A Global lake ecological observatory network (GLEON) for synthesising high-frequency sensor data for validation of deterministic ecological models

A Global Lake Ecological Observatory Network (GLEON; www.gleon.org) has formed to provide a coordinated response to the need for scientific understanding of lake processes, utilising technological advances available from autonomous sensors. The organisation embraces a grassroots approach to engage researchers from varying disciplines, sites spanning geographic and ecological gradients, and novel sensor and cyberinfrastructure to synthesise high-frequency lake data at scales ranging from local to global. The high-frequency data provide a platform to rigorously validate processbased ecological models because model simulation time steps are better aligned with sensor measurements than with lower-frequency, manual samples. Two case studies from Trout Bog, Wisconsin, USA, and Lake Rotoehu, North Island, New Zealand, are presented to demonstrate that in the past, ecological model outputs (e.g., temperature, chlorophyll) have been relatively poorly validated based on a limited number of directly comparable measurements, both in time and space. The case studies demonstrate some of the difficulties of mapping sensor measurements directly to model state variable outputs as well as the opportunities to use deviations between sensor measurements and model simulations to better inform process understanding. Well-validated ecological models provide a mechanism to extrapolate high-frequency sensor data in space and time, thereby potentially creating a fully 3-dimensional simulation of key variables of interest

A Global Lake Ecological Observatory Network (GLEON) for synthesising high–frequency sensor data for validation of deterministic ecological models

A Global Lake Ecological Observatory Network (GLEON; www.gleon.org) has formed to provide a coordinated response to the need for scientific understanding of lake processes, utilising technological advances available from autonomous sensors. The organisation embraces a grassroots approach to engage researchers from varying disciplines, sites spanning geographic and ecological gradients, and novel sensor and cyberinfrastructure to synthesise high-frequency lake data at scales ranging from local to global. The high-frequency data provide a platform to rigorously validate process-based ecological models because model simulation time steps are better aligned with sensor measurements than with lower-frequency, manual samples. Two case studies from Trout Bog, Wisconsin, USA, and Lake Rotoehu, North Island, New Zealand, are presented to demonstrate that in the past, ecological model outputs (e.g., temperature, chlorophyll) have been relatively poorly validated based on a limited number of directly comparable measurements, both in time and space. The case studies demonstrate some of the difficulties of mapping sensor measurements directly to model state variable outputs as well as the opportunities to use deviations between sensor measurements and model simulations to better inform process understanding. Well-validated ecological models provide a mechanism to extrapolate high-frequency sensor data in space and time, thereby potentially creating a fully 3-dimensional simulation of key variables of interest

Long-Term Impacts of Draining a Watershed Wetland on a Downstream Lake, Lake Kinneret, Israel

During the 1950s, the shallow Lake Hula and its adjacent marshes, located in the watershed of Lake Kinneret (LK), were drained in order to increase arable land. The drainage resulted in increasing loads of nutrients in the Jordan River and in oxidative degradation of the underlying peat, followed by Aeolian (mostly) and riverine transport to LK. Peat had been accumulating in LK bed sediments since the 1950s, with peak deposits recorded in the mid-1970s. The routine monitoring of Norg and Corg, associated with the peat, in the watershed streams and in LK water (initiated in 1970) also showed the highest levels in the mid-1970s. During the 1980s, a succession of dense natural vegetation inhibited soil surface erosion and a decline in Aeolian transport of peat to LK was recorded. Inversed temporal patterns appear for oxygen and pH, and this is suggested to result from the dependence of these parameters on the magnitude of respiratory process, induced by peat availability. During the 1970s allochthonous peat resources supported about half of the zooplankton activity in LK and therefore the decline in peat availability during the 1980s was accompanied by a two-fold decline in zooplankton biomass. The subsequent lessening of grazing pressure together with the elevated inflows of bio-available P resulted in a significant rise in LK phytoplankton biomass. The 1980s decline in Norg associated with the peat led to lower N/P ratios in the external sources of nutrients to LK. These conditions may have favored the appearance of N 2 fixing cyanobacteria noted in the lake since 1994

Lake Kinneret : Ecology and Management

XVIII, 683 p. 230 illus., 51 illus. in color.onli

Activity concentrations of radionuclides in 5 short cores taken in 2007-2008 measured by ICP-MS and HPGe gamma spectrometry

Natural radionuclides and man-made 137Cs were analyzed in five short sediment cores taken in northern part of the Gulf of Eilat (Gulf of Aqaba) in order to provide information on sedimentation and mixing rates and sediment sources. The maximum estimates of sedimentation rates based on excess 210Pb were found to vary between 0.105 ± 0.020 and 0.35 ± 0.23 cm · year**-1. Even the lowest estimates are significantly higher than those expected from dust deposition, suggesting other sources and processes being responsible for most of the allochthonous material accumulation, including periodical floods following heavy rain events, internal erosion or triggers, like earthquakes. In 137Cs depth profiles no 1963 related nuclear weapon test maxima were found; instead, the activities decrease monotonically, suggesting that a major process leading to radionuclides' depth distribution might be mixing. The mixing rates calculated from 137Cs, excess 210Pb and excess 228Th reach values up to 2.18 ± 0.69 cm**2 · year**-1

Geochemistry of sediment core Kinneret_AA3

Long-term fire histories provide insight into the effects of climate, ecology and humans on fire activity; they can be generated using accumulation rates of charcoal and soot black carbon in lacustrine sediments. This study uses both charcoal and black carbon, and other paleoclimate indicators from Lake Kinneret (Sea of Galilee), Israel, to reconstruct late Holocene variations in biomass burning and aridity. We compare the fire history data with a regional biomass-burning reconstruction from 18 different charcoal records and with pollen, climate, and population data to decipher the relative impacts of regional climate, vegetation changes, and human activity on fire. We show a long-term decline in fire activity over the past 3070 years, from high biomass burning ~3070-1750 cal yr BP to significantly lower levels after ~1750 cal yr BP. Human modification of the landscape (e.g., forest clearing, agriculture, settlement expansion and early industry) in periods of low to moderate precipitation appears to have been the greatest cause of high biomass burning during the late Holocene in southern Levant, while wetter climate apparently reduced fire activity during periods of both low and high human activity