Flow pathways and nutrient transport mechanisms drive hydrochemical sensitivity to climate change across catchments with different geology and topography

Hydrological processes determine the transport of nutrients and passage of diffuse pollution. Consequently, catchments are likely to exhibit individual hydrochemical responses (sensitivities) to climate change, which are expected to alter the timing and amount of runoff, and to impact in-stream water quality. In developing robust catchment management strategies and quantifying plausible future hydrochemical conditions it is therefore equally important to consider the potential for spatial variability in, and causal factors of, catchment sensitivity, as it is to explore future changes in climatic pressures. This study seeks to identify those factors which influence hydrochemical sensitivity to climate change. A perturbed physics ensemble (PPE), derived from a series of global climate model (GCM) variants with specific climate sensitivities was used to project future climate change and uncertainty. Using the INtegrated CAtchment model of Phosphorus dynamics (INCA-P), we quantified potential hydrochemical responses in four neighbouring catchments (with similar land use but varying topographic and geological characteristics) in southern Ontario, Canada. Responses were assessed by comparing a 30 year baseline (1968-1997) to two future periods: 2020-2049 and 2060-2089. Although projected climate change and uncertainties were similar across these catchments, hydrochemical responses (sensitivities) were highly varied. Sensitivity was governed by quaternary geology (influencing flow pathways) and nutrient transport mechanisms. Clay-rich catchments were most sensitive, with total phosphorus (TP) being rapidly transported to rivers via overland flow. In these catchments large annual reductions in TP loads were projected. Sensitivity in the other two catchments, dominated by sandy loams, was lower due to a larger proportion of soil matrix flow, longer soil water residence times and seasonal variability in soil-P saturation. Here smaller changes in TP loads, predominantly increases, were projected. These results suggest that the clay content of soils could be a good indicator of the sensitivity of catchments to climatic input, and reinforces calls for catchment-specific management plans

The water balance of Middle Fork Toklat headwater glaciers measured as equivalent meters of water a) in the ablation zone; comparing observed (satellite imagery analysis of glacial extent) and modelled (HBV glacial mass balance output) values, and b) analysing net glacial flux from the HBV model.

<p>The water balance of Middle Fork Toklat headwater glaciers measured as equivalent meters of water a) in the ablation zone; comparing observed (satellite imagery analysis of glacial extent) and modelled (HBV glacial mass balance output) values, and b) analysing net glacial flux from the HBV model.</p

Comparison between observed, NCEP and Global Climate Model (GCM) meteorological data, between 1961 and 2000, demonstrating the representativeness of GCMs for a) temperature and b) precipitation.

<p>Comparison between observed, NCEP and Global Climate Model (GCM) meteorological data, between 1961 and 2000, demonstrating the representativeness of GCMs for a) temperature and b) precipitation.</p

Complete modelled time series of a) temperature and b) precipitation across both GCMs and IPCC scenarios.

<p>Complete modelled time series of a) temperature and b) precipitation across both GCMs and IPCC scenarios.</p

Remotely sensed images of headwater glaciers in the Middle Fork Toklat Catchment (63°23'46.67″N, 149°51'43.99″W), analysed using satellite data from 1986–2009, sourced from the U.S. Geological Survey’s Earth Resources Observation and Science (EROS) Centre of 1986-2009.

<p>Remotely sensed images of headwater glaciers in the Middle Fork Toklat Catchment (63°23'46.67″N, 149°51'43.99″W), analysed using satellite data from 1986–2009, sourced from the U.S. Geological Survey’s Earth Resources Observation and Science (EROS) Centre of 1986-2009.</p

Site map of the study catchment (63°31'2.47″N, 150°1'42.80″W), delineating major landuse types, and the location of the pressure transducers at the “flow gauging station”. Landcover data was obtained from the AK I&M Inventory Program (non-proprietary data), through the National Park Service data repository (http://nrdata.nps.gov/). Accessed 2013 August 6).

<p>Site map of the study catchment (63°31'2.47″N, 150°1'42.80″W), delineating major landuse types, and the location of the pressure transducers at the “flow gauging station”. Landcover data was obtained from the AK I&M Inventory Program (<u>non-proprietary data</u>), through the National Park Service data repository (<a href="http://nrdata.nps.gov/" target="_blank">http://nrdata.nps.gov/</a>). Accessed 2013 August 6).</p

Flow exceedance curves under baseline and future climate conditions, demonstrating changes in the percentage of time particular flows are exceeded.

<p>Flow exceedance curves under baseline and future climate conditions, demonstrating changes in the percentage of time particular flows are exceeded.</p

Comparison of observed and modelled discharge data in the Toklat catchment a) on a daily time scale, b) a monthly time scale.

<p>Comparison of observed and modelled discharge data in the Toklat catchment a) on a daily time scale, b) a monthly time scale.</p

Exploratory analysis of the relationships between extreme flow events and a) precipitation, b) temperature.

<p>Exploratory analysis of the relationships between extreme flow events and a) precipitation, b) temperature.</p

Complete modelled time series of a) glacial mass balance and b) river discharge across both GCMs and IPCC scenarios.

<p>Complete modelled time series of a) glacial mass balance and b) river discharge across both GCMs and IPCC scenarios.</p