Remote Sensing of Landslide-Generated Sediment Plumes, Peace River, British Columbia

Quantifying the contribution of sediment delivered to rivers by landslides is needed to assess a river’s sediment load in regions prone to mass wasting. Monitoring such events, however, remains difficult. This study utilised six years of remotely sensed imagery (PlanetScope and RapidEye, Imagery courtesy of Planet Labs, Inc., San Francisco, CA, USA), topographic surveys, and field observation to examine a hydro-geologically controlled, retrogressive landslide near a tributary to the Peace River, British Columbia. The slide has been active since 2014, delivering large amounts of sediment to the Peace River, visible in a persistent plume. Here, we quantify the landslide’s sediment contribution to the Peace River, assess the hydro-meteorological drivers of plume variability, and test whether plume activity can be directly linked to landslide activity for monitoring purposes. Our results show that the landslide on average delivered 165,000 tonnes of sediment per year, a seven-fold increase of the tributary’s regular load and near half of the Peace River’s load at this location. Due to continuous erosion of landslide material, sediment supply is steady and fuelled by repeated failures. Using thresholding, the identification of ‘high’ plume activity was possible, which positively correlated with the water level in a nearby reservoir, a proxy for the state of groundwater in this region. We reason that ‘high’ plume activity is linked to increased groundwater pressure because landslide activity is groundwater-controlled and failures fuel sediment delivery to the Peace River. Using readily available imagery, it is thus possible to monitor the activity of this recurrent landslide when field data are difficult to obtain.

Analyses of Peace River Shallow Water Ice Profiling Sonar data and their implications for the roles played by frazil ice and in situ anchor ice growth in a freezing river

Peace River SWIPS (Shallow Water Ice Profiling Sonar) data were analyzed to quantify the roles of frazil ice and riverbed anchor ice grown in situ during the initial buildup of a seasonal ice cover. Data were derived through quasi-continuous monitoring of frazil parameters throughout the water column, providing direct and indirect measures of anchor ice volume and mass growth rates. Analyses utilized water level and air and water temperature information in conjunction with acoustic volume backscattering coefficient data to track and interpret spatial and temporal changes in riverbed and water column ice. Interest focused on four frazil intervals characterized by anomalously low levels of frazil content (relative to simulations with an anchor-ice-free river ice model) as distinguished by two strikingly different types of time dependences. A simple physical model was proposed to quantitatively account for discrepancies between measured and simulated results in terms of the pronounced dominance of anchor ice as an initial source of river ice volume and mass. The distinctive differences in temporally variable water column frazil content are attributed, in this model, to corresponding differences in the stabilities of riverbed anchor ice layers against detachment and buoyancy-driven movement to the river surface. In accord with earlier observations, the stability of in situ grown riverbed ice layers appears to be inversely proportional to cooling rates. The strength of the coupling between the two studied ice species was shown to be strong enough to detect changes in the anchor ice constituent from variations in water column frazil content.

Diversity, rate, and distribution of wheat midge parasitism in the Peace River region of Alberta, Canada

Wheat midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), is a major pest of wheat (Poaceae) that was first reported in the Peace River region of northwestern Alberta, Canada in 2011. Although parasitism is an important factor of mortality in wheat midge elsewhere, little is known about the prevalence, species, or distribution of wheat midge parasitoids in the Peace River region. To address this knowledge gap, we conducted a survey of wheat midge parasitoids in commercial wheat fields across the region in 2016 and 2017. For a given field, parasitism of wheat midge larvae ranged from 36 to 71%. All but one parasitoid (n = 2167) were identified as Macroglenes penetrans (Kirby) (Hymenoptera: Pteromalidae). The exception was a specimen in the genus Inostemma tentatively identified as I. walkeri Kieffer (Hymenoptera: Platygasteridae). These findings identify parasitism as an important factor that is suppressing populations of wheat midge in the Peace River region, provide the first report of Inostemma walkeri for North America, and provide the first report of this species as a parasitoid of S. mosellana.

A Bayesian mixing model framework for quantifying temporal and spatial variation in source of sediment to lakes across hydrological gradients of floodplains

<p>Episodic flood events are critical for recharging water balance of floodplain lakes and maintaining their ecological integrity, yet are subject to alteration in frequency and magnitude by natural and anthropogenic processes that operate over a range of spatial and temporal scales. To evaluate roles of potential stressors, paleolimnological reconstructions are used to obtain insights into hydrological variability of dynamic floodplain lakes. However, spatial and temporal integration is often underdeveloped because different paleolimnological measurements must be applied across lakes due to the wide range of energy conditions that impart marked differences in sediment composition. Here, we use a linear discriminant analysis to identify 10 significant elemental concentrations in surveyed sediment from multiple sampling campaigns that distinguish the geochemical fingerprints of three end-member sources in lakes at the Peace-Athabasca Delta (PAD; Canada): the Athabasca River, the Peace River and local catchment runoff. Over 90% of the sediment samples were correctly classified into the original groups after cross-validation due to the distinctiveness of the three end members, which permits development of a robust Bayesian mixing model to discern the relative contributions of sediment from the three sources. We evaluate the mixing model at two adjacent lakes in the Athabasca sector of the PAD and demonstrate its effectiveness to discriminate three known hydrological phases during the past 300 years. Notably, the model infers ~60% of the sediment originated from the Peace River during the largest ice-jam flood event on record (1974), which was unrecognized by other methods. We then applied our model to sediment records from 18 lakes spanning the hydrological gradients across the 6000 km<sup>2</sup> PAD to further probe the hydrological evolution during the past ~150 years. Results demonstrate decline in frequency of flooding from both the Athabasca and Peace rivers and lake-level drawdown since the early 20<sup>th</sup> century and align remarkably well with prior interpretation of conventional paleohydrological records of individual lakes. We advocate our approach provides a universal method that can be applied across the full range of sediment composition to quantify change in source, frequency and magnitude of river floodwaters to lakes and is transferable to other dynamic floodplain landscapes where variation of sediment composition challenges efficacy of other approaches.</p>

Seasonal emergence patterns of Sitodiplosis mosellana (Diptera: Cecidomyiidae) in the Peace River region, Alberta, Canada

Wheat midge, Sitodiplosis mosellana Géhin (Diptera: Cecidomyiidae), is an invasive pest of wheat, Triticum spp. (Poaceae), in North America and is found in all wheat-growing regions of the world. Wheat midge biology, particularly post-diapause emergence of adults, varies with geographic region. The biology of wheat midge has not previously been examined in the northernmost area of its range in Canada – the Peace River region of Alberta. Wheat midge adult emergence was compared in situ to two phenological models of wheat midge emergence developed in other geographic regions. In-field adult emergence did not match the published phenological models. In the Peace River region, adults emerged later than are predicted by both models and precision for both models was low. With the Saskatchewan model, accumulated rainfall that was more than 110 mm in May and early June delayed emergence, whereas accumulated rainfall that was less than 43 mm during that period caused earlier than predicted emergence. Multiple peaks of wheat midge emergence, up to 20 days apart, were observed at some sites, supporting the Jacquemin model depicting “waves” of emergence. Including differences in soil temperature accumulation related to precipitation and optimising the model temperature thresholds would improve accuracy of the current Canadian phenological model in the Peace River region.