Primary productivity of papyrus (Cyperus papyrus) in a tropical swamp; Lake Naivasha,Kenya

Papyrus (Cyperus papyrus) standing biomass and the primary productivity of undisturbed and previously harvested areas of papyrus was measured in Lake Naivasha swamp, Kenya. Papyrus culm density in undisturbed swamp was estimated to be 13·1±1·9 culms m⁻² and aerial biomass was 3602 g m⁻². In undisturbed swamp the aerial productivity was 14·1 g m⁻² day⁻¹ while the previously harvested swamp reached a peak of 21·0 g m⁻² after 6 months. The annual aerial production rate of papyrus in Lake Naivasha was estimated to be 5150 g m⁻² year⁻¹. To sustain yields of regularly harvested papyrus swamps, the harvest intervals should exceed 1 year.     

Algal biomass production,N uptake and N2 fixation in a synthetic medium

An experiment was conducted in the growth chamber to quantify the biomass production, N removal and N₂ fixation from a synthetic medium by Chlamydomonas reinhardtii and Anabaena flos-aquae. Nitrogen was supplied at a concentration of 100 mg liter⁻¹ of NO₃⁻−¹⁵N and NH₄⁺−¹⁵ (3·5 atom %), respectively. After 21 days Chlamydomonas reinhardtii removed an average of 83·8 and 78·7 mg N liter⁻¹ as NO₃⁻ and NH₄⁺, respectively. Averages of 0·89 and 0·71 g liter⁻¹ (first batch), 1·63 and 0·95 g liter⁻ (second batch) algal biomass were collected from NO₃⁻ and NH₄⁺ media, respectively. Uptake rates of 0·11 mg ¹⁵N g⁻¹ algae day⁻¹ from NO₃⁻ medium and 0·10 mg ¹⁵N g⁻¹ algae day⁻¹ from NH₄⁺ medium were calculated. Algal cells grown in NO₃⁻ and NH₄⁺ medium contained 71 and 65 g N kg⁻¹ (first batch), 39 and 58 g N kg⁻¹ (second batch), respectively. Anabaena flos-aquae produced averages of 0·58 and 0·46 g liter⁻¹ (first batch), 0·55 and 0·48 g liter⁻¹ (second batch) after 14 days of growth from NO₃⁻ and NH₄⁺ media, respectively. Blue-green algal biomass contained higher N (81–98 g kg⁻¹) than green algae. Isotope dilution method for determining N₂ fixation indicated that 55% and 77% of total N of blue-green algae grown in NO₃⁻ and NH₄⁺ media, respectively, was derived from the atmosphere.     

PRODUCTION AND NUTRIENT REMOVAL BY PERIPHYTON GROWN UNDER DIFFERENT LOADING RATES OF ANAEROBICALLY DIGESTED FLUSHED DAIRY MANURE1

Growing algae to scrub nutrients from manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. The objective of this study was to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in the previous experiments. Algal turfs, with periphyton mainly composed of green algal species, were grown under two light regimes (270 and 390 μmol photons·m^?2· s^?1) and anaerobically digested flushed dairy manure wastewater (ADFDMW) loading rates ranging from 0.8 to 3.7 g total N and 0.12 to 0.58 g total P·m^?2·d^?1. Filamentous cyanobacteria (Oscillatoria spp.) and diatoms (Navicula, Nitzschia, and Cyclotella sp.) partially replaced the filamentous green algae at relatively high ADFDMW loading rates and more prominently under low incident light. Mean algal production increased with loading rate and irradiance from 7.6±2.71 to 19.1±2.73 g dry weight· m^?2·d^?1. The N and P content of algal biomass generally increased with loading rate and ranged from 2.9%–7.3% and 0.5%–1.3% (by weight), respectively. Carbon content remained relatively constant at all loading rates (42%–47%). The maximum removal rates of N and P per unit algal biomass were 70 and 13 mg·g^?1 dry weight·m^?2·d^?1, respectively. Recovery of nutrients in harvested algal biomass accounted for about 31%–52% for N and 30%–59% for P. Recovery of P appeared to be uncoupled with N at higher loading rates, suggesting that algal potential for accumulation of P may have already been saturated. It appears that higher irradiance level enhancing algal growth was the overriding factor in controlling nitrification in the algal turf scrubber units.     

Translocation,remineralization, and turnover of nitrogen in the roots and rhizomes of Spartina alterniflora (Gramineae)

We used ¹⁵N to quantify rates of N translocation from aerial to belowground tissues, foliar leaching, and turnover and production of root and rhizome biomass in the plant-sediment system of short Spartina alterniflora areas of Great Sippewissett Marsh, Massachusetts. Decay of belowground tissues in litterbag incubations at 1- and 10-cm depths resulted in 80% remineralization of the original plant (¹⁵N-labeled) N and 20% burial after 3 years. Translocation of ¹⁵N from plant shoots in hydrologically controlled laboratory lysimeters maintained under field conditions was 38% of the aboveground pool while leaching of N was 10% from June to October. Most of the translocated N was not retranslocated to new aboveground growth in December but appeared to be either remineralized or buried in the sediment. Injection of ¹⁵N into field stands of grass showed initially high incorporation into plants followed by a continuous decline over the next 7 years yielding a gross tumover time of 1.5–1.6yr. Correcting the gross N turnover for recycling of label via translocation and uptake of remineralized label during this period, a net root and rhizome turnover time of 1.0–1.1 yr was obtained. Combining the turnover time with independent estimates of seasonal belowground biomass yielded an estimate of belowground production of 929–1,022 g C m⁻² yr⁻¹, similar to measurements by traditional biomass harvest, CO² based budgets and models for comparable areas of this marsh. Integration of the production and nitrogen balance estimates for short Spartina marsh yielded translocation, 1.4 g N m⁻² yr⁻¹, leaching, 0.4 g N m⁻² yr⁻¹, remineralization, 14.9–16.3 g N m⁻² yr⁻¹, and burial, 3.7–4.1 g N m⁻² yr⁻¹.     

Effects of supplemental nitrogen rate and source on biomass production by three weed species in fallow vegetable land

In 1983, a study was conducted to evaluate three weed species for their biomass yield potential on a fallowed tomato land with various nitrogen (N) rates and sources. Dogfennel (Eupatorium capillifolium (Lam.)Small), sida (Sida rhombifolia L.), and pigweed (Amaranthus hybridus L.), were grown with three N rates: residual, 1x and 2x (1x = 56 kg ha⁻¹ N) and with two N sources: NH₄NO₃ and isobutylidene diurea (IBDU). Sida produced the greatest fresh and dry biomass yields and percentage dry matter, 43·3, 23·3 Mg ha⁻¹ and 54·1%, respectively. Yields of the three crops increased with increasing N rates and were higher with NH₄NO₃ than with IBDU. Overall, sida at the 2x N rate with NH₄NO₃ had the highest fresh, 73·8 Mg ha⁻¹, and dry biomass, 37·9 Mg ha⁻¹, yield. Lowest residual soil total soluble salt concentration, 170 ppm, was found after pigweed, in plots which did not receive additional N. Additional N application increased residual soil total soluble salts after each of the three weeds. Thus, additional N, in NH₄NO₃ form, was necessary for high yields in a fallowed vegetable land, but the additional fertilizer also increased soil total soluble salts, regardless of the plant species.     

Biomass yield and nutrient removal by water hyacinth (Eichhornia crassipes) as influenced by harvesting frequency

The effects of harvesting frequency on productivity, nutrient storage and uptake, and detritus accumulation by water hyacinth (Eichhornia crassipes /Mart/ Solms) cultured outdoors in nutrient-enriched waters were evaluated for a period of 13 months. Significant differences in hyacinth standing crop and productivity were measured with harvesting regimes of 1, 3 (harvest at maximum density) and 21 harvests over a 13-month period. The average plant standing crop decreased from 65 to 20 kg (fresh wt) m⁻² for systems with 1 and 21 harvests, respectively. Total harvested plant biomass was 67 kg (fresh wt) m⁻², 110 kg (fresh wt) m⁻² and 162 kg (fresh wt) m⁻² for 1, 3 and 21 harvests, respectively. The mean net productivity increased from 7·7 to 16·5 and 24·5 g (dry wt) m⁻² day⁻¹ for 1, 3 and 21 harvests, respectively. Nutrient storage in water hyacinth biomass (live, dead and detrital) at the end of the study decreased from 93 to 46 and 30 g N m⁻², and from 20 to 12 and 5 g P m⁻², for 1, 3 and 21 harvests, respectively. For the system with one harvest, 46% of the stored N and 25% of the stored P were recovered in dedrital tissue at the bottom of the tank. For the systtem with 21 harvests, only 11% of the stored N and 15% of the stored P were recovered in detrital tissue at the bottom of the tank. Ammonium-N and soluble reactive P concentrations in the water column were significantly higher for the treatment with one harvest compared to the treatments with 3 and 21 harvests.     

Zooplankton and bacteria contribution to phosphorus and nitrogen internal cycling in a tropical and eutrophic reservoir: Pampulha Lake,Brazil

Nutrient regeneration and respiration rates of natural zooplankton from a tropical reservoir were experimentally measured. Excretion rates of ammonia (E_a), orthophosphate (E_p) and community respiration rates (R) were estimated considering the variations in the concentrations of ammonia, orthophosphate and dissolved oxygen between control and experimental units. The ranges obtained for these rates from the 2 h assays were E_a = 1.95–4.95 μg N-NH₄ · mg · DW⁻¹ · h⁻¹; E_p = 0.12–0.76 μg P-PO₄ mg DW⁻¹ · h⁻¹. Respiratory rates were quite constant (R = 0.01–0.02 mg O₂ · mg DW⁻¹ · h⁻¹). The uptake of nutrients due to bacteria can affect the experimental determination of excretion rates of zooplankton. Orthophosphate release increased from 0.28 to 0.82 μg P-PO₄ · mg DW⁻¹ · h⁻¹ when bacterial activity was depleted by antibiotic addition in experimental vessels (Exp IV). This demonstrates that free living bacteria are able to consume promptly most phosphorus excreted by zooplankton. Ammonia excretion rates were lower in experimental units containing antibiotics. Lower excretion rates were also obtained with longer exposure times and higher biomass levels in the experimental units. Finally, this study also showed that zooplankton excretion can affect significantly turn over rates of total phosphorus in Pampulha Reservoir. In some periods, specially during the dry season when zooplankton biomass was very high, phosphorus release by zooplankton, during one single day, can be as high as 40% of the total phosphorus content in lake water (Turn over time = 2.5 days).     

Nitrogen addition promotes terrestrial plants to allocate more biomass to aboveground organs: A global meta-analysis

A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m⁻² year⁻¹) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%–32.1%) and 14.7% (11.6%–17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition.     

CONSUMPTION OF ULVA LACTUCA (CHLOROPHYTA) BY THE OMNIVOROUS MUD SNAIL ILYANASSA OBSOLETA (SAY)

Marine invertebrate grazing on temperate macroalgae may exert a significant “top-down” control on macroalgal biomass. We conducted two laboratory experiments to test (1) if consumption by the omnivorous mud snail Ilyanassa obsoleta (Say) on the macroalga Ulva lactuca Linnaeus was a function of food quality (nitrogen content) and (2) if grazing on benthic macroalgae occurred at significant rates in the presence of alternative food sources in the sediment (detritus, larvae, benthic microalgae). Grazing rates were higher for N-enriched macroalgae; however, all snails lost weight when grazing on macroalgae alone, indicating that U. lactuca was a poor food source. The presence of sediment from two sites, a sandy lagoon and an adjacent organic-rich muddy tidal creek, did not affect consumption of macroalgae in microcosm experiments, and the grazing snails were capable of significantly reducing macroalgal biomass associated with both sediment types. Grazing rates by this omnivore were as high as 10.83 mg wet weight·individuals ^{− 1}·d ^{− 1} and were similar to those recorded for herbivorous species. In situ loss rates calculated from average grazing rates per individual and snail abundances (up to 3.5 g dry weight·m ^{− 2}·d ^{− 1}) also were comparable with those calculated for herbivorous species. This level of grazing could remove up to 88% of new macroalgal growth at the lagoon site where the N supply was relatively low but had a much smaller effect (18% of new growth) at the high-nutrient creek site. Snails facilitated macroalgal growth at both sites by increasing tissue N content by 40%–80%. Consumption and digestion of macroalgae aided in the recycling of nutrients temporarily bound in the algae and resulted in enrichment of surficial sediments. Increased N sequestration in the sediments also was associated with an interruption of snail burrowing behavior due to persistent anoxia in sediments rich in decaying algal material. Our data suggest that in shallow lagoons where mud snails and benthic macroalgae coexist, grazing may influence N retention in macroalgal biomass.     

Strong seasonal patterns of DOC release by a temperate seaweed community: Implications for the coastal ocean carbon cycle

Release of dissolved organic carbon (DOC) by seaweed underpins the microbial food web and is crucial for the coastal ocean carbon cycle. However, we know relatively little of seasonal DOC release patterns in temperate regions of the southern hemisphere. Strong seasonal changes in inorganic nitrogen availability, irradiance, and temperature regulate the growth of seaweeds on temperate reefs and influence DOC release. We seasonally surveyed and sampled seaweed at Coal Point, Tasmania, over 1 year. Dominant species with or without carbon dioxide (CO₂) concentrating mechanisms (CCMs) were collected for laboratory experiments to determine seasonal rates of DOC release. During spring and summer, substantial DOC release (10.06–33.54 μmol C · g DW⁻¹ · h⁻¹) was observed for all species, between 3 and 27 times greater than during autumn and winter. Our results suggest that inorganic carbon (C_i) uptake strategy does not regulate DOC release. Seasonal patterns of DOC release were likely a result of photosynthetic overflow during periods of high gross photosynthesis indicated by variations in tissue C:N ratios. For each season, we calculated a reef-scale net DOC release for seaweed at Coal Point of 7.84–12.9 g C · m⁻² · d⁻¹ in spring and summer, which was ~16 times greater than in autumn and winter (0.2–1.0 g C · m⁻² · d⁻¹). Phyllospora comosa, which dominated the biomass, contributed the most DOC to the coastal ocean, up to ~14 times more than Ecklonia radiata and the understory assemblage combined. Reef-scale DOC release was driven by seasonal changes in seaweed physiology rather than seaweed biomass.     

A Study of Benthic Communities in Some Saline Lakes in Saskatchewan and Alberta,Canada

The spring benthos of 22 lakes ranging from 1–88 gl⁻¹ salinity contained 58 species of macroinvertebrates, but only 23 species occurred in waters >3 gl⁻¹. The amphipod Hyalella azteca and the chironomids Procladius freemani, Chironomus nr. muratensis and Cryptochironomus spp. were important at lower salinities (1–12 gl⁻¹) whereas the chironomids Tanypus nubifer, Cricotopus ornatus and Chironomus nr. annularis dominated at moderate salinities (5–30 gl⁻¹) and dolichopodid and ephyrid dipterans were the only species in hypersaline lakes (>50 gl⁻¹). Diversity decreased significantly with increased salinity. Mean dry biomass ranged from 0–9.12 gm⁻², showing little correlation with salinity, though hyposaline lakes often had elevated values and hypersaline lakes very low values. Shallow lakes (<5 m) had significantly lower standing crops. There were long term changes in biomass (over 45 years) in some lakes due to cultural eutrophication or secular changes in salinity. Chironomids were by far the dominant contributors to biomass at salinities to 50 gl⁻¹, above which dolichopodid and ephyrid dipterans dominated. The lakes were classified into four groups—subsaline, hyposaline, shallow hypo-mesosaline and hypersaline, reflecting the importance of salinity and also relative depth as major controlling factors.     

Species screening and biomass trials of woody plants in the semi-arid southwest United States

Species screening and selection trials are being conducted to identify appropriate woody species and technology for biofuel farming in the southwest United States. During the initial phase of the program, 26 native and exotic species have been tested at sites in Texas, New Mexico and Arizona. Second season biomass estimates indicate that initial yields of 3·2–8·5 dry Mg ha⁻¹ year⁻¹ are possible without post-establishment irrigation. The species Atriplex canescens (Pursh) Nutt., Prosopis alba Griseb. and Leucaena leucocephala (Lam.) de Wit reached canopy closure within two seasons of growth and are identified as rapid initial biomass producers under the semi-arid conditions of the study area.     

Biosorption of iron(III)–cyanide complex anions to Rhizopus arrhizus: application of adsorption isotherms

The biosorption of iron(III)–cyanide complex anions to Rhizopus arrhizus was investigated. The iron(III)–cyanide complex ion binding capacity of the biosorbent was a function of initial pH, initial iron(III)–cyanide complex ion and biosorbent concentration. These results indicated that a significant reduction of iron(III)–cyanide complex ions was achieved at pH 13, a highly alkaline condition. The maximum loading capacity of biosorbent was 612·2 mg g⁻¹ at 1996·2 mg litre⁻¹ initial iron(III)–cyanide complex ion concentration at this pH. The Freundlich, Langmuir and Redlich–Peterson adsorption models were fitted to the equilibrium data at pH 3·0, 7·0 and 13·0. The equilibrium data could be best fitted to by all the adsorption models over the entire concentration range (50–2000 mg litre⁻¹) at pH 13.     

Primary production of phytoplankton in Lake Valencia (Venezuela)

Lake Valencia is heavily polluted by waste water of domestic, agricultural and industrial origin. The high organic load may have produced important changes in the limnological properties. Cyanobacteria dominated in numbers and biomass (over 90% throughout the year). Chlorophyll-a content averaged 37.7 + 15 μg · 1⁻¹. Maximum concentrations of 50–80 μg · 1⁻¹ were found near the inflows affected by organically polluted affluents. There has been a 50% reduction in the euphotic zone in only 13 years. The maximum rate of gross photosynthesis per hour at light saturation was determined within the uppermost 1-meter layer. The highest value was 16,290 mg O₂ · m⁻³ · h⁻¹. Lake Valencia is among the most productive lakes in the world, with areal net photosynthesis averaging 7.5 g C · m⁻² · d⁻¹.     

Growth and Production of Yellow Eels and Glass Eels in Ponds

Two experiments (I and II) were performed in drainable ponds. Yellow eels Anguilla anguilla (L.) were stocked in early June at three biomasses: 10, 20 and 60 kg · ha⁻¹ in experiment I; and 10, 20 and 40 kg · ha⁻¹ in experiment II. The mean body weights were 27.0 and 24.2 g respectively. Glass eels were stocked only in experiment II at equal densities of 1600·ha⁻¹. In both experiments each biomass of yellow eel was combined in a factorial design with three cyprinid communities differing in biomass and in species- and size-composition. The ponds were drained in autumn. The final body weights at draining ranged from 25.9 to 63.6 g for yellow eel and from 3.9 to 8.8 g for glass eel. The final body weights of yellow eel and of glass eel decreased with increasing biomass of yellow eel. No significant relation was found between the bream Abramis brama (L.) biomass and the growth of eel. The growth rates of yellow eel and glass eel were positively correlated in experiment II. At higher biomasses of yellow eel the percentage females decreased slightly. The recapture rates of yellow eel in experiments I and II amounted to 69.4 ± 9.8 % and 92.2 ± 4.9% (mean ± sd) respectively. The lower recapture rates in experiment I were caused by the inappropriate draining technique used. The glass eels were recaptured with 75.0·5.6% efficiency. The maximum net production of yellow eel occurred at a biomass of 20–40kg·ha⁻¹ and amounted to 19 kg·ha⁻¹.     

Annual Changes of Abundance and Biomass of Planktonic Ciliates in the Gdańsk Basin,Southern Baltic

Seasonal changes in the species composition, abundance and biomass of planktonic ciliates were determined every 2–3 weeks at two sites of 30 m depth and one location of 105 m depth in the southwestern Gdańsk Basin between January 1987 and January 1988. A total of 40 ciliate taxa were observed during this period. Autotrophic Mesodinium rubrum dominated ciliate abundance and biomass: maximal values of 50 · 10⁻¹ ind. ^1-1 and 65 μg C 1⁻¹ were recorded. The annual mean biomass of M. rubrum comprised 6 to 9% of the annual mean phytoplankton biomass. The highest abundances and biomasses of heterotrophic ciliates were noted at all stations in the spring and summer in the euphotic zone with maximum values of 28 · 10³ ind. 1⁻¹ and 23 μg C 1⁻¹. Three ciliates assemblages were distinguished in the epipelagic layer: large and medium-size non-predatory ciliates, achieving peak abundance in spring and autumn; small-size microphagous ciliates and epibiotic ciliates which were abundant in summer, and large-size predacious ciliates dominating in spring. Below 60 m, a separate deep-water ciliate community composed of Prorodon-like ciliates and Metacystis spp. was found. The ciliate biomass in the 60–105 m layer was similar to the ciliate biomass in the euphotic zone. The heterotrophic ciliate community contributed 10 to 13% to the annual mean zooplankton biomass. The potential annual production of M. rubrum comprised 6 to 9% of the total primary production. Carbon demand of non-predatory ciliates, calculated on the basis of their potential production, was estimated to be equivalent to 12–15% of the gross primary production.     

Littoral benthos of the Northern Baltic Sea. IV. Pattern and dynamics of macrobenthos in a sandy-bottom Zostera marina community in Tvärminne

The composition and abundance of the macroscopic biota of a sandy-bottom Zostera marina community at a depth of 3–5 m were studied in Tvärminne, S Finland, in 1968–1971. Zostera occurred contagiously and very sparsely, 6 ± 2 shoots · m⁻², ash-free dry weight (AFDW) 2 ± 1 g · m⁻² (95% confidence interval). Totals of 45 plant and 70 animal taxa were found. Fucus vesiculosus (80%) and Zostera marina (11%) dominated the plant biomass, 16.5 ± 17.8 g · m⁻² in June 1971. At this time animal density was 8540 ± 830 ind. · m⁻² (0.6-mm mesh) and AFDW 17.3 ± 5.0 g · m⁻², 80–90% of the latter consisting of Macoma baltica, Mya arenaria, Corophium volutator, Nereis diversicolor and Hydrobia spp. The same percentage of animal density was made up by Hydrobia spp., M. baltica, C. volutator and Pygospio elegans. Normal analysis by classification of the samples suggested that the community was spatially rather homogeneous in 1971. Inverse analysis, based on interspecific correlations, revealed three distributional groups of species. These groups corresponded to the compositional subdivisions suggested by normal analysis. The community was subdivided into strata characterized by (D) deposit feeders, (Z) Zostera marina and (F) Fucus vesiculosus. The periodicity of the biota in the Zostera-characterized stratum was investigated. The principal dominants, especially Fucus, Zostera and Macoma, showed no distinct seasonal or interannual differences in 1968–1971, which made the community seem very stable. Yet, the species diversity of plants varied with the abundance of filamentous algae. Animal species diversity and mean animal density reached their seasonal minima in late summer, when the parental stocks of many invertebrates were dying and the summer's offspring were often still too small to be obtained by our methods. The recruitment of many important animal species failed in 1968 as compared with the other years.     

Structure,Dynamics and Production of Mesozooplankton Community in the Bothnian Bay,Related to Environmental Factors

Studies on the zooplankton community of the Bothnian Bay (BB), the northernmost basin of the Baltic Sea, were carried out in 1976–78. Only 8–14 taxa dominated in the zooplankton community. The highest abundances and biomasses occurred during the warmest period or immediately afterwards, in July–September. The production of zooplankton was estimated to be 3.1–7.8 g C · m⁻². a⁻¹ in the coastal area and 2.5–3.6 g C · m⁻² · a⁻¹ in the open sea. During the short growing season (June–September) the biomass turnover took place in about 11 days. The productivity of zooplankton is discussed in relation to available food of both autochthonous and allochthonous origin and compared with the other parts of the Baltic Sea.     

CO2浓度升高与氮沉降对南亚热带森林生态系统植物生物量积累及分配格局的影响

 CO₂浓度升高与氮沉降增加对陆地生态系统的耦合作用已成为全球变化的研究热点。应用大型开顶箱(OTC)人工控制手段研究了人工生态系统在1)高CO₂(700±20 μmol·mol^–1)+高氮沉降(100 kg N·hm^–2·a^–1)(CN); 2)高CO₂(700±20 μmol·mol^–1)+背景氮沉降(C＋); 3)高氮沉降(100 kg N· hm^–2·a^–1)＋背景CO₂(N＋); 4)背景CO₂＋背景氮沉降处理(CK) 4种处理条件下荷木 (Schima superba)、红锥(Castanopsis hystrix)、海南红豆(Ormosia pinnata)、肖蒲桃(Acmena acuminatissima)、红鳞蒲桃(Syzygium hancei)等主要南亚热带森林植物的生物量积累模式及其分配格局。连续近3年的实验结果表明: 不同处理条件下, 各参试植物生物量积累具有不同的响应特征, N＋处理显著促进荷木、肖蒲桃及红鳞蒲桃生物量的积累; C＋处理显著促进肖蒲桃、海南红豆生物量的积累; CN处理显著促进除红锥外其他物种生物量的积累, 并且具有两者单独处理的叠加效应。不同处理改变物种生物量的分配模式, N＋处理降低植物的根冠比, 促进地上部分生物量的积累; C＋处理增加红锥和红鳞蒲桃地下部分生物量的分配, 却促进荷木和海南红豆地上部分的积累; CN处理仅促进红磷蒲桃地下部分的积累。群落生物量的积累与分配格局取决于优势物种的生物量及其分配格局在群落中所占的权重。     

Contribution of the polychaete,Neanthes japonica (Izuka), to the oxygen uptake and carbon dioxide production of an intertidal mud-flat of the Nanakita River estuary,Japan

The benthic oxygen consumption and carbon dioxide production of undisturbed and sieved sediment cores with various values for the biomass of polychaetes collected from the intertidal mud-flat of Nanakita River estuary of Japan were measured simultaneously. The benthic oxygen consumption and carbon dioxide production increased in proportion to the biomass of a dominant polychaete species Neanthes japonica (Izuka). This increase was not explained by the respiration of the animals alone. The residual increase in benthic O₂ and CO₂ fluxes may be due to mineralization processes in the burrow wall and enhanced diffusion caused by the pumping activity of the worms. From the average biomass of polychaetes at the study site, total benthic O₂ and CO₂ fluxes were estimated to be 5.2 mmol·m⁻²·h⁻¹ and 7.3 mmol·m⁻²·h⁻¹, respectively, at 20 ° C. The worms were responsible for 79% of the total O₂ flux and 73% of the total CO₂ flux but the respiration of the worms accounted for only 53% of the total O₂ flux and 36% of the total CO₂ flux. The residual enhanced fluxes were 26% and 37% for the total O₂ and CO₂ fluxes, respectively.