Geology topics

L. G. Mitchell

Publications and source records attributed to L. G. Mitchell.

4 recordsLinked to original sources

USGS2024

Incorporating measurements of vertical land motion in wetland surface elevation change analyses

We compared elevation trajectories from 14 rod surface elevation table (RSET) stations and 60 real-time kinematic (RTK) global positioning system (GPS) transects within the Blackwater National Wildlife Refuge (BNWR) from 2010–2013. The results were similar, 7.3 ± 0.9 (mean ± standard error; RSET) versus 6.2 ± 0.6 mm year −1 (RTK) ( P = 0.216), and were greater than relative sea level rise (RSLR) computed at the nearest long-term tide station (3.9 ± 0.29 mm year −1 ). Despite having shown elevation gain, these wetlands continue to drown and convert to open water. Episodic, multi-day GPS measurements on geodetic control marks at BNWR between 2005 and 2023 revealed a substantial vertical land motion (VLM) signal. From 2005 to 2015, three reference marks used to control the 2010–2013 RTK study lost on average 6.0 ± 0.7 mm year −1 , corresponding to 80% and 94% of the elevation gain measured by the RSET and RTK techniques, respectively. The longer 18-year subsidence trend measured on one of these marks was lower, 3.9 ± 0.7 mm year −1 , highlighting important interannual variability. Wetland elevation change measurements need to account for VLM occurring below the reference marks used to measure elevation change. Estimates from the nearest long-term tide station may not be applicable to the wetland if the tide station is in a different geological setting. At BNWR, VLM was higher than the VLM at the Cambridge tide station, which helps explain why wetlands at BNWR are not keeping pace with RSLR despite the measured high rates of elevation gain.

Maryland↗

USGS1989

Gill tissue reactions in walleye Stizostedion vitreum vitreum and common carp Cyprinus carpio to glochidia of the freshwater mussel Lampsilis radiata siliquoidea

The glochidia of many freshwater mussels, which are obligate parasites on the gills, fins, and other body parts of specific fishes, attach to a suitable host, become encapsulated, and develop to the free-living juvenile stage. Using light and electron microscopy we compared gill tissue reactions in a suitable host (walleye Stizostedion vitreum vitreum ) and unsuitable host (common carp Cyprinus carpio ) infected with Lampsilis radiata siliquoidea . Encapsulation of glochidia on walleye gills was completed by 6 h post-infection at 20 to 22°C. Capsular formation and compaction were accompanied by a general increase in epithelioid cells. Fibrotic material appeared in capsules at about 48 h and virtually filled capsular cells from about Day 5 to Day 11 post-infection. Liberation of juvenile mussels was accompanied by thinning of the capsule from about Day 11 to Day l7. Although glochidia attached to the gills of common carp, few became encapsulated. By 48 h post-infection, preliminary capsular growth was evident and necrotic cells and cellular debris appeared at the edges of the growth. However, all glochidia were sloughed from carp gills by 60 h. Host specificity of L. radiata siliquoidea apparently depended on a combination of the attachment response of glochidia, differences in the encapsulation process, and tissue reactions in the fish.

Diseases of Aquatic Organisms↗

USGS1988

Morphology of glochidia of Lampsilis higginsi (Bivalvia: Unionidae) compared with three related species

Glochidia of the endangered unionid mussel Lampsilis higginsi (Lea) are morphologically similar to those of several other species in the upper Mississippi River. Life history details, such as the timing of reproduction and identity of host fish, can be readily studied if the glochidia of L. higginsi can be distinguished from those of related species. Authors used light and scanning electron microscopy and statistical analyses of three shell measurements, shell length, shell height, and hinge length, to compare the glochidia of L. higginsi with those of L. radiata siliquoidea (Barnes), L. ventricosa (Barnes), and Ligumia recta (Lamarck). Glochidia of L. higginsi were differentiated by scanning electron microscopy on the basis of a combined examination of the position of the hinge ligament and the width of dorsal ridges, but were indistinguishable by light microscope examination or by statistical analyses of measurements.

American Malacological Bulletin↗

USGS1985

Artificial infestation of largemouth bass and walleye with glochidia of Lampsilis ventricosa (Pelecypoda: Unionidae)

The unionid mussel Lampsilis ventricosa is a bundant in the upper Mississippi River and provides a model for studies related to recovery of the endangered Higgins' eye mussel ( Lampsilis higginsi ). We tested the suitability of two species of fish species as hosts for glochidia of L. ventricosa. Laboratory-reared largemouth bass (Micropterus salmoides) and walleyes (Stizostedion vitreum) were artificially infested with the glochidia of L. ventricosa and held separately in two flowthrough tanks for 21 days. Tank bottoms were siphoned daily, and the materials collected were examined for detached glochidia and metamorphosed juveniles. Juveniles were found in both tanks from day 13 post-exposure through day 20, indicating that largemouth bass and walleyes are suitable hosts for the glochidia of L. ventricosa .

Upper Mississippi River↗