Geology topics

Kenna J. Gierke

Publications and source records attributed to Kenna J. Gierke.

4 recordsLinked to original sources

USGS2025

Changing dynamic phosphorus forms from field to stream during surface runoff events

The risk of water quality impairment from agricultural runoff depends on nutrient source, transport, and bioavailability. Phosphorus (P) spirals between dissolved and particulate forms as it is transported with suspended sediment (SS) from agricultural fields, through the stream network, to receiving water bodies. This dynamic sorption-desorption influences bioavailability. We quantified P form and abundance in samples collected during surface-runoff events from a farm field in the East River Basin, Wisconsin and compared them to those in stream water collected from the East River. We sampled five events between late March 2022 and June 2023. During most events, P in surface runoff was mainly in dissolved form, with particulate P sorbed to fine clay, the most abundant particle fraction transported from the field, whereas P in stream water was mainly in particulate form and sorbed to silt, even though fine clay was the most abundant particle fraction in the stream during events. Overall capacity for P sorption to SS in the stream varied among events. Total P and SS concentrations were lower during summer baseflow conditions and smaller surface runoff events; however, what SS was present was more P enriched. This shift in P form from field to stream indicates a potential for sorbing dissolved P to SS during transport through the stream network, which changes the bioavailability of P exported downstream with less bioavailable P as dissolved P binds to SS.

Wisconsin↗

USGS2025

River-to-lake transitional areas contribute disproportionately to in-lake nutrient loading

River-to-lake transitional areas are biogeochemically active sections of the aquatic continuum that are often understudied compared to their adjoining environments. Internal nutrient loading from river-to-lake transitional areas may be a considerable source of nutrients to lakes and if overlooked disconnect upstream management initiatives from in-lake improvements. To contextualize internal nutrient loading by river-to-lake sediments, we conducted sediment core incubations and nutrient assays at 3 time points over a field season from a major contributing tributary of Lake Erie. Using statistical and spatial interpolation models, we upscaled internal nitrogen and phosphorus loading rates across the highly impaired mouth of the Maumee River, which drains into the western basin of Lake Erie. We found that internal nutrient dynamics in this river-to-lake transitional area were regulated by spatial differences in the physical composition and nutrient and organic matter contents of sediments. The Maumee river-to-lake transitional area was largely a source of phosphorus and ammonium nitrogen and a sink of nitrate nitrogen through high denitrification rates. Yet, we observed substantial temporal variation whereby internal nutrient loading was greatest in late summer coinciding with near-zero denitrification. Sediments at this time could contribute an additional ~17% more soluble reactive phosphorus and ~3% more total kjeldahl nitrogen in the bioavailable ammonium nitrogen fraction relative to the daily external nutrient load. High internal nutrient loading rates compared to more offshore areas in western Lake Erie suggest that this degraded river-to-lake transitional area has a disproportional biogeochemical significance and a high potential to contribute to nearshore water quality issues.

Ohio↗

USGS2025

Sediment nutrient dynamics in selected Milwaukee metropolitan area streams, Wisconsin, 2022

The U.S. Geological Survey and Milwaukee Metropolitan Sewerage District in Wisconsin have an ongoing partnership to monitor water quality in streams in the Milwaukee metropolitan area and to assess the effects of stream restoration on habitat and water quality. Because sediment nutrient dynamics can improve or further impair water quality, we measured sediment nitrogen and phosphorus concentrations, potential nitrogen removal, and potential phosphorus retention at 32 streams sites in the Milwaukee metropolitan area in summer 2022. Four of the sites were in rehabilitated stream reaches. Based on the results from this project, we provided a rating of good, fair, or poor for the sediment nutrient dynamics at each site. Sediment nitrogen removal and phosphorus retention in stream reaches increased as the proportion of fine particles increased. Bioavailable nitrogen and phosphorus concentrations increased in stream reaches as particle size decreased, especially at locations with more silt and clay. Particle size typically decreased from upstream to downstream, and several of the sites with finer particles were in downstream parts of the study area, especially in the Milwaukee Estuary sites. The sites that had more fine sediment and higher bioavailable nutrients also had elevated rates of nitrification and denitrification enzyme activity, which is a measurement of the potential nitrogen removal when nitrogen and carbon do not limit the denitrifying bacteria. Additionally, sites with fine sediment typically had the highest potential to retain phosphorus as fine sediment provides many binding sites for phosphorus. The binding sites can become saturated with phosphorus, however, increasing the potential for the phosphorus to be released to stream water. Five of the 32 sampled sites were potentially saturated with phosphorus. Sites that contained more agricultural land in their drainage areas were at higher risk of having sediment that was saturated or near-saturation; however, the sites that had more agricultural land in their drainage areas also had higher nitrification rates. Results from this study indicate that stream rehabilitation projects that promote sediment deposition and accumulation of organic matter in the stream channel can increase nitrogen removal and phosphorus retention.

Wisconsin↗

USGS2024

Role of tributary cyanobacterial and nutrient transport and sediment processes on cyanobacterial bloom initiation in Lake Superior nearshore

Watershed fluxes of suspended sediment (SS), nutrients, in particular phosphorus (P), and cyanobacteria may play a role in driving cyanobacterial blooms along the southwestern shore of oligotrophic Lake Superior. To understand how tributary loads contribute to nearshore blooms, we sampled two southwestern shore tributaries, Bois Brule and Siskiwit Rivers. We collected water-quality samples to compute nutrient and sediment loads and to assess cyanobacteria community composition from the tributaries to the nearshore. We collected suspended and streambed sediment to assess the capacity for sediment to store and transport bioavailable P and to assess cyanobacteria community composition. Storm flows drove export of SS, total P, and total nitrogen, with the majority of total P being particulate P. Equilibrium P concentrations revealed that SS sorbed P as it is moved through the stream network across sites and seasons and was a potential source of P to the nearshore. However, streambed sediment in the Bois Brule and Siskiwit River watersheds were P sinks during summer, which potentially delayed transport of dissolved P to the lake. The cyanobacteria community varied spatially and temporally relating to multiple environmental variables including nutrients (P, N, and C) and specific conductivity. Cyanobacteria capable of producing cyanotoxins were present in tributaries and found across multiple environmental compartments indicating a potential for fluvial flow to the nearshore. This study demonstrated that streamflow is a primary driver of total nutrient and sediment loading in both watersheds, which indicates the potential for algal loading to the nearshore via suspended sediment or water.

Wisconsin↗