No description available.

Several Florida lakes with different documented trophic state indices were selected for sediment analysis. Vertical sections of the sediment were taken at depths of .1, .5, 1, 2, 3, 4, 5, 6, 10 and l5 centimeters below the surface of the sediment-water interface. Total Phosphorus analysis was done on each section. The profile presented was then evaluated and was found that the profiles best fit the equation Y = X/ (A + BX), where Y is the Phosphorus Concentration in ppm and X is the sediment depth in cm. Correlation between the trophic state and the profiles characteristics are presented. A hypothesis as to how the sediment profile changes as the lake experiences increased Phosphorus loading is presented, and is used to evaluate the lake studied. This discussion expresses phosphorus dynamics within the sediments in terms of adsorption, chemical changes, biological activity, and molecular and eddy diffusion.

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [75]-79).

No description available.

Natural lake-watershed ecosystems in Oregon compose a diverse and valuable assemblage of land and water resources. With an increasing demand on lakes for recreation, water supplies, and aesthetic values and an increase in available data on Oregon lake systems, there is a need for applicable and timely scientific water management information about lake conditions statewide. This thesis is an attempt to summarize some of the data collected on natural Oregon lake-watershed ecosystems. The purpose of the thesis is to identify the most typical natural systems out of an initial data base of twenty-four variables, measured over ninety-eight lake-watershed ecosystems. The selected variables are reduced to five common factors using principal components factor analysis. K-means cluster analysis is used to create similar groups of lake systems. These groups are compared to ecoregions in Oregon and a typical, representative lake ecosystem is identified for each group. Results show that several lake systems of the state are unique.

No description available.

The littoral of Lake Dunstan, Central Otago, New Zealand, is dominated by the introduced submersed macrophyte Lagarosiphon major (hereafter Lagarosiphon) which effectively excludes native macrophytes from most of the littoral. Lake Dunstan is a large hydro lake that was - after reaching its operational water level in 1993 - rapidly colonized by Lagarosiphon from upstream sources. Because of its extensive biomass and growth, it is believed the macrophyte plays an important part in the lake ecosystem but also that it requires frequent management to allow for recreational activities, to restore aesthetic values of beaches and especially to prevent further spread into unaffected waterways. To assess the integration of Lagarosiphon into the lake ecosystem and possible impacts of extensive macrophyte removal a 3 year study was initiated focusing on invertebrate and fish distribution and diet in relation to Lagarosiphon. A stable isotope analysis was used to reconstruct carbon flows and trophic structure within the littoral of Lake Dunstan. Additionally, a small scale weed management experiment was carried out to assess possible impacts of macrophyte removal on invertebrates and fish. Lagarosiphon harboured a high density and diversity of macroinvertebrates. The invertebrate community was dominated by mollusc species in terms of biomass and abundance. There was little temporal and spatial variation in invertebrate distribution and communities on a large scale (lake-wide variation), but there were differences in invertebrate biomass on a smaller scale in relation to the location of samples within the macrophyte belt. Invertebrate biomass was lowest at the bottom of the dense macrophyte beds. The positive association of common bully (Gobiomorphus cotidianus: Eleotridae) with the dense Lagarosiphon stands and a diet - mainly consisting of invertebrates common on Lagarosiphon - suggested the important role of this macrophyte as a provider of food and shelter for small fish species. Brown and rainbow trout (Salmo trutta, Oncorhynchus mykiss: Salmonidae) diet was dominated by invertebrate species common on this macrophyte as well. Results of the stable isotope analysis suggested a secondary role of Lagarosiphon in the lake food web as a surface provider for the growth of epiphytic algae that appeared to be a major primary producer in the littoral of Lake Dunstan. Detritus (FPOM), assumed to consist partly of decaying Lagarosiphon, played a less important role as a base for the food chain. The main carbon flow pathway was from the primary producers (epiphyton - FPOM) through primary consumers (Mollusca, Chironomidae, Trichoptera) through to the top predators (tertiary consumers: trout and bullies) in the system. A small scale experiment on the influence of macrophyte harvest, i.e. the cutting of channels into dense macrophyte beds, showed that a partial removal of macrophyte biomass could help achieve several management goals: it not only reduced macrophyte biomass to enable recreational activities but also had no negative impacts on invertebrate biomass and diversity. The channels even increased invertebrate abundance and biomass in the treated compared to the untreated control plots along the cut edges. Regrowth of Lagarosiphon was rapid, with the cut channels being completely overgrown within 4 months. All these results taken together suggested a major role of Lagarosiphon in the littoral of Lake Dunstan. Lagarosiphon supported a species rich invertebrate community and was the main provider of food and shelter for fish in this lake. A partial removal of macrophyte biomass might be a more suitable management option than large scale eradication to avoid negative impacts on the lake ecosystem. The most important aspect in management of this weed remains the prevention of further spread into pristine waters.

The species compositions and densities of the littoral and pelagic zooplankton assemblages in Crater Lake were compared. The littoral and pelagic zooplankton assemblages of most lakes are typically different due to different habitat conditions in the two zones. The littoral zone of Crater Lake lacks many of the habitat characteristics, which distinguish a typical littoral zone from the pelagic zone. In fact, none of the water quality variables measured differed significantly between the littoral zone and epilimnion of the pelagic zone in Crater Lake. The littoral and pelagic zones of Crater Lake were sampled with twelve paired sites in August and again in September of 1995. For the purposes of this study, the littoral zone was defined as lakeward from the shoreline to the 10m depth contour. At each paired site the pelagic assemblage was sampled to a depth of 120m at the 200m depth contour. Despite the almost identical water quality between the pelagic and littoral zones of Crater Lake, lack of vascular macrophytes in the littoral zone, and well-mixed epilimnion, the littoral zooplankton assemblage differed from the pelagic assemblage in both species composition and density. Several ubiquitous zooplankton taxa dominated both the littoral and pelagic zooplankton assemblages, although the density of these taxa as well as the relative abundance of these taxa differed between zones. These ubiquitous species reached their maximum densities in the metalimnion of the pelagic zone at a depth range of 10 to 60 meters below the lake surface and were considered primarily pelagic. A shift in wind direction between sampling periods influenced the distribution of pelagic zooplankton taxa in the littoral zone. Twenty-four taxa were recorded in the littoral zone, and aside from infrequent exceptions, none of these taxa were found in the pelagic zooplankton assemblage. Most of the littoral taxa were primarily adapted to the benthic zone. / Graduation date: 1999

Waldo Lake, located in the Oregon Cascades, is considered to be one of the most dilute lakes in the world. Even with very low nutrient concentrations and sparse populations of zooplankton, introduced fish in the lake are large in size and in good condition when compared to fish from other lakes. Fish were originally stocked in Waldo Lake in the late 1800's. The Oregon Department of Fish and Wildlife began stocking in the late 1930's and continued stocking until 1991. Species existing in Waldo Lake today include brook trout, rainbow trout, and kokanee salmon. The overall objective of this thesis was to increase the understanding of the interrelationships that affect the age, growth, and diet of fish in Waldo Lake. The specific objectives were to summarize and synthesize available information on the substrate, climate, water, and biota of the Waldo Lake Basin; describe the cultural history and current cultural values of the Waldo Lake Basin; determine the age, growth, length, weight, condition, diet, and reproduction of introduced fish species in Waldo Lake; interrelate the above information to show how these components of the natural-cultural system are related. Fish were collected one week per month from early June through mid-October in 1992 and 1993. Variable mesh experimental gillnets set in nearshore areas were used to capture fish in 1992. During the 1993 sampling period, experimental gillnets and trapnets were set in the nearshore areas of the lake. Relative age specific growth rates of brook trout in Waldo Lake are comparable to brook trout growth rates in other lakes. Brook trout growth rates generally decreased with age, however, there were no significant differences in the growth rate of each age class between 1991 and 1993. The condition of brook trout in Waldo Lake is also comparable to brook trout in other lakes. The same is true for rainbow trout and kokanee salmon. Fish in Waldo Lake are large in size and in good condition due, in part, to the availability of benthic macroinvertebrates. Taxa found in stomach contents of fish captured in Waldo Lake consisted primarily of aquatic benthic macroinvertebrates, but terrestrial vertebrates and vertebrates, although infrequently consumed, were also part of the total diet. Rainbow trout in Waldo Lake consumed primarily chironomidae larvae and pupae although odonata larvae, ephemeroptera larvae, and amphipods were also consumed. Kokanee salmon fed almost exclusively on chironomid larvae although small numbers of ephemeroptera larvae, odonata larvae, and coleoptera were also consumed. The most important macroinvertebrate taxon consumed by Waldo Lake brook trout was chironomid larvae and pupae, although other species also were important. The diet of Waldo Lake brook trout varied in a complex way that appeared to be related to the relative abundance of macroinvertebrate taxa, feeding location in the lake, and time of year. Brook trout diet also varied by size class. The components of the Waldo Lake natural-cultural system are complexly interrelated and the nature of these relationships are constantly changing. Each component in some way affects and is, in turn, affected by each of the other components. Changes in some components, such as substrate, affect other components along geologic time scales. Other components, such human culture and biota, may change rapidly within a decade. The capacity of natural-cultural systems, such as Waldo Lake, to change over time makes it possible to view the present state of the system only as a snapshot in time. This dynamic nature of the Waldo Lake natural-cultural system is not unique to Waldo Lake, but is expressed in all natural- cultural systems. / Graduation date: 1997

No description available.