COLUMBIA, MD. — Columbia-based Oekos Management Corp. has acquired Rivers Corporate Center, a 280,000-square-foot, nine-building business park in Columbia, from Rivers Center, a group of Howard County, Md.-based investors, for $44 million. The office/research and development buildings are located along Guilford and Old Columbia roads, near the intersection of Route 32 and Route 29, and were 93 percent leased at the time of sale. Tenants include United Healthcare, Applied Data Systems, Staples and St. Agnes Healthcare. Don Schline and Liz Martin of Manekin’s Columbia office were the sole brokers in the sales transaction. Manekin will also serve as leasing agent.