Response of macrophyte litter decomposition in global blue carbon ecosystems to climate change

Blue carbon ecosystems (BCEs) are important nature-based solutions for climate change-mitigation. However, current debates question the reliability and contribution of BCEs under future climatic-scenarios. The answer to this question depends on ecosystem processes driving carbon-sequestration and -storage, such as primary production and decomposition, and their future rates. We performed a global meta-analysis on litter decomposition rate constants (k) in BCEs and predicted changes in carbon release from 309 studies. The relationships between k and climatic factors were examined by extracting remote-sensing data on air temperature, sea-surface temperature, and precipitation aligning to the decomposition time of each experiment. We constructed global numerical models of litter decomposition to forecast k and carbon release under different scenarios. The current k averages at 27 ± 3 × 10⁻² day⁻¹ for macroalgae were higher than for seagrasses (1.7 ± 0.2 × 10⁻² day⁻¹), mangroves (1.6 ± 0.1 × 10⁻² day⁻¹) and tidal marshes (5.9 ± 0.5 × 10⁻³ day⁻¹). Macrophyte k increased with both air temperature and precipitation in intertidal BCEs and with sea surface temperature for subtidal seagrasses. Above a temperature threshold for vascular plant litter at ~25°C and ~20°C for macroalgae, k drastically increased with increasing temperature. However, the direct effect of high temperatures on k are obscured by other factors in field experiments compared with laboratory experiments. We defined “fundamental” and “realized” temperature response to explain this effect. Based on relationships for realized temperature response, we predict that proportions of decomposed litter will increase by 0.9%–5% and 4.7%–28.8% by 2100 under low- (2°C) and high-warming conditions (4°C) compared to 2020, respectively. Net litter carbon sinks in BCEs will increase due to higher increase in litter C production than in decomposition by 2100 compared to 2020 under RCP 8.5. We highlight that BCEs will play an increasingly important role in future climate change-mitigation. Our findings can be leveraged for blue carbon accounting under future climate change scenarios.     

Crab Burrowing Limits Surface Litter Accumulation in a Temperate Salt Marsh: Implications for Ecosystem Functioning and Connectivity

Burial of aboveground plant litter by animals reduces the amount available for surface transport and places it into a different environment, affecting decomposition rates and fluxes of organic matter to adjacent ecosystems. Here we show that in a Southwestern Atlantic salt marsh the burrowing crab Neohelice granulata buries aboveground plant litter at rates (0.5–8 g m^?2 day^?1) comparable to those of litter production (3 g m^?2 day^?1). Buried litter has a low probability (0.6%) of returning to the marsh surface. The formation of burrow excavation mounds on the marsh surface is responsible for most litter burial, whereas litter trapped in burrows was an order of magnitude lower than rates of burial under excavation mounds. Crab exclusion markedly increased surface litter accumulation (3.5-fold in just 21 days). Tides with the potential to transport significant amounts of surface litter are infrequent; hence, most litter is buried before it can be transported elsewhere or decomposes on the surface. Crab litter burial can account for the observed low levels of surface litter accumulation in this ecosystem and likely drives organic matter transformation and export. The impacts of ecosystem engineering by this crab species are therefore substantial and comparable in magnitude to the large effects found for tropical crabs and other litter-burying organisms, such as anecic earthworms.     

Abundance and production of bacteria, and relationship to phytoplankton production, in a large tropical lake (Lake Tanganyika)

1. Abundance and bacterial production (BP) of heterotrophic bacteria (HBact) were measured in the north and south basins of Lake Tanganyika, East Africa, during seasonal sampling series between 2002 and 2007. The major objective of the study was to assess whether BP can supplement phytoplankton particulate primary production (particulate PP) in the pelagic waters, and whether BP and particulate PP are related in this large lake. HBact were enumerated in the 0–100 m surface layer by epifluorescence microscopy and flow cytometry; BP was quantified using ³H‐thymidine incorporation, usually in three mixolimnion layers (0–40, 40–60 and 60–100 m). 2. Flow cytometry allowed three subpopulations to be distinguished: low nucleic acid content bacteria (LNA), high nucleic acid content bacteria (HNA) and Synechococcus‐like picocyanobacteria (PCya). The proportion of HNA was on average 67% of total bacterial abundance, and tended to increase with depth. HBact abundance was between 1.2 × 10⁵ and 4.8 × 10⁶ cells mL⁻¹, and was maximal in the 0–40 m layer (i.e. roughly, the euphotic layer). Using a single conversion factor of 15 fg C cell⁻¹, estimated from biovolume measurements, average HBact biomass (integrated over a 100‐m water column depth) was 1.89 ± 1.05 g C m⁻². 3. Significant differences in BP appeared between seasons, especially in the south basin. The range of BP integrated over the 0–100 m layer was 93–735 mg C m⁻² day⁻¹, and overlapped with the range of particulate PP (150–1687 mg C m⁻² day⁻¹) measured in the same period of time at the same sites. 4. Depth‐integrated BP was significantly correlated to particulate PP and chlorophyll‐a, and BP in the euphotic layer was on average 25% of PP. 5. These results suggest that HBact contribute substantially to the particulate organic carbon available to consumers in Lake Tanganyika, and that BP may be sustained by phytoplankton‐derived organic carbon in the pelagic waters.     

Electron transfer of dissolved organic matter and its potential significance for anaerobic respiration in a northern bog

We investigated electron transfer processes of dissolved organic matter (DOM) and their potential importance for anaerobic heterotrophic respiration in a northern peatland. Electron accepting and donating capacities (EAC, EDC) of DOM were quantified using dissolved H₂S and ferric iron as reactants. Carbon turnover rates were obtained from porewater profiles (CO₂, CH₄) and inverse modeling. Carbon dioxide was released at rates of 0.2–5.9 mmol m⁻² day⁻¹ below the water table. Methane (CH₄) formation contributed <10%, and oxygen consumption 2% to 40%, leaving a major fraction of CO₂ production unexplained. DOM oxidized H₂S to thiosulfate and was reduced by dissolved ferric iron. Reduction with H₂S increased the subsequently determined EDC compared to untreated controls, indicating a reversibility of the electron transfer. In situ redox capacities of DOM ranged from 0.2 to 6.1 mEq g⁻¹ C (EAC) and from 0.0 to 1.4 mEq g⁻¹ C (EDC), respectively. EAC generally decreased with depth and changed after a water table drawdown and rebound by 20 and −45 mEq m⁻², respectively. The change in EAC during the water table fluctuation was similar to CH₄ formation rates. In peatlands, electron transfer of DOM may thus significantly contribute to the oxidation of reduced organic substrates by anaerobic heterotrophic respiration, or by maintaining the respiratory activity of sulfate reducers via provision of thiosulfate. Part of the anaerobic electron flow in peat soils is thus potentially diverted from methanogenesis, decreasing its contribution to the total carbon emitted to the atmosphere.     

KINETICS OF GROWTH AND DEATH IN ANABAENA FLOS-AQUAE (CYANOBACTERIA) UNDER LIGHT LIMITATION AND SUPERSATURATION

The kinetics of population growth and death were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown at light intensities ranging from limitation to photoinhibition (5 W·m⁻² to 160 W·m⁻²) in a nutrient-replete turbidostat. Steady-state growth rate (μ, or dilution rate, D) increased with light intensity from 0.44·day⁻¹ at a light intensity of 5 W·m⁻² to 0.99·day⁻¹ at 20 W·m⁻² and started to decrease above about 22 W·m⁻², reaching 0.56·day⁻¹ at 160 W·m⁻². The Haldane function of enzyme inhibition fit the growth data poorly, largely because of the unusually narrow range of saturation intensity. However, it produced a good fit (P < 0.001) for growth under photoinhibition. Anabaena flos-aquae died at different specific death rates (γ) below and above the saturation intensity. When calculated as the slope of a v_x⁻¹ and D⁻¹ plot, where v_x and D are cell viability (or live cell fraction) and dilution rate, respectively; γ was 0.047·day⁻¹ in the range of light limitation and 0.103·day⁻¹ under photoinhibition. Live vegetative cells and heterocysts, either in numbers or as a percentage of the total cells, showed a peak at the saturation intensity and decreased at lower and higher intensities. The ratio of live heterocysts to live vegetative cells increased with intensity when light was limiting but decreased when light was supersaturating. In cells growing at the same growth rate, the ratio was significantly lower under light inhibition than under subsaturation and the cell N:C ratio was also lower under inhibition. The steady-state rate of dissolved organic carbon (DOC) production increased with light intensity. However, its production as a percentage of the total C fixation was lowest at the optimum intensity and increased as the irradiance decreased or increased. The rate and percentage was significantly higher under photoinhibition than limitation in cells growing at the same growth rate. About 22% of the total fixed carbon was released as DOC at the highest light intensity. No correlation was found between the number of dead cells and DOC.     

Effects of organic matter and season on leaf litter colonisation and breakdown in cave streams

1. Low organic matter availability is thought to be a primary factor influencing evolutionary and ecological processes in cave ecosystems. We examined links among organic matter abundance, macroinvertebrate community structure and breakdown rates of red maple (Acer rubrum) and corn litter (Zea mays) in coarse‐ (10 × 8 mm) and fine‐mesh (500‐μm) litter bags over two seasonal periods in four cave streams in the south‐eastern U.S.A. 2. Organic matter abundance differed among cave streams, averaging from near zero to 850 g ash‐free dry mass m^?2. Each cave system harboured a different macroinvertebrate community. However, trophic structure was similar among caves, with low shredder biomass (2–17% of total biomass). 3. Corn litter breakdown rates (mean k = 0.005 day^?1) were faster than red maple (mean k = 0.003 day^?1). Breakdown rates in coarse‐mesh bags (k = 0.001–0.012 day^?1) were up to three times faster than in fine‐mesh bags (k = 0.001–0.004 day^?1). Neither invertebrate biomass in litter bags nor breakdown rates were correlated with the ambient abundance of organic matter. Litter breakdown rates showed no significant temporal variation. Epigean (surface‐adapted) invertebrates dominated biomass in litter bags, suggesting that their effects on cave ecosystem processes may be greater than hypogean (cave‐adapted) taxa, the traditional focus of cave studies. 4. The functional diversity of our cave communities and litter breakdown rates are comparable to those found in previous litter breakdown studies in cave streams, suggesting that the factors that control organic matter processing (e.g. trophic structure of communities) may be broadly similar across geographically diverse areas.     

Temporal variability in egg production rates of Acartia tonsa Dana in Long Island Sound

The relationship between week-by-week variations in the in situ egg production rates of Acartia tonsa Dana and changes in chlorophyll concentration in several size fractions was investigated by incubating adult females in natural sea water for 24-h periods. Our results indicate that the egg production of A. tonsa in Long Island Sound was better related to the 10 μm chlorophyll size fraction than to the total chlorophyll concentration. The < 10 μm size fraction comprised the greatest percentage of the chlorophyll during July and August when the water column was stratified. Egg production rates were lowest (8.7 eggs · female⁻¹ · day⁻¹) in early August when less than 0.5 μg chlorophyll 1 ⁻¹ was observed in the 10 μm chlorophyll a size fraction. Following destratification in late August, the “fall” diatom bloom occurred and egg production rates increased to the maximum observed rate of 56.6 eggs · female⁻¹ · day⁻¹. At this time, the concentration of the 10μm chlorophyll size fraction was 5.5 μg 1⁻¹. Maximum egg production rates were observed at chlorophyll concentrations as low as 0.8 μg 1⁻¹ in the 10 μm size fraction.     

Characteristics of simultaneous organic and nutrient removal in a pilot-scale vertical submerged membrane bioreactor (VSMBR) treating municipal wastewater at various temperatures

A pilot-scale vertical submerged membrane bioreactor (VSMBR) with anoxic and oxic zones in one reactor was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. Source water with total chemical oxygen demand (TCOD)/total nitrogen (TN) ratio of 5.5 was treated at various temperatures (13–25 °C) over an interval of about 1 year. As a result, total suspended solid (TSS) and TCOD were removed by 100% and higher than 98%, respectively. Moreover, the average removal efficiencies of TN and total phosphorus (TP) were found to be 74% and 78% at 8 h-hydraulic retention time (HRT) and 60-days sludge retention time (SRT). Under these conditions, the specific removal rates (SRR) of TN and TP were found to be 0.093 kg N m⁻³ day⁻¹ and 0.008 kg P m⁻³ day⁻¹, and the daily production of excess sludge (DPES), 0.058 kg TSS day⁻¹.     

Microbial processes of the carbon and sulfur cycles in the White Sea

The present paper contains the results of our microbiological and biogeochemical investigations carried out during a series of expeditions to the White Sea in 2002–2006. The studies were conducted in the open part of the White Sea, as well as in the Onega, Dvina, and Kandalaksha bays. In August 2006, the photosynthetic productivity in the surface water layer was low (47–145 mg C m^?2 day^?1). Quantitative characteristics of microbial numbers and activity of the the key microbial processes occurring in the water column of the White Sea were explored. Over the 5-year period of observations, the total number of bacterial cells in the surface layer of the water column varied from 50 to 600 thousand cells ml^?1. In August 2006, bacterioplankton production (BP) was estimated to be 0.26–3.3 μg C l^?1 day^?1; the P/B coefficient varied from 0.22 to 0.93. The suspended organic matter had a lighter isotope composition (from ?28.0 to ?30.5‰) due to the predominance of terrigenous organic matter delivered by the Northern Dvina waters. The interseasonal and interannual variation coefficients for phytoplankton production and BP numbers are compared. The bacterioplankton community of the White Sea’s deep water was found to be more stable than that of the surface layer. In the surface layer of bottom sediments, methane concentration was 0.2–5.2 μl dm^?3; the rate of bacterial sulfate reduction was 18–260 μg S dm^?3 day^?1; and the rates of methane production and oxidation were 24–123 and 6–13 nl CH₄ dm^?3 day^?1, respectively. We demonstrated that the rates of microbial processes of the carbon and sulfur cycles occurring in the sediments of the White Sea basin were low.     

Effects of feeding propylene glycol to mid-lactating dairy cows

Propylene glycol (PG) is a gluconeogenic precursor widely used to prevent and treat ketosis postpartum. The study has investigated the effects of PG administration to dairy cows at mid stage of lactation. According to a 3 × 3 latin square design, three Italian Brown lactating cows (125 ± 7 days in milk) fitted with rumen cannula were fed a corn silage based diet (CP 14.7%, NDF 41.1% DM) with 0, 200 or 400 g day⁻¹ PG added. Dry matter intake was increased by feeding PG with a significant quadratic component per dose (16.2, 17.2 and 16.5 kg day⁻¹ for 0, 200 and 400 g PG day⁻¹, respectively). Milk yield was not affected by PG, averaging 17.1 kg day⁻¹. Average daily gain increased from 64 to 206 and 302 g day⁻¹ when cows received 200 and 400 g day⁻¹ of PG (linear component per dose P < 0.05). Digestibility of the diet did not differ among treatments, whereas repeated rumen fluid samples, taken 0, 2, 4, 6 and 8 h after the meal, showed a consistently lower acetate to propionate ratio when feeding PG. Blood insulin was not affected by PG administration. Except for therapeutic treatments, PG administration to dairy cows at mid stage of lactation should be advised against. Despite the positive effect on intake, administration of the additive, increasing the molar percentage of rumen propionate, contributes to shift the energy partition from milk production to liveweight gain.     

Production and Utilization of Dissolved Organic Carbon During in situ Phytoplankton Photosynthesis Measurements

Rates of phytoplankton photosynthesis, extracellular release of dissolved organic carbon, and production or utilization of dissolved organic carbon during in situ incubation were measured in a soft-water Vermont lake during summer thermal stratification. Phytoplankton photosynthesis rates were frequently in the range of 300–600 mg C m⁻² of lake surface day⁻¹; extracellular release of previously fixed organic carbon was generally in the range of 20–75% of the carbon incorporated into cell biomass, as determined by gas-phase radio-analysis. Rates of increase or decrease in total dissolved organic carbon occurring in light and dark incubated phytoplankton samples, during brief (4 hour) in situ measurements, indicate that a significant fraction of the total dissolved organic carbon „pool”︁ is probably labile and rapidly being cycled.     

A comparison of models for predicting slurry production on a pig farm

Three methods of predicting slurry production were compared with the volumes actually produced on a 150 sow breeding and fattening pig unit. The methods were based on (a) feed, water and slurry relationships measured in crated and penned pigs; (b) values given in the literature and used by ADAS to predict slurry outputs from pigs; (c) a method based on the digestibility of feed and of water measured at the actual piggery. Method (a) was not found appropriate because of the high overall water:meal ratio found in the unit (13:1). Method (b) was able to predict dry matter production accurately but underestimated the volume produced unless the ADAS allowance of 0·5 litres pig⁻¹ day⁻¹ for washing water and leaking drinkers was increased to 10 litres. Method (c) was the best method for estimating volume but underestimated dry matter production. Combining the better aspects of methods (b) and (c) allows volume, dry matter production and dry matter concentration to be predicted satisfactorily. The daily movements of slurry from the reception pit were very variable. The use of water meters on pig units is recommended to identify wastage.     

Feeding Rate of Brachionus plicatilis O. F. Müller on Two Types of Food Depending on Ambient Temperature and Salinity

Feeding rates of Brachionus plicatilis were studied for two types of food — algae Monochrysis lutheri and baker's yeast Saccharomyces cerevisae. The main regularities of changes in filtration rate and ration were studied in small culture volumes (1 ml) for adult amictic females depending on food concentration (1, 2, 4, 8 and 16 · 10⁶ cells · ml⁻¹), ambient temperature (16 and 26 °C), and salinity (5, 10, 15, 20, 25 and 30 ppt). B. plicatilis ration did not depend on the salinity, but was largely determined by temperature and food concentration. It was found that at 16 and 26 °C the dependence of the ingestion rate (ration) on food concentration differed greatly. A hypothesis was suggested to explain this phenomenon. A critical concentration of both types of food at which the increase in the rotifer ration ceased is 4 · 10⁶ cells · ml^−1. This is the minimum “background” food concentration for B. plicatilis mass cultivation. The average rations measured at the concentration of M. lutheri and S. cerevisae of 4 · 10⁶ cells · ml⁻¹ where 1.3 ± 0.1 and 4.8 ± 1.3 μg dry weight. · ind⁻¹ · day⁻¹ at 26 °C and 0.54 ± 0.1 and 1.9 μg d. w. · ind⁻¹ · day⁻¹ at 16 °C, respectively. The rations obtained in the laboratory were corrected for the conditions of rotifer commercial production in the open field in summer time. The correct values were 0.86 and 0.72 μg d. w. · ind⁻¹ · day⁻¹ for algae and yeast, respectively.     

The effect of dietary inclusion of starch,sucrose and xylose on the utilization of dietary energy in sheep

A calorimetric experiment of 4 × 4 Latin square design was undertaken to study the effect of sugar-beet pulp (SBP), maize starch, sucrose and xylose on energy metabolism in sheep. The four diets comprised a diet (A) of dried grass, soya-bean meal and SBP (450, 50 and 500 g kg⁻¹ on dry matter (DM) basis) and corresponding diets in which 400 g kg⁻¹ of SBP was replaced by maize starch (B), sucrose (C) or xylose (D); all diets were offered at a level of 600 g DM day⁻¹. After the Latin square was completed, energy value of the basal diet of dried grass and soya-bean meal (900 and 100 g kg⁻¹ DM; 600 g day⁻¹) was determined in the same four sheep.Treatment differences in organic matter, gross energy, nitrogen (N) and neutral detergent fibre (NDF) digestibility were non-significant. Differences in N retention were not significant.Digestible energy (DE) contents (MJ kg⁻¹ DM) were 13.27, 13.22, 13.21 and 13.21 MJ kg⁻¹ for diets A, B, C and D, respectively. Energy loss in methane was higher (P < 0.05) for Diet A than for other diets. Metabolizable energy (ME) contents for the diets A-D were 11.25, 11.22, 11.32 and 11.40 MJ kg⁻¹ DM, respectively. Metabolizability (q) of the diets averaged 0.642 and was not significantly affected by the diet given. There was a trend for heat production to be higher in sheep given the sucrose-containing diet (C) than in those given other diets (6.34 versus 6.04 MJ day⁻¹) and as a result, energy retention was lower (0.38 versus 0.64 MJ day⁻¹), but the difference did not reach statistical difference. Efficiencies of utilization of ME for maintenance and fattening (k_mf) averaged 0.67 and were in good agreement with those predicted from equations of the Agricultural Research Council (1980) excepting the lower k_mf (0.63) for Diet C.The mean ME content of SBP calculated by difference was 13.05 MJ kg⁻¹ DM and the corresponding values for mixtures of SBP + starch, SBP + sucrose and SBP + xylose (600 and 400 g kg⁻¹ DM) were 12.98, 13.16 and 13.36 MJ kg⁻¹ DM, respectively.     

Environmental indicators for estimating the potential soil respiration rate in alpine zone

Soil respiration is the main form of carbon flux from soil to atmosphere in the global carbon cycle. The effect of temperature on soil respiration rate is important in evaluating the potential feedback of soil organic carbon to global warming. We incubated soils from the alpine meadow zone and upper rocky zone along an altitudinal gradient (4400–5500 m a.s.l.) on the Tibetan Plateau under various temperature and soil moisture conditions. We evaluated the potential effects of temperature and soil moisture on soil respiration and its variation across altitudes. Soil respiration rates increased as the temperature increased. At 60% of soil water content, they averaged 0.21–5.33 μmol g soil⁻¹ day⁻¹ in the alpine meadow zone and 0.11–0.50 μmol g soil⁻¹ day⁻¹ in the rocky zone over the experimental temperature range. Soil respiration rates in the rocky zone did not increase between 25 and 35 °C, probably because of heat stress. Rates of decomposition of organic matter were high in the rocky zone, where the CN ratio was smaller than in the middle altitudes. Soil respiration rates also increased with increasing soil water content from 10% to 80% at 15 °C, averaging 0.04–2.00 μmol g soil⁻¹ day⁻¹ in the alpine meadow zone and 0.03–0.35 μmol g soil⁻¹ day⁻¹ in the rocky zone. Maximum respiration rates were obtained in the middle part of the alpine slope in any case of experimental temperature and soil moisture. The change patterns in soil respiration rate along altitude showed similar change pattern in soil carbon content. Although the altitude is a variable including various environmental factors, it might be used as a surrogate parameter of soil carbon content in alpine zone. Results suggest that temperature, soil moisture and altitude are used as appropriate environmental indicators for estimating the spatial distribution of potential soil respiration in alpine zone.     

Litter Decomposition of Scirpus maritimus L. in a Mediterranean Coastal Marsh: Importance of the Meiofauna during the Initial Phases of Detached Leaves Decomposition

Growth, senescence and decomposition rates of Scirpus maritimus were studied in a Mediterranean brackish wetland. Plant tussocks were tagged in March, 2002 and were totally dead by September, 2002. Decomposition rates were determined over 360 days using litter bag technique and mass loss, nutrient dynamics, fungal biomass, meiofauna and macroorganisms were determined. Decomposition rate of detached S. maritimus litter was 0.00196 (k, day^–1) with a 54% of mass lost observed in 1 year. The pattern of mass loss was characterized by an initial phase of fast loss of organic matter with high density of meiofauna and a decrease of oxygen content, followed by two slower phases, with no significant losses from 50 to 180 days and with 21% of mass lost from 180 to 360 days. Nitrogen (N) and phosphorus (P) content of plant litter increased during decomposition process whereas atomic C:N and C:P ratios decreased, suggesting a nutrient immobilization on plant detritus. Fungal biomass measured as ergosterol content decreased after submersion of leaves, indicating that their importance in litter decomoposition decreases in submerged leaves during the first days of decomposition. An inverse relationship (r = –0.79, P < 0.005) was observed between ergosterol content and nematodes density on S. maritimus litter. Our results suggest that in Mediterranean brackish marshes, where large amounts of dead organic matter is accumulated over the sediment surface, decomposition process is greatly affected by extremely high temperatures in summer that, if water is available, accelerates microbial activity decreasing oxygen content thus slowing decomposition. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Benthic resources are the key to Daphnia middendorffiana survival in a high arctic pond

1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic–pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a ¹³C‐enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the ¹³C‐enrichment of benthic mats with progressively increasing δ¹³C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter. 3. Daily net production by phytoplankton in the pond (18 mg C m^?2 day^?1) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C m^?2 day^?1), whereas benthic primary production alone (145 mg C m^?2 day^?1) was more than sufficient. 4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient‐limited high arctic ponds.     

Effects of wet brewers grains on milk yield,milk composition and blood components of dairy cows in hot weather

Twenty multiparous Friesian cows, 60–120 days postpartum, were allotted to two groups of ten cows each according to calving date, lactation number and daily yield, and assigned randomly to one of two diets in a crossover design experiment. The control diet was 45% maize silage (dry basis) and contained ground maize, soya bean meal and wheat bran in proportions which would ensure that the dietary dry matter contained 16.5% crude protein, 3.0 Mcal metabolizable energy kg⁻¹ DM and 14% crude fibre. The treatment diet contained wet brewers grains substituted for maize silage, soya bean meal and wheat bran to change the ruminally undegradable protein from 35% to 39% of crude protein. Ground maize was included in the same quantity as in the control diet. The diets were offered individually, in tie-stalls, as total mixed rations in two equal amounts for ad libitum intakes. The experimental period lasted from 18 June to 12 August 1994. The cows were allowed exercise in an open lot without shade. Dry matter intake, milk protein content and yield, as well as content of milk lactose and non-fat solids were not significantly affected by the diet. In contrast, wet brewers grains supplementation increased actual milk yield (24.8 v. 21.7 kg day⁻¹; P < 0.05), 4% fat-corrected milk yield (25.1 v. 21.1 kg day⁻¹; P < 0.01), milk fat content (4.08 v. 3.82%; P < 0.05), milk total solids content (12.89 v. 12.44%; P < 0.05) and milk fat yield (1.01 v. 0.83 kg day⁻¹; P < 0.05). Blood plasma concentrations of glucose, total protein, albumin, urea, triglycerides, cholesterol, phospholipids, sodium, potassium, calcium, phosphorus and magnesium were not affected by treatment.     

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.     

Effect of different CO2 concentrations on biomass,pigment content,and lipid production of the marine diatom Thalassiosira pseudonana

The marine diatom Thalassiosira pseudonana grown under air (0.04% CO₂) and 1 and 5% CO₂ concentrations was evaluated to determine its potential for CO₂ mitigation coupled with biodiesel production. Results indicated that the diatom cultures grown at 1 and 5% CO₂ showed higher growth rates (1.14 and 1.29 div day⁻¹, respectively) and biomass productivities (44 and 48 mg_AFDWL⁻¹ day⁻¹) than air grown cultures (with 1.13 div day⁻¹ and 26 mg_AFDWL⁻¹ day⁻¹). The increase of CO₂ resulted in higher cell volume and pigment content per cell of T. pseudonana. Interestingly, lipid content doubled when air was enriched with 1–5% CO₂. Moreover, the analysis of the fatty acid composition of T. pseudonana revealed the predominance of monounsaturated acids (palmitoleic-16:1 and oleic-18:1) and a decrease of the saturated myristic acid-14:0 and polyunsaturated fatty acids under high CO₂ levels. These results suggested that T. pseudonana seems to be an ideal candidate for biodiesel production using flue gases.