Effects of Cu,Pb and Zn on two Potamogeton species grown under field conditions

Two common macrophyte species, Potamogeton perfoliatus L. and Potamogeton pectinatus L. were grown for 12 weeks at shallow depths in sediments contaminated with 1250 or 2500 g Pb or Cu and/or Zn (gDW sediment)^-1. Control experiments were run at background levels of 4, 13, and 38 g Pb, Cu and Zn (gDW sediment)^-1, respectively. Effects of heavy metals on biomass production and metal uptake and distribution in plants are presented in relation to total amount and plant-available fraction of metals in the sediment.All three studied metals gave reduced biomass production, and the toxicity of the metals decreased in the order Zn>Cu>Pb. The root/shoot biomass ratio increased for P. pectinatus, but decreased for P. perfoliatus with metal treatment. The content of any single metal was higher in shoots than in roots of plants grown on sediments not contaminated with that specific metal, but addition of that metal increased the proportion in roots. The uptake by plants of any of the heavy metals increased with increased metal addition. The magnitude of the plant-available fraction of metals of untreated sediment was Zn>Cu>Pb, and increased in contaminated sediments. Addition of Cu decreased both the plant-available fraction and the total concentration of Zn in the sediment, while increased the uptake of Zn by the plants. The opposite was found for Cu when Zn was added. P. pectinatus accumulated about twice as much Cu as P. perfoliatus. On the other hand, the concentration of Pb was higher in P. perfoliatus than in P. pectinatus, and was negligible in P. pectinatus when cultivated in untreated sediments.     

The ecological significance of sulfur in the energy dynamics of salt marsh and coastal marine sediments

Sulfur is an important element in the metabolism of salt marshes and subtidal, coastal marine sediments because of its role as an electron acceptor, carrier, and donor. Sulfate is the major electron acceptor for respiration in anoxic marine sediments. Anoxic respiration becomes increasingly important in sediments as total respiration increases, and so sulfate reduction accounts for a higher percentage of total sediment respiration in sediments where total respiration is greater. Thus, sulfate accounts for 25% of total sediment respiration in nearshore sediments (200 m water depth or less) where total respiration rates are 0.1 to 0.3gCm^–1 day^–1 , for 50% to 70% in nearshore sediments with higher rates of total respiration (0.3 to 3gCm^–2 day^–1), and for 70% to 90% in salt marsh sediments where total sediment respiration rates are 2.5 to 5.5gcm^–2 day^–1 .During sulfate reduction, large amounts of energy from the respired organic matter are conserved in inorganic reduced sulfur compounds such as soluble sulfides, thiosulfate, elemental sulfur, iron monosulfides, and pyrite. Only a small percentage of the reduced sulfur formed during sulfate reduction is accreted in marine sediments and salt marshes. When these reduced sulfur compounds are oxidized, energy is released. Chemolithoautotrophic bacteria which catalyze these oxidations can use the energy of oxidation with efficiencies (the ratio of energy fixed in organic biomass to energy released in sulfur oxidation) of up to 21–37% to fix CO₂ and produce new organic biomass.Chemolithoautotrophic bacterial production may represent a significant new formation of organic matter in some marine sediments. In some sediments, chemolithoautotrophic bacterial production may even equal or exceed organoheterotrophic bacterial production. The combined cycle of anaerobic decomposition through sulfate reduction, energy conservation as reduced sulfur compounds; and chemolithoautotrophic production of new organic carbon serves to take relatively low-quality organic matter from throughout the sediments and concentrate the energy as living biomass in a discrete zone near the sediment surface where it can be readily grazed by animals.Contribution from a symposium on the role of sulfur in ecosystem processes held August 10, 1983, at the annual meeting of the A.I.B.S., Grand Forks, ND; Myron Mitchell, convenor.     

Distribution differences and active habitat choices of invertebrates between macrophytes of different morphological complexity

This study explores: (1) whether the abundance of macroinvertebrates differs between macrophytes differing in both morphological complexity and tolerance to nutrient enrichment; (2) whether the distribution of invertebrates between macrophytes is due to active habitat choice; and (3) whether invertebrates prefer structurally complex to simple macrophytes. Macroinvertebrate abundance was compared between two common soft-bottom plants of the Baltic Sea that are tolerant to eutrophication, Myriophyllum spicatum and Potamogeton pectinatus, and one common plant that is sensitive to eutrophication, Chara baltica. Both field sampling and habitat choice experiments were conducted. We recorded higher total macroinvertebrate abundance on the structurally complex M. spicatum than on the more simply structured P. pectinatus and C. baltica, but found no difference in macroinvertebrate abundance between P. pectinatus and C. baltica. In accordance with the field results, our experiment indicated that the crustacean Gammarus oceanicus actively chose M. spicatum over the other macrophytes. Besides, we found that G. oceanicus actively preferred complex to simply structured artificial plants, indicating that the animal distribution was at least partly driven by differences in morphological complexity between plant species. In contrast, the gastropod Theodoxus fluviatilis did not make an active habitat choice between the plants. Our findings suggest that human-induced changes in vegetation composition can affect the faunal community. Increased abundance of structurally complex macrophytes, for example, M. spicatum, can result in increased abundance of macroinvertebrates, particularly mobile arthropods that may actively choose a more structurally complex macrophyte.     

Heterotrophic nitrogen fixation in oligotrophic tropical marshes: changes after phosphorus addition

In order to determine the impact of nutrient enrichment on phosphorus (P) limited wetlands, we established experimental P additions in marshes throughout northern Belize. P significantly increased macrophyte primary production, which led to the rapid elimination of cyanobacterial mats. The replacement of cyanobacterial mats by macrophytes constrained autotrophic nitrogen (N) fixation, increased the quantity, and changed the quality of organic matter input to the sediments. We predicted that the activity of sediment heterotrophic N fixers will be impacted by these alterations in carbon input. We used the acetylene reduction technique to measure potential (glucose amended) nitrogenase activity (NA) in sediments from controls and treatment plots that have been P enriched for four years and dominated either by Eleocharis cellulosa, or Typha domingensis for two years. NA in P-enriched plots was 2–3 orders of magnitude higher than NA in controls. NA was positively correlated with the soil reactive P, both total organic and microbial carbon, live root biomass, and total phospholipid fatty acids (PLFA) as an indicator of active microbial biomass. It was negatively correlated with the concentration of ammonium-N. Path analysis revealed that the indirect effect of P on NA through the root biomass was more important than the direct effect of P. NA of the upper sediment layer was consistently higher in Eleocharis than in Typha dominated plots, despite the higher litter input by Typha. We feel that the higher levels of lignin and phenolics occurring in Typha litter, relative to Eleocharis, constrained NA in Typha plots. Handling editor: Luis Mauricio Bini     

Size-related auto-fragment production and carbohydrate storage in auto-fragment of <Emphasis Type="Italic">Myriophyllum spicatum</Emphasis> L. in response to sediment nutrient and plant density

Size-related asexual reproduction of submersed macrophytes is still poorly understood. Here, we investigate how size-related auto-fragmentation in Myriophyllum spicatum L. responds to sediment nutrients and plant density. An experiment was carried out with sediments containing two different nutrient levels and with two levels of plant density. The results show that sediment nutrients and plant density brought about a strong dependency of auto-fragment production and the amount of total non-structural carbohydrate (TNC) storage in auto-fragments on individual plant size (total plant biomass). However, these two factors acted differently on size dependency. Sediment nutrients positively affected auto-fragment production and the amount of TNC in auto-fragments of M. spicatum. High concentrations of sediment nutrients significantly increased these two traits in absolute value and the value relative to plant size. Although the auto-fragment biomass and the amount of TNC in auto-fragments did not differ between density treatments when plant size was considered, the absolute values of these two traits were much larger in the low plant density treatment than in the high plant density treatment, which suggested an indirect negative effect of plant density on the auto-fragmentation of M. spicatum. In addition, higher percentages of large auto-fragments (>100 mg) were produced by plants that grew in nutrient poor sediment and low plant density environment than plants in nutrient rich sediment and high plant density environment. These results do not solely highlight a size-dependent effect, but also a size-independent effect of auto-fragment production and the amount of TNC in auto-fragments of M. spicatum. Furthermore, such size-independent effects can be explained by the significant biomass partitioning differences and the similar TNC-concentrations in auto-fragments under different environmental conditions.     

Sediment nutrient accumulation and nutrient availability in two tidal freshwater marshes along the Mattaponi River, Virginia, USA

Sediment deposition is the main mechanism of nutrient delivery to tidal freshwater marshes (TFMs). We quantified sediment nutrient accumulation in TFMs upstream and downstream of a proposed water withdrawal project on the Mattaponi River, Virginia. Our goal was to assess nutrient availability by comparing relative rates of carbon (C), nitrogen (N), and phosphorus (P) accumulated in sediments with the C, N, and P stoichiometries of surface soils and above ground plant tissues. Surface soil nutrient contents (0.60–0.92% N and 0.09–0.13% P) were low but within reported ranges for TFMs in the eastern US. In both marshes, soil nutrient pools and C, N, and P stoichiometries were closely associated with sedimentation patterns. Differences between marshes were more striking than spatial variations within marshes: both C, N, and P accumulation during summer, and annual P accumulation rates (0.16 and 0.04 g P m^–2 year^–1, respectively) in sediments were significantly higher at the downstream than at the upstream marsh. Nitrogen:P ratios <14 in above ground biomass, surface soils, and sediments suggest that N limits primary production in these marshes, but experimental additions of N and/or P did not significantly increase above ground productivity in either marsh. Lower soil N:P ratios are consistent with higher rates of sediment P accumulation at the downstream site, perhaps due to its greater proximity to the estuarine turbidity maximum.     

Competition between an introduced and an indigenous species: the case of Paspalum paspalodes (Michx) Schribner and Aeluropus littoralis (Gouan) in the Camargue (southern France)

Paspalum paspalodes, an introduced grass species, and Aeluropus littoralis, an indigenous species, develop abundantly in seasonally-flooded marshes in the Camargue (Rhône Delta, France). Although they occur together in many multispecies communities, neither species occurs when the other is dominat. The cultivation of cuttings of P. paspalodes and A. littoralis in a replacement series in a combination of five proportions (0/100, 25/75, 50/50, 75/25 and 100/0) and four salinities (0,2 4, and 6 g Cl^- · 1^-1) gave contrasting results for the two species: (1) strong asymmetrical competition in favour of P. paspalodes at 0 g Cl^- · 1^-1, (2) no significant effect of salinity on the mean above-ground and underground yields per plant for A. littoralis over the range tested, (3) a major decrease in the mean above-ground and belowground yields per plant for P. paspalodes with increasing salinity, (4) a reversal of the competitive balance between the species with increasing salinity. The cultivation of cuttings at high temperatures in a greenhouse in a combination of the same five proportions at two salinities (0 and 4 g Cl^- · 1^-1) refuted the hypothesis that the introduced species is better adapted to summer temperatures. Because it is not salt-tolerant, P. paspalodes cannot be considered as a potentially invasive species in the Camargue. Its abundance depends on newly created and artificially maintained habitats.     

Coexistence and the comparative light relations of the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana Michx.

Summary The Eurasian watermilfoil (Myriophyllum spicatum L.) has partially replaced wild celery (Vallisneria americana Michx.) as a community dominant in the littoral zones of lakes of Madison, Wisconsin. The two species have very different growth forms, with that of M. spicatum corresponding more closely to the optimal growth form simulated by the macrophyte production model WEED. The objective of this research was to investigate the mechanisms by which Vallisneria could compensate for its nonoptimal growth form and coexist with Myriophyllum.A quantification of midsummer growth form for the two species at a rooting depth of 80–90 cm showed that M. spicatum had 68% of its shoot biomass within 30 cm of the surface, whereas V. americana had 62% of its leaf biomass within 30 cm of the bottom. Vallisneria had a light extinction coefficient ranging from 0.013 to 0.019 m²·g^-1, much higher than the value (ca. 0.006 m²·g^-1) for M. spicatum. This indicates less effective penetration of light to lower leaves of V. americana. Half-saturation constants describing the light-dependence of carbon uptake in shade and sun tissues ranged from 60–197 microeinsteins·m^-2·s^-1 for V. americana, and 164–365 einsteins·m^-2·s^-1 for M. spicatum. The optimum temperature for photosynthesis was 33.6°C for M. spicatum and 32.6°C for V. americana, but Myriophyllum was nearly twice as effective at carbon uptake at 10°C. Integration of all of the above features with WEED showed that, for midsummer conditions, V. americana more than compensated for apparently disadvantageous morphological features by its greater physiological adaptability to low light regimes. Coupled with the temperature-dependence of photosynthesis, it appears that V. americana is favored by midsummer conditions, whereas M. spicatum is at an advantage at other times.     

Influence of quantity and lability of sediment organic matter on the biomass of two isoetids,Littorella uniflora and Echinodorus repens

1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects of quantity and lability of sediment organic matter on the biomass of Echinodorus repens and Littorella uniflora and on the force required to uproot plants of L. uniflora. 2. Lake sediments, rich in organic matter, were collected from four lakes, two with healthy populations of isoetids and two from which isoetids had disappeared. The four lake sediments were mixed with sand to prepare a range of experimental sediments that differed in quantity and lability of sediment organic matter. Two isoetid species, E. repens and L. uniflora, were grown in these sediments for 8 weeks. Sediment quality parameters, including elemental composition, nutrient availability and mineralisation rates, were determined on the raw sources of sediment from the lakes. Porewater and surface water were analysed for the chemical composition in all mixtures. At the end of the experiment, plants were harvested and their biomass, tissue nutrient concentration and (for L. uniflora) uprooting force were measured. 3. For both species, all plants survived and showed no signs of stress on all types of sediment. The biomass of E. repens increased as the fraction of organic matter was increased (from 6 to 39% of organic content, depending upon sediment type). However, in some of the sediment types, a higher fraction of organic matter led to a decline in biomass. The biomass of L. uniflora was less responsive to organic content and was decreased significantly only when the least labile sediment source was used to create the gradient of organic matter. The increase in shoot biomass for both species was closely related to higher CO₂ concentrations in the porewater of the sediment. The force required to uproot L. uniflora plants over a range of sediment organic matter fitted a Gaussian model; it reached a maximum at around 15% organic matter and declined significantly above that. 4. Increasing organic matter content of the sediment increased the biomass of isoetid plants, as the positive effects of higher CO₂ production outweighed the negative effects of low oxygen concentration in more (labile) organic sediments. However, sediment organic matter can adversely affect isoetid survival by promoting the uprooting of plants.     

Environmental Stress Determines the Quality of Bacterial Lysate and Its Utilization Efficiency in a Simple Microbial Loop

Heterotrophic bacteria provide the critical link in the microbial loop by converting dissolved organic matter (DOM) into particulate form. In this study, DOM was prepared from recently isolated estuarine bacterial strain Vibrio sp. (DSM14379) grown at different salinities [0.2%, 0.5%, 3%, 5%, or 10% (w/v)], washed, concentrated, and lysed by autoclaving. The corresponding lysate-containing media were designated LM_0.2, LM_0.5, LM₃, LM₅, and LM₁₀. Vibrio sp. cells grown at different salinities had similar C/N/P ratios, but different C/S ratios, different trace element composition, and different 2D gel electrophoresis protein profiles. Pseudoalteromonas sp. (DSM06238) isolated from a similar environment was able to grow on all lysates, and its biomass production was dependent on lysate type. The highest growth rate and biomass production of Pseudoalteromonas sp. at saturation lysate concentrations were observed in LM₃. The biomass production at saturation lysate concentrations was about 3-fold higher as compared to LM_0.2 and LM₁₀. The initial respiration rate, intracellular adenosine triphosphate (ATP) levels, and ³H-Leu and ³H-TdR incorporation rates were lowest in LM₃. On the other hand, in LM_0.2 or LM₁₀ lysates the situation was reversed, the growth rates and biomass production were lowest, whereas ³H-Leu and ³H-TdR incorporation, respiration rates, as well as ATP levels, were highest. These results imply uncoupling of catabolism from growth in either high- or low-salinity lysates. The results also suggest that differences in organic carbon quality generated during Vibrio sp. growth at different NaCl concentrations were propagated through the simple microbial loop, which may have important ecological implications for higher trophic levels that depend on microbial grazing.     

Mesocosm experiments: mimicking seasonal developments of microbial variables in North Sea sediments

This study investigated the suitability of mesocosms for studying the seasonal development of microbial variables in the benthic system of the North Sea. Undisturbed sediment cores were taken from two locations in the North Sea, one with sandy sediment (28 m depth) and the other with silty sediment (38 m depth) and installed in mesocosms in January–April 1989. Cores were kept as in situ temperature in the dark until December 1989. One set of sandy and silty sediments was starved and the other set received a supply of organic matter in May–June, simulating the settlement of the spring bloom of Phaeocystis pouchetii. Seasonal developments in bacterial production (methyl ³H-thymidine incorporation), abundance and biomass of bacteria and nanoflagellates and oxygen consumption were compared between the mesocosms and the field in surface sediments every 1.5 to 2.5 months. Effects of seasonal temperature variations (range 6–17.5 °C) on microbial variables in starved mesocosms were limited, which possibly indicates a subordinate role of temperature in microbial processes in North Sea sediments. Organic matter produced a direct response in bacterial production and oxygen consumption in mesocosms. Bacterial and protozoan abundance also increased. The effect of the organic input disappeared within 2 months and values of enhanced variables declined to initial levels. The organic matter enrichment in mesocosms apparently did not provide sufficient energy to keep the microbenthos active at field levels through summer.These results suggest that in the silty sediments in the field, organic matter is available for bacterial production throughout summer. In sandy sediments, the major organic matter input, which sets the seasonal pattern, appears to be in June. Apparently the seasonal development of microbial variables can be mimicked in mesocosms with organic matter supplies. Differences between the field and mesocosms are further illustrated by carbon budgets. Recycling of bacterial biomass was required to meet the bacterial carbon demand in the budget.Publication No. 22 of the project Applied Scientific Research Neth. Inst. for Sea Res. (BEWON).     

In vitro and in situ studies on nitrate disappearance in water-sediment systems of the Camargue (southern France)

Results of in vitro and in situ experiments on nitrate disappearance from water-sediment systems in the Camargue are described.In the in vitro experiments two factors were studied: temperature and organic matter. After a first addition of KNO₃ to these sediments, the concentration of organic matter exerted a strong influence on the disappearance rate of nitrate at 25 °C and 15 °C but not at 2 °C. After a second addition of nitrate at 25 °C and 15 °C the denitrification rate increased by approximately 10%, probably because the activity of the bacterial population had increased.Experiments in situ in freshwater temporary marshes showed that nitrate disappeared at approximately twice the rate at similar temperature in vitro.After the first addition of nitrate in the in vitro experiments the concentration of nitrite in the water above the sediment reached about 10% of the concentration of total dissolved inorganic nitrogen at 2 °C and 15 °C. These high concentrations were not found after the first addition at 25 °C or after the second addition of nitrate at 25 °C and 15 °C. In the in situ experiments, however, high concentrations of nitrite were found.     

The labyrinth of nutrient cycles and buffers in wetlands: results based on research in the Camargue (southern France)

Wetlands, especially in the Mediterranean area, are subject to severe eutrophication. This may upset the equilibrium between phytoplankton production in undesirable quantities and a quantitatively desirable macrophyte production. In order to manage this equilibrium, a quantitative knowledge of nutrient input and fluxes is essential and the role of sediments in these processes must be understood. This knowledge can be useful even for agriculture, e.g. rice cultivation, where optimal utilization of fertilizers can lead to an economic benefit.In this article different aspects of nutrient cycles are discussed in view of approaching a sufficiently precise quantification. The nutrient input balance of the Camargue was therefore measured which showed that the input of nutrients with the irrigation water, taken from the river Rhone, roughly equals the quantity of fertilizers added.Phytoplankton growth can be approached reasonably with the Monod model, although there are still many practical problems, such as the influence of the pH on P uptake and the problem of measuring P uptake in the field. The situation is worse for macrophyte growth; quantitative data are scarce and studies have often been carried out with unrealistic nutrient concentrations or without addressing the influence of the sediment. This influence can also include negative factors, such as high concentrations of Fe²⁺, H₂S or FeS, but cannot yet be quantified.The nitrogen cycle in wetlands is dominated by denitrification. Most wetlands have sediments with high concentrations of organic matter, therefore with a large reducing capacity. Besides this process, we have shown that denitrification can also be controlled by FeS. In the Camargue sediments this denitrification is mediated by bacteria from the sulfur cycle; this appeared to be the major pathway. It was shown that a stoicheiometric relation exists between nitrate reduced and sulphate produced. The influence of the temperature was quantified and appeared to be stronger at high organic matter concentrations than at lower ones. Denitrification with FeS means that the bacteria use nitrate also for their N demands, while this is not necessarily the case during denitrification with organic matter.Mineralization of macrophytes is a much slower process than that of phytoplankton, probably because of their high C/N ratio. We could, however, not confirm the general assumption that the addition of nitrogen stimulates this mineralization. On the contrary, we found that two amino acids both with a C/N ratio of 6 had different mineralization rates. The amino acid composition of dead macrophytes and the C/N ratio may be of equal importance.Unlike nitrogen, phosphate is always strongly adsorbed onto sediments. The two mechanisms of the adsorption of inorganic phosphate onto sediments, i.e. the adsorption onto Fe(OOH) and the precipitation of apatite, have been quantified. The adsorption of phosphate onto Fe(OOH) can be satisfactory described with the Freundlich adsorption isotherm: P_ads = A^* (o-P)^B. The adsorption coefficient A depends on the pH of the system and the Ca²⁺ concentration of the overlying water and can be quantified preliminarily by A = a.10(^–0.416*pH).(2.86 – (1.86.e^–Ca2+)). B can be approached by 0.333, which means the cube root of the phosphate concentration. The second mechanism is the solubility of apatite. We found a solubility product of 10^–50 for hard waters. The two mechanisms are combined in solubility diagrams which describe equilibrium situations for specific lakes.The conversion of Fe(OOH) to FeS has a strong influence on phosphate adsorption, although the partial reduction of Fe(OOH) P by H₂S does not release significant quantities of phosphate. Even after complete conversion to FeS only a small part of the bound phosphate was released.Besides the two inorganic phosphate compounds, we established the existence of two organic pools, one soluble after extraction with strong acid (ASOP), the other one with strong alkali. The first pool is probably humic bound phosphate, while the larger part of the second pool was phytate. The ASOP was remineralized during the desiccation of a Camargue marsh; this drying up oxidized FeS, thus improving the phosphate adsorption and decreasing the denitrification capacity. It can, therefore, be an important tool for management. The phytate was strongly adsorbed onto Fe(OOH), which explains the non-bioavailability towards bacteria.The fact that the sediment phosphate concentration can be approached by multiplying the relevant sediment adsorption constant with % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaOqaaeaaca% WGVbGaeyOeI0IaamiuaaWcbaGaaG4maaaaaaa!3B8D!\[\sqrt[3]{{o - P}}\] concentration has the consequence that much larger quantities of phosphate accumulate in the sediments than in the overlying water. This means that even if the phosphate input is stopped, the eutrophication will only be reversed very slowly, and not at all, if the shallow waters in wetlands have no through flow — as is often the case in many marshes in Mediterranean wetlands.Abbreviations used o-P = dissolved ortho phosphate (or its concentration) - N_part, P_part = particulate N or P - Tot-N_inorg = Total inorganic nitrogen (= NH₃ + NO ₂ ^– + NO ₃ ^– ) This paper, giving an overview of the research in the sediments of the Camargue, was read during the symposium Nutrient Cycles — A Joy Forever, on the occasion of my retirement, 19th of May 1993 at the I.H.E. in Delft (Netherlands).     

Regional variation in eelgrass (Zostera marina) morphology, production and stable sulfur isotopic composition along the Baltic Sea and Skagerrak coasts

Morphology, total sulfur content and stable sulfur isotopic composition of Zostera marina were examined in the Baltic Sea–Skagerrak transition zone through surveys. The seagrass meadows were denser and less productive at the low salinities in the Baltic Sea (salinity 6–7 psu), and total sulfur accumulations in plants were lower and δ³⁴S values were higher compared to the west coast of Sweden (salinity 21–29 psu). The δ³⁴S values of the three plant compartments (leaves, rhizomes, roots) indicated lower sulfide invasion at low salinities, which was mainly due to environmental conditions (e.g. low epiphytic biomass, low sediment organic matter and low sulfate concentration) and plant characteristics (productivity, shoot morphology). Between 13% and 63% of the sulfur in the plants was derived from sediment sulfides with highest percentages in the roots (27–63%) and lower in rhizomes (13–50%) and leaves (14–51%). The high sulfide invasion on the west coast of Sweden was coincident with high sediment organic matter, probably increasing sulfide pressure on the plants, and high epiphytic biomass, probably constraining the oxygen dynamics in the plants and enhancing sulfide invasion. Regional and spatial variability in the δ³⁴S were extensive, emphasizing the need for detailed analysis of local sources when applying stable sulfur isotopes in food web analyses. The observed invasion of sulfides suggests sulfide as a contributing factor to reported declines of Z. marina in the Skagerrak region.     

Macroinfaunal biomass and energy flow in a shallow reef flat of the northwestern Philippines

Macrofaunal biomass of the Lucero reef flat in the northwestern Philippines accounted for 9 to 52% of total sediment organic matter, and did not exhibit any significant temporal trend. The polychaetes and crustaceans consistently alternated as biomass dominants; the latter group showed monthly and seasonal variations along with the chaetognaths, molluscs, chordates, and chelicerates, among the major groups (p<0.05). Faunal abundance correlated significantly with biomass. Salinity, mean sediment grain size, sediment heterogeneity, and total organic matter were found to significantly influence faunal biomass.The sandy substrate community was characteristically heterotrophic throughout the monitoring period, i.e., P/R<1. Hourly rates of net primary production (p _n ) did not exhibit any significant diurnal pattern. Monthly comparisons yielded significant differences for estimates of daily gross primary production, P, and respiration, R. Values of P were relatively low, and ranged from 2240 (± 1526 S.D.) to 4890 (± 1377) mg O₂ m^–2 d^–1 while R ranged from 3744 (± 1504) to 6879 (± 903) mg O₂ m^–2 d^–1. R was lower during the dry warm months than the wet months. Multiple regression analyses indicate that primary production was a positive function of light intensity and temperature, and a negative correlate of salinity (adjusted R ² = 0.2444, p< 0.05). Respiration (r) did not appear to relate with any environmental variable, with total macroinfaunal abundance nor with biomass.Results of the study suggest that other heterotrophic components of the sand community were probably responsible for most of the energy consumption, and that these may be dependent on external sources of organic matter.     

Effect of total dissolved solids and irradiance on growth and toxin production by Nodularia spumigena

The objective of this work was to determine the influence of total dissolved solids/salinity (TDS mgL^-1) on growth and biomass specific rates of nodularin (hepatotoxin) production by Nodularia spumigena 001E isolated from Lake Alexandrina, South Australia. Maximum biomass yield (dry matter, chlorophyll a and particulate organic carbon/POC) at 80 μmol photon m^-2 s^-1 was recorded at 3300 mg TDS L^-1 and decreased at salinities above or below this value (p < 0.05). The maximum biomass yield (dry matter and chlorophyll a) at 30 μmol m^-2 s^-1 occurred at a higher salinity of 9900 mg TDS L^-1. Cultures grown at 80 μmol m^-2 s^-1, at a TDS> 6600 mg L^-1, had significantly (p < 0.05) lower nodularin content (ml^-1 medium) than cultures grown at the same salinities at 30 μmolm^-2 s^-1. The maximum total toxin concentration (mL^-1 medium) occurred at 9900 and 3300 mg TDS L^-1 at 30 μmol m^-2 s^-1and 80 μmol m^-2 s^-1 respectively. Toxin per unit biomass, expressed as dry matter, chlorophyll a and POC was similar for cultures grown at 30 μmol m^-2 s^-1 or 80 μmol m^-2s^-1 at salinities < 6600 mg TDS L^-1. At salinities > 9900 mg TDS L^-1 the toxin content per unit biomass decreased at both irradiances, however, cultures grown at 30 μmol m^-2s^-1 had a higher toxin content than those grown at 80 μmol m^-2 s^-1. The results indicate that not only do changes in irradiance and salinity directly influence growth and toxin production but that changes in irradiance affected the influence of salinity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Primary production dynamics of dominant hydrophytes in Lake Provala (Serbia)

The objective of this investigation was to analyze the primary production of the dominant hydrophytes by monitoring levels of organic matter and organic carbon and estimating photosynthetic potential via the total chlorophyll content. The survey was conducted in Lake Provala (Serbia) throughout the peak vegetation period of the year 2000. The contents of organic matter and organic carbon for Myriophyllum spicatum L. were 105.11 g m⁻² and 73.66 g m⁻², Nymphoides peltata (Gmel.) Kunt. were 95.51 g m⁻² and 45.26 g m⁻² and Ceratophyllum demersum L. were 52.17 g m⁻² and 29.75 g m⁻². Chlorophyll A (Chl a) and chlorophyll A+B (Chl a+b) pigments ranged from 1.54 mg g⁻¹(Chl a) and 2.1 mg g⁻¹(Chl a+b) in M. spicatum to 5.27 mg g⁻¹(Chl a) and 7.53 mg g⁻¹(Chl a+b) in C. demersum. At full leaf out, the latter aquatic plants exceeded 50% cover of the open water surface. All species achieved maximum growth in June, but significant differences in growth dynamics were observed. At the end of the vegetation period, these plants sink to the bottom and decompose     

Water‐level fluctuations affect sediment properties,carbon flux and growth of the isoetid Littorella uniflora in oligotrophic lakes

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Role of plankton in the turnover of organic matter on the Great Barrier Reef,Australia

Number, biomass and production of phytoplankton, bacteria, micro- and mesozooplankton and turnover of labile and stable organic matter were measured in waters over some Capricornia round reefs, and over the reefs of Lizard Island. Primary production was 10 to 40 mg C m^–3 d^–1 but was lower over the living reefs. Microbial wet biomass in reef waters varied from 100 to 500 mg m^–3, and production from 4 to 68 mg C m^–3 d^–1, which was commensurable with primary production. The biomass of microzooplankton (ciliates, zooflagellates and larvae) in waters of Lizard Island reefs reached 100–300 mg m^–3. Mesozooplankton biomass at night in reef waters of Heron Island varied from 200 to 800 mg m^–3. Its composition depended upon the tide phase. PB coefficients in bacterioplankton were 0.3 to 1.2 per day. The food demand of bacterioplankton in waters over the reefs was 5 to 20 times higher than the primary phytoplankton production. Labile organic matter (LOM) doubled in waters after it stayed over living reef for several hours. The turnover time of LOM in reef waters was as short as 1–2 weeks.     

Sulfate reduction processes in sediments at different sites in Lake Kinneret,Israel

Lake Kinneret, Israel, is a warm (13–30°C) monomictic lake that stratifies in April and turns over in December. Between January and June each year, a heavy bloom (up to 250 g wet weight n^–2 2) of the dinoflagellate Peridinium gatunense dominates the phytoplankton biomass. In early summer, the bloom collapses, and the sinking Peridinium biomass serves as a trigger for intense sulfate-reduction activity throughout the hypolimnion and within the sediments. The availability of organic matter and sulfate was high shortly after the bloom crash and the beginning of stratification and was lowest in December before overturn. Sulfate-reduction rates at three different sites in the lake were studied. In the sediments, the rates varied seasonally and among stations from 5 to 1600 nmol SO₄ ^–2 reduced cm^–3 day^–1, with respect to the distance from the Jordan River, depth, organic content, and stratification period. During years of low lake water levels, intense sulfate reduction occurred in the hypolimnion, resulting in anoxia and high concentrations of H₂S (>400 m). In years with high water levels, early bloom, and delayed stratification, higher rates of sulfate reduction were recorded in the sediments, probably as a result of a greater fraction of the primary production (organic matter) reaching the bottom. Correspondence to: O. Hadas.