Exchange of reduced sulfur gases between lichens and the atmosphere

Fourteen lichens, 10 green algal lichens and four cyanolichens, as well as a cyanobacterium emitted significant quantities of H₂S (0.01–0.04 pmol g dw^–1 s^–1) and DMS (0.005–0.025 pmol g dw^–1 s^–1) but were sinks for COS (0.015–0.14 pmol g dw^–1 s^–1). In contrast, exchange of CH₃SH and CS₂ were sporatic and inconsistent. Although some interspecific variation occurred for the first three gases, exchange rates were relatively uniform and were not influenced by irradiance conditions. In contrast to DMS and H₂S emission, COS uptake was strongly influenced by degree of thallus hydration. Because lichen dominated systems cover extensive terrestrial habitats, COS uptake is potentially important in the world's sulfur budget.     

Leaf Gas Exchange and Water Relations in Polylepis tarapacana at Extreme Altitudes in the Bolivian Andes

Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-line formation at a global scale. We studied gas exchange and water relations of Polylepis tarapacana in the field, considering the possible effects of water stress limitations imposed on net photosynthetic rate (P _N). Daily courses of microclimatic variables, gas exchange, and leaf water potential were measured in both dry-cold and wet-warm seasons at an altitude of 4 300 m. Marked differences in environmental conditions between seasons resulted in differences for the dry-cold and wet-warm seasons in mean leaf water potentials (–1.67 and –1.02 MPa, respectively) and mean leaf conductances (33.5 and 58.9 mmol m^–2 s^–1, respectively), while differences in mean P _N (2.5 and 2.8 mol m^–2 s^–1, respectively) were not as evident. This may be related to limitations imposed by water deficit and lower photon flux densities during dry and wet seasons, respectively. Hence P. tarapacana has coupled its gas exchange characteristics to the extreme daily and seasonal variations in temperature and water availability of high elevations.     

Benthic fluxes in San Francisco Bay

Measurements of benthic fluxes have been made on four occasions between February 1980 and February 1981 at a channel station and a shoal station in South San Francisco Bay, using in situ flux chambers. On each occasion replicate measurements of easily measured substances such as radon, oxygen, ammonia, and silica showed a variability (±1) of 30% or more over distances of a few meters to tens of meters, presumably due to spatial heterogeneity in the benthic community. Fluxes of radon were greater at the shoal station than at the channel station because of greater macrofaunal irrigation at the former, but showed little seasonal variability at either station. At both stations fluxes of oxygen, carbon dioxide, ammonia, and silica were largest following the spring bloom. Fluxes measured during different seasons ranged over factors of 2–3, 3, 4–5, and 3–10 (respectively), due to variations in phytoplankton productivity and temperature. Fluxes of oxygen and carbon dioxide were greater at the shoal station than at the channel station because the net phytoplankton productivity is greater there and the organic matter produced must be rapidly incorporated in the sediment column. Fluxes of silica were greater at the shoal station, probably because of the greater irrigation rates there. N + N (nitrate + nitrite) fluxes were variable in magnitude and in sign. Phosphate fluxes were too small to measure accurately. Alkalinity fluxes were similar at the two stations and are attributed primarily to carbonate dissolution at the shoal station and to sulfate reduction at the channel station. The estimated average fluxes into South Bay, based on results from these two stations over the course of a year, are (in mmol m^–2 d^–1): O₂ = –27 ± 6; TCO₂ = 23 ± 6; Alkalinity = 9 ± 2; N + N = –0.3 ± 0.5; NH₃ = 1.4 ± 0.2; PO₄ = 0.1 ± 0.4; Si = 5.6 ± 1.1. These fluxes are comparable in magnitude to those in other temperate estuaries with similar productivity, although the seasonal variability is smaller, probably because the annual temperature range in San Francisco Bay is smaller.Budgets constructed for South San Francisco Bay show that large fractions of the net annual productivity of carbon (about 90%) and silica (about 65%) are recycled by the benthos. Substantial rates of simultaneous nitrification and denitrification must occur in shoal areas, apparently resulting in conversion to N₂ of 55% of the particulate nitrogen reaching the sediments. In shoal areas, benthic fluxes can replace the water column standing stocks of ammonia in 2–6 days and silica in 17–34 days, indicating the importance of benthic fluxes in the maintenance of productivity.Pore water profiles of nutrients and Rn-222 show that macrofaunal irrigation is extremely important in transport of silica, ammonia, and alkalinity. Calculations of benthic fluxes from these profiles are less accurate, but yield results consistent with chamber measurements and indicate that most of the NH₃, SiO₂, and alkalinity fluxes are sustained by reactions occurring throughout the upper 20–40 cm of the sediment column. In contrast, O₂, CO₂, and N + N fluxes must be dominated by reactions occurring within the upper one cm of the sediment-water interface. While most data support the statements made above, a few flux measurements are contradictory and demonstrate the complexity of benthic exchange.     

Seasonal cycles of zooplankton from San Francisco Bay

The two estuarine systems composing San Francisco Bay have distinct zooplankton communities and seasonal population dynamics. In the South Bay, a shallow lagoon-type estuary, the copepods Acartia spp. and Oithona davisae dominate. As in estuaries along the northeast coast of the U.S., there is a seasonal succession involving the replacement of a cold-season Acartia species (A. clausi s.l.) by a warm-season species (A. californiensis), presumably resulting from the differential production and hatching of dormant eggs. Oithona davisae is most abundant during the fall. Copepods of northern San Francisco Bay, a partially-mixed estuary of the Sacramento-San Joaquin Rivers, organize into discrete populations according to salinity distribution: Sinocalanus doerrii (a recently introduced species) at the riverine boundary, Eurytemora affinis in the oligohaline mixing zone, Acartia spp. in polyhaline waters (18–30\%), and neritic species (e.g., Paracalanus parvus) at the seaward boundary. Sinocalanus doerrii and E. affinis are present year-round. Acartia clausi s.l. is present almost year-round in the northern reach, and A. californiensis occurs only briefly there in summer-fall. The difference in succession of Acartia species between the two regions of San Francisco Bay may reflect differences in the seasonal temperature cycle (the South Bay warms earlier), and the perennial transport of A. clausi s.l. into the northern reach from the seaward boundary by nontidal advection.Large numbers (>10⁶ m^–3) of net microzooplankton (>64 µm), in cluding the rotifer Synchaeta sp. and three species of tintinnid ciliates, occur in the South Bay and in the seaward northern reach where salinity exceeds about 5–10 Maximum densities of these microzooplankton are associated with high concentrations of chlorophyll. Meroplankton (of gastropods, bivalves, barnacles, and polychaetes) constitute a large fraction of zooplankton biomass in the South Bay during winter-spring and in the northern reach during summer-fall.Seasonal cycles of zooplankton abundance appear to be constant among years (1978–1981) and are similar in the deep (>10 m) channels and lateral shoals (<3 m). The seasonal zooplankton community dynamics are discussed in relation to: (1) river discharge which alters salinity distribution and residence time of plankton; (2) temperature which induces production and hatching of dormant copepod eggs; (3) coastal hydrography which brings neritic copepods of different zoogeographic affinities into the bay; and (4) seasonal cycles of phytoplankton.     

Seasonal CO<Subscript>2</Subscript>-exchange variations of temperate semi-desert grassland in Hungary

CO₂ exchange components of a temperate semi-desert sand grassland ecosystem in Hungary were measured 21 times in 2000–2001 using a closed IRGA system. Stand CO₂ uptake and release, soil respiration rate (R _s), and micrometeorological values were determined with two types of closed system chambers to investigate the daily courses of gas exchange. The maximum CO₂ uptake and release were –3.240 and 1.903 mol m^–2 s^–1, respectively, indicating a relatively low carbon sequestration potential. The maximum and the minimum R _s were 1.470 and 0.226 mol(CO₂) m^–2 s^–1, respectively. Water shortage was probably more effective in decreasing photosynthetic rates than R _s, indicating water supply as the primary driving variable for the sink-source relations in this ecosystem type.     

Haematococcus pluvialis cultivation in split-cylinder internal-loop airlift photobioreactor under aeration conditions avoiding cell damage

The effects of superficial gas velocity in the riser (U_Gr) and gas entrance velocity (v) on the growth of Haematococcus pluvialis cultivated in a split-cylinder internal-loop airlift photobioreactor were investigated. Cell growth decreased when U_Gr and v were increased above 12 mm s^–1 and 22.8 m s^–1, respectively. The maximum cell density of H. pluvialis was 110×10⁴ vegetative cells ml^–1 and the chlorophyll-a titer was 7 mg l^–1. The cell damage in the photobioreactor was greater when v was increased by an increase in U_Gr rather than by a decrease in sparger internal diameter. The overall volumetric mass transfer coefficient (k_La) of the photobioreactor was measured at the same U_Gr (6–24 mm s^–1) and v (12–80 m s^–1). The k_La values reached in the airlift photobioreactor were between 10 h^–1 and 32 h^–1.     

Apparent viscosity for non-Newtonian fermentation media in bioreactors

The apparent viscosity of non-Newtonian fermentation media is examined. The present state of this subject is discussed. The energy dissipation rate concept is used for a new evaluation of the apparent viscosity in bioreactors, i.e. stirred tank and bubble column bioreactors. The proposed definition of the apparent viscosity is compared with the definitions available in the literature.List of Symbols A _d m ² downcomer cross-sectional area - A _r m ² riser cross-sectional area - a m^–1 specific surface area - C constant in eq. (13) - D m column diameter - D _I m impeller diameter - g m s^–2 gravitational acceleration - h J m^–2 s^–1 K^–1 heat transfer coefficient - K Pa s ⁿ consistency index in a power-law model - k constant in eq. (3) - k _L m s ^–1 liquid-phase mass transfer coefficient - N s^–1 impeller speed - n flow index in a power-law model - P W power input - Re Reynolds number ND _I ^/2 /(/) - U _sg m s ^–1 superficial gas velocity - (U _sg ) _r m s^–1 superficial gas velocity based on riser - V-m³ liquid volume - v ₀ m s^–1 friction velocity Greek Symbols s^–1 shear rate - _c s^–1 characteristic shear rate - W kg^–1 energy dissipation rate per unit mass - W kg^–1 characteristic energy dissipation rate per unit mass - Pa s viscosity - _app Pa s apparent viscosity - kg m^–3 density - Pa shear stress     

The organic carbon budget of a shallow arctic tundra lake on the Tuktoyaktuk Peninsula,N.W.T., Canada

The organic carbon cycle of a shallow, tundra lake (mean depth 1.45 m) was followed for 5 weeks of the open water period by examining CO₂ fluxes through benthic respiration and anaerobic decomposition, photosynthesis of benthic and phytoplankton communities and gas exchange at the air-water interface. Total photosynthesis (as consumption of carbon dioxide) was 37.5 mmole C m^–2 d^–1, 83% of which was benthic and macrophytic. By direct measurement benthic respiration exceeded benthic photosynthesis by 6.6 mmole C m^–2 d^–1. The lake lost 1.4 × 10⁶ moles C in two weeks after ice melted by degassing C0₂, and 6.8 mmole C m^–2 d^–1 (1.5 × 10⁶ moles) during the remainder of the open water period; 2.2 mmole C m² d^–1 of this was release Of CO₂ stored in the sediments by cryoconcentration the previous winter. Anaerobic microbial decomposition was only 4% of the benthic aerobic respiration rate of 38 mmole C m^–2 d^–1. An annual budget estimate for the lake indicated that 50% of the carbon was produced by the benthic community, 20% by phytoplankton, and 30% was allochthonous material. The relative contribution of allochthonous input was in accordance with measurement of the ¹⁵N of sedimented organic matter.     

Lateral hydraulic conductivity of early metaxylem vessels in Zea mays L. roots

The hydraulic conductivity of the lateral walls of early metaxylem vessels (Lp_x in m · s^–1 · MPa^–1) was measured in young, excised roots of maize using a root pressure probe. Values for this parameter were determined by comparing the root hydraulic conductivities before and after steam-ringing a short zone on each root. Killing of living tissue virtually canceled its hydraulic resistance. There were no suberin lamellae present in the endodermis of the roots used. The value of Lp_x ranged between 3 · 10^–7 and 35 · 10^–7 m · s^–1 · MPa^–1 and was larger than the hydraulic conductivity of the untreated root (Lp_r = 0.7 · 10^–7 to 4.0 · 10^–7 m · s^–1 · MPa^–1) by factor of 3 to 13. Assuming that all flow through the vessel walls was through the pit membranes, which occupied 14% of the total wall area, an upper limit of the hydraulic conductivity of this structure could be given(Lp_pm=21 · 10^–7 to 250 · 10^–7 m · s^–1 · MPa^–1). The specific hydraulic conductivity (Lp_cw) of the wall material of the pit membranes (again an upper limit) ranged from 0.3 · 10^–12 to 3.8 · 10^–12 m² · s^–1 · MPa^–1 and was lower than estimates given in the literature for plant cell walls. From the data, we conclude that the majority of the radial resistance to water movement in the root is contributed by living tissue. However, although the lateral walls of the vessels do not limit the rate of water flow in the intact system, they constitute 8–31% of the total resistance, a value which should not be ignored in a detailed analysis of water flow through roots.Abbreviatations and Symbols k_wr (T ₁ ^2/W ) rate constant (half-time) of water exchange across root (s^–1 or s, respectively) - Lp_cw specific hydraulic conductivity of wall material (m² · s^–1 · MPa^–1) - Lp_pm hydraulic conductivity of pit membranes (m · s ^–1 · MPa^–1) - Lp_r hydraulic conductivity of root (m · s^–1 · MPa^–1) - Lp_x lateralhydraulic conductivity of walls of root xylem (m · s ^–1 · MPa^–1) This research was supported by a grant from the Bilateral Exchange Program funded jointly by the Natural Sciences and Engineering Research Council of Canada and the Deutsche Forschungsgemeinschaft to C.A.P., and by a grant from the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 137, to E.S. The expert technical help of Mr. Burkhard Stumpf and the work of Ms. Martina Murrmann and Ms. Hilde Zimmermann in digitizing chart-recorder strips is gratefully acknowledged.     

Viscous media in tower bioreactors: Hydrodynamic characteristics and mass transfer properties

Studies in tower reactors with viscous liquids on flow regime, effective shear rate, liquid mixing, gas holdup and gas/ liquid mass transfer (k _La) are reviewed. Additional new data are reported for solutions of glycerol, CMC, PAA, and xanthan in bubble columns with diameters of 0.06, 0.14 and 0.30 m diameter. The wide variation of the flow behaviour index (1 to 0.18) allows to evaluate the effective shear rate due to the gas flow. New dimensionless correlations are developed based on the own and literature data, applied to predict k _La in fermentation broths, and compared to other reactor types.List of Symbols a(a) m^–1 specific interfacial area referred to reactor (liquid) volume - Bo Bond number (g D _c ² _L/) - c _L(c _L ^* ) kmol m^–3 (equilibrium) liquid phase oxygen concentration - C coefficient characterising the velocity profile in liquid slugs - C _s m^–1 coefficient in Eq. (2) - d _B(d_vs) m bubble diameter (Sauter mean of d _B) - d ₀ m diameter of the openings in the gas distributor plate - D _c m column diameter - D _L m²s^–1 diffusivity - E _L(E_W) m² s^–1 dispersion coefficient (in water) - E ² square relative error - Fr Froude number (u _G/(g D_c)^0.5) - g m s^–2 gravity acceleration - Ga Gallilei number (g D _c ³ _L ² / _eff ² ) - h m height above the gas distributor the gas holdup is characteristic for - k Pasⁿ fluid consistency index (Eq. 1) - k _L m s^–1 liquid side mass transfer coefficient - k _La(k_La) s^–1 volumetric mass transfer coefficient referred to reactor (liquid) volume - L m dispersion height - n flow behaviour index (Eq. 1) - P W power input - Re liquid slug Reynolds number ( _L(u _G +u _L) D _c/_eff) - Sc Schmidt number ( _eff/( _L D _L )) - Sh Sherwood number (k _La D _c ² /D_L) - t s time - u _B(u_sw) m s^–1 bubble (swarm) rise velocity - u _G(u_L) m s^–1 superficial gas (liquid) velocity - V(V_L) m³ reactor (liquid) volume Greec Symbols W m^–2 K^–1 heat transfer coefficient - y(y _eff) s^–1 (effective) shear rate - _G relative gas holdup - s relaxation time of viscoelastic liquid - _L(_eff) Pa s (effective) liquid viscosity (Eq. 1) - _L kg m^–3 liquid density - N/m surface tension     

Emission of microorganisms from biofilters

Experiments are reported on the discharge of microbial germs by biofilter systems used for the treatment of waste gases containing volatile organic compounds. The systems investigated concern six full-scale filter installations located in the Netherlands in several branches of industry, as well as a laboratory-scale installation used for modelling the discharge process. It is concluded that the number of microbial germs (mainly bacteria and to a much smaller extent moulds) in the outlet gas of the different full scale biofilters varies between 10³ and 10⁴ m^–3, a number which is only slightly higher than the number encountered in open air and of the same order of magnitude encountered in indoor air. It is furthermore concluded that the concentration of microorganisms of a highly contaminated inlet gas is considerably reduced by the filtration process. On the basis of the experiments performed in the laboratory-scale filter bed, it is shown that the effect of the gas velocity on the discharge process results from two distinctive mechanisms: capture and emission. A theoretical model is presented describing the rate processes of both mechanisms. The model presented and the experimentally determined data agree rather well.List of Symbols a _s m^–1 specific area of the packing material - C m^–3 microbial gas phase concentration - C _e , C _i m^–3 microbial concentration in the exit and inlet gas resp. - CFU colony-forming-units - d _c , d _m m diameter of collecting and captured particle resp. - D m diameter of the filter bed - E single particle target efficiency - H m bed height - k _c s^–1 first order capture rate constant per unit of bedvolume - k _e m^–3 emission rate constant per unit of bedvolume - n number of observations - r _c , r _e m^–3 s^–1 capture and emission rate per unit of bed-volume - Re = Reynolds number - S _t = Stokes number - u m s^–1 superficial gas velocity - u _m m s^–1 superficial gas velocity at which C _e = C _i Greek Symbols void fraction of the filter bed - kg m^–3 density of the gas phase - _m kg m^–3 density of captured particle - Pa s dynamic gas phase viscosity - = filter bed efficiency     

Phytoplankton primary production in a shallow,well- mixed,hypertrophic South African lake

This paper reports on a two-year analysis of the wind climateand its effect on phytoplankton primary production in ashallow (mean depth = 1.9 m), hypertrophic South Africancoastal lake, Zeekoevlei. The lake is subject to continuousmixing of the euphotic zone (Z _eu = 0.8 m), andcomplete mixing of the water column to the mean depth on adaily basis. Median annual wind speeds, prevailing fromeither the north or the south, were 6.4 m s^–1. There wasan almost total absence of calms, measured as hourly meanwind speeds of <1 m s^–1. Notwithstanding the highfrequency of mixing, the lake supports a dense population ofphytoplankton, dominated by Cyanophyte and Chlorophytespecies. Mean concentrations of chlorophyll-a were240 g l^–1. The attenuation of photosyntheticallyavailable radiation, PAR, was high, with mean K _dvalues of 6.4 m^–1 and water transparencies of <0.5 m.Levels of primary productivity, determined using the lightand dark bottle oxygen method, were very high, comparable toor exceeding that of the most productive systems yet studied.Maximum volumetric productivity ranged from 525 to 1524 mg Cm^–3 h^–1, and was confined to the upper 0.5 m of thewater column. Daily areal productivity, P _d,varied between 1.2 and 4.3 g C m^–2 d^–1, and that ofthe maximum chlorophyll-a specific photosynthetic rate,P _{B max}, between 1.6 and 7.9 mg C (mgChl-a)^–1 h^–1. Primary production was limited bywater temperature and the attenuation of PAR. The highfrequency of wind-induced mixing resulted in regular mixingof the phytoplankton through the euphotic zone, and reducedthe overall importance of P _max at a single layer inthe depth profile. Similarly, the regularity of mixing wasrecognized as a limitation of the incubation of bottle chainsto determine primary production levels.     

Enhanced shear protection and increased production of an anti-tumor polysaccharide by Agaricus blazei in xanthan-supplemented cultures

Xanthan supplementation provided shear protection and stimulated polysaccharide production by Agaricus blazei. In xanthan-free cultures, the optimal cell yield, 0.63 g biomass g^–1 glucose, and product yield, 0.19 g polysaccharide g^–1 glucose, were, respectively, when the critical impeller tip speed was 50.3 cm s^–1 and 100.5 cm s^–1. Furthermore, the critical impeller tip speed of cell yield shifted from 50.3 cm s^–1 to 100.5 cm s^–1 with the supplementation of 1 g xanthan l^–1. Maximum specific product yield, namely 0.74 g polysaccharide g^–1 biomass, was achieved with inlet air supply of 3% O₂ and impeller tip speed of 100.5 cm s^–1.     

Microcalorimetric investigations of the metabolism of yeasts. growth in batch and chemostat cultures on ethanol medium

Summary In the presence of protein, Hansenula polymorpha cultivation medium exhibits a maximum volumetric mass transfer coefficient, k_La, as function of the employed antifoam agents (soy oil and Desmophen 3600). With diminishing superficial gas velocity this maximum disappeas.Symbols E_G Relative gas holdup - k_La Volumetric mass transfer coefficient (s^–1) - w_SL Superficial liquid velocity (cm s^–1) - w_SG Superficial gas velocity (cm s^–1)     

Optimisation of agitation and aeration in fermenters

The problem of optimising agitation and aeration in a given fermenter is addressed. The objective function is total electric power consumed for agitation, compression and refrigeration. The major constraint considered is to ensure that the dissolved oxygen concentration is above the critical value. It is shown that it is possible to analytically calculate the optimal pair (air flowrate, stirrer speed) and that, at least for the industrial antibiotics fermentation used as case-study, the optimum lies within a window for satisfactory operation, limited by other possible constraints to the problem. Savings achievable by optimal operation as compared with current industrial procedure were found to be around 10% at pilot plant scale (0.26 m³) and 20% at full scale (85 m³).List of Symbols A fermenter cross sectional area (m²) - C dissolved oxygen concentration (mole m^–3) - C ^* DO concentration in equilibrium with the gas (mole m^–3) - C _crit critical DO concentration (mole m^–3) - C _p specific heat of air at constant pressure (J kg^–1 K^–1) - C _sp dissolved oxygen set point (mole m^–3) - C _v specific heat of air at constant volume (J kg^–1 K^–1) - D agitator diameter (m) - f pressure correction of air flow-rate - (Fl _g)_F aeration number at flooding - (Fr _g)_F froude number at flooding - k coefficient in expression for mass transfer coefficient - K _La volumetric oxygen transfer coefficient (s^–1) - m power exponent in expression for mass transfer coefficient - n gas flow rate exponent in expression for mass transfer coefficient - n ^* number of impellers - N rotation speed (s^–1) - N _F rotation speed at flooding (s^–1) - N _p unaerated power number - N _pg aerated power number - OUR Oxygen Uptake Rate (mole m^–3 s^–1) - p ₀ atmospheric pressure (N m^–2) - p ₁ compressor exit pressure (N m^–2) - p ₂ pressure at the bottom of the fermenter (N m^–2) - p ₃ pressure at the top of the fermenter (N m^–2) - P _c compression power (W) - P _d power added by expansion (W) - P _ev power removed by evaporation (W) - P _g agitation power (W) - P _m power added by metabolism (W) - P _r power removed by refrigeration (W) - P _t total power (W) - Q air flow-rate at atmospheric conditions (m³ s^–1) - Q _f air flow-rate at average fermenter conditions (m³ s^–1) - s ₀ absolute humidity at atmospheric conditions - s ₃ absolute humidity at fermenter exit - T tank diameter (m) - V liquid volume (m³) - v _s gas superficial velocity (m s^–1) - _i parameter defined in the text - safety margin for dissolved oxygen (mole m^–3) - ratio of specific heats of air - _g agitation efficiency - _c compression efficiency - _r refrigeration efficiency - liquid density (kg m^–3) - _g air density (kg m^–3) - latent heat of vaporisation of water (J kg^–1) The authors are grateful to Elsa Silva, Carlos Lopes, Carlos Aguiar, Fernando Mendes, and Alexandre Cardoso, who helped with parts of this work, and to CIPAN for permission to publish these data.     

Wind,surface water temperature,surface salinity and pollution in the area of the Banc d'Arguin,Mauritania

Based on meteorological observations at Nouadhibou Airport, Mauritania, over the period 1953–1990 frequency distributions and averages are computed for wind speed and direction. Average wind speed reaches a maximum in May–June (9 m s^–1) and a minimum in November–December (6 m s^–1). About 85% of the time winds blow from northerly directions. Based on a data set collected since 1952 maps of surface water temperatures are constructed. Based on these maps and on observations on salinity an hypothetical current pattern for the shallow area between Nouadhibou and Cap Timiris, Mauritania, is proposed.     

Experimental measurement of resource competition between planktonic microalgae and macroalgae (seaweeds) in mesocosms simulating the San Francisco Bay-Estuary,California

Planktonic algae are not abundant in the brackish waters of San Francisco Bay-estuary (mean chlorophyll a 5 µg 1^–1), despite the high level of nutrients usually present due to the input of treated sewage from 3 million people. Macroalgae (seaweeds) are sometimes locally abundant in the Bay. Phytoplankton are abundant (chlorophyll a > 50 µg 1^–1) and seaweeds uncommon in the almost freshwater Delta and upper estuary despite lower nutrient levels. Direct competition between these algal groups could explain the observed distributions.Given the size of the algae, large containers were needed for the determination of possible resource competition. Experiments were carried out in flow-through mesocosms (analog tanks) of 3 m³ volume. The macroalgae Ulva lactuca or Gigartina exasperata and a diatom-dominated phytoplankton, all from San Francisco Bay, were grown separately and together and with and without treated sewage effluent or other artificial nutrient additions. When grown alone phytoplankton and macroalgae were greatly stimulated by wastewater addition to unmodified baywater. The phytoplankton grew much more slowly in the presence of natural densities of Ulva. Allelochemical effects were tested for but not demonstrated.Resource competition for inorganic nitrogen was determined to be the probable cause of the depression of phytoplankton by Ulva. At its rapid growth rates in the flow-through mesocosms (up to 14% day^–1) this macroalga can reduce inorganic nitrogen to low levels. Ulva has a greater affinity (lower KS) for nitrogen than do some of the plankton of the Bay. Ulva may outcompete phytoplankton by reducing nitrogen to levels below those capable of supporting phytoplankton growth. Other macroalgae such as Gigartina and Enteromorpha need to be studied to determine if they also can depress phytoplankton growth by resource competition.     

Nitrate transformation and water movement in a wetland area

The NO₃ ^– transformation capacity of a riparian zone at Rabis stream, Denmark, was investigated for a period of 2 years. The riparian zone of 15–25 m received NO₃ ^–-containing groundwater from the adjoining agricultural areas. The water flows as surface runoff along the surface of the wetland and in the root zone towards the stream. Changes in water chemistry, water balance and mass transport were investigated. The riparian zone acted as a buffer zone for NO₃ ^–, PO₄ ^3– and dissolved Fe²⁺. The NO₃ ^–-transformation capacity of the wetland was about 400 kg N ha^–1 y^–1, but varied seasonally. A simple rearrangement of drain systems in wetland areas can probably reduce the NO₃ ^– content of Danish surface waters by 20 000–50 000 t N y^–1.     

Seasonal changes in composition and biomass of epilithic algal floras of a chalk stream and a soft water stream with estimates of production

Microscopic epilithic algae in the River Itchen at Otterbourne near Southampton and in the Ober Water in the New Forest were studied during 1984 and 1985. The River Itchen rises from chalk springs and has a steady pH near 8.2 and a mean alkalinity of 236 mg HCO₃ 1^–1; at the study site the river is about 16 m wide and 20 cm deep, with a mean flow rate of 0.33 m s^–1 and a discharge ranging through the year between 0.34 and 2.46 m³ s^–1. The Ober Water, which drains sands and gravels, has a pH between 6.9 and 7.2 and a mean alkalinity of about 50 mg HCO₃ 1^–1; at the study site it is about 6 m wide, with a mean flow rate of 0.27 m s^–1 and a discharge ranging through the year between 0.08 and 1.0 m³ s^–1.Epilithic algae removed from the pebbles that form the major part of the beds of both streams show seasonal changes in abundance and composition. Diatoms peaked in April/May and dominate the epilithic flora in both streams, comprising 70–95% of all algal cells; highest numbers of chlorophytes occurred in summer and cyanophytes increased in autumn. The species composition of the epilithic flora in the two streams was different, as was the population density; algal cell numbers ranged between 500 and 7000 cells mm^–2 of stream floor in the River Itchen and between 8 and 320 cells mm^–2 of stream floor in the Ober Water. The chlorophyll a content of epilithic algae in the River Itchen ranged between 115 and 415 mg m^–2 of stream floor, representing an annual mean biomass of about 8 g m^–2, whereas in the Ober Water a chlorophyll a content of 2.2 to 44 mg m^–2 of stream floor was found, representing an annual mean biomass of about 1 g m^–2. Cautious estimates of the annual production of epilithic algae in these streams suggest a value of about 600 g organic dry weight m^–2 in the River Itchen and about 75 g m^–2 in the Ober Water.     

Animal coat color and radiative heat gain: A re-evaluation

Summary Thermal resistance and heat gain from simulated solar radiation were measured over a range of wind velocities in black and white pigeon plumages. Plumage thermal resistance averaged 39% (feathers depressed) or 16% (feathers erected) of that of an equivalent depth of still air. Feather erection increased plumage depth four-fold and increased plumage thermal resistance about 56%. At low wind speeds, black plumages acquired much greater radiative heat loads than did white plumages. However, associated with the greater penetration of radiation into light than dark plumages, the radiative heating of white plumages is affected less by convective cooling than is that of black plumages. Thus, the heat loads of black and white plumages converge as wind speed is increased. This effect is most prominent in erected plumages, where at wind speeds greater than 3 ms^–1 black plumages acquire lower radiative heat loads than do white plumages. These results suggest that animals with dark-colored coats may acquire lower heat loads under ecologically realistic conditions than those forms with light-colored coats. Thus, the dark coat colors of a number of desert species and the white coat color of polar forms may be thermally advantageous.These results are used to test a new general model that accounts for effects of radiation penetration into a fur or feather coat upon an animal's heat budget. Even using simplifying assumptions, this model's predictions closely match measured values for plumages with feathers depressed (the typical state). Predictions using simplifying assumptions are less accurate for erected plumages. However, the model closely predicts empirical data for erected white plumages if one assumption is obviated by additional measurements. Data are not sufficient to judge whether this is also the case for erected black plumages.List of Symbols A body surface area (m²) - a _L long-wave absorptivity of coat - a _s short-wave absorptivity of coat - d characteristic dimension (m) - E evaporative water loss (kg m^–2 s^–1) - h coat thermal conductance (W m^–2 °C^–1) - k convection constant (s^1/2 m^–1) - l coat thickness (m) - L _i long-wave irradiance at coat surface (W m^–2) - M metabolic heat production (W m^–2) - m body mass (kg) - P plumage mass (kg) - p probability per unit coat depth that a penetrating ray will strike a coat element (m^–1) - q(Z) radiation absorbed at level z (W m^–2) - R _abs radiation absorbed by animal (W m^–2) - r _e external resistance to convective and radiative heat transfer (s m^–1) - r _Ha boundary layer resistance to convective heat transfer (s m^–1) - r _Hb whole-body thermal resistance (s m^–1) - r _Hc coat (plumage) thermal resistance (s m^–1) - r _Ht tissue thermal resistance (s m^–1) - r _s apparent resistance to radiative heat transfer (s m^–1) - r(Z) thermal resistance from level z to coat surface (s m^–1) - S _i short-wave irradiance at coat surface (W m^–2) - S ^– radiant flux going toward skin surface (W m^–2) - S ⁺ radiant flux going away from skin surface (W m^–2) - T _a air temperature (°C) - T _b core body temperature (°C) - T _e equivalent black-body temperature (°C) - T _e air temperature plus temperature increment due to longwave radiation (°C) - u wind velocity (m s^–1) - V heat load on animal from short-wave radiation (W m^–2) - z depth within coat (m) - short-wave absorptivity of individual hairs or feather elements - emissivity - {ie211-1} - latent heat of vaporization of water (J kg^–1) - short-wave reflectivity of individual hairs or feather elements - {ie211-2} short-wave reflectivity of coat - {ie212-1} short-wave reflectivity of skin - c _p volumetric specific heat of air (J m^–3 °C^–1) - Stefan-Boltzmann constant (W m^–2 °K^–4) - short-wave transmissivity of individual hairs or feather elements - {ie212-2} short-wave transmissivity of coat