Effect of Ditching, Fertilization, and Herbicide Application on Groundwater Levels and Groundwater Quality in a Flatwood Spodosol’

Groundwater levels and associated water quality parameters were studied in a young slash pine ( Pinus elliottii Engelm.) plantation following ditching, fertilization, and herbicide application. Drainage ditches surrounding each watershed significantly lowered groundwater levels up to 45 m from the ditch for mean and high water table conditions. Drainage ditches were not deep enough to signifkantly influence groundwater levels during drier periods. A seasonal pattern in nutrient migration to the groundwler was exemplified by NH,+,, NO,+& I‘, Ca, and Mg. Concentration of each nutrient was greatest in July following a dry spring. Potassium was the only nutrient which increased significally in &he groundwater due to fertilization. The herbicide mlfometuron methyl [methyl 2.[[[[L(4,6-dimethylpyrimidinyl). mine] carbonyt] amino] sutfonytl benmate] was not detected in toy groundwater samples. Intensive silvicultural activities, such as draining seasonally wet xeas, fertilizing, and applying pesticides, have been used fbr many years to increase pine (Pinus spp.) growth in southeastern forests (Pritchett. 1979; Duncan and Terry, 1983). Nary et al. (19X5) found slash (Pious &i&i Engelm.) and loblolly pine (Pimu tncrln L.) seedlings growing on a flatwood Spodosol doubled in size following fertilization. Pine growth also doubled after application of t~he hrrbkidcs sulfometuron m e t h y l a n d glyphosatc [N(phosphorromethyl) glycine], and tripled from the combined application of Sertilization and herbicide. I\rater control structures, usually drairrage ditches 01 tile drainage, are often used to drain seasonally wet soils in forested condit~ions (I’riTchett, 1970; Duncan and ‘1.erry, 1983). Objectives of drainage are generally to 1) imps-eve roads for bettersite access; 2) incrrase early survival of planted seedlings; and 3) increase gI~owh and reduce rotation age (Hewlett , 1972). Because the surficial water table ranges from 15 to > 200 cm below ground in poorly dramed flatwood soils. inrensive fi,restry activities potentially alter the water table depth and flrnv pattern as well xs water quality. Associated with inrensivc fwestry practices comes the possibilit~y of diminishing water quality as silvicult~ure in Florida moves toward agricultural intcnsiry levels (Riekcrk, 1982). Mobility, persisterrcc, and fate of fert~ilizer nutricnts and pesticides as nonpuint-source pollution are subjects of’ scientific and ecological interest, (Nary, 1 9 8 5 ; R i r k e r k , 1982; BengTson, 1981). Nonpointwurce contwihutions to the groundwat~er seem minor when compared to iwlated point-source contamination. However, cumulative effects of nrmpoin-source pollution may he as or more significant than concern tratcd point-source contamination. Tlrerelore, i t is mport~ant tu a s se s s t he enviwnmcnt~al inrpact~s a s sociated with intensive forest management practices tu g a i n a bewettmdcrsrarrding o f the alterat~ions which may result across large regions. ‘l%e objectives of this I-esearch were to determine effects of ditches on sul-ficial groundwater lrvcls and fwtilization and herbicide applications on wwer quality in a flatwood Spodosol. Asscssmcnt of these impacts with regard to water qualit~y will provide intorrmatiorr useful in prudent silvicultural resource management.