Byron N. Karns | Geology Reports

USGS2018

Method comparisons for determining concentrations of metals in water samples used in studies of fish migratory histories

Signatures developed from metal concentrations in water and fish bony structures can be used to demonstrate migration of individual fish between connected water bodies. The U.S. Geological Survey (USGS), in cooperation with the National Park Service and the Missouri Department of Conservation, compared two protocols for collecting and analyzing water samples for concentrations of several metals commonly used to develop metal signatures. In 2015, paired seasonal water samples were collected in two study areas incorporating three National Park Service units; paired water samples were collected using USGS protocols and simpler research protocols. Metal concentrations obtained using USGS and research protocols were compared using t-tests, percent differences, and simple linear regression analyses. Graphical plots of median values and measured ranges were used to compare ratios of strontium to calcium (Sr:Ca) and barium to calcium (Ba:Ca) obtained using the different protocols among individual stations within the two study areas. For stations on the Mississippi and St. Croix Rivers, ranges in concentrations of calcium, barium, and strontium (obtained using USGS protocols) were compared between samples collected from 1995 through 2012 and samples collected in this study. Comparisons were used to evaluate the long-term stability of metal concentrations in the environment. Collectively, results presented in this report demonstrated that research protocols provided metal concentration data that were similar to data obtained using USGS protocols for all compared metals except manganese. Holding times of 6–33 weeks prior to filtration and analyses for samples collected using research protocols may have caused greater changes in manganese concentrations compared to other metals. Strontium, barium, and calcium are the metals most commonly used in studies of fish migration, and concentrations of these metals were similar using different protocols. However, rivers within each study area were more easily distinguished from each other using metal concentration data obtained using USGS protocols compared to data obtained using research protocols. Information presented in this report can be used to develop studies that use identified metal signatures in connected water bodies and bony fish structures to demonstrate fish migration.

Mississippi National River and Recreation Area, Na↗

USGS2018

Spatial and temporal variance in fatty acid and stable isotope signatures across trophic levels in large river systems

Fatty acid and stable isotope signatures allow researchers to better understand food webs, food sources, and trophic relationships. Research in marine and lentic systems has indicated that the variance of these biomarkers can exhibit substantial differences across spatial and temporal scales, but this type of analysis has not been completed for large river systems. Our objectives were to evaluate variance structures for fatty acids and stable isotopes (i.e. δ13C and δ15N) of seston, threeridge mussels, hydropsychid caddisflies, gizzard shad, and bluegill across spatial scales (10s-100s km) in large rivers of the Upper Mississippi River Basin, USA that were sampled annually for two years, and to evaluate the implications of this variance on the design and interpretation of trophic studies. The highest variance for both isotopes was present at the largest spatial scale for all taxa (except seston δ15N) indicating that these isotopic signatures are responding to factors at a larger geographic level rather than being influenced by local-scale alterations. Conversely, the highest variance for fatty acids was present at the smallest spatial scale (i.e. among individuals) for all taxa except caddisflies, indicating that the physiological and metabolic processes that influence fatty acid profiles can differ substantially between individuals at a given site. Our results highlight the need to consider the spatial partitioning of variance during sample design and analysis, as some taxa may not be suitable to assess ecological questions at larger spatial scales.

River Research and Applications↗