Geology topics

Leah Lenoch

Publications and source records attributed to Leah Lenoch.

3 recordsLinked to original sources

USGS2023

Stream corridor sources of suspended sediment and sediment-bound phosphorus from an urban tributary to the Great Lakes

Potential sources of suspended sediment and sediment-bound phosphorus (sedP) were studied in the Kinnickinnic River (51 square kilometers), a heavily urbanized tributary to Lake Michigan (90% urban land use) in Milwaukee, Wisconsin. The river is 60% concrete lined channels, with few unlined reaches. From September 2019 through August 2020, an integrated study of sediment budget and sediment fingerprinting was conducted to quantify upland and stream corridor sources of suspended sediment and sedP using Sediment Source Assessment Tool (SedSAT) methods with a suite of trace elements. Passive suspended sediment samplers were installed at three sites. Soft, fine-grained streambed sediment was collected at 10 rapid geomorphic assessment (RGA) sites. An inventory of bank erosion and soft-sediment deposition was done at each of the 18 RGA sites, which were selected to represent a range of stream sizes and geomorphic conditions. Sources of suspended sediment varied with streamflow; the primary source was from roadways in residential areas followed by eroding streambanks. Industrial/commercial areas contributed 1% of the suspended sediment at the streamgage during the study period, whereas green space contributed 18% of the suspended sediment at a mid-basin monitoring location downstream of an unlined reach. The dominant sources of streambed sediment, like suspended sediment, throughout the basin were eroding banks and residential areas, with green space and industrial/commercial area signatures present locally. In contrast with previous studies in agricultural and mixed-use basins, the urban Kinnickinnic River had limited storage of soft sediment, due to the hydrologically flashy system and concrete lined channels. However, eroding streambank sources contribute 50% of the streambed sediment, but only 9% of suspended sediment within this tributary to the Great Lakes.

Wisconsin↗

USGS2022

Whole-ecosystem experiment illustrates short timescale hydrodynamic, light, and nutrient control of primary production in a terminal slough

Estuaries are among the most productive of aquatic ecosystems. Yet the collective understanding of patterns and drivers of primary production in estuaries is incomplete, in part due to complex hydrodynamics and multiple controlling factors that vary at a range of temporal and spatial scales. A whole-ecosystem experiment was conducted in a deep, pelagically dominated terminal channel of the Sacramento-San Joaquin Delta (California, USA) that seasonally appears to become nitrogen limited, to test whether adding calcium nitrate would stimulate primary productivity or increase phytoplankton density. Production did not respond consistently to fertilization, in part because nitrate and phytoplankton were dispersed away from the manipulated area within 1–3 days. Temporal and spatial patterns of gross primary production were more strongly related to stratification and light availability (i.e., turbidity) than nitrogen, highlighting the role of hydrodynamics in regulating system production. Similarly, chlorophyll was positively related not only to stratification but also to nitrogen—with a positive interaction—suggesting stratification may trigger nutrient limitation. The average rate of primary production (4.3 g O 2 m −2 d −1 ), metabolic N demand (0.023 mg N L −1 d −1 ), and ambient dissolved inorganic nitrogen concentration (0.03 mg N L −1 ) indicate that nitrogen can become limiting in time and space, especially during episodic stratification events when phytoplankton are isolated within the photic zone, or farther upstream where water clarity increases, dispersive flux decreases, and stratification is stronger and more frequent. The role of hydrodynamics in organizing habitat connectivity and regulating physical and chemical processes at multiple temporal and spatial scales is critical for determining resource availability and evaluating biogeochemical processes in estuaries.

California↗

USGS2021

Dispersion and stratification dynamics in the upper Sacramento River deep water ship channel

Hydrodynamics control the movement of water and material within and among habitats, where time-scales of mixing can exert bottom-up regulatory effects on aquatic ecosystems through their influence on primary production. The San Francisco Estuary (estuary) is a low-productivity ecosystem, which is in part responsible for constraining higher trophic levels, including fishes. Many research and habitat-restoration efforts trying to increase primary production have been conducted, including, as described here, a whole-ecosystem nutrient addition experiment where calcium nitrate was applied in the Sacramento River Deep Water Ship Channel (DWSC) to see if phytoplankton production could be increased and exported out of the DWSC. As an integral part of this experiment, we investigated the physical mechanisms that control mixing, and how these mechanisms affect the strength and duration of thermal stratification, which we revealed as critical for controlling phytoplankton dynamics in the relatively turbid upper DWSC. Analysis of a suite of mixing mechanisms and time-scales show that both tidal currents and wind control mixing rates and stratification dynamics in the DWSC. Longitudinal and vertical dispersion increased during periods of high wind, during which wind speed influenced dispersion more than tidal currents. Thermal stratification developed most days, which slowed vertical mixing but was rapidly broken down by wind-induced mixing. Stratification rarely persisted for longer than 24 hours, limiting phytoplankton production in the study area. The interaction between physical mechanisms that control mixing rates, mediate stratification dynamics, and ultimately limit primary production in the DWSC may be useful in informing habitat restoration elsewhere in the Delta and in other turbid aquatic environments.

California↗