Ecological, landscape, and climatic regulation of sediment geochemistry in North American sockeye salmon nursery lakes: Insights for paleoecological salmon investigations

Selbie, Daniel T., Bruce P. Finney, David Barto, Lynda Bunting, Guangjie Chen, Peter R. Leavitt, Erland A. MacIsaac, Daniel E. Schindler, Mark D. Shapley, Irene Gregory-Eaves

Limnol. Oceanogr., 54(5), 2009, 1733-1745 | DOI: 10.4319/lo.2009.54.5.1733

ABSTRACT: We used multiple linear regressions across a Northeast Pacific region 56-lake set to examine the influence of sockeye salmon spawner densities and limnological, climatic, and watershed characteristics on sediment stable nitrogen isotope (δ¹⁵N) and C:N signatures, geochemical proxies used in paleolimnological reconstructions of prehistoric salmon abundances. Across all sites (n = 56), sedimentary C:N was primarily related to variables reflecting allochthonous organic matter and nutrient fluxes, with 67% of the variance explained by watershed vegetation type, watershed area, mean slope, and salmon spawner densities. In a subset of sites with nutrient data (n = 41), 63% of variance in C:N was explained by precipitation and watershed vegetation type. Sediment δ¹⁵N was most strongly related to salmon spawner densities, but C:N and watershed area : lake area ratios explained significant residual variance (total 55%). In sites with nutrient data, salmon spawner densities, vegetation type, and spring nitrate explained 62% of the variance in d15N. Sediment C:N and δ¹⁵N values exhibited distinct interregional variation, typically varying inversely. Regional d15N-salmon density relationships (regression slopes) varied strongly with total annual precipitation (r² = 0.89, p = 0.016, n = 5), suggesting watershed organic matter and nutrient loading vary predictably in relation to regional biogeoclimatic conditions. Our findings demonstrate that paleolimnological analyses are useful for quantitative reconstruction of past salmon densities; however, inferences regarding past salmon populations must consider the factors regulating influxes of nitrogen from watershed sources.