Browsing by Author "Cumming, Brian F."

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Open Access
Bottom-Up Forces Drive Increases in the Abundance of Large Daphnids in Four Small Lakes Stocked with Rainbow Trout (Oncorhynchus mykiss), Interior British Columbia, Canada
(Springer, 2019-09-23) Mushet, Graham R.; Laird, Kathleen R.; Leavitt, Peter R.; Maricle, Stephen; Klassen, Andrew; Cumming, Brian F.
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.
Open Access
Effects of spatial variation in benthic phototrophs along a depth gradient on assessments of whole-lake processes
(Wiley, 2021-09-16) Gushulak, Cale A. C.; Haig, Heather A.; Kingsbury, Melanie V.; Wissel, Bjoern; Cumming, Brian F.; Leavitt, Peter R.
1. Phytobenthos are often underrepresented in both limnological and paleolimnological studies but may play key roles in whole-lake production and ecosystem processes including eutrophication, food-web dynamics, and ecosystem state changes. 2. Photosynthetic pigments, stables isotopes, and diatoms were quantified from surface sediments (0-1 cm) collected across a depth transect of a small, DOC-rich, mesotrophic lake in boreal northwestern Ontario to assess spatial variation in phytobenthos abundance and production. 3. Maximal concentrations of siliceous algae and cyanobacteria pigments occurred at ~2–6 m depth, with abundant tychoplanktonic diatoms, depleted sedimentary δ13C C values, and elevated 33 ratios of precursor chlorophyll a to product pheophytin a, all aligning well with the depths of the thermocline, epilimnetic mixing, and maximum light penetration. 4. These patterns demonstrated the presence of three discrete community assemblages, with greatest mass accumulation occurring at intermediate depths where warm illuminated sediments provide habitat for tychoplanktonic diatoms and cyanobacteria between turbulent shallows and cold and dark depths. 5. If widespread among boreal lakes, this tychoplanktonic zone may exert important effects on whole-lake production, carbon sequestration, benthic-pelagic food-web coupling, eutrophication, and ecosystem state change.
Open Access
Impacts of a century of land-use change on the eutrophication of large, shallow, prairie Lake Manitoba in relation to adjacent Lake Winnipeg (Manitoba, Canada)
(John Wiley & Sons Ltd., 2023-11-08) Gushulak, Cale A. C.; Mezzini, Stefano; Moir, Katherine E. M; Simpson, Gavin L.; Bunting, Lynda; Wissel, Björn; Engstrom, Daniel R.; Laird, Kathleen R.; Amand, Ann St.; Cumming, Brian F.; Leavitt, Peter R.
1. Evaluation of large lake response to centennial changes in land use and climate can be complicated by high spatial and hydrological complexity within their catchments, particularly in regions of low relief. Furthermore, large lakes can exhibit abrupt changes in structure and function that obscure causes of eutrophication. 2. We provide the first quantification of historical trends in lake production, cyanobacterial abundance, sediment geochemistry and diatom composition since c. 1800 in Lake Manitoba, the 29th largest lake in the world, and compared them to Lake Winnipeg, a morphologically similar, adjacent basin with a 10-fold larger catchment and an abrupt increase in production around 1990. 3. Before 1900, Lake Manitoba was mesotrophic, with low sedimentary concentrations of carbon, phosphorus, nitrogen, cyanobacteria and algal pigments, as well as assemblages of low-light-adapted benthic diatoms. Analysis of pigment time-series with hierarchical generalised additive models revealed that Lake Manitoba eutrophied during 1900–1930 as a consequence of the development of intensive agriculture within its local catchment, but thereafter exhibited stable cyanobacterial densities with limited expansion of N2-fixing cyanobacteria despite persistent eutrophication. 4. Lake Manitoba did not undergo an abrupt change as seen in Lake Winnipeg. 5. These findings suggest that catchment size had little influence on water quality degradation and that nutrient influx from proximal agricultural sources was sufficient to initially degrade these large prairie lakes. The abrupt change in Lake Winnipeg around 1990 required additional intensification of local land use that did not occur in the Lake Manitoba catchment.
Open Access
Influence of cultural eutrophication, climate, and landscape connectivity on 3 Kawartha lakes (Ontario, Canada) since the early 1800s
(Wiley, 2023-06-02) Laird, Kathleen R.; Li, Shirui; Gushulak, Cale A. C.; Moir, Katherine E.; Wang, Yuxiang; Cumming, Brian F.
Paleolimnological analyses of 3 lakes within the Trent-Severn Waterway (TSW) were analyzed 19 to evaluate the role of regional land-use practices (forestry and agriculture), climate change, and 20 landscape position on cultural eutrophication and lake response over the past ~200 years.
Open Access
Paleolimnological assessment of nutrient enrichment on diatom assemblages in a priori defined nitrogen- and phosphorus-limited lakes downwind of the Athabasca Oil Sands, Canada
(PAGEpress, 2017-04-14) Laird, Kathleen R.; Das, Biplob; Hesjedal, Brittany; Leavitt, Peter R.; Mushet, Graham R.; Scott, Kenneth A.; Simpson, Gavin L.; Wissel, Bjorn; Wolfe, Jared; Cumming, Brian F.
As the industrial footprint of the Athabasca Oil Sands Region (AOSR) continues to expand, concern about the potential impacts of pollutants on the surrounding terrestrial and aquatic ecosystems need to be assessed. An emerging issue is whether recent increases in lake production downwind of the development can be linked to AOSR activities, and/or whether changing climatic conditions are influencing lake nutrient status. To decipher the importance of pollutants, particularly atmospheric deposition of reactive nitrogen (Nr), and the effects of climate change as potential sources of increasing lake production, lakes from both within and outside of the nitrogen deposition zone were analyzed for historical changes in diatom assemblages. Lake sediment cores were collected from a priori defined nitrogen (N) - and phosphorus (P) - limited lakes within and outside the N plume associated with the AOSR. Diatom assemblages were quantified at sub-decadal resolution since ca. 1890 to compare conditions prior to oil sands expansion and regional climate warming, to the more recent conditions in each group of lakes (Reference and Impacted, N- and P-limited lakes). Analyses of changes in assemblage similarity and species turnover indicates that changes in diatom assemblages were minimal both within and across all lake groups. Small changes in percent composition of planktonic taxa, particularly small centric taxa (Discostella and Cyclotella species) and pennate taxa, such as Asterionella formosa and Fragilaria crotonensis, occurred in some of the lakes. While these changes were consistent with potential climate effects on algal growth, water column stability and other factors; the timing and direction of biotic changes were variable among sites suggesting that any apparent response to climate was lake dependent. The absence of a consistent pattern of diatom changes associated with receipt of reactive nitrogen or intrinsic nutrient-limitation status of the lake suggest that downwind AOSR emissions had no demonstrable effect on diatom composition.