Gabor Sass

ABSTRACT Characterizing the spatial and temporal variation in surface hydrological patterns of large boreal landscapes is vital since these patterns define the occurrence of key areas of land- to-lake and land-to-atmosphere hydrological and biogeochemical linkages that are critical in the movement of matter and energy at local to global scales. However, monitoring surface hydrological dynamics over large geographic extents and over long periods of time is a challenge for hydrologists as traditional point measurements are not practical. In this study we used ERS radar imagery to monitor the variation in surface hydrological patterns over a 12 year period and to assess the change in the organization of saturated and inundated areas of the landscape that may form hotspots or hot moments for various biogeochemical and ecological processes. Using the regional Utikuma River drainage basin (1000 km2) as the test area, analyses of patterns of wetlands (including both saturated and inundated areas) indicated that during dry climatic conditions, wetland sizes were small and disconnected from each other and receiving bodies of water. As climatic conditions changed from dry to mesic, wetland numbers increased but were still disconnected from the rest of the landscape. It required very wet climatic conditions before the disjointed wetlands coalesced and connected to lakes. During these wet conditions the response of the lake level at Utikuma Lake was observed to be much higher than under drier conditions. Analyses of individual wetland maps and integrated probability maps have the potential to inform future biogeochemical and ecological investigations and forest management on the Boreal Plain.

ABSTRACT The recent proliferation of spatially and temporally extensive geospatial datasets (e.g., Radarsat, Landsat) has created research opportunities into the characterization of eco-hydrological processes and patterns across Canada's vast forests. Herein, we demonstrate how these space based sensors can be used to establish the hydrologic controls on the range of natural variability (RNV) of lake trophic status and to assess thresholds in disturbance related to human activities that lead to the exceedance in RNV (i.e., lake trophic status that is outside the RNV). We focus on two lake districts in the boreal forest. One is on the western Boreal Plain, where average annual precipitation (P) is less than potential evapotranspiration (PET) (P<PET) and hydrology is characterized by complex surface and subsurface hydrologic interactions. The other is on the eastern Boreal Shield where P>PET and hydrology is characterized by simpler surface hydrologic dynamics. In each of these lake districts, we use Radarsat and Landsat imagery to map surface/near surface hydrologic flow paths (the conveyors of nutrients to and from lakes) and lake trophic status. We establish the RNV of trophic status in landscapes with minimal human presence and compare this to the trophic status of lakes where there is a significant human footprint caused by forest management activities. By building statistical models that account for differences in climate and hydrologic pathways within basins contributing to a lake, we are able to evaluate how much disturbance in forest hydrology is needed to result in a fundamental change in nutrient loading to the lakes and ultimately lake trophic status. We conclude that satellite sensors can assist in the establishment of realistic reference conditions against which effects of forest management activities on lake trophic status can be assessed and management targets can be established.

Trophic status is a broad measure of the productivity of aquatic ecosystems but it can also serve as an important indicator of carbon and nutrient cycling within lakes. In shallow lakes of the boreal region of western Canada, the trophic status is usually clear, dominated by submersed aquatic vegetation, yet very dynamic, with individual lakes exhibiting switching from clear to

The trophic status of shallow lakes on the Boreal Plain of Alberta exhibits high natural variation in space and time. It is not currently known what the dominant controls on this variation are at regional scales and over longer time periods. The aim of this study was to assess the importance of hydrology, captured by climatic and landscape metrics, in explaining the spatial and temporal variation in the trophic status of lakes on the Boreal Plain. The concentration of chlorophyll a (CHLa), an indicator of trophic status, was derived from Landsat images acquired during late summer (August) over a 20 year period from 1984 to 2003. Year-to-year temporal variation in CHLa was related non-linearly to climate, as measured by effective precipitation (precipitation minus potential-evapotranspiration). The relation between CHLa and climate indicated that under wet conditions CHLa decreased possibly due to phosphorus dilution, while under dry conditions, CHLa increased possibly due to phospho...