Factors Influencing Algae–Clay Aggregation

The dumping of bauxite tailings on a clear-water Amazonian lake caused a significant decrease in phytoplankton densities. The influence of these suspended clay particles on algal sinking, through algae–clay aggregation, was investigated under laboratory conditions, by measuring fluctuations in algal population densities over time, with different suspended clay concentrations. The population densities of the four algal species tested, Phormidium amoenum, Mougeotia sp., Staurodesmus convergens and Chlorella sp., were decreased by the algae–clay aggregation. The extent of this process was dependent on algal morphological characteristics such as size and shape, as well as on the concentration of suspended clay particles.     

Grazing effects of a freshwater bivalve (Corbicula leana Prime) and large zooplankton on phytoplankton communities in two Korean lakes

This study examined the effects of a freshwater filter feeding bivalve (Corbicula leana Prime) and large zooplankton (>200 μm, mostly cladocerans and copepods) on the phytoplankton communities in two lakes with contrasting trophic conditions. A controlled experiment was conducted with four treatments (control, zooplankton addition, mussel addition, and both zooplankton and mussel addition), and each established in duplicate 10-l chambers. In both lakes there were significant effects of mussel grazing on phytoplankton density and biomass. The effects were greater in mesotrophic Lake Soyang than in hypertrophic Lake Ilgam. Effects of zooplankton grazing did not differ between these lakes, and zooplankton effects on phytoplankton were much less than the effects of mussels. Although mussels exerted a varying effect on phytoplankton according to their size, mussels reduced densities of almost all phytoplankton taxa. Total mean filtering rate (FR) of mussels in Lake Soyang was significantly greater than that in Lake Ilgam (p=0.002, n=5). Carbon fluxes from phytoplankton to mussels (977–2,379 μgC l^?1d^?1) and to zooplankton (76–264 μgC l^?1 d^?1) were always greater in Lake Ilgam due to the greater phytoplankton biomass (p<0.01, n=6). Based on the C-flux to biomass ratios, the mussels consumed 170–754% (avg. 412%) of phytoplankton standing stock in Lake Soyang, and 38–164% (avg. 106%) in Lake Ilgam per day. The C-flux to biomass ratio for mussels within each lake was much greater than for large zooplankton. Mussels reduced total phosphorus concentration by 5–34%, while increasing phosphate by 30–55% relative to the control. Total nitrogen also was reduced (by 9–25%), but there was no noticeable change in nitrate among treatments. The high consumption rate of phytoplankton by Corbicula leana even in a very eutrophic lake suggests that this mussel could affect planktonic and benthic food web structure and function by preferential feeding on small seston and by nutrient recycling. Control of mussel biomass therefore might be an effective tool for management of water quality in shallow eutrophic lakes and reservoirs in Korea.     

Impact of DOC trends resulting from changing climatic extremes and atmospheric deposition chemistry on periphyton community of a freshwater tropical lake of India

Recent measurements have demonstrated unprecedented increase in atmospheric deposition of nutrients in many parts of India. To determine whether atmospheric nutrient inputs would increase phytoplankton growth and catchment dissolved organic carbon (DOC) flushing to constrain benthic algae, we analyzed NO₃ ^? and PO ₄ ^?3 in atmospheric deposits; nutrients and DOC in runoff and lake water and standing crop biomass of phytoplankton and periphyton at Jaisamand Lake of Rajasthan, India. Atmospheric deposition of NO₃ ^? (7.18–29.95 kg ha^?1 year^?1) and PO ₄ ^?3 (0.56–2.15 kg ha^?1 year^?1) showed a consistently rising trend across the year. Microbial biomass and activity in catchment increased in response to atmospheric deposition. Lake DOC and nutrients showed strong coherence with their terrestrial and atmospheric fluxes. Phytoplankton development showed significant linearity with atmospheric input of nutrients. Air-driven input appeared to have compensated the nutrient constraints to phytoplankton during drought. The N:P stoichiometry of deposition and that of lake water indicated that, although there was a seasonal switchover to N- or P-limitation, phytoplankton were mainly co-limited by N and P due probably to the synergistic effects of combined N + P enrichment in the pelagic zone of the lake. Periphyton standing crop showed inverse relationship with phytoplankton and lake DOC. The study indicated that enhanced phytoplankton development and terrestrial DOC flushing in response to atmospheric nutrient input attenuated light penetration to constrain algal periphyton. We suggests that data on these issues may be considered in developing aquatic ecosystem models to establish future links between changing air–water–land interactions and associated shifts in lake ecosystem functioning for more accurately predicting climate change drivers and designing integrated lake basin management strategies.     

Analysis of long-term variation in phytoplankton biovolume in the northern basin of Lake Biwa

The long-term variation in phytoplankton biovolume in the northern basin of Lake Biwa was analyzed using periodic phytoplankton census data from January 1979 to December 2009. Population densities obtained from census data were transformed into biovolumes, and phytoplankton species were categorized into three size fractions: net phytoplankton (≥4,000 μm³ cell^?1, ≥ca. 20 μm in diameter), large nanophytoplankton (100–4,000 μm³ cell^?1, ca. 6–20 μm in diameter), and small nanophytoplankton (<100 μm³ cell^?1, <ca. 6 μm in diameter). Although the annual total biovolume gradually decreased over time, the total biovolumes in winter and spring were found to increase. Furthermore, a decrease in the biovolume of net phytoplankton and an increase in that of small nanophytoplankton were observed. Because of succession in the phytoplankton community, the average cell volume of the phytoplankton community decreased from 269 μm³ cell^?1 in the 1980s to 56 μm³ cell^?1 in the 2000s. Lake warming accompanied with the intensification of thermal stratification and the augmentation of wind speed were observed at Lake Biwa over the study period. Serial analysis correcting for autocorrelation revealed that oligotrophication in the epilimnion, induced by lake warming and limitation of light available for phytoplankton growth by wind-induced water mixing, was a potential factor in the succession of the phytoplankton community.     

Spatiotemporal distribution of bacteriochlorophylls in the meromictic Lake Suigetsu, Japan

The spatiotemporal distribution of chlorophyll pigments (chloropigments) in the water column of a meromictic lake, Lake Suigetsu (Fukui, Japan), was investigated. Water samples were collected from the central basin of Lake Suigetsu bimonthly between May 2008 and March 2010 at appropriate depths, including the oxic surface, oxic–anoxic interface, and anoxic bottom layers. Chlorophyll a, related to cyanobacteria and eukaryotic phytoplankton, was detected throughout the water column during the years of the study, whereas bacteriochlorophyll e, related to brown-colored green sulfur bacteria, was detected in the anoxic layers below the chemocline at a maximum concentration of 825 μg L^?1. The concentration of bacteriochlorophyll e was generally maximal at or just below the chemocline of the lake. The cellular content of bacteriochlorophyll e was estimated to be low in the upper part of the chemocline and tended to increase with increasing water depth. Bacteriochlorophyll a, which was presumably related to purple sulfur bacteria, was only detected at the chemocline during summer and autumn at concentrations of 5.4–16.3 μg L^?1. Our analysis of the chloropigment distribution for the two years of the study suggested that brown-colored green sulfur bacteria are the predominant phototroph in the anoxic layers of Lake Suigetsu, and that these play a significant role in the carbon and sulfur cycling of the lake, especially from spring to summer.     

Phytoplankton blooms under dim and cold conditions in freshwater lakes of East Antarctica

The seasonal variations of limnological (water temperature, light availability, turbidity, and chlorophyll a concentration) parameters were recorded continuously from January 2004 to February 2005 at two freshwater lakes: Oyako-ike and Hotoke-ike, Sôya Coast, East Antarctica. Water was in a liquid phase throughout the year, with temperatures ranging from 0 to 10°C. The maximum photosynthetically active radiation in Lake Oyako-ike was 23.16 mol m^?2 day^?1 (at 3.8 m) and Hotoke-ike was 53.01 mol m^?2 day^?1 (at 2.2 m) in summer, and chlorophyll a concentration ranged from ca. 0.5 to 2.5 μg L^?1 (Oyako-ike) and from ca. 0.1 to 0.8 μg L^?1 (Hotoke-ike) during the study period. Increase in chlorophyll a fluorescence occurred under dim-light conditions when the lakes were covered with ice in spring and autumn, but the signals were minimum in ice-free summer in both the lakes. During spring and summer, as a result of decreasing snow cover, the chlorophyll a concentration similarly decreased when PAR was relatively high, following periods of heavy winds. The autumnal and spring increase occurred under different PAR levels (ca. 20-fold and 90-fold stronger, respectively, in autumn in both the lakes). Differences in the autumn and spring increases suggest that the spring algal community is more shade-adapted than the autumn algal community. Antarctic phytoplankton appears especially adapted to low-light levels and inhibited by strong light regimes.     

Phytoplankton nitrogen demand and the significance of internal and external nitrogen sources in a large shallow lake (Lake Balaton,Hungary)

Since the middle of 1990s the trend of Lake Balaton towards an increasingly trophic status has been reversed, but N₂-fixing cyanobacteria are occasionally dominant, endangering water quality in summer. The sources of nitrogen and its uptake by growing phytoplankton were therefore studied. Experiments were carried out on samples collected from the middle of the Eastern (Siófok) and Western (Keszthely) basins between February and October 2001. Ammonium, urea and nitrate uptake and ammonium regeneration were measured in the upper 5-cm layer of sediment using the ¹⁵N-technique. Ammonium was determined by an improved microdiffusion assay. N₂ fixation rates were measured by the acetylene-reduction method. Ammonium regeneration rates in the sediment were similar in the two basins. They were relatively low in winter (0.13 and 0.16 μg N cm^?3 day^?1 in the Eastern and Western basin, respectively), increased slowly in the spring (0.38 and 0.45 μg N cm^?3 day^?1) and peaked in late summer (0.82 and 1.29 μg N cm^?3 day^?1, respectively). Ammonium uptake was predominant in spring in the Eastern basin and in summer in the Western basin, coincident with the cyanobacterial bloom. The amount of N₂ fixed was less than one third of the internal load during summer when external N loading was insignificant. Potentially, the phytoplankton N demand could be supported entirely by the internal N load via ammonium regeneration in the water column and sediment. However, the quantity of N from ammonium regeneration in the upper layer of sediment combined with that from the water column would limit the standing phytoplankton crop in spring in both basins and in late summer in the Western basin, especially when the algal biomass increases suddenly.     

Lake Chapo: a baseline study of a deep, oligotrophic North Patagonian lake prior to its use for hydroelectricity generation: I. Physical and chemical properties

A baseline study on a temperate, oligotrophic North Patagonian lake (Lake Chapo, Southern Chile) was made prior to the installation of a hydroelectric power station. Throughout one year (September 1986–October 1987) the physical and chemical properties of the lake were investigated monthly from the surface to a depth of 40 m. Lake Chapo is a deep, transparent (Secchi depth: 17–25 m), glacial lake located at 41°?27.5′?S and 72°?30′?W. It has a maximum depth of 298 m, mean depth of 183 m, surface area of 45.3 km² and water volume of 8.296 km³. The theoretical residence time of the water was 5.5 years. The temperature regime is monomictic with the mixed temperature between 8.1–8.8?°C. Maximum temperature at the surface was 18.7?°C during thermal stratification in summer when the epilimnion had a thickness of about 20 m. The conductivity was low (20.3–23.8 μS cm^?1) as was the buffering capacity of a predominantly CO₂-carbonate system. The predominant cations were Ca⁺²¿ Na⁺¿Mg⁺²¿K⁺. The phosphorous and nitrogen contents were very low (soluble reactive ortophosphate: 0–1.5 μg P l^?1, total phosphorus: 0.3–4 μg P l^?1 and nitrate: 0–35 μg N l^?1), which is typical of North Patagonian lakes.     

Estimation of reference conditions for phytoplankton in a naturally eutrophic shallow lake

Classification of waters using biological quality elements and determination of the degree of deviation from reference levels is a key issue in the Water Framework Directive of EU. Lakes in reference conditions with sufficient biological data are available for several boreal lake types with the exception of naturally eutrophic lakes. An empirical approach is one alternative for estimating the reference conditions of such lakes. We used the water transparency of the naturally eutrophic Lake Tuusulanjärvi recorded in August in the early 1910s to estimate reference values for phytoplankton biomass and chlorophyll a concentrations. Three phytoplankton samples during August 2000–2001 corresponded to the estimated reference values for total biomass (<5.6 mg l^?1) and chlorophyll a (<28 μg l^?1), as did the simultaneous Secchi depths. The phytoplankton assemblage in these samples with 24 eutrophy indicators (17% of the total taxa number) corresponded in general the species list from the early 1900s, which as such could be regarded as reference assemblage. Furthermore, in August 2000, 3 years after intensive fish removal a prominent decrease in cyanobacterial biomass and toxin concentration was observed. The costs of the measures and studies in Lake Tuusulanjärvi during 1989–2003 have been approximately 2.5 million euros.     

Impact of resuspended sediment on zooplankton feeding in Lake Waihola, New Zealand

1. Wind‐induced sediment resuspension in shallow lakes affects many physical and biological processes, including food gathering by zooplankton. The effects of suspended sediment on clearance rate were determined for a dominant cladoceran, Daphnia carinata, and calanoid copepod, Boeckella hamata, in Lake Waihola, New Zealand. 2. Animals were incubated at multiple densities for 4 days in lake water containing different amounts of suspended lake sediment. Rates of harvest of major food organisms were determined for each sediment level (turbidity) from changes in net growth rate with grazer density. 3. Daphnia cleared all food organisms 7–40 μm in length at similar rates, but was less efficient in its removal of free bacteria, phytoplankton <7 μm, and large cyanobacterial filaments. Elevation of sediment turbidity from 2 to 10 nephelometric turbidity units (NTU) (63 mg DW L^?1 added sediment) reduced Daphnia clearance of phytoplankton, heterotrophic flagellates and ciliates by 72–100%, and of amoebae and attached bacteria by 21–44%. Further inhibition occurred at higher turbidity. 4. Boeckella hamata removed microzooplankton primarily, rather than phytoplankton. The rate at which it cleared rotifers was reduced by 56% when turbidity was increased from 2.5 to 100 NTU. 5. In the absence of macrozooplankton, algal growth increased with sediment turbidity, suggesting that sediment also inhibits rotifer grazing. 6. As mid‐day turbidity in Lake Waihola is ≥10 NTU about 40% of the time, sediment resuspension may play a major role in moderating energy flow and structuring pelagic communities in this lake.     

Physical and chemical features of a tropical hypertrophic reservoir permanently stratified

Physical and chemical parameters of Pao-Cachinche reservoir (Venezuela) were measured in four stations (S1-S4) during an eighteen months period from September 1997 to February 1999. The tributaries of this reservoir introduce high amounts of nutrients from domestic wastewaters and from poultry and pig farms located in the basin. Thermal stratification was well established throughout the study period. Mountainous topography protects the water surface from mechanical action of wind, preventing water mixing. Hypoxic/anoxic conditions prevailed from 6–7 m depth down to the bottom in the limnetic stations. A strong smell of H₂S was detected below the 10 m level. The low water transparency (max. 1.5 m) may be mainly attributed to a high biogenic turbidity. Water salinity was low, as the maximum conductivity measured (260 μS cm^?1) suggests. The water was alkaline in the upper layers during the day time (pH >8.0), due to the high phytoplanktonic productivity, whereas in deeper layers, where decomposition processes predominate, pH was acidic (close to 6.0). Orthophosphate concentrations were high, reaching maximal concentrations in the deeper part of the reservoir (greater than 800 μg l^?1). Total phosphorus exceeded 1000 μg l^?1 in the hypolimnion during the dry season. Ammonia was the dominant inorganic nitrogen species, and its values were greater than 4000 μg l^?1 in the hypolimnetic layer during the dry season. Nitrates and nitrites were present in relatively low concentrations, except for the Paito stream entrance, where nitrate concentrations remained above 260 μg l^?1. Pao–Cachinche reservoir can be considered hypertrophic, according to Salas & Martinó’s criteria for tropical warm lakes, and could be classified as meromictic and warm monomictic, according to Lewis tropical lake types.     

Influence of Hydrological Pulse on Bacterial Growth and DOC Uptake in a Clear-Water Amazonian Lake

This study was conducted to evaluate: (1) the bacterial growth and the dissolved organic carbon (DOC) uptake in an Amazonian lake (Lake Batata) at high-water and low-water periods of the flood pulse; (2) the influence of nitrogen and phosphorus (NP) additions on bacterial growth and DOC uptake in Lake Batata at two flood pulse periods; and (3) the bioavailability of the main DOC sources in Lake Batata. Lake Batata is a typical clear-water Amazonian lake, located in the watershed of Trombetas River, Central Amazon, Brazil. Bacterial batch cultures were set up with 90% 0.2-μm filtered water and 10% inoculum from Lake Batata. N-NH₄NO₃ and P-KH₂PO₄, with final concentrations of 50 and 5 μM, respectively, were added to the cultures, except for controls. Extra sources of DOC (e.g., algal lysate, plant leachates) were added to constitute six distinct treatments. Bacterial response was measured by maximum bacterial abundance and rates of bacterial production, respiration, DOC uptake, and bacterial growth efficiency (BGE). Bacterial growth and DOC uptake were higher in NP treatments than in controls, indicating a consistent nutrient limitation in Lake Batata. The composition of DOC also seems to be an important regulating factor of bacterial growth in Lake Batata. Seasonally, bacterial growth and DOC bioavailability were higher at low-water period, when the phytoplankton is a significant extra source of DOC, than at high-water period, when the forest is the main source of DOC. DOC bioavailability was better estimated based on the diversity and the diagenetic stage of carbon compounds than on single classes of labile compounds. Changes in BGE were better related to CNP stoichiometry in the water, and the “excess” of organic substrates was oxidized in catabolism, despite the quality of these compounds for bacterial growth. Finally, we conclude that bacterial growth and DOC uptake vary throughout the flood pulse in clear-water Amazonian ecosystems as a result of changes in nutrient concentration and in DOC composition.     

Long-term nutrient trends and harmful cyanobacterial bloom potential in hypertrophic Lake Taihu,China

Rapid economic development in China’s Lake Taihu basin during the past four decades has accelerated nitrogen (N) and phosphorus (P) loadings to the lake. This has caused a shift from mesotrophic to hypertrophic conditions, symptomized by harmful cyanobacterial blooms (CyanoHABs). The relationships between phytoplankton biomass as chlorophyll a (Chla) and nutrients as total nitrogen (TN) and total phosphorus (TP) were analyzed using historical data from 1992 to 2012 to link the response of CyanoHAB potential to long-term nutrient changes. Over the twenty year study period, annual mean Chla showed significantly positive correlations with both annual mean TN and TP (P < 0.001), reflecting a strong phytoplankton biomass response to changes in nutrient inputs to the lake. However, phytoplankton biomass responded slowly to annual changes in TN after 2002. There was not a well-defined or significant relationship between spring TN and summertime Chla. The loss of a significant fraction of spring N loading due to denitrification likely weakened this relationship. Bioavailability of both N and P during the summer plays a key role in sustaining cyanobacterial blooms. The frequency of occurrence of bloom level Chla (>20 μg L^?1) was compared to TN and TP to determine nutrient-bloom thresholds. A decline in bloom risk is expected if TN remains below 1.0 mg L^?1 and TP below 0.08 mg L^?1.     

Analysis of changes over 44 years in the phytoplankton of Lake Võrtsjärv (Estonia): the effect of nutrients,climate and the investigator on phytoplankton-based water quality indices

We analysed long-term changes in phytoplankton composition in relation to hydrological, meteorological and nutrient loading data in the large (270 km²) shallow (mean depth 2.8 m) Lake Võrtsjärv. Nutrient loads to the lake were heavy in the 1970s and 1980s and decreased considerably thereafter. The average nutrient concentrations for 1985–2004 (1.6 mg l^?1 of total nitrogen and 53 μg l^?1 of total phosphorus) characterize the lake as a eutrophic water body. All four calculated taxonomic indices showed a unidirectional deterioration of the lake’s ecological status, despite reduced concentrations of nutrients. We focused our analysis on the PTSI index, which revealed a stepwise change between the years 1977 and 1979 that coincided with a large increase in water level, but also with a change of investigator. After correcting input data for possible investigator-induced differences, the step change remained because it was caused by major changes in the whole phytoplankton community. The previous dominant Planktolyngbya limnetica was replaced by two species of seasonally altering Limnothrix. Among phytoplankton functional groups, there was a decrease in all groups comprising small-sized phytoplankton species, such as X1, E, F, J, N and an increase in S1 and H1, both represented by filamentous cyanobacteria. Our results suggest a non-linear response of phytoplankton to changing nutrient loadings, and that the change observed between 1977 and 1979 was a regime shift triggered by water level change. High shade tolerance of the new dominants, and their ability to create shade, obviously stabilized the new status making it resistant to restoration efforts.     

Variations in Abundance,Genome Size,Morphology, and Functional Role of the Virioplankton in Lakes Annecy and Bourget over a 1-Year Period

We sampled the surface waters (2–50 m) of two deep peri-alpine lakes over a 1-year period in order to examine (1) the abundance, vertical distribution, genome size, and morphology structures of the virioplankton; (2) the virus-mediated bacterial mortality; and (3) the specific genome size range of double-stranded DNA (dsDNA) phytoplankton viruses. Virus-like particle (VLP) concentrations varied between 4.16?×?10⁷ (January) and 2.08?×?10⁸ part mL^?1 (May) in Lake Bourget and between 2.7?×?10⁷ (June) and 8.39?×?10⁷ part mL^?1 (November) in Lake Annecy. Our flow cytometry analysis revealed at least three viral groups (referred to as virus-like particles 1, 2, and 3) that exhibited distinctive dynamics suggestive of different host types. Phage-induced bacterial mortality varied between 6.1 % (June) and 33.2 % (October) in Lake Bourget and between 7.4 % (June) and 52.6 % (November) in Lake Annecy, suggesting that viral lysis may be a key cause of mortality of the bacterioplankton. Virioplankton genome size ranged from 27 to 486 kb in Lake Bourget, while it reached 620 kb in Lake Annecy for which larger genome sizes were recorded. Our analysis of pulsed field gel electrophoresis bands using different PCR primers targeting both cyanophages and algal viruses showed that (1) dsDNA viruses infecting phytoplankton may range from 65 to 486 kb, and (2) both cyanophage and algal “diversity” were higher in Lake Annecy. Lakes Annecy and Bourget also differed regarding the proportions of both viral families (with the dominance of myoviruses vs. podoviruses) and infected bacterial morphotypes (short rods vs. elongated rods), in each of these lakes, respectively. Overall, our results reveal that (1) viruses displayed distinct temporal and vertical distribution, dynamics, community structure in terms of genome size and morphology, and viral activity in the two lakes; (2) the Myoviridae seemed to be the main cause of bacterial mortality in both lakes and this group seemed to be related to VLP2; and (3) phytoplankton viruses may have a broader range of genome size than previously thought. This study adds to growing evidence that viruses are diverse and play a significant role in freshwater microbial dynamics and more globally lake functioning. It highlights the importance of further considering this biological compartment for a better understanding of plankton ecology in peri-alpine lakes.     

Winter condition of marine plankton populations in Saanich inlet,B.C., canada. I. Phytoplankton and its surrounding environment

Weekly sampling was carried out in Saanich Inlet, British Columbia throughout the winter of 1975–1976. The surface water column was characterized by exposure to low solar radiation energy (<150 g cal·cm^?2 · day^?1), slight stratification with occasional vertical mixing, and abundant algal nutrients. Phytoplankton were mostly distributed above 5 m in the water column, with a fairly low biomass averaging <1 μgchla·1^?1. Dominant phytoplankton organisms were nanoflagellates occasionally accompanied by dinoflagellates as the second dominant. Centric diatoms, which were dominant in the blooms, were always present but less than a few percentage of the total phytoplankton biomass. Daily photosynthetic productivity was exclusively limited by available radiant energy. Low solar radiation and occasional mixing of the surface zone prohibited the centric diatoms from becoming dominant.     

Underwater sinkhole sediments sequester Lake Huron’s carbon

Lake Huron’s submerged sinkhole habitats are impacted by high-conductivity groundwater that allows photosynthetic cyanobacterial mats to form over thick, carbon-rich sediments. To better understand nutrient cycling in these habitats, we measured the stable isotopic content of carbon and nitrogen in organic and inorganic carbon pools in Middle Island sinkhole, a ~23 m deep feature influenced by both groundwater and overlying lake water. Two distinct sources of dissolved CO₂ (DIC) were available to primary producers. Lake water DIC (δ ¹³C = ?0.1 ‰) differed by +5.9 ‰ from groundwater DIC (δ ¹³C = ?6.0 ‰). Organic carbon fixed by primary producers reflected the two DIC sources. Phytoplankton utilizing lake water DIC were more enriched in ¹³C (δ ¹³C = ?22.2 to ?23.2 ‰) than mat cyanobacteria utilizing groundwater DIC (δ ¹³C = ?26.3 to ?30.0 ‰). Sinkhole sediments displayed an isotopic signature (δ ¹³C = ?23.1 ‰) more similar to sedimenting phytoplankton than the cyanobacterial mat. Corroborated by sediment C/N ratios, these data suggest that the carbon deposited in sinkhole sediments originates primarily from planktonic rather than benthic sources. ²¹⁰Pb/¹³⁷Cs radiodating suggests rapid sediment accumulation and sub-bottom imaging indicated a massive deposit of organic carbon beneath the sediment surface. We conclude that submerged sinkholes may therefore act as nutrient sinks within the larger lake ecosystem.     

Assessment of mine drainage remediated streams using diatom assemblages and biofilm enzyme activities

A legacy of pre-regulation coal mining in many areas has been acid mine drainage (metal-rich, low pH water). Today, numerous remediation strategies may be implemented, but there is little data on efficacy in restoring biological condition. Two alkaline doser projects in Ohio were assessed using diatom assemblages, and biofilm extracellular enzyme activities (EEA). In one stream, water quality steadily increased downstream of the doser; pH increased from 3.8 to 7.2 and Fe decreased from 107 to 0.42 mg l^?1. Likewise, the periphyton biomass (chl a 7.15–12.77 mg m^?2) increased and periphyton index scores (4–27) improved. As well, EEA data showed greater activity for phosphorus, nitrogen, and one carbon acquisition enzyme. For the other stream, the conductivity remained high (>720 μS cm^?1) and pH and alkalinity decreased downstream. Biological data, including EEA, varied along the stream length with higher numbers in the middle reach, such as chlorophyll a (0.56 to 87.75 to 2.77 mg m^?2), and index scores (7 to 29 to 11). The first remediation site showed positive results in chemistry, biological community and measures of ecosystem function. The second stream was highly variable in these parameters suggesting further AMD inputs are hampering recovery.     

Roles of dilution rate and nitrogen concentration in competition between the cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> and the diatom <Emphasis Type="Italic">Cyclotella</Emphasis> sp. in eutrophic lakes

In Lake Tega, Japan, the shift of dominant algal species was caused as a result of discharging water from the adjacent river into the lake. The transition from cyanobacteria (mainly the genus Microcystis) to diatoms (mainly the genus Cyclotella) resulted in a disappearance of algal blooms. Although some environmental conditions such as flow rate, nutrient concentration, and transparency were changed by the project, the decisive factor for the transition has not been clarified yet. For the effective control of algal blooms by water discharge, this study aimed to elucidate the effects of daily renewal rate and nitrogen concentration on the interspecific competition between Microcystis aeruginosa and Cyclotella sp. Monoculture experiments were conducted to obtain growth characteristics for each species and mixed culture experiments were performed to examine their competitive abilities under various daily renewal rates of the culture medium (15 and 30 %) and nitrate concentrations (71.4, 178, and 357 μM). In addition to prepared medium, Lake Tega water was also used for mixed culture experiments. The results showed that the increase in a daily renewal rate contributed to the dominance of Cyclotella sp., while a nitrate concentration had little influence on the competition. We conclude that algal blooms composed of the genus Microcystis would be controlled by maintaining a daily renewal rate up to 30 % or more, which corresponded to the dilution rate of 0.36 day^?1, under a nitrate concentration of ≤357 μM. The study would include essential information for the management of lakes suffering from frequent occurrences of algal blooms.