Geology topics

Laurent Chauvaud

Publications and source records attributed to Laurent Chauvaud.

3 recordsLinked to original sources

USGS2015

Human activities and climate variability drive fast-paced change across the world's estuarine-coastal ecosystems

Time series of environmental measurements are essential for detecting, measuring and understanding changes in the Earth system and its biological communities. Observational series have accumulated over the past 2–5 decades from measurements across the world's estuaries, bays, lagoons, inland seas and shelf waters influenced by runoff. We synthesize information contained in these time series to develop a global view of changes occurring in marine systems influenced by connectivity to land. Our review is organized around four themes: (i) human activities as drivers of change; (ii) variability of the climate system as a driver of change; (iii) successes, disappointments and challenges of managing change at the sea-land interface; and (iv) discoveries made from observations over time. Multidecadal time series reveal that many of the world's estuarine–coastal ecosystems are in a continuing state of change, and the pace of change is faster than we could have imagined a decade ago. Some have been transformed into novel ecosystems with habitats, biogeochemistry and biological communities outside the natural range of variability. Change takes many forms including linear and nonlinear trends, abrupt state changes and oscillations. The challenge of managing change is daunting in the coastal zone where diverse human pressures are concentrated and intersect with different responses to climate variability over land and over ocean basins. The pace of change in estuarine–coastal ecosystems will likely accelerate as the human population and economies continue to grow and as global climate change accelerates. Wise stewardship of the resources upon which we depend is critically dependent upon a continuing flow of information from observations to measure, understand and anticipate future changes along the world's coastlines.

Global Change Biology↗

USGS2011

Seasonal variations in ectotherm growth rates: Quantifying growth as an intermittent non steady state compensatory process

Generally, growth rates of living organisms are considered to be at steady state, varying only under environmental forcing factors. For example, these rates may be described as a function of light for plants or organic food resources for animals and these could be regulated (or not) by temperature or other conditions. But, what are the consequences for an individual's growth (and also for the population growth) if growth rate variations are themselves dynamic and not steady state? For organisms presenting phases of dormancy or long periods of stress, this is a crucial question. A dynamic perspective for quantifying short-term growth was explored using the daily growth record of the scallop Pecten maximus (L.). This species is a good biological model for ectotherm growth because the shell records growth striae daily. Independently, a generic mathematical function representing the dynamics of mean daily growth rate (MDGR) was implemented to simulate a diverse set of growth patterns. Once the function was calibrated with the striae patterns, the growth rate dynamics appeared as a forced damped oscillation during the growth period having a basic periodicity during two transitory phases (mean duration 43. days) and appearing at both growth start and growth end. This phase is most likely due to the internal dynamics of energy transfer within the organism rather than to external forcing factors. After growth restart, the transitory regime represents successive phases of over-growth and regulation. This pattern corresponds to a typical representation of compensatory growth, which from an evolutionary perspective can be interpreted as an adaptive strategy to coping with a fluctuating environment.

Journal of Sea Research↗

USGS2003

Clams as CO2 generators: The Potamocorbula amurensis example in San Francisco Bay

Respiration and calcium carbonate production by the invasive Asian clam, Potamocorbula amurensis , were calculated to assess their importance as CO 2 sources in northern San Francisco Bay. Production, calculated using monthly population density and size structure measured at three sites over 7 yr and a shell length/CaCO 3 conversion factor, averaged 221(±184)g CaCO 3 m −2 yr −1 . Net calcium carbonate production by this exotic bivalve releases CO 2 at a mean rate of 18(±17)g C m −2 yr −1 . Respiration by P. amurensis , estimated from secondary production, releases additional CO 2 at a mean rate of 37(±34)g C m −2 yr −1 . Therefore, total net CO 2 production by P. amurensis averages 55(±51)g C m −2 yr −1 in an estuarine domain where net primary production consumes only 20g inorganic C m −2 yr −1 . CO 2 production by P. amurensis in northern San Francisco Bay is an underestimate of the total CO 2 supply from the calcified zoobenthic communities of San Francisco Bay, and results from other studies have suggested that this rate is not unusual for temperate estuaries. Global extrapolation yields a gross CO 2 production rate in the world's estuaries of 1x10 14 g C yr −1 , which suggests that calcified benthic organisms in estuaries generate CO 2 equal in magnitude to the CO 2 emissions from the world's lakes or from planetary volcanism (the net source is determined by the highly variable rate of CO 2 consumption by carbonate dissolution). This biogenic CO 2 source is increasing because of the continuing global translocation of mollusks and their successful colonization of new habitats.

California↗