Craig J Fischenich | USGS Science

USGS2018

Evaluating flow management as a strategy to recover an endangered sturgeon species in the Upper Missouri River, USA

In the Upper Missouri River, Fort Peck and Garrison Dams limit the length of free‐flowing river available to the endangered pallid sturgeon. These barriers restrict the upstream migration of adults and downstream larval dispersal. A one‐dimensional (1D) modelling framework is currently in use to evaluate reservoir operation alternatives and to simulate drift of dispersing free embryos for different flow regimes and reservoir stages. This paper presents the results of a large‐scale tracer experiment conducted in 2016 and associated modelling performed to evaluate flow management scenarios that might aid species recovery. Breakthrough curves from the tracer experiment were used to infer the 1D longitudinal dispersion coefficient from a parameter optimization procedure. Simulations generated using the calibrated 1D advection–dispersion model were compared with field observations of the passive tracer and with larval fish collected during a previous experiment in 2007. When used with the appropriate range of dispersion coefficients, the 1D modelling framework agrees well with the available direct measurements of larval drift distances. Although we cannot unequivocally state whether insufficient length of free‐flowing river alone is causing recruitment failure, given the current thermal regime and our understanding of pallid sturgeon development, the time required for pallid sturgeon to transition to the benthos and initiate feeding might exceed the duration of drift available given constraints of reservoir operations.

Missouri↗

USGS2016

A landscape-scale assessment of above- and belowground primary production in coastal wetlands: Implications for climate change-induced community shifts

Above- and belowground production in coastal wetlands are important contributors to carbon accumulation and ecosystem sustainability. As sea level rises, we can expect shifts to more salt-tolerant communities, which may alter these ecosystem functions and services. Although the direct influence of salinity on species-level primary production has been documented, we lack an understanding of the landscape-level response of coastal wetlands to increasing salinity. What are the indirect effects of sea-level rise, i.e., how does primary production vary across a landscape gradient of increasing salinity that incorporates changes in wetland type? This is the first study to measure both above- and belowground production in four wetland types that span an entire coastal gradient from fresh to saline wetlands. We hypothesized that increasing salinity would limit rates of primary production, and saline marshes would have lower rates of above- and belowground production than fresher marshes. However, along the Northern Gulf of Mexico Coast in Louisiana, USA, we found that aboveground production was highest in brackish marshes, compared with fresh, intermediate, and saline marshes, and belowground production was similar among all wetland types along the salinity gradient. Multiple regression analysis indicated that salinity was the only significant predictor of production, and its influence was dependent upon wetland type. We concluded that (1) salinity had a negative effect on production within wetland type, and this relationship was strongest in the fresh marsh (0–2 PSU) and (2) along the overall landscape gradient, production was maintained by mechanisms at the scale of wetland type, which were likely related to plant energetics. Regardless of wetland type, we found that belowground production was significantly greater than aboveground production. Additionally, inter-annual variation, associated with severe drought conditions, was observed exclusively for belowground production, which may be a more sensitive indicator of ecosystem health than aboveground production.

Estuaries and Coasts↗