Suspended organic particles drive the development of attached algal communities in degraded peatlands

Mineral particles in rivers have been shown to cover adnate algal species, promoting motile and filamentous species. Such effects and the role of detrital particles have not been studied in stagnant waters. In degraded peat lands, detrital particles are very prominent and therefore we studied the interaction of organic particles and attached algae. Field grown communities were translocated to microcosms and exposed to organic particles in the laboratory. Colonization of substrate was also studied in field enclosures that allowed settlement of particles. We compared algal settlement under low particle regime (enclosures) with settlement at high particle concentrations (outside). Suspended particles were found to be trapped by attached algae in proportion to the concentration of particles. The presence of particles in the incubations and field enclosures modified species composition, reducing the share of low-profile forms. These experimental results were verified in a field survey with a wide range of turbidity. The share of low-profile species was lowest in turbid ditches while motile and planktonic algae dominated, in agreement with the results from experiments. It is argued that the strong interactions of attached algae and suspended organic matter found in peat land ditches is a characteristic feature of detritus rich waters.