Spatial distribution and species composition of prosthecate bacteria in Lake Baikal

From the water column of Lake Baikal, several strains of prosthecate bacteria belonging to the genera Caulobacter and Brevundimonas were isolated. In this article, the methods applied for their isolation and cell number determination are described; the occurrence frequency and spatial distribution of these microorganisms in the lake are demonstrated. Characterization of the species composition of cultivable and uncultivable prosthecate bacteria was carried out using the methods of traditional and molecular microbiology, respectively. A comparative phylogenetic analysis of the DNA sequences of uncultivable bacteria, which showed homology to the members of the alpha subclass of proteobacteria, was carried out. It was demonstrated that the lake water column is inhabited by uncultivable alpha-proteobacteria of uncertain phylogenetic affinity, in addition to representatives of the species Caulobacter vibrioides and C. leidyi, which were detected by traditional microbiological methods.     

Lake Baikal climatic record between 310 and 50 ky BP: Interplay between diatoms, watershed weathering and orbital forcing

The environmental record from Lake Baikal, Russia, from 310 to 50 ky BP (MIS 9a to MIS 3) was interpreted using rock magnetic, UV–Vis spectral, mineralogical, and diatom analyses. The age model was based on a correlation of the diatom and chemical weathering records and the summer insolation curve at 55°N and checked against an age model based on the proxy of relative palaeointensity of the Earth's magnetic field. Peaks in chemical weathering within the watershed, inferred from maximum concentration of magnetic and coloured minerals and mica, the lowest mean Fe oxidation state in silicates and highs in expandable clay minerals correlated with the Northern Hemisphere summer insolation minima at 55°N. Reconstructed changes in weathering intensity are better correlated to insolation patterns than to global ice volume records. We propose a scheme of yet missing palaeoenvironmental interpretation of the diatom assemblage, including also some extinct species. Aulacoseira baicalensis and Aulacoseira skvortzowii were abundant in the early stages of lake flora recovery immediately after deglaciation and during MIS 7e and MIS 5e; periods of more pronounced continental climate and peak chemical weathering. Stephanodiscus formosus var. minor, Cyclotella minuta and Cyclotella ornata dominated in intervals of decreased seasonality and decreased humidity at the end of most interglacial/interstadial diatom zones. Stephanodiscus grandis, Stephanodiscus carconeiformis and Stephanodiscus formosus were ubiquitous between MIS 8 and MIS 5, an interval marked by high seasonality, i.e., large differences between winter and summer insolation, and low humidity revealed by a low hydrolysis of expandable clay minerals in the watershed. Diatom concentrations peaked in the climatic optima of MIS 7e and MIS 5e and in the short periods marked by shifts to warmer conditions in the upper sections of MIS 5: MIS 5c (103–99 ky BP), MIS 5b (90–88 ky BP), and MIS 5a (84–79 ky BP) in which increased humidity resulted in enhanced hydrolysis of clay minerals. No such short similar climatic optimums were found from MIS 9a to MIS 6. Sharp climate deteriorations recorded in the diatom and clay mineral records at 107, 94, and 87 ky BP, however, occurred within 1–2 ky of cold extremes in North Atlantic sea surface temperature emphasizing the strong teleconnections between the two localities.     

Isotopic evolution of Glacial Lake Agassiz: New insights from cellulose and porewater isotopic archives

Significantly differing estimates of the oxygen-isotope composition of Lake Agassiz have been obtained from two co-existing isotopic archives within a sediment core originating from Montcalm, Manitoba, in the southern basin of the ancient proglacial lake. Oxygen-isotope analysis of cellulose extracted from the sediments, which originated during the Lockhart phase ∼ 11,700-11,000 ¹⁴C yr BP, suggests that phytoplankton lived in surface waters having δ¹⁸O around − 18 ± 1‰ VSMOW, substantially enriched relative to connate porewaters in the same core, which indicate bottom waters had much lower values of around − 24.5 ± 0.5‰ VSMOW. This difference may be attributable to seasonal isotopic stratification of the upper part of the water column in the 250 m-deep lake. Modern observations from analogous environments in northern Canada suggest that inflow of evaporatively enriched runoff from the large area of deglaciated terrain contributing to Lake Agassiz, possibly enhanced by evaporation from the surface of the lake itself, could readily account for sufficient seasonal ¹⁸O enrichment in the epilimnion. Sediment porewaters, in contrast, have preserved the isotopic signature of hypolimnion waters supplied by a mixture of glacial meltwater and precipitation-derived runoff from the Laurentide Ice Sheet, and lack discernable isotopic alteration by evaporation. These new estimates are combined with inferred lake water compositions from other isotopic archives to develop a speculative framework for the isotopic evolution of the lake, providing improved constraints on the probable isotopic composition of Lake Agassiz outflow over time, which has important implications for efforts to trace and model its changing discharge.     

Abandonment chronology of glacial Lake Agassiz's Northwestern outlet

Spillway scour lakes and basins in northwestern Saskatchewan were cored to determine when the spillways were abandoned. The cores contained the target contact of organic muck (gyttja) overlying inorganic sand or silty-clay rhythmites. New AMS radiocarbon dates on terrestrial macrofossils, in conjunction with previously published and unpublished data from the area, indicate that the spillways were abandoned between 9.07 and 9.59 ¹⁴C kyr BP (10,220-10,810 cal yr BP). Of great interest is whether the channels are associated with northwestern drainage from glacial Lake Agassiz. The radiocarbon ages recording spillway abandonment are consistent with previous work, which claims that overflow through the northwestern outlet ended ∼ 9.5 ¹⁴C kyr BP (10,700 cal yr BP); this is consistent with shifting drainage to the southern outlet at this time. The scarcity of dates from the northwestern outlets and other outlets of Lake Agassiz underscores the need to establish a tighter chronological control on outlet switching before outburst flooding from Lake Agassiz can be assumed to be the trigger for abrupt climate change.     

High- and low-latitude forcing of Plio-Pleistocene East African climate and human evolution

The late Cenozoic climate of East Africa is punctuated by episodes of short, alternating periods of extreme wetness and aridity, superimposed on a regime of subdued moisture availability exhibiting a long-term drying trend. These periods of extreme climate variability appear to correlate with maxima in the 400-thousand-year (kyr) component of the Earth's eccentricity cycle. Prior to 2.7 Ma the wet phases appear every 400 kyrs, whereas after 2.7 Ma, the wet phases appear every 800 kyrs, with periods of precessional-forced extreme climate variability at 2.7-2.5 Ma, 1.9-1.7 Ma, and 1.1-0.9 Ma before present. The last three major lake phases occur at the times of major global climatic transitions, such as the onset of Northern Hemisphere Glaciation (2.7-2.5 Ma), intensification of the Walker Circulation (1.9-1.7 Ma), and the Mid-Pleistocene Revolution (1.0-0.7 Ma). High-latitude forcing is required to compress the Intertropical Convergence Zone so that East Africa becomes locally sensitive to precessional forcing, resulting in rapid shifts from wet to dry conditions. These periods of extreme climate variability may have provided a catalyst for evolutionary change and driven key speciation and dispersal events amongst mammals and hominins in East Africa.     

Management-Induced Reproductive Failure and Breeding Dispersal in Double-Crested Cormorants on Lake Champlain

ABSTRACT We studied breeding dispersal of double-crested cormorants (Phalacrocorax auritus) associated with management practices that suppressed their reproduction on Lake Champlain in the northeastern United States. We implemented an experiment on one colony by spraying corn oil on cormorant eggs in portions of the colony and leaving other portions untreated. Gulls (Larus spp.) consumed cormorant eggs during the oiling process, but we reduced and then eliminated predation levels after the first year of the study. We used mark-recapture techniques within the experimental framework to measure rates of breeding dispersal for cormorants from the experimental colony and an unmanaged colony in Lake Champlain. Egg oiling increased the movement rate to the unmanaged colony by 3% during the year with no egg predation by gulls. When gulls depredated cormorant eggs at high rates during egg oiling, movement to the unmanaged colony increased by 20%. When cormorants are managed to reduce population sizes, methods that limit dispersal away from the managed colony may be most effective. Such methods would mitigate effects to nontarget populations and allow for a greater portion of the metapopulation to be managed.     

Sandhill Crane Abundance and Nesting Ecology at Grays Lake,Idaho

Abstract: We examined population size and factors influencing nest survival of greater sandhill cranes (Grus canadensis tabida) at Grays Lake National Wildlife Refuge, Idaho, USA, during 1997–2000. Average local population of cranes from late April to early May, 1998–2000, was 735 cranes, 34% higher than that reported for May 1970–1971. We estimated 228 (SE = 30) nests in the basin core (excluding renests), 14% higher than a 1971 estimate. Apparent nest success in our study (x̄ = 60%, n = 519 nests) was lower than reported for Grays Lake 30–50 years earlier. Daily survival rates (DSRs) of all nests averaged 0.9707 (41.2%). The best model explaining nest survival included year and water depth and their interaction. Nest survival was highest (DSR = 0.9827) in 1998 compared with other years (0.9698-0.9707). Nest survival changed little relative to water depth in 1998, when flooding was extensive and alternative prey (microtines) irrupted, but declined markedly with lower water levels in 2000, the driest year studied. Hypotheses relating nest survival to vegetation height, land use (idle, summer grazing, fall grazing), and date were not supported. In a before-after-control-impact design using 12 experimental fields, nest survival differed among years but not among management treatments (idle, fall graze, fall burn, and summer—graze—idle rotation), nor was there an interaction between year and treatments. However, DSRs in fall-burn fields declined from 0.9781 in 1997–1998 to 0.9503 in 1999–2000 (posttreatment). Changes in the predator community have likely contributed to declines in nest success since the 1950s and 1970s. Our results did not support earlier concerns about effects of habitat management practices on crane productivity. Nest survival could best be enhanced by managing spring water levels. Managers should continue censuses during late April to evaluate long-term relationships to habitat conditions and management.     

Differential response of invasive malacostracan species to lake level fluctuations

The water level of Lake Balaton (a large, shallow lake) was extremely low in 2003, after a dry period of several years. Due to the intensive precipitation in 2004, a regeneration period commenced. Stones of the littoral zone were sampled near the water surface and from the lake bottom four times in both years at four sampling stations. Malacostraca in the encrustation of the stones were represented by Ponto-Caspian immigrants: the invasive amphipods Chelicorophium curvispinum and Dikerogammarus spp. (D. haemobaphes and D. villosus), the mysid Limnomysis benedeni and the isopod Jaera istri. The amphipods dominated in both years. Species of the amphipod genus Dikerogammarus were relatively less abundant than the amphipod C. curvispinum in the regeneration period as compared to the drought period of 2003. Maximal density of Malacostraca (ind. m⁻² stone surface) was 69,953 in 2003 and 82,465 in 2004. Vertical stratification of animal numbers and specific taxa occurred in May 2003 and throughout the year in 2004, with some exceptions. Many more Malacostraca individuals were recorded at the lake bottom than near the water surface. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Effects of hydrodynamics on phosphorus concentrations in water of Lake Taihu,a large,shallow, eutrophic lake of China

To understand the effect of hydrodynamical process on water phosphorus concentration, wind, wave, and several water quality indices were observed in Meiliang Bay, a shallow and eutrophic bay locates in north of Lake Taihu. During the 7 day observation period, wind speed and significant wave height were recorded more than 3 h per day, and water samples were collected in five water-depth layers once a day. Hydrodynamical disturbance had no significant correlationship with the water quality at the top layer when the significant wave height was smaller than 30 cm, but it significantly increased suspended solids (SS) concentration of the bottom water layer. Concentrations of nutrients showed no positive correlationship with SS concentration in the water body. Intensive sediment resuspension may not have occurred when the hydrodynamic stress on sediment was only a little higher than the critical stress for sediment resuspension. A new method for confirming the critical stress for intensive sediment resuspension and nutrient release still needs to be developed. The range of the water quality indices was quite high during the seven days of observation. High variation seems to be a common character of large shallow lakes like Taihu.     

Vegetation and soil properties in restored wetlands near Lake Taihu,China

Riparian wetlands are important components of the lake ecosystem, and they play essential roles in maintaining system health. Remediation of degraded lakeshore wetlands is an essential component of lake restoration. A study was conducted to investigate the restoration of lakeshore wetlands, which were converted to rice fields and then abandoned for 2, 5, 10 and 15 years, near Lake Taihu. Soil samples (0–20 cm and 20–40 cm) were taken and plant species were investigated. The carbon content in the soil had increased significantly, rising from 0.71% to 1.85% between 2 and 15 years. Organic matter accumulation improved soil texture, and water stable aggregate content (>0.25 mm) and soil porosity increased. Total nitrogen in the soil increased from 0.06% to 0.13%, and total Kjeldahl nitrogen increased from 124.4 mg kg⁻¹ to 351.5 mg kg⁻¹. Total phosphorus in the soil increased from 0.045% to 0.071%, and the Olsen-P value increased from 5.13 mg kg⁻¹ to 16.0 mg kg⁻¹. Results showed that phosphorous did not increase as much as nitrogen. In the vegetation restoration process, plant species composition moved towards a natural wetland community, and spatial heterogeneity and landscape diversity increased. The richness of plant biodiversity increased rapidly in the first 2 years, then more slowly in later restoration stages. The wetlands recovery process may be complicated by interactions of biota and soil and hydrological conditions.