Prepared in cooperation with the New York City Department of Environmental Protection Controls of Stream Chemistry and Fish Populations in the Neversink Watershed, Catskill Mountains, New York he Neversink Watershed Study was initiated in 1991 to T develop an understanding of the key natural processes that control water quality within the forested, 166 km2 64 mi2), Neversink River watershed; part of the New York City drinking water supply system, in the Catskill Mountain region of New York. The study entailed (1) hydrological investigations of water movement from the atmosphere to streams, (2) biogeochemical investigations of nitrogen and calcium, important nutrients in forest and aquatic ecosystems whose availability has been altered by acidic deposition, (3) an investigation of elevational patterns in atmospheric deposition, and (4) fisheries investigations to determine the relative importance of physical habitat and acidic deposition in controlling the abundance and By Gregory B. Lawrence1, Douglas A. Burns1, Barry P. Baldigo1 diversity of fish species in the watershed. This report summarizes Peter S. Murdoch1 and Gary M. Lovett2 the results of these investigations, which have also been presented, 1U.S. Geological Survey, Troy, New York in detail, in peer-reviewed technical articles and reports that are 2Institute of Ecosystem Studies, Millbrook, New York cited throughout the text. Departmentof the Interior WRIR 00-4040 U.S, Geological Survey January 2001 1 INTRODUCTION water is altered by chemical and biological processes that interact in complicated ways. An understanding of these The City of New York relies on six reservoirs in the processes is essential for discerning the effects of human Catskill Mountains to provide 90% of its water supply to activities from undisturbed conditions, and reducing 8 million residents. Historically, the water collected by or eliminating uncertainty in watershed-management these reservoirs has been of high quality as a result of decisions. To ensure a high-quality supply of water the pristine environment throughout much of the Catskill in the future, the City of New York has undertaken a Mountain region. Because most of the area that is comprehensive watershed-analysis and protection program drained by the reservoirs is forested, precipitation follows that includes the Neversink Watershed Study; an a hydrologic pathway through the forest canopy, the soil, investigation to determine the factors that control the and often the underlying rock, before reemerging at the chemistry and fish populations in streams that flow into surface as stream flow. In following this pathway, the the reservoirs. The Neversink Watershed that time, streams have transported and episodic acidification of stream water redeposited some of the till in sand and has been documented in the Neversink The Neversink watershed (fig.1) gravel deposits in the valley bottoms, River Basin in previous studies was chosen for this study because which are referred to as alluvium. (Lawrence and others, 1999; Baldigo it drains the least developed area The climate in the Neversink and Murdoch, 1997). Although acidic within the New York City water- watershed is similar to that of other deposition is not natural, analysis of supply system. The watershed above mountainous regions in the Northeast. the effects of acidic deposition were the Neversink Reservoir covers 166 Mean annual temperature at the Slide included in the study because (1) it has km2 (64 mi2), of which 95 percent Mountain National Weather Service a pronounced effect on water quality in is forested. Fewer than 1000 people Station (fig. 1), which is 808 m above the Neversink watershed, and (2) it is reside in the watershed year-round, sea level, is 4.3o C (40 o F), and beyond local control. and agricultural activities in the basin precipitation is about 175 cm (69 in) are minimal. A few man-made ponds per year, of which about 23 percent are used for recreation, the largest falls as snow. Elevation ranges Topics of Investigation of which are Lake Cole and Round from 480 m (1575 ft) to 1280 m Pond (fig. 1), both of which are less (4200 ft) and hillslopes are steep (up The Neversink Watershed Study than 3 ha (7.4 acres) in area. The to 40%) with deeply incised stream entailed (1) hydrological Neversink River has been renowned channels. Streamflow, therefore, investigations of water movement for more than 100 years for high- increases rapidly in response to from the atmosphere to streams, quality trout fishing. precipitation. Wetlands cover less than (2) biogeochemical investigations of The Catskill Mountains are 5% of the total basin area. Soils are nitrogen and calcium, important underlain by flat-lying, sedimentary classified in the order of Inceptisols nutrients in forest and aquatic bedrock that is highly fractured. are generally 0.5 to 1 m thick and ecosystems whose availability has Bedding planes, or horizontal are generally well drained. The forest been altered by acidic deposition, separations in the bedrock caused by consists primarily of mixed northern (3) an investigation of elevational a change in the ancient pattern of hardwood species dominated by patterns in atmospheric deposition, sediment deposition that formed the American beech (Fagus grandifolia), and (4) fisheries investigations to rock, are also a common feature of sugar maple (Acer saccharum) and determine the relative importance of this bedrock. The rugged terrain of yellow birch (Betula alleghaniensis). physical habitat and acidic deposition the Catskills is largely the result of Balsam fir (Abies balsamea) is in controlling the abundance and erosion by streams and glaciers that common above 1,000-m elevation, and diversity of the primary fish species have resulted in steep-sided valleys and hemlock stands grow in a few areas in the watershed. This report flat-topped mountains. that have poorly drained soils. summarizes the results of these Glacial activity that ended about The Catskill region receives some of investigations, which have also been 15,000 years ago also left behind a the highest rates of acidic deposition presented, in detail, in peer-reviewed veneer of till (sand, gravel and rocks) (acid rain) in the Northeast (Lawrence technical articles and reports that are over the mountains and valleys. Since and others, 1995), and both chronic and cited throughout the text. 2 HYDROLOGY Ground-Water Recharge The coarse-textured soils in the Neversink watershed transmit water Most, if not all, precipitation that falls within the watershed readily, either laterally to stream infiltrates the soil before reaching stream channels because the channels or downward into the decomposing leaves and branches that form the forest floor create underlying till and fractured bedrock. a highly porous layer that allows water to readily move downward. Both soil water and ground water Upon infiltration, water can pass downward through the soil into the (water that has passed below the soil) underlying till and bedrock fractures to be stored in the ground-water play an important role in controlling reservoira process referred to as ground-water recharge. Some of the stream flow and water quality in the infiltrated water is retained within the soil through absorption by soil Neversink watershed. particles, which recharges the soil-water reservoir. 74°44' 74°32' 74°20' Slide Mt. Weather Station Biscuit Brook k Gage o Winnisook Catskill ro NEW YORK B Watershed Mountain it u Region Lake c is Winnisook Delaware River Cole B High Falls Gage Port Jervis Gage Wildcat Upper Tison LOCATION MAP Gage Gage Shelter Creek h nc Tison ra t B Gage as Round Otter Pool E Pond Gage 41°56' West Branch CLARYVILLE East Branch New Hill Gage Gage Gage er U iv L R S ST UL E L R IVA CO Main Branch N U ersink C NT v OU Y e Gage N N TY EXPLANATION Streamflow-gaging station National Weather Service Station Dam 0 5 KILOMETERS Neversink 0 Reservoir 5 MILES 41°48' Base from U.S. Geological Survey 1:24,000 quadrangles Figure 1. Locations of study watersheds and stream flow measuring stations in the Neversink River basin. 3 On average, precipitation in the Neversink watershed is evenly distributed Discharge of Ground Water and throughout the year. Much of the winter precipitation is stored in the snowpack Soil Water to Streams until snowmelt, however, which is typically greatest in March, the month in which the greatest amount of ground-water recharge also occurs (Burns and Ground water in the Neversink others, 1998). During the season when leaves are on the trees (late May watershed typically discharges as through late September), the amount of stored water in the ground-water seeps or springs at the base of steep and soil-water reservoirs tends to decrease because uptake of soil water by slopes and from rock outcrops, or forest vegetation (a process known as transpiration, which is essential for discharges directly into the stream photosynthesis) generally exceeds precipitation, which prevents recharge and channel. Discharge of water from dries the soil (Burns and others, 1998). deep ground-water sources occurs throughout the year, and is the principal source of stream flow during Ground-Water Residence Time the dry summer months. This water has typically moved through bedrock Once precipitation enters the ground, it can be stored for a variable length fractures and bedding planes (fig. of time before being discharged to a stream; a factor referred to as the water’s 2), and generally remains below the subsurface-residence time. Both seasonal variations in stream flow and the surface for several months to more chemical composition of stream water are affected by subsurface-residence than one year. Some water moves time. Chemicals such as calcium and sodium, dissolve slowly from rocks and through the matrix of the bedrock, minerals, and therefore increase in concentration as subsurface-residence time but much slower than through the increases.