Geology topics

James C. Smith

Publications and source records attributed to James C. Smith.

3 recordsLinked to original sources

USGS2025

Diel and spatial variability in cyanobacterial composition, gene abundance, and toxin concentration: A pilot study

We designed a pilot field study to assess relations between sunlight, cyanobacteria, and cyanotoxins. In 2021, we collected day (07:00 h, 10:00 h, 13:00 h, 16:00 h) and night samples (19:00 h, 22:00 h, 01:00 h, 04:00 h) at two locations in Kabetogama Lake, MN, USA. One sample set was collected from the lakeward end of a boat dock and the other on the nearby shoreline. Cyanobacterial phylogenetic eDNA differences over 24 h (pseudo F = 2.0938, p = 0.127) were not significant. Copies of anatoxin ( anaC ) and microcystin ( mcyE ) synthetase genes varied significantly over the sampling times at the dock (Friedman Χ 2 = 15.01, df = 7, p = 0.036; Friedman Χ 2 = 19.22, df = 7, p = 0.008) and the shoreline (Friedman Χ 2 = 19.33, df = 7, p = 0.007; Friedman Χ 2 = 20.56, df = 7, p = 0.005), with the highest anaC counts occurring during the night for both sites. Additionally, the highest total and dissolved microcystin concentrations occurred at night. Despite the proximity of the sampling locations, cyanobacterial phylogenetic eDNA results indicate that the variability between sites (pseudo-F = 27.547, p = 0.001) were greater than temporal differences over 24 h (pseudo F = 2.0938, p = 0.127). Understanding the effect of diel and spatial variability may help researchers and resource managers make informed decisions about sampling and potential exposure.

Minnesota↗

USGS2025

Water quality-based risk assessment for zebra mussel establishment: A case study of single- and multiple-factor methods in northern temperate lakes

Most previous research has used an individual water quality parameter, such as calcium, to predict likelihood of zebra mussel establishment in lakes; we employed two multiple-factor methods, our own susceptibility index for zebra mussels in lakes (SIZL) and aragonite saturation state, to evaluate the risk of mussel establishment. Thirty sites in Voyageurs National Park (VNP) were sampled in 2023 for water quality conditions, including those that play a key role in mussel survivability. These results were combined with existing data sets to determine which lakes, and which locations within the larger lakes, are at greatest risk for zebra mussel establishment. Results for VNP indicate that physical lake characteristics and water quality conditions (both single- and multiple-factor methods) put the large, interconnected lakes in VNP at greater risk of zebra mussel establishment than the smaller interior lakes. All sampled interior lakes had alkalinity and calcium concentrations below thresholds conducive to zebra mussel establishment, although Mukooda and O’Leary lakes were identified as the most at-risk interior lakes. The area in the large lakes most at risk was Sullivan Bay in Kabetogama Lake, where water quality conditions were found to be conducive to zebra mussel establishment. Results from this study could be used by resource managers to focus additional inspections, decontaminations, and regulations to protect the most at-risk lakes. These multiple-factor methods may be useful in determining the risk of zebra mussel infestation in other water bodies.

Minnesota↗

USGS2025

Possible influence of water level management on nutrient flux in nearshore sediments of Kabetogama Lake, Minnesota, USA

Lake water level fluctuations are an important factor driving variation in many ecosystem processes. The nearshore sediments that are periodically exposed and re-inundated can develop distinct physical and chemical characteristics, especially in relationship to the organic matter content of the sediments and the particle size distribution. These sediment characteristics in turn can alter the flux of nitrogen (N) and phosphorus (P) from sediments into the water column when sediments are inundated. Here, we used intact sediment core experiments across a range of sediment inundation frequencies to estimate the effect of inundation frequency on sediment nutrient flux in Kabetogama Lake, Minnesota, USA. We observed associations between elevation or inundation frequency and some sediment characteristics, but in a structural equation model, inundation frequency and the sediment properties we measured were poorly related to inorganic nutrient flux. On the other hand, inundation frequency did have a moderate association with organic N and P flux from sediments, which could be due to decay of terrestrial organic matter that accumulates on exposed sediments. We used our parameterized structural equation model to estimate how three different water level management regimes employed over the past 50 years could influence organic N and P flux from sediments. The models suggested more recent water level management regimes reduced organic N and P flux by 9%–13% and 5.9%–9.8%, respectively. Nearshore sediment flux could sustain and influence harmful algal blooms that occur in this lake, and these fluxes could be influenced by water level management.

Minnesota↗