Comparative primary productivity of algal epiphytes on three species of macrophyte in the littoral zone of Lake Ohrid, Yugoslavia

Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton , and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using ¹⁴C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non-miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.
Mean total surface area available for epiphytic colonization during the study period was 1.032 m² macrophyte surface per m² of littoral zone for Phragmites , 0.810 m² for Potamogeton , and 0.167 m² for Nuphar . Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light-compensation depth ranged from 84–1406 mg C m⁻² littoral zone d⁻¹; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m⁻² littoral zone d⁻¹, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m⁻² littoral zone d⁻¹. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m⁻² littoral zone yr⁻¹. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.     

Phytoplankton ecology in an Antarctic lake

SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.
The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and ¹⁴C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll- a concentration (maximum value 170 mg m⁻²) but carbon fixation remained low, with values <500 mg C m⁻² day⁻¹. The algae contributing to this peak were mainly small chlorophytes and chrysophytes. The summer open-water period (December-March) was characterized by a different phytoplankton population dominated by cryptophytes. Chlorophyll levels were lower ( c . 40 mg m⁻²) but ¹⁴C fixation rates >3 g C m⁻² day⁻¹ were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h⁻¹ mg⁻¹ (chlorophyll- a ) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.     

Production of a stream shredder, Peltoperla maria (Plecoptera: Peltoperlidae) in disturbed and undisturbed hardwood catchments

SUMMARY. (1) The average benthic density of Peltoperla maria in an undisturbed southern Appalachian stream was more than twice that of a nearby stream draining a previously clear-cul catchment in its tenth year of natural secondary succession.
(2) Peltoperla production estimates, using three methods, do not show a significant difference in production between streams draining the two catchments. We attribute these results to quicker growth and slightly higher densities of larger nymphs in the disturbed stream. Production estimates for the disturbed stream ranged from 498 to 560 mg (ash free dry weight) m⁻²y⁻¹ while those for the undisturbed stream were 41–4–515 mg m⁻² y⁻¹.
(3) Our results reinforce the view that conclusions based solely upon numerical densities may lead to erroneus interpretations about the roles organisms play in ecosystems.
(4) Annual frass production by this shredder is about 20 times (10 g m⁻² y⁻¹) the secondary production of P. maria.     

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.     

Seasonal changes in vertical distribution, biomass and faecal production of tubificids in the profundal region of a shallow Japanese lake

Two tubificid species Limnodrilus hoffmeisteri and L. claparedeianus formed more than 93% of the total number of oligochaetes in the profundal. Limnodrilus spp. worms were found down to 33 cm in the sediment but in great numbers in the upper zone in June and October. Worms confined to the top 15 cm of sediment accounted for 53-92% of the total number. There were two annual maxima in population density and biomass, one in late spring (66000 inds m⁻², 17 g wet wt m⁻²) and the other in mid autumn (97000 inds m⁻², 176 g wet wt m⁻²). Two regression lines describing the effect of temperature on faecal production rate were obtained; Log F = 0.0604 T (°C) −0.7660 (below 15°C), Log F = 0.0266 T – 0.2170 (above 15°C). In total 26.8 kg dry wt m⁻² of sediment was defecated annually by Limnodrilus spp. The sediment in the 0–10 cm stratum may pass through the guts of the worms 2.3 times a year. Sedimentation rates in profundal region were very low with respect to the faecal production rates of the tubificids.     

Effect of ultraviolet radiation on accumulation and leakage of 86Rb+ in guard cells of Vicia faba

The effects of UV-C (254 nm), UV-A (365 nm) and broad-band UV (280–380 nm) on guard cells of Vicia faba L. cv. Long Pod were investigated in the presence of white light (450 μmol m⁻² s⁻¹). UV-C (7 μmol m⁻² s⁻¹) was found to cause leakage of ⁸⁶Rb⁺ from guard cells, while UV-A (0.3 μmol m⁻² s⁻¹) stimulated increased uptake in these cells. A relatively small stimulatory effect was observed by broad-band UV (3 μmol m⁻² s⁻¹) during the first 30 min of irradiation with an apparent equilibration of influx and efflux thereafter. Leakage of ⁸⁶Rb⁺ from guard cells continued despite the removal of UV-C and an increase in the amount of white light from 450 to 1500 μmol m⁻² s⁻¹, suggesting that membranes were irreversibly damaged. Irradiation of guard cells with UV-C for 30, 45 and 90 min indicated that these cells began to be affected already by 30 min UV-C irradiation.     

Seasonality and spatial variation in abundance, biomass and activity of heterotrophic bacterioplankton in relation to some biotic and abiotic variables in an Ethiopian rift-valley lake (Awassa)

SUMMARY. I. Seasonality and spatial variation in abundance, biomass and activity of heterotrophic bacterioplankton was studied in a tropical freshwater lake. Variation in phytoplankton biomass and production, and several other limnological parameters, were also quantified.
2. Bacterial number and biomass fluctuated between 3.88–8.33×10⁶ ml⁻¹ and 68–125 mg C m⁻³, respectively. No spatial variation was observed in these bacterial variables, although other limnological parameters showed vertical variation.
3. Seasonal and vertical variation of heterotrophic bacterial activity were estimated from oxygen consumption, ¹⁴CO₂dark uptake and plate counts of colony forming units. All three methods showed vertical heterogeneity, with higher activity in the hypolimnion during the long stratification period (February May). Oxygen consumption rate and plate counts showed seasonality.
4. In spite of the low seasonality of climate in the tropics, several biological, chemical and physical variables were correlated with changes in bacterial variables. Wind and rainfall, and their effects on stratification and mixing, vertical distribution of nutrients and rate of primary production appeared to be the important parameters affecting heterotrophic bacterioplankton.     

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.     

Life history and production of Paranephrops zealandicus in a forest stream, with comments about the sustainable harvest of a freshwater crayfish

1. Life history and production were assessed for the crayfish Paranephrops zealandicus in three reaches of a headwater stream with a catchment of regenerating coniferous-broadleaf forest in the south-east of the South Island of New Zealand.
2. Crayfish density ranged from 3 to 4 m⁻² in riffles and 4–12 m⁻² in pools, depending on reach. Crayfish biomass (4–33 g AFDW m⁻²) and annual production (2–11 g AFDW m⁻²) were high compared with values reported elsewhere, while P:B ratio was low (0.33–0.43). This substantial production was dependent primarily upon high biomass rather than high growth rate.
3. The crayfish of this population rank amongst the longest lived and slowest growing ever recorded. Individuals estimated to be 16+ year of age were not uncommon. Females became reproductively active at 6+ year. Fewer than 4% of females carried eggs, and young remained attached to females for at least 15 months.
4. We propose that characteristics of this population are the consequence of a cool thermal regime (mean daily stream temperature = 7.0 °C, range 1.8–11.9 °C), and that low biomass turnover and poor reproductive rate precludes any sustainable commercial harvest of crayfish from streams in New Zealand with similar thermal regimes.     

Mortality and production of 0+ perch, Perca fluviatilis L., in two Scottish lakes

Mortality of 0+ Eurasian perch was measured directly from the decline in catch in a high-speed plankton sampler and described by a negative exponential model. A mean mortality of 0.063 day ¹ (range=0.020–0.089) was calculated; for 0+ juveniles it was 0.021 day ¹. Mean larval production was 0.85–1.30 mg dry weight m⁻² day⁻¹ in Loch Kinord and 0.08–0.12 in Loch Davan. Annual production of 0+ juveniles was 1.97–7.55 kg wet weight ha ⁻¹ at L. Kinord and 1.01 kg at L. Davan. The contribution of 0+ perch, including the egg stages, to total perch production was 88–96%. Availability of food items on transition to exogenous feeding and through the larval period did not limit survival. Cannibalism by adults accounted for most of larval mortality, and predation by pike and adult perch were responsible for the majority of juvenile losses. The population structure of adult perch, for 12 year classes, was stable at L. Kinord, while year classes at L. Davan exhibited fluctuations in abundance and in two sampling years were eliminated in the first summer. Survival in the eleutheroembryonic phase was variable at L. Davan and observed to be low compared with L. Kinord. It is suggested that this was a result of water turbulence on the exposed and shallow spawning areas at L. Davan.     

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.     

Very high secondary production at a lake outlet

SUMMARY. 1. Larvae and pupae of Simulium noelleri Fried, coated the concrete of parts of an artificial lake outlet in southern England.
2. In the first two (of three) summer generations, development was synchronous and this allowed the calculation of their secondary production by the instantaneous growth method. The production of the two summer generations was, respectively, 229.1 g C m⁻² (7.4 g C m⁻²day⁻¹) and 185.5 g C m⁻² (8.8 g C m⁻² day⁻¹) The contribution of the third summer generation, and the overwintering generation, to annual production would be less than that of the first two summer generations. Nevertheless, annual production will have exceeded 500 g C m⁻² at this site.
3. Larvae are suspension feeders and they captured the rich supply of particulate and dissolved organic material which passed over them after export from the lake. As food is brought to the larvae they only require space for attachment and can thus build up very high population densities (which exceeded 1 × 10⁶ m⁻² on some occasions during the summer). The high population densities result in a high biomass and hence in the high levels of production.     

Vertical distribution and abundance of invertebrates within the sandy substrate of a low-gradient headwater stream

SUMMARY. 1 The vertical distribution of invertebrates (>0.053 mm) was studied in a sandy-bottomed, first-order stream on the Coastal Plain of Virginia, U.S.A. Invertebrate species composition, abundance and bio-mass were determined monthly over one year at sediment depth intervals of 0–1, 1–5, 5–15,15–30 and 30–40 cm.
2. The subsurface community was numerically dominated by species of Chironomidae, Nematoda and Crustacea, while much of the biomass was due to early instars of several species of Trichoptera.
3. Invertebrate density and biomass decreased significantly with depth in the substrate (ANOVA; P <0.05). Annual mean density decreased from 1,346,844 individuals m⁻³ at the surface to 13,578 individuals m⁻³ at 15–30 cm. Annual mean biomass decreased from 66.30 g m⁻³ at the surface to 0.44 g m⁻³ at 15–30 cm.
4. Dissolved oxygen decreased markedly from the surface to the 5 cm depth in the substrate, anaerobic conditions often occurring below 10 cm. Density and biomass both showed a significant positive relationship with dissolved oxygen concentration (Linear regression; P <0.05).
5. Physical forces were important in structuring the subsurface invertebrate community. Besides low dissolved oxygen concentration, sediment scouring resulting from storm discharge dramatically reduced density and biomass     

Production and litter processing by crayfish in an Appalachian mountain stream

SUMMARY 1. Mean annual density and biomass () of Cambarus bartonii in an Appalachian mountain stream (U.S.A.) was 12 individuals m⁻² and 1669 mg (ash-free dry weight) m⁻².
2. Annual production ( P ) of C bartonii was 961 mg AFDW m⁻². Despite high biomass, low growth rates resulted in low production and a low P/ ratio of 0.58.
3. While C bartonii constituted 61% of the total macroinvertebrate biomass, it contributed only 13% of annual community secondary production.
4. Litter processing was positively related to temperature and crayfish size. Cambariis bartotnii was estimated to comminute 36 g m⁻² y⁻¹ of leaf litter (>1 mm²) to 24 g m−^>2 y⁻¹ fine particulate material (<1 mm²). The annual pattern of litter comminution by crayfish was regulated by temperature. As a result, >5()% of shredding activity by crayfish occurred from June to September which was also the period of lowest litter standing crops and activity of other shredding macroinvertebrates.
5. We speculate that during summer crayfish play an important role in temperate woodland streams by converting slowly processed leaf litter species (e.g. Rhododendron ) to fine particles which are then available to collector-gatherers (e.g. Chironomidae, Oligochaeta).     

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.     

Population dynamics of the gastropod Theodoxus jordani (Sowerby) in the Shatt Al-Arab river

SUMMARY. 1. Measurements of the population density of Theodoxus jordani were made for the period July 1980 until June 1981. Numbers showed a well-defined pattern of fluctuation and varied between 390 in February and 1804 snails m⁻² in May after recruitment.
2. The population age structure revealed that the snail was semelparous, and that one generation dominated the population for most of the year.
3. The breeding season was long. Snails laid eggs from early December to the end of April. Eggs were laid in protective capsules and one snail developed per capsule. Total population natality estimated from field samples was 9813 snails m⁻².
4. Age specific mortality was high immediately after recruitment, low during the juvenile stages, and increased sharply at the adult stage with the onset of reproduction.     

A limnological investigation of the tarn Syslaktjønn, W Norway

An investigation covering hydrography, chemistry, vascular and cryptogamic plants, nitrogen fixation, phytoplankton biomass and production, and zooplankton was carried out from April to November 1976 in tarn in W Norway, The volume of the tarn was 18000 m³ and the turnover time about 30 d. Temperature ranged between 3.6 and 23.4°C and pH between 4.8 and 5.5. Nuphar luteum and Carex rostrata were the two dominating vasculars-with biomasses of 117 and 97 g m⁻², respectively The biomass of the bryophytes ( Sphagnum spp.) was about 510 g m⁻² and the production of the order 0.2–2.1 μg (mg d.w.)⁻¹h⁻¹. Nitrogen fixation in association with Sphagnum spp. was estimated at 25 g yr⁻¹ for the whole tarn. Phytoplankton was dominated by diatoms, green algae and chrysophyceans. The chlorophyll a content ranged from 2 to 20 mg m⁻³ and the carbon assimilation rates from 0.03 to 20 mg C m⁻³h⁻¹ at 0–4 m depths. Production in the period was of the magnitude 22 g C m⁻². The copepod Eudiaptomus gracilis was the most common netzooplankter. Large numbers of rotationrians were found during summer.     

Respiration rate in maize roots is related to concentration of reduced nitrogen and proliferation of lateral roots

The relationship between specific rate of respiration (respiration rate per unit root dry weight) and concentration of reduced nitrogen was examined for maize ( Zea mays L.) roots. Plants with 2 primary nodal root axes were grown for 8 days in a split-root hydroponic system in which NO-₃ was supplied to both axes at 1.0 mol m⁻³, to one axis at 1.0 mol m⁻³ and the other axis at 0.0 mol m⁻³ or to both axes at 0.0 mol m⁻³ Respiration rates and root characteristics were measured at 2-day intervals. Specific rate of respiration was positively correlated in a nonlinear relationship with concentration of reduced nitrogen. The lowest specific rates of respiration occurred when neither axis received exogenous NO⁻³ and the concentration of reduced nitrogen in the axes was less than 9 mg g⁻¹. The greatest rates occurred in axes that were actively absorbing NO⁻³ and contained more than 35 mg g⁻¹ of reduced nitrogen. At 23 mg g⁻¹ of reduced nitrogen, below which initiation of lateral branches was decreased by 30–50%. specific rate of respiration was 17% greater for roots actively absorbing NO⁻³ than for roots not absorbing NO⁻³ Increases in specific rate of respiration associated with concentrations of reduced nitrogen greater than 23 mg g⁻¹ were concluded to be attributable primarily to proliferation of lateral branches.     

Measurements of phosphorus uptake by macrophytes and epiphytes from the LaPlatte River (VT) using 32P in stream microcosms

1. Phosphorus (P) uptake by macrophytes and epiphytes from the LaPlatte River (VT) was examined in the laboratory by adding ³²PO₄‐P to recirculating stream microcosms.
2. Water, plugs of sediment and plants were removed from the river and placed into the microcosms. ³²PO₄‐P was then added either to the water or the sediment, and its incorporation into plants and epiphytes was monitored over 3 days. Uptake was examined at both ambient (5 μg L^–1) and increased (50 μg L^–1) soluble reactive phosphorus (SRP) concentrations. A computer program was developed to fit curves to the radiotracer data and calculate rate constants for the simultaneous transfer of ³²P among compartments.
3. Both macrophytes and epiphytes removed P from the water, but epiphyte uptake of P was more rapid. Phosphate enrichment stimulated P uptake by both macrophytes and epiphytes. Macrophytes also obtained P from the sediment. The relative contribution of P to macrophytes from the water vs. that from the sediment appeared to vary with SRP in the overlying water. Accurate estimates of rates of P uptake from sediments by macrophytes were difficult to obtain however, due to very low and highly variable unit rate constants for P uptake and uncertainty about the magnitude of the phosphate pool available for uptake.
4. SRP concentrations were greater in the overlying water than in the sediment pore water of stream microcosms in the present study. Numerous reports in the literature have suggested that this condition favours uptake by macrophyte stems and leaves rather than by roots.
5. Phosphate uptake from the water by macrophytes in shallow streams may be more common than for macrophytes in lakes.     

Photosystem I acceptor side limitation is a prerequisite for the reversible decrease in the maximum extent of P700 oxidation after short-term chilling in the light in four plant species with different chilling sensitivities

Changes in the extent of P700 oxidation (P700⁺) were investigated after chilling of barley, rice, pumpkin, and cucumber leaf segments at 4°C for 1 h under light with various photon flux densities. At 50 µmol photons m⁻² s⁻¹, the decrease in P700⁺ was observed only in cucumber, but at 150 µmol photons m⁻² s⁻¹, it was found in all plants except barley, revealing their expected chilling sensitivities. However, the decrease in P700⁺ by this short-term chilling was reversible in the presence of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea or methyl viologen, and it did not show any causal relationship with the decrease in the electron transfer rate nor with the down-regulation of photosystem II through the accumulation of zeaxanthin and the development of non-photochemical quenching. These results led to the suggestion that photosystem I (PSI) acceptor side limitation is a prerequisite for the decrease of P700⁺. Furthermore, PSI acceptor side limitation could be mainly due to limitation of electron-sink pathways such as CO₂ assimilation and ascorbate–glutathione cycle, because treatment with glycolaldehyde which inhibits the former pathway, and with KCN which inhibits both pathways, decreased P700⁺ by 20–30% in barley leaves after chilling in the light.