Due to unreliable records it is difficult to determine the actual number of active septic

tanks in the basin. This study instead attempts to simply determine the approximate population of

people in the basin using septic tanks. The amount of N input from septic tanks was determined

by estimating the total number of people within the basin that were not on municipal water

supply (therefore assumed to be on septic systems). This was done by multiplying the area of the

basin by the population density of Columbia County to obtain a total population for the basin

(25,123 people), and subtracting the number of citizens served by Lake City's municipal water

supply (approximately 13,500 people) for a total of 11,623. This figure was multiplied by the per

capital load of 4.2kg N/yr (Otis, 1993) for the total annual load from septic tanks. This per capital

figure was used by Katz, et al in a nutrient study of the Suwannee River watershed (Katz, 1999)

as well as Chellette in a study of the Wakulla Springs system (Chellette, 2002).

Land-Uses

 Land-use within a drainage basin is on of the most important factors in determining the

characteristics of runoff and groundwater quality in the basin. Several different types of land-

uses are associated with elevated levels of nitrogen, most obviously agricultural land-uses.

Several studies have used fertilizer sales as a proxy for the amount of nitrogen applied to

agricultural lands (Chelette 2002, Phelps, 2004) though there are several drawbacks to this

technique. There is no guarantee that fertilizer sold in a county is used only in that county, or that

fertilizer is not imported from outside the county and subsequently applied to agricultural land in

the study area.

 This study examines the specific types of land-uses in the Ichetucknee Springshed and the

nutrient loads associated with these lands. This was accomplished using GIS mapping and data.

By overlapping the SRWMD 1995 Land-Use Map with the delineated boundaries of the

Ichetucknee Springshed we were able to determine the area of hectares of every type of land-use