Browsing by Subject "Water resources science"

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Air - water temperature relationships in the trout streams of southeastern Minnesota’s carbonate - sandstone landscape: implications for climate change, brown trout biological processes, and land management.
(2012-06) Krider, Lori A.
Carbonate - sandstone geology in southeastern Minnesota creates a heterogeneous landscape of springs, seeps, and sinkholes that supply groundwater into streams. Air temperatures have been shown to be effective predictors of water temperature in surface - water dominated streams. However, no published work investigates the relationship between air and water temperatures in groundwater - fed streams across watersheds. We used simple linear regression models to examine air - water temperature relationships for 40 groundwater - fed streams in Southeastern Minnesota. A 40 - stream, weekly time scale, composite linear regression model has an R2 of 0.83, a slope of 0.38, and an intercept of 6.63. Regression models were also combined by common intercept and slope and split into winter and non - winter air temperature regimes to allow approximation of winter water temperature regimes based on non - winter data. The air - water temperature relationships for groundwater - fed streams are different in slope and intercept compared to surface - water dominated streams. The high R2 values demonstrate that air - water temperature regression models for groundwater - fed streams may be useful in predicting the thermal regimes for these systems under future climate scenarios. Climate change is expected to alter the thermal regime of groundwater - fed systems but will most strongly affect streams that are more vulnerable to climate change and will do so at a slower rate than surface - water dominated systems. A regression model of intercept vs. slope can be used to identify streams for which water temperatures are more meteorologically controlled than hydrologically controlled, and thus more vulnerable to climate change, with evidence provided by an investigation into the resulting mean summer water temperature under a moderate climate change scenario for various types of linear regression models. Modeling the possible increases in mean summer water temperature provides insight into the potential effects of climate change on the amount of suitable brown trout habitat as well as the possible effects on brown trout biological processes and behavior. Information on possible future thermal conditions and can be used to guide restoration versus management strategies to protect the thermal integrity of trout streams and ensure the persistence of their stenothermic communities.
Application of household flux calculator in determining variability in annual carbon, nitrogen, and phosphorus flux through Falcon Heights, Minnesota households.
(2011-12) Hartzheim, Paul Matthew
As human population has continued to grow and become increasingly more metropolitan, urban ecosystems have become an increasingly important contributor to air and water pollution on a local, regional, and global scale. As such, households provide a useful unit of study, and quantifying environmental impacts from individual households helps provide a clearer picture of what individual household decisions have the largest impact to air and water quality. In this study, a group of University of Minnesota research fellows conducted a series of interviews and field surveys of single-family homeowners in the city of Falcon Heights, Minnesota. The surveys were constructed by a team of faculty members and research associates, for the purpose of collecting detailed information on household consumption, behaviors, and attitudes. The survey was developed to obtain information that could be translated into quantitative data to determine overall flux of carbon (C), nitrogen (N) and phosphorus (P) as they relate to household activities and personal choices. For purposes of this thesis, we define “flux” as the quantitative measurement of inputs and outputs through the household unit, including any portions that are sequestered within or exported from the household. Surveys were conducted with 34 households; 6 or which were eliminated from this analysis due to incomplete data. Approximately 40 variables gathered from the surveys were quantified and directly inputted into the Household Flux Calculator (HFC), a spreadsheet accounting model which was developed as part of this study to estimate the overall fluxes of C, N, and P for each household. This thesis analyzes the variability of C, N, and P flux among the households surveyed, and highlights household activities that have the greatest influence on the inputs and outputs of household C, N, and P, with the goal of developing a better understanding of how decisions and choices made on a household level impact local, regional, and global environments.
Biofilm ecoenzymatic activity, organic carbon and nitrogen in Lake Superior tributary streams
(2011-08) Newman, Brian J.
I compared the ecoenzymatic activity of naturally occurring epilithic biofilm to stream water carbon and nitrogen concentrations in Lake Superior tributary streams along the south and north shores of the western end of Lake Superior. My goal was to determine if the ecoenzymatic activity of biofilm would reflect water chemistry. The streams drain catchments ranging in size from 14-172 km2 of primarily deciduous forest, coniferous forest and woody wetlands. Measurements and samples were collected during base stream flows (June-September). The streams represented a broad range of organic carbon, nitrogen and phosphorous concentrations, which correlated to physical habitat parameters and land usage. I used light absorbance in the ultraviolet and visible light (UV-VIS) spectrum to show differences in dissolved organic matter (DOM) between sites on the north and south shore. The UV-VIS proxies of E2:E3 and SUVA254, which indicate molecular size and degree of aromaticity, were correlated with the percentage of wetlands in the catchment, as well as the specific conductance, pH and the C, N and P concentrations in the water. Eleven different ecoenzymes involved in the breakdown of organic matter were measured. The activities of these enzymes were often positively correlated to each other and correlated to the measured water chemistry. The slopes from Type II linear regression of β-N-acetylglucosaminidase to phosphatase (0.77), β-d-glucosidase to phosphatase (0.68), and -d-glucosidase to β-N-acetylglucosaminidase (0.88) are presented here as metabolic stoichiometric ratios. The molar C:N ratio in epilithic biofilm (11:1) was positively correlated to the ratio of dissolved organic carbon to total dissolved nitrogen (DOC:TDN) in filtered (<0.45 μm) stream water and negatively correlated with biofilm peptidase activity. The expression of the peptidase activity by both L-alanine aminopeptidase and L-leucine aminopeptidase increased in response to dissolved organic nitrogen (DON). Increasing stream-water inorganic nitrogen (DIN) concentrations reduced or inhibited L-alanine aminopeptidase expression and had no apparent influence on L-leucine aminopeptidase. These results along with other studies of biofilm show that the ecoenzymatic activity of biofilm and the C:N ratio in biofilm reflects water chemistry, providing further evidence linking the stoichiometric theory of ecology to metabolic theories of ecology. The ecoenzymatic activity is a measurement of metabolic requirements mediating the stoichiometry of incorporation of nutrients by the biofilm. This study was the first to compare natural epilithic biofilm ecoenzyme activity in the Lake Superior region to water chemistry, land use and habitat characteristics.
Constructed wetland used to treat nitrate pollution generated from agricultural tile drainage waters in Southern Minnesota
(2014-09) Ross, Nikol Bailey
Nitrate molecules are highly soluble in water and are bioavailable to plants. These properties are why excess nitrates in water are one of the main causes of hypoxia in the northern Gulf of Mexico. Over 90% of these nitrates originate from non-point sources such as agricultural fields. In fields with tile drainage systems nitrates have a swift passageway from field to surface waters. This study focuses on one Midwestern farm field located in southern Minnesota, along Elm Creek, a Blue Earth tributary. Tile drainage water from this field discharges into Elm Creek at a concentration averaging 23.0 mg/L NO3 as NO3-N. During the spring of 2013 a three celled treatment wetland was constructed adjacent to Elm Creek. The tile drainage system was re-routed to discharge into the constructed wetland. In the 2013 field season water volumes were monitored continuously and water samples were taken from the inlet, the wetland cells, and the outlet on a periodic basis. During the season the volume of tile drainage water that reached Elm Creek as surface water was reduced by 82%. The concentration of NO3-N in the water was not significantly reduced. However, the total load of NO3-N that reached Elm Creek as surface water was reduced by 262 to 332 pounds (14.4-18.2 lbs./acre). Most of the water that did not reach Elm Creek infiltrated into the subsurface soils and still contained NO3-N. Using the MPCA's (2013) estimates of groundwater denitrification for agroecoregions, a 45% reduction rate was applied at this location. When the 45% reduction rate is applied to the subsurface load it is estimated that 113.0 to 134 lbs. (6.21-7.36 lbs./acre) of NO3-N were removed from the infiltrated water. Thus a total of 124 to 172 lbs. (6.81-9.45 lbs./acre) of NO3-N were removed from the entire wetland system which accounts for 37.1-43.3% of the NO3-N.A concurrent laboratory experiment was set up in 2013 to test the effectiveness of different soils and vegetation at removing nitrate loads. Wetland mesocosm experiments were set up with soil collected from the field site and the design vegetation used in the field cells. Three vegetated mesocosm tanks were planted in Coland soils with Switchgrass (Panicum virgatum), Fringed Sedge (Carex crinita) and a tank with an equal mix of Dark Green Bulrush (Scirpus atrovirens), Panicum virgatum, and Carex crinita. The results showed that the mixed vegetation regime and the Panicum virgatum had significantly greater nitrate removal than the control (Coland bare soil). The mixed vegetation mesocosm had the highest amount of nitrate removal after 10 days at 34.9%. There was no significant difference in the nitrate removal rates in the soils tested.
Diagenesis and sediment-water exchanges in organic-poor sediments of Lake Superior.
(2011-06) Li, Jiying
To investigate early diagenetic processes and the spatial and temporal variability in organic-poor sediments of Lake Superior, we have repeatedly sampled sediments at 8 locations across the lake. Sediment geochemistry was characterized by the penetration depths and uptake rates of oxygen, and the distributions of organic carbon, dissolved Fe(II), nitrate, ammonium, soluble reactive phosphate (SRP), and solid phase Fe(III)/Fe(II) and phosphorus. Oxygen penetrated deeply into the sediments at all locations: from ~3.5 cm at near-shore stations to >12 cm in the deep basins. The total oxygen uptake ranged from 4.44 mmol m-2 d-1 to 7.68 mmol m-2 d-1, averaging 6.10 mmol m-2 d-1. Diffusive oxygen flux averaged 2.92 ± 0.75 mmol m-2 d-1. Aerobic respiration accounted for >90-95% of the total carbon degradation, with denitrification and iron reduction contributing <5% of the total carbon degradation. Reactivity of the organic carbon in the upper 1 cm of sediment was calculated to be ~ 1.2 yr-1, which is typical for organic material less than a year old. Sediment carbon degradation rate of 5.29± 1.20 mmol m-2 d-1 corresponds to ~ 19% of the recently estimated primary production. More than ~ 90% of carbon reaching the lake floor is mineralized, with a sediment carbon burial flux of 0.49 mmol m-2 d-1. Diffusive fluxes of nitrate from sediment into the overlying water averaged 0.17± 0.07 mmol m-2 d-1, recycling ~ 40% of nitrogen sedimentation flux. Phosphorus cycling was strongly associated with the diagenetic cycling of iron. Sediment diffusive effluxes of SRP were small (< ~ 1.5 x 10-3 mmol m-2 d-1) and similar among stations. The efficient trapping of phosphorus in the sediment is interpreted as a result of strong adsorption of phosphorus by iron (hydro)oxides. Sediments in Lake Superior exhibit strong spatial heterogeneity on spatial scales down to hundreds of meters. The presence of multiple Fe- and Mn-rich layers, forming dense crusts and often visible to the naked eye, suggests decadal or longer variations in the sediment’s physical or redox environment. Oxygen diffusive fluxes and carbon degradation rates exhibited strong seasonality, with higher oxygen fluxes and carbon degradation rates in July, and the depth of oxygen penetration varied by several mm to cm.
The effect of high sulfate loading on methylmercury production, partitioning, and transport in mining-imapcted freshwater sediments and lakes in northeastern Minnesota
(2015-02) Bailey, Logan Timothy
Methylmercury (MeHg) is a highly toxic form of mercury with the ability to bioaccumulate in food webs. The bioaccumulation of MeHg leads to elevated MeHg levels in fish tissue and poses a threat to public health. Thus MeHg concentrations in surface waters - which may be a result of water column MeHg production, or sediment MeHg production and subsequent flux from sediment porewater - are of particular concern. The production of MeHg from inorganic mercury (iHg) is primarily a result of sulfate-reducing bacteria (SRB) activity in anoxic aquatic environments.Ongoing and historic mining activity on the Mesabi Iron Range (Minnesota, USA) has led to elevated sulfate levels in the downstream waters of the St. Louis River watershed. In an effort to understand the effect of mining-related sulfur-loading on the production and partitioning of MeHg, sediment samples were collected and analyzed from sulfur impacted and non sulfur-impacted lakes and wetlands within the watershed. Additionally, the water column and inlet and outlet streams of a mesotrophic lake (Lake McQuade) were sampled intensively during summer stratified conditions in order to identify the sources and sinks of MeHg to the lake system and determine the potential for MeHg export downstream.Results suggest that dissolved sulfide plays a large role in governing MeHg dynamics in sulfate-impacted freshwater sediment. Consistent with previous research, net MeHg production appeared to be inhibited in sediments with dissolved sulfide >60 uM. However, these high concentrations of dissolved sulfide were accompanied by increased partitioning of MeHg into the porewater phase, potentially increasing the fraction of MeHg available to be transported into surface waters.Sediment at sulfate-impacted sites was generally characterized by high dissolved sulfide and a low potential for long-term net MeHg production. However, the accumulation of dissolved sulfide in sediment porewaters can be limited by the availability of free labile iron (Fe2+) and consequent iron-sulfide precipitation reactions. In the results presented here, high sulfur-loading at two sites appeared to have consumed the available free labile iron and created conditions which allowed for the accumulation of dissolved sulfide and inhibition of MeHg production in the sediment. However, relatively high sulfur-loading(>100 mg/L) to a third site where iron remains in excess of sulfur in sediment may have led to robust net MeHg production, in absence of inhibitory dissolved sulfide concentrations. Accumulation of MeHg in the hypolimnion of Lake McQuade occurred during summer 2012 during a time when bottom water sulfate was being consumed. Though some uncertainty remains as to the ultimate source of the MeHg, estimates of MeHg inputs and outputs to the hypolimnion suggest that water column production was a primary source of MeHg to the hypolimnion during the stratified summer months. Following the wet spring months when inputs were dominated by upstream flows, the flux of MeHg across the limnetic surface was estimated to be the primary source of MeHg to the epilimnion during the stratified summer months. However, most of MeHg input to the epilimnion was apparently degraded prior to being exported to the outlet stream. Thus, despite mid-summer accumulation of MeHg in the hypolimnion, the combination of stratification and substantial degradation in the epilimnion acted to limit export of MeHg out of Lake McQuade.As a whole, Lake McQuade acted as small net source of MeHg to the surrounding water system during the summer months of 2012. Evidence points to a brief rise in MeHg export immediately following lake turnover in Mid-August due to the release of hypolimnetic MeHg to surface waters during lake mixing.
Effects of repeated early season herbicide treatments of curlyleaf pondweed on native macrophyte assemblages in Minnesota Lakes.
(2010-09) Jones, Ajay Robert
Non-native invasive species have the potential to cause various problems in small isolated ecosystems, these constraints are exemplified in the small, shallow, lakes of Minnesota. Curlyleaf pondweed (Potamogeton crispus L.) is one of the common occurring and most influential non-native invasive species in Minnesota. Characterized by its early spring growth and early summer senescence, curlyleaf has the ability to negatively affect native macrophyte growth by forming dense monotypic canopies in late spring and releasing nutrients in early summer. Because of the negative impact on natural ecosystems along with the problems curlyleaf can cause for people, there is serious interest in the management of curlyleaf. One management practice is the early season application of herbicides, where curlyleaf is targeted before it is capable of producing turions (propagules) and native plants are unlikely to be affected. We examined the response of native plant communities to spring herbicide treatments of curlyleaf pondweed from 2006 through 2009. Thirteen lakes were examined during our study; ten were treated with herbicide and three were used as nontreatment reference lakes. Plant communities were assessed in the littoral zone with the point intercept method in early spring (before treatment), late spring (after treatment) and mid summer (peak native plant growth). For each survey, approximately 40 random biomass samples were taken in each study lake to estimate plant biomass. To determine changes in native plant frequency and biomass throughout the course of consecutive annual treatments, we compared differences between treated and untreated lakes within years for August surveys and compared August surveys between years for treated or untreated lakes. Additionally, we examined inter-seasonal changes, comparing differences within and between treated or untreated lakes from May to June and June to August in every year. In the reference lakes, curlyleaf persisted at moderate to high frequencies over the four years, and no consistent changes in native plant frequencies were seen. Herbicide treatments proved effective for controlling curlyleaf, which decreased in frequency within 1 month following treatment for each year of the study. The total frequency of occurrence of native plants in August did not decrease in most of the treatment lakes between years. Native macrophyte species richness also showed little change with continued treatment, although shifts in abundance of some species were observed. August native plant biomass increased between 2006 and 2009 in most treatment lakes, whereas native biomass varied in untreated lakes. Much of the change in biomass was attributed to a single species in most treatment lakes. We observed increases of Chara spp. frequency and biomass in most treated lakes. However, multiple years of treatment may be needed to obtain increases in native plant abundance as the largest increases occurred after 3 years of treatment. Early-season lake-wide herbicidal treatments of curlyleaf pondweed can reduce curlyleaf occurrence and density without major harm to native plants. Significant inter-seasonal changes in frequency and biomass were observed in both treated and untreated lakes although differences were not observed between treated and untreated lakes. Native species richness increased from May to June and June to August in both treated and untreated lakes. The frequency of native plants increased between May and June but less so between June and August in both treated and untreated lakes. Conversely, native plant biomass increased from June to August more so than from May to June for both treated and untreated lakes. These findings suggest that early season growth primarily manifests in distribution and colonization, while late season growth results in increased biomass. Similarly, many plant species follow the same patterns as the overall native plants, although other plant species may have different frequency and biomass regimes throughout a single season. Despite the differences in native plant species, we did not see any major inter-seasonal detriment caused by the presence of curlyleaf pondweed in untreated lakes, or positive influence of herbicide treatment in treated lakes. These findings suggest that increases in native plant growth may occur only after several annual treatments.
Estimating sediment, nutrient and mercury loads from four western Lake superior watersheds using continuous in-stream turbidity monitoring.
(2010-12) Ruzycki, Elaine M.
Many streams along the Minnesota coast of Lake Superior have been listed as impaired from high turbidity, suspended sediment, or high fish mercury concentrations. Both total suspended sediment (TSS) and total mercury have been shown to be strongly correlated to turbidity in many disturbed watersheds. Total suspended sediments, phosphorus, and total mercury loads were estimated in four western Lake Superior watersheds from 2005-2006 using automated in-stream turbidity measurements. Regression models were developed relating this near-continuous turbidity data to grab sample measures of mercury, suspended sediments and nutrients during differing flow regimes. Suspended sediment and phosphorus loads estimated using the turbidity surrogate were compared to those made using FLUX software, a standard assessment technique based on discharge and grab sampling for TSS. Stream specific turbidity vs. TSS measures were strongly correlated (r2 = 0.6 to 0.95; p < 0.05) and total mercury also showed a close relationship with TSS (r2 = 0.82, n = 23; p < 0.05) for all four streams. Continuous turbidity monitoring appears to be a reasonable surrogate for both suspended sediment and total mercury concentration, providing information when manual sample collection is cost-prohibitive or logistically difficult, and across a wide range of flows.
Extractability of carbon, nitrogen, and phosphorus in United States grasslands
(2015-02) Thompson, Seth K.
Tracking how energy flows within and across ecosystems is imperative for understanding interactions among biogeochemical cycles. Aquatic ecosystem metabolism is inextricably linked to the terrestrial landscape, with many lakes getting over 50% of their carbon from terrestrial sources. Nonetheless, there are few large scale measurements of actual carbon export from terrestrial ecosystems. Instead, scientists have relied on a mass balance approach to estimate the quantity of carbon coming into aquatic ecosystems based on estimates of riverine carbon delivery to the ocean. This approach has left many unanswered questions related to the controls on terrestrial organic matter export, both in terms of quantity and quality. Here I used Water Extractable Organic Carbon (WEOC) to estimate potential terrestrial carbon export and to understand the mechanisms controlling these exports. Results from extractions performed at 19 grassland sites across the United States suggested that 1-5% of their total soil carbon was in the water extractable organic carbon pool. In addition, this work suggested that soils selectively retained nitrogen and phosphorus, with less organic nutrient export relative to organic carbon to aquatic ecosystems. These data demonstrated the usefulness of measuring water extractable organic matter (WEOM) on broad spatial scales to gain a better understanding of both the amounts and types of organic matter that are available for export from terrestrial ecosystems.
Knife River stressor identification, Kanabec County, Minnesota.
(2012-02) Blick, Bethany Lynn
The Environmental Protection Agency (EPA) developed the Stressor Identification (SI) process to identify stressors causing biological impairment. The SI process precedes a TMDL (Total Maximum Daily Load) and offers a means by which developers of a TMDL can more confidently identify stressor(s) causing impairment. The EPA’s Causal Analysis/Diagnosis Decision Information System (CADDIS) framework was utilized to develop a SI for the Knife River Basin, Kanabec County, Minnesota. Data collected by the Minnesota Pollution Control Agency (PCA) during biomonitoring and the EPA’s STORET database were analyzed using nonmetric multidimentional scaling (NMDS) ordination to evaluate the relationships between fish species and abundance, and environmental and chemical stressors. A least-squared regression between fish index of biotic integrity (IBI) scores and environmental variables was also calculated. The NMDS analysis suggests there is similarity between the two headwater sites, which are correlated with low gradient and a high percent fines, agriculture, urban, and rangeland. High gradient, percent forest and percent riffles were correlated with the mid-stream reaches of the Knife River. Only pH was significantly correlated with fish IBI scores (p=0.034). The Knife River SI identified three potential stressors; low dissolved oxygen (DO), high pH, and excess bedded sediment.
Modeling near-inertial waves in Lake Superior
(2014-07) Gloege, Lucas J.
Numerical models were used to investigate basic properties of near-inertial waves in large lakes. The Regional Oceanographic Modeling System (ROMS) was used to run a hierarchy of models to investigate the role wind stress (idealized and semi-realistic), thermal structure (isothermal and two layer), and bathymetry (flat bottom and spatially varying) have on near-inertial waves in lakes. The currents produced by idealized forcing were compared with observations from the Lake Superior mooring array. The inertial response was found to be very sensitive to the duration of the impulse. Idealized wind stress acting for half an inertial period puts a substantial amount of energy into the inertial band of frequencies and little energy into other frequencies.The first models considered were flat bottom square basins with closed boundaries and a two layer thermal structure. The inertial kinetic energy was weakest near the shore and was greatest near the center of the basin. Very little inertial kinetic energy was put into currents when using a uniform thermal structure. Modeling with periodic boundary conditions produced pure inertial oscillations in the upper mixed layer. No thermocline displacements were observed when using periodic boundary conditions, which shows that a transport divergence is necessary to initiate internal waves.Lake Superior was modeled during the period of July 1, 2011 to September 19, 2011 and output from the model was compared with observations from the Lake Superior mooring array. A slow, approximately 30 day, counterclockwise rotation in the direction of wave propagation was observed in the model, which corroborates previous observations made in Lake Superior. Modeling suggests that near-inertial surface kinetic energy is enhanced over the Superior shoal, possibly due to a convergence of waves atop the shoal. The magnitude of the modeled currents agreed well with observations but phase did not. In order to accurately model near-inertial events in large lakes a higher resolution wind field may be needed and surface heat fluxes need to be included in the model.
Modeling the corrosive loss of port infrastructure in the Duluth-Superior Harbor and the North Shore of Lake Superior.
(2012-05) Oster, Ryan John
Corrosion of steel infrastructure in the Duluth-Superior Harbor (DSH) is a concern for those who own and maintain structures that are critical for maritime transportation. Long-term corrosion rates of steel structures in the DSH were 2 to 4 times faster than is typical for other freshwater habitats, ranging from 0.06 to 0.14 mm/yr. The highest rates of steel corrosion were found at moderately to severely corroded sites and were within the lower range for corrosion of steel in seawater. It is important to know the potential roles that water quality and microorganisms play in the corrosion process to better understand why steel structures in the DSH are corroding faster than expected and to develop methods to prevent or mitigate this problem. Dissolved oxygen increased and chloride and sulfate concentrations decreased in the late 20th century in the DSH after the Western Lake Superior Sanitary District became operational. In 2010, only alkalinity, chloride, and conductivity were positively related to long-term steel corrosion rates in the DSH and interestingly, dissolved oxygen was inversely related to it. The Larson-Skold Index, which measures the corrosivity of water towards steel, decreased or remained constant at three sites between 1972 and 1996. The Larson-Skold Index was usually below the threshold for concern in 2010-2011, indicating that changes in water chemistry alone may not be responsible for the severe corrosion of steel in this harbor. Gallionella, a genus of iron-oxidizing bacteria, was more abundant within corrosion tubercles on severely corroded steel structures in the DSH where more than 109 Gallionella 16S rRNA copies/dry g of tubercle were observed, representing 2% to 34% of the total prokaryotic cells recovered from these tubercles. Gallionella bacteria were less abundant (~107 copies/dry g) on steel structures at sites along the north shore of Lake Superior. DNA from Gallionella was not detected in the water surrounding corroding steel structures in the DSH or in harbors on the north shore of Lake Superior, indicating that these bacteria were enriched on corroding steel. Sulfate-reducing bacteria (SRB) were also more abundant within tubercles at severely corroded sites but at least 2 orders of magnitude less abundant than Gallionella bacteria, accounting for less than 1% of prokaryotic cells within these corrosion tubercles. Considered alone, neither the abundance of Gallionella or SRB was related to long-term steel corrosion rates in the DSH. A multiple linear regression model was developed using water quality parameters and bacterial abundances to predict steel corrosion rates. The model used alkalinity, sulfate concentration, and log10 transformed SRB abundance to predict the long-term steel corrosion rate. It overestimated the long-term corrosion rate of a steel structure in one harbor along the north shore of Lake Superior and slightly underestimated the corrosion rate at a second harbor. It is clear that the corrosion of steel structures is accelerated in the DSH compared to other freshwater environments and water chemistry is not likely the sole cause of this corrosion. Rather, a combination of chemical and microbiological factors appears to influence the corrosion of steel structures in this harbor.
Organic matter biogeochemical characteristics in Lake Superior: insights into composition, source and reactivity
(2014-08) Li, Hongyu
Organic matter (OM) composition and its relationship with OM source and dynamics in Lake Superior were investigated with the combination of advanced spectroscopic techniques and multiple-geochemical signatures. Studies of water-column dissolved, water-column particulate, and sedimentary organic matter (DOM, POM, and SOM, respectively) were performed. The composition of DOM obtained with two different solid phase extraction resins (C18 vs SDB-XC) was investigated using Uv-visible spectrometry and negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Lake Superior raw offshore water was found to be very clear; its DOM is low in aromaticity, with primarily non-humic, hydrophilic and low molecular weight materials. Radiocarbon signatures reveal the primarily modern (post-bomb) nature of Lake Superior DOM. With such Lake Superior water, we found SDB-XC disks to outperform C18 disks in the isolation of DOC in terms of both higher recovery and less degree of fractionation to the initial DOM composition. Extracts of the same samples obtained with the different extraction disks share 70% of compounds, which were dominated by lignin-CRAM-like material but also include a variety of other functional groups including lipids, proteins, carbohydrates and condensed hydrocarbon. To assess settling particulate organic matter seasonality and availability to the benthic community, settling particulate matter was studied in terms of mass fluxes and main biochemical characteristics and composition at two Lake Superior offshore sites over the course of a year. Increase in sinking flux was variably associated with sediment resuspension and enhanced surface production. The combination of PCHO-C%, THAA and Fourier transform infrared spectroscopy (FTIR) data revealed that the relative bioavailability and nutritional values of POM to benthic microbes should be lower in spring than summer, although both periods exhibited high sinking fluxes. Isotopic and elemental analyses, FTIR, principal components analysis (PCA), and two dimensional (2D) correlation analysis, where core depth was used as perturbation, were used to study the diagenesis of organic matter (OM) in Lake Superior sediments. Depth-related changes among sites were found to be similar, leading to an increased contribution from inorganic (and possibly refractory aromatic organic) components at each site, and a loss of contribution from other organic components. Synchronous spectra reveal that aliphatic esters and carbohydrates degrade significantly with increasing depth, leading to an increased contribution from clays/ biogenic silica/ inactive carbohydrates. Asynchronous spectra show that, generally, carboxyl groups, including aliphatic ester and amide/protein, degrade first, followed by a group of carbohydrates, and then aromatic compounds and/ or the Si-O framework in clays and biogenic silica.
Photochemical and microbial degradation of dissolved organic matter in the Lake Superior watershed.
(2012-05) Macdonald, Megan J.
Photodegradation of dissolved organic matter (DOM) due to ultraviolet (UV) exposure can have important consequences for coastal zone productivity. The availability of UV radiation to aquatic environments has increased due to ozone depletion. Chromophoric DOM affects the amount of light penetration in a water column. Ecosystem productivity depends in part on the input of DOM into a coastal zone. DOM can protect animals, plants, and microbes from damaging UV light by acting as sunscreen, resulting in increased ecosystem productivity. Alternatively, DOM can decrease ecosystem productivity by absorbing light needed for photosynthesis and forming reaction products that are harmful to coastal zone biota. Increased urbanization of watersheds and seasonal differences in weather patterns change the delivery pathways, reactivity, input, and energy flow of DOM into aquatic systems. Understanding the input and reactivity of DOM in coastal systems as a function of land urbanization and season will help determine the fate of irradiated organic matter and its potential role as a sunscreen in coastal waters. The consequences of energy flow from UV radiation to DOM in aquatic systems will provide useful preliminary data to be used for land-use planning in tributary regions. This study also provides data useful for predictive models of the fate of irradiated organic chemicals and the resultant impact on water quality. In this paper, the study of watershed urbanization and season on the input and photodegradation of DOM in coastal waters is discussed based on organic carbon analysis, UV-Visible spectrophotometry, microbial processing of DOM, and terrestrial (land-use) analysis.
Planktonic archaeal communities change seasonally in Lake Superior.
(2010-08) Kish, Jason Louis
Archaeal abundance and community structure were examined in Lake Superior during 2007 and 2008. When the lake water column was mixed there were approximately 1x106 archaeal 16S rRNA gene copies L-1. After stratification, archaeal 16S rDNA was more abundant below the chlorophyll maximum in the mid- and deep hypolimnion near the sediment but much less abundant in the epilimnion. T-RFLP fingerprints of archaeal communities from various depths were compared during both stratified and mixed lake conditions and with sediment samples collected in September 2007. Planktonic archaeal communities were very similar throughout the water column when the lake was mixed. Two discrete planktonic archaeal assemblages, however, were always present after the lake became thermally stratified. One assemblage was associated with warmer water above the thermocline and deep chlorophyll maximum, while the other assemblage was characteristic of the deep hypolimnion. The greatest difference in T-RFLP fingerprints was seen when sediment and planktonic archaeal communities were compared. Archaeal 16S rRNA gene sequences were obtained from both these assemblages. The composition of archaeal sequences shifted from a predominance of Crenarchaeota in the upper (30m) and mid (145m) water column to Euryarchaeota in the surface sediment. Though past studies have shown Archaea are present in lake ecosystems, many of these studies focused on sediment or were conducted in meromictic lakes where Archaea would be expected in the anoxic zone. My study focused on Archaea in the holomictic freshwater Lake Superior, where planktonic Archaea were present throughout the year but formed discrete communities after the water column became thermally stratified.
Sediment diagenesis in large lakes Superior and Malawi, geochemical cycles and budgets and comparisons to marine sediments
(2014-09) Li, Jiying
Large freshwater lakes, despite their socioeconomic importance, are insufficiently characterized in terms of their geochemical cycling. In systems such as Lake Superior, contributions of several important processes, including those affecting biological productivity, remain poorly quantified. To understand the geochemical controls on sediment diagenesis, we investigated sediments in well-oxygenated temperate Lake Superior and tropical meromictic Lake Malawi. We characterized solid-sediment and porewater geochemistry, calculated diagenetic rates and fluxes, and investigated temporal and geographic variability for the cycles of carbon, nitrogen, phosphorus, iron, and sulfur. Revised nutrient budgets (for N and P) were constructed for both sediment and water column, suggesting a significant contribution of sediments to the geochemical cycling in both lakes. Sedimentation rate and the depth of oxygen penetration (OPD) were found to strongly affect the dynamics of carbon and nutrients. In Lake Superior, the deep (>4 cm) oxygenation of sediments in low-sedimentation areas regulates the remineralization rates of carbon and phosphorus, controls denitrification rates, and creates an unusual sulfur cycle driven by the oxidation of organic sulfur to sulfate. It also makes these deeply oxygenated sediments qualitatively distinct from sediments in nearshore high-sedimentation areas, necessitating their separate consideration in geochemical budgets. Comparisons against data from marine environments suggest that sediment processes in large lakes (both temperate and tropical) can be described by the same quantitative relationships as in marine sediments, facilitating the transfer of knowledge.
Sources, cycling, and fate of organic matter in large lakes: ingishts from stable isotope and radiocarbon analysis in Lakes Malawi and Superior
(2014-08) Kruger, Brittany Ruth
Organic matter (OM) in lake systems is sourced from in situ aquatic primary production (autochthonous), land based plant primary production or detrital material that ultimately originated from photosynthesis (allochthonous), or resuspension of organic rich sedimentary material that was ultimately sourced from a combination of all such sources. Studying the stable and radioisotopic signature of multiple chemical components of lacustrine OM can help elucidate which of the above is the dominant OM source to the lake, as well as how OM is incorporated into and cycles through lake systems. The high organic content and biodiversity in large lakes of the world make them excellent sites to investigate such questions, and this dissertation focuses on such questions in Lake Malawi (SE Africa), and Lake Superior (North America). In Lake Malawi, the organic carbon (OC) recently deposited (within the last 50 years) is largely dominated by aquatic input, and the influence of terrestrial riverine inputs dissipates as distance from shore and water depth increase. This confirms that parameters typically used to investigate historic lake levels (and thereby to infer past climates) can in fact function as robust indicators of distance from shore, and thereby lake level. This is supported by bulk and compound specific stable carbon isotopic and radiocarbon analysis of multiple sediment fractions. Most fractions exhibited isotopic signatures nearshore that were distinct from more offshore, open-lake locations. In Lake Superior, compound specific nitrogen isotope analysis (CSNIA) of specific amino acids from species occupying all levels of the food chain showed that Limnocalanus macrurus, a copepod, occupies a trophic level much higher than expected from known feeding habits, which may indicate the consumption of additional or unique food sources. Bulk radiocarbon analysis of the same suit of species from that lake showed Diporeia, a benthic amphipod, consumes an aged carbon source that does not appear to be significantly incorporated by other (more pelagic) organisms in this study, which rely primarily upon recently synthesized autochthonous organic carbon.
Three dimensional water quality modeling in a shallow lake with complex morphometry; implications for coolwater fish habitat under changing climate
(2014-07) Missaghi, Shahram
Morphologically complex lakes usually have a significant water quality heterogeneity and hydrodynamic gradients that require a three dimensional (3D) model to accurately capture their temporal and spatial dynamics. The objectives of this research were to evaluate and apply a 3D coupled hydrodynamic and ecological model to a morphologically complex lake and to investigate the effects of a changing climate on the lake ecosystem. The research was conducted in a series of four separate studies including modeling investigations and laboratory experiments. First, a 3D hydrodynamic model (ELCOM ) coupled with an ecological model (CAEDYM) was applied to three bays of the morphologically complex Lake Minnetonka, MN, to simulate water temperature, dissolved oxygen, total phosphorus, and algal concentrations. The 3D model was calibrated and validated in two different years, and model results compared well with extensive field data. Lake hydrodynamic and ecological processes were discovered to be sensitive to mixing due to inflow and wind variability over seasonal stratification. In the second study, two sensitivity and uncertainty analysis methods were applied to the model to evaluate uncertainties in the model predictions. The contributions of predicted water temperature, dissolved oxygen, total phosphorus, and algal biomass contributed 3, 13, 26, and 58% of total model output variance, respectively. A laboratory experiment was conducted to measure the influence of fluid motion on growth and vertical distribution of Microcystisin a Plankton Tower bioreactor. The laboratory results indicated that a depth-averaged energy dissipation rate in the range from 3 x 10-7 to 3 x 10-6 m2 s-3 facilitated Microcystis growth. Fourth, the applied calibrated and validated 3D model revealed the influence of local meteorological and global climate conditions on key water quality parameters and fish habitat in 3 bays of Lake Minnetonka. The research was conducted by simulating the model and analyzing the model output results under three climate scenarios of historical normal (HN), future (FU), and future extreme (FE). Water temperature (T) and dissolved oxygen (DO) concentrations were used to investigate the temporal and spatial variability of fish habitat dynamics. The epilimnetic water temperature of the FU and FE climate scenarios were up to 4 °C warmer than the HN scenario during ice-free seasons, stratification periods were predicated to expand up to 23% (46 days), and thermocline depth to increase 49% under the FE climate scenario. In all cases hypolimnion was mostly anoxic by June 15, but started by April 15, May 1, and May 15, under the three climate scenarios of HN, FU, and FE respectively. Under future scenarios the good growth, restricted growth and lethal coolwater fish habitats that were based on T and DO thresholds changed +16%, -18%, and +85% compared to the HN scenario. A modest change (8% of total lake volume) of good growth and restricted growth into lethal habitat separated the summer good growth coolwater fish habitat by over 3 weeks. The research brought out the need for a 3D analysis in capturing the significant water quality heterogeneities and the ecological hot spots in a morphologically complex lake.
Toward setting realistic expectations for agricultural management practices based on water flow paths and lag times.
(2010-11) Ahlstrom, Eric Joel
Agriculture makes up over 40% of all the land area in the United States and influences watersheds both large and small. As water moves through a watershed of any size it moves over the land as runoff into surface waters, infiltrates into the soil to groundwater, and eventually discharges to surface water. In some systems such as forests lateral subsurface flow is dominate and bypasses the groundwater component. Whatever the system the movement of water through the watershed drives the movement of agricultural chemicals. Best Management Practices (BMPs) are used to partially control the movement of water. The goal of this work is to help set realistic expectations of BMPs based on a holistic approach to watershed modeling. To do this, three process-based models were used (GeoWEPP, LEACHM, and MODFLOW) to simulate the spatiotemporal movement of water through three compartments (surface water, vadose zone, and groundwater) of the watershed. Spatial characteristics of a particular field such as its topographical location, distance from stream, and its distance to the groundwater are all factors into the lag time, quantity, and quality of water reaching the stream. Morgan Creek in Maryland was used as an example watershed to illustrate how spatial and temporal differences affect management decisions and expectations. GeoWEPP and LEACHM were used to investigate runoff and infiltration while MODFLOW was used for ground water lag times. Runoff and infiltration values were investigated with slopes ranging from 0-100%, varying management practices, and varying soil types. Runoff and sediment yield values resulting from eight different management practices (Corn – fall mulch, Continuous Corn – no till, Corn/soybeans/wheat/alfalfa – no till, Corn/soybeans/wheat/alfalfa – conventional till, fallow – tilled, alfalfa with cutting, 20 year old forest, and five year old forest) were compared to each other, as were the 3 dominant soil types (Mattapex, Sassafras, and Butlertown). These differences were looked at both spatially and temporally. Subsurface (vadose zone plus ground water) lag times within a single field reveal that within that single field subsurface lag time range from 9 years up to 30 years. A holistic understanding the as to water’s movement through all compartments the within the watershed will improve the decisions being made and the expectations placed on those decisions.

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