The Phragmites communis marshes occupy 250–330 hectares bordering the northern tidal flats of the Tay Estuary. The outer edge of the marsh forms a step up to 50 cm in height. Reed stems grow with densities of 90–150/m2 and break to produce upward facing cylinders which entrap sediments. Measured daily accretion rates in broken stems varied from 001 g to 0.07 g. Sedimentation was greatest during spring tides, but decreased with falling tidal range. Accretion of 16 g per stem is normal and many stem plugs have greater weight. Annual rates of contribution from instem accumulation vary between 0.9 and 2.6 kg/m2 on the marsh margin. Stem fall provides cylindrical sedimentary lumps to the marsh sediments, whose internal structure reveals nodules and thin laminae juxtaposed.

The River Tay, which drains a dominantly metamorphic catchment, has the largest freshwater discharge of any British river. Direct methods of determining the solute, suspension and bed loads at six gauging stations have enabled the river transport to be assessed at 375,000 and 997,000 tonnes annually for dry and average wet years respectively. Added to estimates of loads from the Earn and Isla rivers the load entering the head of the Tay Estuary varies from 646,000 tonnes to 1,648,000 tonnes annually. This corresponds to total losses of 100 t/km2/year to 255 t/km2 year, which equates with an average lowering of the basin surface by 4–5 cm to 11.6 cm per thousand years of dry and average conditions respectively.

Measurements of tidal currents in the outer Tay Estuary, and from the hydraulic model of the estuary, are used to present a tidal atlas of the area and to deduce residual tidal circulation. Additional tests on the model show that the volumetric exchange rate with the sea of the outer estuary can be as high as 58 per cent per tide, but may be lowered to about 35 per cent if multiple tide recirculation is considered. Fresh water discharge into the estuary does not materially affect this exchange rate.

Sediments from the River Tay contained higher concentrations of ammonia than nitrate throughout an 18 month sampling cycle. Sediments from Kingoodie Bay and from the North Sea off the Tay Estuary produced nitrite and ammonia when incubated in the presence of nitrate.

The nitrate-reducing bacteria present in Kingoodie Bay sediments were Aeromonasj Vibrio organisms with smaller numbers of enterobacteria and pseudomonads and even smaller numbers of acinetobacters. Continuous culture enrichments of sediments showed that in media containing no added NaCl, acinetobacters predominated anaerobically in the presence of nitrate and acetate while enterobacteria predominated in the presence of nitrate and glycerol. With 0.2M NaCl added to media enterobacteria were predominant, irrespective of carbon source, while with 0.4M NaCl addition pseudomonads predominated in acetate and enterobacteria in glycerol media.

These results indicate that, at the salinities observed in the Tay Estuary at Kingoodie Bay, fermentative bacteria are most likely to be active in nitrate reduction.

At ten stations in the upper Tay Estuary, surface water, bottom water and sediment samples were taken on 25 March 1976, 5/6 May 1977, 11 April 1978 and 6 June 1978, and investigated quantitatively for the presence of lower marine fungi, chytrids and higher mycelial fungi by means of the water-culture baiting method with pine pollen. The distribution of fungi is discussed as a function of the physical characteristics of the estuary.

The physiology of three nitrate respiring bacteria, identified as Klebsiella strain K312, Pseudomonas strain P388 and Vibrio strain V25, obtained from Kingoodie Bay sediments in the River Tay by enrichment techniques, have been studied in continuous culture. In glycerol limited anaerobic cultures Klebsiella K312 produced NO2 as the primary product of nitrate reduction whereas under N-limited conditions NH4+ was excreted into the culture medium. Nitrate reduction in this organism was accompanied by the synthesis of a paniculate nitrate reductase (NR) whilst under N-limitation a soluble nitrite reductase (NiR) was also produced. In contrast, Pseudomonas P388 dissimilates NO3 directly to gaseous products under anaerobic conditions and was associated with the synthesis of a particulate NR and under N-limited conditions a NiR. Nitrite never accumulated as an intermediate. Vibrio V25 would only reduce NO3 as far as NO2 and was therefore restricted in its use of NO3 under anaerobic conditions. Klebsiella K312 was the most versatile of the three organisms studied and since Klebsiella spp were found in significant numbers in the Kingoodie sediments they may account in part for the high interstitial NH4+ levels found there.

An extensive reed bed on the north shore of the inner Tay Estuary is briefly described. Studies in the summers of 1975, 1976 and 1978 showed it to comprise monodominant stands of Phragmites communis Trin. The standing crop of shoots was sampled at the end of the season of vegetative growth and analysed by simple biometrical methods. Certain important spatial and architectural characteristics of the community varied in a regular manner with position in the bed. Estimates of the above ground productivity of intact stands ranged from 100 to 150 tonnes/ha in a poor growing season. Commercial harvesting operations, conducted since 1975, produced an immediate and consistent decrease in shoot stature, apparently followed by a slow increase in density and productivity. The behaviour of the downshore edge of the bed and the details of its annual development above and below ground require further study.

The distribution of Bathyporeia pilosa is discussed in relation to variations in a number of physical and chemical characters of the sediment on eight transects. Relationships were found between density and median particle diameter, silt content, and water content of the sediment, but stability of the beach appeared to be the main parameter influencing B. pilosa distribution. Sediment preference experiments showed that sediments varied in attractiveness, medium and fine grade sands being preferred: coarse sands and muds were avoided as were sediments with a high silt and clay content. Attractiveness in laboratory conditions was not correlated with observed field densities in some cases, indicating that other parameters were important in determining the distribution. Studies of swimming behaviour demonstrated the importance of current speed during the pelagic phase and it is concluded that hydrological conditions may be as important as sedimentary characteristics in the determination of the distribution of this species.

The distribution of Bathyporeia pilosa within a 30 m × 30 m grid was studied and related to the three major types of habitats constituting the grid. These were defined as Trough, Mound and Pool. B. pilosa was found to colonise the Trough sediments in significantly higher densities than the Mound or Pool sediments. The Pool deposits were found to be similar for 10 out of the 12 physical and chemical characteristics studied, differing only in permeability and penetrability. The coefficient of permeability of the Trough sediments was found to be five times that of the Mound sediments, and the penetrability was found to markedly higher in the permeable area than in that of low permeability: densities of B. pilosa were positively related, therefore, to permeability and penetrability. The causes of the variation between the habitats are considered and the importance of permeability and penetrability in the ecology of B. pilosa is discussed.

Quantitative studies on marine Phycomycetes (thraustochytrids) were carried out at 6 stations between the Fladenground area of the North Sea and the mouth of the River Tay, between September 1975 and September 1976. Five samplings were made of the surface water and the sediment during this period. The number of fungi/litre sea water or sediment increased with the proximity to the mouth of the river compared to the high seas. The fungal population exhibited a seasonal fluctuation, a high number occurring in September and an extremely low number occurring in March. The sediments revealed a very high number of propagules/litre (up to 73,000) compared to the water (up to 384).

The main channels converge at Dundee and form a single outlet passing seawards of the Broughty Ferry-Tayport constriction. The coarsest sediments, often of gravels and shell debris, line the floor of the channel, which is locally cut into late-glacial marine clays. Extensive sandy tidal flats seaward of the constriction pass eastwards into dune-covered sand spits pointing into the North Sea. The entrance bar has a delta-like form which is slowly overriding the fine sands of the North Sea floor.

The median, sorting, and skewness of the sediments, and the covariation of several parameters follow patterns readily related to the physiographic features of the estuary.

Many of the beach and tidal flat areas are in a constant state of change, and repeated topographic surveying reveals the magnitude of these changes on a short time scale. The changes in sediment characteristics demonstrated by repeated sampling and analysis of material from one stretch of Broughty Ferry beach are substantial. Size-frequency distribution plots indicate that up to four sub-populations of grains are present. Natural combinations of these in different proportions produce systematic variations in values of the normally used sediment characterising statistics.

The occurrence of chytridiaceous fungi was investigated during 10 trips along the River Tay between October 1975 and September 1978. The fungi isolated were: Rhizophlyctis harderi Uebelmesser, Phlyctochytrium reinboldtae Persiel, Rhizophydium utriculare Uebelmesser, ? Podochytrium chitinophilum Willoughby, ? Chytriomyces hyalinus Karling, ? Rhizophydium halophilum Uebelmesser and Rhizophydium sp. No seasonal fluctuations could be observed.

In several well-authenticated instances intestinal pathogens, including Salmonella species, have been isolated from water in the absence of bacteria, such as Escherichia coli, commonly used to detect faecal pollution. The present study examines certain anaerobic, non-sporing commensals of the intestinal tract as alternative ‘indicator’ bacteria. The numbers of bifidobacteria and Bacteroides fragilis recovered from faecal specimens were between 109 and 1010 per gram while the Gram-positive, anaerobic cocci numbered only about 106 per gram. In sewage, this numerical difference was eliminated by a rapid loss of viability of bifidobacteria and B. fragilis so that the counts of all three types of bacteria approximated to those of E. coli. Storage tests with aerated and non-aerated sewage established that further loss of viability of bifidobacteria and B. fragilis occurred only fairly slowly. In samples of water from the Dighty Water and River Tay Estuary, shown to be faecally polluted, the three anaerobic types of bacteria were recovered in numbers roughly equal to those of E. coli and their persistence in the surface of the bed of the Dighty Water was also at least equal to that of E. coli.

These results demonstrated that, in spite of their strictly anaerobic growth requirements, Bifidobacteria, B. fragilis and the Gram-positive, anaerobic cocci persist in aerobic, aqueous environments. If their habitat can be shown to be reasonably restricted to the intestinal tract they are likely, under special circumstances, to be useful indicators of faecal pollution.

A one-dimensional mathematical model based on an implicit finite difference scheme is used to predict tidal levels and discharges throughout the Tay Estuary. The model accounts for the transformation of the tidal level curve along the estuary and predicts a maximum tidal range near Flisk. There is a measure of agreement between computed velocities and observed data in the upper reaches of the estuary.