Browsing by Subject "phytoplankton"

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    Distribution, Composition and Biomass of the Crustacean Zooplankton Population in Western Lake Superior
    (Water Resources Research Center, University of Minnesota, 1973-08) Conway, J.B.; Odlaug, T.O.; Olson, T.A.; Ruschmeyer, O.R.
    Although data were collected for two years, 1970 and 1971, the major portion of this research was carried out the second year. This research took place in western Lake Superior and most of the data were collected at two stations, Larsmont and Stony Point, which were twenty miles northeast of Duluth. Each of these stations included two sites, one a half mile and the second two miles from shore. The other area where samples were collected was at the Little Marais and Sugar Loaf Cove stations, some 70 miles north of Duluth. The major purposes of this research were to study the productivity and the vertical, seasonal and horizontal distribution of the crustacean zooplankton population in western Lake Superior. A limited study of the biology of the copepod, Limnocalanus macrurus, was also conducted. Productivity at the Larsmont and Stonv Point area averaged 323 crustaceans per 100 liters of water, and 60 grams per square meter (based on a fifty meter water column). Productivity at the Little Marais and Sugar Loaf Cove area averaged 95 crustaceans per 100 liters and 37 grams per square meter. In general, productivity decreased as the depth increased from zero to 50 meters. If a thermocline was present, then both the toted number of crustaceans and the biomass became relatively scarce below twenty meters. Cladocerans were most frequent1y found in the upper ten meters of the water column whereas copepods were present at every level. Adult copepods were usually heavier than adult cladocerans and it was not unusual to find the mean weight of an organism at 50 meters ten or more times that of one at five meters. Productivity at the Larsmont and Stony Point area was bimodal during the sampling season; the first peak occurred in July and contained primarily copepods and the second, which was the seasonal maximum, occurred in September and contained both copepocls and cladocerans. Surface water temperatures were also bimodal during the sampling season; the peak recorded in July was thirteen degrces centigrade and sixteen degrees was reached in September. The cladoceran, Bosmina, became abundant after the water temperature reached five degrees in July, Another cladoceran, Dapnia, Replaced Bosmina in September when the water temperature was about eleven degrees. Ephippia, the overwintering stage of Daphnia first appeared in late August. Three copepods, Diaptomus, Limnocalanus, and Cyclops were present during most of the sampling season. Limnocalanus was present at all depths from June to early August, but was most numerous at ten meters. When the water temperature warmed above twelve degrees, the population shifted downward and was usually below the thermocline during the davlight hours. At this time, they were most abundant at 40 meters, The copepod, Epischura, was numerous in the upper lavers after the water warmed above eleven degrees. Productivity differences were found between the various sites and stations. These differences point to the lack of homogeneity in the horizontal distribution of the crustacean zooplankton population and support the phenomenon of “zooplankton patchiness". Productivity levels at the Little Marais and Sugar Loaf Cove area were from one-third to two- thirds of those at Larsmont and Stony Point. The Larsmont station was slightly more productive than Stony Point. The Stony Point inshore site was slightly more productive than the offshore site. The period of maximum productivity occurred at the Larsmont inshore site amd at both Stony Point sites in September. Maximum productivity was recorded at the Larsmont offshore site in July. A phytoplankton bloom was observed at the Stony Point station on July 20, 1971, but was not seen on the same day at the Larsmont station. Limnocalanus macrurus contrihuted to the greatest percentage of the crustacean biomass (often more than 90 percent) at depths 30, 40 and 50 meters in western Lake Superior. The male to female ratio established was 1:2. The mean lengths of mature males and females were, 2.09 and 2.16 millimeters, respectively. The length-weight correlation was: Dry weight (mg/100) = 3.31 length (mm) - 2.95. Two cladocerans, new to Lake Superior, were identified. They were: Alona guttata Sars and Holopedium gibberum Zaddach.
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    Evaluation Of A Method For Ballast Water Risk-Release Assessment Using A Protist Surrogate
    (2015-08) Aliff, Meagan
    Aquatic invasive species cost the United States billions of dollars annually and are most often introduced via ships' ballast tanks. The International Maritime Organization (IMO) adopted a set of standards that sets limits on the number of viable organisms that can be discharged with ballast water. These standards require scientific research to determining the risk-release relationship (i.e. the number of propagules needed for an invasion). To examine the risk-release relationship a surrogate invader, the diatom Melosira varians, was used. Varying densities of the surrogate were added to 19-L mesocosms containing water from Duluth-Superior Harbor. Each mesocosm was sampled weekly for four weeks and the response of the phytoplankton community was measured via cell counts. Population responses varied by starting conditions but M. varians establishment was generally noted at higher inoculation densities. These findings suggest the mesocosm approach can inform the understanding of risk-release relationships.
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    A Flourometric Technique for Sampling in Large-River Ecosystems
    (Water Resources Research Center, University of Minnesota, 1971-06) Johann, D.R.; McNabb, C.D.; Miller, E.F.
    Boat-mounted equipment for detecting the movement of rhodamine WT was used in Pool 6 of the upper Mississippi Rover, between navigation dams at Trempealeau, Wisconsin and Winona, Minnesota, to develop a procedure for sampling on paths of turbulent flow in large-river ecosystems. A means of relating sampling points in space and time is described. The expression Cm = (c2 . n) -c1/n-1 where c1 and c2 are concentrations of suspended or dissolved materials on upstream and downstream transects and n is a measure of dilution, can be used to obtain the mean concentration of material in suspension or solution in the water between points that are separated by at least as much as 2400 meters. This procedure in combination with conventional sampling programs in quiet backwaters may allow for more rigorous analysis of large-river ecosystems than has been achieved.
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    The Land Of Blue Green Waters? Describing The Algal Community Dynamics Of Six Minnesota Lakes By Examining Cyanobacterial Dominance And Toxicity
    (2020-02) Bambach, Matthew
    Cyanobacteria are a diverse and ancient group of phytoplankton that are a normal component of aquatic primary producer communities. They can become a problem when they reach high cell densities and form blooms capable of producing toxins that can threaten human and wildlife populations. These occurrences are referred to as cyanobacterial harmful algal blooms (cHABs). Increasing global cHAB frequency and potency have been attributed to warming temperatures and nutrient over-enrichment, but drivers of local and regional occurrence remain poorly understood. In this thesis, I examined six inland Minnesota lakes with different physical, chemical, and biological attributes to highlight patterns in cyanobacterial dominance of the phytoplankton community and understand which lake attributes were closely related to cHAB activity, with a focus on the cyanotoxin Microcystin, from June to September in 2016 and 2017. Cyanobacteria were found to dominate most study lakes, and visible blooms were observed at southern, central, and northern latitude lakes. Microcystin-producing taxa were observed in all study lakes. July and August were the months most likely to experience cHABs, and 2017 showed increased cHAB activity associated with elevated algal biovolume across systems. Specific drivers of cHABs differed among study lakes, but aggregated data for all lakes suggests that increased cyanobacterial dominance of the phytoplankton, total kjeldahl nitrogen, and chlorophyll-a pigment were the attributes most closely associated with harmful conditions. Finally, different harmfulness metrics to safeguard the public from cHABs are compared to discuss their respective protectiveness.
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    The Phytoplankton of Minnesota Lakes - A Preliminary Survey
    (Water Resources Research Center, University of Minnesota, 1971-06) Brook, A.J.
    Between the years 1965 and 1967, phytoplankton collections were taken in the summer from nearly 200 lakes in a diversity of areas throughout the State. About 220 taxa of euplanktonic algae were identified. The analysis of the Minnesota lake phytoplankton indicates there is a diminution in species diversity in the course of the evolutionary progression as lakes change in character from oligotrophy to eutrophy. Many of the markedly eutrophic lakes have suffered severe disturbance of the natural system due to artificial enrichment. Eutrophic lakes in Minnesota are typically dominated in summer and early fall by water blooms of blue green algae as is usual in most productive lakes of temperate regions. Microcystis aeruginosa, M. wesenbergii, Coelosphaerium naegelianium, Aphanizomenon flos aquae, numerous species of Anabena, Lyngbya birgei, and Gloetrichia echinulata are most common.