Estimating Variations in Salinity and Freshwater Flux in the Hudson River Estuary Over the Past 6-7 Millennia

Abstract We are investigating a new method for estimating annual river discharge for the past 6-7 millennia using D/H ratios of fossil leaf waxes in sediment cores in Hudson marshes. We are currently measuring Hydrogen isotopes of leaf waxes in vascular marsh plants (see Figure 1) to be calibrated to salinity and freshwater flux over the past year using data from the United States Geological Survey (USGS). Once the calibration is established, the δD of fossil leaf waxes in marsh cores along the Hudson River will be used to estimate variations in the salinity and thus Hudson River discharge for the past 6,000-7,000 years. This will help us better understand the paleoclimate and paleohydrology of the Hudson River Estuary.

Expected Results For the Calibration Experiment, we expect that the δD of leaf waxes

measured will show strong correlations to the OIPC estimate of δD of growth water with a nearly constant isotopic fractionation between similar plant species. The δD of leaf waxes should then be representative of δD of growth water and salinity shown in Figure 5.

Evaporation, δD of precipitation, and tidal mixing also affect δD of growth water, not just salinity. However, we assume a linear relationship between salinity and δD of growth water since tidal mixing reduces effects of evaporation (the water does not remain stagnant). Since all sites are in same climatic region, they should receive the same δD of precipitation and evaporation throughout the year (δD values at each site should correlate to one another).

Relative humidity seems to have minimal effects on isotopic fractionation in leaf waxes (Hou et al., 2008).

Sponsors:National Aeronautics and Space Administration (NASA)NASA Goddard Institute for Space Studies (GISS)NASA New York City Research Initiative (NYCRI)Lamont Doherty Earth ObservatoryContributors:Baruch Tabanpour, UndergradJonathon Nichols, Post-docPeter Isles, MastersDorothy Peteet, PI

Baruch Tabanpour, UndergraduateDorothy Peteet, PI

Jonathon Nichols, NASA post-docPeter Isles, Graduate Student

Calibration ExperimentFind relationship between:1.Freshwater flow and Salinity2.Salinity and δD of growth water3.δD of growth water and δD of leaf waxesi

1. Freshwater flux from Hudson Valley is related to salinity at various locations in the estuary ([USGS, 2008], [Vries and Weiss, 2001], and [Abood, 2006]). This can be confirmed using USGS measurements (see Figures 2 & 3).

2. Salinity of the water along the estuary is related to the δD of the water. Ocean water contains heavier isotopes of Hydrogen and continental water contains lighter isotopes because of isotopic enrichment due to evaporation. We estimate this relationship using the Online Isotopes in Precipitation Calculator (OIPC). The model calculates average monthly isotopes in precipitation based on interpolation between measurement stations, and climate and elevation (Hou et. al., 2008). (see Figure 4)

3. δD of leaf waxes show strong correlation with δD of growth water at a nearly constant isotopic fractionations ([Huang et al. 2002, 2004], and [Hou et al., 2006]).

MethodsScirpus, Phragmites, Carex, Spartina alterniflora, Spartina patens, Juncus, and Distichlis plant leaves were collected from marshes at all USGS gauge stations and at Iona and Piermont marshes. All plant samples were freeze-dried overnight using the Labconco Freeze Dry System. Freeze-dried plants were put into 40 ml vials. For 3 cycles, 30 ml of Hexane solvent was added to the 40 ml vials and sonicated for 30 minutes in the E/MC Corp. Ultrasonic Cleaner. Samples were then evaporated using the TurboVap LV Evaporator using Pre-purified Nitrogen then re-dissolved in 20 ml of Hexane solvent. Sulfur was removed from all the samples using Copper powder which was then filtered through glass wool. Alkanes were removed through silica gel column chromatography rinsing with Hexane 3X, Dichloromethanol 3X, and Methanol 3X. All fractions were collected in 4 ml glass vials. The Hexane fractions were then evaporated and will be sent to Brown University to be tested with GC-IRMS calibrated to V-SMOW.

All glassware was baked at 550º CConductivity data retrieved from USGS and HRECOS databases online

Figure 1 Calibration Experiment - Marsh Sites

Marshes - YellowUSGS gauge stations - Red

Significance As human demand for water supply and waste disposal have increased, water resources management has become increasingly important (Vries and Weiss, 2001). Freshwater flux and salinity data for the past 6-7 millennia will give us an extended history of droughts and wet seasons for the whole Hudson River Valley since conditions in the Hudson River Estuary are representative of the entire Hudson Valley water table (NYS DEC, 2010). These estimates have implications for better water resources management affecting millions of New Yorkers.

Figure 2USGS Hudson River Salt Front Data

http://ny.water.usgs.gov/projects/dialer_plots/saltfront.html

Figure 3Salinity and freshwater flux are proportional

USGS Data from Below Poughkeepsie gauge station

SPECIFIC CONDUCTANCE

FRESHWATER FLOW

Poughkeepsie

West Point

Hastings on Hudson

Temperature (°C)Salinity (uS/cm at 25C)Freshwater Flux

1992 2002 2010

Figure 4•salinity and δD of pure ocean water: 35 ppt and 0‰•salinity and δD of continental water: 0 ppt and value from OIPC

Future Work•Finish processing leaf waxes and compare δD values to estimates

•Use fossil leaf waxes in sediment cores along Hudson River to estimate variations in the salinity and freshwater flux for the past 6,000-7,000 years (0-14 meters)

•Variation in plant types also affects δD of leaf waxes as different plants have different fractionations (Smith et al.,2005) Plan to use a different proxy to measure changes in vegetation types over larger time scales (i.e. C3 to C4 plant ratio, pollen records)

•Measure δD values from a nearby bog to estimate changes in δD of precip. over thousands of years to account for variations further downcore

References CitedAbood, K., Quirk, Lawler & Matusky Engineers, Environmental Science & Engineering Consultants.(1974) Circulation in the Hudson Estuary. Annals of the New York Academy of Sciences, vol. 250, issue 1 Hudson River , pp. 39-111  Hou, J., Y. Huang, Y. Wang, B. Shuman, W. W. Oswald, E. Faison, and D. R. Foster (2006), Postglacial climate reconstruction based on compound-specific D/H ratios of fatty acids from Blood Pond, New England, Geochem. Geophys. Geosyst., 7, Q03008, doi:10.1029/2005GC001076.  Hou et al. Can sedimentary leaf waxes record D/H ratios of continental precipitation? Field, model, and experimental assessments. Geochimica et Cosmochimica Acta 72 (2008) 3503–3517 Huang Y., Shuman B., Wang Y. and Webb, III., T. (2002) Hydrogen isotope ratios of palmitic acid in lacustrine sediments record late Quaternary climate variations. Geology 30, 1103– 1106.  Huang Y., Shuman B., Wang Y. and Webb, III., T. (2004) Hydrogen isotope ratios of individual lipids in lake sediments as novel tracers of climatic and environmental change: a surface sediment test. 31, 363–375. Geochim. Cosmochim. Acta 59, 5199–5207 NYS Department of Environmental Conservation. Watersheds and Streams Program for the Hudson River Estuary. Retrieved July 14, 2010 from: http://www.dec.ny.gov/lands/5098.html Smith F. A., and Freeman K. H. Influence of physiology and climate on δD of leaf wax n-alkanes from C3 and C4 grasses. Geochmica et Cosmochimica Acta. 70 (2006), 1172-1187 United States Geological Survey. Hudson River Salt Front Data. Retrieved July 14, 2010 from: http://ny.water.usgs.gov/projects/dialer_plots/saltfront.html Vries P. M., and Weiss L. A. (2001) Salt-Front Movement in the Hudson River Estuary, New York—Simulations by One-Dimensional Flow and Solute-Transport Models. US Geological Survey Water-Resources Investigation Report 99-4024 retrieved from: http://ny.water.usgs.gov/pubs/wri/wri994024/wrir99-4024.pdf Weiss, L.A., Schaffranek, R.W., and de Vries, M.P. Flow and chloride transport in the tidal Hudson River, New York, in Hydraulic Engineering ‘94: Proceedings of the American Society of Civil Engineers, 1994, v. 2, p. 1300-1305

Figure 5

DW DP (35 S)

35DP D Precipitation

DW DGrowthWater

Dsample (D /H sample

D /HV SMOW

1)1000