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991.
1. We hypothesized that the fishery management practices of toxaphene application and trout stocking would affect non-target organisms in lakes. Because these practices were rarely monitored in the past, cladoceran and algal assemblages were quantified in sediment cores from two lakes treated 30+ years ago to determine the long-term response of organisms near the base of the food chain. 2. Chydorids were remarkably resistant over the short term (a few years) in both the oligotrophic and eutrophic lakes despite toxaphene treatments that extirpated native fish and other invertebrates. In the oligotrophic lake (Annette Lake), six chydorid taxa were less abundant in the years following treatment, although no loss of species richness was detected. In the eutrophic lake (Chatwin Lake), the dominant Chydorus cf. sphaericus declined coincident with toxaphene treatment, but longer-term declines of all taxa were probably related to food web or other changes rather than to toxaphene toxicity. Cause and effect coupling was complicated by the fact that many chydorids were present at low concentrations in some pretreatment samples. 3. The algal communities (as fossil pigments) responded to treatment differently in the two lakes. In the oligotrophic lake, planktonic diatoms, dinoflagellates and chlorophytes were replaced as dominants by deep-water or benthic blooming cryptophytes, chrysophytes and cyanobacteria. This shift occurred along with increases in large daphnids and the ‘grazing indicator’, pheophorbide a. While both lakes appear to have had enhanced pigment preservation following treatment, the eutrophic lake encountered few long-term changes in its fossil pigment assemblage. Redundancy analysis estimated that the presence or absence of stocked trout explained much of the variation in the algal assemblages, particularly in the oligotrophic lake. 4. Toxaphene remained elevated in profundal sediments from these lakes 30 and 35 years after treatment. 相似文献
992.
Disturbance and the community structure of stream invertebrates: patch-specific effects and the role of refugia 总被引:1,自引:1,他引:0
MARGARET A. PALMER PETER A RENSBURGER P. SILVER BOTTS† CHRISTINE C. HAKENKAMP JANET W. REID‡ 《Freshwater Biology》1995,34(2):343-356
1. We have previously shown that the impact of spates on stream invertebrates may differ among patches separated by distances of metres or less. Here we analyse the species-specific flood responses of larval chironomids and adult and near mature copepods living in different patch types. Four patch types (with eight replicates of each) were compared: the sandy mid-channel, fine sediments around dams, coarse sediments around dams, and dam debris. Additionally, since some fine sediment patches had been shown previously to act as flow refugia while others did not, we also examined species-specific responses in refugium vs. non-refugium fine sediment patches. Detrended correspondence analysis was used to test for changes in assemblage structure (species composition and relative abundance). 2. Species richness was not altered in a predictable manner by floods; the least stable patch types (mid-channel and coarse patches) did not necessarily show reduced species richness during the spate. 3. As indicated by the spread of DCA ordination scores, there was generally a high degree of overlap in the species composition among the four patch types. Nevertheless, copepod species composition and relative abundance were more similar among patch types during the spate than pre-spate. Spates may induce a re-distribution of copepod species among the patch types. Chironomid species composition and relative abundance were no more similar among patch types during the spate than pre- or post-spate. 4. For both chironomids and copepods, species composition and relative abundance (as assessed by DCA ordination scores) in refugium patches changed more in response to the spate than in the non-refugium patches. An influx of individuals from just a few species for each group was responsible for the change in assemblage structure. Thus, despite the fact that our past work has shown that refugia may confer enhanced resistance and resilience of copepod and chironomid assemblages in terms of total faunal abundances, the present work suggests that resistance and resilience of the species composition of the community apparently are no greater in refugium patches than in non-refugium patches. 相似文献
993.
Leaf gas exchange and nitrogen dynamics of N2 -fixing, field-grown Alnus glutinosa under elevated atmospheric CO2 总被引:1,自引:0,他引:1
Few studies have investigated the effects of elevated CO2 on the physiology of symbiotic N2-fixing trees. Tree species grown in low N soils at elevated CO2 generally show a decline in photosynthetic capacity over time relative to ambient CO2 controls. This negative adjustment may be due to a reallocation of leaf N away from the photosynthetic apparatus, allowing for more efficient use of limiting N. We investigated the effect of twice ambient CO2 on net CO2 assimilation (A), photosynthetic capacity, leaf dark respiration, and leaf N content of N2-fixing Alnus glutinosa (black alder) grown in field open top chambers in a low N soil for 160 d. At growth CO2, A was always greater in elevated compared to ambient CO2 plants. Late season A vs. internal leaf p(CO2) response curves indicated no negative adjustment of photosynthesis in elevated CO2 plants. Rather, elevated CO2 plants had 16% greater maximum rate of CO2 fixation by Rubisco. Leaf dark respiration was greater at elevated CO2 on an area basis, but unaffected by CO2 on a mass or N basis. In elevated CO2 plants, leaf N content (μg N cm?2) increased 50% between Julian Date 208 and 264. Leaf N content showed little seasonal change in ambient CO2 plants. A single point acetylene reduction assay of detached, nodulated root segments indicated a 46% increase in specific nitrogenase activity in elevated compared to ambient CO2 plants. Our results suggest that N2-fixing trees will be able to maintain high A with minimal negative adjustment of photosynthetic capacity following prolonged exposure to elevated CO2 on N-poor soils. 相似文献
994.
PETER M. CHAPMAN 《Austral ecology》1995,20(1):7-19
Abstract Bioassay testing includes both toxicity (one or more effects is measured) and bioaccumulation (the phenomenon of tissue accumulation is measured) tests. Both types of bioassay tests have an important place in water quality assessment programmes, ideally beginning with initial screening and as part of tiered testing that includes contaminant analyses and field studies. Both have advantages (e. g. measure bioavailability, provide quantitative data, experimental manipulations can address cause-effect relationships) and disadvantages (e. g. laboratory exposures do not necessarily reflect field conditions, not all organisms can be tested). Both provide essential, but not all, information necessary for holistic water quality assessments. This paper provides a review of the use of bioassays including definitions, applications, advantages and disadvantages, utility and relevance. The utility of bioassays in monitoring programmes is illustrated by two case studies. The first case study, involving novel toxicity studies conducted in the high Arctic, illustrates the versatility of bioassays such that testing conducted in a tent on the ice resulted in new knowledge and a change in industrial discharge limits. The second case study further illustrates the importance of bioassays in decision making. In this case, a decision not to immediately spend hundreds of millions of dollars for sewage treatment, but rather to concentrate on source control, was made based in large part on bioassay testing conducted as part of an integrated environmental assessment. 相似文献
995.
1. We examined selected aspects of the nutritional ecology of larval Ptychoptera paludosa and their role in nutrient cycling in the Breitenbach, a first-order stream in Hesse, Germany.
2. Food preference experiments demonstrated significant preference for sediments with a high organic matter content and live bacteria.
3. pH was circumneutral in all sections of the gut.
4. Enzymatic activity (β-glucosidase and amino-peptidase) in different parts of the gut was measured using 4-methylumbelliferyl-β- D -glucopyranoside (MUF-Glc) and leucine-4-methylcoumarinyl-7-amide (Leu-MCA). β-glucosidase activity was highest in the hindgut.
5. The mean larval gut passage time was between 7 and 8 h.
6. The egestion rate of last instar larvae was about 0.35 mg dry weight (DW) faeces per larva h–1 and about 1.25 mg ash-free dry weight (AFDW) faeces per mg larval AFDW day–1 .
7. Larval faeces contained at least 4–18 times more organic matter than the average in the sediments in which they were feeding, that is, larvae fed selectively, extracting organic matter from sediments.
8. P. paludosa larvae are important in the dynamics of detritus in slow-flowing reaches of the Breitenbach. They gather organic material from the sediment to a depth of 3 cm, and release it as faeces onto the sediment surface. A total of 770 g DW faeces m–2 yr–1 , comprising about 16% organic matter, was produced by the Ptychoptera population. 相似文献
2. Food preference experiments demonstrated significant preference for sediments with a high organic matter content and live bacteria.
3. pH was circumneutral in all sections of the gut.
4. Enzymatic activity (β-glucosidase and amino-peptidase) in different parts of the gut was measured using 4-methylumbelliferyl-β- D -glucopyranoside (MUF-Glc) and leucine-4-methylcoumarinyl-7-amide (Leu-MCA). β-glucosidase activity was highest in the hindgut.
5. The mean larval gut passage time was between 7 and 8 h.
6. The egestion rate of last instar larvae was about 0.35 mg dry weight (DW) faeces per larva h
7. Larval faeces contained at least 4–18 times more organic matter than the average in the sediments in which they were feeding, that is, larvae fed selectively, extracting organic matter from sediments.
8. P. paludosa larvae are important in the dynamics of detritus in slow-flowing reaches of the Breitenbach. They gather organic material from the sediment to a depth of 3 cm, and release it as faeces onto the sediment surface. A total of 770 g DW faeces m
996.
R. PETER H. WELSH PATRICK DENNY 《Biological journal of the Linnean Society. Linnean Society of London》1978,10(1):67-92
A study was made of the aquatic macrophyte ecology of Nyumba ya Mungu; a nine year old man-made lake in northern Tanzania. The vegetation is described with the aid of percentage cover histograms and standing crop estimates. Concurrent physical, chemical and biological studies helped in ecological interpretations. Distinct vegetation communities were found in the deltaic swamps of the two major inflow rivers and it is concluded that this was due to water chemical differences. The water of the more alkaline River Kikuletwa appeared to influence the greater part of the perimeter swamps as the species composition largely coincided with that reported for higher pH, higher conductivity African lakes. Typha domingensis swamp was predominant and extensive, whilst Cyperus alopecuroides and Paspalidium geminatum were also common emergent species. Floating and submerged plants were relatively unimportant in the lake with respect to cover. The major zonations of species appeared to be a function of water depth, while chemistry seemed the main factor controlling vegetation pattern. In conclusion the significance of interrelationships between the macrophytes and other aquatic organisms is discussed. 相似文献
997.
The physiological basis for senescence symptoms induced by spraying attached primary leaves of bean plant (Phaseolus vulgaris L. cv. Brittlewax) with silicone oil emulsions was investigated. It was found that chlorophyll levels declined significantly between 24 and 48 h after spraying, whereas neither protein levels nor respiration rates were affected over a 7-day period. Rates of photosynthesis and reducing sugar levels in silicone-sprayed leaves were however significantly reduced after 1 and 24 h respectively. These responses were obtained using plants grown under low stress controlled environment conditions. By contrast, leaves on greenhouse plants did not senesce in response to silicone sprays. A possible mechanism of silicone oil action based on selective leaf penetration and inhibition of photosynthesis is postulated. 相似文献
998.
Using electropherograms (zymograms) of the phenoloxidase laccase and characteristics of mycelial growth and fruit body production, a distinct morphological and biochemical differentiation of two geographically isolated (allopatric) populations of the wood-rotting basidiomycete Pleurotus ostreatus became evident. No limitation in their outbreeding ability was observed, however. A specific secretory mechanism for an extracellular laccase, genetically different in the two geographical races, could be detected. An approximately 1: 1 segregation of this laccase band in the F1 generation indicates that specific secretion of this enzyme is controlled by one gene only, Different degrees of genetic variation as shown by differences in the respective laccase spectra were found in the two geographical races. Only one enzyme band out of nine multiple laccases was found to be specific for fruit bodies. The value of zymograms for chemotaxonomic purposes, for the understanding of microevolution and for determination of genetic variation in fungi is critically discussed. 相似文献
999.
SUMMARY. The influence of exposure time upon macro-invertebrate colonization on modified Hester-Dendy substrate samplers was investigated over a 60-day period. The duration of exposure affected the number of individuals, taxa and community diversity.
The numbers of individuals colonizing the samplers reached a maximum after 39 days and then began to decrease, due to the emergence of adult insects. Coefficients of variation for the four replicate samples retrieved each sampling day fluctuated extensively throughout the study. No tendencies toward increasing or decreasing coefficients of variation were noted with increasing time of sampler exposure.
The number of taxa colonizing the samplers increased throughout the study period. The community diversity index was calculated for each sampling day and this function tended to increase throughout the same period. This supports the hypothesis that an exposure period of 6 weeks, as recommended by the United States Environmental Protection Agency, may not always provide adequate opportunity for a truly representative community of macro-invertebrates to colonize multiplate samplers.
Many of the taxa were collected in quite substantial proportions after periods of absence or extreme sparseness. This is attributed to the growth of periphyton and the collection of other materials that created food and new habitats suitable for the colonization of new taxa.
Investigation of the relationship between 'equitability' and length of exposure revealed that equitability did not vary like diversity with increased time of exposure. 相似文献
The numbers of individuals colonizing the samplers reached a maximum after 39 days and then began to decrease, due to the emergence of adult insects. Coefficients of variation for the four replicate samples retrieved each sampling day fluctuated extensively throughout the study. No tendencies toward increasing or decreasing coefficients of variation were noted with increasing time of sampler exposure.
The number of taxa colonizing the samplers increased throughout the study period. The community diversity index was calculated for each sampling day and this function tended to increase throughout the same period. This supports the hypothesis that an exposure period of 6 weeks, as recommended by the United States Environmental Protection Agency, may not always provide adequate opportunity for a truly representative community of macro-invertebrates to colonize multiplate samplers.
Many of the taxa were collected in quite substantial proportions after periods of absence or extreme sparseness. This is attributed to the growth of periphyton and the collection of other materials that created food and new habitats suitable for the colonization of new taxa.
Investigation of the relationship between 'equitability' and length of exposure revealed that equitability did not vary like diversity with increased time of exposure. 相似文献
1000.