Effect of trophic status on the culturability and activity of bacteria from a range of lakes in the English Lake District

The bacterioplankton from a number of lakes that differed in nutrient status in the English Lake District was examined with a number of techniques for enumeration and activity assessment. Natural water samples showed a clear correlation between total counts and trophic status. Esterase activity measurements with Chemchrome B were able to distinguish high- and low-nutrient-status lakes, whereas tetrazolium salt (5-cyano-2,3-ditoyltetrazolium chloride) reduction, the direct viable count-cell elongation assay, and culturability measurements could not. Tetrazolium salt reduction and esterase activity measurements labeled a significant number of cells from water of all nutrient levels, whereas the direct viable count-cell elongation method was of use only in oligotrophic waters. Size fractionation of samples showed that the culturable cells were retained by the larger filters, especially in nutrient-rich waters. Esterase activity measurements also favored the larger cells. The differences observed between assays using water that differed in trophic status raise questions about the use of these tests as a definitive measure of viability.     

The microbial loop in the planktonic communities in lakes with various trophic status

The structure of planktic trophic chains was studied in eight lakes of European Russia and five lakes in Central Asia. The lakes differed in the level of productivity, morphometric parameters, and the type of agitation and mineralization. It is found that the microbial loop of picophototrophic organisms, bacteria, heterotrophic flagellates, infusoria, and viruses constitutes 12.3-64.7% of the total plankton biomass. Positive correlation between the biomass of microbial community and the primary production of phytoplankton is observed, whereas no relation is revealed between the share of microorganisms in the plankton biomass and the trophic status of the water body. The presence of a great number of cladocerans decreased the role of the microbial loop in the structural organization of the planktic community. Heterotrophic flagellates consuming 3-81% of daily bacterial production were the principal cause of bacteria elimination only in some of the studied water bodies.     

Strength and uncertainty of phytoplankton metrics for assessing eutrophication impacts in lakes

Phytoplankton constitutes a diverse array of short-lived organisms which derive their nutrients from the water column of lakes. These features make this community the most direct and earliest indicator of the impacts of changing nutrient conditions on lake ecosystems. It also makes them particularly suitable for measuring the success of restoration measures following reductions in nutrient loads. This paper integrates a large volume of work on a number of measures, or metrics, developed for using phytoplankton to assess the ecological status of European lakes, as required for the Water Framework Directive. It assesses the indicator strength of these metrics, specifically in relation to representing the impacts of eutrophication. It also examines how these measures vary naturally at different locations within a lake, as well as between lakes, and how much variability is associated with different replicate samples, different months within a year and between years. On the basis of this analysis, three of the strongest metrics (chlorophyll-a, phytoplankton trophic index (PTI), and cyanobacterial biovolume) are recommended for use as robust measures for assessing the ecological quality of lakes in relation to nutrient-enrichment pressures and a minimum recommended sampling frequency is provided for these three metrics.     

The application of viable count procedures for measuring viable cells in the various marine environments

Aims: To investigate whether the use of direct viable count (DVC), quantitative viable count (qDVC), colony‐forming units and the contribution of capsule‐bearing bacteria to the total number of bacteria and esterase‐active bacteria could be used to clearly differentiate viable cells in various trophic status of seawater. Methods and Results: Hundred and four marine isolates from various marine environments in Turkey (Western Black Sea, northern part of the Sea of Marmara, Northern Aegean Sea and eastern part of the Sea of Marmara) were screened. Seawater samples were taken from the surface (the upper 0–30 cm) and deeper layers (from 5 to 500 m) of the sea at different time periods between February 2002 and June 2007. For the assessment of cell elongation, minor modifications were made on DVC procedure in order to optimize the concentration of yeast extract and incubation time for enumeration of bacteria in response to nutrient addition. The best results were obtained when the yeast extract was used at a final concentration of 250 mg l^?1 (at 35°C 24 h incubation) for bacteria isolated from eutrophic areas and a final concentration of 50 mg l^?1 for those selected from oligotrophic areas. A positive correlation was found between the trophic level and the level of metabolically active bacteria. Among these methods, the bacterial number obtained by qDVC is higher than those gained by other methods. Conclusions: The results indicate that the qDVC procedure could easily differentiate between viable cells and dormant or dead cells. We suggest that this method may be applicable to detecting the level of metabolic potential of bacterial communities in marine environments. Significance and Impact of the Study: The study resulted in increased knowledge on the applicability of the qDVC method that arranges the substrate amount and incubation time as well as on the comparison of various viable bacteria count procedures related to trophic situation of seawater samples.     

Spatial and temporal heterogeneity of trophic variables in a deep lake as reflected by repeated singular samplings

Approaches to compare the strength of pelagic trophic cascades often use singular sampling programs for measuring trophic variables, thus potentially neglecting the spatial and temporal heterogeneity in the distribution of fish, zooplankton and phytoplankton. Here, we compared the composition of six trophic variables from three trophic levels in a deep oligotrophic lake within temporal (diel and seasonal) and spatial (horizontal and vertical) sampling resolutions. Mean values and ratios between the variables were compared between day and night, in three sampling months, four lake basins, and three water depths. Factor analysis was used to determine abiotic variables which may explain the heterogeneous distribution of the trophic variables. All six trophic variables were strongly heterogeneously distributed between the sampling months and the water depths, whereas horizontal and day–night differences were lower. Distribution of fish, zooplankton and phytoplankton correlated with water temperature and nutrient concentrations. Accordingly, for the use in comparative and meta-analyses, singular sampling programs in deep lakes have to integrate the entire water depth and are best repeated over several seasons. Alternatively, mean water temperature and nutrient concentrations may be used as covariates to diminish the unexplained variance between samples from different lakes.     

Differences in food webs and trophic states of Brazilian tropical humid and semi-arid shallow lakes: implications of climate change

Global warming may intensify eutrophication of shallow lakes by affecting nutrient loading, evaporation rates, and water level and thus produce major changes in food webs. We investigated to what degree food webs in tropical humid lakes differed from those in more eutrophic semi-arid lakes of the same latitude. Our results indicate that the catchment area-to-lake area ratio, nutrients, chlorophyll a, suspended solids, abundances of phytoplankton, zooplankton, and omnivorous fish as well as total fish catch per unit effort were all higher in the semi-arid lakes, whereas inlet water-to-evaporation ratio (proxy for water balance), water transparency, percentage macrophytes cover, and the piscivores:omnivores ratio were higher in the humid lakes. Our results suggest that reduced inlet water-to-evaporation ratio will increase lake eutrophication, which, in turn, as in temperate regions, will alter trophic structure of the freshwater community.

     

Catchment land use and trophic state impacts on phytoplankton composition: a case study from the Rotorua lakes’ district, New Zealand

Trophic state of lakes has been related to catchment land use, but direct links between phytoplankton taxa and land use are limited. Phytoplankton composition, represented by relative cell abundance of phyla, was measured over a period of 4 years in 11 lakes in the Rotorua region, New Zealand. The lakes differed in morphometry, trophic state and land use (as percentage catchment area). We tested whether relative proportion of land uses, indirectly representing relative nutrient loading, was the overarching driver of phytoplankton composition. Trophic state was correlated negatively with native forest and positively with pasture and urban area. Cyanoprokaryota were correlated negatively with native forest and positively with pasture and trophic state, Chlorophyta were correlated positively with native forest and urban land use and negatively with pasture and trophic state, and Bacillariophyta were positively correlated with dissolved reactive silica to dissolved inorganic nitrogen (Si:DIN) and Si to dissolved reactive phosphorus (Si:DRP) ratios. Lakes with higher nutrient loads had higher trophic state and Cyanoprokaryota dominance. Chlorophyta were negatively correlated with Cyanoprokaryota and Bacillariophyta, suggesting competition amongst these groups. Our results apply to lakes potentially subject to changes in catchment land use, which may have implications for trophic state, phytoplankton composition and Cyanoprokaryota blooms.     

Differences in the substrate spectrum of extracellular enzymes in shallow lakes of differing trophic status

Organic matter fluxes and food web interactions in lakes depend on the abilities of heterotrophic microbial communities to access and degrade organic matter, a process that begins with extracellular hydrolysis of high molecular weight substrates. In order to determine whether patterns of enzymatic hydrolysis vary among shallow lakes of different trophic status, we investigated the hydrolysis of six specific organic macromolecules (polysaccharides) in the spring and late summer in four adjacent shallow lakes of eutrophic, oligotrophic, and dystrophic status in coastal North Carolina, USA. The spectrum of enzyme activities detected differed strongly between lakes, with all six polysaccharides hydrolyzed in West Mattamuskeet in May, while only two substrates were hydrolyzed in Lake Phelps in August/September. Differences in the spectrum of enzyme activities, and therefore the capabilities of heterotrophic microbial communities, were likely driven by variations among lakes in primary productivity patterns, sediment–water interactions, and/or water chemistry. Our data represent a first step towards a better understanding of carbon substrate availability and differences in carbon cycling pathways in shallow lakes of different trophic status.     

Bacterioplankton Community Composition in Five Lakes Differing in Trophic Status and Humic Content

Abstract To investigate the relation between lake type and bacterioplankton community composition, five Swedish lakes, which differed from each other in nutrient content and water color, were studied. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA was used to examine community composition. The DGGE-patterns of the different samples were analyzed in relation to physical, chemical, and biological data from the lakes by canonical correspondence analysis (CCA). The three variables found to most strongly correlate with the DGGE patterns were biomasses of microzooplankton, cryptophytes, and chrysophytes, suggesting that these biota had an impact on bacterioplankton community structure. Two of the three factors were, in turn, significantly correlated to parameters associated with the trophic status of the lakes, indicating that the nutrient content of the lakes, at least indirectly, influenced the structure of the bacterioplankton community. The relation to water color was less pronounced. Received: 16 February 2000; Accepted: 27 April 2000; Online Publication: 18 July 2000     

PICOPHYTOPLANKTON BIOMASS IN RELATION TO LAKE TROPHIC STATE AND THE TN:TP RATIO OF LAKE WATER IN JAPAN1

Picophytoplankton biomass and its contribution to total phytoplankton biomass were investigated in relation to the nutrient concentration and total N: total P ratio of the epilimnetic waters of 42 Japanese lakes during the warm season in 1991 (April–October). Picophytoplankton biomass (as chlorophyll a) in meso-, eu-, and hypertrophic lakes was significantly higher than those observed in oligotrophic lakes. However, picophytoplankton biomass increased significantly with increased total P concentrations in all systems excluding hypertrophic lakes. Picophytoplankton contribution to total chlorophyll a content was significantly higher in oligo- and mesotrophic lakes than in eu- and hypertrophic lakes and was inversely correlated with total P concentrations in lake water. Picophytoplankton contribution to the total phytoplankton biomass was positively (r = 0.54, n = 42, P = 0.0003) correlated with the total N: total P ratio of lake waters. Each lake trophic type, with the exception of hypertrophic lakes, showed this trend, although the correlation was not significant. We suggest that picophytoplankton contribution is influenced by the total N: total P ratio rather than lake trophic state; however, picophytoplankton were of little importance in hypertrophic lakes.     

Relation of abundance-weighted averages of diatom indicator values to measured environmental conditions in standing freshwaters

Abundance-weighted averages of diatom indicator values for pH, salinity, organic nitrogen availability, oxygen saturation, saprobity and trophic status according to van Dam et al. [Neth. J. Aquat. Ecol. 28 (1994) 117] were calculated for surface sediment and epiphytic diatom assemblages in 186 standing waters distributed throughout Flanders, Belgium, and tested against environmental variables measured in the water column, covering water chemistry, trophic status and organic load. With exception of the pH indication, most scores related rather poorly to variables which they are assumed to reflect and correlated even more strongly to non-target variables. For instance, the trophic indication provided a measure of pH and base status rather than of nutrient levels or phytoplankton productivity. Relations to measured variables differed according to the pH regime. Correction for uneven distribution of indicator values in the species pool usually yielded little improvement and was detrimental in some cases. Compared to epiphyton, weighted averages of species indicator values derived from sediment assemblages tended to be higher in water bodies yielding the most elevated indication scores. Except for the pH and salinity indication, differences between weighted averages pertaining to these different habitats were often considerable. Limitations to the use of abundance-weighted averages of diatom indicator values for environmental monitoring and assessment of lentic waters are discussed.     

Combining multivariate statistical techniques and random forests model to assess and diagnose the trophic status of Poyang Lake in China

Floodplain lakes are valuable to humans because of their various functions. An emerging public concern on lake eutrophication has heightened the need to assess and predict the trophic status in floodplain lakes, particularly for those with high spatial heterogeneity. In this study, combined multivariate statistical techniques and random forests model were used to characterize the water quality and trophic status of Poyang Lake. By classifying and characterizing seasonal water samples comprising 11 water quality parameters collected from 13 sampling sites in Poyang Lake between 2008 and 2014, the dataset was divided into the central and northern lake groups, which corresponded to lentic and lotic regions in Poyang Lake, respectively. The spatial water quality variations and underlying patterns were investigated by performing discriminant analysis and principal component analysis (PCA). Lastly, random forests (RF) were used to predict the chlorophyll a (Chl-a) variations of the central and northern lakes. The PCA results indicated that the water quality of the central and northern areas of the lake was controlled by different environmental variables and underlying pollutant sources. The RF model outperformed the artificial neural network and linear regression and was robust with strong predictive capabilities. It was determined that the most important predictors of the Chl-a variations in the northern lake were water temperature (T) and water level, whereas transparency, T, and water level were the most efficient predictors in the central lake. The RF model can also be applied to trophic prediction in other large lakes with considerable spatial variations. This study will have implications on water quality management and eutrophication prevention in floodplain lakes with high spatial heterogeneity.     

The influence of catchment size on lake trophic status during the hemlock decline and recovery (4800 to 3500 BP) in southern Ontario lakes

We investigated the ecological effects of terrestrial ecosystem change during the hemlock decline and recovery (4,800–3,500 BP) on lake communities (diatoms and chrysophytes). This study specifically assessed the role of catchment area and slope in determining the magnitude of lake eutrophication during the hemlock decline by analyzing sediment cores from five alkaline, holomictic lakes in southeastern Ontario, Canada. The study lakes were similar in most limnological aspects, but differed widely in the relative sizes of their catchments. Diatoms were used to quantitatively infer past lake-water total phosphorus (TP) concentrations.All five lakes showed shifts in their algal communities during the hemlock decline, but most lakes exhibited only minor changes in trophic status. The magnitude of the limnological response appears to be related to catchment size and slope. Long Lake, Burridge Lake, and Gunter Lake possess the smallest catchments and exhibited the weakest responses to the hemlock decline. The catchment area of Flower Round Lake is considerably larger and steeper than these lakes, and was the only lake to show a marked eutrophication. Aulacoseira ambigua bloomed and diatom-inferred TP concentration increased by 14 µg 1^–1.Catchment slope appears to have influenced the type of material exported into the lakes. Lake basins draining catchments with gentle relief received proportionally greater amounts of organic matter, whereas steeper catchments supplied relatively greater proportions of mineral matter. Faster water flow associated with steeper catchment slope may have enhanced mineral erosionFollowing the hemlock decline, nutrient supplies to most of the study lakes were reduced. The period of forest recovery was associated with an 11 µg 1^–1 reduction in diatom-inferred lake-water TP concentration in Flower Round Lake, and algal populations decreased. Our results generally support the ecological theory of forest ecosystem development and secondary succession developed from long-term data collected at the Hubbard Brook Experimental Ecosystem.     

The Relation Between Adenosine Triphosphate and Microbial Biomass in Diverse Aquatic Ecosystems

By using autoradiographic examination of ¹⁴C labeled viable cells, natural phytoplankton communities were separated into living and non-living components. Comparisons of carbon to adenosine triphosphate (ATP) content of living cells yielded consistent ratios with depth, during periods of high and low nutrient supply at Lake Tahoe. Over time the ratio fluctuated by no more than ± 17% of the mean between the time of maximum nutrient supplies and nutrient depletion. The viability of specific phytoplankton groups was surprisingly low at times, indicating that conventional counting methods tend to overestimate live biomass. A survey of lakes differing in trophic states and having diverse phytoplankton and bacterial assemblages has shown that ATP measurements can be used as an accurate measure of total living microbial biomass.     

Legionella incidence and density in potable drinking water supplies.

The incidence and density of Legionella spp. in raw water, water at various stages of treatment, and in potable distribution water were determined by direct immunofluorescence. The number of cells reacting with Legionella-specific fluorescent antibody conjugates in raw waters ranged from about 10(4) to 10(5) cells/liter, whereas the concentrations of fluorescent antibody-positive cells in the distribution waters were generally 10- to 100-fold lower than in the raw source waters. No viable or virulent Legionella strains were isolated from either the source or distribution waters. However, Legionella spp. are infrequently isolated from water at temperatures below 15 degrees C as was the case in the system surveyed in this study.     

Legionella incidence and density in potable drinking water supplies

The incidence and density of Legionella spp. in raw water, water at various stages of treatment, and in potable distribution water were determined by direct immunofluorescence. The number of cells reacting with Legionella-specific fluorescent antibody conjugates in raw waters ranged from about 10(4) to 10(5) cells/liter, whereas the concentrations of fluorescent antibody-positive cells in the distribution waters were generally 10- to 100-fold lower than in the raw source waters. No viable or virulent Legionella strains were isolated from either the source or distribution waters. However, Legionella spp. are infrequently isolated from water at temperatures below 15 degrees C as was the case in the system surveyed in this study.     

Resource Availability and Spatial Heterogeneity Control Bacterial Community Response to Nutrient Enrichment in Lakes

The diversity and composition of ecological communities often co-vary with ecosystem productivity. However, the relative importance of productivity, or resource abundance, versus the spatial distribution of resources in shaping those ecological patterns is not well understood, particularly for the bacterial communities that underlie most important ecosystem functions. Increasing ecosystem productivity in lakes has been shown to influence the composition and ecology of bacterial communities, but existing work has only evaluated the effect of increasing resource supply and not heterogeneity in how those resources are distributed. We quantified how bacterial communities varied with the trophic status of lakes and whether community responses differed in surface and deep habitats in response to heterogeneity in nutrient resources. Using ARISA fingerprinting, we found that bacterial communities were more abundant, richer, and more distinct among habitats as lake trophic state and vertical heterogeneity in nutrients increased, and that spatial resource variation produced habitat specific responses of bacteria in response to increased productivity. Furthermore, changes in communities in high nutrient lakes were not produced by turnover in community composition but from additional taxa augmenting core bacterial communities found in lower productivity lakes. These data suggests that bacterial community responses to nutrient enrichment in lakes vary spatially and are likely influenced disproportionately by rare taxa.     

Potential conflicts between environmental legislation and conservation exemplified by aquatic macrophytes

It is important that legislation on water quality issues of freshwaters is not in conflict with nature conservation purposes. So far, it is however unknown how the assessment of ecological status according to for example the Water Framework Directive (WFD) of the European Community relates to the status of lakes according to the Habitat Directive (HD) or to national environmental objectives including, e.g., the protection of important wetland areas and red-listed species. We used lake macrophyte classification schemes of Norway, Sweden, and Finland and a total of 1,014 lakes to evaluate the possible conflict between these directives and national legislation. The classification schemes represent mainly trophic indices penalizing lakes with elevated phosphorous concentrations. In general, high ecological status according to the WFD did not mean high number of red-listed species or high status according to the HD or other national environmental objectives. In Sweden 78%, in Norway 47%, and in Finland 29% of lakes with red-listed species were classified as lakes of moderate or worse ecological status based on the macrophyte classification scheme. These lakes thus did not fulfill the demands of the WFD. Restoration of surface water toward fulfilling the demands requires in practice a reduction of the trophic status. This might potentially result in for example the loss of red-listed species. To avoid such potential conflicts, we primarily suggest revising the national quality assessment systems toward implicitly incorporating nature conservation aspects, e.g., the number of red-listed species in a multi-metric assessment system.     

鲢鱼的放养对水质影响的研究进展

鲢鱼的放养对水质影响的研究进展董双林（华东师范大学生物系,上海２０００６２）ＥｆｆｅｃｔｏｆＳｉｌｖｅｒＣａｒｐＳｔｏｃｋｉｎｇｏｎＷａｔｅｒＱｕａｌｉｔｙｇ：ＲｅｓｅａｒｃｈＡｄｖａｎｃｅｓ．￥ＤｏｎｇＳｈｕａｎｇｌｉｎ（ＤｅｐａｒｔｍｅｎｔｏｆＢ...