Over the past several years, scientists from Minnesota and Ontario have been collecting sediment cores from the bottom of Lake of the Woods to help understand how phosphorus loadings have changed over time and why. Cores taken from strategic locations in the lake are dated using radioisotopes and the amount of phosphorus in each depth increment is measured; from this, they can estimate historical burial of phosphorus across the entire basin and compare it to historical inputs of phosphorus. What they have discovered is that phosphorus is not readily buried in the bottom sediments, as happens in many lakes. Instead, phosphorus pools at the sediment-water interface in an active layer that can release nutrients and get stirred up from the bottom to re-enter the water column and fuel algae blooms – a process called “internal loading”. So even though phosphorus pollution from tributaries has been greatly reduced over the years, it could take a long time for all the available phosphorus being resuspended to be consumed by algae and removed from the sediments – this, together with climate changes that favour algae growth, makes defining a nutrient budget for the lake a complicated task. For the full story, link to:http://lowwsf.com/unlocking-low