Table 1.

Measured environmental variables at each of the three sampling sites.

	channel depth (m)	channel width (m)	vegetation	flow rate (cm s−1)	salinity (specific gravity)	pH
site 1 (estuary)	2–4	15	no aquatic macrophytes. Sparse overhanging vegetation	−8–10	1.001–1.024	7.2–7.5
site 2 (ditch)	0.6–0.8	2	no aquatic macrophytes, 80–100% cover provided by floating algal mat. Cover provided by tall vegetation on steep banks	1–10	1.006–1.015	7.5
site 3 (ditch)	0.3–0.5	1.5	no aquatic macrophytes. No floating algal mat. Sparse overhanging vegetation	1–10	1.005–1.013	7.3–7.5