Stephen K. Oni

Effect of Climate Change on Soil Temperature in Swedish Boreal Forests

Complex non-linear relationships exist between air and soil temperature responses to climate change. Despite its influence on hydrological and biogeochemical processes, soil temperature has received less attention in climate impact studies. Here we present and apply an empirical soil temperature model to four forest sites along a climatic gradient of Sweden. Future air and soil temperature were projected using an ensemble of regional climate models. Annual average air and soil temperatures were projected to increase, but complex dynamics were projected on a seasonal scale. Future changes in winter soil temperature were strongly dependent on projected snow cover. At the northernmost site, winter soil temperatures changed very little due to insulating effects of snow cover but southern sites with little or no snow cover showed the largest projected winter soil warming. Projected soil warming was greatest in the spring (up to 4°C) in the north, suggesting earlier snowmelt, extension of growing season length and possible northward shifts in the boreal biome. This showed that the projected effects of climate change on soil temperature in snow dominated regions are complex and general assumptions of future soil temperature responses to climate change based on air temperature alone are inadequate and should be avoided in boreal regions.

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.

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.

Phosphorus dynamics across intensively monitored subcatchments in the Beaver River

Abstract We report results from a spatially intensive monitoring and modelling study to assess phosphorus (P) dynamics in the Beaver River, a tributary of Lake Simcoe, Ontario. We established multiple monitoring stations (9 flow and 24 water quality stations) from headwaters to near the outflow that were operated for 2 field seasons, complementing longer term data from a flow monitoring site and water chemistry monitoring site. We applied the Branched-INCA-P model, which allows fully distributed simulations supported by highly distributed monitoring data. Using spatially distributed data helped better understand variable P and sediment dynamics across the catchment and identify key model uncertainties and uncertainties related to catchment P management. Measured and modelled total P concentrations often exceeded provisional water quality thresholds in many areas of the catchment and highlight the value of studying water quality across multiple subcatchments rather than at a single site. Total P export coefficients differed widely among subcatchments, ranging from 2.1–21.4 kg km−2 y−1 over a single year. Export coefficients were most strongly (negatively) related to the proportion of wetland cover in subcatchments. The INCA-P model captured spatial variation in P concentrations relatively well, but short-term temporal variability in the observed data was not well simulated across sites, in part due to unmodelled hydrological phenomena including beaver activity and unknown drivers of P peaks that were not associated with hydrological events.

Local‐ and landscape‐scale impacts of clear‐cuts and climate change on surface water dissolved organic carbon in boreal forests

Forest harvesting and climate change may significantly increase concentrations and fluxes of dissolved organic carbon (DOC) in boreal surface waters. However, the likely magnitude of any effect will vary depending on the landscape-element type and spatial scale. We used a chain of hydrological, empirical and process-based biogeochemical models coupled to an ensemble of downscaled Regional Climate Model (RCM) experiments to develop scenario storylines for local and landscape-scale effects of forest harvesting and climate change on surface water DOC concentrations and fluxes. Local-scale runoff, soil temperature and DOC dynamics were simulated for a range of forest and wetland landscape-element types and at the larger landscape scale. The results indicated that climate change will likely lead to greater winter flows and earlier, smaller spring peaks. Both forest harvesting and climate change scenarios resulted in large increases in summer and autumn runoff and higher DOC fluxes. Forest harvesting effects were clearly apparent at local scales. While at the landscape scale, approximately 1 mg L−1 (or 10%) of the DOC in surface waters can be attributed to clear-cuts, both climate change and intensified forestry can each increase DOC concentrations by another 1 mg L−1 in the future, which is less than that seen in many waterbodies recovering from acidification. These effects of forestry and climate change on surface water DOC concentrations are additive at a landscape scale but not at the local scale, where a range of landscape-element specific responses were observed.

Modelling phosphorus in Lake Simcoe and its subcatchments: scenario analysis to assess alternative management strategies

Abstract In Lake Simcoe (Ontario, Canada), anthropogenic phosphorus (P) loads have contributed to increased algal growth, low hypolimnetic dissolved oxygen concentrations, and impaired fish reproduction. Management targets to control eutrophication require an ambitious programme to reduce P loads to the lake. Remediation strategies rely upon an improved understanding of P sources and assessment of the effectiveness of different control options. Here we present an application of the integrated catchment model for phosphorus (INCA-P) to examine P sources across the Lake Simcoe watershed and simulate in-lake P concentrations. This is the first application of INCA-P to a complex watershed of this nature and the first to include a lake component. We evaluated a set of management actions to simulate anticipated effects of P reduction strategies on in-lake total phosphorus (TP) concentrations. The INCA-P scenarios show the difficulty of achieving large-scale reductions from the watershed, given the low rates of P export; however, the study shows that a multifaceted strategy, including fertilizer reduction, addition of buffer strips, more stringent controls on sewage treatment plant effluent, and reduced deposition of P to the lake surface, could achieve a 25% reduction in lake-water TP concentrations and produce TP close to the target of 0.01 mg L−1.

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.

Dynamic Modelling of the Impact of Climate Change and Power Flow Management Options using STELLA: Application to the Steephill Falls Reservoir, Ontario, Canada

This paper presents a dynamic modelling framework for evaluating the impact of climate change and flow management options on a hydroelectric power reservoir. The model couples the HBV (Hydrologiska Byrns Vattenbalansavdelning) rainfall-runoff model to a generic reservoir routing model. The efficacy of the model was tested on the Steephill Falls hydropower facility located in the Magpie River watershed in Northern Ontario. Both the impact of climate change and future energy demands were evaluated. Using a statistical downscaling approach, future climate under Intergovernmental Panel on Climate Change (IPCC) A1B and A2 emission scenarios was projected from the Canadian Global Circulation Model 3 (CGCM3). Both scenarios suggest a significantly increasing trend in air temperature (p < 0.001) corresponding to a 1.7C increase by the middle of the century and a 2.9C to 3.7C increase by the end of the century relative to the baseline period (19702000). The model performed well in simulating the inter-annual seasonal dynamics of the reservoir. Plausible climate-induced increase in runoff input into the reservoir might be counterbalanced by increased drawdown caused by increasing energy demands and water users, resulting in increased pressure to adjust lower reservoir rule curves, in-stream flow requirements downstream, or a combination of both.

The effectiveness and resilience of phosphorus management practices in the Lake Simcoe watershed, Ontario, Canada

Uncertainty surrounding future climate makes it difficult to have confidence that current nutrient management strategies will remain effective. This study used monitoring and modeling to assess current effectiveness (% phosphorus reduction) and resilience (defined as continued effectiveness under a changing climate) of best management practices (BMPs) within five catchments of the Lake Simcoe watershed, Ontario. The Integrated Catchment Phosphorus model (INCA-P) was used, and monitoring data were used to calibrate and validate a series of management scenarios. To assess current BMP effectiveness, models were run over a baseline period 1985–2014 with and without management scenarios. Climate simulations were run (2070–2099), and BMP resilience was calculated as the percent change in effectiveness between the baseline and future period. Results demonstrated that livestock removal from water courses was the most effective BMP, while manure storage adjustments were the least. Effectiveness varied between catchments, influenced by the dominant hydrological and nutrient transport pathways. Resilience of individual BMPs was associated with catchment sensitivity to climate change. BMPs were most resilient in catchments with high soil water storage capacity and small projected changes in frozen-water availability and in soil moisture deficits. Conversely, BMPs were less resilient in catchments with larger changes in spring melt magnitude and in overland flow proportions. Results indicated that BMPs implemented are not always those most suited to catchment flow pathways, and a more site-specific approach would enhance prospects for maintaining P reduction targets. Furthermore, BMP resilience to climate change can be predicted from catchment physical properties and present-day hydrochemical sensitivity to climate forcing.

Spatial distribution and extent of urban land cover control watershed-scale chloride retention

In some cold regions up to 97% of the chloride (Cl-) entering rivers and lakes is derived from road salts that are applied to impervious surfaces to maintain safe winter travel conditions. While a portion of the Cl- applied as road salt is quickly flushed into streams during melt events via overland flow and flow through storm sewer pipes, the remainder enters the subsurface. Previous studies of individual watersheds have shown that between 28 and 77% of the applied Cl- is retained on an annual basis, however a systematic evaluation of the spatial variability in Cl- retention and potential driving factors has not been carried out. Here we used a mass balance approach to estimate annual Cl- retention in 11 watersheds located in southern Ontario, Canada, which span a gradient of urbanization. We evaluated the influence of multiple landscape variables on the magnitude of Cl- retention as well as the long-term rate of change in stream Cl-concentration for the same systems. We found that mean annual Cl- retention ranged from 40 to 90% and was higher for less urbanized watersheds and for watersheds with urban areas located farther from the stream outlet. This result suggests that less urbanized watersheds and ones with longer flow pathways have more Cl- partitioned into storage and hence the potential for legacy Cl- effects on aquatic organisms. While we did measure statistically significant increasing trends in stream Cl- concentration in some watersheds, there was no consistent relationship between the long-term rate of change in stream Cl- concentrations and patterns of urbanization and the magnitude of Cl- retention. Based on our results we present a detailed conceptual model of watershed Cl- dynamics that can be used to guide future research into the mechanisms of Cl- retention and release within a watershed.