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Lakes in the semiarid Southern Interior Plateau of British Columbia, Canada are vulnerable to future climate-driven changes in water quantity and quality. However, few long-term monitoring records exist to assess the effects of varying hydroclimate conditions on lake function. We present a high-resolution multiproxy paleolimnological record containing subfossil diatoms, μXRF via ITRAX, and chlorophyll-a that spans the past 1800 years from Roche Lake in south-central British Columbia. Generalized additive models indicate that the diatom assemblages were associated with changes in lake level and the accompanying effects of atmospheric forcing on lake thermal structure, and that these forcing mechanisms had a weak relationship with primary production. We infer two pronounced arid periods between ca. AD 600-950 and ca. AD 1730-1950 that correspond to evidence of reduced lake mixing and enhanced anoxia, but variable patterns in primary production. Synthesis of regional proxy records suggests that inferences of moist but possibly warm conditions during the Medieval Climate Anomaly may have occurred because of a complex interaction between prolonged La Niña-like conditions and higher radiative forcing. Overall, lakes in this region are sensitive to changes in hydroclimate generated by interactions between external forcing and Pacific Ocean-atmosphere processes, and the resulting changes in aridity may have potentially negative consequences on salmonid habitat. [ABSTRACT FROM AUTHOR]

The introduction of salmonids into lakes of western North America for sport fishing is a widespread phenomenon. While numerous investigations have documented cascading trophic interactions upon the introduction of fish into naturally fishless systems, little research has been done to investigate the importance of natural fish status (fishless vs. fish bearing) in modulating historical food web response to dual forcing by bottom-up (resource regulation from nutrients) and top-down (planktivory from stocked fish) processes. We used the paleolimnological record to reconstruct food web changes in four lakes in interior British Columbia that have been stocked with rainbow trout since the early to mid-1900s. Analysis of pigments, diatoms, and Cladocera was undertaken in cores from all lakes. We predicted that if fish were important in structuring cladoceran abundance and composition, we would document a decline in the abundance of large daphnids post-stocking in our two naturally fishless lakes, and little change in the two fish-bearing lakes. Instead, we documented increased abundance of large daphnids after stocking in all lakes in the early to mid-1900s, a finding inconsistent with size-selective predation from planktivorous fish. Further, our data suggest that deep, low-oxygen refugia may be important in sustaining populations of large Daphnia, a process which was enhanced by increased nutrients and lake production according to sub-fossil diatom and pigment analyses. This study shows that fish stocking does not invariably result in a decrease in large-bodied Cladocera and that nutrients and lake type can modulate the response of invertebrate planktivores. [ABSTRACT FROM AUTHOR]

Diatom and chironomid analysis of sediments encompassing the past 400 years from Bouchie Lake, British Columbia, suggests two distinct periods of limnological conditions. Prior to 1950 AD, Fragilaria construens and F. pinnata are the most common diatom species, and Chironomus, Procladius and Tanytarsini dominate the chironomid record. Moderately low nutrient concentrations consistent with oligo-mesotrophic lakes are inferred. From 1950, the diatom assemblage is dominated by Stephanodiscus parvus, a eutrophic indicator, whereas the chironomid communities show a relative increase in littoral taxa coincident with lower head capsule abundance. Higher nutrient levels, specifically total phosphorus, which increased from 8 μg L-1 prior to 1950 to 20 μg L-1 currently, are coincident with midge communities indicative of lower oxygen concentrations. Observed biotic changes and nutrient levels inferred from the sediment core correspond to historical land-use changes. [ABSTRACT FROM AUTHOR]

To develop models to predict past lake-water nutrient levels, the sedimentary remains of Cladocera were sampled from 53 lakes in central British Columbia, Canada. At the same time, the lakes were sampled for a suite of chemical variables. In addition, a host of physical and spatial explanatory variables were collected from each site. Canonical correspondence analysis showed that total phosphorus (TP), which ranged from 5 to 146 µg⋅L[sup-1], was the measured environmental variable that best described the differences in species composition among the lakes. Additionally, lake depth and surface water temperature were also important in explaining the distribution of cladoceran taxa. Chydorus brevilabris, Daphnia ambigua, Daphnia cf. pulex, and Graptoleberis testudinaria had a preference for eutrophic lakes, whereas Acroperus harpae, Alonella nana, Alonella excisa, Chydorus piger, Daphnia cf. dentifera, and Eubosmina spp. were found in the less productive lakes. Predictive models to estimate TP from species abundance data were developed using weighted averaging techniques. This research has produced strong and significant inference models, which can now be used to reconstruct past changes in lake trophic status from remains of Cladocera in sediment cores. [ABSTRACT FROM AUTHOR]

The Holocene Thermal Maximum (HTM) is relatively well-understood both in terms of its external drivers and timing of its expression in different regions across the globe, and has previously been used to investigate lake ecosystem response to a warm and drier climate. However, connections between mid-to-late Holocene climate, associated drivers, and lake response are less understood, particularly in western North America (WNA) where complex topography and differences in proximity to the Pacific coast result in spatially variable responses to ocean-atmosphere processes. Here, we present a multi-proxy paleolimnological record spanning 11,000 years from a small lake in the semi-arid southern Interior Plateau (SIP) of British Columbia. Sub-fossil diatom, trace element (μXRF via ITRAX), and pollen data indicate that our study lake was shallow, nutrient-poor, and poorly oxygenated during the HTM. High effective moisture (EM) is inferred throughout the mid-Holocene (∼6500–2000 calibrated years before present (cal yr BP)), followed by a return to low EM after 2000 cal yr BP. Synthesis of additional SIP diatom records show similarities in EM throughout the Holocene, but most notably, the decline in EM at ∼2000 cal yr BP. Comparison of patterns in the SIP with additional climate proxy data across WNA, including lake sediment δ18O records that are interpreted to represent changes in Pacific ocean-atmosphere processes, suggest that shifts in the mean state of the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO), and associated strength and position of the Aleutian Low, are linked with late Holocene declines in EM throughout the SIP. • A multi-proxy paleolimnological record of Holocene environmental change from interior B.C. is presented. • Diatom and micro-X-ray fluorescence data indicate the lake was shallow, nutrient-poor, and anoxic during the HTM. • Effective moisture was higher during the mid-Holocene (∼6500–2000 cal yr BP) compared to the late Holocene. • Diatom records from proximal interior B.C. lakes show coherent declines in effective moisture at ∼2000 cal yr BP. • WNA proxy data demonstrates the importance of PDO/ENSO dynamics on mid-to-late Holocene effective moisture. [ABSTRACT FROM AUTHOR]

Inferences of past climatic conditions from a sedimentary record from Big Lake, British Columbia, Canada, over the past 5,500 years show strong millennial-scale patterns, which oscillate between periods of wet and drier climatic conditions. Higher frequency decadal- to centennial-scale fluctuations also occur within the dominant millennial-scale patterns. These changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core. After periods of relative stability, abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1,220 years. The correspondence of these shifts to millennial-scale variations in records of glacial expansionrecession and ice-rafting events in the Atlantic suggest that abrupt millennial-scale shifts are important to understanding climatic variability in North America during the mid- to late Holocene. Unfortunately, the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood. Similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions.