Abstract. Whole-ecosystem metabolism is an important indicator of the role of organic matter, C cycling, and trophic structure in rivers. Ecosystem metabolism is well studied in small streams, but less is known about metabolism in large rivers. We estimated daily whole-ecosystem metabolism over 2 y for 1 site each at the Mississippi and Chattahoochee Rivers in the USA to understand factors influencing temporal patterns of ecosystem metabolism. We estimated rates of gross primary production (GPP), community respiration (CR), and net ecosystem production (NEP) with a curve-fitting approach with publicly available discharge (Q), dissolved O 2 , temperature, and photosynthetically active radiation (PAR) data. Models were run for week-long blocks, and power analyses suggested that rates should be established at least once for each 10-wk period throughout the year to characterize annual rates of metabolism accurately in these 2 rivers. We analyzed weekly rates averaged over

Riparian buffers can improve stream water and habitat quality by reducing non-point-source pollution (e.g., nutrients and sediment), increasing canopy cover and thereby reducing water temperature, and contributing allochthonous organic matter (e.g., leaf litter and woody debris). However, the influence of riparian buffers on biotic assemblages in streams is poorly understood, particularly in the Midwestern United States. In this study, we evaluated the effects of riparian buffers on instream habitat, fish assemblage structure, and population characteristics (i.e., the growth of two small-bodied species) in three streams in central Iowa. The streams were surveyed at two spatial scales; specifically, 41 reaches were sampled and 247 macrohabitat types (i.e., pool, riffle, and run) were subsampled in the summer of 2007. Fish assemblage structure data were summarized into separate data sets by the relative abundance of individual species (i.e., fish per minute of electrofishing) and guilds (e.g., trophic and spawning). Multivariate analysis of variance was used to evaluate the differences in instream habitat and fish assemblage structure between areas with and without riparian buffers. The results indicated little to no relationship between the presence of buffers and fish assemblage structure and instream habitat characteristics. Nonmetric multidimensional scaling (NMS) was used to evaluate the patterns of fish assemblage structure for the reaches and macrohabitat types. The NMS further illustrated the similarity in fish assemblages between buffered and unbuffered reaches. However, the growth of central stonerollers Campostoma anomalum was greatest in unbuffered reaches, while that of creek chub Semotilus atromaculatus was greatest in buffered reaches. Differences in food availability associated with riparian buffers (e.g., increased algal production and decreased terrestrial invertebrate contributions in unbuffered reaches) probably resulted in growth disparities. The results of this study suggest that while riparian buffers have minimal local effects on instream habitat and fish assemblage structure in Iowa streams, they influence instream features (e.g., food availability) that affect fish population dynamics.

We estimated the sampling effort required to accurately estimate species richness and to detect changes in catch-per-unit-effort (CPUE) in four Great Plains, USA, streams. The number of sampled reaches (i.e., <1 km) required to estimate stream-segment (i.e., 20–28 km) species richness decreased with increased sampled reach length (i.e., 10, 20, 40, or 60 mean stream widths, MSW), whereas total sampling effort decreased with a greater number of shorter sampled reaches. Collecting all species in a stream segment required all sampled reaches (i.e., 10) of a length equal to 40 or 60 MSW. The number of stream reaches sampled with lengths equal to 40 MSW required to detect a 50% change in CPUE of common species (i.e., total abundance > 1% of total catch) with β = 0.80 ranged from 7 to 630 (mean = 99) and decreased with longer sampled reaches. A greater number of sampled reaches were needed to detect 90% of species richness and 25% changes in CPUE when Jaccard’s similarity of samples of stream fish assemblages and habitat heterogeneity was lower within streams. Our results suggest that homogeneous stream segments require more sampled reaches to characterize fish assemblages and monitor trends in fish abundance.

Egg deposition and use of restored spawning substrates by lithophilic fishes (e.g., Lake Sturgeon Acipenser fulvescens, Lake Whitefish Coregonus clupeaformis, and Walleye Sander vitreus) were assessed throughout the St. Clair–Detroit River system from 2005 to 2016. Bayesian models were used to quantify egg abundance and presence/absence relative to site‐specific variables (e.g., depth, velocity, and artificial spawning reef presence) and temperature to evaluate fish use of restored artificial spawning reefs and assess patterns in egg deposition. Lake Whitefish and Walleye egg abundance, probability of detection, and probability of occupancy were assessed with detection‐adjusted methods; Lake Sturgeon egg abundance and probability of occurrence were assessed using delta‐lognormal methods. The models indicated that the probability of Walleye eggs occupying a site increased with water velocity and that the rate of increase decreased with depth, whereas Lake Whitefish egg occupancy was not correlated with any of the attributes considered. Egg deposition by Lake Whitefish and Walleyes was greater at sites with high water velocities and was lower over artificial spawning reefs. Lake Sturgeon eggs were collected least frequently but were more likely to be collected over artificial spawning reefs and in greater abundances than elsewhere. Detection‐adjusted egg abundances were not greater over artificial spawning reefs, indicating that these projects may not directly benefit spawning Walleyes and Lake Whitefish. However, 98% of the Lake Sturgeon eggs observed were collected over artificial spawning reefs, supporting the hypothesis that the reefs provided spawning sites for Lake Sturgeon and could mitigate historic losses of Lake Sturgeon spawning habitat.