Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

Photosynthetic pathways and the ecological distribution of the chenopodiaceae in Isreal

Summary Fifty-four species of the Chenopodiaceae in Israel were examined for their anatomical features, ¹³C values, habitat and phytogeographical distribution. 17 species have ¹³C values between -20 and -30and non-Kranz anatomy (NK) and are therefore considered as C₃ plants. 37 species have ¹³C values between -10 and -18 and Kranz or C₄-Suaeda type anatomy and are therefore considered as C₄ plants. Some C₄ plants have leaf structure which seems to be intermediate between the Kranz and the C₄-Suaeda type of leaf anatomy.The segregation of the species into photosynthetic groups shows tribal and phytogeographical grouping. Most of the C₃ Chenopods are either mesoruderal plants or coastal halophytes, with a distribution area which covers the Euro-Siberian as well as the Mediterranean phytogeographical regions. The C₄ Chenopods are mainly desert or steppe xerohalophytes with a distribution area which includes the Saharo-Arabian and/or Irano-Turanian phytogeographical regions.     

Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

Stable isotopes (¹³C, D) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in¹³C (mean ¹³C; –51.5 ±7.1 and–56.5 ± 4.6 for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(– 63 ± 5). Large seasonal variation was observed in¹³C(32) in the rice paddies, whereas variationinD was much more smaller (20), indicating that variation in¹³C is due mainly to changes in methane production pathways.Values of ¹³C were lower in swamps (–66.1 ±5.1)than in rice paddies. The calculated contribution of acetate fermentation from¹³C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). Din methane from Thai rice paddies (–324± 7 (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from–362 ± 5 (Mito: n=2) to –322 ± 8(Okinawa: n=3), due tohigher D in floodwaters. ¹⁴C content in methane produced fromThai rice paddies (127±1 pMC) show higher ¹⁴Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).     

Effects of short-term storage of gametes on fertilization of Pacific herring eggs

A method is described whereby arrays of samples ofClupea pallasi eggs may be stored during their preparation. The high fertilization potential retained by the eggs during short-term storage allows them to be fertilized synchronously when sample preparation is complete. A variation of the dry method of storage retained maximum fertilization potential (80–85%) of the eggs for about 1 hr, and of milt dilution (18 with 17 S sea water), about 7 hr. Following dry storage, eggs fertilized in salinities of 0–45 showed maximum rates of fertilization in salinities of 10–20, and fertilization rates 50% in salinities of 4.5–42. Salinities of fertilization influenced egg diameter, median hatching time, and larval length at hatching in egg samples transferred 21/2 hr after fertilization to an incubation salinity of 17 at 7°C. Fertilization rates were higher (90–95%) for eggs stored in 17 S at 7°C prior to fertilization. Under such wet storage conditions, maximum fertilization pontential was retained for about 2 hr. Highest fertilization rates (95–96%) were obtained for eggs stored and fertilized in salinities of 12–15. For the species and the area of origin considered (British Columbia), wet storage of eggs should result in maximum fertilization when the eggs are stored at 4°C for a period not greater than 2 hr prior to fertilization in the 12–15 S storage medium.Prepared under the auspices of the Canadian-German Scientific and Technical Cooperation Agreement.     

Foliar 15N natural abundance in Hawaiian rainforest: patterns and possible mechanisms

Summary Foliar samples were obtained from symbiotic nitrogen-fixers and control plants (non-fixers) along elevational and primary successional gradients in volcanic sites in Hawai'i. Most control plants had negative ¹⁵N values (range-10.1 to +0.7), while most nitrogen-fixers were near 0. Foliar ¹⁵N in the native tree Metrosideros polymorpha did not vary with elevation (from sea level to tree-line), but it did increase substantially towards 0 on older soils. The soil in an 197-yr-old site had a ¹⁵N value of approximately-2, while in a 67000-yr-old site it was +3.6. We suggest that inputs of ¹⁵N-depleted nitrogen from precipitation coupled with very low nitrogen outputs cause the strongly negative ¹⁵N values in non-nitrogen-fixing plants on early successional sites.     

Water uptake and transport in lianas and co-occurring trees of a seasonally dry tropical forest

Water uptake and transport were studied in eight liana species in a seasonally dry tropical forest on Barro Colorado Island, Panama. Stable hydrogen isotope composition (D) of xylem and soil water, soil volumetric water content (_v), and basal sap flow were measured during the 1997 and 1998 dry seasons. Sap flow of several neighboring trees was measured to assess differences between lianas and trees in magnitudes and patterns of daily sap flow. Little seasonal change in _v was observed at 90–120 cm depth in both years. Mean soil water D during the dry season was –19 at 0–30 cm, –34 at 30–60 cm, and –50 at 90–120 cm. Average values of xylem D among the liana species ranged from –28 to –44 during the middle of the dry season, suggesting that water uptake was restricted to intermediate soil layers (30–60 cm). By the end of the dry season, all species exhibited more negative xylem D values (–41 to –62), suggesting that they shifted to deeper water sources. Maximum sap flux density in co-occurring lianas and trees were comparable at similar stem diameter (DBH). Furthermore, lianas and trees conformed to the same linear relationship between daily sap flow and DBH. Our observations that lianas tap shallow sources of soil water at the beginning of the dry season and that sap flow is similar in lianas and trees of equivalent stem diameter do not support the common assumptions that lianas rely primarily on deep soil water and that they have higher rates of sap flow than co-occurring trees of similar stem size.     

Genetic differentiation in carbon isotope discrimination and gas exchange in Pseudotsuga menziesii

Patterns of genetic variation in gas-exchange physiology were analyzed in a 15-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation that contains 25 populations grown from seed collected from across the natural distribution of the species. Seed was collected from 33°30 to 53°12 north latitude and from 170 m to 2930 m above sea level, and from the coastal and interior (Rocky Mountain) varieties of the species. Carbon isotope discrimination () ranged from 19.70() to 22.43() and was closely related to geographic location of the seed source. The coastal variety (20.50 (SE=0.21)) was not significantly different from the interior variety (20.91 (0.15)). Instead, most variation was found within the interior variety; populations from the southern Rockies had the highest discrimination (21.53 (0.20)) (lowest water-use efficiency). Carbon isotope discrimination (), stomatal conductance to water vapor (g), the ratio of intercellular to ambient CO₂ concentration (c_i/c_a), and intrinsic water-use efficiency (A/g) were all correlated with altitude of origin (r=0.76, 0.73, 0.74, and –0.63 respectively); all were statistically significant at the 0.01 level. The same variables were correlated with both height and diameter at age 15 (all at P0.0005). Observed patterns in the common garden did not conform to our expectation of higher WUE, measured by both A/g and , in trees from the drier habitats of the interior, nor did they agree with published in situ observations of decreasing g and with altitude. The genetic effect opposes the altitudinal one, leading to some degree of homeostasis in physiological characteri tics in situ.     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

15N natural abundance studies in Australian commercial sugarcane

The measurement of natural ¹⁵N abundance is a well-established technique for the identification and quantification of biological N₂ fixation in plants. Associative N₂ fixing bacteria have been isolated from sugarcane and reported to contribute potentially significant amounts of N to plant growth and development. It has not been established whether Australian commercial sugarcane receives significant input from biological N₂ fixation, even though high populations of N₂ fixing bacteria have been isolated from Australian commercial sugarcane fields and plants. In this study, ¹⁵N measurements were used as a primary measure to identify whether Australian commercial sugarcane was obtaining significant inputs of N via biological N₂ fixation. Quantification of N input, via biological N₂ fixation, was not possible since suitable non-N₂ fixing reference plants were not present in commercial cane fields. The survey of Australian commercially grown sugarcane crops showed the majority had positive leaf ¹⁵N values (73% >3.00, 63% of which were >5.00), which was not indicative of biological N₂ fixation being the major source of N for these crops. However, a small number of sites had low or negative leaf ¹⁵N values. These crops had received high N fertiliser applications in the weeks prior to sampling. Two possible pathways that could result in low ¹⁵N values for sugarcane leaves (other than N₂ fixation) are proposed; high external N concentrations and foliar uptake of volatilised NH₃. The leaf ¹⁵N value of sugarcane grown in aerated solution culture was shown to decrease by approximately 5 with increasing external N concentration (0.5–8.0 mM), with both NO₃ ^– and NH₄ ⁺ nitrogen forms. Foliar uptake of atmospheric NH₃ has been shown to result in depleted leaf ¹⁵N values in many plant species. Acid traps collected atmospheric N with negative ¹⁵N value (–24.45±0.90) from above a field recently surface fertilised with urea. The ¹⁵N of leaves of sugarcane plants either growing directly in the soil or isolated from soil in pots dropped by 3.00 in the same field after the fertiliser application. Both the high concentration of external N in the root zone (following the application of N-fertilisers) and/or subsequent foliar uptake of volatilised NH₃ could have caused the depleted leaf ¹⁵N values measured in the sugarcane crops at these sites.     

The Reaction of the Starfish Asterias amurensisand Patiria pectinifera (Asteroidea) from Vostok Bay (Sea of Japan) to a Salinity Decrease

The reactions of the starfish Asterias amurensis and Patiria pectinifera that live in Vostok Bay at the salinity of 32–33 to a salinity decrease were studied under laboratory conditions. The lower limits of the desalination tolerance range of A. amurensis and P. pectinifera were, respectively, 24 and 20. A. amurensis proved to be less resistant to desalination. Under experimental conditions, all specimens of this species survived the salinity of 22, while those of P. pectinifera tolerated 18. At the same time, A. amurensis responded more actively than P. pectinifera to unfavorable changes in the environment. Turned to their dorsal side and exposed to a salinity of 16 to 32, the former reverted to the normal position within a shorter time than the latter. Being a more euryhaline species, P. pectinifera endured a salinity decrease to 6 or 8 over, respectively, 21 or 28 h. However, only 30–40% of all specimens could recover locomotory activity 12 or 8.5 h after being placed into water of normal salinity.     

Über den Einfluß des Salzgehaltes auf die photosynthetische Leistung verschiedener Standortformen vonDelesseria sanguinea undFucus serratus

Zusammenfassung 1. Es wurde untersucht, welchen Einfluß kurzfristige und langfristige Salzgehaltsveränderungen auf verschiedene Standortformen der RotalgeDelesseria sanguinea und der BraunalgeFucus serratus haben. Als Kriterium des Lebenszustandes wurde die photosynthetische Leistung gewählt. Die Algen wurden folgenden Salzgehaltskonzentrationen ausgesetzt: 0, 5, 10, 15, 20, 30, 40, 50 S.2. Die Versuche ergaben, daß kurzfristige Konzentrationsveränderungen (30 min) — sowohl Erniedrigung als auch Erhöhung des Salzgehaltes — die photosynthetische Leistung stimulieren. Ein langfristiger Aufenthalt (24 Std) unter den veränderten Bedingungen bewirkt, sofern diese innerhalb der Toleranzgrenzen der Algen liegen, einen Ausgleich der anfänglichen Stimulation. Außerhalb der Toleranzgrenzen liegende Konzentrationen rufen nach der Stimulation eine Leistungsdepression hervor. Bei Rückübertragung in den Ausgangssalzgehalt sind die Depressionen teilweise reversibel.3. Im hypotonischen Milieu verhalten sich die Delesserien der verschiedenen Standorte (Helgoland, Kattegat, Kieler Bucht) gleich: in 5 S treten starke Depressionen auf. Nordsee-Delesserien sind im hypertonischen Milieu weniger empfindlich, sie zeigen noch bei 50 S eine gesteigerte photosynthetische Leistung. In diesem Bereich sind die Ostseeformen schon schwer geschädigt. Am empfindlichsten gegenüber allen Konzentrationsänderungen ist die BrackwasserformDelesseria sanguinea formalanceolata aus der Kieler Bucht.4.Fucus serratus aus dem Litoral von Helgoland zeichnet sich im Gegensatz zu der submers lebenden Form der Ostsee, die sich ähnlich wieDelesseria verhält, in allen untersuchten Konzentrationsbereichen durch eine unveränderte photosynthetische Leistung aus. Die beiden Standortformen vonFucus entsprechen gemäß der Einteilung vonMontfort (1931) dem resistenten Typ und dem Stimulations-Depressionstyp.

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On the influence of salinity on photosynthetic performance of various ecotypes ofDelesseria sanguinea andFucus serratus

The phaeophyceanF. serratus and the rhodophyceanD. sanguinea came from the North Sea (30 S) and the Baltic Sea (15 S). The activity of photosynthesis was taken as a criterion of algae vitality. Experiments were made in salinity concentrations of 0, 5, 10, 15, 20, 30, 40 and 50 S. Thirty-minute exposures to sub- or supranormal salinities stimulate photosynthesis. Within their physiological salinity ranges the algae assume normal photosynthetic rates within 24 hours. Extreme salinities cause a reduction in photosynthetic activity; this reduction mostly disappears, however, after re-transfer into normal salinity conditions. At 5 S all test individuals ofDelesseria from different locations exhibit a reduction of photosynthetic rates. At 50 SDelesseria from the North Sea still show increased activity, whileDelesseria from the Baltic are already severely damaged. The brackish-water formD. sanguinea (formalanceolata) is most sensitive to salinity variations. The photosynthetic activity ofF. serratus from Helgoland does not vary in all salinities employed. The range of test salinities corresponds to that of the habitat in the littoral zone, where high salinities occur during air exposure, and low salinities, during rainfall. By contrast, inF. serratus from the Baltic Sea occurring only in the sublittoral zone, photosynthetic rates are similarly affected by salinity as inDelesseria.

     

Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis

Summary The mean stable-carbon isotope ratios (¹³C) for polar bear (Ursus maritimus) tissues (bone collagen –15.7, muscle –17.7, fat –24.7) were close to those of the same tissues from ringed seals (Phoca hispida) (–16.2, –18.1, and –26.1, respectively), which feed exclusively from the marine food chain. The ¹³C values for 4 species of fruits to which polar bears have access when on land in summer ranged from –27.8 to –26.2, typical of terrestrial plants in the Arctic. An animal's ¹³C signature reflects closely the ¹³C signature of it's food. Accordingly, the amount of food that polar bears consume from terrestrial food webs appears negligible, even though some bears spend 1/3 or more of each year on land during the seasons of greatest primary productivity.     

Stable carbon isotope signatures of background tropospheric chloromethane and CFC113

Samples of background air were collected in thelower troposphere of the Northern (high Arctic,northern Ontario, Vancouver and Houston) andSouthern (Baring Head, New Zealand) Hemispheresover the period July 1999 until March 2001.These samples were analysed for the stablecarbon isotope ratios of1,1,1-trichlorotrifluoroethane (CFC113) andCH₃Cl using a gaschromatography-continuous flow on-linecombustion isotope ratio mass spectrometrycombination. For CH₃Cl the global averageof the stable carbon isotope ratio is –36.2± 0.3 (error of mean). The average isbased on 78 data points, standard deviation forall measurements is 2.3, and the 90%confidence interval is –35.8 to –36.6.However, the number of data points from theSouthern Hemisphere is rather limited and thusthis observation is not necessarilyrepresentative for the entire SouthernHemisphere. A simple isotopic budget ofCH₃Cl shows the most important parametersneeding to be defined are the kinetic isotopeeffect of CH₃Cl destruction by OH radicalsand the source composition of CH₃Clemitted by the oceans and biomass burning ofC-4 plants. Present budgets of atmosphericCH₃Cl show a significant deficit in thesource strength. We estimate that the averagestable carbon isotope ratio of the additionalCH₃Cl emissions required to balance thebudget is –41.9 ± 7.8. The averageCFC113 isotopic composition based on 38measurements is –23.3 ± 1.6 (error ofmean), = 9.6 with no significantdifference between the hemispheres.     

Acclimation of the Sea Cucumber Apostichopus japonicus to Decreased Salinity at the Blastula and Gastrula Stages: Its Effect on the Desalination Resistance of Larvae at Subsequent Stages of Development

Apostichopus (= Stichopus) japonicus blastulae and gastrulae were acclimated for 18 h to salinities of 32 (control), 24 and 22 (the lower limit of the range of tolerance), and 20 (below the range of tolerance). Acclimation to 20 resulted in the appearance of teratic larvae, most of which subsequently died. Acclimation to 24, 22, and 20 led to a shift in the range of tolerance of the larvae at further stages of development. With a decrease in salinity, acclimated larvae developed more successfully than unacclimated larvae. Acclimated larvae attained the pentactula stage and settled at a salinity range of 32–20; unacclimated larvae, at 32–22. At different stages of development, acclimated larvae survived greater decreases in salinity than unacclimated larvae. The acclimation effects could be traced up to metamorphosis and settling, i.e., two weeks after the end of the acclimation process.     

Hydrogen isotope discrimination in higher plants: Correlations with photosynthetic pathway and environment

Summary The ratio of deuterium to hydrogen (expressed as D) in hydrogen released as water during the combustion of dried plant material was examined. The D value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C₃ plants show mean D values of-132 for shoots and -117 for roots; C₄ plants show mean D values of -91 for shoots and-77 for roots and CAM plants a D value of-75 for roots and shoots. The difference between the D value of shoot material from C₃ and C₄ plants was confirmed in species growing under a range of glasshouse conditions. This difference in D value between C₃ and C₄ species does not appear to be due to differences in the D value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C₃ and C₄ plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in D values are discussed. In CAM plants grown in the laboratory or collected from the field D values range from-75 to +50 and are correlated with ¹³C values. When deprived of water, the D value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different D value of available water in areas of increasing aridity. Whatever the origin of the variable D value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.     

β-Alanine metabolism and high salinity stress in the sea anemone,Bunodosoma cavernata

Summary During high salinity stress, -alanine accumulates to high levels in the sea anemone,Bunodosoma cavernata. Following a salinity increase from 26 to 40 -alanine increased 28-fold from 1.5 to 41.9 moles/g dry weight. Both whole animal studies and experiments with cell free homogenates indicate that under high salinity conditions an increase in the rate of -alanine synthesis from aspartic acid as well as a decrease in the rate of -alanine oxidation are responsible for the observed accumulation of -alanine. The rate of aspartic acid decarboxylation to -alanine is about 3 times greater in anemones acclimated to 40 than for those in normal salinity water (26). -alanine oxidation to CO₂ and acetyl-CoA proceeds 2.5 to 3 times slower in high salinity adaptedB. cavernata than in those acclimated to normal salinity. There is always a rapid degradation of uracil to -alanine, but this does not change with salinity.Abbreviations CASF cold acid soluble fraction - FAA free amino acids - MES 2(N-morpholino) ethane sulfonic acid - NPS ninhydrin positive substances - PCA perchloric acid - TCA trichloroacetic acid     

Sources of organic and inorganic carbon in a headwater stream: Evidence from carbon isotope studies

A combination of stable isotope studies and ¹⁴Cdating were used to identify the main sources andprocesses controlling streamwater DOC and TIC in atemperate non-forested watershed. ¹³Cvalues for terrestrial (–24.9 to –29.1) and aquatic(–30.5 to –33.5) plants were similar to valuesreported in the literature for similar ecosystems.¹³C values for DOC in soil solution andstreamwater were consistent with soil and terrestrialvegetation, indicating that the terrestrial ecosystemis the dominant source of aquatic DOC in thiswatershed. ¹³C values of soil atmosphereCO₂ (–17.2 to –25.2) were slightly lessnegative than would be expected for production viaaerobic soil microbial decomposition and rootrespiration. There was a close correspondence between¹³C values (–15.5 to –21.5) forstreamwater TIC and soil atmospheric CO₂ in thecentral part of the catchment where the stream drainsCO₂-rich peats. ¹⁴C dating showed thatalthough peat has been accumulating in the watershedfor at least 2700 years, DOC in soil pore water andstreamwater contains carbon of predominantly recentorigin (post-AD 1955).     

Secondary structure determination by NMR spectroscopy of an immunoglobulin-like domain from the giant muscle protein titin

Summary We present the complete ¹⁵N and ¹H NMR assignment and the secondary structure of an immunoglobulin-like domain from the giant muscle protein titin. The assignment was obtained using homonuclear and ¹⁵N heteronuclear 2D and 3D experiments. The complementarity of 3D TOCSY-NOESY and 3D ¹⁵N NOESY-HSQC experiments, using WATERGATE for water suppression, allowed an efficient assignment of otherwise ambiguous cross peaks and was helpful in overcoming poor TOCSY transfer for some amino acids. The secondary structure is derived from specific NOEs between backbone - and amide protons, secondary chemical shifts of -protons and chemical exchange for the backbone amide protons. It consists of eight -strands, forming two -sheets with four strands each, similar to the classical -sandwich of the immunoglobulin superfamily, as previously predicted by sequence analysis. Two of the -strands are connected by type II -turns; the first -strand forms a -bulge. The whole topology is very similar to the only intracellular immunoglobulin-like domain for which a structure has been determined so far, i.e., telokin.     

Origin and trophic importance of detritus-evidence from stable isotopes in the benthos of a small,temperate estuary

Ratios of ¹³C/¹²C and ¹⁵N/¹⁴N were measured in dissolved inorganic carbon (DIC), marginal vegetation, benthic macrodetritus (diameter > 1 mm) and selected invertebrate consumers in the Gamtoos estuary, South Africa to: (1) trace the provenance of benthic detrital deposits, and (2) determine the extent to which three abundant species of macroinvertebrates utilise this resource. DIC was strongly depleted in ¹³C with average ¹³C values (–9.5±0.5) being typical of limnetic waters. Benthic detrital particles (¹³C–24.1±0.3) originated mainly from marginal vegetation (¹³C–25.7±0.3), but their slightly elevated carbon ratio suggests additional input from ¹³C-rich sources-possibly C₄ plants cultivated on the floodplain. Populations of the fossorial ghost shrimp Callianassa kraussi, the bentho-pelagic amphipod Grandidierella lignorum and the epifaunal crab Hymenosoma robiculare together account for 96% of total benthic biomass in the upper regions of this estuary. Marked differences in trophic niches were evident among these three consumer species. Ghost shrimp (¹³C –32.5±0.3) foraged by filter-feeding on fine suspended particulate organic matter (¹³C–31.2±0.5). Amphipods (¹³C–28.0±0.6) utilised some benthic detritus but fed mainly on suspended material. Only the relatively rare crabs (¹³C–23.8±1.5) appeared to utilise benthic detrital particles to any significant extent. In the benthic consumer community of the upper Gamtoos estuary, suspension feeders make up 98% of biomass and thus clearly dominate over deposit feeders. This can be traced to the low contribution of higher plants (c. 13%) to overall carbon production, and detritus originating from macrophytes is consequently relatively unimportant in supporting invertebrate secondary production in this particular system.     

Stable sulfur isotopic biogeochemistry of the Hubbard Brook Experimental Forest, New Hampshire

In natural ecosystems, differences often exist in the relative abundanceof stable S isotopes (°³⁴S) that can provide clues as tothe source, nature, and cycling of S. Values of °³⁴S inprecipitation, throughfall, soils, soil solution, and stream waters weremeasured at the Hubbard Brook Experimental Forest (HBEF), New Hampshire.Values of °³⁴S in precipitation and throughfall weresimilar to each other but differed seasonally. Precipitation°³⁴S values were higher in the dormant season[°³⁴S = 5.9±0.6 (17)][Mean + SE(N)]than in the growing season [°³⁴S = 5.0±0.6(40)] but throughfall growing-season values were higher[°³⁴S = 5.6±0.6(68)] than for the dormantseason [°³⁴S = 4.9±0.7 (9)]. Different treespecies did not affect throughfall °³⁴S values. In soilsolution, °³⁴S values were higher in the growing season(°³⁴S = 8.9±2.8; 8.8±1.7;and 4.0±0.6 for Oa, Bh, and Bs horizons, respectively) thanin the dormant season (°³⁴S = 5.6±1.5;3.7±2.4; and 3.4±1.2 for Oa, Bh, and Bshorizons, respectively). These seasonal differences in°³⁴S were probably caused by biological isotopicfractionation. The °³⁴S values in streams were generally2 lower and more variable than those in precipitation andthroughfall, suggesting fractionation and/or different isotopic sources inthe soil.