PERIPHYTON DEVELOPMENT IN RELATION TO MACROSCALE (GEOLOGY) AND MICROSCALE (VELOCITY) LIMITERS IN 2 GRAVEL-BED RIVERS, NEW-ZEALAND

Periphyton communities were sampled every 4 weeks for a year at five s ites in the Motueka River and at one site in the adjacent Riwaka River , New Zealand. This was in an attempt to distinguish the relative impo rtance of large-scale catchment variables (geology/land use) from smal l-scale local variables (velocity) in determining the development of p eriphyton in the rivers. Cellular nitrogen correlated positively with the proportion of the sub-catchments in marble (r = 0.938, P < 0.01). Growth appeared to be N-limited during the year, thus average chloroph yll biomass also correlated strongly with marble (r = 0.983, P < 0.001 ). However, the maximum low-flow chorophyll a level at each site was s trongly and negatively correlated with water velocity (r = -0.981, P < 0.001). This indicated that the macro-scale factors of the catchment are probably more important in determining longer-term (> 1 year) aver age production, but the micro-scale factors are more important in dete rmining short-term (monthly) temporal biomass dynamics. This supports current ecological theory on the spatial and temporal effects of prima ry versus secondary regulators of stream ecosystem dynamics.