David C Walters

The natural wood regime forms the third leg of a tripod of physical processes that supports river science and management, along with the natural flow and sediment regimes. The wood regime consists of wood recruitment, transport, and storage in river corridors. Each of these components can be characterized in terms of magnitude, frequency, rate, timing, duration, and mode. We distinguish...

Adult aquatic insects are a globally important subsidy in terrestrial food webs. However, our understanding of their importance is largely limited to studies that measure predation of live insects by terrestrial predators. Yet the flux of adult aquatic insects to terrestrial detrital pools may also be an important subsidy pathway, particularly in cases where insect production exceeds the

A multitude of biologically active pharmaceuticals contaminate surface waters globally, yet their presence in aquatic food webs remain largely unknown. Here, we show that over 60 pharmaceutical compounds can be detected in aquatic invertebrates and riparian spiders in six streams near Melbourne, Australia. Similar concentrations in aquatic invertebrate larvae and riparian predators...

We investigated PCB contamination at the Ashtabula River Area of Concern (AOC) following remedial dredging using araneid and tetragnathid spiders. PCB concentrations remain elevated in the AOC compared to reference conditions. Patterns of contamination were strikingly similar between taxa, but were higher in tetragnathids at the most contaminated sites. Spider PCB homolog distributions...

In the Colorado Front Range (USA), disturbance history dictates stream planform. Undisturbed, old-growth streams have multiple channels and large amounts of wood and depositional habitat. Disturbed streams (wildfires and logging

To evaluate the effect of fish growth on mercury (Hg) and polychlorinated biphenyl (PCB) bioaccumulation, a non–steady‐state toxicokinetic model, combined with a Wisconsin bioenergetics model, was developed to simulate Hg and PCB bioaccumulation in bluegill (Lepomis macrochirus). The model was validated by comparing observed with predicted Hg and PCB 180 concentrations across 5 age...

The river stonefly, Pteronarcys californica (aka salmonfly), is an iconic insect in rivers of western North America due to its large size and its support of economically important species like wild trout (Nehring et al. 2011). Their emergence generates a large economic subsidy to local communities, as anglers from around the world travel to western rivers to fish the salmonfly “hatch” (e...

Aquatic invertebrates are a key component of freshwater ecosystems, and understanding aquatic invertebrate taxonomy is a cornerstone of freshwater science. Physical reference collections of expertly identified voucher specimens are the ‘gold-standard’ used to confirm specimen identifications. However, most biologists lack access to such collections, which themselves tend to be highly...

Research in stream metabolism, gas exchange, and sediment dynamics indicates that rivers are an active component of the global carbon cycle and that river form and process can influence partitioning of terrestrially derived carbon among the atmosphere, geosphere, and ocean. Here we develop a conceptual model of carbon dynamics (inputs, outputs, and storage of organic carbon) within a...

Anthropogenic climate change is causing a wide range of stresses in aquatic ecosystems, primarily through warming thermal conditions. Lakes, in response to these changes, are experiencing increases in both summer temperatures and ice-free days. We used continuous records of lake surface temperature and air temperature to create statistical models of daily mean lake surface temperature to...

Insect metamorphosis often results in substantial chemical changes that can alter contaminant concentrations and fractionate isotopes. We exposed larval mayflies (Baetis tricaudatus) and their food (periphyton) to an aqueous zinc gradient (3-340 µg Zn/l) and measured zinc concentrations at different stages of metamorphosis: larval, subimago, and imago. We also measured changes in stable...

Pharmaceuticals and personal care products (PPCPs) are ubiquitous in freshwater ecosystems worldwide and are recognized as contaminants of concern. Currently, contaminants of concern are classified for their persistence, bioaccumulation, and toxicity (PBT criteria). PPCPs are not classified as persistent organic pollutants (POPs), although some PPCPs share characteristics similar to POPs...