Influence of water motion on the spatial distribution of Spirogyra in Lake Baikal

We investigated the diversity of benthic algal communities as well as phytoplankton in Lake Baikal. The structure of benthic algal communities changed in comparison to the period before 2000 due to intense development of filamentous algae, particularly Spirogyra. Percent cover of filamentous algae in different areas of the coastal zone varied from 0 to 100%. The lowest Spirogyra biomass was recorded in the surf and wave-breaking zones, whereas the highest biomass was observed in the area of the bottom less affected by waves. Fragments of Spirogyra thallomes were also recorded in the phytoplankton community of Lake Baikal's southern basin which is a new phenomena not previously recorded in the lake. Hydraulic characteristics of Spirogyra were similar to those of planktonic diatoms. Currents and wave effects on the bottom favored transfer and distribution of Spirogyra from locations with intense development to the coastal area of Lake Baikal. Spirogyra is now found throughout Lake Baikal.     

Changes in the Freshwater Mussel Community of Lake St. Clair: from Unionidae to Dreissena polymorpha in Eight Years

To determine density changes in both the zebra mussel, Dreissena polymorpha, and native mussels, Unionidae, in Lake St. Clair, surveys were conducted in 1990, 1992, and 1994 and compared to a similar survey in 1986 when no D. polymorpha was found. Collection methods were the same each year; divers used the quadrat method to collect 10 replicate samples at 29 sites located throughout the lake. The total number of unionids collected declined from 281 in 1986, to 248 in 1990, 99 in 1992, and 6 in 1994, while the number of species collected in each of the four respective years was 18, 17, 12, and 5. The decline in the unionid community occurred gradually over this time period as the D. polymorpha population expanded from the southeast region of the lake to the northwest region. Mean density and biomass of D. polymorpha throughout the lake was 1,700 m⁻² and 4.7 gDW m⁻² in 1990, 1,500 m⁻² and 3.5 gDW m⁻²in 1992, and 3,200 m⁻² and 3.1 gDW m⁻² in 1994. The density increase can be attributed to the expansion of the population into the northwest region, while the decrease in biomass was mostly a result of a decline in the weight per unit length. Mean biomass of the D. polymorpha population in 1994 was actually lower than the mean biomass of unionids in 1986; however, based on literature-derived filtering rates, the filtering capacity of the D. polymorpha population in 1994 was 12 times greater than the filtering capacity of the unionid community in 1986. This increase has likely led to reported changes in the Lake St. Clair ecosystem (increased water clarity, increased plant growth, and shifts in fish communities).     

Diversity and ecology of phytoplankton in Lake Edward (East Africa): Present status and long-term changes

Lake Edward is one of the African Rift Valley lakes draining into the Nile River basin. We conducted three sampling series in Lake Edward in October-November 2016, March-April 2017 and January 2018, in distinct seasonal conditions and in several sites varying by depth and proximity to river outlets, including the Kazinga Channel, which connects the hypertrophic Lake George to Lake Edward. The phytoplankton was examined using microscopy and marker pigment analysis by high performance liquid chromatography (HPLC) and subsequent CHEMTAX processing for estimating abundance of phytoplankton groups. Chlorophyll a concentration in the pelagic and littoral open lake sites barely exceeded 10 µg L⁻¹ whereas, in contrast, in the semi-enclosed Bay of Katwe influenced by the Kazinga Channel chlorophyll a was up to 100 µg L⁻¹. Despite substantial seasonal variations of limnological conditions such as photic and mixed layer depths, cyanoprokaryotes/cyanobacteria represented on average 60% of the phytoplankton biomass, followed by diatoms, which contributed ~25% of chlorophyll a, and by green algae, chrysophytes and cryptophytes. 248 taxa were identified with clear prevalence of cyanobacteria (104 taxa), from the morphological groups of coccal and filamentous species (non-heterocytous and heterocytous). The high proportion of heterocytous cyanobacteria, along with a relatively high particulate organic carbon to nitrogen (C:N) ratio, suggest N limitation as well as light limitation, most pronounced in the pelagic sites. During the rainy season, the most abundant diatoms in the plankton were needle-like Nitzschia. Comparison with previous studies found differences in water transparency, total phosphorus, and phytoplankton composition.     

High nutrient loading and climatic parameters influence the dominance and dissimilarity of toxigenic cyanobacteria in northern bays of Lake Victoria

Eutrophication of Lake Victoria led to changes in its phytoplankton communities. However, different levels of eutrophication exist in the open lake and the bays, and between embayments. This study utilized spatial and temporal sampling of Napoleon Gulf and Murchison Bay, exhibiting different trophic conditions. Over one year, we investigated phytoplankton biomass, richness, diversity and dissimilarity, and related the dynamics of the dominant species to the limnological and climatic conditions. The results confirmed that Napoleon Gulf and Murchison Bay showed large differences in eutrophication status, with lower nutrient concentrations in Napoleon Gulf than in Murchison Bay, where a strong gradient was observed from inshore to offshore areas. These nutrient dynamics resulted in a 4 to 10 fold higher chlorophyll-a in Murchison Bay than in Napoleon Gulf. From the embayments, 135 phytoplankton taxa were recorded with no significant differences in alpha diversity. However, high dissimilarity in community structure was observed in beta diversity, mostly due to a turnover among the dominant toxigenic species. Thus, from a similar species pool, there was a shift in the dominant toxigenic cyanobacteria from Microcystis flos-aquae and M. aeruginosa in Murchison Bay, Dolichospermum circinale and Planktolyngbya circumcreta in Napoleon Gulf to D. circinale in the offshore stations. These cyanobacteria are toxigenic taxa with known health hazards. Using partial least square models, we showed that both climatic variables (e.g. wind, solar radiation) and levels of inorganic dissolved nutrients (e.g. SRP, NO₃^–, and NH₄⁺) are the main drivers of differences and dominance in cyanobacteria communities in northern Lake Victoria.     

Nearshore benthic blooms of filamentous green algae in Lake Baikal

For the first time, species of the genus Spirogyra, non-typical of the open nearshore waters of Lake Baikal, formed algal mats with Ulothrix zonata, Ulothrix tenerrima, and Ulothrix tenuissima near the village of Listvyanka, Russia. Normally widely distributed in the 0- to 1.5-m depth range, the growth of U. zonata was now evident and dominant (63% of the biomass) in the 2- to 5-m depth range. The overgrowth of the lake bottom by filamentous green algae, changes in distributional boundaries, the emergence and mass development of species of the genus Spirogyra, the presence of the eutrophic diatom indicator Fragilaria capucina var. vaucheriae, elevated abundances of coliform bacteria, and elevated levels of nutrients suggest an early stage of cultural eutrophication in the nearshore of Lake Baikal near Listvyanka, a popular tourist destination. The unusual abundance of Fragilaria associated with the filamentous green algae consisted of long-ribbon colonies of F. capucina var. vaucheriae, a eutrophic species, wound around the filamentous green algae, enhancing the dense algae mats. Historically dominant species, such as Didymosphenia geminata, Tetraspora cylindrica var. bullosa, and Draparnaldioides baicalensis typically observed at deeper depths of Lake Baikal, are now subdominants or minor species in the nearshore along the shoreline near Listvyanka.     

A Comparison of Lake Trout Spawning,Fry Emergence,and Habitat Use in Lakes Michigan,Huron, and Champlain

Restoration of self-sustaining populations of lake trout is underway in all of the Great Lakes and Lake Champlain, but restoration has only been achieved in Lake Superior and in Parry Sound, Lake Huron. We evaluated progress toward restoration by comparing spawning habitat availability, spawner abundance, egg and fry density, and egg survival in Parry Sound in Lake Huron, in Lake Michigan, and in Lake Champlain in 2000–2003. Divers surveyed and assessed abundance of spawners at 5 to 15 sites in each lake. Spawning adults were sampled using standardized gill nets, eggs were sampled using egg bags, and fry were sampled using emergent fry traps and egg bags left on spawning reefs overwinter. Spawning habitat was abundant in each lake. Adult lake trout abundance was low in Lake Michigan and Parry Sound, and very high at one site in Lake Champlain. Egg deposition was lowest in Lake Michigan (0.4–154.5 eggs•m⁻², median = 1.7), intermediate in Parry Sound (39–1,027 eggs•m⁻², median = 278), and highest in Lake Champlain (0.001–9,623 eggs•m⁻², median = 652). Fry collections in fry traps followed the same trend: no fry in Lake Michigan, 0.005–0.06 fry•trap⁻¹ day⁻¹ in Parry Sound, and 0.08–3.6 fry•trap⁻¹ in Lake Champlain. Egg survival to hatch in overwinter egg bags was similar in Lake Michigan (7.6%) and Parry Sound (2.3–8.9%) in 2001–02, and varied in Lake Champlain (0.4–1.1% in 2001–02, and 1.8–18.2 in 2002–03). Lake trout restoration appears unlikely in northern Lake Michigan at current adult densities, and failure of restoration in Lake Champlain suggests that there are sources of high mortality that occur after fry emergence.     

Diversity and biogeography of bacteriophages in biofilms of Lake Baikal based on g23 sequences

Here, we report on the sequences of the g23 communities of phages from biofilms and the surface microlayer in the most ancient lake of the world. The data are interpreted in terms of biogeography of the g23 communities. We show that bacteriophages from biotopes of biofilms of stones and sponges from the littoral zone and of the water from the pelagic zone of Lake Baikal form a common Baikal cluster. Viruses of the surface microlayer in the shallow Maloye More Strait of Lake Baikal group into one cluster with the sequences from polar lakes forming a sisterly clade with the Baikal cluster.     

Recent Changes and Patterns in the Water Chemistry of Lake Simcoe

After the Great Lakes, Lake Simcoe is the largest lake in southern Ontario. Located within a 1 hour drive of half the population of Ontario, there is currently major concern over the impact of rapid urbanization on the nutrient status of the lake. However, despite a more than doubling of the human population in the Lake Simcoe watershed over the past two decades, average total phosphorus (TP) levels were lower in 2000–2003 compared with 1980–1983 at six of eight lake stations, and declines were significant at the most nutrient-enriched near-shore sites located in Kempenfelt Bay (0.29 μg/L/year) and Cook's Bay (0.31–0.41 μg/L/year). Total P concentrations varied two-fold across the lake, and phytoplankton bio-volume followed a similar pattern, with greatest phytoplankton abundance occurring at high TP sites, particularly in Cook's Bay. Nevertheless, steep declines in bio-volume occurred at all sites beginning in the mid-1990s, and water clarity (Secchi disk depth) improved concurrently such that Secchi depths were 40–80% greater in 2000–2003 compared with 1980–1983. Zebra mussels, which became established in Lake Simcoe around 1995, likely contributed to decreased phytoplankton bio-volume and related improvements in water clarity, which began during the mid-1990s. Despite major reductions in phytoplankton bio-volume, average rates of dissolved oxygen (DO) depletion (18 m-bottom zone; normalized to 4°C) did not change substantially over time, and were similar in 2000–2003 (average 1.25 ± 0.21 g O₂/m³/month) compared with 1980-1983 (average 1.26 ± 0.19 g O₂/m³/month). In contrast, minimum, end-of-summer DO levels (18 m-bottom) increased slightly over the period of record. Although there has been some improvement in end-of-summer DO availability, DO concentrations continue to decline to levels that are limiting to many fish species (e.g., 3.8 mg O₂/L in 2001) by the end of the summer stratified period.     

Optical and biological properties of Lake Ülemiste, a water reservoir of the city of Tallinn I: Water transparency and optically active substances in the water

Optical and biological measurements were performed in Lake Ülemiste in the summer of 1997 (four measurement days), and from May to October in 1998 (12 measurement days). This kind of data, describing the type and amount of optically active substances in the water, phytoplankton characteristics, the underwater light field, and temperature–oxygen situation in the lake are necessary when estimating the ecological state of the lake. Lake Ülemiste is the main drinking water reservoir of Tallinn, the capital of Estonia. Phytoplankton abundance and biomass, chlorophyll a and suspended matter were determined from collected Lake Ülemiste water samples in the laboratory. Spectrophotometrical processing of the filtered and unfiltered water was carried out to describe the beam attenuation coefficient spectra and optical influence of yellow substance in the water. Vertical profiles of downwelling irradiance of the PAR (400–700 m) region of the spectrum (and from these data the averaged over depth diffuse attenuation coefficient) were determined. The relative transparency of the water was estimated by using a Secchi disk. Passive optical remote measurements were episodically made from aboard a boat. Results obtained confirmed that Lake Ülemiste is turbid (almost hypertrophic), comparable with most turbid lakes in Estonia (e.g. Lake Võrtsjärv) and Finland (Lake Tuusulanjärvi). Its chlorophyll a content varied within the range 13–121 mg m^–3, phytoplankton biomass 3–107 mg L^–1, phytoplankton abundance 65 000–999 000 mL^–1, suspended matter 8–34 mg L^–1, effective concentration of the yellow substance 6–30 mg L^–1, diffuse attenuation coefficient of light in the PAR region 1.0–3.3 m^–1 and a Secchi disk depth of 0.5–1.75 m. The temporal variation of the spatial averages of these parameters during 1998 was analysed. Almost all characteristics showed an increase from May to midsummer with a maximum in late July or in August (correspondingly the Secchi depth values were minimal in late summer). The amount of yellow substance was an exception, which was nearly constant during the observation period. The maximum level of chlorophyll a content in July and August 1998 markedly exceeded that in 1997, despite the fact that the summer of 1997 was sunny, but the summer of 1998 was cold and rainy. The correlative relationships between the different parameters were investigated together with the respective data for other lakes. They show that the data of Lake Ülemiste supplemented the correlation graph in the region of turbid lakes, whereby in all cases the correlation coefficient increased following the addition of Lake Ülemiste data. The highest correlation coefficient was obtained when light attenuation coefficient values were correlated with a sum of weighted concentrations of chlorophyll a, yellow substance and suspended matter (multiple regression analysis).     

Distribution and Population Characteristics of Cercopagis pengoi in Lake Ontario

The spatial and vertical distribution of a recent exotic species, the predatory cladoceran Cercopagis pengoi, was studied in Lake Ontario in September 1999. Only typical forms of the species C. pengoi, characterized by a relatively long tail with an S-bend and claws with straight or backwardly bent tips, were found. Structure of the Cercopagis population was rather uniform over the lake, consisting mainly (over 90%) of parthenogenetic females. Median epilimnetic abundance and biomass was 295/m³ (max. = 2,544/m³) and 13.4 mg DW/m³ (max. = 113.3 mg DW/m³), respectively. Cercopagis contributed a median of 15.8%, and at maximum 73.8%, of the total crustacean zooplanktonic biomass (exclusive of nauplii). Abundances showed a significant positive relationship with distance from shore (r² = 0.34, p < 0.01), but distribution was independent of the depth and temperature of the epilimnion. Cercopagis did not exhibit any diurnal vertical migration patterns: over 90% of the individuals stayed either in the epilimnion or within the metalimnion during the day and night. The proportion of individuals, both live specimens and carcasses of dead individuals, in cooler layers was negligible (< 3%). The following weight (W) – body length (L) relationship was developed during the study: ln(W) = 2.98*ln(L) - 6.42 (r² = 0.85, p < 0.001).     

Sudden Disappearance of the Amphipod Diporeia from Eastern Lake Ontario, 1993–1995

Diporeia, Oligochaeta, and Sphaeriidae were sampled at three sites (28 to 35 m depth) in the east basin of Lake Ontario, and at one mid-lake site (125 m) from 1982 and 1996. In addition, Diporeia was sampled at 14 more sites located in the south and eastern part of the lake in 1990 and 1995. Before 1991, densities of all three macroinvertebrate taxa fluctuated with peaks occurring between 1988 and 1991. Between 1992 and 1995, Diporeia declined rapidly from > 6,000 per m² to 0 at all three sites in the east basin, while increasing from 1,050 to 5,230 per m² at the mid lake site. Samples from the south and eastern part of the lake confirmed the decline was extensive at depths < 100 m. Abundance and biomass of the Oligochaeta and Sphaeriidae also fluctuated, but remained more similar before 1991 and after 1993. Direct cause for the disappearance of Diporeia is unknown but declines occurred after establishment of nearshore Dreissena colonies. Lake circulation patterns suggest that the nearshore mussel populations may intercept diatoms and other material that had been consumed by Diporeia located further offshore. A substantial biomass of Diporeia (3 g/m² dry) has been lost from the food web of eastern Lake Ontario, with serious consequences to the coldwater fisheries of the lake.     

Distribution and geochemical processes of boron in the multimedia of Lake Qinghai,China

Lake Qinghai on the Qinghai-Tibet plateau is the largest lake in China. This study investigated the concentration and geochemical processes of boron (B) in lake water, lake sediment and river samples collected from Lake Qinghai and the Buha River. In addition, lake sediment pore water samples were analyzed. The concentrations of B and major ions, including K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^? and SO₄^2?, were analyzed in all the water samples. The average concentration of B was 0.07?mg?L^?1, 6.37?mg?L^?1, 12.79) mg?L^?1 and 59.42?mg?kg^?1 for river water, lake water, pore water, and sediment, respectively. There were significant (p?<?0.05) and positive (r?=?0.70) relationships between the B concentrations in bottom water of the lake and in lake sediment, indicating that B diffusion from the sediment plays an important role in the concentration of B in bottom lake water. The differences in B concentrations and B/major ion molar ratios of the river water, lake water, and pore water indicated the following geochemical processes: 1) B is enriched in the lake water through evaporative concentration; 2) B is removed from the lake water through mineral precipitation as well as sorption onto colloids; 3) Solid-phase B in sediments was released through dissolution driven by organic matter mineralization. B/Cl and Na/Cl molar ratios alone are not enough to identify the sources of B in the water of inland closed-basin saline lakes because of these processes.     

Fractioning of petroleum hydrocarbons from seeped oil as a factor of purity preservation of water in Lake Baikal (Russia)

Polycyclic aromatic hydrocarbons (PAHs) and n-alkanes were found in five different types of oil-containing samples emanating from deep oil seeps in Lake Baikal, the deepest and oldest lake in the world containing 20% of the world’s surface freshwater. The n-alkanes were the dominant component of the seeped oil on the water surface. PAHs were minor compounds of the oil, but this group is included in a priority series of organic contaminants that are subject to environmental regulation. The set of studied samples from the seep included: (i) freshly-emitted oil on the lake surface, (ii) oil at the lake bottom, (iii) samples of asphalt towers at the lake bottom, (iv) oil from voids within the sediment core and (v) samples of water from different depths. High variability in the concentrations of n-alkanes and PAHs suggested the presence of oil fractionation at the sediment-water interface. A light fraction of oil enriched by n-alkanes migrates to the surface of the lake’s water column, where n-alkanes are biodegraded by the Baikal microbial community while heavy oil fractions remain at the lake bottom and form asphalt towers in which PAHs with maximum toxicity accumulate. In the lake’s photic water layer, PAHs from light oil can be accumulated by phytoplankton. In the lake’s water column, benzo[a]pyrene was not detected over their detection limit (0.1 ng/L). The Toxic Equivalent (TEQ) value of PAHs identified in the Baikal water ranged from 0.001 to 0.012 ng/L.     

Methane and nitrous oxide measured throughout Lake Erie over all seasons indicate highest emissions from the eutrophic Western Basin

Eutrophication has been linked to increased greenhouse gas emissions from inland waters. Phytoplankton blooms in Lake Erie have increased since the 1990s, although its greenhouse gas emissions are not well characterized. We measured CH₄ and N₂O concentrations and diffusive fluxes in four seasons around the entire lake, and CO₂ fluxes in one summer season. Lake Erie is a source of CH₄ all year across the lake, concentrated in spring and summer in the Western Basin. Methane emissions ranged from 0.03 to 14.87 mg C m⁻² d^-1. Methane is predominantly biogenic, and natural gas leaks are an insignificant source. While Lake Erie is an overall N₂O source, it is an N₂O sink in winter and occasionally during summer. Emissions of N₂O ranged from −0.08 to 1.22 mg N m⁻² d^-1. We also measured CO₂ fluxes in summer only, when Lake Erie is a small atmospheric CO₂ sink. While areal fluxes of CH₄ and N₂O are similar to those observed elsewhere, total fluxes from Lake Erie are higher due to its surface area. Lake Erie emits ~ 6300 (±19%) metric tons of CH₄-C yr⁻¹ and ~600 (±37%) metric tons N₂O-N yr⁻¹: almost 500,000 metric tons CO₂-eq yr⁻¹ total. This is the first comprehensive dataset of CH₄ and N₂O concentrations and diffusive emissions in a very large lake. More measurements and monitoring are needed to determine whether increased eutrophication in the Great Lakes is tied to increased emissions of these powerful climate forcers in a possible positive feedback to climate warming.     

Trophic evolution of Lake Lugano related to external load reduction: Changes in phosphorus and nitrogen as well as oxygen balance and biological parameters

Lake Lugano is located at the border between Italy and Switzerland and is divided into three basins by two narrowings. The geomorphologic characteristics of these basins are very different. The catchment area is characterized by calcareous rock, gneiss and porphyry; the population amounts to approximately 290 000 equivalent inhabitants. The external nutrient load derives from anthropogenic (85%), industrial (10%) and agricultural (5%) sources. The limnological studies carried out by Baldi et al. (1949) and EAWAG (1964) revealed early signs of eutrophication, with a phosphorous concentration of about 30–40 mg m^–3 and an oxygen concentration of less than 4 g m^–3 in the deepest hypolimnion. Subsequently Vollenweider et al. (1964) confirmed these data and was the first to point out the presence of a meromictic layer in the hypolimnion of the northern basin. From the 1960s, as a result of an increase in the population and internal migration, the lake became strongly eutrophic with the P concentration reaching 140 mg m^–3 and the oxygen in the hypolimnion reduced to zero. Fifty‐five per cent of the P was from metabolic sources and 45% from detergents and cleaning products. In 1976, a partial diversion of waste water from the northern to the southern basin was begun, and gradually eight waste water treatment plants came into operation using mechanical, chemical and biological treatments. In 1986, Italy and Switzerland began to eliminate the P in detergents and cleaning products. Since 1995, the main sewage treatment plants have improved their efficiency by introducing P post‐precipitation, denitrification and filtration treatments. The recovery of the lake is due to be completed by the year 2005. Altogether, during the last 20 years recovery measures have reduced the external P load from about 250 to 70–80 tonnes year^–1; the goal to be reached is 40 tonnes year^–1. In‐lake phosphorous concentrations have decreased from 140 to 50–60 mg m^–3, with the target at 30 mg m^–3. Dissolved oxygen concentration is satisfactory only between the depths of 0 and 50 m, falling rapidly to zero in the deepest layers. Below a depth of 90 m, high CH₄, HS^–, NH₄⁺, Fe²⁺ and Mn²⁺ concentrations exist. Primary production has decreased from 420 to 310 g C_ass m^–2 year^–1, notwithstanding an increase in the thickness of the trophogenic layer. Structure and dynamic biomass show marked changes: phytoplankton dry weight has decreased from 16 to 7 g m^–2, while zooplankton dry weight has increased from 3 to 4.5 g m^–2. Chlorophyll concentration has fallen from 14 to 9 mg m^–3 and Secchi disk transparency has increased from 3.5 to 5.5 m. The current sources of the external load are uncollected small urban conglomerations, storm‐water overflows from outfall sewers, and the residual load from sewage treatment plants, particularly those without P post‐precipitation.     

Hydroacoustic Estimates of Abundance and Spatial Distribution of Pelagic Prey Fishes in Western Lake Superior

Lake herring (Coregonus artedi) and rainbow smelt (Osmerus mordax) are a valuable prey resource for the recovering lake trout (Salvelinus namaycush) in Lake Superior. However, prey biomass may be insufficient to support the current predator demand. In August 1997, we assessed the abundance and spatial distribution of pelagic coregonines and rainbow smelt in western Lake Superior by combining a 120 kHz split beam acoustics system with midwater trawls. Coregonines comprised the majority of the midwater trawl catches and the length distributions for trawl caught fish coincided with estimated sizes of acoustic targets. Overall mean pelagic prey fish biomass was 15.56 kg ha⁻¹ with the greatest fish biomass occurring in the Apostle Islands region (27.98 kg ha⁻¹), followed by the Duluth Minnesota region (20.22 kg ha⁻¹), and with the lowest biomass occurring in the open waters of western Lake Superior (9.46 kg ha⁻¹). Biomass estimates from hydroacoustics were typically 2–134 times greater than estimates derived from spring bottom trawl surveys. Prey fish biomass for Lake Superior is about order of magnitude less than acoustic estimates for Lakes Michigan and Ontario. Discrepancies observed between bioenergetics-based estimates of predator consumption of coregonines and earlier coregonine biomass estimates may be accounted for by our hydroacoustic estimates.     

Biological Redistribution of Lake Sediments by Tubificid Oligochaetes: Branchiura sowerbyi and Limnodrilus hoffmeisteri/Tubifex tubifex

Mechanisms and rates of sediment mixing by the largest oligochaete in Lake Erie, Branchiura sowerbyi, have been quantitatively investigated using a multiple ¹³⁷Cs tracer layer microcosm technique and compared with a mixture of the dominant tubificids, Limnodrilus hoffmeisteri + Tubifex tubifex. These worms feed head down in the sediment (up to 20 cm for B. sowerbyi and up to 10 cm for L. hoffmeisteri/T. tubifex) on organic-rich particles and deposit fecal pellets at the sediment-water interface (conveyor-belt feeding). Obliteration of tracer layers by these worms was attributed to mixing by both diffusive- and feeding-style (advective) processes. The downward velocities were 2.87 to 3.66 cm/d/100,000 indiv/m² for the cells with B. sowerbyi (∼10 cm body length, 13 mg body mass) and 0.33 to 0.49 cm/d/100,000 indiv/m² for the cells with L. hoffmeisteri / T. tubifex (∼5 cm body length, 1 mg body mass). These downward velocities correspond to sediment fluxes across the sediment-water interface of 66.4 to 86.4 g dry sediment/indiv/m²/yr in cells with B. sowerbyi and 5.91 to 9.09 g dry sediment/indiv/m²/yr in the cells with L. hoffmeisteri / T. tubifex). The differences between species was due to differences in biomass, with recycling rates of 5.11 to 6.65 and 5.91 to 9.09 g dry sediment/mg biomass/m²/yr for B. sowerbyi and L. hoffmeisteri/T. tubifex, respectively. Similarly, biomass normalized downward velocities were 806 to 1,028 cm/yr/kg biomass/m² and 1,205 to 1,789 cm/yr/kg biomass/m² for B. sowerbyi and L. hoffmeisteri/T. tubifex, respectively. Both B. sowerbyi and L. hoffmeisteri / T. tubifex feed selectively on organic-rich fine-grained particles and showed an increase in particle selectivity with an increase in population density. The particle selectivity factor values ranged from 1.0 to 2.5. Food competition at a higher population density might force these organisms to selectively feed on a smaller size range of sediments. The maximum feeding rate for B. sowerbyi (4,000 to 8,000 indiv/m²) ranged from 9.10 to 13.9 per yr at depths between 11.7 and 13.6 cm while the maximum biodiffusion coefficient, D_b, ranged from 0.78 to 1.02 cm²/yr at depths between 1.6 and 2.3 cm. The maximum feeding rate for L. hoffmeisteri / T. tubifex (20,000 to 40,000 indiv/m²) was 8.13 to 13.1 per yr at depths between 5.21 and 5.27 cm and D_b ranged from 0.20 to 0.72 cm²/yr at depths between 0.87 and 2.0 cm.     

Dreissenids in Lake St. Clair in 2001: Evidence for Population Regulation

Zebra mussel (Dreissena polymorpha [Pallas]) density was surveyed at 12 stations in Lake St. Clair in September 2001. Lake-wide mean density was 1,824 individuals/m²; whole wet biomass was 148 g/m²; and dry tissue biomass was 1.23 g/m². Compared to historical data, density did not change significantly, whereas biomass showed a significant downward trend. Our data support the assertion that the zebra mussel population in Lake St. Clair has undergone important changes since the mid-1990s. Some areas of the lake are now juvenile-dominated, others are adult-dominated, and some have a balanced size distribution. These data are consistent with the hypothesis that zebra mussels have changed the lake ecosystem in two ways that have contributed to their own population limits in a density-dependent manner. First is the reduction of adult microhabitat due to the elimination of native mussels from the lake proper. Second is the massive redirection of larval settlement onto a greatly expanded aquatic macrophyte community which senesces and dies at the end of each season, thus decreasing survivorship of juvenile D. polymorpha. If sustained, these recent changes, especially biomass reduction, suggest that the impact of dreissenids on the Lake St. Clair ecosystem will be more moderate in the future.     

Carbon dioxide in the atmosphere-water system and biogenic elements in the littoral zone of Lake Baikal during period 2004–2018

We report long-term comprehensive measurements of CO₂ in the atmosphere, surface water and the major nutrients obtained for the period 2004–2018. The research was conducted at the Baikal Atmospheric and Limnological Observatory (BALO), which is located in the coastal zone of South Baikal (coordinates 51° 54′ N, 105° 05′ E). The seasonal variation of these characteristics was analyzed. For our site, during the open water period (May-December) we assessed average flux of CO₂, which amounted to −155 mmol m⁻² y⁻¹ (sink from the atmosphere to the water surface). Carbon dioxide content in the near-water air of Lake Baikal rises with a rate of 2.46 ppm per year, which is in good agreement with the global trend. The common effect of many factors (often multi-directional), such as variability of weather conditions, hydrological processes and productivity cycles of aquatic plankton in the Baikal waters, cause strong variations in the water characteristics, which we observed in different seasons and years. Under these conditions of strong inter-annual and seasonal variability of all characteristics, trend calculations using our long-term observations did not allow us to reveal reliable tendencies of changes in surface water CO₂ concentrations.     

Lake Baikal: Model for sustainable development of the territory

Created 20–30 million years ago, Lake Baikal is one of approximately 13 ancient lakes in the world. Lake Baikal is also the deepest lake in the world with 365 rivers flowing into it and holding a full 20% of the liquid fresh water on the surface of the Earth. The lake stretches from the south‐eastern section of Siberia to portions of northern Mongolia. Administratively, it is divided between three members of the Russian Federation: the Republic of Buryatia, Irkutsk Oblast and Chita Oblast. Lake Baikal and its catchment area are characterized by considerable biodiversity and by a vast richness of natural resources. Well over half of the 2615 plant and animal species found in the Baikal region are endemic. Lake Baikal’s unusual biota includes the Baikal seal (Phoca sibirica) which lives nowhere else on Earth and is separated by 3220 km from its nearest relative. These freshwater seals give birth to their young in snow dens on the lake’s ice. The Baikal region is a spectacular example of coexistence among different cultures and faiths over centuries. Over 1000 archaeological remains of past cultures have been found near Lake Baikal shores. Preserving the unique lake culture, values and ecological, ethnic and cultural traditions of the local people is one of the key elements in developing a model for sustainable development in the Baikal region. Lake Baikal is currently still considered clear and healthy overall, however the number and type of pollution sources are growing, and local pollution can be severe. The main sources of pollution in Lake Baikal are industrial wastes and atmospheric emissions from the Baikalsk pulp and paper mill, atmospheric emissions from nearby industrial facilities, excessive nutrient loads from farming and sediment and wastes that flow into Lake Baikal through the Selenga River. In May 1999, protection of Lake Baikal was codified in federal law for the first time. Progress is being made on a number of fronts despite the turbulent political transformations in Russia in the last 10 years. For instance, in the Irkutsk region, stakeholders have worked together to reduce the flow of unpurified drainage into the lake by 10 million m³ year^–1.