Phytoplankton of shallow lakes: Seasonal succession, standing crop and the chief determinants of primary productivity, 1. Cooking Lake, Alberta, Canada

Cooking Lake (113°02′W, 53°26′N), a well-mixed, shallow (mean depth (1.59 m), eutrophic lake in Alberta, Canada, is characterized by eutrophic chlorococcalean and cyanophycean phytoplankton associations, and little change in standing crop with increasing depth. Standing crop and primary productivity are low during the winter but pronounced spring and summer maxima occur. Mean yearly areal standing crop (ΔB) and primary productivity (ΔA) were 212.4 mg m^?2 chlorophyll a and 301.8 mg C h^?1 m^?2 respectively. Annual productivity was estimated at 1322 g C m^?2. The mean increase in the extinction coefficient (?) per unit increase in standing crop (B) was 0.03 In units m^?1. High non-algal light attenuation (?_q) occurred avenging 41 which prevented the ratio B/? from attaining more than 65% of the theoretical maximum except once when algal self-shading occurred. Close correlations existed between B (mg m^?3 chlorophyll a) and A _max (mg h_?1 m_?3) ΔA and ΔB, ΔA and B, A_max, and A_max/?, and ΔA and I_o′, (W m^?2). The depth of the euphotic zone (Z_eu) varied between 0.5 and 1 25 m; the average relationship between z_eu and E was Z_eu= 3.74/?, and the mean standing Crop found in the euphotic zone represented 55.2% of the theoretical maximum, The high ?_q, values made the model of Tailing (1957) inapplicable to Cooking Lake. The Q₁₀ value for the lake was 2.2. The maximum rate of photosynthesis per unit of population per h. Ø^max, (mg C sag chlorophyll a_?1 h_?1) was more closely related to temperature than irradiance and ma depressed by pH values greater than 9.1. Growth of the phytoplankton was not nutrient limited: instead irradiance and temperature were more important. Indirect evidence that free CO₂ limited photosynthetic rates, is provided by the Ø_max: pH relationship.     

A CARBON BUDGET FOR THE AUTOTROPHIC CILIATE MESODINIUM RUBRUM1

Extensive blooms of the autotrophic ciliate Mesodinium rubrum (Lohmann) occurred in the Peru coastal upwelling region at 15°S latitude in March through May 1977 and contributed significantly to the organic productivity of the region. From observations made during the JOINT-II oceanographic expedition, a budget of the carbon flux of these unusual photosynthetic organisms can be constructed. The light dependent C fixation was determined with short (1 h) incubations because of the organisms' sensitivity to confinement and rapid nutrient exhaustion. Maximum photosynthesis occurred at 50% of incident light with a maximum rate of particulate C synthesis of 2187 mg C · m^?3· h^?1. The specific carbon uptake rates were also high with a maximum light saturated value of 16.8 mg C ·(mg chl a)^?1· h^?1. The rate of excretion of dissolved organic C at the productivity maximum ranged from 16.1 to 181.1 mg C · m^?3· h^?1. The range of percent excretion was 1.8–12.5% the total C fixed, similar to the range found in both motile and nonmotile phytoplankton assemblages. Respiration, determined by the decrease in particulate C in the dark, averaged 4.6% of the previously fixed photosynthetic C · h^?1. M. rubrum actively took up amino acids and naturally occurring dissolved organic carbon. The C budget for this ciliate indicates that the daily contribution to the particulate food chain is large, although not as great as is indicated by short incubations. The contribution of M. rubrum to the productivity and elemental fluxes of upwelling and coastal ecosystems has been seriously underestimated.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

Macrophyte-epiphyte biomass and productivity in an eelgrass (Zostera marina L.) community

The biomass, productivity (¹⁴C), and photosynthetic response to light and temperature of eelgrass, Zostera marina L. and its epiphytes was measured in a shallow estuarine system near Beaufort, North Carolina, during 1974. The maximum of the biomass (above-ground) was measured in March; this was followed by a general decline throughout the rest of the year. The average biomass was 105.0 g dry wt m^?2; 80.3 g dry wt m^?2 was eelgrass and 24.7 g dry wt m^?2 was epiphytes. The productivity of eelgrass averaged 0.88 mg C g^?1 h^?1 which was similar to that of the epiphytes, 0.65 mg C g^?1 h^?1. Eelgrass and epiphyte productivity was low during the spring and early summer, gave a maximum during late summer and fall, and declined during the winter; this progression was probably due to environmental factors associated with tidal heights. On an areal basis, the average annual productivity was 0.9 g C m^?2 day^?1 for eelgrass and 0.2 g C m^?2 day^?1 for the epiphytes. Rates of photosynthesis of both eelgrass and epiphytes increased with increasing temperature to an asymptotic value at which the system was light saturated. Both eelgrass and epiphytes had a temperature optimum of < 29 °C. A negative response to higher temperatures was also reflected in biomass measurements which showed the destruction of eelgrass with increasing summer temperatures. The data suggest that the primary productivity cycles of macrophytes and epiphytes are closely interrelated.     

Limnological studies of the lakes and streams of the upper Qu'Appelle River System,Saskatchewan, Canada

High phytoplankton productivity characterizes the eutrophic lakes of the upper Qu'Appelle River system. Annual primary production varied from 187 to 561 g C m^? while daily areal production varied from 290 to 8 575 mg C m^?2. The A_max range was 164 to 315 mg C m^?3h^?1 with the highest rates usually occurring in August or September. A_max values on any given day normally occurred in the top 0.5 m. Blue-green algae (Aphanizomenon flos-aquae, Microcystis aeruginosa, Oscillatoria prolifica) dominated the phytoplankton communities during the summer and fall. Diatoms (Asterionella formosa, Fragilaria capucina, Stephanodiscus niagarae) often dominated the spring communities but sometimes persisted as dominants through the summer. Fragilaria on occasion was present at very high concentrations in the late fall. Ceratium hirundinella was sometimes dominant but was usually an important part of the biomass. Green algae, although always present, rarely formed an important part of the biomass with Pediastrum duplex the only exception. A species list is appended.     

RELATIONSHIP BETWEEN PHOTOSYNTHESIS AND CELL SIZE OF MARINE DIATOMS12

Three photosynthetic parameters of 7 species of marine diatoms were studied using Na₂¹⁴CO₃ at 5–8 C using log phase axenic cultures. The cell volumes of the different species varied from 70 μm³ to 40 × 10⁵μm³. The present experiment is consistent with the interpretation that the initial slope α (mg C · [mg chl a]^?1· h^?1· w^?1· m²) of photosynthesis vs. light curves is controlled by self-shading of chlorophyll a in the cell. Pm, the rate of photosynthesis at light saturation (mg C · [mg cell, C]^?1· h^?1) and R, the intercept at zero light intensity (mg C · [mg cell C]^?1· H^?1) are both dependent on the ratio of surface area to volume of cell.     

Influence of light and temperature on photosynthesis and respiration by Pithophora oedogonia (Mont.) Wittr. (chlorophyceae)

Rates of net photosynthesis and respiration were determined for Pithophora oedogonia (Mont.) Wittr. acclimatized to 56 combinations of light (7–1200 μE m^?2 s^?1) and temperature (5–35°C). Conditions for maximum net photosynthesis were estimated to be 26°C and 970 μE m^?2 s^?1. The rate of net photosyntheses varied considerably with temperature, with the maximum measured value (9.67 mg O₂ h^?1 g dry wt.^?1) occurring at 25°C. Respiration rate increased with temperature and the light received just prior to measurement. The maximum respiration rate (7.05 mg O₂ g^?1 h^?1) occurred at 30°C and 1200 μE m^?2 s^?1. Exposure of Pithophora to light levels of 600 or 1200 μE m^?2 s^?1 prior to determination of the respiration rate resulted in significantly elevated levels of oxygen consumption at temperatures ≥ 15°C. The relationship between light, temperature and photosynthesis and respiration were summarized as three-dimensional response surfaces.     

THE TIME-COURSE OF PHOTOADAPTATION TO LOW-LIGHT IN PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE)1

The estuarine dinoflagellate, Prorocentrum mariaelebouriae (Parke & Ballantine 1957) Faust 1974 undergoes increases in pigmentation and photosynthetic efficiency within several days of downward light shifts. These changes can be described by first-order kinetics, as has been reported previously for Chlorophyll (Chl) a in several phytoplankton species. The studies described in this paper were conducted with isolates of populations of Prorocentrum from the Chesapeake Bay. We determined rates of adaptation to low-light for cultures grown at a range of photon flux densities (I₀= 2.65–26.2 E.m^?2, d^?1, shifted to 6.3–7.0% I₀) at three temperatures (10°, 15°, and 20° C), bracketing the conditions this species experiences in situ. In this paper, I report the time-course of changes in α, P_max Chl a, peridinin, and I_k and first-order rate constants, K₁ for changes in α, Chl a and peridinin. cell^?1. K₁ for changes in α cell^?1 averaged 1.58 × 10^?2 h^?1 for conditions encompassing five light treatments and three temperatures; the corresponding mean for Chl a was 1.59 × 10^?2 h^?1. Increases in peridinin measured for five light treatments at 15° C showed a mean K₁ of 1.22 × 10^?2 h^?1, Average percent changes in per cell α, Chl a, and peridinin ranged from 0.4–4.0% h^?1 (10–90% d^?1) following exposure to low-light. Photoadaptive changes are important to Prorocentrum because in nature it occupies turbid waters (K_t≥ 0.5 m^?1) where the mixing depth often exceeds the depth of the photic layer. Cells are entrained beneath a seasonally-stable density discontinuity and are exposed to very low-light (< I E.m^?2.d^?1) for days to weeks during subpycnocline transport. The ability of this species to undergo changes in pigmentation and photosynthetic physiology confers increased efficiency of light harvesting and contributes to this species’survival in the estuary where it is an important component of the dinoflagellate flora.     

Measurement of net ecosystem exchange,productivity and respiration in three spruce forests in Sweden shows unexpectedly large soil carbon losses

Measurement of net ecosystem exchange was made using the eddy covariance method above three forests along a north-south climatic gradient in Sweden: Flakaliden in the north, Knottåsen in central and Asa in south Sweden. Data were obtained for 2 years at Flakaliden and Knottåsen and for one year at Asa. The net fluxes (N_ep) were separated into their main components, total ecosystem respiration (R_t) and gross primary productivity (P_g). The maximum half-hourly net uptake during the heart of the growing season was highest in the southernmost site with ?0.787 mg CO₂ m^?2 s^?1 followed by Knottåsen with ?0.631 mg CO₂ m^?2 s^?1 and Flakaliden with ?0.429 mg CO₂ m^?2 s^?1. The maximum respiration rates during the summer were highest in Knottåsen with 0.245 mg CO₂ m^?2 s^?1 while it was similar at the two other sites with 0.183 mg CO₂ m^?2 s^?1. The annual N_ep ranged between uptake of ?304 g C m^?2 year^?1 (Asa) and emission of 84 g C m^?2 year^?1 (Knottåsen). The annual R_t and P_g ranged between 793 to 1253 g C m^?2 year^?1 and ?875 to ?1317 g C m^?2 year^?1, respectively. Biomass increment measurements in the footprint area of the towers in combination with the measured net ecosystem productivity were used to estimate the changes in soil carbon and it was found that the soils were losing on average 96–125 g C m^?2 year^?1. The most plausible explanation for these losses was that the studied years were much warmer than normal causing larger respiratory losses. The comparison of net primary productivity and P_g showed that ca 60% of P_g was utilized for autotrophic respiration.     

Seasonal and spatial variations of methane emissions from coastal marshes in the northern Yellow River estuary, China

Aims and methods

To evaluate the seasonal and spatial variations of methane (CH₄) emissions and understand the controlling factors, we measured CH₄ fluxes and their environmental variables for the first time by a static chamber technique in high Suaeda salsa marsh (HSM), middle S. salsa marsh (MSM), low S. salsa marsh (LSM) and bare flat (BF) in the northern Yellow River estuary throughout a year.

Results

CH₄ emissions from coastal marsh varied throughout different times of the day and significant differences were observed in some sampling periods (p?<?0.05). Over all sampling periods, CH₄ fluxes averaged between ?0.392 mgCH₄ m^?2?h^?1 and 0.495 mgCH₄ m^?2?h^?1, and emissions occurred during spring (0.008 mgCH₄ m^?2?h^?1) and autumn (0.068 mgCH₄ m^?2?h^?1) while sinks were observed during summer (?0.110 mgCH₄ m^?2?h^?1) and winter (?0.009 mgCH₄ m^?2?h^?1). CH₄ fluxes from the four marshes were not significantly different (p?>?0.05), and emissions occurred in LSM (0.026 mgCH₄ m^?2?h^?1) and BF (0.055 mgCH₄ m^?2?h^?1) while sinks were observed in HSM (?0.035 mgCH₄ m^?2?h^?1) and MSM (?0.022 mgCH₄ m^?2?h^?1). The annual average CH₄ flux from the intertidal zone was 0.002 mgCH₄ m^?2?h^?1, indicating that coastal marsh acted as a weak CH₄ source. Temporal variations of CH₄ emission were related to the interactions of abiotic factors (temperatures, soil moisture and salinity) and the variations of limited C and mineral N in sediments, while spatial variations were mainly affected by the vegetation composition at spatial scale.

Conclusions

This study observed a large spatial variation of CH₄ fluxes across the coastal marsh of the Yellow River estuary (CV?=?7856.25 %), suggesting that the need to increase the spatial replicates at fine scales before the regional CH₄ budget was evaluated precisely. With increasing exogenous nitrogen loading to the Yellow River estuary, the magnitude of CH₄ emission might be enhanced, which should also be paid more attentions as the annual CH₄ inventory was assessed accurately.     

Effects of sediment properties on benthic primary production in the Columbia River estuary

Effects of sediment properties on benthic primary production were investigated along transects in the intertidal regions of the Columbia River estuary. On the tidal flats, benthic diatoms were the most abundant plants, while microalgae and submergent vascular macrophytes were relatively rare. At five intensive study sites, mean rates of benthic primary production varied between 5 mg C m⁻² h⁻¹ at Clatsop Spit and 84 mg C m⁻² h⁻¹ at Youngs Bay. A regional analysis of data from these sites and from 31 less intensively studied survey sites indicated that Youngs Bay and Baker Bay were more productive than Grays Bay, Cathlamet Bay and the tidal flats in the upper estuary above these bays. This pattern corresponded to the stability and particle size distribution of the sediment in these areas. Benthic gross primary production for the total estuarine area of 410 km² was estimated to be 4895 t carbon per year and represents a mean rate of 72 g C m⁻² year⁻¹. Of the total net primary production in the estuary, benthic plants accounted for about 7%, while phytoplankton and emergent vascular plants in the marshlands contributed approximately 56% and 37%, respectively. Data from this study also suggested that physical processes related to estuarine circulation can ultimately determine the productivity of benthic plant assemblages, and minimize the regulatory and limiting effects of temperature, nutrient supply and consumption by benthic animals.     

Microbial respiration within a floodplain aquifer of a large gravel-bed river

1. Aerobic respiration, productivity and the carbon turnover rate of microbial biofilms were determined at hyporheic and phreatic sites in the Kalispell Valley alluvial aquifer along a transect extending 3.9 km laterally from the main channel of the Flathead River, a sixth order river in Montana (U.S.A.). The effect of experimentally increasing bioavailable organic carbon (acetate) on the respiration rate of biofilms in this carbon‐poor [dissolved organic carbon (DOC) < 2 mg L^?1] aquifer was also measured. 2. Chambers containing natural substratum were placed in‐situ and allowed to colonise for 20 weeks. After 4, 12 and 20 weeks, they were taken to the laboratory where oxygen flux was measured in a computer‐controlled, flow‐through respirometry system. 3. Respiration ranged from 0.01 to 0.33 mg O₂ dm^?3 h^?1 across sites, with means ranging from 0.10 to 0.17 mg O₂ dm^?3 h^?1. Productivity estimates ranged from 0.18 to 0.32 mg C dm^?3 day^?1 (mean 0.25, SE 0.03). The total organic carbon (TOC) of the microbial biofilms ranged from 18.2 to 29.7 mg C dm^?3. Turnover rate ranged from 3.2 to 5.6 year^?1 with a mean of 4.2 year^?1. 4. At the hyporheic site very close to the river, respiration did not significantly increase when samples were supplemented with labile carbon. Respiration increased with increasing DOC addition at hyporheic sites more distant from the river, suggesting a carbon‐limitation gradient within the hyporheic zone. Microbes at the phreatic site did not respond to increasing DOC addition, suggesting that the phreatic biofilm is adapted to low carbon availability. 5. Comparing the volume of the alluvial aquifer (about 0.7 km³) to that of the river benthic sediments (to 0.25 m depth, which amounts to about 1.6 × 10^?4 km³) within the Flathead Valley, leads to the conclusion that interstitial microbial productivity is orders of magnitude greater than benthic productivity. Alluvial aquifers are often voluminous and microbial production is an enormous component of ecosystem production in rivers such as the Flathead.     

Spatial variability of N2O, CH4 and CO2 fluxes within the Xilin River catchment of Inner Mongolia, China: a soil core study

In order to identify the effects of land-use/cover types, soil types and soil properties on the soil-atmosphere exchange of greenhouse gases (GHG) in semiarid grasslands as well as provide a reliable estimate of the midsummer GHG budget, nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) fluxes of soil cores from 30 representative sites were determined in the upper Xilin River catchment in Inner Mongolia. The soil N₂O emissions across all of the investigated sites ranged from 0.18 to 21.8 μg N m^-2 h^-1, with a mean of 3.4 μg N m^-2 h^-1 and a coefficient of variation (CV, which is given as a percentage ratio of one standard deviation to the mean) as large as 130%. CH₄ fluxes ranged from -88.6 to 2,782.8 μg C m^-2 h^-1 (with a CV of 849%). Net CH₄ emissions were only observed from cores taken from a marshland site, whereas all of the other 29 investigated sites showed net CH₄ uptake (mean: -33.3 μg C m^-2 h^-1). CO₂ emissions from all sites ranged from 3.6 to 109.3 mg C m^-2 h^-1, with a mean value of 37.4 mg C m^-2 h^-1 and a CV of 66%. Soil moisture primarily and positively regulated the spatial variability in N₂O and CO₂ emissions (R²?=?0.15–0.28, P?<?0.05). The spatial variation of N₂O emissions was also influenced by soil inorganic N contents (P?<?0.05). By simply up-scaling the site measurements by the various land-use/cover types to the entire catchment area (3,900 km²), the fluxes of N₂O, CH₄ and CO₂ at the time of sampling (mid-summer 2007) were estimated at 29 t CO₂-C-eq d^-1, -26 t CO₂-C-eq d^-1 and 3,223 t C d^-1, respectively. This suggests that, in terms of assessing the spatial variability of total GHG fluxes from the soils at a semiarid catchment/region, intensive studies may focus on CO₂ exchange, which is dominating the global warming potential of midsummer soil-atmosphere GHG fluxes. In addition, average GHG fluxes in midsummer, weighted by the areal extent of these land-use/cover types in the region, were approximately -30.0 μg C m^-2 h^-1 for CH₄, 2.4 μg N m^-2 h^-1 for N₂O and 34.5 mg C m^-2 h^-1 for CO₂.     

The influence of MAILLARD's reaction in sugar cane molasses on the kinetic fermentation parameters of Candida utilis NRRL Y-660

Growth inhibition of Candida utilis NRRL Y-660 took place in molasses stored at 60°C for 120 days. The specific growth rate (μ_max) was reduced from 0.42 h^?1 to 0.200 h^?1 as a result of a lack of affinity from the microorganism to the substrate and the increasing maintenance necessities. The K_s values arose from 1.40 mg/ml to 4.28 mg/ml within the whole experiment. At the same time, the maintenance coefficient (m) increased from 0.250 to 3.80 mg/ml. In a continuous culture the “wash-out” conditions were reached at dilution rate values (D) close to 0.40 h^?1. The process productivity decreased up to 15% from its original value in fresh molasses.     

Upper limits of photosynthetic productivity and problems of scaling

Some 1,370 W m^?2 of light energy reaches the outer atmosphere of earth and on average only 240 W m^?2 reaches the earth’s surface. Only a fraction of this is used to fix CO₂ through photosynthesis, and efficiencies ranging from 0.1?8% for total irradiance have been reported. The theoretical maximum quantum efficiency of carbon fixation is 0.125 mol C (mol quanta)^?1 which relates to a maximum productivity of about 12 g C m^?2 day^?1 or 29.8 g(dw) m^?2 day^?1. This could increase to a maximum of 200 g(dw) m^?2 day^?1 in intermittent light of high frequencies, which is on average eight times higher than the average measured under field conditions where rates approaching 25 g(dw) m^?2 day^?1 are considered high. Several possibilities exist for achieving higher yields and photosynthetic efficiencies, such as limiting the antennae sizes and pulsing light at frequencies equivalent to electron turnover in the electron transport chains of photosynthesis. Scaling from laboratory experimental conditions to large commercial photobioreactors is a major stumbling block and may be the single most important factor responsible for the overall low reported areal production rates.     

Productivity of Chlorella sorokiniana in a short light‐path (SLP) panel photobioreactor under high irradiance

Maximal productivity of a 14 mm light‐path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2,100 µmol photons m^?2 s^?1 with red light emitting diodes (LEDs) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irradiance on a horizontal surface at latitudes lower than 37°. Chlorella sorokiniana, a fast‐growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 to 0.26 h^?1. The maximal productivity was reached at a dilution rate of 0.24 h^?1, with a value of 7.7 g dw m^?2 h^?1 (m² of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g dw L^?1 h^?1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L^?1 and the photosynthetic efficiency was 1.0 g dw mol photons. This biomass yield on light energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons^?1 which must be related to photosaturation and thermal dissipation of absorbed light energy. Biotechnol. Bioeng. 2009; 104: 352–359 © 2009 Wiley Periodicals, Inc.     

Aspects of microbial heterotrophic production in a highly turbid estuary

The uptake of ¹⁴C glucose by natural microbial populations has been studied in the Severn Estuary and Bristol Channel, U.K.; the turbidity (suspended solids) in the estuary varied between < 5 mg · 1^?1 at the seaward extremity to >800 mg · 1^?1 in the estuary proper. The heterotrophic potential, V_m, was found to correlate with turbidity and particulate organic carbon but there was no correlation between microbial biomass, as assessed by plate counts, and turbidity or V_m; measurement of V_m ranged from 0.9 × 10^?4 to 288 × 10^?4μgC·1^?1·h^?1 and turnover time from <2 to >100 h. In 17 out of 42 experiments, the uptake of ¹⁴C glucose did not conform to Michaelis kinetics and in five of these experiments the data suggested that there may be a threshold of glucose concentration below which there is no uptake.     

ADAPTATION OF STYROFOAM SUBSTRATE TO BENTHIC ALGAL PRODUCTIVITY STUDIES IN LAKE TAHOE,CALIFORNIA-NEVADA1

A routine sampling technique has been developed using artificial styrofoam substrate to estimate benthic algal productivity in the littoral zone of lakes. Estimation of maximum carbon fixed in Lake Tahoe ranged from 11.1 mg C·m^?2· day^?1 at 0.5 m to 17.1 mg C·m^?2· day^?1 at 1.0 m. Estimates were made for communities composed of both diatom and green algal populations in water between 0.5 and 3.0 m. Maximum productivity occurred between 1–2 m. The technique developed can give comparable estimates of productivity if adequate replication is undertaken to decrease problems associated with periphytic heterogeneity.     

Effects of copper on production of periphyton, nitrogen fixation and processing of leaf litter in a Sierra Nevada, California, stream

SUMMARY.

• 1 Production of periphyton, nitrogen fixation and processing of leaf litter were examined in an oligotrophic Sierra Nevada stream and the responses of these processes to copper (2.5, 5 and 10μg 1^-1 Cu_T [total filtrable copper]; approximately 12, 25 and 50 ng 1^-1 Cu²⁺) were determined.
• 2 Autotrophic and total production were estimated from 3-week accumulations of biomass on artificial substrates. Mean autotrophic production in the control ranged from 0.22 to 0.58 mg C m^-2 h^-1 in summer-autumn 1979, but declined to 0.08–0.28 mg C m ² h^-1 after peak discharge in summer 1980, apparently due to phosphorus-limited growth. Total production in the control ranged from 0.30 to 0.82 mg C m^-2 h ^-1 in summer-autumn 1979 and from 0.16 to 0,68 mg C m ^-2 h ^-1 in 1980. Mean autotrophic productivity, estimated by ^l4C-bicarbonate uptake in daylight, ranged from 0.30 to 2.8 mg C m^-2 h^-1.
• 3 Autotrophic productivity was reduced by 57–81% at 2.5μg 1^-1 Cu_T, 55–96% at 5μg 1^-1 Cu_T, and 81–100% at 10μg 1^-1 CU_T, Heterotrophic productivity (based on dark ³⁵S-sulphate uptake) was inhibited to a lesser extent (28–63% at 2.5μg 1^-1 Cu_T, 24–84% at 5μg 1^-1 Cu_T, and 67–92% at 10μg 1^-1 Cu_T), The inhibition of autotrophic and heterotrophic productivity persisted through the year of exposure. Production in stream sections previously exposed to 2.5 and 5μg 1^-1Cu_T increased to control levels within 4 weeks after dosing, but remained depressed for more than 7 weeks after exposure to 10μg 1^-1 Cu_T.
• 4 The specific rate of photosynthesis (mg C mg chlorophyll a^-1 h^-1) of mature periphyton communities declined at all test concentrations of copper, but the rate for periphyton on newly-colonized surfaces did not change. The species composition of benthic algae shifted during exposure to an assemblage more tolerant of copper. Achrtanthes minutissima and Fragilaria crotonensis were the primary replacement species on newly-colonized surfaces.
• 5 The nitrogenase activity of blue-green algae was low. with controls ranging from 2.4 to 12 nmol C₂H₂ m^-2 h^-1. Nitrogenase activity was inhibited during the initial weeks of exposure by 5 and 10μg 1^-1 Cu_T. However, after 9 months of exposure, control and copper-treated sections did not differ.
• 6 The rate of processing of leaf litter, estimated by microbial respiration and nutrient quality of litter of resident riparian woodland taxa, was inhibited at all test concentrations of copper.

     

A comparative study of microalgae isolated from flooded rice paddies: light-limited growth,C fixation,growth efficiency and relative N and P requirement

Seven unialgal isolates from rice paddies,Ankistrodesmus convolutus, Chlorella sp.,Scenedesmus quadricauda, Frustulia vulgaris, Anabaena sp.,Microcystis aeruginosa andPhormidium mucicola, were investigated for their light-limited growth and photosynthetic characteristics, growth efficiency, and relative requirement for N and P as well as their storage potentials. The maximum growth rate (μ_max) ranged from 1.27 to 2.72 d^?1 among species. The slope of light-limited growth (α_g) showed only small interspecies differences (0.126–0.204 d^?1 W^?1 m²) except inS. quadricauda (0.092 d^?1 W^?1 m²). Similarly, the ratio of μ_max to α_g, I_k(g), varied within a narrow range (8.7–13.9 W m^?2) with the exception ofS. quadricauda (19.5 W m^?2). The slope of the photosynthetic curve based on chlorophylla (chla), α_p(a), was significantly higher in cyanobacteria (0.118–0.189 mg C mg chla ^?1h^?1W^?1m²) than in other species (0.070–0.094 mg C mg chla ^?1h^?1W^?1m²). The maximum photosynthetic rate based on chla (P_max(a)) was similar (2.95–3.83 mg C mg chla ^?1 h^?1) with the exception of a high value (6.17 mg C mg chla ^?1 h^?1) inM. aeruginosa. A significant correlation (P<0.001) existed between α_p(a) and P_max(a). The C-specific maximum photosynthetic rate (P_max(c)) was inversely correlated to the C/chla ratio. Growth efficiency (μ_eff), the efficiency to retain photosynthetically-fixed C for growth, showed an interspecies variation ranging from 73–93% and was correlated to the μ_max:P_max(c) ratio. Cyanobacteria exhibited higher efficiency than others. The ratio of P_max:α_p, I_k(p), was higher than I_k(g) by 2.0 to 3.8 times. The optimum N:P ratio, determined as the ratio of minimum cell quotas of N to P (q_oN:q_oP), showed a wide interspecies variability. It was highest inP. mucicola (54) and lowest inF. vulgaris (10). The maximum storage capacity for excess P and N also varied among species; the maximum capacity for P ranged from 2 to 14 times of its immediate need and the capacity for N varied from 1.2 to 4 times.