Abstract: The three lakes investigated gain water- from adjoining water-table aquifer and lose water to Floridan aquifer by downward leakage. Net seepage (net exchange of water between lake and aquifers) can be estimated by equation S = AX + BY, where S is net seepage, X represents hydraulic gradient between lake and water-table aquifer, A is lumped parameter representing effect of hydaulic conductivity and cross-sectional area of materials in flow section of water-table aquifer, Y is head difference between lake level and potentiometric surface of Floridan aquifer, and B is lumped parameter representing effect of hydraulic conductivity, area, and thickness of materials between lake bottom and Floridan aquifer. If values of S, X, and Y are available for two contrasting water-level conditions, coefficients A and B are determinable by solution of two simultaneous equations. If the relation between lake- and ground-water level is same on all sides of the lake with regard to each aquifer and if X and Y are truly representative of these relations, then X and Y terms of equation provide valid estimates of inflow to lake from water-table aquifer and outflow from lake to Floridan aquifer.

Abstract: Concentrations of nitrate, chloride, and total sol ids in water in the Magothy aquifer, southeast Nassau County, N.Y., show a steadily increasing trend from the early 1950's to 1973. Vertical distribution of nitrate, chloride, and total-solids concentrations as shown in sections of the study area indicate downward movement of these constituents. Maximum concentrations are in a zone underlying the areas of Westbury, Hicksvil.le, and Plainview. Nitrate (as nitrogen) concentration increased from 4-5 milligrams per liter to 7 milligrams per liter in the area of Westbury and from 3 to 10 milligrams per liter in Plainview during the period 1950-73. During this same period, a 10 milligram-per-liter line of equal-chloride concentration on a cross section in the Westbury area moved downward a distance of less than 50 feet (15 meters), and in the area of Hicksville nearly 150 feet (45 meters). Total-solids concentration doubled in the area of Plainview, where maximum downward movement of pollutants was observed.

Samples of water, fish, and benthic macroinvertebrates collected at 10 sampling stations over a 10-month period indicate that Sacony Creek and its major tributaries possess water of good to excellent quality. No excessive quantities of dissolved nutrients, oxidizable matter, or fecal coliform bacteria were detected. Fish inhabitants include a sizable wild trout population in the upper Sacony basin and a diverse warm-water population, dominated by white suckers (Catostomus commersoni), in the lower basin. A population of 590 trout or 119 pounds per acre (133 kilograms per square hectometer) was estimated for good habitat in the upper basin. A maximum standing crop of 558 pounds per acre (626 kilograms per square hectometer) was measured at' one of the more productive reaches. Benthic macroinvertebrate collections tended to support the water chemistry and fish population studies. Diversity (d) and Redundancy (r) ranged from 2.44 to 3.46 and 0.14 to 0.38, respectively. Such diversity and redundancy values indicate good quality water at all stations.