Long-term spatial trends in sedimentary algal pigments in a narrow river-valley reservoir, Lake Diefenbaker, Canada T.J. Tse a,b, ⁎, L.E. Doig a,b , P.R. Leavitt c , Z.J. Quiñones-Rivera c , G. Codling a , B.T. Lucas a,b , K. Liber a,b,e , J.P. Giesy a,b,f , H. Wheater b , P.D. Jones a,b,d a Toxicology Center, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, S7N 5B3, Canada b Global Institute for Water Security, University of Saskatchewan, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada c Department of Biology, Limnology Laboratory, University of Regina, 3737 Wascana Parkway, Regina, SK, S4S 0A2, Canada d School of Environment and Sustainability, University of Saskatchewan, 117 Science Place, Saskatoon, SK, S7N 5C3, Canada e Institute of Loess Plateau, Shanxi University, Taiyuan, Shanxi, PR China f Department of Veterinary Biomedical Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada abstract article info Article history: Received 9 July 2014 Accepted 7 August 2015 Available online 1 September 2015 Communicated by Rebecca L North Index words: Reservoir Pigments Spatial structure Temporal trend Sediment Chlorophyll a Narrow river-valley reservoirs are typically spatially heterogeneous. Little is known about how (a) water quality and algal community composition change longitudinally along a reservoir and (b) how algal composition and production change as a reservoir ages. To address these unknowns, multiple sediment cores were collected from mid-channel locations along the longitudinal axis of Lake Diefenbaker, Saskatchewan, Canada, a long, nar- row river-valley reservoir on the Canadian Prairies. Profiles of concentrations of various pigments in sediment cores were measured to infer spatial and temporal trends in algal biomass and community composition. Diverse mixtures of pigments derived from filamentous and colonial cyanobacteria, diatoms, chlorophytes, and other phyla were observed. Spatial patterns of sedimentation of pigments (nmol m -2 yr -1 ) in surficial sediments sug- gest increases in algal biomass with distance down-reservoir, with maximum inferred biomass occurring in mid- reservoir. This is consistent with general knowledge of patterns of primary production in narrow, river-valley res- ervoirs. However, myxoxanthophyll, a biomarker of filamentous or colonial cyanobacteria, detected only at sites furthest down-reservoir, did not follow this general trend. Temporally, an increase in algal biomass occurred at down-reservoir locations after 1990, followed by a substantial increase after 2000 at the majority of sites. Profiles of concentrations of pigments exhibited no clear trends to support the prevailing paradigm that predicts an initial upsurge in trophic status upon formation of reservoirs. This pattern may result from limited penetration of light in the early years after reservoir formation. This study reinforces the need for paleolimnological analyses among hydrologic zones of large reservoirs. © 2015 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved. Introduction Water quality of lakes and reservoirs in some areas of North America and Europe is believed to be deteriorating (Cooke et al., 2005). In partic- ular, cultural eutrophication is causing undesirable changes in aquatic communities (Pretty et al., 2003) due to changes in trophic relation- ships, elevated external nutrient loads, nutrient stoichiometry, and transport of nutrients from benthic to pelagic regions (Schindler, 2006). Water quality loss is especially problematic for potable supplies where costly purification processes must be used to reduce offensive tastes, odors and algal toxins, while minimizing production of hazard- ous disinfection by-products. Unfortunately, long-term monitoring data are often lacking for potable water supplies within the Canadian Prairies. Such information is essential to assess long-term trends in environmental quality and inform resource management decisions. Monitoring can be performed by local water authorities, but the param- eters measured are often limited in scope and spatial extent. Long-term monitoring efforts tend to be initiated only after serious problems arise (Kohler, 2010). Therefore, various paleolimnological tools, especially those involving analysis of chemical characteristics and biological re- mains within the sediments, are gaining popularity as a means of reconstructing past changes in the environmental quality of inland wa- ters. To date, such studies are abundant for natural lakes but are less commonly used for manmade reservoirs. This trend, however, appears to be changing since it has been recognized that stratigraphies of undis- turbed sediments can be found in deeper regions of reservoirs (Sholbolt et al., 2001) and that these sediments represent potential sources of long-term environmental information that can be used to inform ongo- ing management decisions. Paleolimnological investigations typically rely on a small number of sampling stations, often a single representative site, to assess the overall Journal of Great Lakes Research 41 Supplement 2 (2015) 56–66 ⁎ Corresponding author. Tel.: +1 306 966 4557. E-mail address: tse.tjt@gmail.com (T.J. Tse). http://dx.doi.org/10.1016/j.jglr.2015.08.002 0380-1330/© 2015 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Great Lakes Research journal homepage: www.elsevier.com/locate/jglr