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B.C. Knights

Publications and source records attributed to B.C. Knights.

7 recordsLinked to original sources
USGS2006

Mercury in soils, lakes, and fish in Voyageurs National Park (Minnesota): Importance of atmospheric deposition and ecosystem factors

Concentrations of methylmercury in game fish from many interior lakes in Voyageurs National Park (MN, U.S.A.) substantially exceed criteria for the protection of human health. We assessed the importance of atmospheric and geologic sources of mercury to interior lakes and watersheds within the Park and identified ecosystem factors associated with variation in methylmercury contamination of lacustrine food webs. Geologic sources of mercury were small, based on analyses of underlying bedrock and C-horizon soils, and nearly all mercury in the O- and A-horizon soils was derived from atmospheric deposition. Analyses of dated sediment cores from five lakes showed that most (63% ?? 13%) of the mercury accumulated in lake sediments during the 1900s was from anthropogenic sources. Contamination of food webs was assessed by analysis of whole, 1-year-old yellow perch (Perca flavescens), a regionally important prey fish. The concentrations of total mercury in yellow perch and of methylmercury in lake water varied substantially among lakes, reflecting the influence of ecosystem processes and variables that affect the microbial production and abundance of methylmercury. Models developed with the information-theoretic approach (Akaike Information Criteria) identified lake water pH, dissolved sulfate, and total organic carbon (an indicator of wetland influence) as factors influencing methylmercury concentrations in lake water and fish. We conclude that nearly all of the mercury in fish in this seemingly pristine landscape was derived from atmospheric deposition, that most of this bioaccumulated mercury was from anthropogenic sources, and that both watershed and lacustrine factors exert important controls on the bioaccumulation of methylmercury. ?? 2006 American Chemical Society.

Environmental Science & Technology↗
USGS2006

Persistent disturbance by commercial navigation afters the relative abundance of channel-dwelling fishes in a large river

We provide the first evidence for chronic effects of disturbance by commercial vessels on the spatial distribution and abundance of fishes in the channels of a large river. Most of the world's large rivers are intensively managed to satisfy increasing demands for commercial shipping, but little research has been conducted to identify and alleviate any adverse consequences of commercial navigation. We used a combination of a gradient sampling design incorporating quasicontrol areas with Akaike's information criterion (AIC)-weighted model averaging to estimate effects of disturbances by commercial vessels on fishes in the upper Mississippi River. Species density, which mainly measured species evenness, decreased with increasing disturbance frequency. The most abundant species - gizzard shad (Dorosoma cepedianum) and freshwater drum (Aplodinotus grunniens) - and the less abundant shovelnose sturgeon (Scaphirhynchus platorhynchus) and flathead catfish (Pylodictis olivaris) were seemingly unaffected by traffic disturbance. In contrast, the relative abundance of the toothed herrings (Hiodon spp.), redhorses (Moxostoma spp.), buffaloes (Ictiobus spp.), channel catfish (Ictalurus punctatus), sauger (Sander canadensis), and white bass (Morone chrysops) decreased with increasing traffic in the navigation channel. We hypothesized that the combination of alteration of hydraulic features within navigation channels and rehabilitation of secondary channels might benefit channel-dependent species. ?? 2006 NRC.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2004

Hydrologic and hydraulic factors affecting passage of paddlefish through dams in the Upper Mississippi River

Populations of paddlefish Polyodon spathula have been adversely affected by dams that can block their movements. Unlike high-head dams that preclude fish passage (unless they are equipped with fishways), the dams on the upper Mississippi River are typically low-head dams with bottom release gates that may allow fish passage under certain conditions. We evaluated the relation of dam head and river discharge to the passage of radio-tagged paddlefish through dams in the upper Mississippi River. Radio transmitters were surgically implanted into 71 paddlefish from Navigation Pools 5A and 8 of the upper Mississippi River and from two tributary rivers during fall 1994 through fall 1996. We tracked paddlefish through September 1997 and documented 53 passages through dams, 20 upstream and 33 downstream. Passages occurred mostly during spring (71%) but also occurred sporadically during summer and fall (29%). Spring passages varied among years in response to hydrologic conditions. We evaluated patterns in upstream and downstream passages with Cox proportional hazard regression models. Model results indicated that dam head height strongly affected the upstream passage of paddlefish but not the downstream passage. Several paddlefish, however, passed upstream through a dam during periods when the minimum head at the dam was substantial ( ≥1 m ). In these cases, we hypothesize that paddlefish moved upstream through the lock chamber.

Illinois, Iowa, Minnesota, Wisconsin↗
USGS2003

Movement and habitat use by radio-tagged paddlefish in the upper Mississippi River and tributaries

We used radio telemetry to evaluate the movement and habitat use of paddlefish Polyodon spathula in the upper Mississippi River and two tributary rivers. Radio transmitters were surgically implanted into 71 paddlefish in Navigation Pools 5A and 8 of the upper Mississippi River, the Chippewa River, and the Wisconsin River during fall 1994 through fall 1996. Radiotagged paddlefish were located through summer 1997. The range of paddlefish movement was typically low during all seasons except spring, but some paddlefish moved throughout the 420-km extent of the study area. Paddlefish tagged in the Chippewa River were closely linked with the upper Mississippi River, as substantial portions of the population inhabited the adjacent Navigation Pool 4 each spring; paddlefish in the Wisconsin River, however, rarely ventured out of that tributary. The use of aquatic area types by paddlefish varied among the study reaches. A cartographic model of paddlefish habitat suitability was developed for Navigation Pool 8 based on geographic information systems (GIS) coverages of bathymetry and current velocity. The value of paddlefish habitat in the cartographic model increased with depth and decreased with current velocity. For example, areas modeled as excellent corresponded to regions classified as having both deep water (greater than or equal to6.0 m) and negligible (<5 cm/s) current velocities. Our study suggests that aquatic area types are an inadequate basis for making sound management decisions regarding the critical habitats of paddlefish in complex riverine systems because such strata rely on gross geomorpological features rather than on the physicochemical variables that fish use to choose habitats. The development of systemic GIS coverages of such variables could improve the understanding of fish habitat selection and management in the upper Mississippi River.

North American Journal of Fisheries Management↗
USGS1995

Responses of bluegills and black crappies to dissolved oxygen, temperature, and current in backwater lakes of the upper Mississippi River during winter

We conducted a radiotelemetry study to examine the effects of dissolved oxygen (DO), water temperature, and current velocity on winter habitat selection by bluegills Lepomis macrochirus and black crappies Pomoxis nigromaculatus in the Finger Lakes backwater complex, Pool 5, on the upper Mississippi River. When DO was above 2 mg/L, both species selected areas with water temperature greater than 1°C and undetectable current. As dissolved oxygen concentrations fell below 2 mg/L, fish moved to areas with higher DO, despite water temperatures of 1°C and lower and current velocities of 1 cm/s. Areas with water temperature less than 1°C and current velocity greater than 1 cm/s were avoided. To incorporate the winter habitat requirements of bluegills and black crappies into habitat restoration projects, we recommend designs that allow the inflow of oxygenated water to maintain adequate DO without substantially decreasing temperature and increasing current velocity.

Minnesota↗
USGS1992

A sediment suspension system for bioassays with small aquatic organisms

Exposure of aquatic organisms to suspended sediments can impair growth and survival and increase bioaccumulation of sediment-associated contaminants. However, evaluation of the effects of suspended sediments and their associated contaminants on aquatic organisms has been hampered by the lack of a practical and inexpensive exposure system for conducting bioassays. We present a cost-effective system for assessing the effects of suspended sediments and associated contaminants on small aquatic organisms. A 7-day suspension test was conducted with nominal sediment concentrations ranging from 0.0 to 5.0 g 1 −1 . The system maintained relatively constant suspended sediment concentrations, as measured by turbidity, and caused minimal mortality to test organisms.

Hydrobiologia↗