Effects of barley straw (Hordeum vulgare) on freshwater and brackish phytoplankton and cyanobacteria

A short-term laboratory study was conducted to investigate the effect of barley straw in controlling several common phytoplankton and cyanobacterial species. Following a one-month incubation of barley straw in coarsely filtered fresh Potomac River and brackish Patuxent River waters, the growth of six autotrophic taxa was followed in culture. Barley straw slurry reduced the yield of three taxa (Ankistrodesmus falcatus, Chlorella capsulata, Isochrysis sp.) in comparison with cultures not receiving the slurry. Although no significant changes in growth were detected with three other taxa (Cyclotella sp., Prorocentrum minimum, freshwater Pseudanabaena sp.), some patterns indicated potential impacts of the barley straw. First, a higher addition of straw to Cyclotella sp. resulted in a lower biomass accumulation than in cultures receiving lower levels. Second, the bloom-forming dinoflagellate Prorcentrum minimum was apparently stimulated at low barley straw levels, perhaps suggesting conditions associated with the straw (metals-chelation, bacterial-produced nutrients) might stimulate dinoflagellate growth. Third, species shifts were observed in two of the cultures, with barley straw favoring shifts from Isochrysis to a Cyclotella sp. - Thalassiosira sp. mixture and shifts from Pseudanabaena to a Pseudanabaena - Scenedesmus mixture. These results provide new records for the susceptibility of freshwater and brackish phytoplankton taxa to barley straw exposure, including species-specific responses and shifts in species dominance in mixed assemblages.