Abstract not available.

Photodegradation rates of methylmercury (MeHg) were measured in water samples from several lakes in the Lake Berthelot region in Quebec in order to investigate the impact of drainage basin logging and associated changes in dissolved organic carbon (DOC) concentrations on MeHg levels in lake water. The lakes were selected on the basis of the amount of logging that had previously taken place in the drainage basin, and on DOC levels which were correspondingly higher in logged lakes due to increased runoff. Lakes DA9 and DF9 had DOC concentrations of 12.3 and 20.9 ppm, respectively and were designated as high DOC for the purposes of this study. Lakes N55 and N70 had DOC concentrations of 6.9 and 6.8 ppm, respectively and were designated as low DOC lakes. Experiments were conducted with both ambient and 2 ppt spiked MeHg levels in the high and low DOC lakes to determine whether the spiked levels reflect photodegradation patterns occurring in nature. The effect of different sized DOC fractions on photodegradation rates were also examined. Upon spiking, the binding of added MeHg reached equilibrium virtually immediately (within minutes) for all size fractions. It was hypothesized that less photodegradation of MeHg would be found in high DOC lakes than in low DOC lakes. In contrast to expected results, no photodegradation was observed in the two lower DOC lakes, but there was photodegradation in the two higher DOC lakes. Hypothesizing that larger size fractions of DOC would result in lower methylmercury (MeHg) photodegradation rates, water samples were fractionated into three DOC size fractions (300 kDa, 30 kDa, and 5 kDa). In the two high DOC lakes in which photodegradation was detected, DOC size fractions had an effect on photodegradation rates, though this effect varied. Average k values (hr-1) for DA9 were -1.25 x 10-1 for the 5 kDa fraction, -1.16 x 10 -1 for the 30 kDa fraction, and -9.21 x 10-2 for the 300 kDa fraction, indicating a decrease in photodegradation rates with larger fractions. For DF9, average k values were -1.69 x 10-1 for the 5 kDa fraction, -6.38 x 10-2 for the 30 kDa fraction, and -1.34 x 10-1 for the 300 kDa fraction, which does not indicate a clear trend in photodegradation rates with respect to DOC size fraction. A comparison of samples from a wetland outflow using ambient MeHg levels demonstrated that 300 kDa DOC fractions showed no photodegradation while 5 kDa DOC showed photodegradation with a k value of -9.12 x 10-2 (hr-1). Overall, watershed logging status was found not to affect MeHg photodegradation rates in the lakes studied. A possible contributor to the variation in photodegradation rates between lakes was postulated to be pH, with H+ ions displacing MeHg from binding sites on DOC and rendering it available for photodegradation. To study the relationship between rates of photodegradation and pH, water samples were adjusted to pH values of approximately 4.5, 6.5, and 7.5 and incubated in sunlight. Rates of photodegradation increased with decreasing pH conditions in all lakes, except for one lake (N55) which also had no detectable photodegradation during the initial field trials. In the remaining three lakes studied, however, lower pH values (4.1-4.6) resulted in greater photodegradation than higher pH values that resulted in little or no photodegradation. It appears that this effect only occurs in lakes with a potential for photodegradation. As results suggested that the size of DOC controls rates of photodegradation, samples were analyzed for the size of DOC and corresponding MeHg content using tangential flow ultrafiltration (TFUF). The efficacy of the TFUF system as a means of both removing microbes as well as fractionating DOC into differing size fractions was evaluated. Results indicated that this is an effective field-portable method. Mass balances for MeHg recovery after filtering large volumes of water were found to be 96% for the 5 kDa filter, 81% for the 30 kDa filter, and 109% for the 300 kDa filter, while flow rates decreased by 26%, 17%, and 50% respectively. Potential artifacts of DOC fractionation using the TFUF were investigated. The amount of DOC passing through the filter was found to decrease with increasing volume of filtrate that passed through the membrane.

Sixty-seven sample sites in 45 streams across the National Capital Region and Gatineau Park were sampled between the summers of 2001 and 2008 in order to describe communities within the Park and assess differences in stream fish and invertebrate assemblages along a gradient of urbanization. Additionally the relationships between nutrient concentration and biomass of algae, invertebrates, and fish were quantified, and changes in the size distribution of benthic invertebrates and fish along a gradient of nutrient and anthropogenic impacts were described. Principal Component Analyses indicated that urban and agricultural sites were easily distinguished from forested sites using water quality parameters. Invertebrate and fish assemblages did not differ as clearly among site categories. There were increased nutrient levels in agricultural and urbanized watersheds, however the biomass of primary producers did not proportionally track the increase in nutrients. Slopes of the relationships between biomass and nutrient concentration declined with increasing trophic level, indicating a reduction of the efficiency of energy transfer in more eutrophic systems. Size spectra from nitrogen enriched streams had elevated intercepts and increased residual variance was noted in perturbed watersheds. The current study has provided baseline data for stream communities within and outside of Gatineau Park and in doing so it is clear that Gatineau Park streams are in good, but variable health. In order to monitor change, protect diversity within the Park, and mitigate further stress to these streams, it may be useful to use aspects of the size spectra such as normalized density and the residual variance.

As urban populations increase globally, the conversion of natural land cover to anthropogenic land use is on the rise. Diffuse perturbations that accompany such land use changes are considered a chief threat to headwater streams, which provide habitat for diverse faunas of macroinvertebrates, fish, and amphibians and are important sources of sediments, nutrients, and organic matter for downstream systems. Although environmental assessments of stream ecosystems generally measure responses to these perturbations as shifts in community structures, functional rather than structural properties may provide a better indicator of land use impacts since measures of ecosystem function can reveal more about the mechanisms that alter running water ecosystems. The primary objective of this thesis was to quantify stream productivity along a gradient of forest cover and assess bottom-up and top-down mechanisms for observed patterns in stream productivity. In the first chapter, I quantified algal, invertebrate, and fish biomass, the single best correlate of productivity, at 38 first-third order streams along a forest cover gradient at 55 spatial scales and determined that subcatchment forest cover was consistently the best predictor of biomass at all trophic levels in terms of the variation explained by forest cover and the unexplained residual variance. When considering the independent effects of forest cover on biomass at three coarse scales, subcatchment forest cover was the only significant predictor of biomass, suggesting that the common practice of maintaining riparian buffers is an ineffective management practice for protecting stream function from catchment-wide impacts. In the second chapter, I developed two time-saving approaches for processing benthic invertebrate samples that reduced laboratory processing time by 37% and 82% and provided production estimates that were strongly related to production estimates obtained from standard processing techniques. These time-saving approaches were used in chapter 3 so that I could measure algal, invertebrate, and fish production at 12 sites along a gradient of subcatchment forest cover, which I determined to be the most influential spatial scale on biomass in chapter 1. Total nitrogen was a significant bottom-up force that explained 34-83% of the variation in stream productivity at all three trophic levels. However, consumer production to consumption ratios indicated that predators and grazers can potentially deplete their food sources, and that top-down forces are therefore also important contributors to observed patterns in productivity and biomass along the forested gradient.

The impacts of waterpower management on select fish in the Ottawa River are examined in this study and are presented in four manuscripts: (1) a systematic review of published literature on water power management; (2) examining potential causes of variation in lake sturgeon abundance among river reaches; (3) community structure and abundance among water management regimes; and (4) evaluating the predictive power of a lake sturgeon habitat suitability model at multiple scales. (1) Three meta-analyses were completed: (i) macroinvertebrate abundance is lower in zones or areas that have been dewatered due to water fluctuations or low flows (overall effect size -1.64 (-2.51/-0.77; 95% CI)); (ii) a hypolimnetic draw reduces the abundance of aquatic communities (overall effect size -0.84 (-1.38/-0.33; 95% CI)) and macroinvertebrates (overall effect size -0.73 (-1.24/-0.22; 95% CI)) downstream of a dam; (iii) altered flows has a negative effect on the abundance fluvial specialists (-0.42 (-0.81/-0.02; 95% CI) but does not affect habitat generalists (overall effect size -0.14 (-0.61/0.32; 95% CI)). (2) Three main stressors were examined to explain variation in lake sturgeon abundance among river reaches: contaminants, commercial harvest and water power management. Results were consistent with water power management impeding lake sturgeon recovery: abundance was significantly greater in unimpounded river reaches; growth rates were significantly greater in impounded reaches suggesting food was not limiting; and size/age structure in managed reaches was skewed to larger, older fish suggesting recruitment was impaired. (3) Variation in community structure and abundance was assessed for 11 fish species among three water management regimes: winter reservoirs, run-of-the-river and unimpounded. Littoral zone benthivores were significantly lower in abundance in winter reservoirs whereas species that are planktivorous for portions of their life were significantly greater. Lake sturgeon was the only fast water spawning species affected in run-of-the-river reaches. (4) The predictive power of a lake sturgeon habitat suitability model was assessed by paired net sets in good (habitat suitability index (HSI)>0.6) and poor (HSI<0.3) habitat. Lake sturgeon catch-per-unit-effort (CUE) was significantly greater for adults and juveniles in good habitat however, predictive power of the model was low (r2 < 0.18). Standard index netting lake sturgeon CUE corresponded with overall foraging component which suggests the model is a good predictor of sturgeon abundance at multiple scales.

Mercury (Hg) is a persistent contaminant present naturally in our environment but, as a result of anthropogenic activity, has now accumulated in lake sediments at concentrations 2.2 times greater than those found in pre-industrial sediments (pre-1850) (Chapter 2). However, present spatial patterns of mercury accumulation do not match patterns in natural mercury accumulation (Chapter 4). Once spatially uniform across south-central Ontario, mercury concentrations in present-day lake sediment display strong spatial correlation. Further, the broad scale spatial patterns (>500 km) which correlate with mean annual precipitation (MAP) found to significantly predict pre-industrial sediment Hg, has now been replaced with finer scale spatial patterns (<120km). Rather than one significant spatial scale explaining sediment Hg, as during the pre-industrial era (p = 0.01), present sediment Hg are predicted by more than one spatial scale (p < 0.001, p < 0.001) both of which are highly correlated with lake pH. While MAP and lake pH explain much variance in mercury accumulation, their significance is spatially dependent. In addition to differences in spatial trends, models which suggest that pre-industrial sediment Hg was in steady state with watershed accumulation do not apply to present day Hg accumulation (Chapter 2). Instead, Hg enrichment in lake sediment decreased as a function of drainage ratio (R2 = 0.458, p = 0.0001), suggesting that Hg export from watersheds may be lagging behind atmospheric Hg deposition. The enrichment of Hg since the pre-industrial era is also influenced by the amount of open water (r = 0.91, p = 0.035), mining activity (r = 0.94, p = 0.019) and organic deposits within surficial geology (r = -0.91, p = 0.034) which lead to local hot and cold spots (Chapter 4). There is a close link between the present-day sediment Hg concentrations and that in dorsal muscle of smallmouth bass (Micropterus dolomieul) (r = 0.92, p = 0.0002) (Chapter 3). However, the discrepancies that do exist between these two components are determined by landcover, longitude, and dissolved organic carbon. An examination of methylmercury in two catchments revealed that the concentration of methylmercury in stream water from ten watersheds is predicted from a time sensitive (lagged regression) interaction among sulfate (tpartial = 9.60, p < 0.001), dissolved organic carbon (tpartial = 7.06, p < 0.001), and temperature (tpartial = 4.44, p < 0.001) (Appendix A). The error of which decreases exponentially with increasing wetland size (R2 = 0.838, p = 0.0105). The difference between methylmercury inflow and outflow (MeHgNet) within these two catchments (a dystrophic and an oligotrophic lake) was seasonally dependent (Chapter 5). However, seasonal accumulation and loss of methylmercury was significantly larger in magnitude within the dystrophic lake. Further, a net production of methylmercury was found in the dystrophic lake alone (1.9 +/- 0.3 mg·d -1). This study examines Hg contamination in a relatively pristine, remote environment which like other regions, has been challenged by contaminants originating from far distances.

Mercury methylation in aquatic systems has been linked to the activity of various anaerobic microbes, including sulfate-reducers (SRB), iron-reducers (FeRP) and methanogens (MPA). This study focuses on the biogeochemical factors, i.e., the relative importance of the diverse groups of anaerobic microbes, that affect net methyl mercury formation in freshwater. Methylation and demethylation were measured separately using enriched stable isotopes of mercury in microcosms treated with specific microbial inhibitors and abiotic control systems. Non-contaminated sediments from the Mer Blue wetland in Ottawa, Ontario, were used to test the proper set up and methods to be used for future experiments. Mercury-contaminated sediments of the St. Lawrence River (SLR) in Cornwall (Zone 1), Ontario, were investigated because they have been found to be a potential source of MeHg in the food web and the river system. In the Zone 1 SLR sediments, strong positive correlations were observed between methylation rate constants and sulfate reducing rates, as well as demethylation rates constants and methane production rates, indicating that SRB are primary methylators and MPA have the leading role in methylmercury demethylation. The inhibition of both SRB and MPA enhanced iron-reduction while MeHg production was not completely stopped, indicating that iron-reduction might however be another important process in MeHg production in the Zone 1 SLR sediments, probably by decreasing demethylation rather than favouring methylation, as shown by the strong negative correlation between Kd and iron-reduction rates. Similar findings were obtained for the Mer Bleue sediments, with the exception that SRB were involved in both methylation and demethylation. A new modified procedure for measuring mercury isotopes in sediment samples was also proposed. The procedure uses acid leaching-ion exchange-thiosulfate extraction (TSE) to isolate and purify the methylated mercury from the matrix. Major advantages of the TSE procedure include the extraction and analysis of a large number of samples in a short time, excellent analyte recoveries, and the lack of artefact formation. Recoveries between 94 and 106% were obtained for the standards CRMs, BCR 580 and IAEA 405. Comparisons between TSE and other procedures (distillation, acid-leaching) have shown good agreement of methylmercury values.

In 1995, Squaw and Flash creeks were renovated with Antimycin-A to eradicate non-native fish. After renovation, 129 Apache trout from Flash Creek were introduced into Squaw Creek. Two years later, all size classes were present. Apache trout above a natural barrier on Flash Creek were allowed to repopulate the renovated section. Three years later, 45 Apache trout were found below the natural barrier. In both streams, adults selected deep, slow moving areas. Juveniles selected shallow areas with fast currents. Both size classes selected open areas exposed to sunlight with surface turbulence and other forms of instream cover. Apache and Gila trout were experimentally PIT-tagged in the: (1) pelvic girdle; (2) abdominal cavity; and (3) dorsal musculature to determine the best tagging location. Fish tagged in the dorsal musculature had 0% tag loss and 98% survival. The minimum size Apache and Gila trout could be tagged was 90 mm TL.

Consistent with the presence of CH$\sb4$ oxidizing bacteria at the sediment-water interface in a north Florida flooded forest and in Everglades Cladium marshes with peat soils, CH$\sb4$ emitted from the flood water was enriched in $\sp{13}$C relative to sedimentary CH$\sb4$. In contrast, CH$\sb4$ emitted from the flood water over Everglades marl soils, where CH$\sb4$ oxidizing bacteria were absent, was not enriched in $\sp{13}$C relative to sedimentary CH$\sb4$. / Stable isotopes gave no indication that CH$\sb4$ oxidation was occurring in the rhizosphere of Everglades Cladium marshes. Rhizospheric oxidation did not cause $\sp{13}$C enriched CH$\sb4$ to enter the plant and be emitted to the atmosphere. The carbon and hydrogen stable isotopic composition of sedimentary CH$\sb4$ was the same in marl and peat soils and gave no evidence that CH$\sb4$ oxidation affected the bulk sedimentary CH$\sb4$. Rhizospheric oxidation in Cladium was either not occurring due to O$\sb2$ limitation or occurred quantitatively in discrete zones imparting no isotopic signal to sedimentary CH$\sb4$. / A carbon budget developed for the flooded forest indicated that the carbon remineralization rate of soil organic matter was dependent on the hydo condition (flooded/dry) of the forest. The rate under dry conditions was 33.72 mol C m$\sp{-2}$ yr$\sp{-1}$, 3 times greater the rate under flooded conditions (11.92 mol C m$\sp{-2}$ yr$\sp{-1}$). Under flooded conditions a significant amount (48%) of the carbon remineralization was via non-methanogenic (presumably mostly aerobic) processes. / Due to the presence of insoluble organic surface films on the flood water in the flooded forest, which retard the transfer of gases across the water-air interface, calculation of fluxes from Fick's First Law overestimates the diffusive flux of CH$\sb4$ and CO$\sb2$ from the flood water to the atmosphere. The measured diffusive flux of CH$\sb4$ and CO$\sb2$ and 1.7 $\pm$ 1.7 and 3.9 $\pm$ 1.1 times less than the respective calculated flux. Consistent with surface films inhibiting the transfer of the larger and heavier CO$\sb2$ to a greater extent than CH$\sb4$, surface films also inhibited the transfer of $\sp{13}$CH$\sb4$ to a greater extent than $\sp{12}$CH$\sb4$. / Source: Dissertation Abstracts International, Volume: 53-11, Section: B, page: 5601. / Major Professor: Jeffrey P. Chanton. / Thesis (Ph.D.)--The Florida State University, 1992.

The distribution of iron in three different environments has been studied in an attempt to understand what processes control its concentration in the open ocean. In the Ochlockonee Estuary, dissolved Fe concentrations are dominated by a high molecular weight colloidal fraction ($>$10,000 molecular weight) that is also significant in controlling the dissolved organic carbon concentration. These Fe-oxyhydroxides are greater than 80% removed before the salinity reaches open ocean values. In the eastern Atlantic ocean, surface water Fe concentrations are controlled by atmospheric deposition of Saharan dust as evidenced by a strong correlation with Al. The concentration of Fe in the surface waters of the Sargasso Sea show a large variation between spring and fall with the highest concentrations in the fall correlating with a time of high atmospheric deposition. During this period of elevated surface water concentrations, between 60 and 80 percent of the Fe is not truly dissolved but colloidal in size (between 1000 molecular weight and 0.45 $\mu$m). The colloidal size fraction plays a significant role in the dissolved Fe cycle when concentrations greatly exceed saturation ($>$1 nM). / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6619. / Major Professor: William M. Landing. / Thesis (Ph.D.)--The Florida State University, 1995.