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Showing papers by "Dalhousie University published in 1986"


Journal ArticleDOI
14 Nov 1986-Science
TL;DR: Direct measurements of rates of turbulent kinetic energy dissipation, coupled with highly resolved vertical profiles of nitrate and density in the oligotrophic eastern Atlantic showed that rates of transport are consistent with a biologically unproductive oligOTrophic ocean.
Abstract: The vertical flux of nitrate across the thermocline in the upper ocean imposes a rigorous constraint on the rate of export of organic carbon from the surface layer of the sea. This export is the primary means by which the oceans can serve as a sink for atmospheric carbon dioxide. For the oligotrophic open ocean regions, which make up more than 75% of the world's ocean, the rate of export is currently uncertain by an order of magnitude. For most of the year, the vertical flux of nitrate is that due to vertical turbulent transport of deep water rich in nitrate into the relatively impoverished surface layer. Direct measurements of rates of turbulent kinetic energy dissipation, coupled with highly resolved vertical profiles of nitrate and density in the oligotrophic eastern Atlantic showed that the rate of transport, averaged over 2 weeks, was 0.14 (0.002 to 0.89, 95% confidence interval) millimole of nitrate per square meter per day and was statistically no different from the integrated rate of nitrate uptake as measured by incorporation of (15)N-labeled nitrate. The stoichiometrically equivalent loss of carbon from the upper ocean, which is the relevant quantity for the carbon dioxide and climate question, is then fixed at 0.90 (0.01 to 5.70) millimole of carbon per square meter per day. These rates are much lower than recent estimates based on in situ changes in oxygen over annual scales; they are consistent with a biologically unproductive oligotrophic ocean.

327 citations



Journal ArticleDOI
TL;DR: Variation in the amino-acid composition among the seven algal diets analysed was small and did not explain the observed differences in oyster growth response with the diets, and there was no clear trend between the protein level of the diet and the growth response of the oysters.

254 citations


Journal ArticleDOI
TL;DR: It is demonstrated that destruction of the GHT in the hamster alters phase shifting in response to periods of light or dark, and a role for the G HT in mediating several photic effects on the circadian system is indicated.
Abstract: We have investigated the effects of destruction of the geniculo-hypothalamic tract (GHT) on the circadian system of golden hamsters. In the first experiment, intact hamsters were housed in constant darkness, and phase shifts in running-wheel activity rhythms were assessed following 15-min light pulses administered at circadian time (CT) 12 (defined as the beginning of activity), CT 14, CT 18, and CT 20. Responses to light pulses at the same CTs were then reassessed after GHT lesions. Hamsters with complete lesions showed decreases in phase advances caused by light pulses at CT 18 and CT 20. Phase delays elicited by light at CT 12 and CT 14 were not altered. In a second study, intact and GHT-ablated hamsters housed in constant light received 6-hr dark pulses at various CTs. Hamsters with complete GHT ablation showed smaller advances than controls to dark pulses centered on CT 8-10. After 110 days in constant light, 7 of 10 intact hamsters showed splitting of their activity rhythms into two components, while only 1 of the 8 similarly treated ablated hamsters displayed dissociated activity components. Ablated hamsters had significantly shorter free-running periods during the first 35 days of exposure to constant light than did the intact hamsters. These results demonstrate that destruction of the GHT in the hamster alters phase shifting in response to periods of light or dark, and they indicate a role for the GHT in mediating several photic effects on the circadian system.

234 citations


Journal ArticleDOI
TL;DR: The anatomy of the human extrinsic cardiac nerves and ganglia was reinvestigated because detailed analyses of subhuman mammalian cardiac innervation reveal considerable similarities among species and the anatomic pattern of cardiac innervation observed in subhuman mammals differs significantly from those described for humans.
Abstract: The anatomy of the human extrinsic cardiac nerves and ganglia was reinvestigated because descriptions of human cardiac innervation vary, detailed analyses of subhuman mammallaan cardiac innervation reveal considerable similarities among species and the anatomic pattern of cardiac innervation observed in subhuman mammals differs significantly from those described for humans. The presence of a consistent pattern of cardiac innervation in subhuman mammals raised the question as to whether a similar pattern exists M humans. To investigate this, the cervical and thoracic autonomic nerves and ganglia were dissected in 13 embalmed and 10 autopsy cadavers. All major sympathetic cardiopulmonary nerves were found to arise from the stellate ganglia and the caudal halves of the cervical sympathetic trunks below the level of the cricoid cartilage. These sympathetic cardiopulmonary nerves usually consisted of 3 nerves on the right side and 4 on the left. In contrast to widely accepted reports, no sympathetic cardiopulmonary nerves were found to arise from the superior cervical ganglia or the thoracic sympathetic trunks inferior to the stellate ganglia. Parasympathetic cardiopulmonary nerves were found to arise from the recurrent laryngeal nerves and the thoracic vagi immediately distal to them. These nerves interconnected with sympathetic cardiopulmonary nerves anterior and posterior to the main pulmonary artery to form the ventral and dorsal cardiopulmonary plexuses. These plexuses contained relatively large discrete nerves as well as smaller interconnections. Emerging from these plexuses to innervate the ventricles were 3 distinct relatively large cardiac nerves, the right and left coronary cardiac nerves and the left lateral cardiac nerve. In addition to these 3 major nerves, small cardiac nerves arose from the plexuses and the thoracic vagi. Histologic examination of representative dissections confirmed the presence of neural tissue and identified the locations of neuronal cell bodies in these structures. Cell bodies were located in the nodose, superior cervical, middle cervical, stellate and thoracic sympathetic ganglia. The middle cervical ganglia varied in size and number. Neuronal cell bodies were found In the cervical and thoracic sympathetic trunks and in small mediastinal ganglia located along the courses of the cardiopulmonary and cardiac nerves. Marked similarities exist between the anatomy of the cardiopulmonary nerves and ganglia of humans and baboons.

234 citations


Journal ArticleDOI
TL;DR: The Wang and Conover (1986) hypothesis that pigment destruction by the digestive process was the most probable explanation for the discrepancy between ingestion rates generated by the two methods is tested.
Abstract: By use of biogenic silica as an inert marker, it is shown that chlorophyll a and its derivatives can be destroyed or absorbed during passage through the gut of a herbivorous copepod. This observation is contradictory to the hypothesis that chlorophyll a is converted to pheophorbide a with 100% molar efficiency. The currently used equations for measuring chlorophyll and pheopigment by fluorescence cannot be used to give concentration of phcopigment. Determining quantitatively the role of zooplankton as intermediates in material and energy transfer in aquatic food chains remains a formidable challenge for biological oceanographers. Several kinds of in vivo or in situ techniques have been developed to avoid the lengthy incubations usually required to measure grazing rates in the laboratory, with their attendant problems of interpretation and application. Probably the most widely used of these is the gut chlorophyll method (Mackas and Bohrer 1976). The usefulness of this technique to examine short term variability in zooplankton feeding has been frequently demonstrated (Boyd et al. 1980; Dagg and Grill 1980; Dagg and Wyman 1983; Nicolajsen et al. 1983; Head et al. 1984). On the other hand, there have been relatively few attempts to relate ingestion based on gut pigment contents with ingestion derived from conventional grazing experiments and, when this has been attempted, the results have been contradictory. Kiorboe et al. (1982) carried out a parallel series of grazing experiments and gut chlorophyll ingestion measurements under the same conditions of food and temperature, but at different times, and then used somewhat different models to describe their results, concluding that the agreement was good enough to make (p. 192) “the prospects for application of the indirect method (i.e. gut pigment method) to field situations promising.” Wang and Conover (1986) addressed the same problem by measuring the accumulation of gut pigment and the rate of its removal by grazing simultaneously, but they found that more chlorophyll was ingested than could be accounted for by that found in the gut and that disappearing from the animal during defecation. Several possible explanations for the discrepancy between the ingestion rates generated by the two methods in Wang and Conover’s ( 1986) studies come to mind. First, to convert the level of gut pigment in an animal to a rate of ingestion requires an estimate of gut turnover or evacuation rate, which are assumed to be equivalent. Evacuation rate is usually determined from loss of gut pigment in previously fed animals after transfer to filtered seawater (Mackas and Bohrer 1976; Dagg and Grill 1980; Kiorboe et al. 1982; Wang and Conover 1986). However, an evacuation rate for starving animals might underestimate turnover rate for those that are feeding regularly. Or alternatively there could be loss of pigment, perhaps through exposure to light or carbon dioxide or as a consequence of freezing (Nicolajsen et al. 1983). Or conceivably, a portion of the pigment actually ingested is digested or destroyed in the gut. Wang and Conover (1986) examined these several possibilities and concluded that pigment destruction by the digestive process was the most probable explanation. Here we test this hypothesis. In their original description of the gut pigment method, Mackas and Bohrer (1976)

230 citations


Journal ArticleDOI
TL;DR: The overall photic responsiveness of SCN neurons indicated that they are specialized for luminance coding in the range of light intensities naturally occurring at dawn and dusk, which makes these cells suitable to mediate photic entrainment of circadian rhythms as well as the measurement of photoperiod.

218 citations


Journal ArticleDOI
TL;DR: The acclimation of herbivores to variation in their phytoplankton food source was expressed mathematically and its effect on phy Topolankton, herbivore and nutrient cycles explored with a plankton model.
Abstract: The acclimation of herbivores to variation in their phytoplankton food source was expressed mathematically and its effect on phytoplankton, herbivore and nutrient cycles explored with a plankton model. The grazing formulation is a modified version of the function experimentally determined by Mayzaud and Poulet. Their function differs from the traditional Ivlev expression for herbivore grazing in that there is no asymptotic limit to the grazing rate. The steady-state solutions of the phytoplankton-herbivorenutrient model were similar with the two grazing formulations, but the time-dependent behaviour of the two models differed markedly. The model with Ivlev grazing showed oscillations when the grazing pressure was high. The model with acclimated herbivore grazing showed only small, highly damped oscillations as it approached steady state. The latter is more similar to the evolution of plankton trophic levels observed in controlled ecosystem experiments.

211 citations


Journal ArticleDOI
TL;DR: Small amounts of arsenic are metabolized in a variety of ways and are largely rapidly methylated and excreted by man and animals, and toxic manifestations in man occur at the cellular level and may appear in many organ systems.
Abstract: (1986). Clinical and Environmental Aspects of Arsenic Toxicity. CRC Critical Reviews in Clinical Laboratory Sciences: Vol. 23, No. 4, pp. 315-347.

210 citations


Journal ArticleDOI
TL;DR: A classification of the radiographic appearance of elongated and mineralized stylohyoid ligament complexes based on three types of complexes based in a case of Eagle's syndrome in a 55-year-old Mexican-American man with symptoms of chronic otalgia and cephalgia is illustrated.

199 citations


Journal ArticleDOI
15 Feb 1986-Cancer
TL;DR: With the aid of newer imaging techniques, localization, biopsy diagnosis and resection of the atrial tumors are now being achieved more often, with some improvement in survival.
Abstract: Forty-five cases of cardiac angiosarcomas were reviewed, and the data were compared with those of a 1968 review of 41 other cases which revealed these tumors to be typically located within the right atrium as large symptomatic masses and to be rapidly fatal, with the diagnoses usually determined only at autopsy. The relationship of these tumors to Kaposi's sarcoma was also examined. The findings paralleled those of the previous review. Additionally, the following points emerged: With the aid of newer imaging techniques, localization, biopsy diagnosis and resection of the atrial tumors are now being achieved more often, with some improvement in survival. Like angiosarcomas of other organs, atrial angiosarcomas exhibit highly variable histologic patterns, which often overlap those of Kaposi's sarcoma, and may also present metastatic patterns simulating widespread Kaposi's sarcoma or malignant melanoma. In reported cases of classical, endemic, or epidemic Kaposi's sarcoma, cardiac lesions are uncommon and typically are small, asymptomatic, restricted to the epicardium/or pericardium and, thus, are clearly different, both clinically and pathologically, from the atrial tumor group. The justification for designating cases of the latter group as "primary cardiac Kaposi's sarcoma" is open to debate. A case report illustrates many of the above points.

Journal ArticleDOI
TL;DR: In rats with unilateral 6-hydroxydopamine lesions of the substantia nigra, a specific D1 dopamine receptor agonist, SKF 38393A, at a dose that does not itself produce turning, significantly increased the contralateral rotation observed following a low dose of the specific D2 agonist LY 171555.

Journal ArticleDOI
TL;DR: In the field, diatom films were patchy on a scale of centimetres, corresponding to the structure of sand ripples as discussed by the authors, which explained the heterogeneous distribution of films with respect to ripple topography in the field.
Abstract: Field and laboratory flume studies were used to examine the stabilization of intertidal sands by diatom mucus films. Films were delineated by analyzing colloid carbohydrates, chlorophyll, and by scanning electron microscopy on intact sediment samples. In the field, diatom films were patchy on a scale of centimetres, corresponding to the structure of sand ripples. Films were present on the sediment surface after calm weather and absent after storms. Extracellular polysaccharides accounted for a maximum of 20% of microalgal carbon. Erosion of intact cores in the flume showed that although films stabilized local areas of the bed, portions of the film were also washed away or buried. Stabilized areas of the bed were transposed to new ripple locations as the bedform moved ‘through’ the film. This observation explained the heterogeneous distribution of films with respect to ripple topography in the field. SEM showed diatom cells attached between sand grains with mucus strands, particularly in samples from the films. Mucus attachment due to protozoa, fungi, and other organisms was also observed. In the flume, diatom cells were washed away leaving mucus strands behind. A flume core with diatom films lost smaller amounts of chlorophyll than a core without films, under similar stages of erosion. At the highest flow, many grains were cleaned of mucus coatings; the grains appeared similar to those from sites of active transport (crests) in the field. We conclude that sediment stabilization by biofilms must be studied on a spatial scale of centimetres, and a temporal scale of days to weeks. The most important effect of microbial binding of sediments may be their role in the transfer of organic matter between the sediment and the water column.

Journal ArticleDOI
TL;DR: In this article, the authors compare macroalgal communities in areas where sea urchins died off 1, 3, and 4 years previously and to a mature kelp bed with no sea worms, showing that large-scale reciprocal fluctuations in kelp and sea worms' biomass may characterize the trajectory of a dynamic system which cycles between two alternate community states: kelp beds and sea-worms dominated barren grounds.
Abstract: Recurrent outbreaks of disease between 1980 and 1983 caused catastrophic mortality of sea urchins (>260,000 t fresh weight) along 280 km (straight line distance) of the Atlantic coast of Nova Scotia. The complete elimination of sea urchins and concomitant development of fleshy macroalgal communities have occurred along different parts of this coast in different years. Macroalgal communities in areas where sea urchins died off 1, 3 and 4 years previously are compared to existing sea urchin-dominated barren grounds and to a mature kelp bed without sea urchins. Changes in macroalgal cover and species composition, and increases in biomass, density and size of kelp (Laminaria) species, characterize the succession from barren grounds to 3- and 4-year-old kelp beds. The greatest change occurred between one and three years following sea urchin mass mortality. Within 3 years, kelp beds attained a level of biomass (7.6 kg m-2) comparable to that of mature beds. Recovery of sea urchin populations via recruitment of planktonic larvae has been slow and spatially variable. Large-scale reciprocal fluctuations in kelp and sea urchin biomass may characterize the trajectory of a dynamic system which cycles between two alternate community states: kelp beds and sea urchin-dominated barren grounds. Periodic decimation of sea urchin populations by disease may be an important mechanism underlying this cyclicity.

Journal ArticleDOI
TL;DR: In this article, the authors considered nonlinear programming problems with stochastic constraints and showed that the deterministic surrogate problem CE-P contains a penalty function which penalizes violation of the constraints in the mean.
Abstract: We consider nonlinear programming problem P with stochastic constraints. The Lagrangean corresponding to such problems has a stochastic part, which in this work is replaced by its certainty equivalent in the sense of expected utility theory. It is shown that the deterministic surrogate problem CE-P thus obtained, contains a penalty function which penalizes violation of the constraints in the mean. The approach is related to several known methods in stochastic programming such as: chance constraints, stochastic goal programming, reliability programming and mean-variance analysis. The dual problem of CE-P is studied for problems with stochastic righthand sides in the constraints and a comprehensive duality theory is developed by introducing a new certainty equivalent NCE concept. Motivation for the NCE and its potential role in Decision Theory are discussed, as well as mean-variance approximations.

Journal ArticleDOI
TL;DR: The results indicate that higher oyster growth rates are possible with additional carbohydrate, provided that adequate protein and essential fatty acids are supplied.

Journal ArticleDOI
TL;DR: The clavicle of the embryonic chick shares all of the features and epigenetic requirements of the craniofacial the embryonic chicks shares all-of-the-features and epigenetics requirements of of the Craniof facial membrane bones, but is more dependent upon biomechanical factors for its growth.
Abstract: There has been debate in the literature concerning whether the clavicle arises by intramembranous ossification, i.e. is a membrane bone, and whether secondary cartilage develops from its periosteal cells. A histological study of carefully staged embryos revealed that preclavicular mesenchyme undergoes condensation at H. H. stage 31–32, bone forms by H. H. stage 33 and that a transitory secondary cartilage appears late in H. H. stage 35, only to disappear by H. H. stage 36. Except for the transitory nature of the secondary cartilage, this histogenetic sequence is as seen in craniofacial membrane bones. Enzymic removal of the epithelium overlying clavicular mesenchyme from embryos of H. H. stages 26–34 and chorioallantoic grafting of the isolated mesenchyme, revealed an epithelial requirement for initiation of intramembranous ossification during H.H. stages 26–29, again similar to initiation of craniofacial osteogenesis. Secondary chondrogenesis was initiated neither in embryos paralysed with decamethonium iodide nor when clavicular mesenchyme (H.H. stages 29–33·5) was grafted to the chorioallantoic membranes of paralysed embryos, but did form in a small percentage (16–23 %) of clavicles grafted to the membranes of mobile embryos. Failure of chondrogenesis in the former was attributed to a requirement for movement as a proximate chondrogenic stimulus and the low incidence of chondrogenesis in the latter to the stimulus provided by amniotic movements which persist in paralysed embryos. Secondary cartilage did form when clavicles were organ cultured, either submerged, or at the air-medium interface. This stands in contrast to craniofacial membrane bone such as the quadratojugal, which only forms secondary cartilage in vitro when cultured submerged. Growth of the clavicle was shown to increase 53-fold between 10 and 11 days of incubation, an increase which was diminished but not eliminated in paralysed embryos, and which correlated closely with the dramatic increase in embryonic movement which occurs between 10 and 11 days of incubation. Thus, the clavicle of the embryonic chick shares all of the features and epigenetic requirements of the craniofacial membrane bones, but is more dependent upon biomechanical factors for its growth.

Journal ArticleDOI
TL;DR: In this paper, a general study of regular points of Lipschitz and strictly differentiable mappings with applications to tangent cone analysis, inversion theorems, perturbed optimization problems, and higher-order conditions is presented.
Abstract: We undertake a general study of regular points of Lipschitz and strictly differentiable mappings with applications to tangent cone analysis, inversion theorems, perturbed optimization problems, and higher-order conditions

Journal ArticleDOI
P Keast1
TL;DR: In this paper, a quadratic formula of degrees 4 to 8 for numerical integration over the tetrahedron was constructed, and the formulas are fully symmetric with respect to the tetraset.
Abstract: Quadrature formulas of degrees 4 to 8 for numerical integration over the tetrahedron are constructed. The formulas are fully symmetric with respect to the tetrahedron, and in some cases are the minimum point rules with this symmetry.

Journal ArticleDOI
TL;DR: The results suggest that activation of A1‐receptors in the spinal cord can produce antinociception, and that Activation of A2‐receptorors may produce an additional effect, but the relative activity of CHA in this component of activity is unusual.
Abstract: Analogues of adenosine were injected intrathecally into rats implanted with chronic indwelling cannulae in order to determine a rank order of potency and hence characterize adenosine receptors involved in spinal antinociception. In the tail flick test L-N6-phenylisopropyl adenosine (L-PIA), cyclohexyladenosine (CHA) and 5'-N-ethylcarboxamide adenosine (NECA) produced dose-related antinociception which attained a plateau level. NECA and CHA also produced an additional distinct second phase of antinociception. D-N6-Phenylisopropyl adenosine (D-PIA) and 2-chloroadenosine (CADO) had very little antinociceptive activity in this test. The rank order of potency in producing the plateau effect was L-PIA greater than CHA greater than NECA greater than D-PIA = CADO, while that for the second phase of antinociception was NECA greater than-CHA. Pretreatment with both theophylline and 8-phenyltheophylline (8-PT) antagonized antinociception produced by CHA, with 8-PT being at least an order of magnitude more potent than theophylline. Both antagonists produced a significant hyperalgesia in the tail flick test. L-PIA and CHA also produced methylxanthine-sensitive antinociception in the hot plate test. These results suggest that activation of A1-receptors in the spinal cord can produce antinociception. Activation of A2-receptors may produce an additional effect, but the relative activity of CHA in this component of activity is unusual.

Journal ArticleDOI
TL;DR: It is suggested that the instability of the surface crust contributes significantly to inhibition of algal settlement on Phymatolithon, and the possibility of chemical inhibition cannot be ruled out.

Journal ArticleDOI
TL;DR: The pattern of Lacuna grazing on Laminaria is suggested to be governed by the distribution of anti-herbivore chemicals in the plants, and variations in the toughness and nutritional quality of different regions of the plant.

Journal ArticleDOI
TL;DR: Exercise testing may be indicated for improved risk assessment and the assessment of the significance of minor rest electrocardiographic abnormalities in middle-aged men with elevated levels of coronary heart disease risk factors.

Journal ArticleDOI
TL;DR: The St Anthony Complex of Newfoundland is best interpreted in terms of a high-temperature shear zone formed between down-going continental margin rocks and overriding oceanic lithosphere in a subduction zone as mentioned in this paper.
Abstract: Mctamorphic rocks of the St Anthony Complex of north-western Newfoundland are best interpreted in terms of a high-temperature shear zone formed between down-going continental margin rocks and overriding oceanic lithosphere in a subduction zone. High-grade rocks, immediately beneath the oceanic lithosphere peridotite, display retrograde meta-morphism in high-strain zones, whereas lower grade rocks, near the base of the metamorphic complex, display prograde metamorphism in high-strain zones. Mylonite zones in meta-basitcs at all levels in the complex contain the assemblage epidote-hornblende-albite-sodic oligoclase. These observations suggest that the ‘inverted metamorphic gradient’within the St Anthony Complex results from the fortuitous preservation of residual metamorphic assemblages from different crustal levels within an epidote amphibolite facies shear zone. The degree of re-equilibration is strongly dependent on the degree of strain, and is best achieved in synmetamorphic mylonite zones. This interpretation of the St Anthony Complex can be extended to other sub-ophiolite metamorphic sheets, which show very similar relationships. It is proposed that most metamorphic sheets beneath ophiolites are high temperature shear zones, the P-T paths of which preserve records of burial and exhumation in subduction zones.

Journal ArticleDOI
David Regan1
TL;DR: Evidence is presented supporting the idea that the human visual system has several specific sensitivities to different kinds of relative motion that may be of use in distinguishing rigid nonrotating objects from nonrigid or rotating objects.

Journal ArticleDOI
01 Jan 1986
TL;DR: A miniature optical backscatter sensor (MOBS) and an electro-magnetic flowmeter were deployed seaward of the surf zone at Pte Sapin, New Brunswick during the first Canadian Coastal Sediment Study (C 2 S 2 ), autumn 1983 as discussed by the authors.
Abstract: A miniature optical backscatter sensor (MOBS) and an electro-magnetic flowmeter were deployed seaward of the surf zone at Pte Sapin, New Brunswick during the first Canadian Coastal Sediment Study (C 2 S 2 ), autumn 1983. The MOBS had sensing elements at five vertical locations above the sea bed, and was sampled at 10 Hz. The suspension of sand is well correlated with the passage of individual waves and also with wave groups, with the influence of wave groups progressively more dominant at higher elevations above the bed. Suspension appears to be stronger during the onshore directed phase of the wave motion than during the offshore motion and there is evidence that initiation of suspension may be determined by fluid acceleration more than velocity. Time lags between suspension events at different heights suggest that vertical gradients in sediment flux are more important than horizontal gradients.

Journal ArticleDOI
01 Dec 1986-Nature
TL;DR: In this article, the chemistry of Nova Scotian lakes and ponds on base-poor terrains was analyzed and correlations and regressions between hydrogen ion (H+) concentrations and each of four predictors: dissolved organic carbon (DOC) (a surrogate for complex coloured organic acids, often of high molecular weight), non-marine sulphate (denoted by the prefixed asterisk as *SO42−), a surrogate for acid deposition, and the sum of the other non marine base cations sodium, magnesium and potassium (*(Na+ + Mg2+ + K+)).
Abstract: Controversy has arisen over the recent acidification of lakes1–4, ascribed by many to anthropogenic acid deposition from the atmosphere5,6, and by some to natural processes of soil acidification enhanced by the regrowth of forests after cutting and burning7–10. Here we show, by analysing the chemistry of Nova Scotian lakes and ponds on base-poor terrains, that both anthropogenic and natural acidification can be important. We calculated correlations and regressions between hydrogen ion (H+) concentrations and each of four predictors: dissolved organic carbon (DOC) (a surrogate for complex coloured organic acids, often of high molecular weight11,12), non-marine sulphate (denoted by the prefixed asterisk as *SO42−; a surrogate for acid deposition13), non-marine calcium (*Ca2+; the major basic cation from soil weathering and ion exchange), and the sum of the other non-marine base cations sodium, magnesium and potassium (*(Na+ + Mg2+ + K+)). The results indicate that acidity in these waters is affected both by organic acids from peatland catchments and by acid deposition from long-range and local sources (see ref. 14).

Journal ArticleDOI
TL;DR: The topological properties of the charge density of hydrogen-bonded complexes between nitrites and hydrogen chloride correlate linearly with theoretical estimates of the hydrogenbond energy.

Journal ArticleDOI
TL;DR: It was observed that haemolymph from parasitized larvae does not melanize in vitro; this phenomenon may be associated with a greatly increased stability of oencytoids.

Journal ArticleDOI
TL;DR: A review of the literature on trace metal concentrations and speciation can be found in this paper, where the dominant mechanism in control of concentration for most metals appears to be adsorption on biologically produced particulate matter.