The bioenergetics of a detritus—feeding stonefly Pteronarcys scotti, were invetigated. The nymphs were collected from a north Georgia trout stream and held under simulated field conditions of temperature and photoperiod in a laboratory stream. Rates of respiration and egestion were measured at temperatures approximating those in the field at the time of collection. An estimate of the growth rate of nymphs was made from a statistical analysis of monthly field samples. Calorimetric determinations were made of nymphs, molted exoskeletons, and feces. A 17—month energy budget for the average nymph was tabulated on the basis of the data collected. Assimilation and growth efficiencies were found to be low with mean values of 10.6%, 34.2%, and 3.6% for assimilation and net and gross growth efficiencies, respectively. An assessment was made of the rate of leaf breakdown by the nymphs, and a value of approximately 29.1% of the dry body weight per day was calculated. The functional importance of the organism to the stream community is discussed.

The relationship between nutrient element concentration and stream discharge during storm events was studied in a nutrient-rich first order stream. Stream concentrations of NO 3 -N, phosphate-P, Ca, and Mg were determined during the course of and following thunderstorms. Nutrient element trajectories were constructed for the elements monitored and some recognizable and reproducible patterns in nutrient concentrations emerged. NO3-N and phosphate-P generally increased in concentration during the early stages of increasing stream discharge resulting in a general clockwise trajectory. Ca and Mg consistently showed decreases in concentration during rising water, but the pattern of the trajectories was less constant. The patterns seen for NO3-N and phosphate-P suggest surface run-off as their origin while the patterns for Ca and Mg reflect their primary origin in groundwater. The ability to detect these differences from the analysis of nutrient trajectories suggests the use of this technique for determining the source of other elements in streams.

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Water chemistry and benthic invertebrate communities were investigated at 37 sites on acid streams originating on the Stockton-Denniston Plateau, North Westland, New Zealand . The region is characterised by high rainfall and runoff, highly acidic soils and the presence of extensive coal measures that have been mined for over 120 years . Four groups of streams were identified : naturally acid plateau streams with clear water and very low conductivity ; brown water (humic) streams with pH<4 and low conductivity ; coastal plains streams with higher pH and conductivity ; and streams contaminated by acid mine drainage . TWINSPAN and cluster analysis also grouped streams into four groups based on presence-absence of invertebrate taxa, the groups being similar to, but not identical to those based on physico-chemical factors . Diptera (mainly Chironomidae) were represented by most species in all site groups followed by Plecoptera in plateau streams, and Trichoptera on the coastal plain and where mine drainage occurred . Species of Orthocladiinae (Chironomidae), Plecoptera and Trichoptera were found at the most contaminated sites (pH <3, conductivity >900 tS cm -1 , total reactive aluminium >25 mg 1 -1 ) . The leptophlebiid mayfly Deleatidium was found at 32 of the 37 sites, and some species of Plecoptera, Trichoptera and Chironomidae were also widely distributed . Our findings indicate that species tolerant of low pH (i .e ., <4 .5) are not confined to humic waters as has been postulated, but also occur in soft, non-humic waters where concentrations of labile, non-organically bound aluminium may be elevated .

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