I have a few sites which are purely whitehat with lots of unique content. These sites are one year old or older. Recently I observed that I am losing long tail traffic from these traffic by about 80%. Before my long tail keywords usually used to rank in first 3 positions of Google, now most of them have moved to the second page. Is there any recent Google algorithm update causing this? I used to build backlinks to all pages targeting long tail keywords using only bookmarking. Is Google discounting bookmarking links? I'd appreciate if you share your thoughts.