The physico-chemical, organic matter, and benthic macroiinvertebrates features of the AWU-GUNG river system situated on Mt. Slamet (3,428 m), one of the active vulcanoes in Central Java, Indonesia were investigated from June 1993 to Desember 1993 and from April 1994 to April 1995 at two study sites namely : JAVADAT 1 and JAVADAT 2. the study site JAVADAT 1 (AWU) at an altitude of about 1,300 m a.s.l., a second order stream, is entirely within the rain forest. The study site JAVADAT 2 (GUNG) is located in the middle of densely cultivated land polluting the river.
The upper, AWU (JAVADAT 1) is characterised by low water temperature, low conductivity and TDS, circum neutral pH, low alkalinity, low Ca, Mg, and Total Hardness. Progressive increase of pH, conductivity and TDS, hardness, Orthophosphate- P, Si, and N-compound (except Ammonium- N) occur downstream. At both study sites all physico-chemical show variations in connection to the temporal and seasonal aspect with the only exception for pH at JAVADAT 2.
The organic content of the sediment was measured as total organic bound Carbon (TOC) and Total Organic Nitrogen (TON) using a LECO CHN Analyzer. At JAVADAT 1, Total Organic Carbon (TOC) concentrations (mg/g) in sands are significantly higher than gravel, but the temporal patterns of TOC concentrations are similar in gravel and sand sediments with highest mean values in the dry season. At JAVADAT 2, differences in TOC concentrations in sands and gravel are paralel as in JAVADAT 1. In contrast to JAVADAT 1, no clear seasonal pattern is evident neither on the basis of seasonal means. At both study sites TOC contents (mg/kg DW) follow closely the temporal pattern of concentrations and the TOC contents are significantly higher in JAVADAT 2 than in JAVADAT 1.
In JAVADAT 1, Total Organic Nitrogen (TON) concentrations (mg/g) in sandy sediments are twice as high as in gravel sediments. The temporal pattern is distinct with highest concentrations in the dry seasons is apparent. In JAVADAT 2, TON differences between sand and gravel are about 1 order of magnitude. Temporal patterns are roughly paralel and monthly means indicate higher TON concentrations in the dry seasons . The temporal patterns of TON contents (mg/kg DW) follow closely the temporal pattern of concentrations and the TON contents are significantly higher in JAVADAT 2 than in JAVADAT 1.
C/N ratios are rough measures of digestibility of organic matter for consumers, C/N ratios smaller than about 15 indicate good food quality. In JAVADAT 1, C/N ratios indicate that food quality is poor. In time there is a continuous decrease of food quality and no correlation between seasons and food quality. Generally food quality in JAVADAT 2 is better than in JAVADAT 1 and the temporal patterns are similar to JAVADAT 1.
A total of 43 invertebrates species have been identified from JAVADAT 1 and JAVADAT 2. The class Insecta represented by 39 species belonging to 10 orders and 39 families is predominating in both study sites. In general, JAVADAT 2 has a higher species diversity than JAVADAT 1. In both study sites, numerically the riffle habitats supported a higher density of the major taxa of benthic fauna. The seasonal fluctuations of the majority of benthic fauna taxa were described in this present study and it seems this seasonalities were partially caused by scouring of the streambed during spates as was found in other Asian rivers and streams.