IDENTIFIKASI JENIS, KERAPATAN DAN DIVERSITAS PLANKTON BENTOS SEBAGAI BIOINDIKATOR PERAIRAN SUNGAI PEPE SURAKARTA (IDENTIFICATION, DENSITY AND DIVERSITY OF PLANKTON AND BENTOS AS BIOINDICATOR AT PEPE RIVER SURAKARTA) (Department of Biology Education Faculty of Teacher Training and Education Sebelas Maret Un, 2012)