A seasonal and ecological study of the phytoplankton of Loch Lomond

The seasonal succession of phytoplankton in Loch Lomond has been studied both quantitatively and from observations on net plankton. From a qualitative investigation of net phytoplankton Loch Lomond may be described as diatom-desmid in nature although from the quantitative studies the general domination of the population by diatoms becomes clear. During the vernal phytoplankton increase diatoms contributed more than 90% of the population throughout the loch. The bulk of the phytoplankton production occurred in the southern region, where the standing crop was considerably greater throughout the year than in other regions of the loch.Patterns of seasonal succession are described for all species which make an important contribution to the productivity of the loch and the observed successions related to measured physical and chemical changes in the water. Explanations are put forward to account for the absence of a second (autumnal) pulse ofMelosira in Loch Lomond. The appearance ofAnabaena circinalis is a possible indication of the changing trophic status of the southern region of the loch.     

Zooplankton in Loch Lomond: perspectives,predation and powan

Published and unpublished accounts of the zooplankton community of Loch Lomond are reviewed. Loch Lomond's zooplankton community is unique amongst those of Scotland's other large lochs. Holopedium gibberum appeared in Loch Lomond in the years between the studies of Slack & Hamilton in the 1950s and zooplankton surveys in the late 1970s.The annual cycles of Eudiaptomus gracilis, Cyclops strenuus abyssorum and Mesocyclops leuckarti are described for the mid basin of Loch Lomond. E. gracilis overwinter mainly as adult with variable egg production during their lifespan of 5–8 months. The cyclopoid copepods have variable life history characteristics. C. str. abyssorum produce a single generation per year, overwinter by means of resting eggs and a small population of planktonic adults, while M. leuckarti is present in the plankton throughout the year, but in low numbers during winter.Zooplankton populations in Loch Lomond are predated by the diverse fish community which includes a facultative planktivore in the powan, Coregonus lavaretus. Powan feed heavily on zooplankton from late spring until late autumn. Powan display selectivity in the prey species taken, in the size distribution and morph types taken within prey species. Zooplankton species, morphs and forms in Loch Lomond tend to reflect this predation.Zoology Department, University of St. AndrewsZoology Department, University of St. Andrews     

Modern pollen from the catchment and surficial sediments of a Scottish sea loch (fjord)

Modern pollen was extracted both from moss polster samples collected from a range of sites across the land surface of the Loch Sunart catchment, north‐west Scotland and from a number of marine sediment‐water interface sites in the sea loch. Comparisons between the pollen results and the major vegetation types growing in the catchment area revealed that in general the moss polsters contained a localised picture of the vegetation whilst the sea loch sediments varied much less from sample to sample and better represented a regional picture of the vegetation. It was anticipated that the pollen in the sea loch samples would be in a much poorer state of preservation because of the many pathways through which it travels in order to become incorporated into the sediments of the loch. However, this proved not to be the case and the study demonstrates that marine sediments of the kind found in Loch Sunart have the potential to provide a new source of Holocene vegetation data which is as good as the freshwater lake sediments that have been preferentially sampled in the past.     

The ecology of Synchaeta kitina Rousselet in Loch Leven,Scotland

Synchaeta kitina Rousselet reached population densities of up to 5000 ind.l^–1 in Loch Leven, between January 1977 and December 1982. The species was found over the entire range of temperatures recorded (0.4–21.4 °C), but was most abundant at temperatures above 7 °C. Embryo development times, determined under laboratory conditions, ranged from 122 h at 2 °C to 12.5 h at 20 °C. There was a marked inverse relationship between populations of S. kitina and Daphnia hyalina var. lacustris in the loch. It seems unlikely that this was due to interference competition from Daphnia. S. kitina can be cultured on Rhodomonas minuta var. lacustris and there is some evidence that this rotifer also feeds on small flagellates in its natural environment.     

The physico-Chemical limnology of Loch Lomond

Loch Lomond, the largest freshwater lake in Britain, is physically divided into a number of distinct basins by geological structures. The northern part of the loch is long, narrow and deep whilst the southern area is broad and shallow with many islands scattered throughout it.The water chemistry of the loch is dictated by the geology of catchment and the quality of the rivers flowing into it. The two major rivers, the Falloch and the Endrick Water, are both of good quality with low nutrient content. Consequently, the loch is regarded as oligotrophic, though the southern area verges towards being mesotrophic.     

Changes in Rotifer Species Composition and Abundance along a Trophic Gradient in Loch Lomond,Scotland, UK

Loch Lomond is the second largest body of freshwater in Great Britain. It is a long, narrow lake (36.4 km long, 8.8 km wide). The northern basin is fjord-like and surrounded by a mountainous, base-poor, rocky catchment. In contrast, the southern basin is much broader and shallower with a mainly lowland, calcareous, agricultural catchment. This causes a trophic gradient along the length of the loch that runs from the oligotrophic northern basin to the more mesotrophic southern basin. Rotifer samples were collected at monthly intervals between May and October 2002 at three locations along the length of the loch. More than 12 species were found, the commonest of which were Keratella cochlearis (Gosse) and Trichocerca stylata (Gosse). Although the species composition of the rotifer community varied very little among the sites, rotifer abundance increased markedly from north to south, apparently reflecting the trophic gradient along the length of the loch. The results suggest that rotifer abundance may be a more sensitive indicator of trophic state, and changes in trophic state, than species composition.     

Vegetation and land use in the Loch Lomond catchment

The Loch Lomond catchment lies across the boundary between the Lowlands and Highlands of Scotland, and its vegetation and land-use are influenced by the environmental contrasts which occur on either side of the Highland Boundary Fault. In the northern part of the catchment area elevations exceed 800 metres, and thus there is an altitudinal zonation component to vegetation and land-use patterns.The role of man has been profound in modifying natural vegetation, and recent land-utilisation is reviewed. Changing human and environmental circumstances have a significant effect on vegetation and land-use, and these factors are evaluated. Though natural and semi-natural vegetation occupies only a small fraction of the catchment, its conservation importance is considerable. In terms of scenic and heritage resources, the whole area has international significance and the Loch Lomond catchment requires special protection and management.     

Has habitat heterogeneity promoted phenotypic and ecological sub‐structuring among a Coregonus lavaretus population in a large Scottish lake?

Differences in stable‐isotope values, morphology and ecology in whitefish Coregonus lavaretus were investigated between the three basins of Loch Lomond. The results are discussed with reference to a genetic investigation to elucidate any substructuring or spawning site fidelity. Foraging fidelity between basins of Loch Lomond was indicated by δ¹³C and δ¹⁵N values of C. lavaretus muscle tissue. There was, however, no evidence of the existence of sympatric morphs in the C. lavaretus population. A previous report of two C. lavaretus‘species’ in Loch Lomond probably reflects natural variation between individuals within a single mixed population.     

Impacts of acidification on brown trout Salmo trutta populations and the contribution of stocking to population recovery and genetic diversity

Anthropogenic acidification in SW-Scotland, from the early 19th Century onwards, led to the extinction of several loch (lake) brown trout (Salmo trutta) populations and substantial reductions in numbers in many others. Higher altitude populations with no stocking influence, which are isolated above natural and artificial barriers and subjected to the greatest effect of acidification, exhibited the least intrapopulation genetic diversity (34% of the allelic richness of the populations accessible to anadromous S. trutta). These, however, were characterised by the greatest interpopulation divergence (highest pairwise D_EST 0.61 and F_ST 0.53 in contemporary samples) based on 16 microsatellite loci and are among the most differentiated S. trutta populations in NW-Europe. Five lochs above impassable waterfalls, where S. trutta were thought to be extinct, are documented as having been stocked in the late 1980s or 1990s. All five lochs now support self-sustaining S. trutta populations; three as a direct result of restoration stocking and two adjoining lochs largely arising from a small remnant wild population in one, but with some stocking input. The genetically unique Loch Grannoch S. trutta, which has been shown to have a heritable increased tolerance to acid conditions, was successfully used as a donor stock to restore populations in two acidic lochs. Loch Fleet S. trutta, which were re-established from four separate donor sources in the late 1980s, showed differential contribution from these ancestors and a higher genetic diversity than all 17 natural loch populations examined in the area. Genetically distinct inlet and outlet spawning S. trutta populations were found in this loch. Three genetically distinct sympatric populations of S. trutta were identified in Loch Grannoch, most likely representing recruitment from the three main spawning rivers. A distinct genetic signature of Loch Leven S. trutta, the progenitor of many Scottish farm strains, facilitated detection of stocking with these strains. One artificially created loch was shown to have a population genetically very similar to Loch Leven S. trutta. In spite of recorded historical supplemental stocking with Loch Leven derived farm strains, much of the indigenous S. trutta genetic diversity in the area remains intact, aside from the effects of acidification induced bottlenecks. Overall genetic diversity and extant populations have been increased by allochthonous stocking.     

An assessment,using stable isotopes,of the importance of allochthonous organic carbon sources to the pelagic food web in Loch Ness

The natural abundance of stable isotopes (δ¹³C and δ¹³15N) was determined for components of the pelagic food web in Loch Ness, a deep oligotrophic lake in northern Scotland, and compared with values from the inflow rivers and the catchment vegetation. Phytoplankton δ¹³C was low compared to values reported from other lakes, possibly reflecting a high use of ¹³C-depleted carbon dioxide from respired organic matter before further isotopic fractionation during photosynthesis. Phytoplankton δ¹³C was appreciably lower than that of dissolved and particulate organic matter (DOM and POM) in the loch. The DOM and POM were evidently overwhelmingly of allochthonous origin and ultimately derived from terrestrial plant detritus. The distinctive δ¹³C values for phytoplankton and detritus in the loch allowed the use of food sources by grazing crustacean zooplankton to be assessed, and the contributions of phytoplankton carbon and detrital carbon to zooplankton total body carbon appeared to be about equal. Comparison of δ¹³C and δ¹⁵N values for zooplankton and fish allowed assessment of trophic structure in the loch. The very high dependence of the pelagic food web in Loch Ness on allochthonous organic matter inputs from the catchment may be exceptional in a large lake, but has important implications for our understanding of lake ecosystem processes as well as for lake management.     

Notes on the Scottish flora

Background: Abernethy Forest, an area of native Caledonian Scots pine forest, includes areas of open or sparsely forested peatland, largely ombrotrophic, but locally influenced by water from mineral ground.

Aims: To relate vegetation species-composition to the limit of ombrotrophy inferred from water chemistry.

Methods: Species composition was listed in 300 sample quadrats; chemical analyses of water samples were available from 200 of these. The vegetation data were classified using TWINSPAN. Relationships between vegetation and chemical results were analysed statistically using contingency tables.

Results: Eleven ‘vegetation types’ were recognised, five (189 samples) judged as primarily ombrotrophic-bog vegetation. The others showed evidence of flushing, or transition to forest. A previous analysis of major cations in the 200 water samples indicated that a limiting Ca/Mg ratio of 1.0 divided 61 samples showing telluric influence from 139 essentially ombrotrophic samples. Neither division was sharp. Contingency tables showed that the division based on vegetation types was strongly associated with the division of the water samples based on cation ratios.

Conclusions: Large areas of bog south and east of Loch Garten are unequivocally ombrotrophic; the main telluric-influenced sites occupy openings in the forest west of the loch. The limited ‘fen’ flora probably reflects the small size and isolation of the calcium-rich sites and the dominating influence of the ombrotrophic peats.     

Role of aquatic vegetation coverage on hypoxia and sunfish abundance in bays of a eutrophic reservoir

We studied the relation between aquatic vegetation coverage, summer dissolved oxygen and density of sunfishes (Lepomis spp.) in 10 shallow bays of a eutrophic reservoir. The bays ranged 5.2–15.7 ha in area, 0.6–1.3 m mean depth and 6–91% vegetation area coverage. Over the 10 bays mean dissolved oxygen concentration ranged 5.8–9.0 mg l^-1 in open water at least 20 m away from the vegetation, 0.8–8.1 mg l^-1 at the vegetation-water edge and 0.5–7.7 mg l^-1 in dense vegetation. Dissolved oxygen concentrations were inversely related to vegetation coverage. In open water, dissolved oxygen levels were consistently higher than 8 mg l^-1 when vegetation coverage was <20% of the bay and decreased to about 6 mg l^-1 at coverages near 80%. At the vegetation-water edge and within dense vegetation, dissolved oxygen levels dropped rapidly as vegetation coverage increased to 20% of the bay; when vegetation reached about 50% coverage, dissolved oxygen remained near 1.5 mg l^-1at the vegetation-water edge, but oxygen dropped below 1 mg l^-1in dense vegetation. Scarce vegetation harbored high Lepomis relative abundance (fish per m² of vegetation) whereas extensive vegetation harbored low relative abundance, both contributing little to absolute abundance (total fish in all vegetation); however, intermediate coverage offered a combination of mid-level fish relative abundance that together with mid-level plant coverage translated into high absolute fish abundance. We suggest this response is related to hypoxia, and where aquatic vegetation is extensive, the effect of vegetation on hypoxia and water quality in general may influence fish populations in a way similar to that often attributed to reduced foraging efficiency and increased competitive interactions.     

The ecology of lampreys (Petromyzonidae) in the Loch Lomond area

All three lamprey species occurring in western Europe are found in the Loch Lomond area: Sea Lamprey Petromyzon marinus L., River Lamprey Lampetra fluviatilis (L.) and Brook Lamprey Lampetra planeri (Bloch). There are major differences in ecology among the three species and in each some features seem to be unique to the Lomond populations. Available data on the ecology of the three species in the area are presented and existing threats reviewed. Future research and conservation requirements are outlined.     

The macrophytic vegetation of Loch Urigill and other lochs of the Ullapool area

Summary

From the 15 lochs examined at altitudes between 9 and 267 m in western Sutherland and Wester Ross, a few areas of tall fen (with Hippuris, Sparganium erectum, Osmunda etc.) survive to indicate its potential distribution. Predominant grazed fen comprises patches of short Juncus articulatus and Carex nigra. Reedswamp is scarce, being dominated by Eleocharis palustris, Carex lasiocarpa and Schoenoplectus lacustris and, rarely, by Phragmites and Sparganium erectum. Floating-leaved vegetation was only encountered twice. Submerged vegetation to water depths of at least 1 m consists in the main of sparse Lobelia-Littorella with Juncus bulbosus, typical of the prevailing stony shores in every loch. Extensive Isoetes lacustris meadows may occur beyond that, with Potamogeton praelongus or P. perfoliatus stands in waters of alkalinities over 0·45 m-equiv 1^-1, reaching depths of 3 m in Loch Urigill. Loch Urigill is unusual in having dominant Isoetes at a water alkalinity of 0·76 m-equiv 1^-1 along with abundant Anabaena species and some Potamogeton filiformis.     

A pollen diagram from Pitbladdo,Fife

Summary

Pollen analytical data are presented from a site near Cupar, Fife. The stratigraphy and pollen spectra are used to infer the changing patterns of vegetation in the area during the Lateglacial and Postglacial periods. In the Lateglacial Interstadial the local development of Betula-Juniperus scrub was followed by a period of open habitat during the colder Loch Lomond Stadial. The early Postglacial forest was dominated by Corylus and Betula, although Ulmus was also a major woodland component before the arrival of Alnus. Following some initial deforestation due to anthropogenic activity, subsequent woodland clearance was almost total and open habitat communities dominated.     

Productivity and water relations of burnt and long-unburnt semi-arid shrubland in Western Australia

This study provides a comparison between vegetation of relatively recent and long-unburnt shrubland in terms of structural and functional groups, annual net primary productivity and water relations. Adjacent areas of vegetation long-unburnt or burnt 5 years previously were compared within a remnant block of Acacia–Allocasuarina–Melaleuca arid shrubland at Kalannie, south west Western Australia. Species were classified according to growth and life form, fire response, phenology and rooting morphology and densities, mean plant above-ground dry weights and shoot:root dry mass ratios of each assessed. Species compositions, seedling densities and absence of recruitment in the long-unburnt area suggested marked dependence on fire in maintenance of biodiversity. Comparisons of above-ground standing dry biomass and annual net primary productivity of total (above-ground plus below-ground) dry matter showed the 4.09 kg m^–2 biomass of long-unburnt vegetation to be increasing at 0.52 kg m^–2 year^–1 versus 0.45 and 0.18 kg m^–2 year^–1 for vegetation of the burnt area. Water relations of soils indicated consistently wetter profiles in burnt than long-unburnt areas and no deep drainage during the year of study. Lower water stress of key species in burnt than long-unburnt areas were indicated by less negative pre-dawn water potentials and higher stomatal conductance during the year of study and more negative carbon-isotope composition (¹³C) in wood laid down over the past 5 years. Budgets for water use were estimated for both sites and compared with annual net primary productivities. Data suggested much greater transpiration loss per unit dry matter gain by the rapidly growing plants at the burnt site (437 ml H₂O g^–1 DM) than by the plants of the long-unburnt community (92 ml H₂O g^–1 DM). Results are discussed in relation to composition and functioning of other Western Australian ecosystems. It is clear that time since fire affects productivity and water-use of vegetation of semi-arid shrublands and is therefore an important consideration for management and protection of remnant vegetation.     

The Relationship Between Spatial Distribution and Diet of Arctic Charr, Salvelinus Alpinus, In Loch Ness, U.K.

The pelagic fish community of Loch Ness, U.K., is dominated by Arctic charr, Salvelinus alpinus. Previous studies have shown that the distribution of zooplankton along the south-west to north-east axis of this elongate loch is very dynamic and determined largely by prevailing winds, but Arctic charr are consistently more abundant in the southern half of the loch. In July 1993, the diet compositions of 161 Arctic charr from 53 to 330mm in length were determined and related to their spatial distribution and those of microcrustacean zooplankton and pelagic chironomid larvae and pupae. Diets were dominated by chironomid larvae, with chironomid pupae, Bythotrephes longimanus, Bosmina coregoni and Daphnia hyalina also frequently taken. Over the whole study period, B. longimanus were more important in the diet of fish from the northern half of the loch, while chironomid larvae were more important for fish from the southern half. As a result, per capita prey weight of fish from the south was greater than that of fish from the north. However, wind-induced changes in the distribution of zooplankton along the loch were accompanied by a change in the diet composition of Arctic charr from the south.     

Light limitation of phytoplankton development in an oligotrophic lake - Loch Ness, Scotland

• 1 The underwater light climate in Loch Ness is described in terms of mixing depth (Z_m) and depth of the euphoric zone (Z_eu). During periods of complete mixing, Z_m equates with the mean depth of the loch (132 m), but even during summer stratification the morphometry of the loch and the strong prevailing winds produce a deep thermocline and an epilimnetic mixed layer of about 30 m or greater. Hence, throughout the year the quotient Z_m/Z_eu is exceptionally high and the underwater light climate particularly unfavourable for phytoplankton production and growth.
• 2 Phytoplankton biomass expressed as chlorophyll a is very low in Loch Ness, with a late summer maximum of less than 1.5 mg chlorophyll a m^-3 in the upper 30 m of the water column. This low biomass and the resulting very low photosynthetic carbon fixation within the water column are evidence that a severe restraint is imposed on the rate at which phytoplankton can grow in the loch.
• 3 The chlorophyll a content per unit of phytoplankton biovolume and the maximum, light-saturated specific rate of photosynthesis are both parameters which might be influenced by the light climate under which the phytoplankton have grown. However, values obtained from Loch Ness for both chlorophyll a content (mean 0.0045 mg mm^-3) and maximum photosynthetic rate (1–4 mg C mg Chla^-1 h^-1) are within the range reported from other lakes.
• 4 Laboratory bioassays with the natural phytoplankton community from Loch Ness on two occasions in late summer when the light climate in the loch is at its most favourable, suggest that even then limitation of phytoplankton growth is finely balanced between light and phosphorus limitation. Hence, for most of the year, when the light climate is less favourable, phytoplankton growth will be light limited.
• 5 Quotients relating mean annual algal biomass as chlorophyll a (c. 0.5 mg Chla m^-3) and the probable annual specific areal loading of total phosphorus (0.4–1.7 g TP m^-2 yr^-1) suggest that the efficiency with which phytoplankton is produced in Loch Ness per unit of TP loading is extremely low when compared with values from other Scottish lochs for which such an index has been calculated. This apparent inefficiency can be attributed to suppression of photosynthetic productivity in the water column due to the unfavourable underwater light climate.
• 6 These several independent sources of evidence lead to the conclusion that phytoplankton development in Loch Ness is constrained by light rather than by nutrients. Loch Ness thus appears to provide an exception to the generally accepted paradigm that phytoplankton development in lakes of an oligotrophic character is constrained by nutrient availability.

     

Commercially cut reed as a new and sustainable habitat for the globally threatened Aquatic Warbler

The Aquatic Warbler (Acrocephalus paludicola) is a song bird breeding in fen mires and similarly structured other wetlands with a water depth of 1–10 cm. Widespread in central-European wetlands at the beginning of the 20th century, the species is now globally threatened. The westernmost and genetically distinct Pomeranian population is even on the verge of extinction. The major challenge in the conservation of remaining habitat is the cost-efficient removal of biomass. About 50% of the Pomeranian population survives in a valley fen near Rozwarowo in Northwest Poland, where between 1993 and 2007 a conspicuous change in breeding habitat has taken place from summer grazed sedge meadows to commercial winter cut reed beds. We compared vegetation structure, site conditions, and potential prey abundance with the distribution and abundance of Aquatic Warblers in Rozwarowo Marshes and studied temporal changes and the compatibility of conservation and reed cutting interests. Aquatic Warblers now occur almost exclusively in sparsely growing, low reed with abundant Thelypteris palustris, Carex elata, and Lysimachia vulgaris. This vegetation type provides more potential prey for Aquatic Warblers than the higher productive tall reed, whereas the patches of sedge vegetation have become too small following succession after abandonment. Currently, commercial reed cutting maintains suitable Aquatic Warbler breeding habitat. Considering the impending changes in the reed market, there is a need for flexible agri-environmental schemes (AES) to ensure that stripes are left uncut and to prevent eutrophication by high and long flooding of the site.