1. PALEOLIMNOLOGICAL INVESTIGATION OF THE RECLAMATION
OF ARM PIT AND ASHBY LAKE
Bethany L. Kile, Shana K. Shepard, Jeffery R. Stone, & Jennifer C. Latimer
Department of Earth and Environmental Systems, Indiana State University, Terre Haute, IN
Abstract
A short sediment core was collected from the center of both Arm Pit and Ashby lakes. The lake sediments were sampled at a 0.5-cm resolution to analyze changes in fossil diatom assemblages, major/minor element concentrations, and detailed phosphorus geochemistry. Diatoms are particularly sensitive biological indicators of acidity in aquatic systems and are commonly used to evaluate potential changes in water quality over time. A sequential extraction technique was employed to elucidate sedimentary phosphorus associations to assess how the nutrient status of the lake has changed over time. Changes in the elemental concentrations will be evaluated by hand-held XRF and ICP-OES to determine heavy metal loads resulting from past mining activities and ongoing acidic drainage. Together these geochemical proxies will be used to explore landscape/watershed/lake interactions. Combining the geochemical and fossil diatom assemblage results will allow us to reconstruct the temporal variability in biogeochemical cycling of nutrients and metals within this aquatic system.
Methods
A 30-cm core was collected from Arm Pit and a 33.5-cm core was collected from Ashby Lake in the spring of Sediment from each core was extruded at half-centimeter intervals.  These samples were subsampled for diatom and detailed phosphorus geochemistry (SEDEX, Table 1).  After samples were dried and powdered, ~0.1 g of sediment was weighed into new 15 mL polyethylene centrifuge tubes.  SEDEX uses a sequential extraction technique to evaluate different sedimentary associations of phosphorus: adsorbed or oxide-associated, mineral, and organic.  The sum of step II and step III is referred to as "mineral P". Approximately 20% of the samples were evaluated as replicate sample to evaluate analytical precision. NIST SRM1646a (estuarine sediment) was also analyzed to evaluate accuracy.  All samples were analyzed using a Shimadzu UV-Visible scanning spectrophotometer at 880 nm using the molybdate blue color development technique (Parsons and Strickland, 1972).  The CDB reagents (step I) interfere with color development requiring an additional processing step that requires combustion and additional extraction with HCl prior to analysis.
For diatom analysis, each sample was weighed and processed in 30% hydrogen peroxide to remove organic matter. The samples were then rinsed and microspheres were added to each sample to enable the calculation of valves per gram. Slides were mounted using Naphrax . Up to 300 diatom valves (when available) were identified to genus on a transmitted light microscope.
Diatom Results 5 10 15 20 25 30
Discostella 40 60 80
100
Fragilaria
Eunotia
Diploneis
Navicula
Stauroneis
Pinnularia
Encyonema
Gomphonema
Nitzschia
Suriella
Benthic
Diatoms Sparse
Depth (cm)
Relative Abundance of Diatoms in Arm Pit Core
Table 1 explains the serial extraction method used. There are four steps; each step isolates a different type of phosphorus. Step 1 must be prepared for spectrophotometer analysis differently from Steps 2, 3, and 4. 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Cyclotella
Discostella
Fragilaria
Distrionella
Staurosira
Achnanthidium
Cocconeis
Eunotia 40
Brachysira
Amphipleura
Craticula
Hippodonta
Mastogloia
Navicula
Stauroneis
Pinnularia
Caloneis
Amphora
Encyonema
Encyonopsis
Gomphonema
Nitzschia
Rhopalodia
Surirella
Cymatopleura
Depth (cm)
Relative Abundance of Diatoms in Ashby Lake Core
Table 1. Extraction steps (after Ruttenberg, 1992; Anderson and Delaney, 2000; Mortlock and Froelich, 1989)
Step
Reagents
Isolated P Component
oxide-associated
10mL CDB Solution (6 hr)
absorbed and reducible or reactive
(0.22 M Na-Citrate, 0.11 M NaHCO3,
Fe-bound P
0.13 M Na-dithionite), 10mL 1M MgCl2
(2 hr), 10mL H2O (2 hr)
authigenic
10mL Na-acetate buffered to PH 4 (5 hr)
carbonate fluorapatite (CFAP),
with acetic acid, 10mL 1M MgCl2 (2 hr)
biogenic hydroxyl apatite, and CaCO3-bound P
twice, 10mL H2O (2 hr)
detrital
10mL 1M HCl (16 hr)
detrital P
organic
1mL 50% MgNO3, dry in low oven,
organic P
ash at 550°C (2 hr), add 10mL 1M HCl
Objectives
To explore the potential impact of acidic drainage on this system
To assess the effectiveness of the reclamation process on water quality over the past several decades.
Phosphorus Results
Site Description
Arm Pit and Ashby Lakes are located in the Sugar Ridge Fish and Wildlife Area in Winslow, Indiana. These lakes was formerly part of a region used as a coal strip mine that was donated to the Division of Fish and Wildlife in Since then, they have been reclaimed along with many other aquatic systems in the area (Sugar Ridge, 2015). 2 4 6 8 3 9 12 24 36 20 40 60
% Oxide P
% Mineral P 80
% Organic P 2 4 6 8 10 12 14 16 18 20 22 24 26 28
% Oxide P
% Mineral P
% Organic P
Surirella sp.
Stauroneis sp.
Navicula sp.
Mastogloia sp.
Future Work
The Ashby Lake core needs to be counted to species. We also plan to analyze the samples using a hand-held X-ray fluorescence analyzer and inductively coupled plasma-optical emission spectrometry for major and minor elements.
Ashby Lake
Arm Pit
Acknowledgements
We would like to thank Tina M. Williams and David A. McLennan who assisted with phosphorous extraction and Erica Memmer who assisted with field work and site selection.
Conclusions
Organic phosphorus percentages were rather high in both lakes. Phosphorus results indicate that the lake is highly productive, evident by high relative organic phosphorus concentration and high total phosphorus burial. Preliminary diatom data shows major transitions throughout the record, potentially attributed to lake evolution. To see if these changes are related to acidity and to determine the relationship of the phosphorus record and diatom assemblage changes, diatoms will need to be counted to species.
References
Anderson, L.D., and Delaney, M.L., Sequential extraction and analysis of Phosphorus in marine sediments: streamlining of the SEDEX procedure. Limnology and Oceanography, 45:
Sugar Ridge Fish and Wildlife Area. Department of Natural Resources. Web. 15 May 2015.
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