Characteristics of softwater streams in Rhode Island. III. Distribution of macrophytic vegetation in a small drainage basin

Abstract

The Wood River watershed, a small well-defined drainage basin in Rhode Island was monitored seasonally for all macrophytic vegetation and various physical variables. Twenty-four segments, 20 m in length were sampled. Mean stream depth, width and current velocity increased by 3 to 8 fold from lst-to 4th-order segments. Light penetration was positively correlated with the above variables (p < 0.05) and increased by 11 fold from the headwaters to the mouth during September when the riparian canopy was maximum. 74 subgeneric taxa of macrophytes were collected in the Wood River basin, 36% algae, 13% bryophytes, 4% vascular cryptograms and 45% angiosperms. The highest diversity occurred in the 4th-order segments throughout the year. Species numbers were positively correlated with depth, width and light penetration (p < 0.05). Vascular plants dominated all orders, but their proportion doubled from lst-to 4th-order streams. Macrophyte cover was twice as high in the 4th-order segments in June and September as in the other orders. Macrophyte abundance was positively correlated to light penetration and negatively correlated to the ratio of nonvascular: vascular plants (p < 0.05). Two distinct clusters were found for the predominant species. The first cluster contained mostly large angiosperms, which were rooted in sediments, while the second cluster was composed of small epilithic algae and bryophytes. The moss, Fontinalis antipyretica, was the most frequent species, occurring in 51% of the samples and in all 4 orders throughout the year.

Fragmentation and groundwater supply as major drivers of algal and plant diversity and relative cover dynamics along a highly modified lowland river

“…By contrast, the RHI sites, along with the GWD sites, exhibited the highest degree of diversity and cover values. Their heterogeneous hard substrate (micro-, mesolithal; Table 1) and general stream-like characteristics support these results (Sheath et al, 1986;Krupek et al, 2012). However, both the POT and RHI stretch types were characterized by a relatively low number of algal taxa.…”

“…Our findings along the longitudinal gradient of the Oglio River also highlight the key role played by soft-bodied benthic algae in structuring lowland riverbed primary producer assemblages. Hydro-geomorphology and human alterations may be considered good predictors of taxa diversity and community structure as regards both algae and vascular plants, and vice versa (Sheath et al, 1986;Riis and Biggs, 2003;Ibáñez et al, 2012b).…”

“…This is due to the increase in habitat complexity and nutrient availability in downstream sectors. At the same time, the non-vascular/ vascular ratio is expected to drop as the river sections become wider and the water deeper (Sheath et al, 1986). However, the progressive increase in water abuse and worsening quality documented in lowland rivers throughout the world has led to a progressive loss of vascular species to algae, which has in turn had dramatic effects on river functionality (Steffen et al, 2013).…”

“…Very few studies have addressed the relative contribution of algae and vascular macrophytes to local primary producer diversity and community structure, or their relative responses to environmental determinants (Sheath et al, 1986;Coring and Bäthe, 2011). In general, the larger the river, the greater the diversity of aquatic primary producers.…”

Red Algae

“…As such, they compete with a complex association of microalgae, usually dominated by diatoms during early colonization stages (e.g., Steinman and McIntire, 1986). Bryophytes are frequent dominants in upper reaches where red algae occur (e.g., Sheath et al, 1986). In later stages of succession, filamentous and stalked species can form an upper story where they have a competitive advantage for light and nutrient replenishment.…”