Diatom distribution and diatom inferred pH in the sediment of four alpine lakes

The diatom distribution in the sediment of four alpine lakes in the central alpine area (Ötztaler Alpen, Tyrolia, and Mölltal, Carinthia) has been analysed in order to assess possible influences of atmospheric pollutants on remote lakes. The lakes are located more than 2000 m above sea level on poorly buffered bedrock (granite, gneiss and mica schist) and are therefore susceptible to acidification by acid deposition. The pH history of the lakes has been calculated by using Index B from Renberg & Hellberg (1982), which has been adjusted to central European conditions and applied in this region for the first time. The results indicate that there have been no pH decreases in three of the lakes, while in one lake diatom composition and distribution change significantly towards the sediment surface. But taxonomical problems and difficulties in the pH classification of the rarely found diatoms complicate the interpretation of the results. Important taxa will be discussed in view of their ecological significance.     

Limnological research on northern Apennine lakes (Italy) in relation to eutrophication and acidification risk

Substantial variability was found in the water chemistry of 22 northern Apennine lakes. In a group of lakes there is evidence of disturbance linked to eutrophication processes. Other lakes showed weak ion concentrations and alkalinity below the acidification risk threshold. However no acidified lakes were found. The lack of waterbodies with severely altered hydrochemistry may explain why no clear relationship between plankton community structure and water chemistry was observed.     

Correlation of surface sediment diatoms with the present lake water pH in 28 Algoma lakes,Ontario, Canada

The surface sediment diatom analysis of 28 Algoma lakes (pH 4.40–8.13) indicates that even though each lake has a widely different aquatic environment and characteristic diatom assemblage, a definite relationship exists between the lake water pH and their diatom assemblages. In the acidic lakes acidobiontic and acidophilous diatom species predominate whereas in circumneutral and alkaline lakes circumneutral and alkaliphilous diatoms were most common. Cluster analysis of the pH indicator diatom assemblages grouped the study lakes into three distinct cluster groups. These groups also closely corresponded to lake water pH. On the basis of published ecological information as well as their presence in our study lakes, the pH indicator status of a number of diatom taxa have been discussed. A detailed listing of the diatom taxa identified and their pH indicator status is provided in order to facilitate their use in future diatom-inferred pH studies.     

A comparison of impoundments and natural drainage lakes in the Northeast USA*

We classified 235 randomly selected lentic waterbodies (>1 ha) in the Northeast USA as human created, or natural. We compared geographic extent and distribution, morphology and hydrology, trophic state, and fish assemblage metrics of impoundments and natural drainage lakes. We estimated that 46% of the 10 608 (±1695; 95% CI) lentic waterbodies in the region were impoundments or quarries; 68% of Uplands lakes and 26% of Lowlands lakes were natural. Impoundments were smaller, shallower, had shorter water residence times, and were in watersheds with greater human activity than were natural drainage lakes. More than half (55%) of Lowlands impoundments were eutrophic, accounting for 67% of eutrophic or hypereutrophic lentic waterbodies in the Northeast. An estimated 90% of eutrophic lakes and impoundments were <23 ha. Impoundments had greater proportions of fish species and individuals tolerant of human disturbance, and greater proportions of non-native species and individuals than did natural drainage lakes. We discuss some management implications of the differences between impoundments and natural drainage lakes.     

Phytoplankton and its dynamics in two tropical lakes: a tropical and temperate zone comparison

Temporal patterns of phytoplankton biomass and community structure are described for two Kenyan lakes and subsequently compared with patterns reported in other tropical and temperate lakes. Lake Naivasha had a lower and more seasonally variable (10×) biomass, with a seasonal shift between diatoms and blue-greens, while the L. Oloidien biomass was less variable (3.7×) and dominated by blue-greens. Biomass and chlorophyll a were strongly correlated and in turn were coupled to the level of total phosphorus. A total of 143 and 94 taxa were described for L. Naivasha and L. Oloidien, respectively.The comparative analysis showed: a) a paucity of exclusively tropical species; b) that more than 30 percent of the species in two highly saline Kenyan lakes were also present in the two freshwater lakes; c) no evidence for a postulated decline of phytoplankton species abundance with latitude from the temperate zone to the tropics; d) that the low fraction of chrysophyte biomass in tropical lakes is a function of trophy rather than of latitude; e) that the fraction of chlorophyte biomass in tropical lakes is generally higher than in temperate lakes; f) that the proportion of nannoplankton in the two Kenyan freshwater lakes is not different from that in temperate lakes of the same trophy; g) that seasonal or annual biomass oscillations in the tropics are not systematically lower than in the temperate zone; h) evidence for large inter-year difference in the max.:min. biomass ratio in the only tropical lake (L. Naivasha) for which such data are available; i) that an average biomass ratio appears predictable for tropical lakes from the proportion of the sediment surface in contact with epilimnetic water. Overall, no evidence was found that the freshwater tropical phytoplankton composition or dynamics differ in any fundamental fashion from that observed in the temperate lakes during the summer.Contribution number 147 of the Limnology Research Centre, McGill University.     

Phytoplankton distribution along trophic gradients within and among reservoirs in Catalonia (Spain)

1. Longitudinal gradients in the epilimnetic waters of stratified reservoirs provide a useful database to study changing environmental conditions. The spatial distribution, assemblage structure and specific adaptations of phytoplankton assemblages can be analysed along these gradients over short time scales. 2. Four reservoirs with a similar typology, located along an altitudinal gradient in the same eco‐region, were sampled along their longitudinal axes. In total, 19 sampling stations provided a trophic spectrum, ranging from oligo‐mesotrophy to hypertrophy, which was quantified by calculating the trophic state index of each sampling station in the four reservoirs. 3. Several patterns in phytoplankton assemblage structure were detected. Total chlorophyll‐a (Chl‐a), biovolume, abundance and the relative biomass contribution of the main algal groups (chlorophytes, cyanobacteria, cryptophytes and diatoms) were highly correlated with their location along the trophic gradient. 4. We also adopted the functional classification of Reynolds et al. (2002) : this effectively summarized differences among phytoplankton assemblages under varying resource‐limiting combinations, especially nutrients and underwater light climate. 5. In terms of relationships with the trophic gradient, diatoms and cyanobacteria exhibited significant opposing trends in both their relative chlorophyll contribution to total Chl‐a and biovolume. Chlorophytes were more abundant at an intermediate position along the trophic spectrum. 6. The identified patterns are consistent with models of self‐organization of phytoplankton assemblages. In particular, light availability was a strong determinant of size and shape diversity, especially in hypertrophic conditions, where ‘R‐strategist’, needle shaped species, dominated the system. In contrast, under decreased availability of nutrients and higher light extinction coefficients (K_d), the system was co‐dominated by C‐ and S‐strategist species, having shapes with a higher surface/volume ratio.     

Correlations between type‐indicator fish species and lake productivity in German lowland lakes

Morphotypes for 67 lakes in the German lowlands were derived, based on maximum depth and mixis type. A threshold of 11 m maximum depth was identified to be the best level to discriminate shallow from deep lake morphotypes. The fish communities in these two morphotypes were significantly different. Indicator species analyses based on fish biomasses found vendace Coregonus albula in deep lakes and ruffe Gymnocephalus cernuus , bream Abramis brama , white bream Abramis bjoerkna , roach Rutilus rutilus , pikeperch Sander lucioperca and small perch Perca fluviatilis in shallow lakes to be the most representative species of their communities. Lake productivity was closely related to biomass and in part abundance of the type‐indicator species, with vendace declining with increasing chlorophyll a concentration in the deep lakes, whereas biomass of pikeperch, bream, white bream and ruffe increased and biomass of small perch decreased with increasing chlorophyll a . These results indicate that assessment of ecological integrity of lakes by their fish fauna is generally possible, if lakes are initially separated according to a depth‐related morphotype before the assessment, and if eutrophication is considered to be the main anthropogenic degradation.     

Determination of the trophic state by qualitative and quantitative phytoplankton analysis in two gravel pit lakes

The phytoplankton of two gravel pits with comparable nutrient concentrations but different chlorophyll-a concentrations and phytoplankton biovolume was investigated qualitatively and quantitatively over a period of two years. This study deals with the phytoplankton-rich ‘Rotter See’ and the phytoplankton-poor ‘Paulsmaar’, both South of Cologne. The trophic state of both lakes was determined comparatively according to Ryding &; Rast (1989) and the categories used by Brettum (1989). The results were compared with each other. The trophic lake index according to Hörnström (1981) was modified slightly and subsequently determined for both lakes. A combination of qualitative and quantitative phytoplankton analysis made a proposal of a rehabilitation for the Rotter See possible.     

Reconstruction of pH by chrysophycean scales in some lakes of the Southern Alps

Chrysophycean scales were examined in surface sediments collected from 22 high mountain lakes on the southern slope of the Central Alps, some in Italy and some in Switzerland. The study area receives slightly acidic precipitation and summer lake pH ranges between 5.2 and 8.0. In each lake chrysophycean scale assemblage was dominated by one or two species and its composition was related to lakewater pH. Five short cores were examined in low-alkalinity lakes and evidence of recent lake acidification was found.     

Factors related to gizzard shad and the threadfin shad occurrence and abundance in Florida lakes

Gizzard shad Dorosoma cepedianum were collected in 23 and threadfin shad D. petenense were collected in 22 of the 60 Florida lakes sampled. Logistic regression equations were 94% effective for predicting gizzard shad occurrence from chlorophyll and lake surface area, and 84% effective for predicting threadfin shad occurrence from lake surface area and lake volume inhabited (PVI). Occurrence of both shad species was related positively to lake size. In lakes where gizzard shad or threadfin shad were collected, shad density and biomass of both shad species were related positively to chlorophyll. Gizzard shad populations were generally vulnerable to predation in lakes, with the per cent of gizzard shad ≤200mm L _T values exceeding 60% with few exceptions. Effects of gizzard shad and threadfin shad on fish community dynamics may be confined to relatively large (>100 ha) and fertile (chlorophyll >20–30μg l⁻¹) Florida lakes.     

Driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status

1. We studied driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status, the oligotrophic deep Lake Fuxian and the eutrophic shallow Lake Xingyun. 2. Phytoplankton samples were taken monthly for a year and phytoplankton species were sorted into the main taxonomic groups and associations proposed by Reynolds. A canonical correspondence analysis (CCA) was used to test the occurrence of these classification schemes and to determine their discriminatory power. 3. The results suggest that the major driving forces in Lake Fuxian were physical variables, and particularly the underwater light climate, whereas, nutrients were the important driving force in Lake Xingyun. 4. Top–down control through zooplankton grazing in Lake Fuxian was hardly ever a significant determinant itself, because of the scarcity of zooplankton and their low grazing efficiency of predation while a dominance of inedible cyanobacteria throughout the year rendered top–down controls ineffective failing in Lake Xingyun. Hence phytoplankton communities in both lakes appear to be regulated primarily by bottom–up controls.     

Algal flora of lakes in the High Tatra Mountains (Slovakia)

Eighty seven from a total of 120 lakes in the Slovak part of the High Tatra Mts. have been visited since 1982. Their summer phytoplankton and algae growing on stones were collected, identified and documented. Some species that are interesting, rare, or not previously known in Slovakia have been found: Clastidium setigerum, Colacium calvum, Chroococcus subnudus, Chr. quaternarius, Coelastrum printzii, Coenocystis quadriguloides, Oocystis naegelii, Scopulonema polonicum, Thelesphaera alpina, Trochiscia prescottii. The number of algal species, found in the open water of the lakes, decrease with altitude and increase with pH.     

Assessing anthropogenic impact on boreal lakes with historical fish species distribution data and hydrogeochemical modeling

Quantifying the effects of human activity on the natural environment is dependent on credible estimates of reference conditions to define the state of the environment before the onset of adverse human impacts. In Europe, emission controls that aimed at restoring ecological status were based on hindcasts from process‐based models or paleolimnological reconstructions. For instance, 1860 is used in Europe as the target for restoration from acidification concerning biological and chemical parameters. A more practical problem is that the historical states of ecosystems and their function cannot be observed directly. Therefore, we (i) compare estimates of acidification based on long‐term observations of roach (Rutilus rutilus) populations with hindcast pH from the hydrogeochemical model MAGIC; (ii) discuss policy implications and possible scope for use of long‐term archival data for assessing human impacts on the natural environment and (iii) present a novel conceptual model for interpreting the importance of physico‐chemical and ecological deviations from reference conditions. Of the 85 lakes studied, 78 were coherently classified by both methods. In 1980, 28 lakes were classified as acidified with the MAGIC model, however, roach was present in 14 of these. In 2010, MAGIC predicted chemical recovery in 50% of the lakes, however roach only recolonized in five lakes after 1990, showing a lag between chemical and biological recovery. Our study is the first study of its kind to use long‐term archival biological data in concert with hydrogeochemical modeling for regional assessments of anthropogenic acidification. Based on our results, we show how the conceptual model can be used to understand and prioritize management of physico‐chemical and ecological effects of anthropogenic stressors on surface water quality.     

Ants as ecological indicators of rainforest restoration: Community convergence and the development of an Ant Forest Indicator Index in the Australian wet tropics

Ecosystem restoration can help reverse biodiversity loss, but whether faunal communities of forests undergoing restoration converge with those of primary forest over time remains contentious. There is a need to develop faunal indicators of restoration success that more comprehensively reflect changes in biodiversity and ecosystem function. Ants are an ecologically dominant faunal group and are widely advocated as ecological indicators. We examine ant species and functional group responses on a chronosequence of rainforest restoration in northern Australia, and develop a novel method for selecting and using indicator species. Four sampling techniques were used to survey ants at 48 sites, from grassland, through various ages (1–24 years) of restoration plantings, to mature forest. From principal components analysis of seven vegetation metrics, we derived a Forest Development Index (FDI) of vegetation change along the chronosequence. A novel Ant Forest Indicator Index (AFII), based on the occurrences of ten key indicator species associated with either grassland or mature forest, was used to assess ant community change with forest restoration. Grasslands and mature forests supported compositionally distinct ant communities at both species and functional levels. The AFII was strongly correlated with forest development (FDI). At forest restoration sites older than 5–10 years that had a relatively closed canopy, ant communities converged on those of mature rainforest, indicating a promising restoration trajectory for fauna as well as plants. Our findings reinforce the utility of ants as ecological indicators and emphasize the importance of restoration methods that achieve rapid closed‐canopy conditions. The novel AFII assessed restoration status from diverse and patchily distributed species, closely tracking ant community succession using comprehensive species‐level data. It has wide applicability for assessing forest restoration in a way that is relatively independent of sampling methodology and intensity, and without a need for new comparative data from reference sites.     

Predation by introduced fish constrains the thermal distribution of aquatic Coleoptera in mountain lakes

1. Most high mountain lakes were free of fish until humans stocked them. This provides the opportunity to study the extent to which predation constrains the thermal distribution of large macroinvertebrates, among lakes of a suitable temperature for them. 2. We analysed the distribution of aquatic beetles (Coleoptera, Dytisicidae, including the genera Agabus, Platambus, Hydroporus and Boreonectes) in a set of 82 lakes in the Pyrenees. Temperature was the most important variable explaining the overall distribution of dytiscids (out of 29 environmental variables considered). The presence of fish (i.e. salmonids) and macrophyte cover (plants provide refuge from predators) was also important. Indeed, either salmonids or macrophytes as single factors explained more of the variance in dytiscid distribution than temperature. 3. Further analysis showed that the presence of salmonids was particularly important for the medium‐sized dytiscid Agabus bipustulatus. This species is generally eurythermic, although in the Pyrenees it is found mainly in cold lakes. This is attributed to predation pressure from fish, since the latter are more likely to be present in warm lakes. As a consequence, salmonids increase fragmentation of A. bipustulatus with respect to populations occupying lowland habitats. 4. Predation can therefore constrain the distribution of species to a fraction of habitats that appear suitable based on simple thermal responses. As humans also facilitate the dispersal of non‐native fish, the consequent modification of distribution patterns in fresh waters could make it difficult to predict how distributions might change in relation to climate warming.     

The content of chlorophyll in the sediment of the volcanic maar lakes in the Eifel region (Germany) as an indicator for eutrophication

The content of chlorophyll a and its degradation products has been measured in cores of nine volcanic lakes in the Eifel region. The primary production increased at the beginning of Post Glacial Period but degreased after Atlantic Period. During the last three decades the production of biomass increased again due to anthropogenic eutrophication.     

A study of species richness and diversity in seed banks and its use for the environmental mitigation of a proposed holiday village development in a coniferized woodland in south east England

A survey was carried out to determine the density and species composition of germinable seed in the surface soil layers of 30 plots within a coniferized lowland woodland in East Kent in order to establish the resources available for habitat creation in the event of some areas being modified during a proposed holiday village development. The selected plots included conifer plantations (up to 69 years old), broad-leaved plantations and the semi-natural broad-leaved edges that remain on parts of the perimeter of the site which were used as the control. A total of 13 682 seedlings emerged from the soil samples during the four-month germination trials. Fifty-two species were identified of which eight were ancient woodland indicator species for south-east England. The most abundant species represented in the seed banks were: Juncus effusus, Rubus fruticosus, Carex sylvatica, Betula pendula and Agrostis tenuis. Between-site comparisons of coniferous plots of different ages revealed a marked reduction in the seed species and seed density in plantations over 65 years old. Results of soil nutrient and texture analyses ruled out the likelihood of edaphic factors being responsible for between-site differences in seed bank composition. Seed species richness and diversity (Shannon-Wiener diversity index) were greatest in the semi-natural broad-leaved edges, but the diversity index used also showed that two replanted conifer sites had high values despite few species being present. The usefulness and limitations of diversity indices in the context of seed bank studies is discussed. From the results of the study, management proposals for the site have been put forward in order to maintain floristic diversity and mitigate the impact of the proposed development.     

Factors influencing the distribution of chironomids and oligochaetes in profundal areas of Spanish reservoirs

A canonical correlation analysis was performed in order to explain the distribution and abundance of the profundal macrozoobenthos in 71 Spanish reservoirs. Two sets of variables were considered: one set consisted of subgroups of benthic organisms based on their feeding strategy, and the other consisted of environmental variables related to the trophic state of the reservoir.The results showed that densities of phytophagous chironomids decreased with water depth and increased with oxygen content in the bottom waters, while Tanypodinae densities increased with rising densities of phytophagous chironomids and/or oligochaetes, revealing their strong dependence on the abundance of available prey. The abundance of oligochaetes and phytophagous chironomids showed a disjunct distribution with season and depth, suggesting the importance of food quality and sediment texture.Oxygen availability and water depth acted as governing factors for the zoobenthos. Chlorophyll-a was of secondary importance and correlated inversely with the abundance of benthic fauna, especially in summer. Autogenic production coupled with inputs of allochthonous coarse particulate organic matter and a long stratification period lead to long lasting anoxia that reduces the benthic fauna in Spanish reservoirs.Only up to 18% of the variability in the biological data could be associated with the environmental factors considered. Thus, factors other than the trophic state are much more important in reservoirs. Fluctuations of the water level and inputs of organic and inorganic materials coming from the basin are greater than in lakes and act as stressing factors for the benthic fauna.     

Gastropod diversity,distribution and abundance in habitats with and without anthropogenic disturbances in Lake Victoria,Kenya

We investigated freshwater gastropod diversity, abundance and distribution in habitats with and without anthropogenic disturbance in two localities, Ndere in the Winam Gulf and Mbita Point, Lake Victoria, Kenya, from May 2002 to January 2004. A total of 133 984 gastropod specimens belonging to 15 species were recorded, 14 from Mbita and 12 from Ndere. Two species, Ferrissia kavirondica and Cleopatra cridlandi, which were recorded only from undisturbed habitats, could be indicators of least disturbed habitats. Water chemistry did differ between fish landing sites and undisturbed habitats at some sampling times, indicating that differences due to human impact do exist, but these are dependent on periods of calm weather. The study shows that anthropogenic disturbances cause ecological changes that can be exploited by some snail species, especially Biomphalaria choanomphala and Melanoides tuberculata, while other species may not tolerate these changes. In order to protect gastropod diversity and avoid dominance of intermediate hosts, such as B. choanomphala, a management plan for the use of these fish landing sites should be developed. This could include rules on how to dispose of fish remnants and other wastes so as to reduce local eutrophication, thereby reducing risks associated with transmission of potential snail-borne diseases.