Oligotrophic Communities Research Articles

A hypothesis for the assessment of the importance of microbial food web linkages in nearshore and offshore habitats of the Laurentian Great Lakes

Our work in the Laurentian Great Lakes of North America indicates that significant fluxes of carbon and phosphorus can pass through the microbial food webs (MFW) of these lakes. Here we present a synthesis of our recent investigations conducted largely along a trophic axis from the heavily eutrophic coastal Sandusky Bay to offshore communities near the international boundary in the central basin of Lake Erie. We find that the significance of the MFW in transporting C and P to higher trophic levels differs along a trophic gradient. In relatively eutrophic nearshore communities, most C and P are fixed into phytoplankton, transport of materials is largely dependent on grazing by cladocerans, and transport through the MFW is relatively insignificant. In contrast, in relatively oligotrophic offshore communities bacterial biomass often exceeds phytoplankton biomass, the majority of P is fixed into bacteria, bacterivorous grazers (e.g. rotifers and protozoa) dominate, copepods are the dominant microcrustacean, and transport of C and P through the MFW represents a major pathway. We suggest that the management of large-lake ecosystems is largely based on relatively eutrophic “nearshore” views of the base of the food web and needs to be modified to include considerations of the MFW in the more oligotrophic offshore regions of these lakes.

Mire development across the fen–bog transition on the Teifi floodplain at Tregaron Bog, Ceredigion, Wales, and a comparison with 13 other raised bogs

Summary A literature comparison of 14 radiocarbon‐dated macrofossil records of raised peat bog initiation indicates that there is a relationship between the prevailing climate and the character of the first ombrotrophic vegetation communities at peatland sites in Britain and Ireland. All that is required for ombrotrophy is the separation of the mire growing surface from the influence of surface and subsurface waters. This could occur via vertical accumulation of the peat mass or a lowering of the water table. The establishment of bog species can be rapid once isolation occurs. Peatlands may become ombrotrophic in a variety of water table conditions and climatic regimes. There are at least two distinctive routes to ombrotrophy, via a ‘dry‐pioneer oligotrophic community’ or via a ‘wet‐pioneer oligotrophic community’. Tregaron South‐east Bog does not fit the pattern suggested by the literature comparison. The Fen–Bog Transition (FBT) occurred in a period of increased effective precipitation but the first ombrotrophic community was indicative of relatively dry, ‘hummocky’ bog and a deep or unstable water table. The transitional poor fen communities at Tregaron South‐east Bog were short‐lived. Sphagnum palustre mire lasted for 90 years compared to 300 years at Bolton Fell Moss in Cumbria, and the FBT was synchronous across much of the bog. The Tregaron peatland complex has a long history of water table fluctuations as shown by the stratigraphy of the marginal peats. Channel incision in the River Teifi could have contributed to the development of ‘dry hummock’ pioneer bog in the humid climatic conditions at 7300 cal. BP, by reducing the level of lagg streams.

Relationships between cluster root-bearing taxa and laterite across landscapes in southwest Western Australia: an approach using airborne radiometric and digital elevation models

As part of a general soil and regolith mapping exercise across cleared and remnant bush land, radiometric data for distribution of potassium (K), uranium (U) and thorium (Th) were examined alongside relief models and floristic and soil surveys in test catchments at Elashgin and Toolibin in the Western Australian wheat-belt. The Elashgin survey showed that highly weathered low K soils co-concentrated U and Th and were vegetated mainly by cluster root-bearing Proteaceae and Casuarinaceae. In granitic soils ratios of U to Th were higher and cluster root bearing taxa much less prominent, except where ferricrete gravels were concentrated. Draping of radiometric imagery over a digital elevation model showed spiral waveforms of high and low U and Th signal which were largely independent of topography but demarcated different oligotrophic communities. General observations and a detailed 900-m transect along an aeolian sand plume at Toolibin showed very high U and Th in ferricrete gravels where Proteaceae were dominant, but failed to separate proteaceous versus myrtaceous shrublands on deep sands due to truncation of signal. Augering along the transect and examination of floristic, soil and signal composition of 32 sites in the Lake Toolibin catchment confirmed presence and degree of development of ferricretes in the rhizosphere of Proteaceae-dominated communities and showed high reactivity scores for Al in `Bs' horizons in profiles carrying such vegetation. Highly specific associations between Proteaceae and very high U and Th were generally evident on exposed ferricrete gravels. The data are discussed in relation to the effects of root exudates on ferricrete formation and destruction and how the broader spatial pattern of such processes might relate to competition for soil phosphorous.

Response of the Banda Sea to the southeast monsoon

Three mechanisms are suggested to describe the physical response in the Banda Sea to the seasonal winds of the southeast monsoon: basin-wide wind-induced mixing, upwelling primarily on the eastern side, and a more complex basin circulation. We use the distribution of chl a in the Banda Sea, from both shipboard and satellite data, as an indicator of the dominant mechanism. An east-west transect of stations through the central Banda Sea in September 1998 shows higher phyto- plankton biomass to the east, suggesting a remnant upwelling signal from the southeast monsoon in the previous months. Phytoplankton pigment data indicate a community dominated by diatoms to the east, and a more oligotrophic community (e.g. cyanobacteria) to the west. Furthermore, satellite images reveal a strong seasonal signal, an east-west gradient in chl a, and coincidentally, the related impact of the 1997-1998 El Nino. Overall, the bio-optical data support the idea that the Banda Sea responds to the southeast monsoon through upwelling in the eastern part of the basin.

Retarded wetland succession: anthropogenic and climatic signals in a Holocene peat bog profile from north‐east Hungary

Summary 1 Pollen, plant macrofossil and humification data supplemented by chemical and physical analyses of a Holocene peat sequence from Nagymohos, Kelemer, north-east Hungary, have been used to study local wetland vegetation dynamics and upland vegetation development in the early and mid Holocene. An attempt was made to distinguish between autogenic successional processes and allogenic environmental forces. 2 Holocene sedimentation began c. 7500 cal. bc. The basin was occupied by a shallow open lake with substantial input of inorganic material until c. 6200 cal. bc, when floating reedswamp vegetation encroached on the lake surface. This turned to Carex fen within c. 100 years. Sphagnum transitional bog became established by c. 5300 cal. bc. 3 The local mire water table in the Sphagnum bog phases was elevated between c. 5700–6000 cal. bc, c. 5000–5250 cal. bc and c. 4500–4700 cal. bc. The most distinctive feature of the record is the coincidence of upland vegetation changes with reconstructed wet-shifts in mire hydrology. The upland pollen data imply selective exploitation of Ulmus and Corylus coupled with burning and soil erosion during the second and third wet periods. 4 Succession from shallow open lake to Sphagnum-bog is an autogenic process, although superimposed allogenic perturbation (human induced soil erosion and climate change) modified the expected progression from wetter to drier and from minerotrophic-water dependent to oligotrophic communities.

The importance of submerged macrophytes as indicators for the nutrient concentration in a small stream (Rotbach, Bavaria)

The relationship between the macrophyte vegetation and the nutrient concentration of the water and the sediment of a stream was studied. The small stream is fed by calcareous groundwater. The alteration in the macrophyte vegetation of the stream Rotbach from oligotrophic community towards more eutrophic species is associated with an increasing concentration of nutrients in the sediment. Particularly the concentration of SRP-P in the interstitial water changes significantly. In terms of the macrophyte vegetation the stream can be divided into 4 floristic zones, A-D. The zones are labelled in a sequence according to their sediment's nutrient content. The chemical analyses of the water and the sediment show the highest concentrations in zone D. It is characterized by the presence of Zannichellia palustris. The zones A-C have almost the same very low nutrient concentration in the water but show a different content of nutrients in the sediment, particularly of the SRP-P in the interstitial water. Zone A which is dominated by Chara hispida shows the lowest SRP-P in the interstitial water. Within zone B which is characterized by Mentha aquatica and Nasturtium officinale and even more in zone C where Chara hispida is less abundant and Elodea canadensis occurs, the SRP-P content is elevated. The nutrient concentration in the sediment is clearly associated with changes in the macrophyte vegetation of the stream Rotbach.

Tansley Review No. 114

A cyclic behaviour in the intensity of maritime conditions which varies with the periodic behaviour of the North Atlantic oscillation has recently become apparent in the climatic record of northern Europe. Periodic increases in oceanicity are usually viewed as having a positive effect on plant survival, as milder winters, reduction of temperature extremes, low risk of exposure to frost, and freedom from drought reduce many aspects of environmental stress. However, warmer winters in maritime environments may also have a powerful influence in creating habitats that are unfavourable for many species. The dangers of long periods of soil saturation for overwintering plants, soaking injury to germinating seeds, premature bud burst in spring, depression of treelines by increased cloud cover and high lapse rates, as well as the constant leaching of soils, are all negative aspects of the maritime environment. Woody species in which root dormancy is delayed by mild winters are particularly vulnerable to the consequences of winter flooding. Subsequent re‐exposure to oxygen as water tables fall in spring can aggravate flooding damage through post‐anoxic injury, leading to severe dieback of anchoring roots. Soil leaching, particularly after human disturbance, can induce nutrient deficiencies and the establishment of oligotrophic communities with reduced productivity. Podzolization and iron pan formation have in the past facilitated the processes of paludification in oceanic regions. The resulting spread of bogs and acid moorlands can further reduce the potential for productivity in both agriculture and natural plant communities. Given the probability that current climatic trends may increase the degree of oceanicity in western and northern regions of Europe, the potentially negative consequences of such a climatic change need to be considered in relation to future ecological changes and their consequences for conservation and land use. contents Summary 257 I. defining and quantifying oceanicity 257 II. ecological consequences of oceanicity 261 III. ecological history of oceanicity in western europe 263 IV. positive and negative influences of oceanicity 267 V. modifying effects of oceanicity on plant distribution 269 VI. physiological impact of warm winters 271 VII. treelines and oceanicity 276 VIII. conclusions 278 Acknowledgements 279

The Impact of a Road Upon Adjacent Heathland Vegetation: Effects on Plant Species Composition

1. The effect of a road upon heathland vegetation was investigated at five sites adjacent to the main trunk road through the New Forest, Hampshire, UK, with nine supplementary sites adjacent to five minor roads. 2. There was enhanced growth of vascular plants, notably heather and grass species near the road, which was probably due to oxides of nitrogen from vehicle exhausts. There was a decrease in the abundance and health of lichens near the road. 3. There was an increase in the abundance of grasses in the heathland near roads, which may be due to the changes in relative competitive ability of plant species under conditions of eutrophication. 4. The extent of the edge effect in the heath was closely correlated with the amount of traffic carried by the road, with a maximum edge effect of 200 m adjacent to a dual carriageway. This should be taken into account when considering the environmental impact of new roads. Road widening with its associated increase in traffic can also be expected to impact on existing oligotrophic communities beyond the actual land-take. Such schemes should include buffer zones to protect oligotrophic communities or other measures to minimize the pollution input from vehicle exhausts to environmentally sensitive areas.

Relationship between freshwater gastropods and plant communities reflecting various trophic levels

Plant communities were examined in ponds in Brittany (north-west France) and then classified into six types reflecting different trophic levels: oligotrophic, oligodystrophic, mesotrophic, meso-dystrophic, meso-eutrophic an eutrophic. In 45 of these ponds, aquatic snails were sampled in order to determine the relationship between the gastropod species richness and the water trophic levels as indicated by plant community types. The second aim of this study was to determine whether some gastropod species were characteristic of a particular trophic level. The number of plant communities in the ponds was also taken into consideration. A trophic gradient was found along the F1 axis on the principal plane of the correspondence analyses. The species richnesses low or zero and especially the lymneid, Lymnaea glabra were close to the oligo-dystrophic and oligotrophic communities. In contrast, the highest numbers of snail species (5 and above) were found in the most eutrophic ponds where Hippeutis complanatus, Planorbis planorbis, Lymnaea stagnalis and Planorbarius corneus were particularly common. The latter species inhabited the ponds including on average the greatest number of macrophyte communities but no significant differences were found between snail species. The ponds which contained the greatest numbers of plant communities included the richest gastropod communities (7 and more) but also the poorest ones (0 or 1 species). Relationships between freshwater snails, macrophytes and trophic levels are discussed.

Differences between oligotrophic communities resulting from old-field succession in relation to bedrock

Dehesa ecosystems on granite and on slate clearly differ in soil characteristics. Our aim was to find out whether floristic composition differed too. we selected an equal number of plots, on both granite and slate, in different successional stages of development and at various ages after field abandonment (the youngest 15–20 years). Plots with rock-outcrops, which had never been cultivated, were also included in the study. The results showed that floristic differences between granite and slate communities were not detectable in the younger successional stages. However, they showed up with time and on stabilized grasslands became significant. But on plots with rock-outcrops the differences were not observable. This was undoubtedly influenced by the peculiar features of these plots, characterised by poor arid soils and surface parent material. In fact they did not show significant differences in the analysed soil parameters either. Species diversity and biomass showed a similar pattern of differences to floristic composition. The highest species diversity was found on plots with lower biomass (the youngest ones). The lowest biomass in conjunction with quite low species diversity was found on plots with rock-outcrops, which again is consistent with their peculiar features.

Investigations of radiocaesium in the natural terrestrial environment in Norway following the Chernobyl accident.

Radioactive fallout from the Chernobyl accident affected parts of central Norway to a considerable extent, in particular the 134Cs+137Cs deposition had a significant impact on the natural environment. When this became apparent, a comprehensive radioecological research programme was initiated in order to study the behaviour of radiocaesium in boreal and alpine ecosystems, with emphasis on food-chains leading to exposure of species used for human consumption, i.e., reindeer and freshwater fish. In this paper results from the terrestrial part of this research programme during the period 1986-1990 are presented. The work was mainly confined to the mountain areas of Dovre and Rondane. Parallel studies were performed in eutrophic and strongly oligotrophic communities. The influence of local variations in topography and microclimate on the observed radiocaesium levels in topsoils, lichens and vascular plants was studied in detail. Currently a significant re-distribution of radiocaesium from the originally strongly exposed surfaces to those that were less exposed is observed. In the soil, radiocaesium is strongly retained in the litter and raw humus layers. Current levels in lichens are 1-2 orders of magnitude higher than in vascular plants. This strongly affects the seasonal variation of radiocaesium in reindeer, showing winter maxima of about 5 times higher than the August levels. The radiocaesium levels in reindeer showed a decline of approximately a factor of 3 during the period 1987-1990. Other animal species studied in the programme exhibited substantially lower radiocaesium levels than reindeer, but a considerable interspecies variation was observed.

Studies on the ingestion of radiocesium from contaminated pastures in reindeer

Grazing experiment with two oesophageally fistulated reindeer were conducted during June to August 1987 in the Jotunheimen mountain range (1000-1400 m). Grazing in 4 different plant communities was compared: Mesotrophic birch forest dominated by heather, Oligotrophic community with poor snow- cover dominated by heather and Dwarf birch, Oligotrophic community with moderate snowcover domi­ nated by lichens and sedges and a snowbed community dominated by Least willow and lichens. The radioactivity in food samples obtained from the fistula changed through the summer and differed be­ tween communities, from 8000 Bq/kg dry matter to 49000 Bq/kg dry matter. The major factor responsible for these changes was variations in the amounts of lichens ingested. Lichens beside mosses had the highest levels of radiocesium and consequently the amount of lichens consumed was the major single food item responsible for high intake of radioactivity.

La végétation des contreforts des Laurentides : une analyse des gradients écologiques et du niveau successionnel des communautés

The forest vegetation of the foothills of the Laurentians was studied to determine which ecological factors are most strongly correlated with vegetation variation. Vegetation and ecological factors were sampled within 78 plots distributed systematically on 19 transects. Ordination and classification analyses show that soil moisture and richness, two factors strongly associated to topographical variations, are the ecological factors that best explain vegetation distribution. Eleven community types were identified. Oligotrophic–xeric community types, characterized by Pinus strobus and Quercus rubra, are generally found in sites at high elevation, where soils are thin, well drained and nutrient poor. The Acer saccharum community types, of the mesotrophic–mesic group, are situated at the base of slopes with deep, rich soils. Fagus grandifolia, Acer rubrum, and Tsuga canadensis characterize a third group of oligotrophic–mesic community types, found on sites with relatively poorly drained and nutrient-poor soils, in topographic positions intermediate to the first two groups. A community type successionnal status index, based on the homogeneity and similarity of the tree and sapling strata, shows that natural and anthropogenic disturbances are also responsible for part of the vegetation variation. Hemlock and beech forests are the most successionnally advanced community types of the oligotrophic–mesic group. On richer soils fed by seepage, the maple–hickory community type is also relatively stable. These results contribute to the ongoing discussion about the eventual outcome of succession on mesic sites in northeastern North America.

The maintenance of structural integrity in freshwater protozoan communities under stress

The structural assimilative capacity (ability to maintain biological integrity under stress) of protozoan communities from nine lakes in the area of the University of Michigan Biological Station, Pellston, Michigan, and six stations at Smith Mountain Lake, Virginia, were studied (1) to determine if communities from lakes of differing trophic state differ in their ability to assimilate various amounts of copper sulfate, and (2) to explore the possible influence of average density of individuals and/or qualitative differences in the types of species present on any observed differences in assimilative capacity. In both the northern Michigan and Smith Mountain Lake studies, a trend in response was demonstrated along the eutrophic-oligotrophic gradient; eutrophic communities had a greater structural assimilative capacity than did oligotrophic communities. Both mean species density and community composition appear to be important factors in the ability to maintain structural integrity.

Edaphic Climax Pattern of the Pygmy Forest Region of California

The dwarfed conifer forests occurring on the coastal terraces of Mendocino County, California, are oligotrophic communities containing edaphic endemics as dominants. Species distributions and community characteristics are traced along a gradient in podzolization of the soils from these pygmy conifer stands on highly weathered terrace spodosols, to redwood stands on weakly developed slope spodsols. Vegetation stature, canopy closure, species richness, litter biomass and pH generally decrease along the gradient as podzolization and nutrient impoverishment increase, whereas soil organic matter and available water capacity tend to be highest at the gradient extremes. Analyses of pygmy forest soils show low levels of macro— and micro—nutrients, and high levels of exchangeable aluminum. When ordinations of stands based on vegetational data are compared with rankings based on environmental data, changes in pH of the soil A horizon are found to correlate most highly with vegetation changes. Nutrient loss and acidification, initiated by varying rates of soil weathering in the pygmy forest region, may be aggravated, in the case of pygmy forest soils, by a series of feedback effects, including solubilization of possibly toxic amounts of aluminum by low pH, which may contribute to the observed plant stunting and shrinking pools of nutrients in the biomass. A ranking of stands along a soil nutrient gradient, based on field observations and presence data for species, correlated successively less strongly with ordinations computed by similarity—projection, Bray—Curtis method, importance—projection, principal components analysis, and factor analysis. Although these ordinations were expected to produce distortions in the interstand relations due to the modal and even polymodal nature of species response curves and to the presence of species not spanning the range of the data set, additional distortions due to variability in sample data were also highlighted.

The Future of Salmonid Communities in the Laurentian Great Lakes

The effects of human population growth, industrialization, and the introduction of marine fishes have reduced the suitability of each of the Great Lakes for oligotrophic fish communities. The ultimate consequence has been a reduction of fishery productivity that has ranged from extreme in Lake Ontario to moderate in Lake Superior. If measures are not taken to alleviate the adverse effects of marine invaders and trends in environmental quality, a major reduction in fishery productivity can eventually be expected throughout the Great Lakes.Prospects for the next century will be improved if the lakes can be intensively managed. More stringent control of the sea lamprey (Petromyzon marinus), and subsequent reduction of the alewife (Alosa pseudoharengus), by the reestablishment of populations of large piscivores, should permit the recovery of some of the previous predator and prey species, or the development of populations of new species that are more compatible with a reduced number of lampreys. Even if marine species can be reduced greatly, the full restoration of the former fishery productivity remains uncertain and will require a high degree of coordination among all management and research agencies that have responsibilities on the Great Lakes.Unfavorable trends toward progressive degradation of water quality pose the greatest threat to restoration of the fishery resources of the Great Lakes. Where changes in water quality have been the greatest, oligotrophic species have become scarce or absent, and in the deepwater regions no other species have reoccupied the vacated niches.

Studies of the post-glacial history of British vegetation X. Correlation between climate, forest composition, prehistoric agriculture and peat stratigraphy in sub-Boreal and sub-Atlantic peats of the Somerset levels

It has already been shown that the site at Decoy Pool Wood gives very good evidence of two flooding episodes, each demonstrated by vegetation of a eutrophic character, and each succeeded by drier conditions in which oligotrophic communities recovered the bog surface (part VIII). The pollen samples taken at intervals of only 1 in. (2*5 cm.) apart, yield a remarkable amount of information about the correlations of the two swamping horizons which they cross, and the alterations of climate, prehistoric agriculture and forest composition. It has already been shown that the pollen of local origin from plants growing on the bog surface reflects in detail the modification of the plant communities.