*2.1. Study Area*

The watershed under study is situated in the lower southwestern part of Kentucky in the USA. The watershed is called the Upper Green River watershed as the main stem of Green River, and its tributaries flow through it. The watershed consists of Russell, Adair, Taylor, Metcalfe, Green, Barren, Hart, and Edmonson counties. Although the watershed contains various land uses such as deciduous, evergreen, mixed forest, transitional, low and high intensity residential, commercial, industrial/transportation, open water, pasture or hay, emergent herbaceous wetlands, row crops, woody wetlands, they can be primarily

grouped into three types of land using: urban, forest, and agricultural. The Green River flows through Edmonson, Hart, Green, and Taylor counties and joins the Ohio river downstream of the watershed. Extensive underground karst formations and springs exist between the tributaries of the main stem Green River. The watershed primarily consists of flat-lying limestones, sandstones, and shales forming the karst topography that passes all the surface water through caves and smaller underground passages below the ground surface [28]. The watershed is rated as the fourth most crucial watershed in the United States by the Nature Conservancy and the Natural Heritage Program. It is also the most critical watershed in Kentucky to protect fish and mussel species.

In this watershed, many rural households are not connected to wastewater treatment plants, and the untreated wastewater is directly discharged to streams and creeks, onto overland plains and soils, or into empty spaces of underground. This form of release is known as "straight pipe" discharge. Due to such discharges and failed septic systems, increased fecal coliform bacteria concentrations are found in various portions of the watershed and have essentially impacted the water quality of the Upper Green River basin [28]. The increased concentration of bacteria is so high that the streams are unsafe for fishing, swimming, and body contact. The storage and carefully timed application of animal manure as a fertilizer has been shown to reduce bacteria entering ground water and reduce the need for expensive chemical fertilizers.
