High Frequency Radar Wind Turbine Interference Community Working Group Report

Land-based High Frequency (HF) Radars provide critically important observations of the coastal ocean that will be adversely affected by the spinning blades of utility-scale wind turbines. Pathways to mitigate the interference of turbines on HF radar observations exist for small number of turbines; however, a greatly increased pace of research is required to understand how to minimize the complex interference patterns that will be caused by the large arrays of turbines planned for the U.S. outer continental shelf. To support the U.S.’s operational and scientific needs, HF radars must be able to collect high-quality measurements of the ocean’s surface inand around areas with significant numbers of wind turbines. This is a solvable problem, but given the rapid pace of wind energy development, immediate action is needed to ensure that HF radar wind turbine interference mitigation efforts keep pace with the planned build out of turbines

Diffusion Coefficients Calculated Using 137Cs Profiles Applied to 210Pb Dating in Lake Core Sediments

Several processes change the radionuclide profiles in lake sediment cores. Two important processes are sediment mixing by worms and microbes, and molecular diffusion in the pore waters. Simple diffusion is used to estimate these influences upon the 210Pb distribution using an analytic solution to the Constant Flux Constant Sedimentation (CFCS) model. Diffusion coefficients are calculated by fitting Gaussian curves to 137Cs distributions before diffusion (based on fallout measured in precipitation during nuclear testing) and after diffusion (distributions measured in sediment cores). Diffusion coefficients ranged from 0.01 cm2/yr to over 2 cm2/yr, with an average value of 0.64 cm2/yr. When significant diffusion is seen, corrections must be applied to the dates calculated using CFCS and Constant Rate of Supply (CRS) models. Using 22 lakes dated by the University of Maine Department of Physics, the corrections resulted in an average increase in the age of sediment at a given depth by 36%

Climate-induced changes in lake ecosystem structure inferred from coupled neo- and paleoecological approaches

Over the 20th century, surface water temperatures have increased in many lake ecosystems around the world, but long-term trends in the vertical thermal structure of lakes remain unclear, despite the strong control that thermal stratification exerts on the biological response of lakes to climate change. Here we used both neo- and paleoecological approaches to develop a fossil-based inference model for lake mixing depths and thereby refine understanding of lake thermal structure change. We focused on three common planktonic diatom taxa, the distributions of which previous research suggests might be affected by mixing depth. Comparative lake surveys and growth rate experiments revealed that these species respond to lake thermal structure when nitrogen is sufficient, with species optima ranging from shallower to deeper mixing depths. The diatom-based mixing depth model was applied to sedimentary diatom profiles extending back to 1750 AD in two lakes with moderate nitrate concentrations but differing climate settings. Thermal reconstructions were consistent with expected changes, with shallower mixing depths inferred for an alpine lake where treeline has advanced, and deeper mixing depths inferred for a boreal lake where wind strength has increased. The inference model developed here provides a new tool to expand and refine understanding of climate-induced changes in lake ecosystems

Appendix G. Analysis of model performance.

Analysis of model performance

Appendix E. A table showing select physical and chemical characteristics of the 17 study lakes, along with the percentage relative abundance of the three target species in surface sediment samples.

A table showing select physical and chemical characteristics of the 17 study lakes, along with the percentage relative abundance of the three target species in surface sediment samples

Appendix B. A table showing select characteristics of Hidden and Siskiwit lakes.

A table showing select characteristics of Hidden and Siskiwit lakes

Appendix D. Results of two-way ANOVA of growth rate experiment for each species, with significant factors and interactions in bold.

Results of two-way ANOVA of growth rate experiment for each species, with significant factors and interactions in bold