The contribution of flood disturbance, catchment geology and land use to the habitat template of periphyton in stream ecosystems

Abstract

SUMMARY: 1. Periphyton chlorophyll a (chl a), ash‐free dry mass, taxonomic composition, and cellular and water‐column nutrients were analysed every 4 weeks for a year at sixteen stream sites in New Zealand. The hypothesis was investigated that broad‐scale differences in mean monthly periphyton development are defined primarily by the frequency of flood disturbances and the periphyton's interaction with the nutrients. it us of the streams as determined by catchment geology and land use. 2. Overall, mean monthly chl a concentration declined with increasing flood frequency (r= ‐0.711, P < 0.001), and seasonality in chl a was better defined at sites with a low frequency of floods. Chlorophyll a concentration was generally low throughout the year at sites with frequent floods (> 15 yr−1). 3. No relationship existed between inorganic nutrient concentrations and catchment geology or land development. However, conductivity declined significantly as a function of the percentage of the catchment underlain by nutrient‐poor, hard rocks (plutonic and fine‐grained metamorphic rocks) (r= ‐0.515, P < 0.05), but increased significantly with the percentage of the catchment in intensive agricultural land use (r= 0.799, P < 0.001). 4. Cellular nutrient concentrations suggested that nitrogen was the nutrient most commonly limiting periphyton production. In turn, cellular N concentrations declined significantly with increasing percentage of the catchment in hard rock (r= ‐0.5M, P < 0.05) and increased with percentage of the catchments in intensive agricultlural land use (r= 0.948, P < 0.001). 5.The sites were classified into three enrichment groups (high, moderate and low) based 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 chl a decreased significantly with increases in the annual 80th percentile velocity. However, the relationship was significantly 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 explaining variation in mean monthly chl a among the sites (r 2= 89%). 8. Overall, the results showed that flood disturbance and catchment enrichment regimes are probably the principal axes of the habitat template of periphyton among the study streams, and could be used to explain and predict broad‐scale differences in periphyton development among other temperate stream ecosystems.