Patterns of ecosystem metabolism in the Tonle Sap Lake, Cambodia with links to capture fisheries.

Written by

Related Articles

Patterns of ecosystem metabolism in the Tonle Sap Lake, Cambodia with links to capture fisheries.

PLoS One. 2013;8(8):e71395

Authors: Holtgrieve GW, Arias ME, Irvine KN, Lamberts D, Ward EJ, Kummu M, Koponen J, Sarkkula J, Richey JE

Abstract
The Tonle Sap Lake in Cambodia is a dynamic flood-pulsed ecosystem that annually increases its surface area from roughly 2,500 km(2) to over 12,500 km(2) driven by seasonal flooding from the Mekong River. This flooding is thought to structure many of the critical ecological processes, including aquatic primary and secondary productivity. The lake also has a large fishery that supports the livelihoods of nearly 2 million people. We used a state-space oxygen mass balance model and continuous dissolved oxygen measurements from four locations to provide the first estimates of gross primary productivity (GPP) and ecosystem respiration (ER) for the Tonle Sap. GPP averaged 4.1±2.3 g O2 m(-3) d(-1) with minimal differences among sites. There was a negative correlation between monthly GPP and lake level (r = 0.45) and positive correlation with turbidity (r = 0.65). ER averaged 24.9±20.0 g O2 m(-3) d(-1) but had greater than six-fold variation among sites and minimal seasonal change. Repeated hypoxia was observed at most sampling sites along with persistent net heterotrophy (GPP<ER), indicating significant bacterial metabolism of organic matter that is likely incorporated into the larger food web. Using our measurements of GPP, we calibrated a hydrodynamic-productivity model and predicted aquatic net primary production (aNPP) of 2.0±0.2 g C m(-2) d(-1) (2.4±0.2 million tonnes C y(-1)). Considering a range of plausible values for the total fisheries catch, we estimate that fisheries harvest is an equivalent of 7-69% of total aNPP, which is substantially larger than global average for marine and freshwater systems. This is likely due to relatively efficient carbon transfer through the food web and support of fish production from terrestrial NPP. These analyses are an important first-step in quantifying the resource pathways that support this important ecosystem.

PMID: 23967203 [PubMed – indexed for MEDLINE]

via pubmed: school of aquatic an… http://ift.tt/1n0wnwL

Patterns of ecosystem metabolism in the tonle sap lake, cambodia with links to capture fisheries.

Written by

Related Articles

Patterns of ecosystem metabolism in the tonle sap lake, cambodia with links to capture fisheries.

PLoS One. 2013;8(8):e71395

Authors: Holtgrieve GW, Arias ME, Irvine KN, Lamberts D, Ward EJ, Kummu M, Koponen J, Sarkkula J, Richey JE

Abstract
The Tonle Sap Lake in Cambodia is a dynamic flood-pulsed ecosystem that annually increases its surface area from roughly 2,500 km(2) to over 12,500 km(2) driven by seasonal flooding from the Mekong River. This flooding is thought to structure many of the critical ecological processes, including aquatic primary and secondary productivity. The lake also has a large fishery that supports the livelihoods of nearly 2 million people. We used a state-space oxygen mass balance model and continuous dissolved oxygen measurements from four locations to provide the first estimates of gross primary productivity (GPP) and ecosystem respiration (ER) for the Tonle Sap. GPP averaged 4.1±2.3 g O2 m(-3) d(-1) with minimal differences among sites. There was a negative correlation between monthly GPP and lake level (r = 0.45) and positive correlation with turbidity (r = 0.65). ER averaged 24.9±20.0 g O2 m(-3) d(-1) but had greater than six-fold variation among sites and minimal seasonal change. Repeated hypoxia was observed at most sampling sites along with persistent net heterotrophy (GPP<ER), indicating significant bacterial metabolism of organic matter that is likely incorporated into the larger food web. Using our measurements of GPP, we calibrated a hydrodynamic-productivity model and predicted aquatic net primary production (aNPP) of 2.0±0.2 g C m(-2) d(-1) (2.4±0.2 million tonnes C y(-1)). Considering a range of plausible values for the total fisheries catch, we estimate that fisheries harvest is an equivalent of 7-69% of total aNPP, which is substantially larger than global average for marine and freshwater systems. This is likely due to relatively efficient carbon transfer through the food web and support of fish production from terrestrial NPP. These analyses are an important first-step in quantifying the resource pathways that support this important ecosystem.

PMID: 23967203 [PubMed – in process]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/pubmed/23967203?dopt=Abstract

Centennial-scale fluctuations and regional complexity characterize Pacific salmon population dynamics over the past five centuries.

Written by

Centennial-scale fluctuations and regional complexity characterize Pacific salmon population dynamics over the past five centuries.

Proc Natl Acad Sci U S A. 2013 Jan 15;

Authors: Rogers LA, Schindler DE, Lisi PJ, Holtgrieve GW, Leavitt PR, Bunting L, Finney BP, Selbie DT, Chen G, Gregory-Eaves I, Lisac MJ, Walsh PB

Abstract
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 ∼500 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.

PMID: 23322737 [PubMed – as supplied by publisher]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/PubMed/23322737?dopt=Abstract