH4 partial pressures. H2 emission rates, on the other hand, were less than 3 orders of magnitude lower than the CH4 emission rates indicating that H2 and CH4 were oxidized to a different extent in the rhizosphere of the soil before they reached the atmosphere, or that H2 was produced by the plants. More than 70% of the emitted H2 reached the atmosphere via plant-mediated flux. The rest was emitted via ebullition from the anoxic soil and, in addition, was produced in the paddy water. A significant amount of H2 was indeed found to be produced in the water under conditions where thallic algae and submerged parts of the rice plants produced oxygen by photosynthesis. Very little H2 was emitted via molecular diffusion through the paddy water; in addition, this amount was less than expected from the degree of supersaturation and the diffusional emission rate of CH4 indicating a relatively high rate of H2 consumption in the surface film of the paddy water. The total H2 source strength of rice paddies and other freshwater environments was estimated to be less than 1 Tg yr-1, being negligible in the atmospheric budget of H2.

Terrain Geochemistry Surveys, Permafrost Studies, and Arctic Limnology, District of Keewatin, N.W.T.: Implications for Water Quality Monitoring in the North

Abstract Geochemical studies and surveys conducted by the Geological Survey of Canada have provided considerable information about the natural geochemical variations in glacial drift, lake sediments, and lake waters in south-central District of Keewatin. In addition to their intended contribution to mineral exploration, these activities yielded much basic background data that may be applied to the planning of water quality monitoring programs in the region. Studies of permafrost features, and arctic limnology have furnished knowledge about natural geomorphic and diagenetic processes that influence surface water quality. Cryoturbation, on land and in the shallow areas of lakes underlain by permafrost, plays a major role in the transfer of particulate and dissolved drift constituents to surface waters. In spite of the abundance of mineral detritus on shore, profundal lake sediments are typically highly diatomaceous and possess conspicuous oxic surface layers that likely have a strong capacity to sequester both nutrients and trace metals.