Impacts of climate and river flooding on the hydro-ecology of a floodplain basin, Peace-Athabasca Delta, Canada since A.D. 1700

Abstract

Multi-proxy paleolimnological analyses on lake sediment cores from "Spruce Island Lake" (58° 50.82′ N, 111° 28.84′ W), a perched basin in the northern Peace sector of the Peace-Athabasca Delta (PAD), Canada, give insights into the relative roles of flow regulation of the Peace River and climatic variability on the basin hydro-ecology. Results indicate substantial variability in basin hydro-ecology over the past 300 years ranging from seasonal to periodic desiccation in the 1700s to markedly wetter conditions during the early 1800s to early 1900s. The reconstruction is consistent with (1) dry climatic conditions that defined the peak of the Little Ice Age and subsequent amelioration evident in conventional ring-width and isotopic analyses of tree-ring records located hydrologically and climatically upstream of the PAD, and (2) Peace River flood history inferred from sub-annual magnetic susceptibility measurements from another lake sediment record in the Peace sector of the PAD. Although regulation of the Peace River for hydroelectric power generation since 1968 has long been considered a major stressor of the PAD ecosystem leading to reduced frequency of ice-jam and open-water flooding and an extended period of drying, our results show that current hydro-ecological status is not unprecedented as both wetter and drier conditions have persisted for decades in the recent past under natural climatic variability. Furthermore, paleolimnological evidence from Spruce Island Lake indicates that recently observed dryness is part of a longer trend which began some 20�"40 years prior to Peace River regulation.

Flood Frequency Variability During the Past 80 Years in the Slave River Delta, NWT, as Determined from Multi-Proxy Paleolimnological Analysis

“…To supplement discharge data from the sparse river gauge network, multi-proxy paleolimnological studies of lake sediment records have been conducted in the PAD to investigate long-term variability in flood frequency. These studies aimed to tease apart the effects of multiple stressors on the hydrological regime of northern rivers, and to provide context within which to evaluate causes of contemporary hydrological change (Wolfe et al, 2005;2008a;b). Results have revealed that lakes perched above the river system may persist for decades in the absence of spring flooding (Wolfe et al, 2005), while others may dry up within a decade following a flood event (Peters et al, 2006a;Jaques, 1989).…”

“…These studies aimed to tease apart the effects of multiple stressors on the hydrological regime of northern rivers, and to provide context within which to evaluate causes of contemporary hydrological change (Wolfe et al, 2005;2008a;b). Results have revealed that lakes perched above the river system may persist for decades in the absence of spring flooding (Wolfe et al, 2005), while others may dry up within a decade following a flood event (Peters et al, 2006a;Jaques, 1989). Additionally, there have been oscillating multi-decadal periods of both high and low flood frequency over the last several hundred years, suggesting marked natural variability in flood recurrence intervals (Wolfe et al, 2006;2008a).…”

Application of Floodplain Stratigraphy to Determine the Recurrence of Ice-Jam Flooding Along the Lower Peace and Athabasca Rivers, Alberta

“…In the absence of lengthy hydrometric time series, a number of studies have used indirect proxy methods to extend the record of ice-jam flood activity in the PAD (Thomson, 1993;Peterson, 1995;Timoney et al, 1997;Timoney, 2002;Wolfe et al, 2005;. One approach involved historical documents, local knowledge and hydrometric data to develop a lengthy chronology of ice-jam floods along the lower Peace River (Thomson, 1993;Peterson, 1995;Timoney et al, 1997).…”

“…The compilation of information indicates 28 ice-jam floods ranging in magnitude from moderate to major occurred along the lower Peace River between 1826 and 2000, which translates to a 16% probability of recurrence in any given year (Timoney et al, 1997;Timoney, 2002). More recently, Wolfe et al (2005; used lake sediment cores to reconstruct water levels in perched basins as a proxy for ice-jam flooding. From high-resolution records extending back 300 years, Wolfe et al (2005; interpreted a highly variable flood chronology with several multi-decadal periods of low water levels.…”

“…More recently, Wolfe et al (2005; used lake sediment cores to reconstruct water levels in perched basins as a proxy for ice-jam flooding. From high-resolution records extending back 300 years, Wolfe et al (2005; interpreted a highly variable flood chronology with several multi-decadal periods of low water levels. These results indicate that prolonged periods when ice-jam flooding is absent or low in magnitude are a natural feature of the PAD ecosystem, independent of anthropogenic flow regulation associated with the W.A.C.…”