Seasonally distinct taxonomic and functional shifts in macroinvertebrate communities following dam removal

Dam removal is an increasingly popular restoration tool, but our understanding of ecological responses to dam removal over time is still in the early stages. We quantified seasonal benthic macroinvertebrate density, taxonomic composition, and functional traits for three years after lowhead dam removal in three reaches of the Olentangy River (Ohio, USA): two upstream of former dam (one restored, one unrestored), and one downstream of former dam. Macroinvertebrate community density, generic richness, and Shannon–Wiener diversity decreased between ∼9 and ∼15 months after dam removal; all three variables consistently increased thereafter. These threshold responses were dependent on reach location: density and richness increased ∼15 months after removal in upstream reaches versus ∼19 months downstream of the former dam. Initial macroinvertebrate density declines were likely related to seasonality or life-history characteristics, but density increased up to 2.27× from year to year in three out of four seasons (late autumn, early spring, summer) across all reaches. Macroinvertebrate community composition was similar among the three reaches, but differed seasonally based on non-metric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM). Seasonal differences among communities tended to decrease after dam removal. We detected community-wide shifts in functional traits such as multivoltinism, depositional habitat use, burrowing, and collector-gatherer feeding mode. We observed that these traits were expressed most strongly with Chironomidae, which was the most abundant family. Our results suggest that seasonal environmental conditions can play a role in the response and recovery of macroinvertebrate communities—often used to monitor ecosystem condition—following dam removal. In particular, macroinvertebrate density and diversity can show recovery after dam removal, especially in seasons when macroinvertebrate density is typically lowest, with concomitant changes to functional trait abundance. Thus, we recommend scientists and managers consider responses to dam removal throughout the year. Further, similar density, generic richness, and functional traits among reaches suggest that channel restoration after dam removal may initially have equivocal effects on invertebrate communities

Ecosystem size and flooding drive trophic dynamics of riparian spiders in a fire-prone Sierra Nevada river system

Disturbance can play an important role in structuring stream food webs. Although floods have received the greatest attention as a disturbance agent in rivers, wildfire â which can strongly influence fluvial ecosystem structure and function â may also drive consumer trophic dynamics. We measured the relative effects of wildfire, hydrologic disturbance, ecosystem size, and canopy openness (as a proxy for in-stream productivity) on trophic position and reliance on aquatically-derived nutritional subsidies of riparian spiders of the family Tetragnathidae along two rivers on the west slope of the Sierra Nevada in California, USA. Ecosystem size received strong support as an environmental determinant of both trophic measures, with variability in flood magnitude emerging as an important mechanism linking ecosystem size and trophic responses. Piecewise linear regression revealed significant breakpoints in spider trophic position and reliance on aquatically-derived nutritional subsidies that were related to thresholds in fire extent within the catchment. These non-linear relationships with wildfire may lend additional insight into the potential interactions among ecosystem size, productivity, and disturbance that determine stream-riparian food web architecture.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Riverine Landscape Patch Heterogeneity Drives Riparian Ant Assemblages in the Scioto River Basin, USA

<div><p>Although the principles of landscape ecology are increasingly extended to include riverine landscapes, explicit applications are few. We investigated associations between patch heterogeneity and riparian ant assemblages at 12 riverine landscapes of the Scioto River, Ohio, USA, that represent urban/developed, agricultural, and mixed (primarily forested, but also wetland, grassland/fallow, and exurban) land-use settings. Using remotely-sensed and ground-collected data, we delineated riverine landscape patch types (crop, grass/herbaceous, gravel, lawn, mudflat, open water, shrub, swamp, and woody vegetation), computed patch metrics (area, density, edge, richness, and shape), and conducted coordinated sampling of surface-active Formicidae assemblages. Ant density and species richness was lower in agricultural riverine landscapes than at mixed or developed reaches (measured using <i>S</i> [total number of species], but not using Menhinick’s Index [<i>D</i>_M]), whereas ant diversity (using the Berger-Park Index [<i>D_BP</i>]) was highest in agricultural reaches. We found no differences in ant density, richness, or diversity among internal riverine landscape patches. However, certain characteristics of patches influenced ant communities. Patch shape and density were significant predictors of richness (<i>S</i>: <i>R</i>² = 0.72; <i>D</i>_M: <i>R</i>²=0.57). Patch area, edge, and shape emerged as important predictors of <i>D_BP</i> (<i>R</i>² = 0.62) whereas patch area, edge, and density were strongly related to ant density (<i>R</i>² = 0.65). Non-metric multidimensional scaling and analysis of similarities distinguished ant assemblage composition in grass and swamp patches from crop, gravel, lawn, and shrub as well as ant assemblages in woody vegetation patches from crop, lawn, and gravel (stress = 0.18, <i>R</i>² = 0.64). These findings lend insight into the utility of landscape ecology to river science by providing evidence that spatial habitat patterns within riverine landscapes can influence assemblage characteristics of riparian arthropods.</p></div

Riverine landscape patch types at the twelve Scioto and Olentangy River study reaches delineated from field and remotely-sensed data.

<p>Patch classification was adapted from Johansen, Phinn and Witte [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124807#pone.0124807.ref040" target="_blank">40</a>].</p><p>Riverine landscape patch types at the twelve Scioto and Olentangy River study reaches delineated from field and remotely-sensed data.</p

Patch metrics, measures, units, and descriptions used to quantify riverine landscape composition and configuration of the twelve study reaches of the Scioto and Olentangy Rivers, Ohio, USA.

<p>Detailed metric descriptions and formulas are provided in McGarigal and Marks [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124807#pone.0124807.ref089" target="_blank">89</a>].</p><p>Patch metrics, measures, units, and descriptions used to quantify riverine landscape composition and configuration of the twelve study reaches of the Scioto and Olentangy Rivers, Ohio, USA.</p

Summary statistics of ants surveyed by riverine landscape land-use class (agriculture, mixed, developed) including total ant abundance and mean and standard deviation of density and diversity measures by patch type.

<p>Note that not all patch types were observed in all three riverine land-use classes.</p><p>Summary statistics of ants surveyed by riverine landscape land-use class (agriculture, mixed, developed) including total ant abundance and mean and standard deviation of density and diversity measures by patch type.</p

Summary statistics of patch metrics for all twelve study riverine landscapes as well as summary statistics for patches broken out by the three land-use classes.

<p>Note that values for MPE and TE were scaled down by a factor of 1,000.</p><p>Summary statistics of patch metrics for all twelve study riverine landscapes as well as summary statistics for patches broken out by the three land-use classes.</p