RESULTS AND DISCUSSION

Tables 6, 7, 8, and 9 list the analytical results for the determination of element concentrations in sediment, sawgrass leaf, sawgrass root, and water samples discussed in this report. Due to convention, many of the analyses for sediment and vegetation have been converted from a measured ash-weight basis to a dry-weight basis.

Sedimentation, Core Dating and Element Accumulation Rates

Parameters used in the calculation of depth-related sediment ages, sediment deposition rates, and element accumulation rates are given in Table 10. The sedimentation rate, as measured in the core material, for most sites ranged from 0.03 - 0.16 cm yr^-1 (table 10). The sedimentation rate for core TS1, at the upper-most end of Taylor Slough where canal water was continuously being directed by gates into the Slough, was about 1.5 cm yr^-1. Because of the unconsolidated and flocculent nature of the sediment/water interface, it was difficult to accurately sample or preserve intact the 0-2 cm portion of core. Although dating was successful in some instances above 2 cm, dating usually began below this level. With a sedimentation rate of 0.1 cm yr^-1, the removal of the top 2 cm of material means a potential loss of about 20 years of sediment record.

As mentioned above, the table 10 data were obtained from a core ("geochronology core") collected adjacent to the core used for geochemical analysis. Because our geochemical samples were collected at 5-cm intervals, and not at the 2-cm interval used for the geochronology cores, the geochemistry dates presented in subsequent discussions are calculated for the 5-cm depth intervals using simple linear regression:

Y = a + b(X);

where Y (age at a specific depth) = (intercept, a) + (slope, b) x (depth in cm, X). For example, using the data below for core 1, the calculation of core age at 12 cm takes the form Y = 1997 + (-1.26(12)), or 1982.

Core	Regression estimates		n (count)	R2
	Intercept	Slope
TS1	1997	-1.26	12	0.99
TS7	2038	-20.9	8	1.00
TS9	1996	-19.5	10	1.00
TS7E	1995	-6.88	9	1.00
TS15	2012	-5.28	9	0.95
TS2	2011	-7.42	9	1.00

The mass of sediment that accumulates per year (gm cm^-2 yr^-1) is the product of the bulk density of the core sample material (gm cm^-3) and the sedimentation rate (cm yr^-1). The determination of element mass accumulation rates (EAR, µg m^-2yr^-1 or g m^-2yr^-1) is then a simple calculation of element concentration (µg g^-1) times the sediment mass accumulation rate (g m^-2 yr^-1). Tables 11 and 12 give the EAR down-core trends for selected major and minor elements, respectively, for cores TS1, TS7, TS7E, TS9, and TS15. 

Next: Results and Discussion continued - Sediment Geochemistry

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