The roles of aquatic and riparian vegetation at the aquatic-terrestrial interface of southeastern streams

Streambed stone stability, packing, and embeddedness were assessed within and adjacent to beds of the macrophyte Justicia americana L. (Vahl.) in 5 Alabama streams. Force needed to dislodge stones and embeddedness was ∼2-fold lower outside of J. americana beds than within the macrophyte beds.; In-stream experiments were done to determine if and by what mechanisms J. americiana enhances streambed stability and influences benthic organisms. Treatments included removal of aboveground stems, removal of stems and rhizomes, and a control. Lower substrate stability and embeddedness were found in the stem-rhizome removal treatment, indicating that both the presence of below-ground structures binding stones and greater degree of stone embeddedness were responsible for differences in stone stability among treatments. Sedentary unionid mussels were more abundant in the control vs stem and rhizome removal treatment, whereas abundance of more mobile pleurocerid snails (Elimia ucheensis) and sessile epilithic plants (Podostemon ceratophyllum and mosses) did not differ among treatments. Periphyton accrural was primarily limited by shading by J. americana, and secondarily by grazing snails.; Another study in 6 east-central Alabama streams was done to determine if the distribution of several benthic macroinvertebrates differed between areas within and outside of J. americana beds. Densities and biomass of burrowing taxa (including the Asiatic clam Corbicula fluminea) were higher within J. americana beds. In contrast, densities and biomass of more mobile taxa (i.e., snails) did not differ between habitat types or were significantly higher outside J. americana beds (i.e., turbellarians).; The relative effects of disturbance level, abundance of root parasites, and ambient physicochemical conditions on biomass allocation in J. americana were investigated across 6 south-central Alabama streams. Ambient physicochemical conditions, especially light, current velocity, water depth, conductivity, explained most of the variation in biomass and biomass allocation, whereas disturbance by flooding (measured as stream reach instability) and root-parasitizing nematodes explained insignificant amounts of variation observed across the study sites.; The biomass and decomposition of roots within streambed sediments were compared with leaves and wood in 3 Coastal Plain intermittent streams with different riparian zone treatments. Riparian roots (live and dead) within the upper 30 cm of sediment contributed 24% of CPOM in stream channels and 42% in banks. Decomposition rates were slow (exponential decay coefficient range: 0.0010–0.0023) and did not differ among buried substrate types or riparian zone treatments after 1 y.