Following exposure in situ for periods of 3 to 24 h of samples of lake or sea waters to which 14 C-bicarbonate had been added, radioactivity was found in dissolved organic matter in the water as well as in the cells of phytoplankton. The amount in the water was between 7 and 50% of the total carbon fixed in the photic zone of the water column. This production of extracellular 14 C-labelled organic matter was found under a wide variety of conditions and with many different types of phytoplankton community. It thus seems likely that the widely used method, in which fixation of 14 C in particulate matter only is determined, under­estimates total primary productivity. The labelled organic substances in the water are probably liberated by intact photosynthesizing cells rather than by breakage of cells during filtration. Glycollic acid is likely to be one of the principal substances concerned. Over a wide range of light intensities liberation of extracellular products by a given phytoplankton population was proportional to the amount of carbon fixed in the cells, except that it tended to be relatively greater at low light intensities (< 1 kilolux) and at light intensities high enough to inhibit photosynthesis ( > 50 kilolux), when as much as 95% of the total organic 14 C might be extracellular. Population density, period of exposure to 14 C-bicarbonate and species differences also affect the extent of excretion. The implications of extensive liberation by phytoplankton of extracellular products of photosynthesis for our understanding of the trophic relationships in aquatic habitats seem to be considerable.

1983. Evidence of acidification sf some Nova Scotian rivers and its impact on Atlantic salmon, Salmo snlar. Can. J. Fish. Aquat. Sci. 40: 462-473.River pH's in Nova Scotia are closely reIated to geology, and seasonal pH variation is well correlated with river discharge rates. In the geologically sensitive areas (granite and metamorphic rocks), river pH's have fallen significantly over the past 27 yr at an apparent average rate of 0.017 pH units/year. Concomitant with this decrease are a decline in HCOi concentrations and increases in AIWC and SOT. On average, 73% of the increase in acid is attributabie to increased SOT. Changes in Na', K9, Ca'+. and Mg" concentrations were not significant. In rivers presently at mean annual pH's c4.7, the Atlantic salmon (S~lrno s a k r ) runs have disappeared and are presumed extinct. Rivers in the pH range 4.7-5.0 show a decline in salmon angling returns of 2.8%/yr, beginning about 1854, and low densities of juvenile salmon. Rivers presently of pH > 5.0 generally have normal juvenile densities and show no significant trend in angling returns. WATT, W. D., $1. B. SCOTT, AND W. J. WHITE. 1983. Evidence of acidification of some Nova Scotian rivers and its impact on Atlantic salmon, Snlrno solar. Can. 5. Fish. Aquat. Sci. 44): 462-473. En Pdouvelle-kcosse, le pH des rivieres est en ktroite relation avec la geologic. et les variations saisonnihes le sorat avec le dkbit des rivikres. Dans les regions gt5ologiques plus sensibaes (granite et r o c k s mktamorphiques). le pH des rivikres a baisse de faqon significative au cours des 27 dernikres annkes et cela 5 un taux moyen de 0.017 unit& pH/annCe. 11 s'est produit en m6me temps un dCclin de concentration de HCOi et un aceroissement de Al"' et SO:. En moyenne, 73 % de I'augmentation de l'acide est attribuable a l'augmentation de SO:. Drarant la mCme @riode, il ne s'est produit aucun ehangement significatif des concentrations de Na', K', Ca'* et Mg". Les populations de saumsns ataantiques (Saltno salar) ont disparu des rivi5res dont le pH annuel moyen est infbrieur B 4,7 et sont pr6sumkes Cteintes.Les rivikres B pH de 4,7-5,0 montrent un dCclin des prises sportives de 2,8 % par annie patir de 1954 et de faibies densites de juvkniles. Les rivieres B pH srm@rieur a 5,0 snt en gCn6ral des densitCs de saumoneaux normales et ne montrent abscune tendance significative des prises sportives.

No abstract

1993. Metazoan parasite communities of yellow eels (Anguilla rostrata) in acidic and limed rivers of Nova Scotia. Can. J. Zool. 71: 177-184. Metazoan parasite communities of 269 yellow eels (Anguilla rostrata) inhabiting acidic (pH 4.5 -5.0) and deacidified (limed to a pH of 6.0-7.0) portions of a watershed in southwest Nova Scotia were compared over 3 years. Paraquimperia tenerrima, Ergasilus celestis, Bothriocephalus claviceps, Proteocephalus macrocephalus, Crepidostomum brevivitellum, and Azygia longa were found. Species richness was greater and there were more multiple infections in the component community in eels from the limed portion of the watershed than in the community in the acidic river. Differential susceptibility of the parasites or their intermediate hosts to acidification appears to be involved in structuring the community. Digeneans were absent from eels in the acidic river. The copepod E. celestis occurred throughout the watershed but was less common in the acidic river. The occurrences of two species, B. claviceps, and P. macrocephalus, were similar at acidified and limed sites. Numbers of infected fish and prevalence of the dominant parasite, P. tenerrima, were highly variable in eels from the acidic region, but were relatively stable at the limed site. It is concluded that the assemblage of metazoan parasites of fish may be useful as environmental indicators, and may also provide information on the dynamics of altered food webs. CONE, D. K., MARCOGLIESE, D. J., et WATT, W. D. 1993. Metazoan parasite communities of yellow eels (Anguilla rostrata) in acidic and limed rivers of Nova Scotia. Can. J. Zool. 71 : 177-184. Nous avons comparC les communautCs de mktazoaires parasites chez 269 anguilles Anguilla rostrata dans les eaux acides (pH 4,5 -5,O) et dans les eaux dCsacidifiCes (chaulkes jusqu'a pH 6,O-7,O) d'un bassin du sud-ouest de la Nouvelle-Ecosse au cours d'une Ctude de 3 ans. Paraquimperia tenerrima, Ergasilus celestis, Bothriocephalus claviceps, Proteocephalus macrocephalus, Crepidostomum brevivitellum et Azygia longa ont Ct C trouvks chez les poissons.Chez les anguilles de la portion dCsacidifiCe du bassin, la communautC de parasites avait une richesse en espkces plus ClevCe et les infections multiples y Ctaient plus frkquentes que chez les anguilles de la rivikre acide. La sensibilitC diffkrentielle des parasites ou de leurs h8tes intermkdiaires a l'acidification semble rCgir la structure de la communautC. Les Digknes Ctaient absents des anguilles de la rivikre acide. Le copCpode E. celestis a Ct C trouvC dans tout le bassin, mais il Ctait moins commun dans la rivikre acide. La frkquence de deux espkces, B. claviceps et P. macrocephalus, Ctait semblable dans les deux types de milieu. Le nombre de poissons infect& et la prevalence du parasite dominant, P. tenerrima, Ctaient trks variables dans la rivikre acide, mais Ctaient relativement stables dans le milieu dCsacidifiC. La communautC de mCtazoaires parasites des poissons semble donc pouvoir constituer un indicateur Ccologique trks ut...

Sixteen of 23 lakes sampled in 1955 show no sign of significant physical alterations within their drainage basins over a 21‐year interval, so that chemical changes in these lakes can be assumed to reflect changes in atmospheric inputs. In all 16, the pH levels have declined, with greater declines in the higher pH (near neutrality) lakes. After correction for sea‐salt input, concentrations of sodium, magnesium, calcium, potassium, and sulfate show no significant change. Sulfate and hydrogen ions are significantly correlated and both show significant regressions on distance from the major sulfur‐emitting industrial sources in the Halifax area. Although the area as a whole may be subject to an influx of acid pollutants via long distance atmospheric transport, for lakes near Halifax the high acid levels are largely due to local pollution.