Showing papers in "Limnology and Oceanography in 1988"
TL;DR: It is concluded that the extent and severity of N limitation in the marine environment remain an open question, despite the fact that by the late seventies the evidence for P limitation had become so great that phosphorus control was recommended as the legislated basis for controlling eutrophication in North American and European inland waters.
Abstract: Phytoplankton can become limited by the availability of nutrients when light and temperature are adequate and loss rates are not excessive. The current paradigms for nutrient limitations in freshwater, estuarine, and marine environments are quite different. A review of the experimental and observational data used to infer P or N limitation of phytoplankton growth indicates that P limitation in freshwater environments can be demonstrated rigorously at several hierarchical levels of system complexity, from algal cultures to whole lakes. A similarly rigorous demonstration of N limitation has not been achieved for marine waters. Therefore, we conclude that the extent and severity of N limitation in the marine environment remain an open question. Culture studies have established that internal cellular concentrations of nutrients determine phytoplankton growth rates, and these studies have shown that it is often difficult to relate growth rates to external concentrations, especially in natural situations. This should lead to a greater reliance on the composition of particulate matter and biomass-based physiological rates to infer nutrient limitation. Such measurements have demonstrated their utility in a wide variety of freshwater and marine environments, and, most importantly, they can be applied to systems that are difficult to manipulate experimentally or budget accurately. Dissolved nutrient concentrations are most useful in determining nutrient loading rates of aquatic ecosystems. The relative proportions of nutrients supplied to phytoplankton can be a strong selective force shaping phytoplankton communities and affecting the biomass yield per unit of limiting nutrient. A current dogma of aquatic science is that marine and estuarine phytoplankton tend to be nitrogen limited, while freshwater phytoplankton tend to be phosphorus limited. Carpenter and Capone (1983) documented the preeminence of N studies in the literature on brackish and marine ecosystems. In 1970 there were equal numbers of references per year to N and P. The decade of the seventies saw a nearly fourfold increase in references to N, while the number of P references per year remained essentially unchanged. No trend was evident for the freshwater literature despite the fact that by the late seventies the evidence for P limitation had become so great that phosphorus control was recommended as the legislated basis for controlling eutrophication in North American and European inland waters (e.g.
1,594 citations
TL;DR: Denitrification occurs in essentially all river, lake, and coastal marine ecosystems that have been studied as discussed by the authors, and the major source of nitrate for denitrification in most river and lake sediments underlying an aerobic water column is nitrate produced in the sediments, not nitrate diffusing into the overlying water.
Abstract: Denitrification occurs in essentially all river, lake, and coastal marine ecosystems that have been studied. In general, the range of denitrification rates measured in coastal marine sediments is greater than that measured in lake or river sediments. In various estuarine and coastal marine sediments, rates commonly range between 50 and 250 µmol N m−2 h−1, with extremes from 0 to 1,067. Rates of denitrification in lake sediments measured at near-ambient conditions range from 2 to 171 µmol N m−2 h−1. Denitrification rates in river and stream sediments range from 0 to 345 µmol N m−2 h−1. The higher rates are from systems that receive substantial amounts of anthropogenic nutrient input. In lakes, denitrification also occurs in low oxygen hypolimnetic waters, where rates generally range from 0.2 to 1.9 µmol N liter−1 d−1. In lakes where denitrification rates in both the water and sediments have been measured, denitrification is greater in the sediments.
The major source of nitrate for denitrification in most river, lake, and coastal marine sediments underlying an aerobic water column is nitrate produced in the sediments, not nitrate diffusing into the sediments from the overlying water. During the mineralization of organic matter in sediments, a major portion of the mineralized nitrogen is lost from the ecosystem via denitrification. In freshwater sediments, denitrification appears to remove a larger percentage of the mineralized nitrogen. N2 fluxes accounted for 76–100% of the sediment-water nitrogen flux in rivers and lakes, but only 15–70% in estuarine and coastal marine sediments. Benthic N2O fluxes were always small compared to N, fluxes.
The loss of nitrogen via denitrification exceeds the input of nitrogen via N2 fixation in almost all river, lake, and coastal marine ecosystems in which both processes have been measured.
Denitrification is also important relative to other inputs of fixed N in both freshwater and coastal marine ecosystems. In the two rivers where both denitrification measurements and N input data were available, denitrification removed an amount of nitrogen equivalent to 7 and 35% of the external nitrogen loading. In six lakes and six estuaries where data are available, denitrification is estimated to remove an amount of nitrogen equivalent to between 1 and 36% of the input to the lakes and between 20 and 50% of the input to the estuaries.
1,571 citations
TL;DR: In this paper, the authors identify and address general applicable criteria for deeming a water body “bloom sensitive” and incorporate such criteria into the design of water quality management strategies applicable to both coastal marine and freshwater habitats.
Abstract: Multiple interacting physical, chemical, and biotic factors, in proper combination, lead to the development and persistence of nuisance algal blooms. Upon examining combinations of environmental conditions most likely to elicit nuisance blooms, commonalities and analog situations become more apparent among coastal marine (dinoflagellate-dominated), estuarine (dinoflagellate- and cyanobacteria-dominated), and freshwater (cyanobacteria-dominated) ecosystems. A combination of the following hydrological, chemical, and biotic factors will most likely lead to bloom-sensitive waters: a horizontally distinct water mass; a vertically stratified water column; warm weather conditions, as typified by dry monsoon tropical climates and summer seasons in temperate zones; high incident photosynthetically active radiation (PAR); enhanced allochthonous organic matter loading (both as DOC and POC); enhanced allochthonous inorganic nutrient loading (nitrogen and/or phosphorus); adequate availability of essential metals, supplied by terrigenous inputs or upwelling; underlying sediments physically and nutritionally suitable as “seed beds” for resting cysts and akinetes; algal-bacterial synergism, which exhibits positive impacts on phycosphere nutrient cycling; algal-micrograzer (protists and rotifers) synergism, which also enhances nutrient cycling without consumption of filamentous and colonial nuisance taxa; and selective (for non-nuisance taxa) activities of macrograzers (crustacean zooplankton, larval fish).
Nuisance bloom taxa share numerous additional physiological and ecological characteristics, including limited heterotrophic capabilities, high degrees of motility, and toxicity. Given such a set of commonalities, it would appear useful and timely to identify and address generally applicable criteria for deeming a water body “bloom sensitive” and to incorporate such criteria into the design of water quality management strategies applicable to both coastal marine and freshwater habitats.
997 citations
TL;DR: The primary mode of interaction of dissolved phosphate with fluvial inorganic suspended particles is via a reversible two-step sorption process as discussed by the authors, which is dependent on the time history of the previous surface sorption and the chemistry of the solid diffusional layer.
Abstract: The primary mode of interaction of dissolved phosphate with fluvial inorganic suspended particles is via a reversible two-step sorption process. The first step, adsorption/desorption on surfaces, has fast kinetics (minutes-hours). The second step, solid-state diffusion of adsorbed phosphate from the surface into the interior of particles, has slow kinetics (days-months) and is dependent on the time history of the previous surface sorption and the chemistry of the solid diffusional layer. Natural clay particles with a surficial armoring of reactive iron and aluminum hydroxyoxides resulting from chemical weathering of rocks and soils have a high capacity for absorbing phosphate in the second step and for maintaining low “equilibrium phosphate concentrations” in solution. Extrapolation of laboratory sorption and extraction experiments with natural soils and suspended sediments to the environment suggests that the phosphate concentrations of unperturbed turbid rivers (SPM > 50 mg liter I) are controlled near the dynamic equilibrium phosphate concentration of their particles (EPC, = 0.2-l .5 PM) and that fluvial suspended particles “at equilibrium” contain up to 10 pmol-P g-l that is desorbable. Release of this phosphate from particles entering the sea produces the characteristic shape and magnitude of input profiles of dissolved phosphate observed in unperturbed estuaries. On a global scale, fluvial particulates could transport from 1.4 to 14 x 1O’O mol yr-I of reactive phosphate to the sea, some 2-5 times more than that in the dissolved load alone.
977 citations
TL;DR: In this paper, a combination of stable isotopic measurements was used to study food web structure of Georges Bank, an important northwestern Atlantic fishing ground, in order to test δ13C, δ15N and δ34S measurements as trophic-level indicators in offshore systems.
Abstract: A combination of stable isotopic measurements was used to study food web structure of Georges Bank, an important northwestern Atlantic fishing ground. Particulate, invertebrate, and fish samples were analyzed to test δ13C, δ15N, and δ34S measurements as trophic-level indicators in offshore systems. Neither sulfur nor carbon measurements proved valuable. Sulfur isotopic compositions showed little change with trophic level, and an apparent diversity of phytoplankton carbon isotopic inputs at the base of the food web complicated use of δ13C to estimate trophic position. Nitrogen isotopic distributions were, however, robust measures of trophic position and showed four broad trophic levels; unsampled large top carnivores may represent a fifth trophic level.
782 citations
TL;DR: The microbiota of freshwater and marine sediments serve similar roles in carbon degradation and nutrient regeneration, however, because of differences in the chemical environment between freshwater and Marine systems, distinct physiological groups of bacteria dominate terminal carbon catabolism in each system.
Abstract: The microbiota of freshwater and marine sediments serve similar roles in carbon degradation and nutrient regeneration. However, because of differences in the chemical environment between freshwater and marine systems, distinct physiological groups of bacteria dominate terminal carbon catabolism in each system. In general, the distribution and rates of microbial activities within a sediment are determined by availability of electron acceptors for respiration and metabolizable organic substrates. Sulfate ion is a primary factor in the distribution of microbial activities in anoxic sediments. At the high sulfate concentration found in seawater, sulfate reduction exceeds methanogenesis and is responsible for most of the organic carbon oxidation. The importance of methanogenesis in sediment metabolism increases as salinity and, hence, sulfate decreases. In freshwaters, methanogenesis is responsible for the bulk of terminal metabolism under anoxic conditions. The higher affinity of sulfate reducers for substrates that can be used by both groups (e.g. hydrogen, acetate, methanol), as well as the more favorable thermodynamic energy yields of sulfate respiration compared to methanogenesis, may account for the dominance of sulfate respiration under sulfate replete conditions. The sources of organic matter to marine and freshwater sediments can be qualitatively different. Complex structural polysaccharides and phenolic polymers (i.e. ligno-cellulose) may comprise a greater fraction of the organic input to freshwater systems. Organic compounds that act as osmoregulatory solutes in marine plants and animals may be unique substrates for bacteria of marine sediments. It is likely that these differences also result in distinct assemblages of microorganisms responsible for the breakdown of organic carbon. The quantity of organic matter present in the scdimcnts is also a major factor determining the magnitude and distribution of various microbial activities. Near the extremes of high and low organic loading, organic matter input may play a greater role than sulfate concentration in determining the relative importance of sulfate reduction or methanogenesis. In marine systems, methanogenesis occurs in the presence of sulfate ion, but only at the expense of substrates not utilized by sulfate reducers (“noncompetitive” substrates), such as methylamines and, possibly, methylated reduced sulfur compounds. Methanogenesis from noncompetitive substrates represents only a small fraction of the sulfate reduction or carbon catabolism observed in marine sediments. In marine systems with very high rates of organic matter deposition, sulfate can bc depleted to the extent that methanogenesis takes on quantitative significance. Although sulfate concentrations are usually insufficient to permit much sulfate reduction in lacustrine environments, in lakes with relatively low organic deposition, sulfate concentrations in the water (and that supplied to the sediments) can bc sufficient to allow for a more significant contribution of sulfate respiration to carbon catabolism.
592 citations
TL;DR: Nitrogen fixation appears important in making up deficits in nitrogen availability relative to phosphorus availability in many lakes, contributing to the phosphorus-limited status of these systems.
Abstract: Nitrogen fixation is mediated by a variety of autotrophic and heterotrophic bacteria. Cyanobacteria appear responsible for most planktonic fixation in aquatic ecosystems, and rates of fixation are high only when thcsc organisms make up a major percentage of the planktonic biomass, Planktonic nitrogen fixation tends to be low in oligotrophic and mesotrophic lakes (generally 20% of the nitrogen input to the Asko region of the Baltic Sea and 17% of the nitrogen input to the PeelHarvey estuary in Australia. Fixation in sediments of estuaries and eutrophic and mesotrophic lakes usually constitutes a small percentage of the nitrogen inputs to these systems. However, benthic fixation appears to be a major source of nitrogen for many oligotrophic tropical lagoons and for some oligotrophic lakes, even though fixation rates are moderate because other nitrogen inputs tend to be low. Nitrogen fixation probably is a fairly minor input of nitrogen to marine wetlands, which are generally open to other inputs, but contributes roughly half the total nitrogen input to some freshwater wetlands (bogs, cypress domes), where other inputs are more limited. Nitrogen fixation appears important in making up deficits in nitrogen availability relative to phosphorus availability in many lakes, contributing to the phosphorus-limited status of these systems. That many estuaries and coastal seas are nitrogen limited is due in part to the generally low rates of nitrogen fixation found in these systems.
540 citations
TL;DR: It is suggested that the DOM pathway may be ecologically more significant than the POM (particulate organic matter) pathway and that processes analogous to those shown for lakes and rivers probably occur in estuarine and coastal waters.
Abstract: In both freshwater and marine habitats, vascular marine plants arc little used by animals that graze directly on them, because they have a relatively high content of indigestible fiber and a low content of nitrogen. The chief emphasis of detritus research in the 1970s was to show how microorganisms progressively reduce the content of fiber and increase the content of nitrogren in vascular plant detritus, rendering it nutritious for animals. Algal (seaweed, diatom, etc.) detritus starts with a lower fiber content and a higher nitrogen content. Many animals can use it directly, and a very short period of microbial colonization renders it highly nutritious. As a result, a high proportion of the algal carbon originally produced passes into animals via detrital food webs, while a low proportion of vascular plant carbon does so. Much more of the latter simply supports microbial respiration. In the 1980s it was shown, particularly for freshwater habitats, that the dissolved organic matter (DOM) released by plants while living or in the early stages of decomposition readily precipitates on surfaces and forms amorphous particulate matter with a low content of refractory material. These particles are highly nutritious for animals and are used directly by freshwater fish such as Sarotherodon (= Tifapia), which is commercially important, especially in Africa and South America. It is suggested that the DOM pathway may be ecologically more significant than the POM (particulate organic matter) pathway and that processes analogous to those shown for lakes and rivers probably occur in estuarine and coastal waters. There is much circumstantial evidence to suggest that planktonic food webs based on DOM are much more important than previously thought. The conversion of DOM to POM through the “microbial loop” and its utilization in higher trophic levels is a.n urgent topic for further study.
523 citations
TL;DR: The settling velocities of undisturbed macroscopic aggregates known as marine snow were measured with SCUBA in surface waters off southern California and analyzed as a function of aggregate size, mass, and density as discussed by the authors.
Abstract: The settling velocities of undisturbed macroscopic aggregates known as marine snow were measured with SCUBA in surface waters off southern California and analyzed as a function of aggregate size, mass, and density. The mean settling velocity was 74f39 m d-l for aggregates ranging from 2.4 to 75 mm in maximum length. Sinking rates in the field varied exponentially with aggregate size and dry weight and were consistently up to four times slower than rates measured in the laboratory. The excess densities of the 80 aggregates examined were calculated from volume and dry weight and ranged over four orders of magnitude with a median of 1.4 x 1O-4 g cm-3. Aggregates of marine snow sank more slowly than predicted for either solid or porous spheres of equivalent volume and density, although their velocities were within the range expected for equivalent sinking prolate ellipsoids. No relationships between settling velocity and either excess density or particle shape were found. Drag coefficients of marine snow were also higher than predicted by theory for spheres of equivalent volume and density. These deviations from theoretical expectations may be partially explained by errors in the estimation of the excess densities of aggregates. Variability in the densities of the heterogeneous primary particles comprising marine snow (fecal pellets, claymineral particlcs, phytoplankton, molts, etc.) and the potential for buoyancy regulation by individual phytoplankton cells inhabiting aggregates make determination of excess density especially
516 citations
505 citations
TL;DR: Copper titrations were conducted at sea with differential pulse anodic stripping voltammetry to examine the degree to which copper was associated with organic ligands as discussed by the authors, finding that approximately 50-70% of the total dissolved copper was in the organically complexed form.
Abstract: Copper titrations were conducted at sea with differential pulse anodic stripping voltammetry to examine the degree to which copper was associated with organic ligands. Greater than 99.7% of the total dissolved copper in surface waters of the central Northeast Pacific shallower than 200 m was estimated to be associated with strong organic complexes. Below 200 m, increasing proportions of inorganic or labile copper spccics were observed. At middepths (1,000 m), about 50-70% of the total dissolved copper was in the organically complexed form. Whereas total copper varies by a factor of only three from the surface to middepths (0.6-I .8 nM), copper complexation gives rise to extremely low cupric ion activities in surface waters ({Cu!‘} = 1.4 x lo-l4 M) and higher values at middepth ({Cuz-I} = lo- I1 M)-a variation of three orders of magnitude. Two classes of copperbinding ligands were found to be responsible for this complexation: an extremely strong ligand class [log K’cond (cu,j = 11.5 J at low concentrations (- 1.8 nM) -which dominated copper complexation in the surface waters and decreased with depth, and a weaker class of ligands [log K’cond(Cu3 = 8.51 at higher concentrations (8-10 nM) which was observed throughout the water column and showed no apparent structure in its vertical distribution. These findings have significant implications concerning the toxicity and bioavailability of copper in open ocean systems.
TL;DR: In this paper, seasonal variability in stable carbon (S’XZ) and nitrogen (b15N) isotope ratios was observed in suspended particulate matter of the Delaware estuary.
Abstract: ,Qbstract Seasonal variability in stable carbon (S’XZ) and nitrogen (b15N) isotope ratios was observed in suspended particulate matter of the Delaware estuary. Two major pools of organic matter were found in the estuary-phytoplankton growing in situ and a mixture of planktonic and terrestrial detritus. In general, the 6°C and 615N of suspended particulate matter reflected planktonic dominance. With the background chemical and physical information available for the estuary, it is evident that biogeochemical processes influence isotopic distributions in the estuary to a greater extent than does physical mixing. During spring, we postulate that isotopic fractionation of ammonium assimilated at concentrations >20 PM resulted in more negative 615N values for organic matter fixed by phytoplankton. As algal growth proceeded, the 615N of seston reached a maximum (+ 1 SY&) because phytoplankton were using a pool of NH,+ enriched in 15N as a result of previous fractionation during assimilation. Similarly, maximal 813C values were related to high rates of primary productivity associated with algal growth. Decreased isotopic fractionation occurred at high rates of production, implying that diffusion of CO, across the cell membrane became increasingly rate limiting. The 613C values in bottom sediments were equivalent to those in suspended particulate matter, but a 2Y60 difference in 615N was found between suspended and bottom sediments. With nitrogen isotopic differences between water-column seston and surficial sediments, we estimate that 1530% of planktonic production is deposited in the sediments during spring. If this organic matter is remineralized in late summer and fall, it could support up to 20% of primary production at that time.
TL;DR: In this article, the areal and temporal average flux of sulfur (DMS) from the North Sea to the atmosphere during summer are of the order of lo3 pg S m-2 d-l, a 60-fold increase over winter flux.
Abstract: Concentrations of biogenic dimethyl sulfide (DMS) in seawater around mainland Britain in winter and summer (1985) ranged from 1 to 1,100 ng S (DMS) liter-‘. The mean winter DMS concentration was 4 ng S (DMS) liter-’ compared with the mean summer concentration of 220. Analyses of phytoplankton species composition in summer indicate that the main sources of DMS were coccolithophores, various dinoflagellates including the bloom species Gyrodinium aureolum, and certain unidentified taxa of small flagellates. Concentrations of dimethylsulfoniopropionate (DMSP), the precursor of DMS, were measured in 53 of the summer samples, and its mean concentration was about an order of magnitude greater than that of DMS. Particulate (>0.2 pm) and dissolved fractions of DMSP were operationally resolved, with the latter showing the stronger correlation with DMS. Preliminary estimates for the areal and temporal average flux of sulfur (DMS) from the North Sea to the atmosphere during summer are of the order of lo3 pg S m-2 d-l, a 60-fold increase over winter flux. Biogenic emission in summer is equivalent to about 16% of the spatially averaged anthropogenic emission from Europe.
TL;DR: The tendency toward less nitrogen fixation by plankton in estuaries and coastal marine ecosystems than in lakes subject to similar loadings of nitrogen and phosphorus may be due to a lower availability in oxic seawater of one or more trace elements required for nitrogen fixation, such as molybdenum and iron.
Abstract: Planktonic nitrogen fixation in lakes is strongly related to lake trophic status, with moderate and high rates usually occurring only in eutrophic lakes. Among eutrophic lakes, nitrogen fixation is related to the ratio of nitrogen loading to phosphorus loading to the lake; significant nitrogen fixation by planktonic organisms generally occurs only when the N: P ratio of the nutrient loading is near or below the Redfield ratio of 16: 1. In contrast, nitrogen fixation by planktonic organisms is generally low in estuaries even when the N: P ratio of nutrients inputs is low.
The tendency toward less nitrogen fixation by plankton in estuaries and coastal marine ecosystems than in lakes subject to similar loadings of nitrogen and phosphorus may be due to a lower availability in oxic seawater of one or more trace elements required for nitrogen fixation, such as molybdenum and iron. Iron concentrations are generally lower in estuarine waters and seawater than in most lakes. And although molybdenum concentrations in seawater are actually higher than in lakes, molybdenum availability is probably lower, since sulfate inhibits molybdate assimilation by microbes. Molybdate is the primary form of molybdenum in oxic seawater, and the ratio of sulfate: molybdate is greater than in lakes. However, even in lakes sulfate is several orders of magnitude more abundant than molybdenum, and the ratio of dissolved sulfate to dissolved molybdenum typically is much greater than the ratio of sulfur to molybdenum apparently required by nitrogen-fixing cyanobacteria. Consequently, assimilation of molybdate by cyanobacteria is probably an energetically expensive process in all natural waters, but more so in seawater than in freshwaters. High concentrations of dissolved organic matter are known to favor blooms of cyanobacteria, perhaps by increasing iron and/or molybdenum availability through chelation.
The primary controls on nitrogen fixation in sediments, wetlands, macrophyte beds, and cyanobacterial mats may be different from those for fixation by planktonic organisms. Both molybdenum and iron are probably more available in these systems than in oxic waters, since reducing conditions and high DOC concentrations will increase iron solubility and favor the stability of reduced forms of molybdenum; sulfate should not inhibit the assimilation of these reduced molybdenum compounds. Consequently, nitrogenase synthesis (and, therefore, nitrogen fixation) in wetlands and in sediments may be less energetically expensive than in oxic water columns. A major control on nitrogen fixation in sediments may be repression of nitrogenase synthesis by high concentrations of ammonium, a factor less important to planktonic fixation because of the much lower concentrations of ammonium generally found in water columns than in sediments.
TL;DR: Algal picoplankton are a ubiquitous component of the microbial plankton communities of both marine and freshwater ecosystems, and in oligotrophic oceans and lakes can be responsible for up to 80-90% of the total daily or annual carbon production.
Abstract: Algal picoplankton are a ubiquitous component of the microbial plankton communities of both marine and freshwater ecosystems. They contribute significantly to the total biomass of phytoplankton communities, and in oligotrophic oceans and lakes can be responsible for up to 80-90% of the total daily or annual carbon production. As part of the “microbial loop,” they are thought to be grazed by flagellates, ciliates, rotifers, copepods, and other metazoans, and contribute to the flow of energy to higher trophic levels. This presentation highlights their discovery, distribution, physiology, production, and contribution to pelagic food webs in marine and freshwater systems.
TL;DR: In this paper, a large part of total P in sediments of Lake Sempach, an 87m deep eutrophic lake, was estimated to be incorporated in bacterial biomass, and laboratory experiments indicated that sediment microorganisms can rapidly take up and release soluble reactive P (SRP), depending on rcdox conditions.
Abstract: Cycling of phosphorus at the sediment-water interface is traditionally considered to bc controlled by pH- and rcdox-dependent, abiotic processes, such as formation and dissolution of FeOOH-POd complexes. In this study, however, a large part of total P in sediments of Lake Sempach, an 87-m deep eutrophic lake, was estimated to bc incorporated in bacterial biomass. Laboratory experiments indicated that sediment microorganisms can rapidly take up and release soluble reactive P (SRP), depending on rcdox conditions, and that sterilization ofoxic sediments decreased their SRI? sorption capacity. In an in situ experiment conducted in the lake, bacteria also contributed considerably to SRP fixation when water enclosed within a sediment flux chamber was reoxygenated following anoxia, Moreover, in that experiment and in data sets from several other lakes, anoxic releases of Fc and P from sediments appeared to be partly uncoupled. As part of an ongoing revision of the classical model for P exchange across the sediment-water interface, these results provide direct cvidencc that fixation and release of SRP may be controlled part! y by rcdox-dependent changes in microbial physiology,as Wellas by productionand dc~ornmsitionOfmicrobial biomass.
TL;DR: There is strong evidence that rotifers cannot become abundant members of freshwater zooplankton communities in the presence of large Daphnia, and small cladocerans generally do not mechanically interfere withRotifers, are less likely to deplete food resources, are themselves more likely to be suppressed by exploitative competition with rotifer, and usually are more susceptible to invertebrate predation.
Abstract: There is strong evidence that rotifers cannot become abundant members of freshwater zooplankton communities in the presence of large (z 1.2 mm) Daphnia. Indirect evidence comes from field observations and experiments showing that rotifers are replaced by Daphnia in seasonal successions, that rotifers are much Jess common in communities with than without Daphnia, and that the experimental addition of zooplanktivorous fish causes the removal of Daphnia and a simultaneous increase in rotifer abundance, while the experimental removal of fish has just the opposite effect. Direct evidence comes from field experiments showing that the removal of Daphnia from communities causes a marked increase in the fertility and abundance of rotifers, and from laboratory experiments showing that Daphnia can kill and rapidly exclude rotifers in mixed-species cultures. Rotifers are suppressed by large Daplznia both through exploitative competition for shared, Iimiting food resources and through mechanical interference. This interference can cause high mortality rates on susceptible rotifer species, even at low (1-5 ind. liter–]) Daphtzia densities and should affect the species structure of rotifers able to coexist with Daphnia in natural communities. Rotifers seem to be much less inhibited by small (S 1.2 mm) cladocerans and often co-occur with them at high densities in natural communities in the absence of large Daphnia. There are several reasons why small c[adocerans are less likely than large Daphnia to competitively suppress rotifers: small cladocerans generally do not mechanically interfere with rotifers, are less likely to deplete food resources, are themselves more likely to be suppressed by exploitative competition with rotifers, and usually are more susceptible to invertebrate predation. High rotifer abundance in the absence of Daphnia competition may have an important secondary effect in natural communities —the development of populations of invertebrate predators dependent on rotifer prey.
TL;DR: Although freshwater and marine systems both receive light and heat energy from the sun and are mixed by the wind, only marine systems receive additional mechanical energy from wind as discussed by the authors, which is very small relative to the flux of solar energy but may exceed that from wind.
Abstract: Although freshwater and marine systems both receive light and heat energy from the sun and are mixed by the wind, only marine systems receive additional mechanical energy from the tide. This input is very small relative to the flux of solar energy but may exceed that from wind. Some obvious physical consequences of this additional energy input include the development of intertidal habitats, the presence of stronger currents, and more vigorous vertical mixing. It is argued that these (and perhaps other) consequences lead to coastal marine ecosystems which differ in a number of important ways from temperate lakes. There is some evidence that coastal marine systems generally maintain a larger standing crop of benthic animals and that these fauna are more effective in mixing the bottom sediments. As a result of better sediment mixing (and perhaps warmer and better oxygenated bottom water), organic matter deposited on the bottom of coastal marine areas may be more completely metabolized and less C, N, and P retained than in lake sediments. Materials that are more tightly bound to particles, like many metals, may behave similarly in lake and marine sediments. Although many lakes are strong sinks for nutrients and metals, marine bays and estuaries may bc much less effective in retaining nutrients. A major consequence of the input of tidal energy appears to be a more intensive yield of fish from marinc systems compared with temperate lakes. The data suggest that this more intense yield is not due to the size or interconnection of marine areas or to higher primary production. Rather, the efficiency of transfer of primary production to fish appears to be greater. Tropical lakes appear more like marine systems in this regard, and this may be related to lower thermal stability and more efficient wind energy transfer because of a small Coriolis effect at low latitudes.
TL;DR: The importance of the zooplankton community in regulating the relative degree of N or P limitation was confirmed and a hierarchical view of the function of planktonic systems, in which biotic interactions structure the response of the algal community to a given nutrient load, was supported.
Abstract: Limitation of algal growth by nitrogen and phosphorus was assessed in three north-temperate lakes with physiological bioassays and nutrient enrichment experiments. In addition, mesocosm experiments were performed in the three lakes to examine the effects of nutrient enrichment and zooplankton biomass and size on algal nutrient status. In situ indicators of N and P availability were inversely related in magnitude and transitions between N and P limitation were abrupt. Physiological bioassay results did not indicate simultaneous limitation by N and P. However, limited responses to single-nutrient enrichment and pronounced responses to simultaneous N and P addition in enrichment experiments suggested that potential limitation by the secondary nutrient was usually in close proximity to limitation by the primary nutrient. Transitions between N and P limitation closely accompanied major shifts in the zooplankton community. The importance of the zooplankton community in regulating the relative degree of N or P limitation was confirmed by the mesocosm experiments, which demonstrated that transitions between algal N or P limitation could be induced by manipulations of zooplankton biomass or size. This result supports a hierarchical view of the function of planktonic systems, in which biotic interactions structure the response of the algal community to a given nutrient load.
TL;DR: The number of predator species to which a clone responds shows a positive correlation with average body size of the Daphnia, although there was a tendency (not statistically significant) for the number of responses to decrease with lake size.
Abstract: Eight different clones (seven species) of Daphnia had behavioral responses to fish and invertebrate predators. The behavioral response was measured in the laboratory as a change in the average population depth, relative to controls, when exposed to a predator. Behavior for each clone was tested with three common predators: Chaoborus, Lepomis, and Notonecta. Each Daphnia clone responded to at least one predator. Some clones responded to all three predators. The responses are both predator and. prey-specific. The stimulus produced by the predator is a water-soluble chemical that persists for up to 7 h in the laboratory. The number of predator species to which a clone responds shows a positive correlation with average body size of the Daphnia. Number of responses per clone is independent of lake size, although there was a tendency (not statistically significant) for the number of responses to decrease with lake size. Behavioral responses may be components of diel vertical migration and horizontal distribution patterns seen in nature.
TL;DR: Sediment trap and net plankton samples were collected monthly for a year at three depths in a marine bay (Dabob Bay, Washington). These materials and subsamples from a sediment box core were analyzed for lignin oxidation products as well as elemental and stable carbon isotope compositions as mentioned in this paper.
Abstract: Sediment trap and net plankton samples were collected monthly for a year at three depths in a marine bay (Dabob Bay, Washington). These materials and subsamples from a sediment box core were analyzed for lignin oxidation products as well as elemental and stable carbon isotope compositions. The sediment core was compositionally uniform over its entire 50-cm length. The elemental and lignin compositions of the sediment trap and core samples indicate nitrogen-rich (atomic C : N = 7.5) plankton-derived organic matter mixed with vascular plant debris. At most, vascular plant debris accounts for 10% (nonwinter months) to 35% (winter months) of the total organic carbon in the upper water column (30 m) sediment trap samples and consists predominantly of gymnosperm wood along with some nonwoody gymnosperm tissues and angiosperm woods. Bulk land-derived organic matter in Dabob Bay contains a maximum of 50% vascular plant debris and comprises an average of one-third of the total organic carbon in the sediment trap samples and two-thirds of the total organic carbon in the underlying sediments. Lignin in the sediment trap and core samples shows evidence (from elevated vanillic acid:vanillin ratios) of white-rot fungal degradation before (but not after) introduction to the water column at the study site. Vascular plant debris introduced to the bay has already lost almost half of its initial bulk polysaccharide. Glucose yields are particularly low whereas rhamnose and fucose are obtained in excess of expected yields and must have additional sources. Lignin and neutral sugars together account for ~20% of the total organic carbon in the sediment trap and core samples. Overall, the sediments of Dabob Bay compositionally resemble the gymnosperm wood-rich particulate material introduced to the overlying water column during winter and poorly record the input of plankton and other types of vascular plant debris during nonwinter months.
TL;DR: In this article, the effect of epipelic algal photosynthesis on sediment oxygen dynamics and the concomitant pattern of phosphorus release from lake sediments was examined using oxygen-sensitive microelectrodes.
Abstract: Previous studies utilizing oxygen-sensitive microelectrodes have demonstrated that as a result of epipelic algal photosynthesis and microbial metabolism, and regardless of the oxygen concentration of the overlying water, sediments within the euphotic zone of lakes undergo marked diel fluctuations in the extent of oxygen penetration. This investigation utilized oxygen-sensitive microelcctrodes, 32P0,3- radiotracer, and a novel flow-through system to examine the effect of epipelic algal photosynthesis on sediment oxygen dynamics and the concomitant pattern of phosphorus release from lake sediments. Epipelic algae mediated release of phosphorus from sediments to overlying water via daily formation and breakdown ofthe oxidized microzone. During illumination, surficial sediments rapidly became oxygenated, and release of phosphorus diffusing from deeper sediment layers was inhibited. During darkness the microzone became anoxic, and phosphorus was released to overlying water at an accelerated rate, producing marked diel fluctuation in efflux rate. Observed patterns of release are consistent with recent evidence for a mechanism consisting of rapid uptake or rclcase of dissolved phosphate by sediment microorganisms in response to respective oxic or anoxic conditions. Microbial metabolism in aquatic sediments regenerates inorganic phosphate that accumulates in interstitial water and forms concentration gradients. Subsequent diffusive transport to overlying water can be retarded by a number of processes that either temporarily or permanently immobilize phosphate. Mortimer (1941, 1942) demonstrated that the presence of an oxidized microzone at the sediment surface inhibited phosphorus release but that a decrease in redox potential of the microzone following the onset of anoxic conditions in the overlying water stimulated the reduction of Fe(III), thus releasing phosphate bound in hydrous oxides and gels at the sediment surface. This key role of oxygen has been substantiated in numerous studies in various lake and sediment types @Lamp-Nielsen 1974; Patrick and Khalid 1974; Frevert 1980). Also identified as factors affecting the rate of P flux from sediments are pH, tem
TL;DR: In this article, the early stages of cultural eutrophication of Lake Tahoe have been studied and the relationship between the primary productivity and transparency has been analyzed, showing that a gradual increase in the N:P may be a general evolutionary characteristic of oligotrophic lakes during the earliest stages of eutrophic evolution.
Abstract: For more than half a century, the trophic status of water bodies has been of interest to Iimnologists and oceanographers alike. This report demonstrates the close, inverse relationship between ‘4C-estimated primary productivity and transparency during the earliest stages of cultural eutrophication. As the population in the Tahoe basin has rapidly increased, Lake Tahoe has been characterized by an increase in primary productivity that has averaged 5.6% yr1 for the last 28 yr. There has been a concomitant decline in transparency of 0.37 m yr”. During winter months when transparency is highest, the average annual loss has been slightly greater (0.40 m yr‘). The average annual Secchi depth has decreased by 7 m during the last 19 yr of intensive monitoring. There has also”been a significant increase in the light extinction coefficient. Photosynthetic efficiency has increased while there has been a gradual shrinkage of the euphotic zone. During the same period the total NO~--N content of the lake has increased significantly, but total P content has not. Lake Tahoe primary production has become increasingly P sensitive during the last decade as N has accumulated in the system. A gradual increase in the N:P may prove to be a general evolutionary characteristic of oligotrophic lakes during the earliest stages of eutrophication. The importance of long-term studies in detecting gradual change that may be masked by considerable interannual variability is particularly evident from this study. Since Naumann (1919) introduced the concept of the trophic status of lakes, there has been interest by limnologists and oceanographers in the evolutionary state, degree of fertility, and both cause and effect of eutrophication in lakes and estuaries. At an international symposium on eutrophication in 1965, Thomas (1969) reviewed eutrophication in central European lakes, Rodhe (1969) in northern Europe, Stra3kraba and Stra3krabov& ( 1969) in eastern Europe, and Horie (1969) in Asia. W. T. Edmondson (1969), to whom this paper is dedicated, reviewed the North American lakes, excluding the Great Lakes, which were treated by Beeton (1965, 1969). Hutchinson (1969, p. 19), in his unique and scholarly fashion, made the important point “that we should think not of oligotrophic or eutrophic water types, but of lakes and their drainage basins and sediments as forming oligotrophic or eutrophic systems.” He emphasized the dynamics of nutrients in aquatic systems and the need to understand and use the information available, describing a now-classic example of cultural eutrophication recon‘ Supported by NSF grant BSR 87-05170. strutted from sediment Monterosi, which began of the Via Cassia about cores of Lago di with the building 171 B.C. In a later work, he further examined both the scientific and practical implications of eutrophication (Hutchinson 1973). Edmondson’s studies of Lake Washington document a success in reversing eutrophication of a lake with a short retention time through sewage diversion (Edmondson 196 1). Beeton and Edmondson ( 1972) thus regarded nutrient input as a determinant of the trophic status of lakes as the experience with Lake Washington had demonstrated. Subsequently, Carlson (1977) used transparency, chlorophyll, and total phosphorus data from the Lake Washington studies to develop a numerical trophic state index for general application. Emphasis on phosphorus as a limiting factor launched international efforts to control phosphorus loading (Vollenweider 1968, 1975). The importance of phosphorus cycling had been recognized for many years (Einsele 1941), and rapid uptake and turnover of P were demonstrated by Rigler (1956). Although the predictive aspects of the Vollenweider nutrient-loading model have been challenged by Thomann (1977)
TL;DR: Methods that can be used to explore the spatial structure of ecological data and to include spatial location as a variable in the study of relationships and models are described.
Abstract: Microbial ecologists often obtain data from sampling a piece of geographic space. These are likely to be spatially autocorrelated. Autocorrelation removes degrees of freedom from the usual tests of inferential statistics and can generate spurious correlations among variables, with the consequence that suspected causal relations may not hold. This paper describes methods that can be used to explore the spatial structure of ecological data and to include spatial location as a variable in the study of relationships and models. The relationship between environmental heterotrophic bacteria and phytoplankton, well established in aquatic environments, is re-examined in the Thau brackish lagoon (Mediterranean coast of France). It did not hold for the bacteria growing on bioMCrieux nutrient agar (BNA), which are presumably of continental origin; their spatial gradient can only partly be explained by the particulate organic carbon variable (POC) and not at all by phytoplankton biomass (CHL A), despite the existence of a spurious correlation between BNA and CHL A. The spatial gradient of abundance of heterotrophs growing on marine agar (MA), expected to bc mostly of marine origin, can be entirely explained by POC and CHL A. Different segments of the bacterial community, both reacting positively to variations ofthe particulate organic carbon, may follow partly, or not, variations of phytoplankton biomass. The mode of analysis developed here extends to many other spatially distributed processes in ecology and other fields.
TL;DR: In this paper, the authors analyzed the relationship between COZ, 02, CH4, and CO, and found that about 50% of carbon mineralization on the floodplain is anaerobic, with 20% lost to the atmosphere as CH.
Abstract: Concentrations of COZ, 02, CH4, and N,O in the Amazon River system reflect an oxidationreduction sequence in combination with physical mixing between the floodplain and the mainstem. Concentrations of CO, ranged from 150 PM in the Amazon mainstem to 200-300 PM in aerobic environments and up to 1,000 PM in oxygen-depleted environments of the floodplain. Apparent oxygen utilization (AOU) ranged from 80 to 250 PM. Methane was highly supersaturated with respect to atmospheric equilibrium. Concentrations ranged from 0.06 PM in the mainstem to 100 PM on the floodplain. Concentrations of N,O were slightly supersaturated in the mainstem (- 13 nM) but were undcrsaturated on the floodplain (averaging 9 nM). Fluxes calculated from these concentrations indicated decomposition of - 1,600 g C m-2 yr-’ of organic carbon in Amazon floodplain waters. Analysis of relationships between CH,, 02, and CO, concentrations indicated that about 50% of carbon mineralization on the floodplain is anaerobic, with 20% lost to the atmosphere as CH,. The predominance of anaerobic metabolism leads to consumption of N20 on the floodplain. Elevated concentrations of CH, in the mainstem probably reflect input from the floodplain, while high levels of CO, in the mainstem are derived from a combination of floodplain drainage and in situ respiration.
TL;DR: In this paper, vertical fluxes of bulk particulate material, organic carbon, nitrogen, lignin-derived phenols, and neutral sugars through the water column and into surface sediments of Dabob Bay, Washington, were determined monthly for 1 yr by sediment trap deployments at 30, 60, and 90 m at a site 110 m deep.
Abstract: Vertical fluxes of bulk particulate material, organic carbon, nitrogen, lignin-derived phenols, and neutral sugars through the water column and into surface sediments of Dabob Bay, Washington, were determined monthly for 1 yr by sediment trap deployments at 30, 60, and 90 m at a site 110 m deep. Vertical fluxes of sinking bulk particulate material in this marine bay were elevated during winter and increased in consistent proportion to sediment trap deployment depth throughout the year. Although annual average particle fluxes at 30 and 60 m bracketed the mean accumulation rate of the underlying sediment, the flux at 90 m was higher by a factor of 2 due to resuspension, horizontal advection, or both. The monthly fluxes of lignin-derived phenols paralleled those of total particulate material, indicating a common riverine origin. The annual average fluxes of vanillyl and cinnamyl phenols through the water column closely matched the corresponding accumulation rates in the underlying sediment, whereas about a third of the total syringyl phenol input was degraded at the watersediment interface. Although p-hydroxyacetophenone exhibited a stability typical of lignin-derived phenols, the distinctly higher reactivities (> 60% degradation) ofp-hydroxybenzaldehyde and p-hydroxybenzoic acid indicate a predominantly nonlignin source. On average, 60 and 70%, respectively, of the total particulate organic carbon and nitrogen and 65-75% of all neutral sugars settling through the midwater column were degraded at the watersediment interface. The elemental and carbohydrate composition of the degraded material was similar to that of local net plankton except for higher percentages of glucose and total neutral sugars. Land-derived organic material accounted for about one-third of the total organic carbon passing through the midwater column and two-thirds of the organic carbon accumulating in the underlying sediments. The amounts of plankton-derived organic matter sinking through the midwater column and being preserved in the sediments below corresponded to 14 and 3% of the annual mean primary productivity. Plankton-derived organic matter exhibited about 5 times the reactivity of local land-derived organic matter at the water-sediment interface of Dabob Bay and supported essentially all of the benthic respiration.
TL;DR: The inverse relation found between surplus P : C and APA : C ratios during a Microcystis aeruginosa bloom and the positive relation between P: C ratio and growth rate of the cryptophytedominated community in summer indicate that the phytoplankton were P limited during most of the ice-free period.
Abstract: The phosphorus status [total phosphorus (P), surplus P, and alkaline phosphatase activity (APA)] of phytoplankton and bacteria were followed in a eutrophic Norwegian lake. On average 36% (range 20-60) of the particulate P and 57% (range 10-l 00) of the surplus P were bound by bacteria. The P : C ratio of phytoplankton and bacteria varied between 2.5 and 55 (median 5.1) and 34 and 360 (median 89) pg P (mg C))‘, indicating that bacteria have a substantially higher P requirement than do phytoplankton. The inverse relation found between surplus P : C and APA : C ratios during a Microcystis aeruginosa bloom and the positive relation between P: C ratio and growth rate of the cryptophytedominated community in summer indicate that the phytoplankton were P limited during most of the ice-free period. This is supported by the fact that the data from the cryptophyte-dominated community could be described by the Droop model for nutrient-limited growth. For the bacteria a positive relation was found between growth rate and cellular P (i.e. the P : C and the surplus P : C ratios), as predicted by the Droop model. Although the bacteria obviously were P subsaturated, it cannot be concluded that they were P limited since C may have been supplied at an even lower rate. Because of their high P requirements the bacteria acted as consumers of inorganic P and their net consumption of P was four times higher than that of the phytoplankton.
TL;DR: Morphometry, oxygen concentration, temperature, and transparency were studied in 39 natural lakes in Cameroon, West Africa, and data from published studies were used to calculate stability of thermal stratification and evaluate morphological correlates of mixing depth.
Abstract: Morphometry, oxygen concentration, temperature, and transparency were studied in 39 natural lakes in Cameroon, West Africa. Thermal profiles from 3 1 of the lakes and data from published studies were used to calculate stability of thermal stratification and evaluate morphological correlates of mixing depth. Twenty-six lakes showed some degree of stratification and 17 had distinct thermoclines and well-developed, anoxic hypolimnia. Total stability of the water column ranged from 0 to 5,784 J m-2. The high values were similar to or greater than those of other tropical and temperate lakes. Lake depth seems to exert a stronger influence on stability than does lake area, but depth or stability measures alone provide little information about heat distribution or mixing regime. A strong positive relationship between water transparency and thermocline depth in both tropical and temperate lakes suggests that reductions in buoyant resistance to vertical mixing, caused by deeper penetration of solar radiation, are important in establishing mixing depths in various lakes. Comparisons of persistent thermocline depth in tropical vs. temperate lakes, regardless of size, indicate that mixing depths in tropical lakes are often greater than those in their temperate counterparts. This difference is caused in part by the narrow ranges of temperature and smaller absolute density gradients in these tropical lakes, against which the mixed layer is deepened.
TL;DR: In this paper, the size structure of the purple sea urchin Strongylocentrotus purpuratus was sampled from central California to central Oregon (36°-45°N).
Abstract: Size structure of the purple sea urchin Strongylocentrotus purpuratus was sampled from central California to central Oregon (36°– 45°N). Size frequency and inferred recruitment events are correlated with major topographic features. Capes and headlands—predictable sites of upwelling and locations of cold water plumes— show size frequencies indicative of low recruitment rates. Sites without predictable upwelling or regions that are between headlands have size frequencies that indicate substantial annual recruitment.