Colin Plank - Academia.edu (original) (raw)

Papers by Colin Plank

Global and Planetary Change, Nov 1, 2013

ABSTRACT We have investigated the variability of the magnetic properties of surface sediments acr... more ABSTRACT We have investigated the variability of the magnetic properties of surface sediments across eight Minnesota lake basins. The measured magnetic properties are controlled by the competing fluxes of allochthonous and autochthonous magnetic particles, and differ according to location in the basin. Shoreline sediments are dominated by detrital magnetic particles, whereas littoral and profundal sediments are characterized by a combination of bacterial magnetosomes and detrital particles. The position of the oxic-anoxic interface, which may occur in the water or within the sediment column, controls the depth at which living magnetotactic bacteria occur, and determines the degree of preservation of their magnetosome chains in the surface sediment. The preservation potential of undisturbed chains is higher for bacterial magnetite formed at the top of the sediment column in the littoral area than for magnetosomes originating in the water column in the profundal area. Bacterial magnetite in the profundal facies will contain a higher proportion of chains collapsed during settlement through the water column to the lake bottom. This process increases the fraction of interacting magnetosomes, which in turn artificially lowers the ARM ratio (χARM/IRM), which ceases to be a reliable grain size indicator in the profundal environment. Our results indicate that a holistic approach to interpreting limnologically-derived paleoecological data should be employed. Specifically, a thorough understanding of evolving and interrelated factors such as basin morphology and limnologic conditions is crucial for a more confident interpretation of the sedimentary record in terms of environmental conditions at the time of sediment deposition.

Ground Water Monitoring and Remediation, Jun 1, 2023

At Eglin Air Force Base (AFB) in the Florida Panhandle, a groundwater extraction and treatment sy... more At Eglin Air Force Base (AFB) in the Florida Panhandle, a groundwater extraction and treatment system was installed to contain and remediate a chlorinated solvent plume. After 2 years of operation, the system was not removing the contaminant mass at the rate predicted or required to meet performance‐based contract terms. As a result, a sequence‐stratigraphic analysis was initiated to develop a strategy to improve performance. Sequence Stratigraphy methods were employed to identify a marine flooding surface (mfs) formed during a relative sea level highstand. The analysis also found that the mfs was locally eroded away, indicating that incised valleys were eroded into the formation during a relative lowstand of sea level. These valleys were backfilled with coarse‐grained fluvial and estuarine strata. The analysis concluded that the groundwater extraction system lacked an extraction well screened within the coarse‐grained valley fill. An additional extraction well was installed, which targeted the incised valley fill and resulted in a significant increase in contaminant mass removal rate without increasing system capacity or operational costs. This case study suggests that efficiency improvements are tenable at many sites where groundwater remediation is occurring within the Surficial Aquifer System of the Gulf Coast (Citronelle Formation) as well as sites in similar geologic settings worldwide.

Journal of Climate, Aug 1, 2009

New Mexico Geological Society Annual Spring Meeting, Apr 8, 2016

Kirtland Air Force Base discovered a leak at the former fuel offloading rack in 1999, leading to ... more Kirtland Air Force Base discovered a leak at the former fuel offloading rack in 1999, leading to a soil and groundwater investigation to determine the nature and extent of contamination resulting from the release of aviation gas into the environment. The majority of contamination is limited to the source area on the Air Force base with dissolved constituents extending off-base. Ethylene dibromide (EDB) is the primary risk driver for the site, with the dissolved phase plume extending approximately 7,000 feet down gradient towards the Albuquerque Bernalillo County Water Utility Authority Ridgecrest water supply wells. Depth to groundwater at the site is betwen 460 to 480 feet and flows to the north-northeast towards a cone of depression located near the Ridgecrest well field. Utilizing geologist soil boring logs, continuous cores, and geophysical analyses, environmental sequence stratigraphy cross-sections have been developed at regional and plume scales. These cross-sections are consistent with the geologic understanding of the Abuquerque Basin synthesized by Connell (2008). Regional cross sections show that the EDB plume migrates within the portion of the groundwater system comprised of braided river deposits of the Ancestral Rio Grande, one of three primary depositional systems that filled the Rio Grande Rift Basins over time (Champion et al., 2015). Plume scale sections show that the coarse channel-fill and bar sediments are interbedded with silts and clays deposited in overbank and incipient floodplain settings (Champion et al., 2016). The depositional morphology of these fluvial deposits appears to influence plume hydraulics, resulting in the lateral spreading of the plume parallel and perpendicular to the regional hydraulic gradient. Understanding the basin geology, specifically the orientation and extent of the braided channel deposits, at a variety of scales is critical for the design and implementation of the remediation technologies used to address EDB in groundwater. Locations of extraction wells for the ongoing EDB plume collapse interim measure were largely informed by the site stratigraphy and the simulation of plume capture using three-dimensional fate and transport models.

AGU Fall Meeting Abstracts, Dec 1, 2008

ABSTRACT To assess the controls on sedimentary magnetic signatures in lakes, we analyzed the char... more ABSTRACT To assess the controls on sedimentary magnetic signatures in lakes, we analyzed the characteristics of core, surface, sediment trap, and catchment samples collected from small, temperate-climate lakes, which are commonly used in paleoenvironmental reconstructions. Magnetic properties of sediments were evaluated using room temperature measurements (susceptibility, IRM, ARM), hysteresis parameters, low temperature magnetization curves, and modeling of bulk coercivity spectra, obtained from IRM and ARM acquisition and demagnetization curves. The results highlight several characteristics of lacustrine sediments: 1) Magnetic- mineral assemblages are dominated by low-coercivity minerals (e.g. magnetite); 2) Saturation magnetization, rather than remanent magnetization, is a better overall indicator of concentration, due to differences in grain size; 3) Shoreline samples contain almost exclusively detrital multi-domain (MD) magnetite grains, while littoral and profundal sediments contain a mixture of MD and in-lake produced single-domain (SD) grains; 4) Profundal sediments, deposited in seasonally-anoxic waters, exhibit dissolution of finer-grained particles; 5) Calculated contributions of a biogenic source differ depending on method utilized. ARM/IRM ratios and delta/delta ratios are more conservative in this aspect, indicating a maximum of 50% contribution of biogenic magnetite. Hysteresis and coercivity analyses yield up to 75% contribution of biogenic particles; 6) There is a direct linear relation between percent mass organic matter (OM) and ARM/IRM, showing a dependence of magnetic grain size on organic carbon concentration. This correlation highlights the role OM has in the process of production and preservation of magnetosomes. Organic matter decomposition depletes the dissolved oxygen and leads to temporary or permanent anoxic conditions in the sediment. If conditions are suboxic (e.g. in the littoral zone, where oxygen can diffuse into the sediment from the overlying oxic water column), magnetite has a better chance of being preserved. If bottom waters and sediments are anoxic, dissolution of magnetic grains will occur, with smaller particles being preferentially dissolved.

AGU Fall Meeting Abstracts, Dec 1, 2007

Spatial variation in the water levels of lakes provides a useful record of past moisture regimes ... more Spatial variation in the water levels of lakes provides a useful record of past moisture regimes and their associated synoptic climate patterns. Here, we present updated maps of North American lake levels over the past 15,000 years. Data have been assembled from published lake records in all regions of the continent, and focus on records that provide direct evidence of past shoreline elevations. The results show both the effects of short- term climate variability and the sensitivity of moisture gradients to the boundary conditions of the global climate system. For example, some lakes like Hidden Lake, Colorado, record the infrequent decadal-to-centennial "megadroughts" of the past two millennia that have been captured in tree-ring data, and nearly all lakes in the Rockies and Great Plains record persistently dry conditions for multiple millennia between 8000 and 5000 years BP. Regional climate model simulations show that the documented long-term aridity may have resulted from the direct effects of orbitally-driven changes in seasonal insolation patterns. Consequently, although "megadroughts" may be part of the natural moisture regimes of the late-Holocene, large magnitude shifts in boundary conditions both in the past (e.g., insolation) and future (i.e., greenhouse gases) have the potential to fundamentally alter the availability of water.

AGUFM, Dec 1, 2007

ABSTRACT Magnetic properties of lake sediments are routinely measured as part of paleolimnologica... more ABSTRACT Magnetic properties of lake sediments are routinely measured as part of paleolimnological and paleoclimatic research. Basic parameters such as magnetic susceptibility (MS), anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM) are used for correlating cores from different sites in the same basin, tracking erosion history and lake level changes, or investigating eutrophication and microbial processes. However, a detailed investigation of the syn-depositional processes that control the distribution of magnetic minerals across lake basins is lacking for most types of lake systems. In order to understand the main controls on environmental magnetic records, we systematically investigated the magnetic properties of surface sediments collected along transects in nine Minnesota lakes. The lakes are small (

Proceedings, Apr 1, 2003

ABSTRACT Environmental Sensitivity Index (ESI) maps and digital databases have been generated for... more ABSTRACT Environmental Sensitivity Index (ESI) maps and digital databases have been generated for the Hawaiian Islands. ESI atlases integrate the most recent data available in three general categories: shoreline habitats, biological resources, and human-use resources, to provide spill responders with a synopsis of critical information. The new Hawaii atlas was prepared using standardized ESI data collection and analysis methods. For the first time, the spatial accuracy of the ESI shoreline classification method has been quantitatively measured using GPS. Shoreline classification methodology consisted of low-altitude overflights during the 2.5 hours preceding and following low-tide. Aerial classifications were then checked on the ground throughout the study area. USGS 7.5 minute basemaps were used in the field and shoreline segmentation annotation was transcribed from scanned field maps to a digital shoreline provided by the State. ESI surveys in August of 2000 resulted in nineteen shoreline classes for th...

AGU Fall Meeting Abstracts, Dec 1, 2005

ABSTRACT Low lake stands during the Holocene document a period of drier than modern conditions in... more ABSTRACT Low lake stands during the Holocene document a period of drier than modern conditions in the upper Midwest after 8000 cal yr B.P. Here, we seek to compare the magnitudes and spatial extent of these mid-Holocene water-level changes with the changes that occurred during the 1930s Dust Bowl drought. The comparison allows us to consider the potential range of hydrologic conditions in the mid-continent, and to detect similarities or differences between the two periods as a way to learn more about the climatic controls on the mid-Holocene moisture-balance. (How good an analog is the 1930s drought for the mid-Holocene aridity?) Each lake record, however, is unique and comparisons among lakes have been hindered by local hydrologic influences and sedimentary processes. We therefore test the simple methodological assumption that the stratigraphic records of small lakes may be used in concert to produce valid and meaningful maps of Holocene moisture balance. First we confirm that broad regional trends in lake area reflect long-term moisture balance patterns by studying the 1930s aerial photography. Second, we confirm that regionally coherent patterns of sedimentary change related to past water levels can be detected for the mid-Holocene via GPR profiles. Changes in open water surface area in response to the 1930's drought are quantified and mapped for over 300 small (1km sq. or less) lakes of northern and central Minnesota in order to determine if small basins responded to drought with explainable regional coherency. A map of percent area change (between AD 1930 and 2003) reveals that coherent trends in surface area response reflect the gradient of moisture balance change over the same period. We found a trend in percent surface area change from east to west with western lakes completely drying out (>100% change), a wider variability of responses in central Minnesota, and eastern lakes undergoing almost no change (

Geology, Feb 1, 2011

... P.,; Donnelly JP,; Tarbox A.,; Webb T. III. , 2005, A record of late Quaternary moisture-bala... more ... P.,; Donnelly JP,; Tarbox A.,; Webb T. III. , 2005, A record of late Quaternary moisture-balance change and vegetation response from the White Mountains, New Hampshire: Association of American Geographers Annals , v. 95, p. 237248, doi: 10.1111/j.1467-8306.2005.00458.x. ...

Journal of Environmental Protection, 2018

This paper presents a case study for a complex contaminated groundwater site impacted by a histor... more This paper presents a case study for a complex contaminated groundwater site impacted by a historical release of chlorinated solvents in Silicon Valley, California. The original conceptual site model (CSM) inferred a contaminant migration pathway based on the groundwater gradient interpreted from groundwater elevation data, which is based on the underlying assumption that the subsurface conditions are homogeneous. However, the buried channel deposits render the underlying geology highly heterogeneous, and this heterogeneity plays a significant role in the subsurface migration of contaminants. Chemical fingerprinting evidence suggested that contamination at the downgradient property boundary was related to an off-site contaminant source. But, this alone was not a compelling argument. However, Environmental Sequence Stratigraphy (ESS), a geology-based environmental forensic technique, was applied to define the permeability architecture or the "plumbing" that controls subsurface fluid flow and contaminant migration. First, the geologic and depositional setting was synthesized based on regional geologic data, and representative facies models were identified for the site. Second, the existing CSM and site lithology data were reviewed and existing lithology data were graphically presented to display vertical grain-size patterns. This analysis focused on the nexus between the depositional environment and the site-specific subsurface data resulting in correlations/interpretations between and beyond data points that are based on established stratigraphic principles.

Groundwater Monitoring & Remediation

Proceedings Volume: "Geohazards in New Mexico and Surrounding Areas", New Mexico Geological Society, 2016 Annual Spring Meeting

International Oil Spill Conference Proceedings, 2003

Global and Planetary Change, 2013

Geology, 2011