Weitzel, R L creator ASTM text USA ASTM 1979 monographic Freshwater algae--Measurement Freshwater microbiology--Methodology Algal communities Water quality biological assessment--Methodology http://books.google.com.pk/books/about/Methods_and_Measurements_of_Periphyton_C.html?id=eEVRAAAAMAAJ&redir_esc=y http://books.google.com.pk/books/about/Methods_and_Measurements_of_Periphyton_C.html?id=eEVRAAAAMAAJ&redir_esc=y