Distribution of aquatic Oligochaeta in the Finnish Lake District

SUMMARY. The distribution of oligochaetes was examined at sampling stations grouped into three types: (1), in eutrophic and dystrophic areas or in areas polluted by pulp-mill wastewaters; (2), slightly eutrophic stations; (3), 'clean' stations unaffected by sewage or other inputs. Limnodrilus hoffmeisteri and Potamothrix hammoniensis were practically the only species in group 1, and the same species accounted for two thirds of the total numbers in group 2, although Peloscolex ferox and some other species also occurred. At the cleanest stations the dominating species were P. ferox, Psammoryctides barbatus, Stylodrilus heringianus and Tubifex tubifex . A factor analysis showed that L. hoffmeisteri and P. hammoniensis were associated with increased nutrients and water colour in the lower part of the epilimnion. In the metalimnion the relationship of S. heringianus and P. ferox to water colour and total nitrogen differed from that of L. hoffmeisteri and P. hammoniensis . Winter oxygen content was important for S. heringianus .     

Invasion Gateways and Corridors in the Carpathian Basin: Biological Invasions in Hungary

Biological invasions in Hungary are causing severe problems as a result of recent introductions and rapid land use changes. Poorly managed agricultural and rural, disturbed areas, and aquatic ecosystems are the most prone to plant invasions. Dry grasslands and semi-natural forests are less prone to invasions. A few plant species have led to human health (allergenic) problems. Some insect species have caused economic problems to crop production. A number of monitoring networks and control measures are in place for selected plants and insects. This revised version was published online in July 2006 with corrections to the Cover Date.     

Allee Effect and Control of Lake System Invasion

We consider the model of invasion prevention in a system of lakes that are connected via traffic of recreational boats. It is shown that in presence of an Allee effect, the general optimal control problem can be reduced to a significantly simpler stationary optimization problem of optimal invasion stopping. We consider possible values of model parameters for zebra mussels. The general N-lake control problem has to be solved numerically, and we show a number of typical features of solutions: distribution of control efforts in space and optimal stopping configurations related with the clusters in lake connection structure.     

Studies on mountain streams in the English Lake District

Sodium and potassium in streamwater were measured over a period of 2 years, and concentrations of other major ions were occasionally monitored. The supply of sodium, potassium and calcium in rainfall was measured over a period of 1 year. A tentative budget is given for annual income and output of sodium, potassium and calcium in the Duddon catchment. Sodium and potassium concentrations in streamwater were independent of stream discharge; both ions displayed an annual cycle of high concentrations in winter and low concentrations in summer. The input of sodium was dependent on rainfall, wind direction and wind speed; 40% of the annual supply in rain was precipitated in the autumn. Sodium income in rainfall during the remaining 9 months of the year was insufficient to balance the output in streamwater. Annual income of potassium in rainfall was equal to annual output in streamwater. But potassium was retained on the catchment during spring and summer and was slowly released to the streams in autumn and winter. Only about 10% of the annual calcium output was derived from atmospheric sources.     

Lake Characteristics,Population Properties and Invasion History Determine Impact of Invasive Bivalves on Lake Nutrient Dynamics

Ecosystems - Invasive species can have large impacts on ecosystems, including the cycling and distribution of nutrients. To determine the whole-ecosystem effects of invasive zebra mussels on lake...     

Invasion dynamics of the snail Pseudoplotia scabra in Lake Kinneret

The freshwater snail Pseudoplotia scabra Müller (Thiaridae) was first spotted in Lake Kinneret, Israel, in the mid 2000s. In a series of field surveys we followed its spread, documenting how by the end of 2010 this invasive mollusc formed >95 % of the snails in Lake Kinneret, nearly eradicating four native species.     

Paleolimnology of the Peten Lake District,Guatemala

Long-term changes of sedimentary particle-size distribution in two tropical lowland lakes were compared with changes of human population sizes, estimated archaeologically, in the drainage basins. Mean particle size of silt and clay fractions (<64 µm) varied between 3 and 15 µm. High positive skewness and kurtosis of the distributions were associated with smaller particle sizes; hence small mean size resulted from greater influx of small particles while influx of larger particles was probably constant. An inverse correlation between mean particle size and human population size is interpreted to mean that disturbance-induced erosion results in delivery of very fine inorganic particles at higher rates. Within any one basin, particle-size stratigraphy is more precisely related to archaeological time periods than is pollen stratigraphy. An absolute chronology still eludes us, owing to the failure of ¹⁴C dating of calcareous, colluvial sediments, but our relative chronology is now more precise than before. If certain assumptions about past hydrologic relations can be met, particle-size analysis is a way of comparing the histories of geographically very different lakes, including lakes from tropical, temperate, and arctic regions.     

Observations and experiments on the phytoplankton of Blelham Tarn, English Lake District

Tubes composed of butyl rubber have been placed in a small English lake in an area where the water is 11-12 m deep. Each tube, when fully distended, contains over 18 000 m³ of water. The tubes are anchored to the shore and lake bottom. A boat can be rowed into them over a specially strengthened portion ofthe margin. The first was installed and its water isolated from that in the lake by the end of July 1970 and the second tube at the beginning of October 1970. The installation, maintenance, and performance of the tubes are described; as are suggested improvements. The temperature regime in the tubes closely follows that in the lake. If the chemical conditions are favourable, the seasonal cycle of Melosira in a tube is similar to that n i the lake. Contamination of the water in the tubes by that in the lake is slight and has a negligible effect on chemical conditions within them. Water can be lost from the tubes under certain conditions. The reverse does not happen. The phytoplankton communities in the tubes are similar in quality to those ofthe lake, even after 2-5 years of separation. The evidence suggests that the tubes are suitable for investigations on certain factors determining the abundance and seasonal cycles of algae in lakes and for other limnological studies.     

Geography of Invasion in Mountain Streams: Consequences of Headwater Lake Fish Introductions

The introduction of fish into high-elevation lakes can provide a geographic and demographic boost to their invasion of stream networks, thereby further endangering the native stream fauna. Increasingly, remaining populations of native salmonids are concentrated in fragmented headwater refugia that are protected by physical or biological barriers from introduced fishes that originate in the pervasive source populations established at lower elevations. Although fish introduced near mainstem rivers frequently encounter obstacles to upstream dispersal, such as steep slopes or falls, we found that brook trout (Salvelinus fontinalis) dispersed downstream through channel slopes of 80% and 18-m-high falls. Thus, headwater lake stocking provides source populations that may be capable of invading most downstream habitats, including headwater refugia of native fishes. The extent of additional area invasible from lakes, beyond that invasible from downstream, depends on the geography of the stream network, particularly the density and distribution of headwater lakes and their location relative to barriers inhibiting upstream dispersal. In the thermal and trophic environments downstream of lakes, fish commonly grow faster and thus mature earlier and have higher fecundity-at-age than their counterparts in other high-elevation streams. The resulting higher rates of population growth facilitate invasion. Larger body sizes also potentially aid the fish in overcoming barriers to invasion. Trout introductions to high-elevation headwater lakes thus pose disproportionately large risks to native fishes—even when the place of introduction may appear to be spatially dissociated from populations of the native species. Mapping the potential invasible area can help to establish priorities in stocking and eradication efforts. Received 28 March 2000; accepted 9 February 2001.     

The effects of electrofishing on the invertebrates of a Lake District stream

Summary The experiments were performed in Dale Park Beck, a stony stream in the English Lake District. Two operators electrofished the sampling area (length 20 m in April and July 1970, and 40 m in May 1971) three times (runs 1, 2, 3) in each experiment.Electrofishing caused a marked increase in the number of invertebrates drifting out of the sampling area, and nearly all taxa taken in the bottom samples were also found in the drift samples. The fish shocker was chiefly responsible for the increased drifting of Plecoptera, Ephemeroptera and Gammarus pulex, and these taxa were dislodged from the substratum more easily than Trichoptera, Coleoptera, Diptera and Polycelis felina. The increased drifting of the latter taxa was chiefly due to the disturbance of the substratum by the two operators.Most of the invertebrates drifting from the upstream end of the experimental section returned to the bottom within the sampling area. The invertebrate drift out of the sampling area came chiefly from the downstream end of the section, and was equivalent to a loss of only 5% from the total benthos in the sampling area (losses varied between <1 and 13% for individual taxa).     

Invasion of ancient Lake Titicaca by the globally invasive Physa acuta (Gastropoda: Pulmonata: Hygrophila)

A vital population of Physa acuta, a globally invasive species of freshwater gastropods was dicovered in ancient Lake Titicaca in April 2007. The population was found near Chucuito (Bahia de Puno) on the Peruvian side in close proximity to a boat landing of the aquaculture facility of the University of Puno. Physids occured in great abundances at this site on macrophytes in depths from 0 to 2 m. Physa acuta was associated with members of the Heleobia andicola species complex as well as with Heleobia otorni, Biomphalaria andecola, and Uncancylus crequi. Species identity was confirmed by morphological and molecular methods. We discuss the mode of introduction and raise a cautionary note on the potential impact of this global invader on the endemic gastropod fauna of ancient Lake Titicaca.     

The lichens of high ground in the English Lake District

Abstract: A general account of the lichens of high-level acid habitats in the Lake District is provided. This is followed by detailed studies of base-rich sites in the Helvellyn range, acid outcrops in Langdale, and three upland tarns, one of which is of outstanding importance. The lichen vegetation is richer than in Snowdonia or the Northern Pennines, but its diversity is considerably less than that of certain individual mountains in the Scottish Highlands. The montane element is interpreted as representing the last remnants of communities that have declined gradually through the Postglacial Period. Many species are extremely rare. Current restraints on the alpine lichen flora include the climate, the predominance of wet, acid rock and heavy sheep grazing. Rhizocarpon simillimum is reported as new to the British lichen flora.