{'biological oxygen demand': [0, 0, 0, 3], 'freshwater ecosystem': [0, 0, 0, 1], 'low plant biomass accumulation': [0, 0, 0, 1], 'large biomass accumulation': [0, 0, 0, 1], 'organic matter pollution': [0, 0, 0, 1], 'factors': [0, 0, 1, 0], 'sewage': [0, 0, 0, 1], 'bod': [1, 0, 0, 3], 'decomposition': [1, 0, 1, 9]}