Optimizing land management strategies for maximum improvements in lake dissolved oxygen concentrations.

Eutrophication and anoxia are unresolved issues in many large waterbodies. Globally, management success has been inconsistent, highlighting the need to identify approaches which reliably improve water quality. We used a process-based model chain to quantify effectiveness of terrestrial nutrient control measures on in-lake nitrogen, phosphorus, chlorophyll and dissolved oxygen (DO) concentrations in Lake Simcoe, Canada. Across a baseline period of 2010-2016 hydrochemical outputs from catchment models INCA-N and INCA-P were used to drive the lake model PROTECH, which simulated water quality in the three main basins of the lake. Five terrestrial nutrient control strategies were evaluated. Effectiveness differed between catchments, and water quality responses to nutrient load reductions varied between deep and shallow lake basins. Nutrient load reductions were a significant driver of increased DO concentrations, however strategies which reduced tributary inflow had a greater impact on lake restoration, associated with changes in water temperature and chemistry. Importantly, when multiple strategies were implemented simultaneously, resultant large flow reductions induced warming throughout the water column. Negative impacts of lake warming on DO overwhelmed the positive effects of nutrient reduction, and limited the effectiveness of lake restoration strategies. This study indicates that rates of lake recovery may be accelerated through a coordinated management approach, which considers strategy interactions, and the potential for temperature change-induced physical and biological feedbacks. Identified impacts of flow and temperature on rates of lake recovery have implications for management sustainability under a changing climate.

Never say never: circumventing a contraindication to control apnoea-induced epileptic events with a mandibular advancement device.

BACKGROUND: The benefit of mandibular advancement devices in patients with sleep-disordered breathing and as a potential option for obstructive sleep apnoea syndrome is well recognised. Their use in the setting of epilepsy or other seizure disorders is typically contraindicated.Case reportA 48-year-old patient with a history of poorly controlled epilepsy and obstructive sleep apnoea syndrome was referred for ENT review for possible tracheostomy. The patient was wheelchair-bound with 24-hour continuous positive airway pressure, but sleep studies demonstrated persistent, severe episodes of apnoea and notable sleep disturbance. Sleep nasendoscopy demonstrated marked improvement on capnography with the laryngeal mask airway in situ, and this was maintained with mandibular advancement using jaw thrust following removal of the laryngeal mask airway. A mandibular advancement device was subsequently trialled; this had no subjective benefit for the patient, but the seizures resolved and control of apnoea was achieved with the combination of a mandibular advancement device and continuous positive airway pressure. CONCLUSION: This paper highlights a novel application of mandibular advancement devices, used in combination with continuous positive airway pressure, which resulted in complete resolution of sleep deprivation and apnoea-induced epileptic events.

Relative Recovery of Thermal Energy and Fresh Water in Aquifer Storage and Recovery Systems.

This paper explores the relationship between thermal energy and fresh water recoveries from an aquifer storage recovery (ASR) well in a brackish confined aquifer. It reveals the spatial and temporal distributions of temperature and conservative solutes between injected and recovered water. The evaluation is based on a review of processes affecting heat and solute transport in a homogeneous aquifer. In this simplified analysis, it is assumed that the aquifer is sufficiently anisotropic to inhibit density-affected flow, flow is axisymmetric, and the analysis is limited to a single ASR cycle. Results show that the radial extent of fresh water at the end of injection is greater than that of the temperature change due to the heating or cooling of the geological matrix as well as the interstitial water. While solutes progress only marginally into low permeability aquitards by diffusion, conduction of heat into aquitards above and below is more substantial. Consequently, the heat recovery is less than the solute recovery when the volume of the recovered water is lower than the injection volume. When the full volume of injected water is recovered the temperature mixing ratio divided by the solute mixing ratio for recovered water ranges from 0.95 to 0.6 for ratios of maximum plume radius to aquifer thickness of 0.6 to 4.6. This work is intended to assist conceptual design for dual use of ASR for conjunctive storage of water and thermal energy to maximize the potential benefits.

Uncertainty assessments and hydrological implications of climate change in two adjacent agricultural catchments of a rapidly urbanizing watershed.

Lake Simcoe is the most important inland lake in Southern Ontario. The watershed is predominantly agricultural and under increasing pressure from urbanization, leading to changing runoff patterns in rivers draining to the lake. Uncertainties in rainfall-runoff modeling in tributary catchments of the Lake Simcoe Watershed (LSW) can be an order of magnitude larger than pristine watersheds, hampering water quality predictions and export calculations. Here we conduct a robust assessment to constrain the uncertainty in hydrological simulations and projections in the LSW using two representative adjacent agricultural catchments. Downscaled CGCM 3 projections using A1B and A2 emission scenarios projected increases of 4°C in air temperature and a 26% longer growing season. The fraction of precipitation falling as snow will decrease. Spring runoff is an important event in LSW but individual HBV best calibrated parameter sets under-predicted peak flows by up to 32%. Using an ensemble of behavioral parameter sets achieved credible representations of present day hydrology and constrained uncertainties in future projections. Parameter uncertainty analysis showed that the catchments differ in terms of their snow accumulation/melt and groundwater dynamics. Human activities exacerbate the differences in hydrological response. Model parameterization in one catchment could not generate credible hydrological simulations in the other. We cautioned against extrapolating results from monitored to ungauged catchments in managed watersheds like the LSW.

Using the INCA-Hg model of mercury cycling to simulate total and methyl mercury concentrations in forest streams and catchments.

We present a new, catchment-scale, process-based dynamic model for simulating mercury (Hg) in soils and surface waters. The Integrated Catchments Model for Mercury (INCA-Hg) simulates transport of gaseous, dissolved and solid Hg and transformations between elemental (Hg(0)), ionic (Hg(II)) and methyl (MeHg) Hg in natural and semi-natural landscapes. The mathematical description represents the model as a series of linked, first-order differential equations describing chemical and hydrological processes in catchment soils and waters which we believe control surface water Hg dynamics. The model simulates daily time series between one and 100 years long and can be applied to catchments ranging in size from <1 to ~10,000 km(2). Here we present applications of the model to two boreal forest headwater catchments in central Canada where we were able to reproduce observed patterns of stream water total mercury (THg) and MeHg fluxes and concentrations. Model performance was assessed using Monte Carlo techniques. Simulated in-stream THg and MeHg concentrations were sensitive to hydrologic controls and terrestrial and aquatic process rates.

Modelling the long term impact of climate change on the carbon budget of Lake Simcoe, Ontario using INCA-C.

This study presents a process-based model of dissolved organic carbon concentration ([DOC]) in catchments draining into Lake Simcoe, Ontario. INCA-C, the Integrated Catchment model for Carbon, incorporates carbon biogeochemical processes in a terrestrial system with hydrologic flow paths to simulate watershed wide [DOC]. The model successfully simulates present-day inter-annual and seasonal [DOC] dynamics in tributaries draining catchments with mixed or contrasting land cover in the Lake Simcoe watershed (LSW). The sensitivity of INCA-C to soil moisture, hydrologic controls and land uses within a watershed demonstrates its significance as a tool to explore pertinent environmental issues specific to the LSW. Projections of climate change under A1B and A2 SRES scenarios suggest a continuous monotonic increase in [DOC] in surface waters draining into Lake Simcoe. Large variations in seasonal DOC dynamics are predicted to occur during summer with a possibility of displacement of summer [DOC] maxima towards winter and a prolongation of summer [DOC] levels into the autumn. INCA-C also predicts possible increases in dissolved inorganic carbon in some tributaries with rising temperature suggesting increased CO(2) emissions from rivers as climate changes.

Modelling phosphorus dynamics in multi-branch river systems: a study of the Black River, Lake Simcoe, Ontario, Canada.

High rates of nutrient loading from agricultural and urban development have resulted in surface water eutrophication and groundwater contamination in regions of Ontario. In Lake Simcoe (Ontario, Canada), anthropogenic nutrient contributions have contributed to increased algal growth, low hypolimnetic oxygen concentrations, and impaired fish reproduction. An ambitious programme has been initiated to reduce phosphorus loads to the lake, aiming to achieve at least a 40% reduction in phosphorus loads by 2045. Achievement of this target necessitates effective remediation strategies, which will rely upon an improved understanding of controls on nutrient export from tributaries of Lake Simcoe as well as improved understanding of the importance of phosphorus cycling within the lake. In this paper, we describe a new model structure for the integrated dynamic and process-based model INCA-P, which allows fully-distributed applications, suited to branched river networks. We demonstrate application of this model to the Black River, a tributary of Lake Simcoe, and use INCA-P to simulate the fluxes of P entering the lake system, apportion phosphorus among different sources in the catchment, and explore future scenarios of land-use change and nutrient management to identify high priority sites for implementation of watershed best management practises.

Laboratory assessment of factors affecting soil clogging of soil aquifer treatment systems.

In this study the effect of soil type, level of pre-treatment, ponding depth, temperature and sunlight on clogging of soil aquifer treatment (SAT) systems was evaluated over an eight week duration in constant temperature and glasshouse environments. Of the two soil types tested, the more permeable sand media clogged more than the loam, but still retained an order of magnitude higher absolute permeability. A 6- to 8-fold difference in hydraulic loading rates was observed between the four source water types tested (one potable water and three recycled waters), with improved water quality resulting in significantly higher infiltration. Infiltration rates for ponding depths of 30 cm and 50 cm were higher than 10 cm, although for 50 cm clogging rates were higher due to greater compaction of the clogging layer. Overall, physical clogging was more significant than other forms of clogging. Microbial clogging becomes increasingly important when the particulate concentrations in the source waters are reduced through pre-treatment and for finer textured soils due to the higher specific surface area of the media. Clogging by gas binding took place in the glasshouse but not in the lab, and mechanical clogging associated with particle rearrangement was evident in the sand media but not in the loam. These results offer insight into the soil, water quality and operating conditions needed to achieve viable SAT systems.

Application of a risk management framework to a drinking water supply augmented by stormwater recharge.

The Blue Lake is an important water resource for the city of Mount Gambier and the surrounding region, primarily as the drinking water supply source, but also as a tourist attraction. Mount Gambier's stormwater is discharged directly via drainage wells into the unconfined, karstic Gambier Limestone aquifer, which in turn provides the majority of recharge to Blue Lake. Discharge of urban runoff to the aquifer commenced in the 1800s as a means of stormwater management, but is now recognised as contributing to the drinking water supply in Blue Lake. Recently, guidelines for managing the risks associated with water recycling and augmenting drinking water supplies have been developed. This paper examines the organic chemical hazards associated with a stormwater to potable recycling scheme as an example of the current risk management framework.

Factors affecting the performance and risks to human health of on-site wastewater treatment systems.

Aerobic wastewater treatment systems (aerobic systems) are the preferred choice in a region overlying a karstic aquifer used for drinking water supplies, as they are thought to provide better protection to groundwater and human health than standard septic systems. However, aerobic systems in operation do not always perform to design standard; while this is often blamed on lack of maintenance, few studies have investigated the link directly. This study investigates the performance of domestic on-site wastewater treatment systems in South Australia, and compares effluent quality to maintenance records. Effluent from 29 septic tanks and 31 aerobic systems was analysed for nutrients, physico-chemical parameters and microbiological indicators. Aerobic systems generally provided greater treatment than septic tanks, yet most aerobic systems did not meet regulatory guidelines with high levels of indicator bacteria in 71% of samples. The effect of system size, number of household occupants and maintenance on aerobic system treatment performance was analysed: chlorine levels were positively correlated with time of last service, and nutrient concentrations were positively correlated with the number of occupants. A microbial risk assessment revealed the observed irrigation practices to be high risk; and sufficient residence time in the aquifer cannot be guaranteed for protection of groundwater used for drinking. Additional preventive measures such as irrigation management or post treatment of drinking water supply (such as UV disinfection) are required to meet public health targets.

Spatio-temporal variation in the characteristics of dissolved organic matter in the streams of boreal forests: impacts on modelled copper speciation.

Dissolved organic matter (DOM) is an important constituent of natural waters that controls numerous biogeochemical processes such as the toxicity and mobility of metals. In order to predict how metals behave in the presence of DOM, it is necessary to understand its acidic properties. In this study, we report the variations in the acid character of aquatic organic acids using 30 years of sampling data collected from three boreal streams. Based on a charge balance model, significant spatial and temporal variation in carboxylic acid site density was observed. The seasonal average carboxylic group density ranged from 8.01 +/- 1.47 to 12.0 +/- 1.90 microeq mg C(-1) and the overall (multi-site) average site density (winter excluded) was 9.66 +/- 0.125 microeq mg C(-1) (n = 3193). Both different sources of DOM and seasonal differences in source availability were found to contribute to variations in site density. In the deciduous catchment where wetland contributions to DOM were negligible, the seasonal variability in site density was highly marked with increases of up to 50% observed between spring and fall. Less seasonal variation was noted at the coniferous sites, which had relatively high wetland source contributions. The geochemical equilibrium speciation model MINTEQA2 showed that the increase in site density observed from winter to fall coincided with a decrease in free copper concentration. We conclude that some source-based differences in DOM that may result from variation in both catchment characteristics and seasonal DOC loadings necessitate the determination of location-specific and/or seasonal site density values due to the resulting variability in metal speciation that has been predicted through modelling.

Effects of formulations of the fungicide, pentachloronitrobenzene on early life stage development of the Japanese medaka (Oryzias latipes).

Quintozene is a fungicide containing the active ingredient, pentachloronitrobenzene (PCNB) that is used to control "snow mold" on golf courses in temperate regions of North America. In this study, quintozene and a formulation of quintozene widely used on golf courses, FFII were tested for toxicity to early life stages of the Japanese medaka, Oryzias latipes. For medaka exposed in static non-renewal assays to quintozene for 17d from the fertilized egg stage to yolk resorption at the fry stage, the LC(50) for mortality was a nominal concentration of 707 microgl(-1) and the effective concentration for 50% hatch (i.e. EC(50)) was a nominal concentration of 71 microgl(-1). Eggs and fry showed developmental abnormalities, including ocular malformations and retarded development of the brain, notochord, organs and body segmentation, which were interpreted as teratogenic responses to exposure to PCNB. For medaka exposed to quintozene, the LOECs for abnormalities of the eye and all other developmental abnormalities were 750 and 100 microgl(-1), respectively. In medaka exposed to the FFII formulation, similar patterns of mortalities, reduced hatching success and developmental abnormalities were observed, but at higher test concentrations that were consistent with the proportion of quintozene in the formulation. For medaka exposed to the formulation, the LOECs for abnormalities of the eye and all other developmental abnormalities were 10,000 and 1,000microgl(-1), respectively. Overall, these data indicate that studies should be conducted to assess the risk of exposure of early life stages of fish to quintozene in watersheds impacted by golf courses.

Climate variability and forecasting surface water recovery from acidification: modelling drought-induced sulphate release from wetlands.

Climate-induced drought events have been shown to have a significant influence on sulphate (SO(4)(2-)) export from forested catchments in central Ontario, subsequently delaying recovery of surface waters from acidification. Field and modelling studies have demonstrated that water table drawdown during drought periods promotes oxidation of previously stored (reduced) sulphur (S) compounds in wetlands, with subsequent efflux of SO(4)(2-) upon re-wetting. Although climate-induced changes in processes are generally not integrated into soil-acidification models, MAGIC (Model of Acidification of Groundwater in Catchments) includes a wetland compartment that incorporates redox processes driven by drought events. The potential confounding influence of climate-induced drought events on acidification recovery at Plastic Lake, south-central Ontario (under proposed future S emission reductions) was investigated using MAGIC and two climate scenarios: monthly precipitation and runoff based on long-term means (average-climate scenario), and variable precipitation and runoff based on the past 20 years of observed monthly data (variable-climate scenario). The variable-climate scenario included several periods of summer drought owing to lower than average rainfall and higher then average temperature. Nonetheless, long-term regional trends in precipitation and temperature suggest that the variable-climate scenario may be a conservative estimate of future climate. The average-climate scenario indicated good recovery potential with acid neutralising capacity (ANC) reaching approximately 40 micromol(c)L(-1) by 2020 and 50 micromol(c)L(-1) by 2080. In contrast, the forecasted recovery potential under the variable-climate scenario was very much reduced. By 2080, ANC was forecasted to increase to 2.6 micromol(c)L(-1) from -10.0 micromol(c)L(-1) in 2000. Elevated SO(4)(2-) efflux following drought events (introduced under the variable-climate scenario) has a dramatic impact on simulated future surface water chemistry. The results clearly demonstrate that prediction of future water quality, using models such as MAGIC, should take into account changes or variability in climate as well as acid deposition.

Mercury concentration in black flies Simulium spp. (Diptera, Simuliidae) from soft-water streams in Ontario, Canada.

Total Hg in Simulium spp. (Diptera, Simuliidae) was measured in 17 soft-water streams in the District of Muskoka and Haliburton County (Ontario, Canada) during 2003 and 2004. Black flies contained 0.07-0.64 microg/g total Hg (dry weight). The methylmercury concentration was measured in 6 samples of the 17, and ranged from 58% to 93% of total Hg. The concentration of total Hg is much higher than has been found in other filter feeding insects, and represents a significant potential source of Hg to fish. Mercury concentrations in Simulium spp. at different sites were strongly positively correlated with dissolved organic carbon, and the proportion of land within each catchment that was wetland. There was also a strong negative correlation with pH. By examining Hg concentration in filter feeding insects we have found a significant entry point for Hg and MeHg into the food web.

Climate-induced episodic acidification of streams in central ontario.

In this study we have analyzed the hydrochemical effect of drought conditions during 311 hydrological episodes in nine headwater streams in central Ontario over the past 20 years. Acid Neutralization Capacity (ANC) was logarithmically correlated (p<0.05) to antecedent discharge in eight of the nine streams, with the largest decline in ANC occurring after low antecedent flow. In eight of the nine streams SO4(2-) was the most important driving mechanism of ANC decline, but dilution as well as organic acidity was important in several streams. No decrease in the SO4(2-) driven ANC decline was observed over the 20 year study period despite a approximately 40% reduction in SO4(2-) deposition. The strong correlation between ANC decline and low antecedent discharge demonstrates that episodic acidification during rain events is strongly associated with preceding drought conditions, especially in wetland-dominated catchments. The results have important implications for recoveryfrom acidification, especially in northern ecosystems where climate scenarios forecast that warmer and drier conditions will be more common.

Monitoring the results of Canada/U.S.A. acid rain control programs: some lake responses.

Aquatic acidification by deposition of airborne pollutants emerged as an environmental issue in southeastern Canada during the 1970s. Drawing information from the extensive research and monitoring programs, a sequence of issue assessments demonstrated the necessity of reducing the anthropogenic emissions of acidifying pollutants, particularly sulphur dioxide (SO2). The 1991 Canada-U.S. Air Quality Agreement (AQA) was negotiated to reduce North American SO2 emissions by approximately 40% relative to 1980 levels by 2010, and at present, both countries have reduced emissions beyond their AQA commitment. In response to reduced SO2 emissions, atmospheric deposition of sulphate (SO4(2-)) and SO4(2-) concentrations in many lakes have declined, particularly in south-central Ontario and southern Québec. Sulphate deposition still exceeds aquatic critical loads throughout southeastern Canada however. Increasing pH or alkalinity (commonly deemed 'recovery') has been observed in only some lakes. Several biogeochemical factors have intervened to modify the lake chemistry response to reduced SO4(2-) input, notably release of stored SO4(2-) from wetlands following periods of drought and reduction in the export of base cations from terrestrial soils. Three examples from Ontario are presented to illustrate these responses. Significant increases in pH and alkalinity have been observed in many lakes in the Sudbury area of Ontario due to the large reductions in local SO2 emissions; 'early-stage' biological recovery is evident in these lakes. An integrated assessment model predicts that AQA emission reductions will not be sufficient to promote widespread chemical or biological recovery of Canadian lakes. Monitoring and modeling are mutually supporting assessment activities and both must continue.

Separation and characterization of NOM by high-performance liquid chromatography and on-line three-dimensional excitation emission matrix fluorescence detection.

By using high-performance size exclusion chromatography (HPSEC) and reversed-phase high-performance liquid chromatography with on-line three-dimensional excitation emission matrix fluorescence detection, we measured fluorescence properties of natural organic matter (NOM) as a function of molecular size (MS) and polarity. The work was carried out with Suwannee River Fulvic Acid, Aldrich Humic Acid, and a naturally occurring river NOM sample. Significant differences in fluorescence maximum pattern were found as NOM was separated chromatographically based on MS and polarity. There existed a strong relationship between MS, fluorescence pattern, and polarity. Humic-, fulvic-, and protein-like fluorescence fractions had distinct hydrophilic/hydrophobic nature. The results suggest that HPSEC may be better for characterizing major fulvic-like fluorescence and smaller MS fractions but not those having humic- and protein-like fluorescence and larger MS, which may be strongly adsorbed onto the HPSEC column because of their hydrophobic nature. This study has significant implications for further understanding the nature of NOM and its complexation with trace metals.

Comparison of iron accumulation in lakes using sediment core and mass balance calculations.

The accumulation of iron (Fe) in several lakes in Ontario, Canada was determined by two independent approaches. First, Fe accumulation was calculated in cores collected from several sites in each lake by integrating Fe concentration profiles with sediment accumulation rates determined from Pb210 dating. These site-specific accumulation rates were corrected for sediment focussing so that whole-lake Fe accumulation values could be derived. Using this approach, recent whole-lake Fe accumulation in eight lakes ranged between approximately 750 and 4000 mg/m2 per year. Second, whole-lake Fe accumulation was estimated from lake mass budgets, which were measured over a maximum of 14 years. Accumulation measured using the mass balances ranged from 10 to 1330 mg/m2 per year. Comparison of the two approaches indicated that retentions calculated from the sediment cores were much greater than those estimated from the mass balances. The most likely explanation for this difference is that, in the two decades since the cores were collected, there has been a substantial decline in Fe retention (in mass units but not percent) in the study lakes, principally as a result of reduced inputs of Fe from the catchments.

Comparison of superior vena caval and femoroiliac venous pressure measurements during normal and inverse ratio ventilation.

OBJECTIVE: The aim of this study was to estimate the agreement between superior vena caval pressure (SVCP) and femoroiliac venous pressure (FIVP) measurements by using short (<20 cm) femoral catheters commonly used in an adult intensive care unit. In addition, the effects of two modes of ventilation on agreement were assessed. DESIGN: Measurements of central venous pressure were recorded from both sites by using the same pressure transducer connected to the catheters via a three-way stopcock. SVCP and FIVP were recorded at 5-min intervals for 40 mins with the patient in the supine position. Recordings were taken from ventilated patients during a randomized crossover sequence of normal and inverse ratio ventilation (IRV). Analyses included Pearson's correlation (r), intraclass correlation (ri), Bland-Altman plots, and repeated measures analysis of variance with crossover tests for period and period-treatment interactions. SETTING: Adult intensive care unit. PATIENTS: Adult intensive care patients. MEASUREMENTS: Central venous pressure. RESULTS: Twenty-two patients were enrolled in the study, giving 162 paired measurements; r was .97 (p < .0001), and ri was .96. The bias for SVCP-FIVP measurements was -0.75 mm Hg (95% confidence interval = -1.31 to -0.18), with 95% limits of agreement of -3.30 to 1.81 mm Hg. Seventeen patients were suitable for randomization to normal ratio ventilation and IRV. IRV significantly increased SVCP and FIVP (p < .002). Tests for the effect of mode of ventilation on agreement (p = .36), for period (p = .26), and for period-treatment interaction (p = .84) were not significant. CONCLUSION: The study showed excellent overall agreement with acceptable clinical agreement for SVCP and FIVP measurements that was not affected by changing the mode of ventilation. IRV significantly increased central venous pressure measurements from both catheter sites but had no effect on overall agreement.

Single nucleotide polymorphic discrimination by an electronic dot blot assay on semiconductor microchips.

We have developed a rapid assay for single nucleotide polymorphism (SNP) detection that utilizes electronic circuitry on silicon microchips. The method was validated by the accurate discrimination of blinded DNA samples for the complex quadra-allelic SNP of mannose binding protein. The microchip directed the transport, concentration, and attachment of amplified patient DNA to selected electrodes (test sites) creating an array of DNA samples. Through control of the electric field, the microchip enabled accurate genetic identification of these samples using fluorescently labeled DNA reporter probes. The accuracy of this approach was established by internal controls of dual labeled reporters and by using mismatched sequences in addition to the wild-type and variant reporter sequences to validate the SNP-genotype. The ability to customize this assay for multiple genes has advantages over other existing approaches.