Browsing by Subject "lake superior"
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Item 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.Item Effects of Enrichment on Lake Superior Periphyton(Water Resources Research Center, University of Minnesota, 1973-05) Krogstad, B.O.; Nelson, R.R.; Odlaug, T.O.; Olson, T.A.; Ruschmeyer, O.R.The primary objective of this research as carried out in the summer and fall of 1969 and 1970 was to determine the possible changes which would take place in Lake Superior periphvton when polluting or enriching substances were added to the lake Hater. To this end, two natural rock basins were constructed at the lakeside along the north shore at Castle Danger, Minnesota for the purpose of exposing naturcll1y grown and regrowth periphyton to higher-than-normal levels of phosphate and nitrate. At weekly intervals, samples were collected and productivity was measured by enumeration of organisms, chlorophyll analysis, and weight, dry and organic. Lake Superior periphyton responds dramatical1 y to increased additions of phosphorus and nitrogen. If the near-shore area of Lake Superior ever received nutrients, such as those added to the experimental test pool at Castle Danger, a drastic change in the Lake.'s biota could occur. For example, as enrichment increased, the predominant clean-water diatom forms could eventually be replaced by the more tolerant green or blue-green algae. In addition, the very composition of the macrobenthic forms found in Lake Superior could be altered as a result of their dependence on the periphyton, which, as primary producers, form the first link in the food chain. Likewise, certain fish which depend on benthic organisms for their food may be adversely affected as an indirect result of a changing periphyton community. Having established that enrichment of Lake Superior water will drnmatically change the normal periphyton growth, another baseline has been established for future reference in the event that phosphorus and nitrogen rich wastes should be added to the 1ake. If certain types of algae appear as replacements of the normal flora now characterizing the periphyton and the productivity increases, one will have a means [or assessing the possible changes taking place in the water quality of Lake Superior.Item Response of Nearshore Periphyton in Western Lake Superior to Thermal Additions(Water Resources Research Center, University of Minnesota, 1974-10) Drown, D.B.; Odlaug, T.O.; Olson, T.A.The intent of this research was to ascertain what effects a temperature increase in the order of 10 degrees to 12 degrees C would have on the near-shore periphyton assemblage of Western Lake Superior. To this end a field station, complete with holding tanks and a hot water source, was constructed on a rock ledge of the Lake Superior shore near Castle Danger, Minnesota. During the summer and fall of 1971 and 1972 periphyton covered rocks from the local area of the lake were placed in the experimental holding tanks where they were exposed to a continuous flow of lake water. In addition, denuded rocks were included as part of a regrowth study. One system provided a flow-through of unheated lake water while in the other the temperature was raised above ambient. Growth patterns were followed under both sets of conditions. Periphyton samples were collected on a weekly basis from the ambient control and heated water tanks and were analyzed for photosynthetic pigment concentration, dray and organic weight and total cell count. A quantitative and qualitative examination of the phyletic distribution of algae from the two systems was emphasized. Some of the more important findings and conclusions were as follows: 1. Diatoms were found to be the most prevalent algal type in both heated and cold water tanks. 2. Normal populations of Lake Superior periphytic diatoms (control), in terms of percent composition of the entire assemblage, were not greatly altered by the temperature increases used during the course of this study. 3. Three of the most common algal genera; Synedra, Navicula, and Achnanthes, showed essentially no difference in maximum growth levels attained in cold or heated water other than the fact that, in heated regrowth samples, peak concentrations were reached in a shorter period of time. 4. Several of the periphytic diatoms common to Lake Superior would continue to survive at temperatures well in excess of normal seasonal maxim. 5. Lake Superior contains genera of non-filamentous green algae which have species capable of adapting to extremely high ambient water temperatures. 6. The warm water system was more favorable to green filamentous algae, such as Mougeotia and Zygnema, than was the cold water system. 7. A prevalent green alga found in Lake Superior, Ulothrix zonata, was inhibited by the warmer water conditions. 8. In general, green algae common to Lake Superior are favored by temperatures in excess of those normally found in the lake. 9. Under conditions of these experiments blue-green algae did not increase as a result of thermal addition. 10. Analysis of pheo-pigments indicated that a substantial amount of “apparent” chlorophyll a was actually pheophytin a, a degradation product. Hence, the pheophytin analysis is important to any study dealing with the chlorophyll content of periphyton. 11. Concentrations of pheo-pigments were higher in the cold water tank than in the warm water system. 12. Supplementary observations have suggested that a separate invertebrate community occupied each of the tanks. While the above findings and conclusions indicate that a great deal more needs to be learned of the effects of thermal additions on Lake Superior, this study has pointed out that, if near-shore areas of the lake were warmed to the extent that could occur as the result of a thermal-electric generating station discharge, changes in the phyletic composition of the local periphyton community could be expected. The very nature of a change from diatoms to greens could have serious repercussions on benthic grazers and indeed the entire foodweb of the affected area.Item A Synoptic Study of Food Habits of 30 Fish Species from Western Lake Superior(Minnesota Agricultural Experiment Station, 1971) Anderson, Emory D.; Smith, Lloyd L.