Lexington author Meg Muckenhoupt will give a lecture on the history of open space in Arlington at the town’s fifth annual “EcoFest” next weekend. The free event, that will also feature entertainment and displays by local environmental groups and vendors, will be held in Arlington Town Hall Saturday , from 10 a.m. to 2 p.m. This year’s EcoFest will focus on the ecological impacts people and places have on the environment. Muckenhoupt will give a talk titled “From Glaciers to the Great Meadows: 15,000 Years in Arlington’s Open Space”; and Grammy-nominated singer Judy Pancoast will perform for children of all ages. The EcoFest is coordinated by the Arlington Garden Club, the Vision 2020 Sustainable Arlington group, and the town’s planning and public works department. More information can be found on the town’s website at www.arlingtonma.gov/ecofest.