Periphyton development in relation to macro‐scale (geology) and micro‐scale (velocity) limiters in two gravel‐bed rivers, New Zealand

Periphyton communities were sampled every 4 weeks for a year at five sites in the Motueka River and at one site in the adjacent Riwaka River, New Zealand. This was in an attempt to distinguish the relative importance of large‐scale catchment variables (geology/land use) from small‐scale local variables (velocity) in determining the development of periphyton 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 chlorophyll biomass also correlated strongly with marble (r = 0.983, P < 0.001). However, the maximum low‐flow chorophyll a level at each site was strongly 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) average production, but the micro‐scale factors are more important in determining short‐term (monthly) temporal biomass dynamics. This supports current ecological theory on the spatial and temporal effects of primary versus secondary regulators of stream ecosystem dynamics.