Abstract
Using an automated water quality station in the lower Brantas River, East Java, Indonesia, highly time-resolved time series (1 min^1) of main parameters that govern water quality have been measured (oxygen, chlorophyll-a, turbidity, nutrients, total inorganic and organic carbon) from 2003 to 2008. All parameters showed distinct seasonal variations related to dry and wet seasons. Due to the large input of organic material from sewage and industry into the river the most important parameter is the dissolved oxygen that displays a distinct seasonal behaviour with relatively large values during wet season and very low values in dry season. In addition, during dry season high variations between day and night were observed with zero oxygen concentrations at night. From highly time-resolved oxygen time series the main metabolic rates (primary production, respiration) together with atmospheric exchange rates could be calculated in a semi-quantitative way. From this, it could be estimated that the anthropogenic carbon input into the river has to be reduced from about 70 t/d BOD equivalents to at least 33 t/d in order to prevent anaerobic conditions.
