THE CONTRIBUTION OF FLOOD DISTURBANCE, CATCHMENT GEOLOGY AND LAND-USETO THE HABITAT TEMPLATE OF PERIPHYTON IN STREAM ECOSYSTEMS

1. Periphyton chlorophyll a (chi a), ash-free dry mass, taxonomic comp osition, and cellular and water-column nutrients were analysed every 4 weeks for a year at sixteen stream sites in New Zealand. The hypothes is was investigated that broad-scale differences in mean monthly perip hyton development are defined primarily by the frequency of flood dist urbances and the periphyton's interaction with the nutrient status of the streams as determined by catchment geology and land use. 2. Overal l, mean monthly chi a concentration declined with increasing flood fre quency (r = -0.711, P < 0.001), and seasonality in chi a was better de fined at sites with a low frequency of floods. Chlorophyll a concentra tion was generally low throughout the year at sites with frequent floo ds (> 15 yr-l). 3. No relationship existed between inorganic nutrient concentrations and catchment geology or land development. However, con ductivity declined significantly as a function of the percentage of th e catchment underlain by nutrient-poor, hard rocks (plutonic and fine- grained metamorphic rocks) (r = -0.515, P < 0.05), but increased signi ficantly with the percentage of the catchment in intensive agricultura l land use (r = 0.799, P < 0.001). 4. Cellular nutrient concentrations suggested that nitrogen was the nutrient most commonly limiting perip hyton production. In turn, cellular N concentrations declined signific antly with increasing percentage of the catchment in hard rock (r = -0 .561, P < 0.05) and increased with percentage of the catchments in int ensive agricultural land use (r = 0.948, P < 0.001). 5. The sites were classified into three enrichment groups (high, moderate and low) base d on their land use and underlying geology. Cellular N concentrations varied significantly among these enrichment groups (ANOVA F = 14.661, P < 0.001). 6. Log chi a decreased significantly with increases in the annual 80th percentile velocity. However, the relationship was signif icantly different among the enrichment groups. 7. A stepwise multiple regression on the full dataset identified that the frequency of floods , proportion of the catchment in high-intensity agricultural land use and proportion in alkaline rocks were the most significant factors exp laining variation in mean monthly chi a among the sites (r(2) = 89%). 8. Overall, the results showed that flood disturbance and catchment en richment regimes are probably the principal axes of the habitat templa te of periphyton among the study streams, and could be used to explain and predict broad-scale differences in periphyton development among o ther temperate stream ecosystems.