18 research outputs found
Centennial-scale fluctuations and regional complexity characterize Pacific salmon population dynamics over the past five centuries
Observational data from the past century have highlighted the importance of interdecadal modes of variability in fish population dynamics, but how these patterns of variation fit into a broader temporal and spatial context remains largely unknown. We analyzed time series of stable nitrogen isotopes from the sediments of 20 sockeye salmon nursery lakes across western Alaska to characterize temporal and spatial patterns in salmon abundance over the past âŒ500 y. Although some stocks varied on interdecadal time scales (30- to 80-y cycles), centennial-scale variation, undetectable in modern-day catch records and survey data, has dominated salmon population dynamics over the past 500 y. Before 1900, variation in abundance was clearly not synchronous among stocks, and the only temporal signal common to lake sediment records from this region was the onset of commercial fishing in the late 1800s. Thus, historical changes in climate did not synchronize stock dynamics over centennial time scales, emphasizing that ecosystem complexity can produce a diversity of ecological responses to regional climate forcing. Our results show that marine fish populations may alternate between naturally driven periods of high and low abundance over time scales of decades to centuries and suggest that management models that assume time-invariant productivity or carrying capacity parameters may be poor representations of the biological reality in these systems
Centennial-scale fluctuations and regional complexity characterize Pacific salmon population dynamics over the past five centuries
Observational data from the past century have highlighted the importance of interdecadal modes of variability in fish population dynamics, but how these patterns of variation fit into a broader temporal and spatial context remains largely unknown. We analyzed time series of stable nitrogen isotopes from the sediments of 20 sockeye salmon nursery lakes across western Alaska to characterize temporal and spatial patterns in salmon abundance over the past âŒ500 y. Although some stocks varied on interdecadal time scales (30- to 80-y cycles), centennial-scale variation, undetectable in modern-day catch records and survey data, has dominated salmon population dynamics over the past 500 y. Before 1900, variation in abundance was clearly not synchronous among stocks, and the only temporal signal common to lake sediment records from this region was the onset of commercial fishing in the late 1800s. Thus, historical changes in climate did not synchronize stock dynamics over centennial time scales, emphasizing that ecosystem complexity can produce a diversity of ecological responses to regional climate forcing. Our results show that marine fish populations may alternate between naturally driven periods of high and low abundance over time scales of decades to centuries and suggest that management models that assume time-invariant productivity or carrying capacity parameters may be poor representations of the biological reality in these systems
Large increases in carbon burial in northern lakes during the Anthropocene
This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the articleâs Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/Northern forests are important ecosystems for carbon (C) cycling and lakes within them process and bury large amounts of organic-C. Current burial estimates are poorly constrained and may discount other shifts in organic-C burial driven by global change. Here we analyse a suite of northern lakes to determine trends in organic-C burial throughout the Anthropocene. We found burial rates increased significantly over the last century and are up to five times greater than previous estimates. Despite a correlation with temperature, warming alone did not explain the increase in burial, suggesting the importance of other drivers including atmospherically deposited reactive nitrogen. Upscaling mean lake burial rates for each time period to global northern forests yields up to 4.5âPgâC accumulated in the last 100 yearsâ20% of the total burial over the Holocene. Our results indicate that lakes will become increasingly important for C burial under future global change scenarios
Seasonal and regional controls of phytoplankton production along a climate gradient in south-west greenland during ice-cover and ice-free conditions
Across a small geographic area (< 180 km), the region of South West Greenland covers a
natural climate gradient. Variation in temperature and precipitation result in marked
differences in limnology at three discrete locations: ice sheet margin, inland and the coast.
Replicate lakes from each location were sampled for physical (temperature, light), chemical
(dissolved oxygen, pH, conductivity, nutrients) and biological (chlorophyll a (Chl a),
photosynthetic pigments) variables on three occasions within a 12 month period: July - August 2010, April - May 2011 and June - July 2011 spanning ice cover. Variation in ice
phenology was linked to the climate gradient; however phytoplankton production and
community composition did not differ regionally. Large-scale seasonal fluctuations in
temperature and nutrient availability were the strongest predictors of phytoplankton
production, with a shift from nitrate to phosphorus controlled production between ice cover
and ice free conditions. Underlying seasonal drivers, variables predicting production were
unique to each location: ice sheet margin (soluble reactive phosphorus), inland (temperature)
and coast (silicate) and reflect local differences in nutrient availability. Results from the
current study have important consequences when controls over phytoplankton production in Arctic lakes are inferred from a limited number of sites, but up-scaled to represent pan-Arctic trends