ABSTRACT Characterizing the spatial and temporal variation in surface hydrological patterns of la... more 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.
Mapping groundwater discharge zones at broad spatial scales remains a challenge, particularly in ... more Mapping groundwater discharge zones at broad spatial scales remains a challenge, particularly in data sparse regions. We applied a regional scale mapping approach based on thermal remote sensing to map discharge zones in a complex watershed with a broad diversity of geological materials, land cover and topographic variation situated within the Prairie Parkland of northern Alberta, Canada. We acquired winter thermal imagery from the USGS Landsat archive to demonstrate the utility of this data source for applications that can complement both scientific and management programs. We showed that the thermally determined potential discharge areas were corroborated with hydrological (spring locations) and chemical (conservative tracers of groundwater) data. This study demonstrates how thermal remote sensing can form part of a comprehensive mapping framework to investigate groundwater resources over broad spatial scales.
ABSTRACT The recent proliferation of spatially and temporally extensive geospatial datasets (e.g.... more 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... more 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
Shallow lakes are known to exhibit alternative states in their biotic structure. Lakes dominated ... more Shallow lakes are known to exhibit alternative states in their biotic structure. Lakes dominated by submersed aquatic vegetation (SAV) are ''clear,'' while lakes dominated by algae (high concentrations of chlorophyll a [Chl a]) are ''turbid.'' The roles of total phosphorus (TP) and SAV in defining these alternative states were examined for up to 6 yr in 24 naturally eutrophic shallow lakes (12.4-670.4 mg TP L 21 ) with variable SAV cover (0-100%) on the western Boreal Plain in Alberta, Canada. Clear lakes had ,18 mg Chl a L 21 . Sixty-seven percent of lakes were clear in any given year, but individual lakes did not remain clear over consecutive years. While 29% did not switch, 71% of lakes were unstable, with 57% switching states once and 14% switching more than once. To increase the temporal and spatial scale of analysis, we used Landsat Thematic Mapper satellite imagery (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) to classify clarity for up to 20 yr in 82 naturally eutrophic shallow lakes. Approximately 80% of lakes were unstable, with 7% switching once and more than 73% switching 2-9 times. Only 20% of lakes were stable and clear. Switches in lake clarity were related to TP but were also dependent on the abundance of SAV. For lakes with high SAV, the TP threshold for the transition from clear to turbid was 275 mg TP L 21 , while for lakes with low SAV, the TP threshold was 50 mg TP L 21 . Given the harsh winter conditions, including lakes with ice depths of up to 0.7 m and anoxia leading to winterkill of aquatic communities, these systems are strongly abiotically regulated and lack mechanisms that maintain a lake in a stable state.
The trophic status of shallow lakes on the Boreal Plain of Alberta exhibits high natural variatio... more 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...
Mapping groundwater discharge zones at broad spatial scales remains a challenge, particularly in ... more Mapping groundwater discharge zones at broad spatial scales remains a challenge, particularly in data sparse regions. We applied a regional scale mapping approach based on thermal remote sensing to map discharge zones in a complex watershed with a broad diversity of geological materials, land cover and topographic variation situated within the Prairie Parkland of northern Alberta, Canada. We acquired winter thermal imagery from the USGS Landsat archive to demonstrate the utility of this data source for applications that can complement both scientific and management programs. We showed that the thermally determined potential discharge areas were corroborated with hydrological (spring locations) and chemical (conservative tracers of groundwater) data. This study demonstrates how thermal remote sensing can form part of a comprehensive mapping framework to investigate groundwater resources over broad spatial scales.
Characterizing the spatial and temporal variation in surface hydrological dynamics of large borea... more Characterizing the spatial and temporal variation in surface hydrological dynamics 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 European Remote Sensing satellite 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. Using the regional Utikuma River drainage basin (2900 km 2 ) as the test area, the analyses of patterns of wetlands 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. Very wet climatic conditions were required before the disconnected 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 wetland probability maps have the potential to inform future biogeochemical and ecological investigations and forest management on the Boreal Plain.
Hjerdt N. 2009. Nature as the "natural" goal for water management: a conversation. Ambio 38: 209-... more Hjerdt N. 2009. Nature as the "natural" goal for water management: a conversation. Ambio 38: 209-214. Blenckner T. 2005. A conceptual model of climate-related effects on lake ecosystems. Hydrobiologia 533: 1-14. Brockerhoff EG, Jactel H, Parrotta JA, Quine CP, Sayer J. 2008. Plantation forests and biodiversity: oxymoron or opportunity? Biodiversity and Conservation 17: 925-951. Brooks RT. 2009. Potential impacts of global climate change on the hydrology and ecology of ephemeral freshwater systems of the forests of the northeastern United States. Climatic Change 95: 469-483. Buttle JM. 2002. Rethinking the donut-the case for hydrologicallyrelevant buffer zones. Hydrological Processes 16: 3093-3096. Chapin FS. 2009. Managing ecosystems sustainably: the key role of resilience. In Principles of Ecosystem Stewardship: Resilience-Based Natural Resource Management in a Changing World , Chapin FS, Kofinas GP, Folke C (eds). Springer: New York; 29-53. Creed IF, Sanford SE, Beall FD, Molot LA, Dillon PJ. 2003. Cryptic wetlands: integrating hidden wetlands in regression models of the export of dissolved organic carbon from forested landscapes. Hydrological Processes 17: 3629-3648. Creed IF, Sass GZ, Wolniewicz MB, Devito KJ. 2008. Incorporating hydrological dynamics into buffer strip design on the sub-humid Boreal Plain of Alberta. Forest Ecology and Management 256: 1984-1994. Creed IF, Sass GZ, Beall FD, Buttle JM, Moore RD, Donnelly M. In press (a). Hydrological principles for water conservation and sustainable forest management. A State of Knowledge report. Sustainable Forest Management Network, Edmonton, Alberta. Creed IF, Sass GZ, Beall FD, Buttle JM, Moore RD, Donnelly M. In press (b). Conserving water resources in our changing forested landscapes: a synthesis of the state-of-knowledge on scientific theory, data, and techniques. A State of Knowledge report. Sustainable Forest Management Network, Edmonton, Alberta. Creed IF, Sass GZ. 2011. Digital terrain analysis approaches for tracking hydrological and biogeochemical pathways and processes in forested landscapes. In Forest Hydrology and Biogeochemistry: Synthesis of Past Research and Future Directions, Levia D, Carlyle-Moses D, Tanaka T (eds). Springer-Verlag: New York. Creed IF, Beall FD. 2009. Distributed topographic indicators for predicting nitrogen export from headwater catchments. Water Resources Research 45: W10407. Croke JC, Hairsine PB. 2006. Sediment delivery in managed forests: a review.
The science of hydrology is on the threshold of major advances, driven by new hydrologic measurem... more The science of hydrology is on the threshold of major advances, driven by new hydrologic measurements, new methods for analyzing hydrologic data, and new approaches to modeling hydrologic systems . . . scientific progress will mostly be achieved through the collision of theory and data .
We would argue that any mapping or characterization of landscape heterogeneity and process comple... more We would argue that any mapping or characterization of landscape heterogeneity and process complexity must be driven by a desire to generalize and extrapolate observations from one place to another, or across multiple scales, and must not be allowed to perpetuate the notion of characterization or mapping for its own sake.
There is a critical need for spatially and temporally extensive information on the trophic status... more There is a critical need for spatially and temporally extensive information on the trophic status of lakes to assist in scientifically sound forest management decisions. To meet this need, this study examined the utility of Landsat TM imagery in deriving indicators of trophic status in remote and relatively undisturbed lakes on the Boreal Plain of northern Alberta. Based on data collected during a survey of lakes in 2001, normalized exoatmospheric reflectance values of the red band explained 68, 82, and 47% of the variance in chlorophyll a, turbidity, and Secchi disk depth, respectively. To understand the natural variation in trophic status in the lakes, we applied the linear regression equations to images collected during late summer (i.e., August) for 18 out of 20 years from 1984 to 2003 and performed a two-way analysis of variance to decompose the total variation into space, time, and space × time interaction factors. We found that temporal factors accounted for 10% and spatial factors accounted for 50% of the total variation in trophic status, with a minimum of 10 years and 20 lakes needed to reach stability in the contributions of these factors. This study suggests that regional factors that are external to the lake explained the majority (60%) of the variation in trophic status of the lakes.
1] We explored relations between climate and trophic status of shallow lakes (lake area > 5 ha, m... more 1] We explored relations between climate and trophic status of shallow lakes (lake area > 5 ha, mean depth < 3.2 m) located on the subhumid western Boreal Plain of Canada. Correlation and regression analyses were used to assess the association between indicators of climate and satellite-based estimates of trophic status (chlorophyll a (Chl a)). Chl a was derived using red band reflectance of Landsat satellite images for 76 lakes, which were then averaged for each year to produce a landscape median for summer (August) over a 20-year period from 1984 and 2003. Our results showed that climate was related to interannual changes in trophic status. Average May temperature was positively correlated to Chl a, suggesting the importance of conditions in the early part of the growing season. Growing season effective precipitation (P -PET) was negatively correlated to Chl a such that wetter conditions seemed to lead to a dilution of Chl a. Very wet years resulted in a larger Chl a drop than one expected by a linear model, suggesting greater water contribution from the landscape. P -PET explained 64% of the variance in Chl a using a nonlinear regression tree. Our study offers clues as to how shallow lake systems may behave on the subhumid Boreal Plain as a function of future climate change.
1] We used metrics of surface water and groundwater connectivity as explanatory variables in nonp... more 1] We used metrics of surface water and groundwater connectivity as explanatory variables in nonparametric regression models to explain the spatial heterogeneity in trophic status of shallow lakes. The concentration of chlorophyll a (Chl a) was used as an indicator of trophic status and was estimated from 17 Landsat images acquired during the end of summer (August) over a 20-year period from 1984 to 2003. A long-term median of Chl a was computed for each of 40 lakes on the basis of the 17-year data set. Hydrologic metrics explained 72% of the spatial variation in Chl a. The regression tree showed that lakes with a higher concentration of calcium plus magnesium (Ca + Mg) exhibited higher Chl a than lakes with a lower Ca + Mg. We hypothesized that this trend was a result of either higher internal nutrient loading in high Ca + Mg lakes due to groundwater discharge or differences in surficial geology. Among high Ca + Mg lakes, lakes with no inflowing streams had lower Chl a, while connected lakes had higher Chl a, possibly reflecting enhanced nutrient delivery to lakes connected to the stream network. Among low Ca + Mg lakes, lakes with larger wetland cover in their drainage basins had lower Chl a, while lakes with smaller wetland cover in their drainage basins had higher Chl a, possibly reflecting differential water loading rates between small and large wetlands that lead to either Chl a concentration or dilution. These results suggest that relatively simple hydrologic metrics can be used to predict the trophic status of lakes in this area of the boreal forest.
An airborne scanning light detection and ranging (lidar) survey using a discrete pulse return air... more An airborne scanning light detection and ranging (lidar) survey using a discrete pulse return airborne laser terrain mapper (ALTM) was conducted over the Utikuma boreal wetland area of northern Alberta in August 2002. These data were analysed to quantify vegetation class dependent errors in lidar ground surface elevation and vegetation canopy surface height. The sensitivity of lidar-derived land-cover frictional parameters to these height errors was also investigated. Aquatic vegetation was associated with the largest error in lidar ground surface definition (+0.15 m, SD = 0.22, probability of no difference in height P < 0.01), likely a result of saturated ground conditions. The largest absolute errors in lidar canopy surface height were associated with tall vegetation classes; however, the largest relative errors were associated with low shrub (63%, -0.52 m, P < 0.01) and aquatic vegetation (54%, -0.24 m, P < 0.01) classes. The openness and orientation of vegetation foliage (i.e., minimal projection of horizontal area) were thought to enhance laser pulse canopy surface penetration in these two classes. Raster canopy height models (CHMs) underestimated field heights by between 3% (aspens and black spruce) and 64% (aquatic vegetation). Lidar canopy surface height errors led to hydraulic Darcy-Weisbach friction factor underestimates of 10%-49% for short (<2 m) vegetation classes and overestimates of 12%-41% for taller vegetation classes.
We would argue that any mapping or characterization of landscape heterogeneity and process comple... more We would argue that any mapping or characterization of landscape heterogeneity and process complexity must be driven by a desire to generalize and extrapolate observations from one place to another, or across multiple scales, and must not be allowed to perpetuate the notion of characterization or mapping for its own sake.
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