Wave breaking turbulence at the offshore front of the Columbia River Plume

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 41 (2014): 8987–8993, doi:10.1002/2014GL062274.Observations at the Columbia River plume show that wave breaking is an important source of turbulence at the offshore front, which may contribute to plume mixing. The lateral gradient of current associated with the plume front is sufficient to block (and break) shorter waves. The intense whitecapping that then occurs at the front is a significant source of turbulence, which diffuses downward from the surface according to a scaling determined by the wave height and the gradient of wave energy flux. This process is distinct from the shear-driven mixing that occurs at the interface of river water and ocean water. Observations with and without short waves are examined, especially in two cases in which the background conditions (i.e., tidal flows and river discharge) are otherwise identical.This work was supported by the Office of Naval Research, as part of the Data Assimilation and Remote Sensing for Littoral Applications (DARLA) project and in coordination with the Rivers and Inlets (RIVET) program

Juvenile Salmon Passage in Sloped-Baffled Culverts

The connectivity of river drainages has been decreased by the installation of roadway culverts, particularly for the salmonids of the Pacific Northwest. Thousands of culverts within the State of Washington have been designated by the state DOT as fish passage barriers. Though it is well known that the anadromous salmon travel upstream to spawn, recent evidence suggests that juvenile salmon also travel upstream to seek preferred habitats for feeding, which may ultimately improve their survival at sea. Retrofitting culverts is an economical solution that has been initially implemented to improve adult salmon passage. Baffles increase water depth for low flow conditions and reduce velocities for higher flowrates. To determine the effect of baffles on upstream passage of juveniles, sloped-baffles were studied at a culvert test bed near Tenino, Washington. Using an Acoustic Doppler Velocimeter (ADV), 3-D velocity fields were collected in a full-sized 12.2 m (40’) long, 1.8 m (6’) diameter corrugated culvert. The culvert slope, baffle spacing, and baffle height were varied to observe flow regime trends that describe conditions suitable for fish passage. This project is unique from other hydraulic studies in that biological testing was conducted in conjunction with the hydrodynamic measurements. Biologists randomly selected 100 juvenile Coho salmon from the on-site rearing facility and allowed the fish to ascend the culvert during a three hour period. The movement of the fish was recorded with video cameras and the passage rate was determined.Results indicate that there is considerable spatial variability in the flow created by the baffles within the culvert. The flow is asymmetric, consisting of a jet traveling over the low side of the baffle and an area of re-circulating water on the high side of the baffle. The asymmetry decreases as the discharge increases and the mean water height surpasses the baffle height. The diversity of flow structures created by this asymmetry is important because it increases the number of reduced velocity paths that fish may travel. The fish passage success rates are also consistent with the trends of asymmetry: as the culvert discharge increases fish are limited to fewer possible paths, and passage rates decrease. The results suggest that both the structure of the flow and the average speed of the flow affect the passage rate. We present a scaling equation that relates the occurrence of flow structures to the independent study parameters in order to provide guidance in baffle implementation. Recommendations for future work include further biological interpretation and testing, so that the hydraulic and biological results may be more closely coupled

Viral and microbial community dynamics in four aquatic environments

The species composition and metabolic potential of microbial and viral communities are predictable and stable for most ecosystems. This apparent stability contradicts theoretical models as well as the viral–microbial dynamics observed in simple ecosystems, both of which show Kill-the-Winner behavior causing cycling of the dominant taxa. Microbial and viral metagenomes were obtained from four human-controlled aquatic environments at various time points separated by one day to \u3e1 year. These environments were maintained within narrow geochemical bounds and had characteristic species composition and metabolic potentials at all time points. However, underlying this stability were rapid changes at the fine-grained level of viral genotypes and microbial strains. These results suggest a model wherein functionally redundant microbial and viral taxa are cycling at the level of viral genotypes and virus-sensitive microbial strains. Microbial taxa, viral taxa, and metabolic function persist over time in stable ecosystems and both communities fluctuate in a Kill-the-Winner manner at the level of viral genotypes and microbial strains