A.E. Bailey-Watts

Poor water quality in Loch Leven (Scotland) in 1995 in spite of reduced phosphorus loadings since 1985 : the influences of catchment management and inter-annual weather variation

Eight tonnes of phosphorus in all forms (total phosphorus, TP) entered Loch Leven from its catchment in 1995, compared to 20 t in 1985. Diffuse run-off from the land, and waste from over-wintering geese contributed 59% of the total loading in 1995 cf. 42% in 1985. Point-sources of sewage, and waste-water from fish-rearing ponds, produced the rest. Inputs of phosphorus in soluble reactive form (SRP) totalled 5 t, i.e. 63% of the TP loading in 1995, as compared with 1985 values of 11.8 t and 59%. Point-sources of SRP contributed 54% of the total SRP input in 1995 cf. 69% in 1985. Loadings from three sewage treatment works (STW) totalled 3.1 t TP in 1995 as compared with 5.3 t in 1985; this included 2.6 t SRP (cf. 3.6 t). Daily per capita outputs of the upgraded Kinross North and Milnathort STWs were 0.68 g and 0.81 g TP, respectively, compared with pre-upgrade values of 1.77 g and 2.03 g. Nett reductions in TP and SRP loadings between 1985 and 1995, are 55% and 59% respectively. These values are attributable as much to the lower rainfall of 890 mm over the period of study in 1995, compared to 1250 mm in 1985, as to ‘managed’ elimination of P usage at a major industrial source, and upgrades of STWs. In spite of these cutbacks, a combination of the lower rainfall and an extraordinarily hot summer in 1995 negated the expected reduction in lake phosphorus and chlorophyll levels. The lowered specific areal loading of ca. 0.7 g P m−2 estimated for 1995 still considerably exceeds the ideal maximum for the loch. These statistics nevertheless ignore the significance of a reduction of ca. 7 t in P entering the system in bio-available form, a recently completed upgrade of a major STW and channelling of effluent from a small works out of the catchment.

A contribution to the taxonomy of Stephanodiscus hantzschii Grunow, a common freshwater planktonic diatom

Water samples taken from Loch Leven, Scotland, contained unicellular centric diatoms dominated by a taxon we called Stephanodiscus hantzschii Grunow. It existed as several morphotypes, and these are described and compared with the type material of S. hantzschii from the Rabenhorst exsiccata 1104. The morphological features of material subjected to experimental nutrient enrichment are also briefly described. Two very distinct morphotypes and an additional three morphotypes, with more or less constant features of valve pattern have been distinguished. In addition, the presence of hemispherical valves made it possible to describe stages in the life cycle of this very common centric diatom, and an amended description of S. hantzschii is given.

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 effects of factorial nutrient enrichments on a planktonic unicellular centrales-dominated assemblage: clues to the factors controlling biomass in Loch Leven late winter-early spring in 1981.

A previous paper showed that in spite of short daylengths and low temperatures (2–4°C) during late winter-early spring 1981, Loch Leven produced a dense crop of unicellular centric diatoms (37,000 cells ml-1) and a considerable population of Asterionella (ca 9,400 cells ml-1). More recently acquired data suggest that these populations must also have suffered losses owing to occasional periods of rapid throughput of water, i.e. equivalent to 30% of the loch volume per month. The present study shows that samples taken from open water in February and subjected to ecologically representative, factorial additions of nitrate, phosphate and silica exhibited no major differences in total biomass after one week, to samples to which no nutrients were added. Moreover, the net change in biomass in the experimental bags was negligible. These results are in keeping with the field observations regarding low light and abundant nutrients at this time. The results of subsequent experiments also supported the conclusions dr...

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.