Browsing by Subject "Water Resources science"

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    Comparison of the structure and composition of bacterioplankton communities in the ballast water of commercial ships and the Duluth-Superior Harbor
    (2012-08) Welch, Jacqueline B.
    Ship ballast water is a potential vector for the introduction and spread of aquatic nonindigenous species (NIS). Although most studies focus on invasive plants and animals, there is an increased interest in the potential for invasive microbes. The Duluth- Superior Harbor (DSH), located in a freshwater estuary at the confluence of Lake Superior and the St. Louis River, receives more ballast water discharge than any other Great Lakes port yet little is known about the bacterioplankton communities in the harbor or the ballast water released into the harbor. The two most important factors affecting the successful establishment of an aquatic NIS through ballast water discharge are propagule pressure, and the abiotic and biotic characteristics of the new environment. Water was collected at six sites in Lake Superior, the Duluth-Superior Harbor, and the lower St. Louis River to characterize bacterioplankton communities. Other water samples were collected from the ballast tanks of ten commercial ships visiting the Duluth-Superior Harbor and the Western Lake Superior Sanitary District (WLSSD) because these sources may influence the genetic structure and composition of natural bacterioplankton communities in the harbor. Three distinct bacterioplankton communities representative of Lake Superior, the Duluth-Superior Harbor, and the St. Louis River habitats were detected in water samples collected on one day in early September 2009 (ANOSIM, p < 0.05) using a DNA fingerprint analysis (T-RFLP). These results were consistent with findings of other investigations that found distinct bacterioplankton communities in estuarine mixing zones. Water temperature, dissolved organic carbon (DOC), ammonium (NH4 +), and nitrate (NO3 −) were more highly correlated with differences in the genetic structure of bacterioplankton communities along a transect from the river through the harbor than other environmental variables. DNA fingerprint analyses also indicated that bacterioplankton communities discharged into the DSH with ballast water and treated wastewater effluent were different from bacterioplankton communities found within the harbor. The most common bacterial phyla found in freshwater habitats (i.e., Alphaproteobacteria, Betaproteobacteria, Actinobacteria, Bacteroidetes) were also seen in 16S rRNA gene clone libraries of freshwater ballast and the Duluth-Superior Harbor. The genetic structure and species composition of the seawater ballast bacterioplankton community from an ocean-going ship was fundamentally different than the bacterioplankton communities in freshwater ballast, and was uncharacteristically dominated by bacteria from the Epsilonproteobacteria. Interestingly, three environmental DNA sequences from the seawater ballast of this ship were similar to Tennacibaculum soleae, a marine fish pathogen (phylum Bacteroidetes, Class Flavobacteria). DNA from this pathogenic marine bacterium, if not its intake cells, survived in the ballast tank of a transoceanic ship for at least two weeks before the ballast water arrived at the Duluth-Superior Harbor. This example illustrates the potential for transporting potentially harmful bacteria over long distances in the ballast water of commercial ships to harbors in the Laurentian Great Lakes.
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    Spatial and temporal dynamics of phytoplankton nutrient status in the deep chlorophyll layer (DCL) of Lake Superior
    (2011-12) Van Der Werff, Jessica
    Total phosphorus and chlorophyll have been declining over the last few decades in the ultra-oligotrophic Lake Superior. A region in the water column where chlorophyll exceeds that of the mixed layer during the stratified period, referred to in this study as the deep chlorophyll layer (DCL), is presumably ideal in terms of nutrients and light for primary producers. Investigating the nutrient status of these primary producers could aid in understanding the nutrient dynamics in this large, low nutrient lake. Lake nutrient concentration and phytoplankton nutrient status measurements were determined to evaluate seasonal, temporal, and spatial patterns both across the lake and with depth. Additionally, active fluorometry was measured in order to compare its efficacy as a nutrient status indicator with more traditional methods. Water samples were collected above, within, and below the DCL across the lake during the summer of 2010. Chemical analyses including chlorophyll a, particulate nutrients (carbon, nitrogen, and phosphorus), soluble reactive phosphorus, total and total dissolved phosphorus, total and total dissolved nitrogen, ammonium, nitrate, and soluble reactive silica were performed in conjunction with bioassays (N and P debt, alkaline phosphatase activity) and active fluorometry (PhytoPAM) to fully assess phytoplankton nutrient status. Results indicated extreme P deficiency across the lake in the epilimnion and metalimnion with the most extreme deficiency seeming to occur in the epilimnion and occasional deficiency in the hypolimnion. Also, a P deficiency indicator exhibited a diurnal pattern with higher deficiency during the daytime. Deficiency also appeared to be highest in the spring and decline over the course of the summer; however, even in September, samples still indicated extreme deficiency. Additionally, N debt data suggests N deficiency in spring which had disappeared by August. Active fluorometry was consistent with nutrient bioassays in suggesting that the epilimnion was more stressed than the metalimnion or hypolimnion. Strong nutrient concentration gradients across the lake and with depth as well as with time were absent, although there appears to be a seasonal decrease in SRP, nitrate, and silica and an increase in TN and TDN from June to September. Nutrient concentration and phytoplankton nutrient status could have been influenced by many factors in Lake Superior including a seasonal shift in algal species composition, zooplankton nutrient translocation, contribution to deficiency by picobacterioplankton, borderline iron (Fe) limitation, and reallocation of nutrients for purposes other than photochemistry.