摘要:

The benthic communities on individual rocks (large pebble to large cobble) were sampled in a third-order stream to examine the relationship between macroinvertebrate distribution and surface area. The number of individuals, number of taxa, and species diversity were correlated significantly with rock surface area. The number of taxa per 100 cm2was significantly greater on the smaller substrates. Abundance of each of the seven dominant taxa was also correlated with rock size, but only two taxa (Pseudocloeonsp. andEpeorussp.) showed distinct preferences for larger substrates. Multivariate analysis of these data, based on abundance of dominant taxa, indicated high similarity in distribution of macroinvertebrates on intermediate cobble substrate.

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665165

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Twenty-seven shallow tilapia culture ponds, having fish densities of 0.1 to 12 individuals · m−2were studied in Guanacaste Province, Costa Rica. Temporal changes in plankton community structure following the emptying and subsequent filling of each pond were noted. In general, newly filled ponds were initially colonized by microflagellates, which in turn were replaced by green and finally blue green algae.Microcystis aeruginosafrequently became the dominant phytoplankter. Its density was correlated with both high tilapia densities and low zooplankton concentrations. When tilapia densities were maintained below 0.5 fish · m−2, the copepodMesocyclops leukartiidominated the zooplankton community, and algal biomass was moderate. At higher tilapia densities, rotifers replaced copepods as the dominant zooplankters. When tilapia densities exceeded two adult fish m−2, negligible zooplankton levels were attained, and phytoplankton densities reached their highest levels (>2 × 10 cells · ml−1). At these high algal densities, nighttime dissolved oxygen concentrations were so low that the tilapia were forced to the water's surface to breathe. As a result, tilapia predation by fish-eating birds was significant.

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665166

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The macroinvertebrate fauna of Bear Creek, a 83 km stream which flows through six oxbow lakes, and two off-stream lakes in the same watershed was studied for two years. Bear Creek, a tributary of the Yazoo River in the Delta region of Mississippi, drains 330 km of Intensively cultivated agricultural land and carries a continuing sediment concentration during the rainy season of up to 1300 mg l−1. Benthic organisms were collected monthly from August, 1976 through August, 1978 at six stream stations and at 14 lake stations, across a variety of substrates, and at depths ranging from 0.5 to 6.5 m. In most lake and stream sections of the creek,Chaoborus(one species), Chironomidae (nineteen genera), and Oligochaeta (three species), dominated the benthos. Thirteen other genera of insects were represented as were Bryozoa (four genera), Mollusca (nine genera), Hirudinea (five genera), and Crustacea (three genera). There was continuous stress from high rates of sedimentation (up to seven cm yr−) as indicated by low taxa rlchness(s) and diversity (đ) at a majority of stations sampled. Most creek stations were subject not only to annual sedimentation and flushing but also to fluctuations in water level and drying. Secondary productivity varied greatly (one to 31 g dry wt m−2yr−1) and was almost totally dependent on three taxa of pollution tolerant organisms except In unstressed stream reaches. Low productivity in riverine lakes, when compared to stream sections was partially due to differences in species distribution in lotic and lentic habitats. The mayflyHexagenia bilineata, the clamSphaerium rhomboldeum, and the bryozoanPectinatella magnifica, responded negatively to environmental stresses Induced by seasonally high concentrations of suspended sediments.

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665167

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Diel changes of dissolved oxygen (DO) and pH were measured during 1981–1982 in Pool 1, a shallow reservoir in southeast Missouri. Diel changes in spring and fall were about half those of summer when extensive macrophyte biomass apparently had a strong influence on dynamics of DO and pH. During summer, daily pulses averaged 5.45 mg/L DO and 0.88 pH units, and extreme diel changes were 10–14 mg/L DO and 2–3 pH units. Ambient values of DO and pH were directly related to each other as was the magnitude of their daily changes because in the low alkalinity water of Pool 1, pH as well as DO responded to photosynthesis and respiration. Magnitudes of DO and pH changes at night were strongly related to fluctuations during the day, suggesting that community respiration was in a steady state relationship with photosynthesis over time.

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665168

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The efficacy of a regional stream classification system, based on the principle that streams reflect the character of the lands they drain, was evaluated in Arkansas. The classification consisted of six aquatic ecoregions defined by relatively homogeneous types of land-surface form, soil, potential natural vegetation and land use. Fish, physical habitat and water quality were sampled in 22 streams throughout the state. Data subjected to ordination analysis generally showed greater similarity in streams within the same ecoregion than in streams in different ecoregions. The patterns developed separately from fish, physical habitat and water quality data sets were relatively concordant. The null hypothesis that the classification did not reflect fundamental differences among the streams was rejected. We concluded that a regional stream classification is potentially useful for evaluating and managing streams. The identification of regions containing streams with similar character can aid in selecting reference streams for impact assessments or in selecting monitoring sites from which results may be extrapolated regionally.

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665169

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Production of smallmouth bass (Micropterus dolomieui) of ages I through V were calculated in the Maquoketa River, Iowa, from 1978 through 1982. Total production of smallmouth bass ranged from 6.4 kg/ha during 1981 to 15.0 kg/ha in 1979; mean production for the five years was 10.1 kg/ha (S.D. = 3.53). Age III smallmouth bass contributed 41% of the total production over the five years while age II fish were second at 27%. The mean production/biomass ratio of 0.34 was found to be lower than most warm-water fish species.

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665170

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665171

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665172

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665173

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1987.9665154

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor