摘要:

Changes in benthic macroinvertebrate population density and diversity were studied in a mesotrophic lake with seasonal hypoxia/anoxia prior to and following aluminum sulfate (alum) treatment and hypolimnetic oxygenation. Historically, low oxygen concentrations created a benthic zone with reduced fish predation pressures which allowed chaoborids to flourish. Population densities of chironomids and oligochaetes were suppressed by prolonged periods of summer anoxia Benthic macroinvertebrate community diversity values were indicative of poor water quality and/or habitat quality.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663423

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The environmental fate of the organophosphate insecticide phorate and its metabolites, phorate sulfone and phorate sulfoxide was examined in mesocosms placed in South Dakota wetlands. Three treatment concentrations of phorate (1.2, 2.4, and 4.8 kg/ha) were applied to wetland mesocosms. Phorate, phorate sulfone, and phorate sulfoxide were present in water and sediment during the entire study (28 days) in all treatments. Maximum phorate concentrations in water were measured one day after treatment and decreased significantly during a 28-day period. The metabolites of phorate increased significantly in the water during the study. Phorate was present in higher concentrations in sediments than either phorate sulfone or phorate sulfoxide throughout the study.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663424

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A 500 m transect was established in a large wetland on an exposed shoreline in Saginaw Bay. It extended from shore to just beyond the limit of emergent vegetation. During the spring of the year before development of vegetation, water along the transect had homogeneous characteristics. This was not the case when concentrations of electrolytes, electric conductivity, turbidity, planktonic chlorophyllaand periphytic chlorophyllawere measured in mid-summer. At that time, submersed and emergent vegetation was at annual maximum biomass and a discontinuity bar existed where parameters changed rapidly with distance along the transect. Location of the bar changed from time-to-time within a zone 250–350 m from shore as water surged shoreward and then receded during seiches. Currents associated with these changes were measured in the vicinity of the bar. They ran perpendicular to the shoreline and were generally on the order of 2–7 cm/s. During a severe storm depth of water in the wetland increased more than 50 cm in one hour with flow rates rising to about 10 cm/s. Mixing between near-shore and offshore water in the wetland occurred during this event, but the discontinuity was not broken down. Temperature and solute-related density differences in water on opposite sides of the discontinuity were always small. Aquatic plants appeared to dampen currents and mixing enough to allow these and other differences to persist as prominent mid-summer features of this wetland.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663425

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effects of temperature and daylength were studied in the germination of American pondweed (Potamogeton nodosusPoir.) tubers. Germination was examined at temperatures ranging from 5 to 30°C in conjunction with light treatments of short and long daylength and continuous darkness. Greatest percentage of tuber germination occurred between 15 and 20°C. Within this temperature range, daylength did not significantly affect germination. Outside this temperature range, however, the absence of light inhibited germination. From these results, we conclude that temperature was the most important factor controlling germination, with an optimal range of 15 to 20°C. Daylength (14:10 versus 10:14) had no effect on germination, but the absence of light suppressed germination at 10, 25, and 30°C. The results were further supported by similar data obtained from a pond study ofP. nodosus.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663426

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Weight-length data were compiled from 289 redear sunfishLepomis microlophuspopulations. We applied the regression-line-percentile (RLP) technique to weight-length data for 150 redear sunfish populations to develop a new 75th-percentile standard weight (Ws) equation. The proposed RLPWsequation, log10Ws= −4.968 + 3.119log10TL where Ws is the standard weight in grams and TL is the total length in millimeters, is valid for fish >70 mm TL. The English-unit equivalent, log10Wg = −3.263 + 3.119log10TL whereWsis the standard weight in pounds and TL is the total length in inches, is valid for fish >3 in TL. We used the remaining 139 independent populations to evaluate the current [log10Ws= −5.164 + 3.227(log10TL)] and RLPWsequations for any length-related biases. We confirmed that the currentWsequation is length-biased. That is, relative weight (Wr) values significantly decreased with increasing fish length for far more populations (N=45) than they increased (N=7). We tested the proposed RLPWsequation with the same 139 populations, and found no consistent length-related bias inWrvalues calculated with the proposed RLP Ws equation (N=38, 29). Thus, we recommend the use of the proposed RLPWsequation for redear sunfish.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663427

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Over two field seasons, 319 downstream-moving leopard frogs (Rana pipiens) were captured and retained by a salmonid smolt trap operated in the Bois Brule River of northern Wisconsin. Most leopard frog movement occurred during late summer and autumn but was not conclusively correlated with any environmental factors. This movement was part of a macrodrift that included other larger taxa (e.g.BufoandOrconectes) not typically retained by the drift nets used by aquatic ecologists to sample aquatic insects. Smolt traps, by virtue of the large volumes of water they strain, can be used to provide hard-to-obtain life history information for a variety of aquatic organisms.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663428

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Spatial and temporal variation of physicochemical parameters of Cisne reservoir were studied. A clear spatial pattern was observed between the tributaries and the reservoir, with the highest values of conductivity, alkalinity, pH, silicate and phosphate (SRP) in the tributaries. The incorporation of bicarbonate, silicate, SRP and other nutrients by littoral vegetation and the decomposition process of macrophytes could explain the spatial pattern and the temporal variation of the nutrients. The freshwater marsh situated between the tributaries and reservoir acts as sink for silicate and SRP. The temporal and spatial pattern of total phosphorus (TP) was correlated with suspended matter values. The low nitrogen concentration and the ratio of the inorganic nitrogen to SRP suggest that nitrogen is a limiting factor for primary production.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663429

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We obtained age-and-growth data from 34 black crappie (Pomoxis nigromaculatus) samples from 25 water bodies and nine white crappie (P. annularis) samples from four water bodies in South Dakota from 1990 through 1993. Mean back-calculated length for black crappie was significantly different among water body type [i.e., small impoundments (< 40 ha), reservoirs (≥ 40 ha) and natural lakes] for all ages (P ≤ 0.01). Growth was slowest in small impoundments and fastest in natural lakes. Ultimate length (L.) was significantly correlated with mean back-calculated length at age (P ≤ 0.01). Mean length at time of capture varied monthly for white crappies. Age-2 white crappies completed 71% of their growth in length during July and August.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663430

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We examined the zooplankton community and physicochemical parameters of the lower Trinity River, Texas during March 1992-March 1993, and evaluated the suitability of each for survival of paddlefishPolyodon spathula. Samples were collected every 2–4 weeks from mid-river channel and backwater stations at each of four sites. Eight paddlefish stomachs were analyzed, and eighteen paddlefish were aged and their relative weight values were determined. Physicochemical parameters generally were suitable for paddlefish survival. Zooplankton densities were low (overall mean 30.1 organisms/L) but similar to other river systems supporting paddlefish. The zooplankton community was dominated by rotifers; cladocerans and copepods were not abundant. Paddlefish stomach analysis indicated rotifers were being consumed by paddlefish. Paddlefish growth appeared to be rapid despite seemingly low food densities.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663431

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We assessed the length structure of walleyeStizostedion vitreumpopulations over time in five high-elevation (> 1340 m above mean sea level) reservoirs in Wyoming using relative stock density (RSD). Four populations showed moderate to large fluctuations in RSD values across years, while one population was relatively stable. Fluctuations in RSD values were associated with variability in annual recruitment. Incremental RSD values allowed identification and tracking of weak year classes through time. Because of inconsistent annual recruitment, the utility of RSD for assessing the rates of recruitment, growth, and mortality of walleye populations in large reservoirs is limited.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663432

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor