Showing papers in "Limnology and Oceanography in 1984"

Carbon and nitrogen determinations of carbonate‐containing solids1

Abstract: Two methods are described for determination of organic carbon, inorganic carbon, and total nitrogen in sediments, sediment trap materials, and plankton. Both methods discriminate organic and inorganic carbon by acidification, avoid losses of acid-soluble organic and inorganic matter, and utilize an automated CHN analyzer for all elemental determinations. Short-term precisions for organic carbon and total nitrogen are about ± 1% of the measured value with blank levels < 1.5 µg for each element.

The role of sedimentary organic matter in bacterial sulfate reduction: The G model tested1

Abstract: Laboratory study of the bacterial decomposition of Long Island Sound plankton in oxygenated seawater over a period of 2 years shows that the organic material undergoes decomposition via first-order kinetics and can be divided into two decomposable fractions, of considerably different reactivity, and a nonmetabolizable fraction. This planktonic material, after undergoing varying degrees of oxic degradation, was added in the laboratory to anoxic sediment taken from a depth of 1 m at the NWC site of Long Island Sound and the rate of bacterial sulfate reduction in the sediment measured by the ?S radiotracer technique. The stimulated rate of sulfate reduction was in direct proportion to the amount of planktonic carbon added. This provides direct confirmation of the first-order decomposition, or C; model, for marine sediments and proves that the in situ rate of sulfate reduction is organic-matter limited. Slower sulfate reduction rates resulted when oxically degraded plankton rather than fresh plankton was added, and the results confirm the presence of the same two fractions of organic matter deduced from the oxic degradation studies. Near-surface Long Island Sound sediment, which already contains abundant readily decomposable organic matter, was also subjected to anoxic decomposition by bacterial sulfate reduction. The decrease in sulfate reduction rate with time parallels decreases in the amount of organic matter, and these results also indicate the presence of two fractions of organic carbon of distinctly different reactivity. From plots of the log of reduction rate vs. time two first-order rate constants were obtained that agree well with those derived from the plankton addition experiment. Together, the two experiments confirm the use of a simple multi-first-order rate law for organic matter decomposition in marine sediments.

The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere1

Abstract: Previous work on the solubility of oxygen in freshwater has been extended to seawater. Measurements of the Henry coefficient in the ranges 0° < t < 45°C and 0< S < 50 fit the Setschenow relationship for the variation with salinity. The temperature dependence of the Setschenow coefficient for oxygen is found to be K = 0.0225034 ‒ 13.6083/T + 2,565.68/T2. The equation for the Henry coefficient as a function of temperature and salinity is used to calculate values for unit standard atmospheric concentrations (USAC) in freshwater and seawater in equilibrium with air at a total pressure of 1 atmosphere. It is estimated that the possible error in the new USAC values is no greater than ±0.1% and probably less. Tables and equations are presented for obtaining accurate USAC values in the ranges 0° < t < 40°C and 0 < S < 40. Simple procedures are given for calculating standard atmospheric concentrations at pressures different from 1 atm. The presence of sea salt has a negligible effect on the fractionation of the oxygen isotopes during solution.

Phosphorus versus nitrogen limitation in the marine environment1

Abstract: Limnological and marine geochemical opinion favors phosphorus limitation of organic production in aquatic environments, while marine biological opinion favors nitrogen limitation. Clues in the literature and nutrient budgets for selected marine ecosystems suggest that phosphorus vs. nitrogen limitation is a function of the relative rates of water exchange and internal biochemical processes acting to adjust the ratio of ecosystem N:P availability.

Prevention of growth of potentially dense phytoplankton populations by zooplankton grazing, in the presence of zooplanktivorous fish, in a shallow wetland ecosystem

Abstract: In two linked, shallow, freshwater basins, phytoplankton densities in summer were very different. Hudsons Bay supported a large stand of water lilies, and the adjacent open water was clear with chlorophyll a concentrations generally 100 pg*literl. Hudsons Bay water, in bioassays, could support great phytoplankton growth in summer and did so in spring and fall. The period of clear water coincided with the presence of the lily stand. Zooplankton populations were of rotifers and small-bodied Cladocera in Hoveton Great Broad, but mostly of Cladocera, including large-bodied individuals of plantassociated species, in Hudsons Bay. Zooplanktivorous fish were present and there was evidence of feeding by them in both basins. Coexistence with fish of the large, apparently efficiently grazing Cladocera in Hudsons Bay depended on provision of daytime refuges for the Cladocera among the lilies, and grazing was greatest in the adjacent open water at night. Grazing control was helped by a hydrological regime which favored small and rapidly growing phytoplankters, rather than inedible colonial forms with slow growth. Weed-associated grazers may be important in maintaining the dominance of aquatic plants in shallow lakes which would otherwise more rapidly become dominated by phytoplankton as nutrient loading increased.

The coupling of nitrification and denitrification in two estuarine sediments1,2

Abstract: Nitrification and denitrification in estuarine sediments were measured by /sup 15/N isotopic tracer techniques at two stations in the Patuxent River estuary for April and August. A close coupling of the two processes was demonstrated directly from the evolution of labeled N/sub 2/ following /sup 15/NH/sub 4//sup +/ amendments during spring experiments. In contrast, this coupled nitrification-denitrification was decreased by two orders of magnitude in the summer, even though the capacity for denitrification remained similar to spring levels. This pattern of sharply seasonal nitrification was corroborated with measurements of bacterial relative abundance. Ambient rates of nitrification-denitrification were inferred from /sup 15/N experiments in these sediments.

Dependence of relationship between inherent and apparent optical properties of water on solar altitude

Abstract: A computer simulation study, using the Monte Carlo calculation procedure, has been carried out to determine in what way the relationships between the apparent and the inherent optical properties of natural waters are affected by the angle of incidence of the photons on the surface. With the particular normalized volume scattering function used in these simulations, the vertical attenuation coefficient for downward irradiance at the midpoint of the euphotic zone, Kd(zm), can be expressed as a function of the absorption (a) and (b) coefficients, and the cosine of the incident photons just below the surface (µo), in accordance with Thus, as the direction of the incident light departs increasingly from the vertical, Kd(zm) increases but becomes progressively less responsive to increases in scattering at constant absorption. The irradiance reflectance just below the surface [R(0)] at all angles of incidence increases linearly with the ratio of the backscattering coefficient (bb) to the absorption coefficient, and at any value of bb/ a increases as the angle of the light departs further from the vertical, in approximate conformity with

Empirical analysis of zooplankton filtering and feeding rates1

Abstract: Multiple regression analysis of published zooplankton filtering and feeding rates yielded separate regression equations for cladocerans, marine Calanoid copepods, and all zooplankton. Ingestion rate was found to increase significantly with animal size, food concentration, and temperature. Filtering rate also increased with animal size and temperature, but declined as food concentration increased. The analysis suggests a difference in particle size preference between cladocerans and copepods. Experimental conditions such as crowding and duration also significantly affected filtering and feeding rates. The regression models allow examination of differences and similarities among zooplankton taxa, functional response, particle size selection, energy allocation, and threshold food concentration. The statistical models describe suspension feeding more precisely than either average literature values or verbal descriptions of trend. The results also suggest possible mechanisms of feeding limitation and provide a heuristic framework for the design of experimental analyses of zooplankton feeding in marine and freshwater systems.

A comparison of the abilities of freshwater algae and bacteria to acquire and retain phosphorus1

Abstract: Extant physiological and in situ data provide contradictory answers to the question of whether the bacterioplankton can outcompete the phytoplankton for phosphorus at natural concentrations. Two phytoplankton species and three bacterial spccics isolated from the epilimnion of Lake Memphremagog, Quebec, were grown in phosphorus-limited continuous cultures and their abilities to take up and retain phosphorus compared. The algae showed orthophosphate uptake kinetics comparable to those reported elsewhere. In contrast, the specific orthophosphate uptake rates (i.c. uptake per unit cell P) by the bacteria were variable, but much higher than the algal rates at the low P concentrations characteristic of natural waters. Algal and bacterial alkaline phosphatase activities were similar and provided no evidence that the algae could utilize organic P more efficiently than the bacteria. The bacteria showed some tendency to excrete P more readily than the algae but mixed culture experiments indicated that excretion did little to alter the long term partitioning of phosphorus between the algae and the bacteria. The kinetic data suggest that planktonic bacteria are unlikely to be limited by phosphorus in situ. Furthermore, our results are consistent with the hypothesis that the bacteria should bc markedly superior competitors at natural phosphate concentrations.

The prediction of internal phosphorus load in lakes with anoxic hypolimnia1

Abstract: Lakes with anoxic hypolimnia (anoxic lakes) have significantly lower values for phosphorus retention than do lakes with aerobic hypolimnia (oxic lakes). This difference may reflect an increased internal phosphorus load from the anoxic hypolimnia. Two models are given to predict internal phosphorus load (L;,,) in such lakes. The first predicts internal load as the difference between the observed phosphorus retention in anoxic lakes and that predicted (Rpred) by a formula that adequately describes phosphorus retention in oxic lakes. The second predicts internal load as the product of an average rate of phosphorus release from anoxic sediments, the surface area of the anoxic sediment, and the period of anoxia. Predictions of the first model compare favorably with 17 observed values of internal load; further data are required to test the second model. These models suggest that mean phosphorus concentration (TP) in anoxic lakes can be predicted in two ways. One can use whole-lake phosphorus budget models which implicilly incorporate internal phosphorus load, because they include a measurement of phosphorus retention. Alternatively, a term to account for the internal load can be added to current models based on external load (L,,,) and predicted retention (I&J, where

The marine biogeochemistry of selenium: A re-evaluation1

Abstract: Vertical and horizontal profiles from the North and South Pacific Oceans demonstrate the existence of three species of dissolved selenium: selenite, selenate, and organic selenide (operationally defined). In surface waters, organic selenide makes up about 80% of the total dissolved selenium, selenite concentrations are uniformly low, and selenate concentrations rise with increased vertical mixing. The organic selenide maximum (thought to consist of seleno-amino acids in peptides) coincides with the maxima of primary productivity, pigments, bioluminescence, and dissolved free amino acids. Deep ocean waters are enriched in selenite and selenate, while organic selenide is nondetectable. In suboxic waters of the tropical northeastern Pacific, organic selenide concentrations rise, while selenite values decrease. The downward flux of particulate selenium generally decreases with depth, and fluxing particulate selenium is found to be primarily in the (-2) oxidation state. These data allow a re-evaluation of the internal biogeochemical cycle of selenium. This cycle includes selective uptake, reductive incorporation, particulate transport, a multistep regeneration, and kinetic stabilization of thermodynamically unstable species. The marine biogeochemical cycles of many trace elements include the processes of uptake from dissolved to particulate form, particulate transport, and regeneration back to the dissolved state. Uptake can occur passively by adsorption onto particle surfaces and coprecipitation into solid phases, or actively by selective incorporation into biological tissues and skeletal material. The vertical transport of trace elements from the surface zone to the deep sea via detrital matter is a function of the type of carrier and of sinking rates. The regeneration of a particulate-bound trace element to the dissolved state can occur by simple dissolution of the carrier or by the complex microbial process of oxidative degradation. The regeneration of nitrogen provides an example of this latter process; several intermediates (e.g. ammonia, nitrite) occur in the production of nitrate from organic nitrogen. Oxidation-reduction reactions may also be an important process for trace elements such as selenium. Dissolved selenium may exist as selenate (+ 6), selenite (+4), or several possible forms of selenide (2). Previous studies have dealt with different aspects of the marine biogeochemical cycle of selenium. Sugimura et al. ( 1977) showed L This work supported by the National Science Foundation (OCE 79-23322 and 79-19928). 2 Present address: Department of Oceanography, Old Dominion University, Norfolk, Virginia 23508. both selenite and selenate to be present in oxic seawater, with higher concentrations in deep waters than at the surface. The presence of substantial amounts of selenite throughout the water column was surprising, since thermodynamics would predict that only selenate should be present in oxic seawater. Measures and Burton (1980a) and Measures et al. (1980) presented the first oceanographically consistent vertical profiles of selenate and selenite in the Atlantic and Pacific Oceans. They concluded that selenium displays nutrient-type behavior. Multiple correlations with silicate and phosphate were made, and it was suggested that selenium has both deep and shallow regeneration cycles, depending on the particulate phase (i.e. selenite is found with silica phases, while selenate is found in soft tissues as is phosphate). It was pointed out, however, that these conclusions assumed preservation of the original oxidation states. If, on the other hand, selenate was reduced during incorporation, oxidative regeneration could then produce the thermodynamically unstable selenite. The work by Measures et al. (1980) during the GEOSECS-I reoccupation emphasized a model involving particulate transport of selenite and selenate to deep water. Cutter (1982) found that in Saanich Inlet selenite and selenate concentrations decrease in the suboxic zone and are at the detection limits in anoxic water. The major

The effect of the Asiatic clam, Corbicula fluminea, on phytoplankton of the Potomac River, Maryland

Abstract: In the summers of the 1960s and 197Os, phytoplankton in the fresh, tidal Potomac River showed a downstream gradient of low to high abundance. Phytoplankton abundance in a 6-8-km segment ofthe river, in summer 1980 and 198 1, was 40-60% below that upstream and downstream, forming a “sag.” In 1980, the highest densities of the Asiatic clam Corbicula fluminea in the reach as the phytoplankton sag. Filtration rates indicate that the volume of the sag reach could be pumped through the Corbicula population in 3-4 days. Corbicula removed 30% of the phytoplankton chlorophyll a from a river water sample in 2 h. Pheophytin a in surficial sediments correlated well with clam biomass as a consequence of phytoplankton excreted in pseudofeces. The hypotheses that peak discharges, zooplankton, toxic substances, and nutrient limitation induced the sag were not supported.

Ammonium adsorption in marine sediments1

Abstract: One important reaction which affects dissolved NH4+ distributions in marine sediments is reversible adsorption on sediment solids. We investigate both the temperature dependency and spatial variability of the NH4+ linear adsorption coefficient, K, in marine sediments. For a wide range of environments, because of approximately offsetting variations in sediment porosity and properties such as clay mineral and organic matter content, K is nearly constant (1.3 ± 0.1) in terrigenous, surface, marine sediments. The value of K also does not vary significantly as a function of temperature. In biogenic and very high porosity (≳0.95) sediments K may be somewhat lower than for other sedimentary environments. Sediments containing seagrass detritus such as Thalassia may be expected to exhibit relatively high K values.

The relative importance of bacterioplankton and phytoplankton in phosphorus uptake in freshwater1

Abstract: In several studies of orthophosphate cycling in lakes, most of the phosphorus uptake has been associated with the smallest limnetic particles. The hypothesis that bacteria rather than phytoplankton are responsible for most P uptake in situ was tested in Lake Memphremagog by means of size fractionation of [32P]orthophosphatc uptake, [14C]glucose uptake (as an indicator of bacterial activity), and both [r4C]bicarbonate uptake and chlorophyll a (as indicators of algal activity). In biweekly samples from May to October, particles ~3.0 pm accounted for 72-98% (median 94%) of the uptake of orthophosphate. There was no diel variation in the fraction of uptake by particles ~3.0 pm. The bacterial contribution to the total community uptake of orthophosphate was estimated to range between 97 and 100% over all samples collected. However, the phosphorus released (shown not to be orthophosphate) was taken up almost entirely by the phytoplankton. The bacterioplankton apparently strongly dominates orthophosphate cycling in situ, while the phytoplankton seems to obtain most of its phosphorus from excreted organic P compounds.

Denitrification and nitrous oxide production in a coastal marine ecosystem1

Abstract: Denitrification was measured directly as the flux of N, from sediment cores collected at various times of year at three stations in the Narragansett Bay, R.I., area. Rates of N, production ranged from about 10 to 115 pmol N*m-2*h-1, with lowest values at 2°C in winter and highest at 15°C in summer. Denitrification represents a major sink for fixed N in the bay; annually the N, production is equal to about 50% of the fixed inorganic N loading to the bay from rivers, land, and sewage. About 35% of the organic nitrogen mineralized in the sediments is removed from the ecosystem by denitrification. The percentage of organic nitrogen being mineralized in the sediments as N20 relative to N, or N03- + NO,- is higher in polluted sediments than in relatively unpolluted sediments, but in all cases is < 10%. Brandt (1899) suggested that denitrifying bacteria were important in controlling the supply of available nitrogen in the ocean and, therefore, plankton production. While it is now established that N is usually the nutrient most limiting to phytoplankton production in marine waters (Thomas 1969; Ryther and Dunstan 197 l), the mechanisms controlling its supply are still not well understood. If Brandt’s hypothesis is correct, the role of denitrification should be especially evident in estuaries and other coastal areas where a significant portion of the nutrient supply comes from mineralization of organic matter in the sediments (see Nixon 198 1). During denitrification, nitrate or nitrite, instead of 02, is used as the terminal electro%acceptor for the oxidation of organic matter, and gaseous nitrogen is produced (Payne 1973). The abundant supply of organic matter and the low oxygen concentrations in coastal sediments would present favorable conditions for denitrification. No direct measurements of N2 production from subtidal coastal sediments have been reported other than those of Seitzinger et al. (1980). There is, however, considerable circumstantial evidence that denitrifi

The paradox of the plankton: Fluctuations of phosphorus availability maintain diversity of phytoplankton in flow-through cultures1

Abstract: Competition experiments with phytoplankton under steady state conditions have largely verified the competitive exclusion principle. Coexistence of species limited by different resources contributes little to the explanation of the natural diversity of phytoplankton. It is shown by multispecies experiments in flow-through cultures that pulsed input of a key nutrient allows the coexistence of species competing for the same resource.

Above‐ and belowground emergent macrophyte production and turnover in a coastal marsh ecosystem, Georgia1

Abstract: Seasonal patterns of aboveground plant mass and the depth distribution of live roots, rhizomes, and dead belowground organic matter were measured for Spartina alterniflora and Spartina cynosuroides in Georgia tidal marshes. Peak live aboveground biomass was 1.6 x higher for S. cynosuroides than for S. alterniflora. Live biomass was 2.4 x more belowground thanaboveground for S. cynosuroides and 1.7 x for S. alterniflora. Rhizomes made up 76 and 87% of live belowground biomass during the year. Mirrored patterns of biomass accumulation and loss in above- and belowground tissues during the year suggest the importance of seasonal storage and redistribution of organic matter. Belowground production was measured with a technique that partially accounts for midseason decomposition. Total plant production was estimated to be 7,620 g dry mass~m+.yr-’ for S. alterniJlora and 7,708 for S. cynosuroides. Belowground production was roughly 1.6 x aboveground production. Turnover rates for belowground live material were 1.42.yr’ for S. cynosuroides and 3.22.yr-’ for S. alterniflora. The fate of root and rhizome material, including the extent to which such material enters the estuarine or nearshore food webs, is not clear.

Chaoborus predation on typical and spined morphs of Daphnia pulex: Behavioral observations1

Abstract: Behavioral observations of Chaoborus americanus predation on juvenile instars of typical and spined forms of Daphnia pulex were used to answer two questions: Does the spincd morph (SM) have a higher escape efficiency than the typical morph (TM)? Is handling time of ingested SM longer than that of TM? Results indicate that SM was clearly superior to TM in escaping the grasp of both third and fourth instar Chaoborus larvae and visible injuries to escapees were rare. The escape efficiency of larger Daphnia was higher than that of smaller Daphnia when tested with fourth instar Chaoborus. Differences in handling time for the two morphs could not be demonstrated. Handling times were short but highly variable, being partly dependent on Chaoborus length and orientation of the prey item. Within the range of 0.8-1.3 mm, Daphnia body length had no discernible influence on handling time.

Porewater evidence for a dynamic sedimentary iron cycle in salt marshes1

Abstract: Dynamic transformations of iron occur seasonally at Great Sippewissett Marsh, Massachusetts. Small changes in the dissolved iron concentration in prewater represent only a small fraction of the iron involved in transformation reactions during the year. During the growing season, salt marsh grasses oxidize the sediment, and a large percentage of sedimentary pyrite is converted to an oxidized iron mineral. Over the fall and winter there is a net increase in pyrite as the grass is anaerobically decomposed. When oxidation rates in summer are high enough to neutralize the alkalinity produced by sulfate reduction and substantially lower the pH, oxidized iron minerals become increasingly soluble and iron levels in the porewater increase. If large amounts of soluble iron are lost by tidal flushing, iron availability may limit pyrite formation in later years. Sulfide concentrations in the porewater would then increase, leading to depressed growth of Spartina alterniflora. For most of the year the porewaters of Great Sippewissett were undersaturated with respect to all iron monosulfide minerals and supersaturated with respect to pyrite (FeS/sub 2/). Thus pyrite formation at Great Sippewissett probably occurs directly by reaction of polysulfides with iron and not by reactions of FeS with elemental sulfur. Porewaters were alwaysmore » undersaturated with respect to manganese minerals. Porewaters taken from marshes at Sapelo Island, Georgia, in fall were supersaturated with respect to pyrite at all depths and appear to be saturated for iron monosulfides below 12 cm at all sites.« less

Night synthesis of protein by algae1

Abstract: Dunaliella tertiolecta in culture showed rates of net protein synthesis at night nearly equal to those during the day. In night protein synthesis carbon stored in carbohydrates and metabolite pools was used, whereas sulfate was assimilated from the medium as needed. As a result, whole cell C:S ratios varied systematically over the diel cycle, while the C:S ratio of isolated protein remained constant. In the stationary phase, sulfate incorporation into protein, unlike carbon incorporation, measured net protein synthesis rather than turnover. Diel experiments with natural populations of marine and freshwater algae demonstrated that night protein synthesis is a general phenomenon in phytoplankton. For samples previously exposed to saturating light, day and night rates of protein synthesis were similar. The use of carbohydrate and metabolic pool carbon for night protein synthesis not only increased protein to the food web, but also altered ratios of protein, carbohydrate, and lipid to one another. The latter might result in changes in the nutritional value of phytoplankton to herbivores.

Activity of heterotrophic bacteria and its coupling to primary production during the spring phytoplankton bloom in the southern bight of the North Sea

Abstract: Parallel measurements were made of particulate and dissolved products of primary production, utilization rate of amino acids, monosaccharides, and glycollate, thymidine incorporation into DNA, and exoproteolytic activity before and during the spring bloom at different stations in the southern bight of the North Sea and in the English Channel. High correlations were found between the three methods used for estimating the activities of heterotrophic bacteria. A reasonable quantitative agreement was found between the estimate of bacterial production based on thymidine incorporation into DNA and the estimate of total carbon utilization based on the sum of the utilization rates of amino acids, monosaccharides, and glycollate. A close coupling between microheterotrophic activity and primary production was demonstrated. Examination of the nitrogen balance during the spring bloom shows that microheterotrophic activity could play an important role in food-web dynamics by partly satisfying the nitrogen needs of phytoplankton, which represents about twice the mineral nitrogen stock initially present in the water column.

Carbon flow through oxygen and sulfate reduction pathways in salt marsh sediments1

Abstract: Surface oxygen uptake, sulfate reduction and total sediment metabolism were measured in sediments (0-30 cm) supporting stands of short Spartina alterniflora in a New England salt marsh. Surface oxygen uptake varied seasonally and was highly correlated with total sediment metabolism. Rates of oxygen uptake ranged from about 75 to 121 mmol/sq m/day during winter to a maximum in August of 363. Total carbon dioxide production followed the same trend with a winter low of 65 mmol/sq m/day and a maximum in August of 415. The sulfate concentration in porewater from the 0-2 cm interval was about that expected from seawater at the salinity of the interstitial water. Below this depth sulfate decreased to values of about 21.6 mmol/liter. Time-course experiments using carbon dioxide production and sulfate reduction indicate that the aqua regia technique is not reliable for measuring sulfate reaction and that the rate of sulfate reduction is much less than previously reported for this marsh. Carbon mineralization is estimated to average about 180 mmol C/sq m/day, among the highest measured for marine sediments. Simultaneous measurements of oxygen uptake, carbon dioxide production and sulfate reduction suggest that at least half of this decomposition occurs via sulfate reduction. 54 references, 7more » figures.« less

Utilization of detritus by the copepod, Acartia tonsa1

Abstract: Ingestion, survivorship, and growth experiments were conducted with the marine Calanoid copepod, Acartia tonsa, various concentrations of the diatom, Thalassiosira weissjlogii, and detritus derived from the macrophyte, Thalassia testudinum. Copepod ingestion rates of detritus increased with detritus concentration from ~50 to > 1,700 pg Celiter-I. Copepod survival in detritus suspensions was significantly greater than in filtered seawater controls. The instantaneous mortality coefficient, z, of A. tonsa was a linear (negative) function of the diatom concentration (r2 = 0.783 1). When T. weissfrogii suspensions were supplemented with detritus (I ,000 pg C.liter-l), the copepod instantaneous mortality rate decreased (0.3002-O. 1362 in 50 pg Caliter-’ T. weissj’logii; 0.1345-0.0406 in 200 pg C-liter-l T. weissflogii). The growth rate of A. tonsa was a linear function of diatom concentration (r2 = 0.8816). When the diatom suspensions were supplemented with T. testudinum detritus, the growth rate of the copepod increased. Thalassiosira weissfrogii contained 12 x the protein, 8 x the fatty acids, and a greater amount and diversity ofamino acids and polyunsaturated fatty acids per unit dry weight than T. testudinum detritus. Although A. tonsa could not grow from egg to adult on a detrital diet, T. testudinum detritus did supplement algal diets to increase copepod production rates.

High phytoplankton growth and production rates in oligotrophic Hawaiian coastal waters1

Abstract: Plankton biomass, material fluxes, e.g. 14C uptake, and specific growth rates are related quantities. In the course of comparing various methods of measuring these properties in September 1982 off Oahu, Hawaii, we found specific growth rates of l-2.d-I. Such rates approach the maximum expected values observed in laboratory cultures. Plankton production is reported to be low in subtropical oceanic gyres compared with coastal waters at similar latitudes (Steemann Nielsen 1955; Koblentz-Mishke et al. 1970). Standing stocks, e.g. chlorophyll concentrations, are lower in the gyres, and plant nutrient levels are scarcely detectable by standard methods. We report here on a

Importance of ultraviolet radiation in photoinhibition of microalgal growth1

Abstract: Algae vary greatly in their long term ability to adapt to levels of natural solar ultraviolet radiation encountered near the surface of the sea. Photosynthetically active radiation (where PAR is defined as quantum flux between 400 and 700 nm) produced little or no growth inhibition even at full surface intensity. In some species the capacity to tolerate intense PAR did not carry into the range of UV-A (315-400 nm) or of UV-B radiation (280-315 nm) or both. Photo-inhibition became increasingly severe above 20% of surface intensity among the species sensitive to UV radiation. PAR flux in excess of that required for maximum growth was not inhibitory, but rather the higher levels of associated UV radiation reduced growth rate. These results support a previous suggestion that other molecules besides chlorophyll sensitize or shield algae in the UV portion of the solar spectrum.

Classification and dynamic simulation of the vertical density structure of lakes1

Abstract: Field data from two lakes of widely differing geometry and size are analyzed in terms of four nondimensional numbers which allow the principal mixing processes in each lake to be identified. The numbers are based on basin geometry, density stratification, wind stress, and rates of inflow and outflow. The procedure highlights the differences in the dynamics of the two lakes and allows assessment of the validity of the assumption of one-dimensionality. The result is that both lakes were dominated by one-dimensional, but different processes. The dynamics of the epilimnion of the smaller lake were dominated by stirring from surface wind and cooling, whereas shear at the pycnocline was also significant in the larger lake. In neither case did the effects of the earth’s rotation, inflow, or outflow generate significant horizontal gradients. A one-dimensional numerical model (DYRESM) was used to simulate the vertical temperature and salinity structures of both lakes over lengthy periods, with good results. The model is based on the parameterization of the important physical processes in a framework of horizontal layers of variable thickness and was applied in both lakes without alteration. The interpretative power of the model is demonstrated by examination of the formation and erosion of a thermal inversion in the larger lake.

Organic matter degradation and biogenic element cycling in a nearshore sediment (Kiel Bight)

Abstract: Benthic degradation of organic matter and the cycling of its C, N, P components was investigated at a coastal station (20 m) in Kiel Bight (western Baltic). Annual rates of carbon combustion and nutrient release from the sediment were derived from a comparison of input and burial of organic matter in the top sediment layers and from sediment oxygen consumption and nutrient release rates as determined by in situ enclosure experiments (2.9 mol 02*m-2.yr-1, 0.16 mol N*m-2*yr-1, 0.020 mol P.m-2.yr-1, and 0.58 mol Si*m-2*yr-‘). A long term incubation was used to simulate chemical changes during the transition to anoxic conditions. The comparison of diffusive fluxes calculated from porewater profiles with total release rates indicates that the sediment surface is the major site of organic matter degradation, as a consequence of low sedimentation rate. From the organic matter reaching the bottom via sedimentation only 22% of the organic carbon (13% N,, and 15% POJ is accumulated below 10 cm as sedimentary carbon and its reduced sulfur equivalent. While 75% of the carbon and 66% of the organic phosphorus input are returned to the water column, only half of the nitrogen input is released from the bottom; the rest is probably lost due to denitrification. Benthic flux contributes ~20% to the annual P and N requirements for the pelagic primary producers.

The asphyxiation technique: An approach to distinguishing between molecular diffusion and biologically mediated transport at the sediment—water interface

Abstract: On the assumption that lack of oxygen will cause the activity of benthic infauna to cease and thereby limit solute transport to that accomplished by molecular diffusion, we have measured the flux of dissolved silicate across the sediment-water interface of sediments incubated in situ under parallel benthic flux chambers. In one chamber the oxygen concentration was allowed to go to zero, and in the other the oxygen and pH remained at ambient values. As long as oxygen was present in the chambers, the measured summer and fall fluxes were 210 times those calculated from porewater profiles assuming one-dimensional molecular diffusion. The differences in fluxes predicted from the densities of macrobenthos at two different sites agree well with the flux measurements. After oxygen depletion, the silicate fluxes decreased and approached the values calculated on the basis of molecular diffusion. In one experiment the ratio between the oxic and anoxic fluxes was nearly identical to the ratio between the effective diffusion coefficient, as measured under oxic conditions using 22Na as a tracer, and the whole-sediment molecular diffusion coefficient. In winter (- 1’C) measured and calculated Fickian fluxes agreed closely, indicating a negligible effect of benthos on solute transport.

Interstitial water sampling by dialysis: Methodological notes

Abstract: The dialysis technique for sampling interstitial waters is subject to several potential sources of error. Cellulose-based membranes can lead to the underestimation or overestimation of porewater solutes. Polycarbonate was found unsuitable for dialyzer construction because of iron precipitation problems. The initial presence of dissolved O2 in the compartments can significantly affect sample composition. Equilibration times of 15–20 days were found adequate for most sediments. An efficient technique for pH measurement in small volumes of porewater is described.

The energetic cost of response to blue-green algal filaments by cladocerans1

Abstract: On examine l'effet de l'augmentation de la concentration en filaments d'Anabaena sur le comportement alimentaire et la depense energetique de Daphnia parvula, Ceriodaphnia lacustris et Bosmina longirostris cohabitant. Cet effet a une relation avec la taille de l'animal