Restoring macrophyte diversity in shallow temperate lakes: biotic versus abiotic constraints

Although many lake restoration projects have led to decreased nutrient loads and increased water transparency, the establishment or expansion of macrophytes does not immediately follow the improved abiotic conditions and it is often unclear whether vegetation with high macrophyte diversity will return. We provide an overview of the potential bottlenecks for restoration of submerged macrophyte vegetation with a high biodiversity and focus on the biotic factors, including the availability of propagules, herbivory, plant competition and the role of remnant populations. We found that the potential for restoration in many lakes is large when clear water conditions are met, even though the macrophyte community composition of the early 1900s, the start of human-induced large-scale eutrophication in Northwestern Europe, could not be restored. However, emerging charophytes and species rich vegetation are often lost due to competition with eutrophic species. Disturbances such as herbivory can limit dominance by eutrophic species and improve macrophyte diversity. We conclude that it is imperative to study the role of propagule availability more closely as well as the biotic interactions including herbivory and plant competition. After abiotic conditions are met, these will further determine macrophyte diversity and define what exactly can be restored and what not.     

Lignin biomarkers as tracers of mercury sources in lakes water column

This study presents the role of specific terrigenous organic compounds as important vectors of mercury (Hg) transported from watersheds to lakes of the Canadian boreal forest. In order to differentiate the autochthonous from the allochthonous organic matter (OM), lignin derived biomarker signatures [Lambda, S/V, C/V, P/(V + S), 3,5-Bd/V and (Ad/Al)v] were used. Since lignin is exclusively produced by terrigenous plants, this approach can give a non equivocal picture of the watershed inputs to the lakes. Moreover, it allows a characterization of the source of OM and its state of degradation. The water column of six lakes from the Canadian Shield was sampled monthly between June and September 2005. Lake total dissolved Hg concentrations and Lambda were positively correlated, meaning that Hg and ligneous inputs are linked (dissolved OM r ² = 0.62, p < 0.0001; particulate OM r ² = 0.76, p < 0.0001). Ratios of P/(V + S) and 3,5-Bd/V from both dissolved OM and particulate OM of the water column suggest an inverse relationship between the progressive state of pedogenesis and maturation of the OM in soil before entering the lake, and the Hg concentrations in the water column. No relation was found between Hg levels in the lakes and the watershed flora composition—angiosperm versus gymnosperm or woody versus non-woody compounds. This study has significant implications for watershed management of ecosystems since limiting fresh terrestrial OM inputs should reduce Hg inputs to the aquatic systems. This is particularly the case for large-scale land-use impacts, such as deforestation, agriculture and urbanization, associated to large quantities of soil OM being transferred to aquatic systems.     

The effect of water column mixing on phytoplankton succession, diversity and similarity

The lake number was used to describe the mixing condition forthree consecutive years (1992–1994) in Lake Tegel, Berlin,and compared to the successions of diatoms, dinoflagellatesand cyanobacteria, the main phytoplankton groups in the lake,as well as to diversity and similarity indices. Using both diversityand similarity indices in juxtaposition provides an indicationof the growth type of prevailing species (r- or K-strategists)and the degree of competition in the aqua-ecological system.A genera] pattern of these indices can be recognized as threephases: (i) high diversity—during spring, summer and autumn,interrupted by (ii) phases of low diversity during the latespring clear-water phase as the number of spring species plummeted,and (iii) during the late summer, climax populations of K-strategists.On a smaller time scale, similarity and diversity proved toreact sensitively to disturbances at frequencies intermediatein relation to the generation times of the phytoplankton. Thissupports the ‘intermediate disturbance hypothesis’,as proposed for phytoplankton by Padisak et al. [(eds) IntermediateDisturbance Hypothesis in Phytoplankton Ecology. Kluwer Academic,1993]. Diversity may remain quite high even for extended periodsduring summer climax situations, in conjunction with a highdegree of similarity, if deeper mixing of the epilimnion occursat time intervals of 2–3 weeks, as during the summer of1993. This enables the prevalence of ‘ruderal’ species,together with some motile K-strategists who actively seek optimaldepths for photosynthesis. During such summer situations describedby frequent occurrences of lower lake numbers, the epilimnionof Lake Tegel is mixed deeply enough to support ruderals, butnot too vigorously to counteract competitive advantages of motilespecies. Thus, vertical niche separation enhances diversity.     

The roles of biotic resistance and nitrogen deposition in regulating non-native understory plant diversity

Understanding the mechanisms that allow for plant invasions is important for both ecologists and land managers, due to both the environmental and economic impacts of native biodiversity losses. We conducted an observational field study in 2008 to examine the relationship between native and non-native forest understory plant species and to investigate the influence of soil nitrogen (N) on plant community richness and diversity. In 2009, we conducted a companion fertilization experiment to investigate how various forms of N deposition (inorganic and organic) influenced native and non-native species richness and diversity. We found that native species richness and diversity were negatively correlated with 1) non-native species richness and diversity and 2) higher total soil inorganic N. In the deposition experiment, adding organic N fertilizers decreased native richness and diversity compared to inorganic N fertilizers. Together, these results indicate that increasing soil N can be detrimental to native species; however, native species richness and diversity may counteract the N-stimulation of non-native species. Furthermore, the negative effects of organic N deposition on native plants may be just as strong, if not stronger, than the effects of inorganic N deposition.     

Microbial diversity and biogeochemical cycling in soda lakes

Soda lakes contain high concentrations of sodium carbonates resulting in a stable elevated pH, which provide a unique habitat to a rich diversity of haloalkaliphilic bacteria and archaea. Both cultivation-dependent and -independent methods have aided the identification of key processes and genes in the microbially mediated carbon, nitrogen, and sulfur biogeochemical cycles in soda lakes. In order to survive in this extreme environment, haloalkaliphiles have developed various bioenergetic and structural adaptations to maintain pH homeostasis and intracellular osmotic pressure. The cultivation of a handful of strains has led to the isolation of a number of extremozymes, which allow the cell to perform enzymatic reactions at these extreme conditions. These enzymes potentially contribute to biotechnological applications. In addition, microbial species active in the sulfur cycle can be used for sulfur remediation purposes. Future research should combine both innovative culture methods and state-of-the-art ‘meta-omic’ techniques to gain a comprehensive understanding of the microbes that flourish in these extreme environments and the processes they mediate. Coupling the biogeochemical C, N, and S cycles and identifying where each process takes place on a spatial and temporal scale could unravel the interspecies relationships and thereby reveal more about the ecosystem dynamics of these enigmatic extreme environments.     

Seasonal changes in the underwater light climate of two Canadian shield lakes

This study examines the seasonal variation in the underwater spectral distribution of light in a mesotrophic (Lake Cromwell) and an oligo-mesotrophic (Lake Croche) temperate lake. Gilvin is primarily responsible for the strong selective attenuation of blue light in both lakes. As a result of differing gilvin concentrations light transmission maxima of downwelling and upwelling spectra are near 615 nm in Lake Cromwell and 599 nm in Lake Croche. With increases in depth both upwelling and downwelling radiance fluxes decrease, are shifted to longer wavelengths and become more monochromatic. The greatest penetration of light occurs in the summer and spring after which a gradual decrease occurs through fall to a minimum value in winter. Under the winter cover the P ₅₀ of downwelling light shifts 10 to 20 nm towards shorter wavelengths. Seasonal changes in downwelling irradiance are related to solar altitude, concentration of suspended particles, phytoplankton populations, amount of gilvin, mixing and winter cover. The brownish colouration of these lakes is explained by reflectance of spectrally impure orangish-red light.     

The causes of change in the diversity and stability of phytoplankton communities in small lakes

SUMMARY. 1. A study of the diversity and stability of phytoplankton communities during one vegetation period (February-October 1984) was carried out in four small lakes in the Pfynwald region of Canton Valais, Switzerland: Kaminsee I, Kaminsee II, Grossee and Rosensee. The diversity was calculated according to Shannon & Weaver (1949). The change in diversity ΔH; and SIMI (similarity index according to Stander. 1970) were used as measures of stability. 2. On average, the diversity was highest in the oligotrophic Rosensee (annual mean 3.19) and least in the hypereutrophic Kaminsee I (annual mean 1.34). In Kaminsee I and Grossee, the diversity corresponded in the main to the relative frequency of Cryptomonas erosa Ehrenberg: i.e. the diversity was low when the relative frequency of C. erosa was high and vice versa (Kaminsee I: max. diversity 2.74; min. 0.13. Grossee: max. 3.62; min. 0.28; annual mean 2.21). Kaminsee II and Rosensee exhibited only slight variations in their phytoplankton community structure (Kaminsee II: max. diversity 2.83; min. 1.26; annual mean 2.10. Rosensee: max. 3.79; min. 2.81). High values of diversity, or increases in diversity, were a result of low nutrient availability and grazing pressure. Lower diversity values. or decreases in diversity, were a result of a plentiful nutrient supply, low grazing pressure and grazer selectivity with respect to food organisms. 3. Because values of the diversity index vary by different amounts during the course of a year depending on the water body, the characterization of a phytoplankton community on the basis of one value alone is unsatisfactory. It is suggested that the mean and either standard deviation or range of the diversity be cited in order to overcome this drawback at least partially. 4. No generally accepted measure exists for the calculation of stability. According to the measure of stability employed, a community may appear to be more or less stable. A statement concerning the stability of a community without mentioning the measure employed is therefore worthless. The factors determining the stability of a phytoplankton community do not have the same effect on all measures of stability. 5. The change in diversity ΔH’was influenced in the main by alterations     

Distribution, diversity, and activity of sulfate-reducing bacteria in the water column in Gek-Gel Lake, Azerbaijan

The distribution and activity of sulfate-reducing bacteria (SRB) in the water column of the alpine meromictic Gek-Gel lake were studied. Apart from traditional microbiological methods based on cultivation and on measuring the process rates with radioactive labels, in situ fluorescent hybridization (FISH) was used, which enables identification and quantification without cultivating organisms. The peak rate of sulfate reduction, 0.486 microg S/(l day), was found in the chemocline at 33 m. The peak SRB number of 2.5 x 106 cells/ml, as determined by the end-point dilutions method on selective media, was found at the same depth. The phylogenetic position of the SRB, as determined by FISH, revealed the predominance of the Desulfovibrio spp., Desulfobulbus spp., and Desulfoarculus spp./Desulfomonile spp. groups. The numbers of spore-forming Desulfotomaculum spp. increased with depth. The low measured rates of sulfate reduction accompanied with high SRB numbers and the predominance of the groups capable of reducing a wide range of substrates permit us to propose utilization of electron acceptors other than sulfate as the main activity of the SRB in the water column.     

Distribution, diversity, and activity of sulfate-reducing bacteria in the water column in Gek-Gel lake, Azerbaijan

The distribution and activity of sulfate-reducing bacteria (SRB) in the water column of the alpine meromictic Gek-Gel lake were studied. Apart from traditional microbiological methods based on cultivation and on measuring the process rates with radioactive labels, in situ fluorescent hybridization (FISH) was used, which enables identification and quantification without cultivating organisms. The peak rate of sulfate reduction, 0.486 μg S 1⁻¹ day⁻¹, was found in the chemocline at 33 m. The peak SRB number of 2.5×10⁶ cells/ml, as determined by the most probable number method on selective media, was found at the same depth. The phylogenetic affiliation of the SRB, as determined by FISH, revealed the predominance of the Desulfovibrio spp., Desulfobulbus spp., and Desulfoarculus spp./Desulfomonile spp. groups. The numbers of spore-forming Desulfotomaculum spp. increased with depth. The low measured rates of sulfate reduction accompanied by high SRB numbers and the predominance of the groups capable of reducing a wide range of substrates permit us to assume utilization of electron acceptors other than sulfate as the main activity of the SRB in the water column. Original Russian Text ? O.V. Karnachuk, N.V. Pimenov, S.K. Yusupov, Yu.A. Frank, Ya.A. Puhakka, M.V. Ivanov, 2006, published in Mikrobiologiya, 2006, Vol. 75, No. 1, pp. 101–109.     

Classification of central amazon lakes on the basis of their microbiological and physico-chemical characteristics

Twenty-four Central Amazonian Várzea and Ria lakes, lateral to the Rio Negro and the Rio Solimões, were studied for a year and are classified here in terms of physical, chemical and microbiological characteristics. White water (W), mixed water (M) and black water (B) lakes are ranked according to bacterial densities, electrical conductivity, pH, DO, POC, Fe, Si0₂ and PO₄ consumption in the following order W > M > B. The range of V_max decreased as net primary production increased. Further differentiation among the three lake types is made on the basis of dominant algal species and species diversity.     

Measuring the responses of macroinvertebrate communities to water pollution: a comparison of multivariate approaches, biotic and diversity indices

The responses of macroinvertebrate communities to pollution by sewage effluent in the River Trent system (UK) were investigated using a variety of multivariate approaches, biotic indices and diversity indices. It was found that multivariate analyses clearly illuminated the change of community structure along the pollution gradient. CY Dissimilarity Measure (CYD)-based Non-Metric Multidimensional Scaling (NMDS) appeared to perform better than DCA and clustering. Species richness, the BMWP, BMWP-ASPT, the Chandler Score, Chandler-ASPT could detect the effects of major pollution. However, these indices showed varying sensitivity to different ranges of pollution, for example, Chandler-ASPT and BMWP-ASPT are more sensitive to the change in clean/slightly polluted range than in the moderate/very polluted range. The diversity indices were the least informative. The advantages and disadvantages of the various approaches were discussed.     

Genetic diversity of cyanobacteria in four eutrophic lakes

Recent studies indicate genetic diversity of cyanobacteria in eutrophic lakes is not represented well by culture collections or morphology. Yet, few studies have investigated genetic richness and evenness of cyanobacteria using culture-independent methods. We compared the genetic structure of cyanobacteria supported by four neighboring eutrophic lakes during the ice-free season. The partial phycobilincpcB/A genes plus intergenic spacer (PC-IGS) was used as a genetic marker.Sequences were phylogeneticallygrouped by maximum likelihood into genotypes representing sub-genera of the major taxa. Genotypes fell into genera commonly observed by microscopy in these lakes including Microcystis, Aphanizomenon, Chroococcus, Anabaena, and Cylindrospermopsis. Only three genotypes were shared among all four lakes, despite significant water flowage between lakes.A Parsimony P-test indicated lakes were significantly (p=0.01) clustered on the maximum likelihood tree. Pairwise differences using Unifrac distance were moderately or not significant. Analysis of molecular variance (AMOVA) indicated genetic variation among all genotypes (φ=0.06, p<0.001) and 94% of variability occurred within lakes rather than between lakes (6%), explaining the lack of pairwise differences between lakes. Lorenze curves of genotype abundance in each lake showed genetic structure was only moderately uneven (Gini coefficients of 0.37-0.5) indicating lakes did not support dominant genotypes. Overall, results from this study suggest diversity of cyanobacteria is shaped by heterogeneity within lakes (temporally or spatially) and relatively even population structures.     

Comparative analysis of ammonia monooxygenase (amoA) genes in the water column and sediment-water interface of two lakes and the Baltic Sea

The functional gene amoA was used to compare the diversity of ammonia-oxidizing bacteria (AOB) in the water column and sediment-water interface of the two freshwater lakes Plusssee and Sch?hsee and the Baltic Sea. Nested amplifications were used to increase the sensitivity of amoA detection, and to amplify a 789-bp fragment from which clone libraries were prepared. The larger part of the sequences was only distantly related to any of the cultured AOB and is considered to represent new clusters of AOB within the Nitrosomonas/Nitrosospira group. Almost all sequences from the water column of the Baltic Sea and from 1-m depth of Sch?hsee were related to different Nitrosospira clusters 0 and 2, respectively. The majority of sequences from Plusssee and Sch?hsee were associated with sequences from Chesapeake Bay, from a previous study of Plusssee and from rice roots in Nitrosospira-like cluster A, which lacks sequences from Baltic Sea. Two groups of sequences from Baltic Sea sediment were related to clonal sequences from other brackish/marine habitats in the purely environmental Nitrosospira-like cluster B and the Nitrosomonas-like cluster. This confirms previous results from 16S rRNA gene libraries that indicated the existence of hitherto uncultivated AOB in lake and Baltic Sea samples, and showed a differential distribution of AOB along the water column and sediment of these environments.     

Modelling of underwater light in freshwater lakes using survival and failure time analysis

1. This study presents a new approach to modelling subsurface irradiance using concepts from survival and failure time analysis. The model applies a modified Weibull distribution function to predict downwelling irradiance. Data sets from forty-seven Norwegian sites show extremely high coefficients of determination, up to 99.99%, when analysed by the Weibull model.
2. The uncritical use of a single k _d value to model underwater light conditions is likely to result in poor estimates of received irradiance. This error may amount to several hundred per cent. The practice of force-fitting linear least-squares regressions to log-transformed irradiance data inevitably leads to highly biased estimates of the true fraction of incident irradiance entering the water.
3. Wave effects causing fluctuations of subsurface irradiance are modelled with synthetic data and compared with field observations. Fluctuations of surface elevation by waves produce skewed frequency distributions of the underwater light field. The result of these effects, which are to reduce the accuracy of estimated model parameters, can be largely eliminated by carefully designing field procedures used for the acquisition of subsurface light data.     

Modelling of underwater light in freshwater lakes using survival and failure time analysis

1. This study presents a new approach to modelling subsurface irradiance using concepts from survival and failure time analysis. The model applies a modified Weibull distribution function to predict downwelling irradiance. Data sets from forty-seven Norwegian sites show extremely high coefficients of determination, up to 99.99%, when analysed by the Weibull model.
2. The uncritical use of a single k _d value to model underwater light conditions is likely to result in poor estimates of received irradiance. This error may amount to several hundred per cent. The practice of force-fitting linear least-squares regressions to log-transformed irradiance data inevitably leads to highly biased estimates of the true fraction of incident irradiance entering the water.
3. Wave effects causing fluctuations of subsurface irradiance are modelled with synthetic data and compared with field observations. Fluctuations of surface elevation by waves produce skewed frequency distributions of the underwater light field. The result of these effects, which are to reduce the accuracy of estimated model parameters, can be largely eliminated by carefully designing field procedures used for the acquisition of subsurface light data.     

Comparison of the diversity of sulfate-reducing bacterial communities in the water column and the surface sediments of a Japanese meromictic lake

The diversity and abundance of sulfate-reducing bacteria (SRB) were investigated in Lake Suigetsu, a meromictic lake in Japan characterized by a permanent oxycline at a depth between 3 and 8 m separating the aerobic freshwater epilimnion from the anaerobic, saline, sulfidogenic hypolimnion. A quantitative competitive PCR targeting the gene coding for a portion of the α-subunit of dissimilatory sulfite reductase (dsrA) was used to assess the distribution of the SRB in the stratified water column and the surface sediments. The diversity of the SRB communities was assessed using a sequence analysis of the differing dsrA isomers. The dsrA gene copy numbers of SRB in the hypolimnic waters were from 9.6 × 10³ to 7.5 × 10⁵ copies ml⁻¹, whereas higher dsrA copy numbers of SRB were observed in surface sediments, ranging from 1.8–8.1 × 10⁷ copies ml⁻¹ as estimated by competitive PCR. Phylogenetic analysis of the dsrA sequences retrieved from the surface sediments shows most belong to a deeply branching lineage of diverse dsrA sequences not related to any cultured SRB group. In contrast, dsrA sequences found in the oxycline waters were related to sequences of members of the genera Desulfonema, Desulfosarcina, and Dusulfococcus and to sequences of the incomplete oxidizers from the Desulfobulbaceae family. Diversity and abundance of dsrA genes significantly differed between the samples from the oxycline waters and the surface sediments of Lake Suigetsu, indicating habitat-specific SRB communities may contribute to the biogeochemical cycling of carbon and sulfur.     

The effect of water movement on the distribution of Oligochaeta in lakes

The Oligochaeta are more exposed to disturbance under conditions of intense water movement than other invertebrates, particularly when the substrate is unstable. Furthermore, low mobility of bottom water, which can lead to excessive accumulation of organic matter in sediments, and to the formation of sapropel, can also be limiting to the distribution of oligochaetes. Organic contamination in conditions of low water dynamics can result in the absence of Oligochaeta through oxygen depletion. Dynamic water movement can stimulate the mass development of Oligochaeta in organically polluted areas.     

Damaging UV radiation and invertebrate predation: conflicting selective pressures for zooplankton vertical distribution in the water column of low DOC lakes

In nature most organisms have to manage conflicting demands of food gathering, predator avoidance, and finding a favorable abiotic environment (oxygen, temperature, etc.) in order to maximize their fitness. In the vertical water column of lakes with high solar ultraviolet radiation (UV) and invertebrate predators, zooplankton face two particularly strong and conflicting selective pressures. During daylight hours invertebrate predators often induce an upward vertical migration of zooplankton prey while potentially damaging UV forces a downward migration. We used 2.2 m long columns suspended vertically in a lake to conduct 2×2 factorial experiments to examine patterns of depth selection behavior by zooplankton in the presence and absence of both the invertebrate predator Chaoborus and UV. We hypothesized that Chaoborus and UV both affect the distribution of zooplankton and a combination of both factors would lead to a narrowing of depth distribution. We found that when Chaoborus were present zooplankton tended to be distributed at shallower depths in the columns, while in the presence of UV they exhibited a deeper distribution. Chaoborus themselves were always found near the bottom of the columns regardless of the UV treatment. Simultaneous exposure to predators and UV resulted in a peak of zooplankton (especially Daphnia catawba) distribution at intermediate depths. In a significant number of cases, depth range was narrowed in response to Chaoborus, UV, or both.