Measuring submerged macrophyte standing crop in shallow rivers: a test of methodology

High natural variability in space and time can make accurate measurements of macrophyte standing crop difficult. Accuracy of such measurements could be improved by quantifying the relationships between the different methods of measuring standing crop which are available to researchers. In this study we compare cover, volume, and biomass as measures of standing crop. Percentage cover, percentage volume, and dry weight biomass estimates were positively related (R2(adj) range = 54–96%), but these relationships were significantly different between sites, and to a lesser extent between months. Biomass was related (R2(adj) range = 18–73%) to stand height. Furthermore, cover, volume and biomass indicated different seasonal trends in standing crop at the two study sites. Our study presents a suite of standing crop measures that exhibit close congruence, can be measured efficiently and minimise destructive sampling in situ, attributes which will aid in the design and implementation of future macrophyte measurement protocols for shallow rivers.