Antarctic stream ecosystems: physiological ecology of a blue-green algal epilithon

SUMMARY. 1. Several dozen summer meltwater streams are located in the McMurdo Sound region (c. 78°S 165°E) of southern Victoria Land. They are characterized by a highly variable flow regime at diel, seasonal and annual times caleis; wide fluctuations in temperature and nutrient content; and a very simple epilithic community of cyanophytes ( Nostoc spp., Oscillatoriaceae), bacteria, fungi and microherbivores.
2. The epilithon survives the dark Antarctic winter as dry, frozen mats which provide a large inoculum for growth the following summer. This overwintering assemblage retains a high metabolic capacity and responds rapidly to rehydration.
3. In a series of artificial substrate experiments, biomass accumulation rates were generally less than 0.1 In units d⁻¹. Colonization and growth on the substrates was inversely related to the suspended sediment load of the stream. There was also a visual correspondence between per cent algal cover of the natural streambed and the clarity of the streamwater. Sloughing losses may limit community biomass, particularly in the turbid flowing waters.
4. During running water conditions the mature communities had very low gross photosynthetic rates per unit chlorophyll (<0,1 μg C (μg chl a .h)⁻¹ and per unit carbon (<0,2 μg C (mg biomass C.h)⁻¹). Respiration was generally a high percentage (up to 92%) of gross photosynthesis, which probably reflected the high population densities of microheterotrophs in the community.
5. The floristically simple epilithic mats slowly accumulate to extreme biomass levels (>20 μg chl a cm ⁻², <20 mg C cm⁻²). Production rates per unit biomass are low, probably in response to the cold temperatures of the Antarctic stream environment, and the accumulated biomass represents several seasons of growth.     

Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies ( Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.
2. Mean densities of larvae (range 234–2318 m⁻²) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m⁻²) was always highest at the stable, spring-fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.
3. Annual production was high at the more stable, alkaline site (10.35 gLDW m⁻²) but much lower at the other sites (2.49–3.77 g m⁻²).
4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).
5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).
6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.     

The periphyton communities of Nyumba ya Mungu reservoir, Tanzania

The periphyton communities established in Nyumba ya Mungu were investigated between July and September 1974.
One hundred and ninety-two taxa were identified. One hundred and fifteen taxa were collected in the southern end of the lake, where 97 taxa were non-selectively distributed in the littorine epiphytic, epilithic, and epixylic environments. The offshore epixylon supported only 53 taxa. The epipelon and epipsammon were poorly developed at the southern end of the lake but were well developed in the northern inflow regions.
Diatoms and cyanophytes were the dominant phyla which contributed over 80% of the algal numbers. Chlorophytes were not common. Taxonomic compositions of periphyton on artificial and natural surfaces were similar, but artificial substrata accumulated greater proportional representations of diatoms.
The mean net production rates of periphyton on artificial substrata located at depths from 0-0.65 m for 28 days ranged from 140 mg organic dry weight m^-2 day^-1 on shoots in the macrophyte zone to 820 mg organic dry weight m^-2 day^-1 on glass surfaces on a rocky shore. The epiphytic environments produced the least standing crops of less than 250, 000 individuals cm^-2, but maximum densities of over 2,000,000 individuals cm^-2 were recorded in the epilithon.     

Oxygen consumption in Oreochromis niloticus (L.) in relation to development, salinity, temperature and time of day

Oxygen consumption of Oreochromis niloticus at different stages of development was studied in relation to salinity, temperature and time of day, using a Warburg apparatus. The oxygen consumption of newly hatched (0–14 h) larvae was 3.40 μl O₂ larva⁻¹ h⁻¹, of older yolk sac larvae 10.09 μl O₂ larva⁻¹ h⁻¹, and of one-month-old fry 32.99 μl O₂ larva⁻¹ h⁻¹. The QO₂ values showed a decrease with development and growth, ranging from 21.2–26.0 μl O₂ mg⁻¹ h⁻¹ in newly hatched larvae to 2.97 μl mg⁻¹ h⁻¹ in one-month-old fry. Changes in oxygen consumption occurred with salinity, the highest being at 17%o. Active larvae (12-24 mm T.L.) showed a doubling of consumption with a 10° C rise in temperature, and their Q₁₀ factor increased from 2.25 to 3.43 with increasing size. Day-old yolk-sac larvae, late yolk-sac larvae (5 days old) and fry of 12 14 mm length all showed a depression in oxygen consumption at midnight followed by a dawn rise.     

Heterotrophic bacterioplankton production and grazing mortality rates in an Ethiopian rift-valley lake (Awassa)

SUMMARY. 1. Heterotrophic bacterioplankton growth and production rates were estimated in a tropical lake by various methods. Mean growth rates, determined by tritiated thymidine incoporation into DNA, frequency of dividing cells and increase in cell density varied between 0.013 and 0.014 (with a range of 0.006–0.026) h⁻¹ corresponding to bacterial production of 1.16–1.22 (0.34–3.63) mg C m⁻³ h⁻¹.
2. Heterotrophic bacterial production estimated from oxygen and inorganic carbon consumption in the dark were compared with these values. The oxygen method gave similar results, while values from dark carbon uptake were as much as 2.5 times higher.
3. Although the different estimates of rates of bacterial production showed different patterns, the existence of spatial (vertical) and temporal (diel and seasonal) variation was demonstrated. Bacterial production was 13–41% of the net primary production and 10–30% of gross primary production.
4. Bacterial grazing mortality rate was estimated from size-fractionation and metablic inhibitor experiments. Average grazing rates were between 0.34 and 3.77 mg C m⁻³ h⁻¹ corresponding to 76–120% of the mean bacterial production rate. Organisms 1–12 μm in size, possibly mainly ciliates. were implicated as important bacterial grazers.     

Photosynthesis and photoassimilation of glucose during photomixotrophic growth of Marchantia polymorpha cells in suspension culture

Even in the presence of glucose the growth of Marchantia polymorpha L. (cell line HYH-2F) requires light, and growth is more sensitive to 10⁻⁶ M 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea than to 10⁻⁴ Antimycin A. The inability of the cells to grow in the dark is due to the low level of respiration. The respiration rate under light increased to four times the dark value. The values of the compensation ratio (the photosyntehtic rate/the respiration rate) for the oxygen exchange were below 1.0 daring the growth period, although oxygen evolution was found. At the early exponential phase, oxygen evolution was 0.373 μmol (mg cell dry weight)⁻¹ h⁻¹ [61.7 μmol (mg chlorophyll)⁻¹ h⁻¹]. M. polymorpha cells are unable to grow anaerobically in the light without a supply of carbon dioxide. When 1% carbon dioxide in nitrogen is supplied, photochemically produced oxygen and energy are sufficient for sustained growth although at significantly reduced yields in both cell dry weight and chlorophyll. Photosyntehtic CO₂ assimilation rate was 0.13 μmol (mg cell dry weight)⁻¹ h⁻¹[11.3 μmol (mg chlorophyll)⁻¹ h⁻¹]. At least one-third of the carbon atoms in cellular constituents seem to be derived from atmospheric carbon dioxide, which indicates that M. polymorpha cells grow photomixotrophicaily.     

Photoautotrophic growth in suspension culture of cells from the moss, Barbula unguiculata

Chlorophyllous cells in suspension culture from the moss, Barbula unguculata Hedw., grown under photoheterotrophic conditions were transferred to photoautotrophic conditions. The cells started to grow photoautotrophically without selection. Maximum growth was observed under irradiances of more than 5 W m² and in an atmosphere enriched with 1% (v/v) CO₂. Under optimum growth conditions, dry weight and chlorophyll content in the culture had increased 20-fold after 20 days of cell growth. High concentration of chlorophyll [10–20 μg (mg dry weight)⁻¹] and high photosynthetic actively [30–70 μmol O₂ evolved (mg chlorophyll)⁻¹ h⁻¹] were observed throughout the culture period. In sugar-free culture medium, cell growth did not occur in the dark or in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) under light, although cell growth was observed in glucose-containing medium under those conditions. When cells that were grown photoautotrophically for one year were transferred to glucose-containing medium under ordinary air, they started to grow heterotrophically both in the light and in the dark.     

Denitrification in stream epilithon: Seasonal variation in Gelbæk and Rabis Bæk, Denmark

Abstract Seasonal variations of denitrification activity were determined and compared with various environmental parameters in undisrupted epilithon communities (biofilm) from two Danish lowland streams. In the nutrient-rich Gelbæk, denitrification activity followed extensive changes in biofilm thickness, dry weight and chlorophyll a content during the season. The absolute maximum of denitrification (1.4 mmol N m⁻² d⁻¹, dark incubation) was recorded when the biofilm was best developed in the spring (April and May). Activity decreased dramatically after most of the biofilm suddenly disintegrated and peeled off in early summer. Photosynthetic O₂ production was an important controlling factor of denitrification on a diurnal scale, since the activities were always 2–3 fold lower in the light (50 μE m⁻² s⁻¹) than in the dark. In the more nutrient-poor Rabis Bæk, the biofilm was much less developed and denitrification activities were relatively small (maximum of 0.2 mmol N m⁻² d⁻¹ under dark incubation). The results indicate that productivity of the micro-algae regulates both the seasonal and diurnal patterns of denitrification in the biofilms.     

Heterotrophic prokaryotic production in ultraoligotrophic alpine karst aquifers and ecological implications

Spring waters from alpine karst aquifers are important drinking water resources. To investigate in situ heterotrophic prokaryotic production and its controlling factors, two different alpine karst springs were studied over two annual cycles. Heterotrophic production in spring water, as determined by [³H]leucine incorporation, was extremely low ranging from 0.06 to 6.83 pmol C L⁻¹ h⁻¹ (DKAS1, dolomitic-karst-spring) and from 0.50 to 75.6 pmol C L⁻¹ h⁻¹ (LKAS2, limestone-karst-spring). Microautoradiography combined with catalyzed reporter deposition-FISH showed that only about 7% of the picoplankton community took up [³H]leucine, resulting in generation times of 3–684 days. Principal component analysis, applying hydrological, chemical and biological parameters demonstrated that planktonic heterotrophic production in LKAS2 was governed by the respective hydrological conditions, whereas variations in DKAS1 changed seemingly independent from discharge. Measurements in sediments recovered from LKAS2, DKAS1 and similar alpine karst aquifers ( n =12) revealed a 10⁶-fold higher heterotrophic production (average 19 μmol C dm⁻³ h⁻¹) with significantly lower generation times as compared with the planktonic fraction, highlighting the potential of surface-associated communities to add to self-purification processes. Estimates of the microbially mediated CO₂ in this compartment indicated a possible contribution to karstification.     

A new type of metabolism chamber for the determination of active and postprandial metabolism offish, and consideration of results for coregonid and salmon juveniles

The optomotor reaction of juvenile Coregonus schinzipalea Val. et Cuv. and Salmo salar L. was utilized to develop a circular tube metabolism chamber to measure oxygen consumption and ammonia excretion as a function of swimming speed. The metabolism chamber with a constant water flow assured the maintenance of stable conditions. The unidirectional movement of fish was measured in a circular tube with a single narrowing. The relationships between the swimming speed and oxygen consumption or ammonia excretion described by exponential equations allowed the extrapolation towards the standard metabolism, i.e., zero swimming speed. For a juvenile coregonid (0.1–0.15 g individual weight, 2.6–2.8 cm total length) standard metabolism at 14° C was estimated as 0.65 mg0₂ g⁻¹ h⁻¹ and 17.3 μg N(NH₃)g⁻¹ h⁻¹, whereas for juvenile salmon (136mg individual weight) respective values at 22° C were 0.047mg0₂g⁻¹h⁻¹ and 0.61 μg N(NH₃)g⁻¹ h⁻¹. The feeding test with juvenile salmon was also performed in this circular chamber, and in both energy and nitrogen budgets after a meal the partitioning could be precisely attributed to standard metabolism, active metabolism and specific dynamic action (in the case of oxygen consumption) or postprandial nitrogen increase.
The new metabolism chamber allowed the relationship between metabolism and swimming velocity of juvenile fish with developed rheotactic response. It could be used with adult fish for similar purposes.     

Immobilization of dissolved organic matter from groundwater discharging through the stream bed

SUMMARY. 1. In laboratory experiments, 9.7–25.7% of dissolved organic carbon (DOC) in groundwater (at concentrations of 18.7–24.8 mg 1-⁻¹) was immobilized after perfusion through 8-cm-deep (22-cm-diameter) cores of stony stream-bed substratum.
2. This represented immobilization rates of 7.1–23.5 mg m⁻² h⁻¹ or, extrapolated across the year, potential immobilization rates within the stream bed of 62.2–205.9g m⁻² yr⁻¹. Actual rates in the entire stream bed were probably higher because perfusion through the experimental cores did not reduce groundwater DOC concentrations to levels measured in the adjacent stream.
3. Natural concentrations of dissolved free amino acids (DFAAs) in groundwater were generally unchanged following perfusion through the cores, suggesting the maintenance of a dynamic equilibrium in their concentrations.
4. Selective enrichments of amino acids in groundwater (up to 20-fold) were entirely immobilized following perfusion, indicating their rapid retention and flux in this environment. Thus, immobilization of the bulk DOC in stream-bed cores probably did not reflect net reductions in dissolved free, low-molecular-weight material, with higher molecular weight, more 'refractory' material being immobilized instead.
5. We conclude that groundwater can contribute substantial amounts of DOC, both high and low molecular weight, to a stream ecosystem. The stream bed is the site at which much of this material could be initially immobilized and made available to the stream trophic structure.     

Lactic acid production by Lactobacillus delbrueckii in a dual reactor system using packed bed biofilm reactor

Aims:  An integrated dual reactor system for continuous production of lactic acid by Lactobacillus delbrueckii using biofilms developed on reticulated polyurethane foam (PUF) is demonstrated.
Methods and Results:  Lactobacillus delbrueckii was immobilized on PUF, packed in a bioreactor and used in lactic acid fermentation. The rate of lactic acid production was significantly high with a volumetric productivity of 5 g l⁻¹ h⁻¹ over extended period of time. When coupled to a bioreactor, the system could be operated as dual reactor for over 1000 h continuously without augmentation of inoculum and no compromise on productivity.
Conclusions:  Polyurethane foams offer an excellent support for biofilm formation.
Significance and Impact of the Study:  The system was very robust and could be operated for prolonged period at a volumetric productivity of 4–6 g l⁻¹ h⁻¹.     

Oxygen uptake in developing eggs and larvae of the cod, Gadus morhua L.

Unfertilised cod eggs showed a mean oxygen uptake rate at 5°C of 0.089 μl O₂, dry wt.⁻¹ h⁻¹; this gradually rose to 0.768 μl O₂ mg dry wt.⁻¹ h⁻¹ in eggs about to hatch. From hatching to complete yolk absorption larvae respired at 1.6 μl O₂, mg dry wt.⁻¹ h⁻¹. During starvation following yolk absorption, uptake fell significantly to 1.1 μl O₂, mg dry ⁻¹ h⁻¹. Much of this decrease in oxygen consumption was shown to be caused by reduction in activity. Loss of weight during the embryo and larval phases could not easily be reconciled with total oxygen consumption; it is suggested that cod embryos and larvae may not rely solely upon endogenous energy reserves during development.     

The effects of water hardness upon the uptake, accumulation and excretion of zinc in the brown trout, Salmo trutta L.

The effects of water hardness (9 and 220 mgl⁻¹ as CaCO₃) upon zinc exchange in brown trout exposed to 0.77 μmol Zn 1⁻¹ have been investigated using artificial soft water (<49.9 μmol Ca ^l-1, <40.1 μmol Mg 1⁻¹) and mains hard water (1671.7 μmol Ca 1⁻¹, 493.6 μmol Mg 1⁻¹) of known composition. Both hard and soft water-adapted fish exhibited a bimodal pattern of net zinc influx. Net zinc influxes during both fast and slow uptake phases were significantly greater ( P <0.001) in soft (82.9 and 6.2 μmol Zn 100 g⁻¹ h⁻¹) than in hard water (46.3 and 2.4 μmol Zn 100 g h⁻¹). Zinc efflux (- 0.2 μmol Zn 100 g⁻¹ h⁻¹) was enhanced only in hard water during the slow net influx phase.
Brown trout exposed to zinc in hard water and placed in metal-free media exhibited a greater net efflux (- 25.6 μmol Zn 100 g⁻¹ h⁻¹) of the metal than did fish in soft water (-4.2 μmol Zn 100 g⁻¹ h⁻¹) treated in the same manner. Tissue ⁶⁵Zn activities reflected both the differences in uptake and excretion rates of the metal between hard and soft water fish. During zinc exposure (0.77 μmol Zn 1⁻¹) high water hardness reduced tissue burdens of the metal by reducing net branchial influx, and enhancing efflux of the metal in hard water fish.     

Abrupt change in primary productivity in a littoral zone of Lake Biwa with the development of a filamentous green-algal community

1. Some characteristics of the photosynthesis and primary production of benthic and planktonic algal communities were investigated in a littoral zone covered with gravel in the north basin of Lake Biwa, paying special attention to the recent development of filamentous green algae (FGA) in the benthic algal community.
2. P_max (maximum gross photosynthesis rate) values of the benthic algal community (0.1–1.2 mg C mg chl. a ⁻¹ h⁻¹) obtained from photosynthesis–irradiance (P–I) curves were lower than those of the planktonic algal community (2.4–11.5 mg C mg chl. a ⁻¹ h⁻¹). This is apparently a result of the high degree of self shading in the benthic algal community and its low turnover as compared with that of the planktonic algal community.
3. Relatively high I_k values (150–200 μmol photon m⁻² s⁻¹) were observed in the benthic algal community only in June–July when a FGA, Spirogyra sp., was abundant. This reflected a photosynthetic characteristic of the Spirogyra itself, in which photosynthesis was saturated at high light intensity.
4. The FGA community established in the layer between planktonic and sessile (benthic algae except for FGA) algal communities. It brought about extraordinarily high organic matter production in the littoral zone at the expense of production in the sessile algal community.     

Predicting the growth of age-0 yellow perch populations from measures of whole-lake productivity

SUMMARY. 1. The relationship was examined between four measures of lake productivity [total phosphorus (TP) and chlorophyll a (Chl a) concentrations, zooplankton density and biomass] and growth in length and weight of age-0 yellow perch in ten central Alberta lakes.
2. In these lakes, average summer TP and Chl a levels were in the range 11–51 and 1.4–19.5 μg1⁻¹, respectively. The interaction of TP and Chl a could explain 61% and 57% of the variance in total length and wet weight, respectively, of age-0 yellow perch sampled at the end of August.
3. The ability to predict first year fish growth from lake productivity is strongest at low levels of productivity (TP<35μgl⁻¹). In the lakes studied, fish community structure is more complex at high levels of productivity (TP>35μg1⁻¹), and more data on complex community level interactions seem necessary to predict fish growth in these systems.     

The respiration of young coho Oncorhynchus kisutch at gradually declining oxygen levels and during recovery from oxygen deprivation

The respiration of coho salmon, Oncorhynchus kisutch , weighing between 15 and 50 g was measured at gradually declining oxygen levels and at temperatures ranging between 14 and 17°C. The maximum and minimum oxygen concentrations tested were 250 and 40 μmol L⁻¹, respectively. Respiration rates were measured for 1 h periods before oxygen concentration was lowered by 12.5 or 25.0 μmol oxygen L⁻¹. At the end of these endurance tests the oxygen level was returned to normoxic conditions and respiration rates were determined for the recovery period. Under normoxic conditions (> 200 μmol L⁻¹) the respiration of coho levelled around 5.1 μmol g⁻¹ wet weight h⁻¹. At intermediate levels between 150 and 200 μmol oxygen L⁻¹, the average rate increased to 5.8 μmol g⁻¹ h⁻¹, which could be attributed to higher spontaneous activity of the test animals. At low oxygen levels (< 150 μmol⁻¹) average respiration rates dropped to values between 5.5 and 5.7 μmol g⁻¹ h⁻¹, reaching a minimum of 3.8 μmol g⁻¹ h⁻¹ at oxygen levels below 50 μmol L^μ. First mortality was observed in this range. After exposure to reduced oxygen levels the fish maintained a higher respiration rate when again exposed to normoxic oxygen levels above 200 μmol L⁻¹. Increased respiration rates were observed for a recovery period of 6 h.     

Simultaneous phototrophic and chemotrophic growth in the purple sulfur bacterium Thiocapsa roseopersicina M1

Abstract The anoxygenic phototrophic purple sulfur bacterium Thiocapsa roseopersicina was grown in illuminated continuous cultures with thiosulfate as growth limiting substrate. Aeration resulted in completely colorless cells growing chemotrophically, whereafter the conditions were changed to a 23 h oxic/1 h anoxic regime. After 11 volume changes at a dilution rate of 0.031 h⁻¹ (35% of μ_max) a time dependent equilibrium was established. During the 23 h oxic periods bacteriochlorophyll a synthesis (BChl a ) was not observed, whereas during the 1 h anoxic periods synthesis was maximal (i.e. 1.1 μg (mg protein)⁻¹ h⁻¹). As a result the BChl a concentration gradually increased from zero to an average value over 24 h of 1.9 μg (mg protein)⁻¹. Concomitantly, the protein concentration increased from 13.9 mg 1⁻¹ during continuous oxic conditions to 28.8 mg 1⁻¹. For comparison, the protein concentration during fully phototrophic growth at an identical thiosulfate concentration in the inflowing medium was 53.7 mg 1⁻¹. The specific respiration rate was 8 μmol O₂ (mg protein)⁻¹ h⁻¹ during full chemotrophic growth and gradually decreased to 3.5 μmol O₂ (mg protein)⁻¹ h⁻¹ after 11 volume changes at the regime employed. These data show that T. rosepersicina is able to simultaneously utilize light and aerobic respiration of thiosulfate as sources of energy. The ecological relevance of the data is discussed.     

Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake

SUMMARY. 1. Regeneration of ammonium and phosphate by macro-zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×10⁴ and 3×10⁵ individuals m⁻².
2. Phosphate regeneration ranged from 0.2 to 1.3 μ mol PO₄ m⁻² b⁻¹at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO₄ m⁻² h ⁻¹ at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH₄ m⁻² h⁻¹. respectively.
3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.     

The use of a perfused, whole-body preparation to measure the branchial and intestinal influx of 137-caesium in the rainbow trout (Oncorhynchus mykiss)

The branchial and intestinal influx of caesium (Cs) in the rainbow trout ( Oncorhynchus mykiss ) were measured using a perfused whole-body preparation. The branchial influx of Cs was small, 0–31 μmoles kg⁻¹ h⁻¹ at an external concentration of 1 mm. Branchial Cs influx was saturable, with a K_m of 1–92 mm and a J_max of l.05μmoles kg⁻¹ h⁻¹. Intestinal Cs influx was not saturable, but was directly proportional to the mucosal Cs concentration. Intestinal Cs influx was approximately 10–40 times greater than branchial Cs influx over a wide range of external Cs concentrations. These results are discussed with respect to mechanisms of Cs uptake and to the relative accumulation of radiocaesium from water and food in the environment.