Maximum growing depth of macrophytes in Loch Leven,Scotland, United Kingdom,in relation to historical changes in estimated phosphorus loading

Eutrophication is common in shallow lakes in lowland areas. In their natural state, most shallow lakes would have clear water and a thriving aquatic plant community. However, eutrophication often causes turbid water, high algal productivity, and low species diversity and abundance of submerged macrophytes. A key indicator of the ecological state of lake ecosystems is the maximum growing depth (MGD) of aquatic plants. However, few studies have yet quantified the relationship between changes in external phosphorus (P) input to a lake and associated variation in MGD. This study examines the relationship between these variables in Loch Leven, a shallow, eutrophic loch in Scotland, UK. A baseline MGD value from 1905 and a series of more recent MGD values collected between 1972 and 2006 are compared with estimated P loads over a period of eutrophication and recovery. The results suggest a close relationship between changes in MGD of macrophytes and changes in the external P load to the loch. Variation in MGD reflected the ‘light history’ that submerged macrophytes had been exposed to over the 5-year period prior to sampling, rather than responding to short term, within year, variations in water clarity. This suggests that changes in macrophyte MGD may be a good indicator of overall, long term, changes in water quality that occur during the eutrophication and restoration of shallow lakes.     

Short-term changes in-stream macroinvertebrate communities following a severe fire in the Lake Tahoe basin,California

Rivers, lakes and wetlands are good examples of ecosystems that provide multiple, concurrent, services to mankind. Human society has often exploited these systems by enhancing one ecosystem service at the expense of another. Loch Leven, Scotland, UK, is a good example of this. Over the past 150 years, the lake has been subjected to hydrological modification, fish stocking and pollution control to improve the delivery of key goods and services. This study uses historical records to explore the results of these interventions on the ecosystem services that were targeted for improvement and the knock-on effects on other services provided by the lake. The results suggest that, when management changes are being considered to enhance particular ecosystem services, the potentially damaging effects on other ecosystem services should be taken into account. This requires a better understanding of the role of ecosystem function in delivering ecosystem services, and of the links between multiple ecosystem services, than is currently available. While further research is clearly needed, the value of long-term datasets in providing knowledge and understanding through ‘hindsight’ should not be underestimated. The study concludes that successful management actions are likely to be those that incorporate lessons learned from previous decisions.     

Long-term variation and regulation of internal phosphorus loading in Loch Leven

Long-term monitoring data (1968–2008) were used to investigate internal phosphorus (P) loading following external P loading reduction in shallow Loch Leven, Scotland. A whole-lake sediment P inventory (upper 3 cm of sediment; 2005) suggested a release-potential of 29.7 tonnes (t) from the release sensitive sediment P pools. 18.5 t was contained within shallow water sediments (<4.5 m water depth) with 7.6 t in deeper water sediments below the photic zone (>5 m water depth). The “observed” release (<5.1 t), estimated using a water column P mass balance approach (1989–2008), was <5.1 t, indicating the presence of regulating mechanisms. Observed P release declined between 1989 and 2008, with the exception of 2003–2006. Observed P release estimates were positively correlated with annual average water column P concentration after 1989, highlighting the role of internal loading in maintaining poor water quality conditions after management intervention. Multiple regression analysis suggested that internal loading was driven by the wave mixed depth in spring (positive driver), summer water temperature (positive driver) and spring water clarity transparency (negative driver). The potential importance of biological and physico-chemical feedback mechanisms in the regulation of benthic–pelagic coupling and water quality in Loch Leven are discussed.     

Invertebrate food sources for waterbirds provided by the reconstructed wetland of Nyirkai-Hany,northwestern Hungary

Detailed studies of the macroinvertebrate benthos and zooplankton communities in Loch Leven, the largest shallow lowland lake in Scotland, UK, were carried out from 1966 to 1973 as part of the International Biological Programme (IBP). The results revealed a reduction in species diversity that was attributed to increasing eutrophication. This work provides a baseline against which the response of the invertebrate communities to subsequent changes in management can be assessed. This article compares macroinvertebrate benthos and zooplankton data from the IBP study with the post-IBP era during which changes at Loch Leven included a 60% reduction in the phosphorus input from external sources and variations in fish stocking rates. Only in recent years has there been evidence of ecological recovery by the invertebrate communities: the number of macroinvertebrate and zooplankton taxa has increased (including taxa considered to be sensitive to nutrient enrichment) and invertebrate abundances have declined. These changes appear to reflect the improvements in water quality and habitat conditions at Loch Leven that have occurred as a result of the recent reduction in nutrient loads, albeit with a substantial delay before any ecological response could be detected. This time lag in recovery has important implications for assessing improvements in the ecological status of other lake systems, as is required by the EU Water Framework Directive.     

Sediment phosphorus cycling in a large shallow lake: spatio-temporal variation in phosphorus pools and release

Sediment and water column phosphorus fractions were recorded monthly for one year (April 2004–April 2005) in a shallow lake recovering from nutrient pollution (Loch Leven, Scotland). Equilibrium phosphate concentration (EPC0) and gross sediment phosphorus (P) release rates were estimated from laboratory experiments. Pore water and organic P pools were lowest during warm water periods whereas bottom water P was lowest during cold water periods. Reductant-soluble, organic, metal oxide-adsorbed, residual and sediment total phosphorus pools all varied significantly with overlying water depth. Short-term, high magnitude, redox initiated P release events occurred in late summer and winter as a result of anoxic sediment conditions. Lower magnitude long-term release conditions were maintained for most of the year, most likely as a result of organic P cycling and maintenance of high concentration gradients between the pore and bottom water P pools. Estimates of summer P uptake/release rates, across an intact sediment-water interface, suggested that maximum gross internal release was ~12 mg SRP m⁻² lake surface area d⁻¹ with EPC0 values ranging between 180 and 270 μg P L⁻¹. This study highlights the biological mediation of internal loading in shallow eutrophic lakes, and in particular, the role of sediment algae in decreasing, and sediment bacteria in enhancing, sediment P release.     

Long-term variations in waterfowl populations in Loch Leven: identifying discontinuities between local and national trends

Loch Leven has been designated as a UK Ramsar Site (1976), a Site of Special Scientific Interest (1985) and a Special Protection Area (2000) due to its importance as a site for overwintering waterfowl. However, no comprehensive assessment of trends in waterfowl at the local versus national scale has been conducted at the site. Coherence between trends in 5-year mean species abundance for Loch Leven and Underhill Indexing Method values for Scotland (or GB in the case of geese) were assessed using principal components analysis for ten study species between 1968 and 2006. Five species showed trends at Loch Leven that were coherent with those at the Scottish scale (Eurasian Teal, Mute Swan, Great Cormorant, Pink-footed and Greylag geese). These species may not respond positively to local scale management. However, the other five species (Mallard, Coot, Great Crested Grebe, Tufted Duck and Pochard) showed distinct differences between local and national trends. A study of the feeding ecology for these species, the re-establishment of ringing effort and an assessment of waterfowl–wetland relationships are recommended to determine how changes in local food resources and habitat quality interact with macro-scale population dynamics to influence local and regional patterns of abundance.     

An evaluation of methods for sampling macrophyte maximum colonisation depth in Loch Leven, Scotland

The maximum colonisation depth (MCD) of macrophytes in lakes is considered a robust ecological indicator of system health. The accuracy of five boat-based survey methods (double-headed rake, Ekman grab, bathyscope, hydroacoustics, and underwater photography) was evaluated along depth-transects within a shallow eutrophic loch (Loch Leven, Scotland, UK) in 2006. Data from an earlier field campaign conducted in 1993 (33 transects) were used to assess sample frequency and error associated with the use of the double-headed rake method. The double-headed rake consistently sampled more species than the Ekman grab or bathyscope, probably as a result of its ability to sample relatively larger areas of the lake bed in comparison to the other methods. The bathyscope method underestimated the MCD in comparison to all other methods. This appeared to be because the turbidity of the water-column restricted the depth of view when using the bathyscope. The double-headed rake and underwater photography methods were in good agreement, with maximum observed MCD estimates of 5.0 m and 4.5 m water depth, respectively (2006). Using the 1993 data (MCD observations taken from 33 selected transects), we estimated that over 5 transects were required to ensure a MCD estimate greater than the 75th percentile from the distribution of all 33 colonisation depths, more than 15 replicate transects were required to ensure an estimate greater than the 90th percentile, and more than 20 replicate transects were required to ensure an estimate greater than the 95th percentile.     

On the ecology of notholca squamula muller in Loch Leven,Kinross, Scotland

Notholca squamula was rarely found in Loch Leven when the water temperature rose above 10°C. Under favourable temperature conditions its abundance appeared to be closely related to that of Asterionella formosa. In the laboratory the animal was seen to feed on this diatom by breaking open the frustule and ingesting the cell contents.Part of a dissertation for the Degree of Doctor of Philosophy to the Council for National Academic Awards at Paisley College, Scotland, in conjunction with the Institute of Terrestrial Ecology, Edinburgh, Scotland     

Deep water waves in lakes

The properties of waves on a lake surface and the influence of water depth on these properties are discussed. The method, derived by the Beach Erosion Board, of predicting wave characteristics if the wind speed and fetch are known is outlined and the validity of the method in Loch Leven, Scotland, is confirmed. This prediction technique is then combined with the equations of classical hydrodynamics to form a method of assessing the nature and extent of wave action in lakes without direct measurement. The value of the ratio of the wave-mixed volume to the total lake volume as a meausre of hydraulic conditions in lakes is suggested.     

The relationship between Trichocerca pusilla (Jennings), Aulacoseira spp. and water temperature in Loch Leven,Scotland, U.K.

Loch Leven is a shallow, eutrophic lake in the Scottish lowlands that is famous for its brown trout (Salmo trutta L.) fishery. Studies of planktonic rotifer populations began here in January 1977. Since then, samples have been collected and analysed at more or less weekly intervals. Additional information on the composition and abundance of phytoplankton and crustacean zooplankton species, and on a variety of physical and chemical determinants, has been recorded on each sampling occasion.Long-term datasets, such as that described above, are invaluable for identifying interactions between components of the plankton that only appear for short periods each year, as these interactions would probably be overlooked in data spanning a shorter period of time. This study uses the long-term data from Loch Leven to examine the food and temperature requirements of the summer rotifer species Trichocerca pusilla (Lauterborn). The results suggest that T. pusilla prefers water temperatures above 12 °C and that it feeds, primarily, on the filamentous diatom Aulacoseira spp. During the summer months, its abundance was closely related to the availability of this diatom. When filaments of Aulacoseira spp. were abundant, rotifer densities reached 1000–3000 ind. l^–1 and when they were scarce (e.g. 1980, 1997 and 1998) T. pusilla densities also remained low (i.e. less than 100 ind. l^–1). The reason for the success or failure of Aulacoseira during the summer months each year is unclear but, in general, its abundance was related to the availability of dissolved silica in the water.     

The sensitivity of phytoplankton in Loch Leven (U.K.) to changes in nutrient load and water temperature

1. Loch Leven is a shallow, eutrophic lake in Scotland, U.K. It has experienced much change over the 30 years that it has been studied; this has primarily been due to reduced nutrient loads to the lake through active catchment management. Its recovery has been slow and, therefore, we used a phytoplankton community model (PROTECH) to test its sensitivity to changing nutrient loads and water temperature.
2. PROTECH was initialized to simulate the observed phytoplankton community in 1995 and was then repeatedly run through a combination of step-wise changes in water temperature and nutrient load (two treatments were simulated for nutrient load: one changing both nitrate and phosphorus, and one changing just phosphorus). The effect on total chlorophyll- a concentration, cyanobacteria abundance and phytoplankton diversity was examined.
3. Whilst changes in temperature had little effect, variations in the nutrient load produced a range of responses. Increasing only the phosphorus load caused a large increase in Anabaena abundance and total chlorophyll- a concentration. However, the opposite response was recorded when nitrate load was changed as well, with Anabaena increasing its biomass under reduced nutrient load scenarios.
4. The key factor determining the type of response appeared to be nitrogen availability. Anabaena , a nitrogen fixer, could exploit the phosphorus resource of Loch Leven under limiting nitrogen conditions, allowing it to dominate under most of the scenarios tested apart from those supplying extra nitrogen to the lake. The model predictions agree with the observed data, which show that Anabaena continues to dominate the summer phytoplankton bloom in Loch Leven despite the considerable reduction in phosphorus supply from the catchment. This research provides a possible explanation for this.     

Historical changes (1905–2005) in external phosphorus loads to Loch Leven, Scotland, UK

This article reviews historical changes in the total phosphorus (TP) inputs to Loch Leven, Scotland, UK. Data derived from palaeolimnological records suggest that inputs in the early 1900s were about 6 t TP year⁻¹ (0.45 g TP m⁻² year⁻¹). By 1985, this had risen to about 20 t TP year⁻¹ (1.5 g TP m⁻² year⁻¹) due to increases in runoff from agricultural land and discharges from point sources. By the late 1970s, increased TP inputs were causing serious degradation of lake water quality. Most noticeably, there had been an increase in cyanobacterial blooms. A catchment management plan was implemented in the early 1990s. This resulted in a 60% reduction in the annual TP input between 1985 (20 t TP year⁻¹/1.5 g TP m⁻² year⁻¹) and 1995 (8 t TP year⁻¹/0.6 g TP m⁻² year⁻¹). The main reduction was associated with better control of point source discharges, but attempts were also made to reduce inputs from diffuse sources. The reduction in external TP loading to the lake led to a marked decline in TP retention by the lake each year.     

The long-term (1979–2005) effects of the North Atlantic Oscillation on wind-induced wave mixing in Loch Leven (Scotland)

We report on long-term covariation (1979–2005) between indices of the North Atlantic Oscillation (NAO) and wind speed and direction in Loch Leven. The effects of the observed variations in wind speed and direction were combined to produce modelled wave-mixed depths (Zc). Positive correlations were observed between seasonal and annual wind speeds and westerly frequency and indices of the NAO that are in line with general perception: positive NAO was correlated with stronger, more westerly winds and these correlations were strongest in winter and spring. Correlations between NAO and estimates of Zc were strongest in the most westerly exposed site in spring (r ² = 0.701; Zc_spring versus spring NAO index). On average, over a 25-year period Zc was deeper in spring and shallower in summer. Major anomalies from the 25-year seasonal means were observed in 1982, 1979, and 1991. Annual average Zc was low in the late 1970s and early 1980s (shallowest average annual Zc of 1.0 m (1984)), high in the late 1980s and early 1990s (deepest average annual Zc of 1.9 m (1990)) and moderate in recent years (up to 2005). This study has major implications for our understanding of potential climate change drivers and the related responses of shallow lake ecosystems, including alterations to littoral habitat quality and benthic–pelagic coupling.     

Effect of incubation temperature on the hatching of rotifer resting eggs collected from sediments

Sediment samples from Loch Leven, Scotland, were incubated at 5°C, 10°C and 15°C to induce hatching of rotifer resting eggs. The emergent animals were identified and counted. The temperature which induced hatching varied among the nine species studied. These results are discussed in relation to seasonality and temperature preferences previously recorded for the most abundant species. Resting egg densities of 2.2–13.9 eggs cm^–3 were recorded in the upper 5 cm of sediment.     

Changes in phytoplankton over various time scales in a shallow, eutrophic: the Loch Leven experience with special reference to the influence of flushing rate

SUMMARY. 1. The pattern of fluctuations in the total biomass and species composition of phytoplankton in the shallow, eutrophic Loch Leven exhibits considerable inter-annual and within-year variability. Nevertheless, studies over the 18-year period reviewed here (1968–85) show that many of the observed changes can be explained in -terms of light regimes and the concentrations and fluxes of nutrients. On occasion, the incidence of fungal parasitism and of protozoan, rotiferan and crustacean grazing is also important. 2. Changes in annual mean algal biomass from very high levels in the late 1960s and early 1970s to somewhat lower levels in the late 1970s, followed by occasional high peaks in the present decade, are attributed to shifts in phosphorus loading-particularly from a P-rich industrial source. 3. In spite of complex and erratic sequences of algal species, seasonal patterns in the size distribution of the phytoplankton assemblage have been identified. However, these also changed. During the 4 years prior to 1971, Daphnia hyalina was not recorded in the plankton, and small algae have been abundant only in late winter or early spring. 4. The potential importance of the weather is highlighted as one of the possible causes of the irregular appearance of algal species. The effect of the characteristically variable, oceanicclimate of Northern Britain on this large (13.3 km²), shallow (z?= 3.9 m) loch is thought to be of particular importance. 5. The influence of the weather on phytoplankton sequences is explored by comparing records of monthly flushing rate values with time-series data on aspects of the aquatic environment and plankton populations. The preliminary assessment suggests that variation in flushing rate ( p ) has a considerable effect on temperature regimes and the supplies and in-loch dynamics of nutrients; through such changes, p controls major features of phytoplankton succession such as the temporal abundance of diatoms, as well as detailed sequences of events relating to the development and collapse of particular algal species - and. as a consequence, in some cases, of the animals preying on them. 6. Concluding remarks emphasize how little would have been understood about the functioning of shallow lakes, had the long-term commitment to Loch Leven research been abandoned. The view is also expressed that the findings are of considerably greater relevance to research on ‘classic’ stratifying lake systems, than the focus on the shallow waterbody might hitherto have suggested.     

Spectral intensity in some Scottish freshwater lochs

In the course of investigations on the ecology of submerged aquatic macrophytes a narrow-bandwidth spectroradiometer has been used to measure underwater spectral intensity (390–750 nm) in a series of lochs approaching the extremes in optical and chemical properties of Scottish fresh waters. Cosine response and immersion-effect properties of the collector were determined in the laboratory with a colUmated hght source. Diffuse attenuation coefficients, Ee, ranged from 0·55 in Loch Croispol, a calcareous loch, to 2·9 in Loch Leven, a lowland eutrophic loch. Underwater spectral intensity (1 m) relative to subsurface values show a proportional increase in short-wave radiation in the blue-green water of Loch Croispol, while the converse is true of the peaty brown water of Loch Uanagan. Attenuation coefficients were derived over 25 nm wavebands in Lochs Croispol, Leven and Uanagan. The water in the latter two lochs is optically similar although Leven is rich in phytopiankton and has an extinction peak at 675 nm. Uanagan represents the brown-water type of loch most common in Scotland. Loch Croispol has attenuation coefficients for shorter wave-lengths at least ten times lower than the other two lochs and only approaches their values at 750 nm. Croispol resembles Crater Lake, Oregon. The colour range at the maximum colonizable depths by rooted macrophytes of brown (Uanagan 4 m) to blue-green (Croispol 6 m) water is equivalent to 196·0 and 230·6 kJ/Einstein (48·2 and 55·6 kcal/Einstein). Red/far-red ratios even in plankton-rich water (Leven) were at least three times the value for sunlight (1·3) and within the total photic zone reached three-figure proportions. Possible implications for light-sensitive seeds of aquatic species and for morphogenesis and zonation are discussed.     

An aeromonad epidemic in the brown trout (Salmo trutta L.)

The pathology and bacteriology of an aeromonad epidemic in the spawning population of brown trout ( Salmo trutta L.) of the freshwater Loch Leven, Kinross, Scotland, is described, together with estimates of its quantitative effect on the stock of trout.     

Long-term zooplankton composition data reveal impacts of invasions on community composition in the Waikato lakes,New Zealand

Data collected on zooplankton community composition over longer time periods (>?10 years) are rare. We examined among-lake spatial and temporal trends of zooplankton communities from a monitoring programme undertaken in the Waikato region, New Zealand. A total of 39 lakes were sampled over a period of 12 years, between 2007 and 2019, with varying degrees of temporal effort. We focussed particularly on eight lakes, considered here as ‘long-term lakes’, where samples were collected with greater regularity (including 5 with 12 years of data). Among lakes, suspended sediment concentrations and indicators of lake trophic state were inferred to be important in determining the zooplankton distributions; as this region is dominated by shallow lakes, the relative importance of suspended sediments was high. Among the long-term lakes, the greatest dissimilarities in zooplankton community composition among years were in Lake Waahi, where the Australian Boeckella symmetrica was first detected in 2012. That is, the greatest temporal changes to zooplankton composition during the study period were due to the invasion by non-indigenous species, rather than changes in trophic state or other environmental variables; non-native species commonly dominated the individual counts of species through much of 2014 and 2015, with most samples since 2016 being again dominated by native species. Following this lake, the largest and shallowest lakes in the dataset—Whangape and Waikare—exhibited the greatest variability in community composition among years.

     

Does interference competition from Daphnia affect populations of Keratella cochlearis in Loch Leven, Scotland?

A very marked inverse relationship between Daphnia hyalina var.lacustris Sars and Keratella cochlearis (Gosse) population densitieswas observed in Loch Leven, Scotland, UK between 1978 and 1982.The natural death rates of the rotifer population were far lowerthan would have been expected in response to interference competitionfrom Daphnia. Keratella birth rates fell, along with chlorophylla concentrations, when Daphnia filtration rates were high. Theresults indicate that, when Daphnia were abundant, direct competitionfor food was the most likely factor suppressing Keratella populationgrowth.     

Phytoplankton and primary production in clear-vegetated,inorganic-turbid,and algal-turbid shallow lakes from the pampa plain (Argentina)

Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material, and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic properties (based on ¹⁴C method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The underwater light climate was characterized. Clear-vegetated lakes were more transparent (K _d 4.5–7.7 m⁻¹), had high DOC concentrations (>45 mg l⁻¹), low phytoplankton Chl a (1.6–2.7 μg l⁻¹) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (α ~ 0.03 mgC mgChla ⁻¹ h⁻¹ W⁻¹ m²) were relatively low. Inorganic-turbid lakes showed highest K _d values (59.8–61.4 m⁻¹), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3 μg l⁻¹. Phytoplankton-turbid lakes showed, in general, high K _d (4.9–58.5 m⁻¹) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2–125.7 μg l⁻¹), and the highest productivities and efficiencies (maximum 0.56 mgC mgChla ⁻¹ h⁻¹ W⁻¹ m²). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently of their type (0.086 × 10⁵–41.7 × 10⁵ cells ml⁻¹). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America. Handling editor: J. Padisak