Showing papers in "Limnology and Oceanography in 1983"

C:N:P ratios of benthic marine plants1

Abstract: The median C:N:P atomic ratio of benthic marine macroalgae and seagrasses is about 550:30:1. Benthic plants are much more depleted in P and less in N, relative to C, than phytoplankton. The amount of nutrients required to support a particular level of net production is much lower for benthic marine plants than it is for phytoplankton.

Time and space scales of vertical mixing and advection of phytoplankton in the upper ocean

Abstract: The dependence of phytoplankton photosynthesis on light intensity may be altered by the range and frequency of variations in light intensity recentlv experienced by the organisms. A major source of the fluctuations in light intensity experienced by phytoplankton in the upper ocean is vertical motion. We estimate time and space scales for \\Tertical displacements of phytoplankton caused by turbulent mixing, internal waves, Langmuir circulations, and double diffusive processes. In the surface layer, depending on windspeed, current shear and stratification, we find that time scales for cycling of phytoplankton by turbulent eddies and mixing vary from about 0.5 h to hundreds of hours for vertical displacements of the order of 10 m. In the seasonal thermocline, turbulent diffusive time scales for displacements as small as several meters are weeks to months, whereas similar displacements by internal waves occur over periods of several minutes to several hours, according to the strength of the density stratification, and are then dominant. Langmuir cells seem to scale as the large turbulent eddies and need not be treated separately, and double diffusive processes seem to be of minor importance. The formulation used here of a vertical turbulent diffusion coefficient K, as a function of observable quantities-e the rate of dissipation of turbulent kinetic energy, and N the local buoyancy frequency-should also be us&d for estimating vertical fluxes of nutrients. In addition, this formulation is reversible in time and can be used to estimate the recent depth and light history of phytoplankton taken from the upper ocean. Traditionally the dependence of the photosynthetic production rate of phytoplankton on light intensity has been described by “P vs. I” curves relating the rate of photosynthetic production, P, to increasing light intensity, I, determined usually from experiments where portions of the same sample are incubated at several different constant light intensities for the same period. The uptake of labeled carbon over that period is measured and considered to be an index of the photosynthetic production (Peterson 1980). Division by the time interval gives the photosynthetic rate. A smooth curve fitted through the data resembles one of the family of curves shown in Fig. 1 (which, for illustration, has been generated from the model equation of Platt et al. 1980): P(I) = aem”‘( 1 eeVr). (1) Several problems exist: different curves are often found at different times of day (provided the incubation period is sufficiently brief, say 2-4 h), at different depths, during different seasons, and with different organisms (Harris 1973; MacCaull and Platt 1977; Platt et al. 1980). Furthermore, time-course measurements of varying photosynthetic production P(t)

Limitation of marine phytoplankton reproductive rates by zinc, manganese, and iron1

Abstract: The reproductive rates of 21 species of marine phytoplankton were measured in media in which free zinc, manganese, and iron ion activities were controlled at different levels using EDTA-trace metal ion buffer systems. In general, the reproductive rates of neritic species were limited by zinc activities below 1O-11.5 M, while those of oceanic species were either not limited or only slightly limited at the lowest zinc activity attained in the experiment, ca. lo-l3 M. The reproductive rates of oceanic coccolithophores were either not limited or only slightly limited by the lowest manganese ion activity attained, ca. 10-l’ M, but those of a neritic coccolithophore and all diatoms, both neritic and oceanic, were limited below a manganese activity of 10-l” M. Neritic species had reduced reproductive rates in media containing clod7 M iron while oceanic species reproduced at maximal or close to maximal rates in the media with the lowest iron concentrations, ca. IO+’ M. The habitat-related patterns in zinc, manganese, and iron requirements of oceanic and neritic species are consistent with the oceanic-neritic distributions of concentrations of these metals. This similarity in requirement and distributional patterns provides evidence that Zn, Mn, and Fe availability have been important selective forces on marine phytoplankton populations and communities. The nutrients most frequently considered to limit the reproductive rates of phytoplankton in the ocean are the macronutrients nitrogen, phosphorus, and silicon. The possibility that trace metal micronutrients can be of significance in the ecology of phytoplankton has been considered occasionally (Harvey 1947; Ryther and Guillard 1959; Ryther and Kramer 1961; Barber and Ryther 1969), but they have not received the attention and quantitative analysis that macronutrients

Microelectrode studies of the photosynthesis and O2, H2S, and pH profiles of a microbial mat1

Abstract: The profiles of O,, H,S, and pH within a microbial mat of the hypcrsaline pond Solar Lake, Sinai, were measured by 2-208pm-thick microelectrodes during diurnal and artificial light cycles. The oxygen concentration in the photic layer varied from a maximum of 1,400 PM during the day to 0 during the night. The pH in the same layer varied between 9.6 in the early afternoon and 7.7 in the early morning. Sulfide was not present in the photic zone during the day, but built up to about 50 /IM during the night. The diffusion gradients of sulfide and oxygen were very steep and the two compounds coexisted in a layer only 0.25 mm thick during the day. Diffusion flux calculations showed that the average turnover time of sulfide within this layer was 21 s. The rapid turnover indicated that the oxidation of sulfide must be biologically mediated. Oxygenic photosynthesis was measured by a new oxygen microprofile method which accurately determines the vertical distribution of photosynthetic activity. There was no difference in the efficiency of photosynthesis between morning and afternoon. The photosynthetic efficiency of the whole mat was about fourfold higher at low light intensities, ~120 PEinst. m-z.s-1, than at high light intensities, 120-1,600 pEinst*m-“es-‘. Anoxygenic photosynthesis within the mat was not quantitatively important.

Hydrodynamic processes affecting benthic recruitment1

Abstract: Recruitment of animals into initially dcfaunated sites containing simulated stalks of a marsh grass was studied on an intertidal sandflat Laboratory flume experiments were used to predict the effects of these structures on near-bed flow, the sediment size-frequency composition, and the patterns and rates of benthic recruitment The effects of simulated stalks on both rates of fluid transport near the bed and boundary shear stress change profoundly with their numerical density Patterns of sedimentation in the field and patterns and rates of rccruitment of several taxa depended strongly on the presence and numerical density of these structures, in agreement with a priori predictions assuming passive (ie purely hydrodynamic) dispersal Hydrodynamic (or other physical) effects of manipulation are important and form an additional, but infrequently posed, null hypothesis against which biological effects such as substrate selection, competition, predation, or disturbance should be tested

Sedimentation, accretion, and subsidence in marshes of Barataria Basin, Louisiana1

Abstract: Vertical accretion and sediment accumulation rates were determined from the distribution of 137Cs in cores collected from freshwater, intermediate, brackish, and salt marshes in the Barataria Basin, Louisiana. Vertical accretion rates vary from about 1.3 cm*yr-l in levee areas to 0.7 in backmarshes. Mineral sediment content of the marsh soil profile decreased with distance from the coast. However, vertical accretion rates were about equivalent in areas of the same type. Autochthonous organic matter appears to be an important factor defining the process and rate of vertical accretion, especially in the freshwater marshes. Except in natural levee areas, marsh accretion rates are less than subsidence measured by water level data, however this alone cannot account for observed land-loss patterns in the basin area.

Optical efficiency factors of some phytoplankters1

Abstract: Absorption and total scattering coefficients of four phytoplankton species grown in batch cultures were measured simultaneously. Backscattering coefficients were obtained by using an integrating sphere. These coefficients are transformed into specific coefficients, i.e. related to a unit of concentration in chlorophyll a, and also into dimensionless efficiency factors characteristic of the cells. The specific coefficients differ noticeably from one species to another. Total scattering and backscattering coefficients are clearly depressed near and inside the absorption bands. These minima can be interpreted by combining the theory of anomalous dispersion with Mie-Lorentz theory applied to polydisperse suspensions. The backscattering efficiency (ratio of backscattering to total scattering) of algal cells appears to be very low (typically ~0.1%). These different results must be taken into consideration when interpreting and modeling the optical properties of seawater, particularly ocean color. They also must be considered when modeling photosynthesis, since the variations in the light-harvesting ability of the cells intervene directly in the quantum yield estimate. The optical properties of natural waters depart from those of ideally pure water because of the presence, in variable amounts, of diverse dissolved and particulate substances. From an optical point of view, these can be considered as belonging to four groups: live algal cells; biogenous detritus associated with and deriving from these algae; terrigenous particles and resuspended sediment; and dissolved organic (yellow) substances. Of these, phytoplankton, as the only primary producer in the pelagic environment, is of particular interest. In addition, the algal cells and their debris predominantly determine the optical properties of the water in the open sea, away from land and bottom influence. Depending on the physiological state of the algae and on environmental conditions, primary production is effected through photosynthesis, with a varying yield. Such a yield, estimated on a quan

Photosynthesis and structure of benthic microbial mats: Microelectrode and SEM studies of four cyanobacterial communities1

Abstract: The microzonation of photosynthetic organisms in four cyanobacterial mats of Solar Lake, Sinai, was studied by light and scanning electron microscopy. The zonation was compared to the distribution of photosynthesis and of O/sub 2/, H/sub 2/S, and pH. Microelectrodes were used to measure the chemical gradients as well as the photosynthetic rates by a newly developed technique which allows a spatial resolution of 100 ..mu..m. Two-dimensional maps of oxygen and photosynthesis distribution at the mat surface demonstrated a strong heterogeneity with rapid oxygen production within dense diatom tufts of 0.2-0.5-mm diameter overgrowing the cyanobacteria. Gas bubbles within the mat served as dynamic reservoirs for oxygen during light-dark cycles and buffered against extreme diurnal variations between oxygen and sulfide.

Nitrogen cycling in different types of sediments from Danish waters1

Abstract: Variations in sediment N:C ratios were correlated with water depth and season. 15NH,+ was used to measure the rates of NH,+ production (d) and incorporation into bacterial cells (i) in sediments from different stations, at different seasons. The validity of the rates d and i was indicated by the predicted correlation of cl:i ratios with N:C ratios of the sediment, and the predicted N:C ratio at which net NH4+ uptake occurred. There was also a correlation between rate cl and product (total NH,+). In the O-2-cm stratum correlations were also established between d, exchangeable NH4+ pool, ratio exchangeable NH?+ : porewater NH4+, flux of NH,+ from sediment, and flux of NH4+ into exchangeable pool. The NO:,- flux from sediment was correlated with nitrification rate and with season. Benthic infauna increased the flux of NHI’ from the sediment by 50%. The rates of transfer of nitrogen (NO,-, NH?+, N,) from sediment to water were 44-66% of the net rates of organic nitrogen mineralization (d - i). Flux of NO,- + NII,+ from the sediment could supply 30-82% of the nitrogen requirement of the planktonic primary producers.

Microbial degradation of dissolved proteins in seawater1

Abstract: An experimental protocol using radiolabeled proteins was developed to investigate the rates and mechanisms whereby dissolved proteins are degraded in natural marine plankton communities. The results of field observations and laboratory experiments indicate that proteins are degraded by a particle-bound, thermolabile system, presumably bacteria-associated enzymes, with an apparent half-saturation constant of ca. 25 ..mu..g bovine serum albumin (BSA) per liter. Gel permeation chromatography indicated that peptides of chain length intermediate between BSA and the final products of degradation (MW<700) do not accumulate in the medium. Competition experiments indicate that the system is relatively nonspecific. Turnover rates for the protein pool in samples collected in the Southern California Bight were of the same order of magnitude as the turnover rate of the L-leucine pool and were correlated with primary productivity, chlorophyll a concentrations, bacterial abundance and biomass, and L-leucine turnover rate. These data suggest that amino acids derived from proteins are utilized preferentially and do not completely mix with the amino acids in the bulk phase.

Day‐to‐day variations in the spring‐summer photosynthetic parameters of coastal marine phytoplankton

Abstract: The day-to-day variations over a 70-day period in the parameters describing the lightsaturation curve of natural assemblages of coastal marine phytoplankton were examined and related to changing environmental conditions. The initial slope, ~8, and the light-saturated rate, P mB, both showed a threefold variation. Correlation and regression analysis attributed most of the variation in aS and P, B to factors relating to community structure. Changes in community structure resulting from the normal progression of spring-summer conditions were interrupted periodically by transient physical phenomena (passage of storms, periods of upwelling, etc.). The importance of physical transients to the short term dynamics of the phytoplankton production system places severe constraints on the development of predictive models of phytoplankton production.

Food limitation of production by adult Acartia tonsa in Narragansett Bay, Rhode Island1

Abstract: Egg production, dry weight, cephalothorax length, and condition factor were measured for adult Acartia tonsa females collected twice weekly from Narragansett Bay, R.I., during summer 1979 and incubated in ambient bay water and in ambient bay water enriched with laboratorycultured algae. Egg production, dry weight, and condition factor of copepods in the ambient bay water fluctuated considerably (ranges 1.6-51.6 eggsafemale-‘*d-l, 7.37-16.60 fig dry wt, and 1.09-2.37 condition factor) and closely followed the seasonal trends in Chl a and particulate carbon and nitrogen. Cephalothorax length remained fairly constant during the study. The overall mean egg production rate, dry weight, and cephalothorax length of the copepods after incubation for 48 h in the algae-enriched water were significantly greater than for copepods incubated in ambient bay water (mean values 45.9 vs. 25.3 eggsafemale-‘*d-l, 13.2 vs. 11.8 kg dry wt, and 901.7 vs. 891.8 pm long). Since body size and egg production in adult A. tonsa responded rapidly to a change in food availability, the copepods must have been continuously food limited in Narragansett Bay during summer.

Starvation in Daphnia: Energy reserves and reproductive allocation1

Abstract: The relationship between energy reserves (biomass and triacylglycerol) and starvation time is investigated for two planktonic Cladocera, Daphnia. galeata mendotae and Daphnia magna. Triacylglycerol storage is correlated to total individual biomass independently of body size. Adult biomass increases twofold to threefold during the intermolt, with triacylglycerol accounting for 16% of the total increase. The amount of triacylglycerol transferred into each egg depends on the adult’s feeding success. Starvation time is correlated to body mass; however, triacylglycerol storage and reproductive allocation modify the relationship. Although adult biomass and percentage of lipid both increase during intermolt, animals in late intermolt starve sooner than those in early-middle intermolt because of the transfer of energy reserves to the ovaries for reproduction. Daphnia magna neonates with high maternal lipid survived twice as long as neonates with low maternal lipid but similar body mass.

Relationships between bacteria and grain surfaces in intertidal sediments1

Abstract: Seasonal changes in total bacterial numbers and their associated mucus coatings in surficial sediments were examined. Bacterial numbers followed the temperature cycle, with highest numbers in summer. The specific surface areas of the sediments were measured rather than inferred from other granulometric properties; bacterial numbers were proportional to surface areas only for sample suites collected at the same time. Bacteria inhabited shallow depressions on sand and silt grains; they were not found on grains smaller than about 10 pm or inside smaller pores like those on weathered feldspar grains. Mucus coatings also followed a seasonal cycle, increasing in abundance and coalescence from spring into summer. These coatings accumulated clay grains, suggesting that the relationship of bacteria to surface area may be due to bacterial control of surface area rather than the reverse. Organic carbon concentrations in grain size separates of these sediments increased with decreasing size until the fine silt fraction, and decreased in the clay fraction; it is not clear, however, whether this trend is a result or a cause of bacterial colonization patterns. Particle surfaces are important habitats for sedimentary bacteria. Adsorption of nutrients to solid surfaces and an accompanying increase in bacterial biomass was demonstrated in the early laboratory work of ZoBell(1943). Subsequent measurements of bacterial numbers or metabolic activities in sediments have exhibited a strong inverse correlation with sediment grain size, implying a surface area dependence (Dale 1974; Hargrave 1972). However, this surface area dependence of bacteria has not yet been verified with direct measures of surface area. The difficulties in relating measured surface areas to other granulometric parameters have been pointed out by Mayer and Rossi (1982). Microtopography of sediment grains has also been implicated as a factor influencing bacterial colonization on sediment grains. In an optical microscope study of sand grains, Meadows and Anderson (1966) found bacteria in patches with large ’ This work was supported by NSF ISP 8011448 and NOAA Sea Grant WLRF-45. Contribution 8302 of the Maine Benthic Oceanography Group. 2 Present address: Department of LMarine Science, University of South Florida, St. Petersburg 33701. 3 To whom reprint requests should be directed. areas of bare suface between them; these patches were often found in hollows and cracks. Weise and Rheinheimer (1978) found the density of bacterial cells to be determined by microtopography, with the highest densities on subrounded or subangular grains. Frankel (1977) found that subangular to subrounded grains of hornblende supported fewer bacteria than relatively smooth biotite grains. The separated folia of the biotite grains provided a more protected habitat and consequently supported a larger population. The degree of protection seems to influence the population size of colonizing microbiota. Surface morphology affected both the total biomass and the community structure of the microbiota (including bacteria, algae, and grazers) on silica grains in a running seawater experiment (Nickels et al. 1981). Total microbial biomass was higher on grains with more surface irregularities. Smooth grains of the same size supported a lower population of procaryotes and microalgae, with an increase of microeucaryotic grazers. Extracellular exudates of bacteria have become subjects of increasing interest due to their potential roles in affecting the sedimentological and trophic status of sediments. There is, however, a limited literature describing mucus coatings on

Grazing on epiphytes1

Abstract: Abstruct A correlation was found between the seasonal epiphyte cycle in Lake Memphremagog (Quebec-Vermont), with a maximum in mid-June, and the abundance of grazers (mainly oligochaetes and chironomids). Evidence for a carrse and effect relationship was provided by exclosure-enclosure experiments. When grazers were excluded epiphyte biomass did not decline as it did in the lake. Addition of grazers to a dense epiphyte cover resulted in a decline qualitatively and quantitatively similar to that in the lake. Grazing pressure, calculated from general empirical equations for aquatic deposit feeders, was of the required order of magnitude to explain the decline in epiphyte biomass. Because similar seasonal epiphyte cycles have been described elsewhere these findings should have a wider relevance.

The development of marine calanoid copepods with comment on the isochronal rule1

Abstract: Development times of seven species of planktonic marine copepods were determined at 15°C and excess food. Although details of instar durations varied among species, common trends were evident in relatively brief prefeeding stages and disproportionately long first-feeding and C5 stages. Males tended to mature before females. There was no relationship between generation time and species size; ecologically dominant species developed from egg to adult in roughly the same time, 19–21 days. Isochronal development was most closely approached by species of Acartia but was not strictly followed by any of the animals studied. In population dynamics studies, the assumption of isochronality can result in substantial errors in estimates of instar-specific mortality rates and, consequently, can seriously bias the interpretation of mortality patterns in nature and their possible causes.

Coprecipitation of phosphate with calcite in a naturally eutrophic lake

Abstract: Phosphorus-rich deposits of Eocene volcanic rock have caused some lakes in the interior of British Columbia to become eutrophic without direct human influence. In Black Lake the soluble reactive phosphorus (SRP) usually exceeds 250 pg Pmliter-‘. When calcite precipitation occurred during blooms of Aphanizomenon, SRP was completely removed from the photic zone. In blooms with no calcite formation, SRP changed little. These observations were replicated by splitting the lake with a curtain. Calcite precipitation was also observed several times in four large enclosures (limnocorrals). The subsequent disappearance of phosphatc was correlated with an increase in pII and a reduction of Ca and alkalinity and not necessarily with primary production or algal biomass. Black Lake is a hypertrophic lake that is naturally enriched in phosphate derived from nearby volcanic rock. The drainage basin is uninhabited, so that Black Lake provides an opportunity to study eutrophication processes without high loadings of organic and toxic wastes. The soluble reactive phosphate (SRP) levels in the inlet stream and the adjoining Black and Yellow Lakes usually exceed 250 ,zg Pliter-‘. These high SRP levels allow direct observation of phosphorus biogeochemistry that previously has only been inferred from laboratory studies. The only major change in SRP concentration occurs early in August during a dense bloom of Aphanixomenon flos-aquae (surface Chl a: 150 pg. liter-l). -Calcium carbonate precipitation induced by the Aphanixomenon bloom appeared to be responsible for the removal of SRP by a coprecipitation reaction. We thank A. Tautz for assistance in 1979, especially for providing laboratory analysis. 0. Smith and S. Liptak provided occasional assistance. D. Nuttley did the chlorophyll cl analysis. W. H. Mathews provided advice on the Okanagan geology. A. Mudroch did the sediment analysis. K. Burnison, J. Barica, and K. Kelts reviewed the manuscript.

The effect of food quality on feeding and respiration by Daphnia and Diaptomus1

Abstract: measured in southern Green Bay water mixed with algal cultures to produce varying proportions of blue-green algae. These measurements along with observations of Daphnia mouthpart responses to these foods were used to assess the relative competitive potential of Duphniu and Calanoid copepods in lakes of varying trophy. Ratios of filtering and ingestion rate to respiration rate were used as a measure of energy input per unit of energy expended. Passive filtering and subsequent rejection of inedible algae by Duphniu result in higher ratios than those shown by Diuptomus in high quality foods, suggesting a competitive advantage in oligotrophic or mesotrophic lakes. Diuptomus selective feeding, on the other hand, results in higher ratios in the low quality food characteristic of eutrophic conditions. These results and data from the literature are used to propose a two-dimensional niche model to demonstrate the interaction between food quality and abundance on the competitive interaction between Calanoid copepods and Daphnia-like cladocerans.

Modes of cell capture in calanoid copepods1

Abstract: High-speed cinematography was used to observe adult female copepods feeding in pure cultures of roughly spherical algal cells ranging from 4.5 to 22.0 pm in diameter. Eucalanus pileatus and Puraculunus puruus detect and handle individual cells as small as 12 pm. Continuous low amplitude movement of the second maxillae and combing of the appendages is used by E. pileutus to capture cells smaller than the 12qm sensitivity threshold. Different energetic costs are probably associated with capturing small and large cells, and the probability of copepods encountering large cells should be greatly increased due to remote detection. The above suggests that descriptions of selective feeding in grazing trials using Coulter Counter data are influenced by the size above which the copepods can detect individual cells and by the proportions of the pregrazing particle spectrum larger and smaller than this threshold.

Carotenoid enhancement and its role in maintaining blue-green algal (Microcystis aeruginosa) surface blooms1

Abstract: Ah tract Photosynthetic pigment alteration by Microcystis aeruginosa in surface blooms was related to persistence and dominance by this blue-green alga. The progression of summer blooms coincided with rising carotenoid : chlorophyll a ratios. When analyzed by high performance liqllid chromatography (HPLC), carotenoids exhibited strong in vitro absorbance in the UV and near-UV regions. Increased cellular carotenoid content was accompanied by increased sulfate photosynthesis as well as increased photosynthetic efficiencies in surface Microcystis populations. These data indicate that radiant energy is most effectively utilized as a source of photoreducing power in the presence of elevated cellular carotenoid : chlorophyll a ratios of surface populations. It is concluded that enhanced cellular carotenoid synthesis increases light utilization in the low and middle regions of the photosynthetically active radiation (PAR) spectrum and provides protection from UV damage. This is shown to have a positive effect on photosynthetic CO, fixation and bloom persistence in surface waters.

Effect of competitive interactions between manganese and copper on cellular manganese and growth in estuarine and oceanic species of the diatom Thalassiosira1,2

Abstract: We investigated the relationship between growth rate and cellular manganese concentrations for an estuarine diatom Thalassiosira pseudonana (clone 3H) and a related oceanic species Thassiosira oceanica (clone 13-1). Both species were exposed to a matrix of low manganese and cupric ion activities using ethylenediaminetetraacetic acid (EDTA)-trace metal ion buffered seawater media. The growth rate of Mn-limited cultures was related to the cellular concentration of Mn, which in turn was directly related to manganese ion activity an d inversely to cupric ion activity. The interaction between manganese and cupric ion activities in controlling cellular manganese and growth rate could be explained quantitatively by competitive binding models in which copper competitively blocked either cellular manganese uptake or the binding of manganese within intracellular pools. Clone 13-1, isolated from Mn-poor Sargasso seawater, was able to grow more rapidly at low manganese ion activities than clone 3I-I, isolated from a eutrophic estuary, provided that cupric ion activity remained below ca. 10-l’ mol *liter-‘. Adaptation of 13-1 to growth at low Mn activities appeared to involve two mechanisms: a greater ability for cellular uptake of manganese and a lower cellular manganese requirement (i.e. Mn cell quota) for growth. Comparison of our data with estimates of manganese and cupric ion activities in marine waters suggests that manganese deficiency could be important in controlling phytoplankton growth rate or community composition in some marine waters.

Sulfate reduction in the salt marshes at Sapelo Island, Georgia1

Abstract: Sulfate reduction rates were measured in stands of Spartina dternijh-a at Sapelo Island, Georgia, in November 1980 by injecting tracer amounts of ‘%04’- into cores, incubating overnight, and analyzing for the incorporation oi ‘% into reduced sulfur compounds. Qualitatively, sulfate reduction in the Georgia marsh is very similar to that in the Massachusetts marshes we have studied: FeS, (pyrite or marcasite) is the major end product. Lesser amounts of soluble sulfides, iron monosulfides, and elemental sulfur are also formed. The rate of sulfate reduction (determined by the same method) is significantly lower during November in Georgia than in the Great Sippewissett Marsh in Massachusetts, 0.090 vs. 0.27 moles S042-*m--2* cl-l in stands of short Spartina. The lower rates in Georgia may reflect a lower rate of organic carbon input by belowground production. Sulfate reduction appears to be the major form of respiration in the sediments of salt marshes in Georgia as well as in Massachusetts.

A simple model to predict extinction coefficients and phytoplankton biomass in eutrophic waters1

Abstract: Data from nutrient-saturated rivers, estuaries, and coastal upwelling zones imply a simple relationship between phytoplankton standing crop, depth of the mixed layer, and extinction due to nonliving material. Systems evolve to a steady state where the optical depth of the mixed layer is between 5 and 10. The observations are interpreted using a model for light-limited growth of phytoplankton. Model parameters can be evaluated using measurements of total extinction coefficient, mixed layer depth, chlorophyll concentration, and suspended sediment concentration. Simple equations are derived for the capacity of polluted rivers to assimilate anthropogenic nutrients. These relations may be used to assess the effects of water pollution control projects on water quality.

Interactions of marine plankton with transuranic elements. 1. Biokinetics of neptunium, plutonium, americium, and californium in phytoplankton

Abstract: The abilities of seven clones of marine phytoplankton, belonging to six different algal classes, to accumulate transuranic elements were evaluated in laboratory culture experiments, Plutonium, americium, and californium were rapidly concentrated by all species, resulting in volume/volume concentration f&tors generally >105 for all species and all isotopes Two natural assemblages from the coastal Mediterranean behaved like the algal cultures Isotopes associated with cells by a passive adsorption to cell surfaces, with equilibrium between cells and water reached in 34 days Uptake of isotope was directly proportional to the number of suspended particles and the isotope concentration in the culture Equilibrium isotope concentrations differed between species, reflecting different numbers of transuranic binding sites on the cell surfaces Generally, the green and blue-green cells had less reactive surfaces than the diatoms Once accumulated, Am was lost more rapidly by green algae than by diatoms Elimination proceeded in two phases, a rapid initial loss and then a slower release The biological half-life for Am turnover in the slowly exchanging compartment in the diatom was lo-12 days No substantial diflerences in uptake were noted between cultures receiving Pu in the III-IV and V-VI oxidation states In contrast to the other elements, neptunium showed no detectable accumulation by any of the cells The results suggest that Pu, Cf, and Am would associate with marine particles which could transport them vertically, transfer them into the marine food web, or both, while Np would behave essentially conservatively in seawater

A continuous‐flow periphyton bioassay: Tests of nutrient limitation in a tundra stream1

Abstract: The effect of added nutrients on the periphyton of a tundra stream was tested during July and August. Flow-through systems consisting of a bank of clear plastic tubes containing racks of microscope slides were suspended from floats in the stream. Nutrients were enriched in the experimental tubes by siphoning concentrated nutrient solutions from Mariotte bottles into the upstream end of each tube. Slides from each tube were assayed at 2–6-day intervals for chlorophyll content and photosynthetic 14CO2 uptake. Levels of chlorophyll and CO2 uptake were significantly higher than the controls both in the tubes with 10 µg PO4-P · liter−1 of stream water and in those with P plus 100 µg NH4NO3− N·liter−1. Nitrogen alone gave no stimulation.