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

We quantified spatial patterns of stable isotopes of N and C ((delta)^15N, (delta)^13C) 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 (delta)^15N (4.3% (plus-minus) 0.7%) and d13C (-26.3%(plus-minus) 1.2%) varied directly ((delta)^15N) or inversely ((delta)^13C) with water column depth, whereas concentrations of most fossil pigments from algae were negatively correlated with depth. Sediment (delta)^15N and (delta)^13C 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.