Spatial variability of stable isotopes and fossil pigments in surface sediments of Alaskan coastal lakes: Constraints on quantitative estimates of past salmon abundance

Abstract

We quantified spatial patterns of stable isotopes of N and C (δ15N, δ13C) and fossil pigment concentrations in the uppermost 10 mm of sediment (,10 yr) from 74 profundal locations and three spawning‐stream discharge areas in Lake Nerka, southwest Alaska. Sediment δ15N (4.3% ± 0.7%) and δ13C (−26.3% ± 1.2%) varied directly (δ15N) or inversely (δ13C) with water column depth, whereas concentrations of most fossil pigments from algae were negatively correlated with depth. Sediment δ15N and δ13C were poorly correlated with either fossil pigment abundance or the local densities of spawning salmon. Instead, coastal nursery lakes appeared to integrate marine‐derived nutrients rapidly into lakewide nutrient pools, suggesting that while individual cores may be used to reconstruct whole‐lake salmon densities, habitat‐specific variations of past fish populations cannot be quantified reliably from sedimentary analyses.