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 reservoira 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. This process, termed mineral weathering, neutralizes the acidity of fractures and bedding planes. The the water, thereby increasing pH and ANC (acid-neutralizing capacity). discharge rate of these springs tends Estimates of the subsurface-residence time measured in discharging ground to vary from season to season, but water at two locations, and in stream water during base flow (between storms) does not respond to individual storms in tributary watersheds of the Neversink River, ranged from about 6 months to 2 (fig. 3A; Burns and others, 1998). years during 1992-93 (Burns and others, 1998). These estimates (table 1) were During extended periods of rainfall derived from concentration measurements of 18O (oxygen that is part of the or snowmelt, rates of recharge can water molecule, but heavier than the common form of oxygen) and 35S (atoms exceed rates of discharge, which of sulfur that are part of the sulfate ion, but heavier than the common form results in upward movement of the of sulfur) in water samples. The abundance of each of these isotopes changes water table (the level below which all through physical, chemical, and biological processes that occur as the water pore spaces and fractures are filled moves from the atmosphere through the subsurface and finally into streams. with water). In March or April Comparison of the isotope values when the water fell as precipitation with the water table is likely to be in the values at the time of discharge can be used to estimate the subsurface residence soil profile, within centimeters of the time. surface, whereas in late summer, the Relative differences in subsurface-residence time of water throughout the water table is likely to be below the watershed also were estimated using data on topography and soil depth available soil profile, and possibly below the in a geographic information system (Wolock and others, 1997). In general, till (fig. 3B, Burns and others, 1998). subsurface-residence time of water was least at the uppermost parts of the As the water table rises, subsurface watershed and systematically increased with decreasing elevation. Throughout water is able to discharge from the till the watershed, the subsurface-residence time also increased with increasing pH, and the soil, as well as from bedrock ANC and the concentration of calcium. (fig. 2). When the water table rises into the soil, high stream flow Table 1. Estimated watershed residence time at four sites in the is maintained between storms, and Neversink River Basin rapid increases in stream flow occur during rainstorms and snowmelt, as Residence Time Residence Time ephemeral streams form in channels Site 18O Method (days) 35S Method (days) that are dry throughout most of the Winnisook stream 330 247-319 year. Stream water under these Winnisook spring 660 187-302 conditions is a mixture of ground Shelter Creek tributary 375 187-302 Shelter Creek Spring 345 319-596 water and soil water that reflects a range of subsurface-residence times. During drier times of the year, heavy

4 Recharge Recharge Sub-Vertical Bedding Fractures Planes

Till

Spring Spring Wetland Alluvium

Sandstone Bedrock

Shallow Ground Water

Figure 2. A conceptual model of how subsurface water moves to the stream channel.

rainstorms can also rapidly increase Nitrate, one of the most common concentrations of nitrogen in surface stream flows for short periods of time, forms of nitrogen, has a U.S. water and ground water (mostly through lateral transport of water Environmental Protection Agency as nitrate and to a lesser extent, through the soil and upper ground recommended health standard of 10 as organic nitrogen). Rates of water reservoirs, even though the mg/L. Concentrations above this atmospheric nitrogen deposition in water table is deep in the till or level can cause methemoglobemia the Neversink watershed are among bedrock (Brown and others, 1999). (blue-baby disease), a blood disorder the highest in the northeastern Once the rain stops, however, in infants. U.S.about 10-20 kg N/ha/yr from streamflow quickly recedes to low, Because the Neversink watershed wet and dry deposited forms. This pre-storm levels. is sparsely populated, and has almost nitrogen is deposited from the no agriculture, inputs of nitrogen atmosphere mainly in the form of occur through (1) natural fixation of nitric acid, and ammonium and NITROGEN gaseous nitrogen in the atmosphere nitrate salts. TRANSFORMATIONS AND by plants, and (2) atmospheric If nitrogen availability exceeds MOVEMENT deposition of pollutants (acid rain). plant demand in forest soils (a Nitrogen fixation can be performed condition termed nitrogen saturation), Nitrogen is the nutrient that is only by a small number of the microbial process termed generally most limiting to plant specialized plant species, therefore, nitrification is stimulated. Through growth and, therefore, is used natural inputs of nitrogen to this process, nitric acid is produced, extensively for crop fertilization. ecosystems tend to be low, and which can (1) acidify soils and An essential component of proteins, the growth of non-nitrogen fixing surface waters, (2) affect the nitrogen is also found in high plants tends to be limited in the availability and movement of other concentrations in both animal and absence of nitrogen from fertilization chemicals in the soil that can be either human waste. For these reasons, or pollution. In these types of toxic or beneficial, and (3) adversely agriculture and development often ecosystems, the high plant demand effect aquatic life. The following result in elevated levels of nitrogen for nitrogen results in little or no sections describe the transformations in ground water and surface water, nitrogen reaching surface waters. and transport (referred to as cycling) where it may promote algal growth In the northeastern U.S., high of nitrogen that has been and associated eutrophication, levels of atmospheric deposition for atmospherically deposited in the particularly in coastal waters. several decades has led to elevated Neversink watershed.

5 12

Stream

Spring 10

8

6

4 Y DISCHARGE, IN MILLIMETERS IL

DA 2

0 11 13 15 17 19 21 23 25

SEPTEMBER 1996 A. STREAM AND SPRING DISCHARGE, SEPTEMBER 1996

900

YER, Mean for eight wells 800 Upper limit (1 standard deviation)

700 Lower limit (1 standard deviation)

600

500 VE IMPERMEABLE LA

400 ABLE ABO IN MILLIMETERS

T 300

TER 200 WA

100

0

HEIGHT OF Jan 1 July 1 Jan 1 July 1 Jan 1 July 1 Jan 1 1994 1995 1996

B. WATER-TABLE HEIGHT AT EIGHT WELLS, 1994-96

Figure 3. Ground water measurements: (a) discharge of a Neversink River tributary and a nearby spring during a 53 mm and a 26mm rain storm. (b) mean height of water table above the impermeable layer (±1 standard error), based on eight wells in a tributary watershed of the Neversink River basin.

6 Branch Neversink River (fig. 1), despite

R 60 increased atmospheric deposition of 50 r2=0.31 .

TION, nitrogen at upper elevations of this 40 . watershed (Lawrence and others, 2000). . . Increased levels of nitrogen deposition 30 . . . . at high elevations would be expected to 20 . . result in higher stream concentrations of . . nitrate at upper elevations than lower OMOLES PER LITE 10 E CONCENTRA elevations. The opposite relationship AT 0 4 4.5 5 5.5 6 6.5 was observed, however, because organic IN MICR NITR matter in the soil, derived from leaves MEAN AIR TEMPERATURE, IN DEGREES CELSIUS and needles, accumulates at a greater rate at upper elevations where cooler temperatures slows decomposition rates. Nitrogen incorporated in the organic FIGURE 4. Relations between stream nitrate concentrations and air temperature at Biscuit Brook for water year 1984-85. matter cannot be released to stream water without first being decomposed. Although other studies in Europe Retention and Release of Soil Nitrogen and North America have shown that long-term atmospheric deposition of Although the primary form of nitrogen deposited from the atmosphere is in nitrogen is directly related to elevated the form of nitrate (from nitric acid or ammonium nitrate salt), as is most of nitrate concentrations in surface the nitrogen in stream water, analysis of the isotopic composition of nitrate in waters, results of the Neversink precipitation, soil water, and stream water, showed that most of this nutrient in watershed investigations indicate that soil water and stream water has cycled through the biota at least once and been assessment of the effects of released again by microbial processes (Burns and Kendall, in review). This atmospheric deposition on stream- conversion can be identified through isotope analysis because root or microbial water chemistry requires consideration uptake of deposited nitrogen changes the isotopic composition; a change that of natural biological processes in the can be identified by the comparison of nitrate in precipitation with nitrate soil, and the manner in which physical found in stream water and soils. Microbial processes can convert nitrogen factors such as climate affect the rates from organic matter to ammonium (called nitrogen mineralization), and from of these biological processes. ammonium to nitrate (called nitrification). Because nitrate is the form of nitrogen that is most easily transported by water from the soil to the stream, these microbial processes play an important role in controlling the release of Role of Ground-Water Seeps nitrogen to surface waters. Atmospheric deposition is an important source of the nitrogen that cycles The deep ground water flow system through the Neversink watershed, but average nitrate concentrations in stream discussed earlier strongly affects the water in any given year are not related to the amount of atmospheric nitrogen concentrations of nitrate in stream deposition that year. Instead, average annual concentrations in Biscuit water during the summer. As Brook (a tributary of the Neversink River) increase as the average annual conditions become progressively drier air temperature increases (fig. 4; Murdoch and others, 1998). Warmer over the summer, stream flow consists temperatures stimulate microbial activity, which leads to increased rates of of a greater proportion of deep ground mineralization and nitrification, and greater loss of nitrate from soil to streams. water. Subsurface-residence times and A buildup of nitrogen in the soil from several decades of acidic deposition monthly hydrologic budgets indicate has apparently shifted the control of nitrogen retention from root uptake that much of this deep ground water to microbial assimilation once nitrogen availability exceeded the nutrient was recharged during early spring and demands of the trees. Uptake of nitrogen by roots results in long-term storage late fall, when nitrogen was not actively in trees, but the short lifespan of microbes results in frequent release of organic taken up by forest vegetation (Burns nitrogen as microbes die, which subsequently can be mineralized, nitrified and and others, 1998). The concentration transported to streams. of nitrate in soil water is greater during Nitrate concentrations were also found to decrease in the upstream direction these recharge periods than during in the Winnisook watershed, a headwater tributary of the upper West the summer growing season (fig. 5a).

7 Therefore, groundwater with relatively high nitrate concentrations discharges and denitrification (conversion of from these seeps to nearby streams throughout the summer (fig. 5b; Burns nitrate to gaseous nitrogen by and others, 1998). bacteria in the oxygen-poor sediments of the wetlands; Ashby and others, 1998). These wetlands Role of Wetlands appear to play a particularly important role in limiting the The Neversink watershed contains no large wetlands, however, small, amount of nitrogen that enters riparian (stream-side) wetlands with dense growths of herbaceous plants streams during the growing season. and mosses are formed in the vicinity of ground-water discharges (Hall, 1997). Surface water that passes through these wetlands undergoes significant decreases in nitrate concentrations during spring, summer, and Role of Stream Processes fall (Burns and others, 1998) through uptake by the herbaceous vegetation Once nitrate enters the stream, concentrations can be lowered through processes that are similar to those in riparian wetlands (Burns, 1998). Monitoring of all inputs and losses of A. SPRING WATER (5 SPRINGS) nitrate in two stream-reaches of the 40 Mean concentration Neversink River during four, 48-hour Upper limit (1 standard deviation) periods of baseflow in April, June, Lower limit (1 standard deviation) July, and September of 1992, showed R 30 a net loss of nitrate (when compared to more conservatively transported constituents such as chloride and 20 sulfate) during each sampling interval in both reaches (fig. 6). Nitrate concentrations in stream water of 10 these reaches also varied over the OMOLES PER LITE B. SOIL WATER (7 LYSIMETERS) course of each dayconcentrations were highest in the early morning 50 before sunrise and were lowest in the IN MICR late afternoon, when photosynthesis 40 rates and plant uptake rates were TION, probably highest. Analysis of stream sediments at three locations in these 30 reaches revealed that mixing with upwelling ground water did not 20 result in a loss of nitrate, except

E CONCENTRA at one downstream location, where

AT nitrate was completely removed by 10 denitrification as stream water mixed

NITR with ground water that tends to

0 be oxygen-poor. In general, plant uptake and denitrification in the Neversink River is important in -10 reaches with slow-moving water Jan Mar May July Sept Nov Jan and fine-grained sediments, but less effective in reaches with turbulent, fast-moving waterthe type of Figure 5. Mean nitrate concentration from (a) five springs and (b) seven C horizon lysimeters in a tributary watershed of the stream reach that is most common in Neversink River basin. the Neversink watershed.

8 Depletion of Soil Calcium 10

Acid rain has been suspected to 0 cause calcium depletion in forest soils since the 1970’s, but little E -10 evidence of this process was AG available until the 1990’s. Results CH -20 of the Neversink Watershed Study significantly contributed to these -30 advances by establishing clear CI- linkages among acidic deposition, loss of calcium in the soil, and -40 NO - acidification of stream water. 3 -50 A. UPPER REACH

Calcium Transformations and EXPRESSED AS PERCENT

Movement in Forested Watersheds W,

Calcium, the most abundant acid 0 neutralizing cation (or base cation) in forest soil, is an essential nutrient -20 for tree growth, and is used in the formation of wood and in the maintenance of cell walls, the primary -40 structure of plant tissue. Trees obtain TER AND STREAMFLO WA calcium from the soil, but to be taken AL MASS DIVIDED BY SUM OF ENTERING REA -60 up by roots, the calcium (a positively

charged ion) must first be dissolved OUND -80 SO 2- in soil water. Exchangeable calcium, RESIDU 4 calcium adsorbed to negatively AS GR -100 - charged surfaces of soil particles, can NO3 be readily dissolved, and therefore is the primary source of calcium -120 APRIL JULY available to roots. JUNE SEPT Some calcium is also deposited B. LOWER REACH onto forests in dust and precipitation or is returned to the soil through decomposing leaves and branches that form the forest floor. Most of the calcium in soil, however, is bound within the mineral structure of rocks within the underlying mineral soil, Figure 6. Mass balances for (a) nitrate and chloride in which makes it unavailable for roots an upstream study reach, and (b) nitrate and sulfate in and prevents it from being leached a downstream study reach during four sampling periods, into surface waters. Weathering, the expressed as the residual of the stream reach mass balance divided by the sum of the mass that entered physical and chemical breakdown of each reach from ground-water and tributary flow. Negative rocks, gradually releases calcium to values indicate a mass loss of the constituent through soil water; a process that neutralizes the reach; positive values indicate a mass gain of the acidity and increases the pH of soil constitiuent through the reach. Chloride was included water and the surface waters into because it tends to be unreactive in stream water, and therefore can serve as a meaurement check . A large which it flows. Acid deposition can net loss or gain of chloride would indicate that inputs or greatly increase the rate of leaching, losses of water along the study reach were not measured

9 450 2- A. Atmospheric deposition (SO4 )

ARE 400

350

300

AL DEPOSITION, IN 250 P < 0.01

MOLES PER HECT 200 ANNU R2 = 0.66 150

B. Mineral soil (Ca2++Mg2++ Na+ + K+) , IN

L 1.5

1

0.5 P < 0.08 PER KILOGRAM SOI R2 = 0.06 CENTIMOLES OF CHARGE EXCHANGEABLE BASES 0 C. Buried soil bags collected after 1 year (Ca2++ Mg2+ + Na+ + K+) 0.6

, IN Initial concentration L 0.5

0.4

0.3

0.2 P < 0.01 PER KILOGRAM SOI 0.1 R2 = 0.25 CENTIMOLES OF CHARGE EXCHANGEABLE BASES 0 2+ 2+ + + 2- - D. Stream water ({Ca + Mg + Na + K }/{ SO4 +NO3- + Cl }) lents) lents) va va 0.35

TIONS (equi 0.3 P < 0.01 ID ANIONS (equi R2 = 0.84 AC BASE CA 0.25 750 800 850 900 950 1000 1050 1100 1150 1200 1250

ELEVATION, IN METERS ABOVE SEA LEVEL

Figure 7. Elevational gradients for selected chemical constituents in Winnisook watershed; (a) annual mean atmospheric sulfate deposition; (b) exchangeable base cation concentrations in mineral soil samples; (c) exchangeable base cation concentrations in initially uniform mineral soil samples that were placed in mesh bags and leached in the mineral soil profile for one year; (d) ratio of base-cation concentrations to acid-anion concentrations from the samples collected on dates when the highest 20% of flow occurred.

10 and possibly deplete the exchangeable An elevational gradient of acidic to enable the possible effects of acidic calcium reserves in the soil, however, deposition in Winnisook watershed deposition to be more clearly detected. if the leaching rate exceeds the provided a unique opportunity to Analysis of the samples after one rate at which calcium is released evaluate the effects of varying year confirmed a distinct upslope through weathering. Calcium leached amounts of acidic deposition on decrease in base cation concentrations out of the soil into surface waters concentrations of calcium (and other (fig. 7C) and in base saturation is an essential nutrient for aquatic base cations) in soil and stream water (the base-cation concentration as a plants and animals. Therefore, (Lawrence and others, 1999). Results percentage of total cation exchange an insufficient supply of calcium in showed that rates of atmospheric capacity of the soil). Detailed the soil can adversely affect aquatic deposition of sulfuric acid increased analysis of other factors that could ecosystems. from the lowest elevations to the cause an elevational gradient in soil highest elevations (Lovett and others, acidity and leaching of base cations 1999), whereas the concentrations were found to have either minimal or Depletion of Soil Calcium In of exchangeable base cations in undetectable effects. The elevational Relation to Stream Recovery soil showed a reversed trend with gradient of acidic deposition resulted from Acid Deposition increasing elevation (fig. 7). in greater depletion of base cations in To further investigate relations the soil bags at upper elevations than Rates of acid deposition in the between atmospheric deposition rates lower elevations; a result consistent Northeast have been declining since and soil chemistry, a large quantity of with results obtained from analysis of the 1970’s, but most of the acidified soil was collected at a mid-elevation the native soils. surface waters in the region have site in the Neversink watershed, where The relation between atmospheric unexpectedly shown little or no exchangeable base-cation deposition and soil chemistry was corresponding increase in pH or concentrations were somewhat higher also reflected in an elevational trend ANC. This lack of response has than in the Winnisook watershed. in stream-water chemistry. The been attributed to decreases in This soil was thoroughly mixed, ratio of base cations to acid anions concentrations of calcium in placed in mesh bags, and reburied in stream water decreased with streamwater, a trend that is related in the soil in stands of mixed increasing elevation, which indicated to changes in the availability of northern hardwoods near the soil- an uplsope increase in stream acidity calcium in the soil. Before the sampling locations to equilibrate with (fig. 7D). A laboratory soil Neversink Watershed Study, however, the existing soil conditions for a experiment demonstrated that this little evidence had been obtained to year. This approach removed the ratio in soil water was directly link acidic deposition to changes in effects of natural factors, such as correlated with soil-base saturation. soil chemistry. spatial variations in soil mineralogy, These results, therefore, link the

50 40 Ca2+ P < 0.05

S 30 20 LENT R 10 TION, IN VA 0 P < 0.01 -10 OEQUI PER LITE -20 -30 ANC CONCENTRA MICR -40 -50 1983 1985 1987 1989 1991 1993 1995 1997

Figure 8. Calcium concentrations and acid-neutralizing capacity (ANC) of stream water in a subbasin of the Neversink River Basin.

11 upslope increase in atmospheric deposition to the elevational trends in calcium Effect of Stream Acidification on availability in the soil and stream-water acidification. Fish Communities of the Neversink The relations observed in Winnisook watershed provide an explanation for why surface water acidity hasn’t decreased in response to decreasing Water chemistry data indicate that levels of acidic deposition. For the ANC of surface waters to decrease, stream acidification within the the ratio of base cations to acid anions must increase. This ratio in soil Neversink watershed varies among water will not increase, however, until the base saturation increases.Therefore, reaches. Sixteen sites were grouped a sustained recovery of surface waters will require a preceding increase in into four categories (minimally, soil concentrations of available calcium. Long-term trends in concentrations moderately, strongly, and severely of calcium and ANC in the Neversink Basin have both shown significant acidified) on the basis of mean decreases for 1984-97 (fig.8), which indicates that soil-base saturation has ANC, pH, and inorganic aluminum decreased during this period. concentrations at baseflow during a study of the relations of fish population indices to water chemistry ATMOSPHERIC DEPOSITION from July 1991 through June 1994 (Baldigo and Lawrence, 2000). Data from the long-term precipitation monitoring station at Biscuit The study sites differed not only Brook (data can be viewed at http://nadp.sws.uiuc.edu/nadpdata/siteinfo.asp? in pH, ANC, and inorganic aluminum id=NY68&net=NADP) suggests that deposition of pollutants like sulfur and concentrations, but also in the nitrogen are higher in the Catskills than nearly anywhere else in the temporal variability of these factors. Northeast. However, that single monitoring station does not tell the whole Fluctuations of inorganic aluminum story. Atmospheric pollutants are deposited in several forms. Rain and snow concentrations tended to be largest are the best known, but particles, gases, and cloud droplets in the air can also at the severely acidified sites and deliver pollutants to forest ecosystems. Furthermore, all of these forms of least at the least acidified sites. deposition tend to increase with elevation in mountainous terrain. As a result, Inorganic aluminum concentrations deposition levels in this mountainous watershed are even higher than the also typically increased with precipitation monitoring station would indicate. Research in the headwaters increasing flows throughout the of the Neversink River indicates that deposition of sulfur increases by a factor Neversink River watershed. During of two between 750 and 1250 m elevation (fig. 7), and that most of that storms, concentrations of inorganic increase is a result of gases, particles, and cloud droplets rather than rain or aluminum and pH (4.97 – 5.39) at snow (Lovett and others, 1999). The same pattern probably holds for the strongly acidified sites, such as New deposition of nitrogen and acidity as well. Part of the increase results from Hill and Tisons (fig. 9) commonly the presence of evergreen trees at the highest elevations, which effectively exceeded the survival threshold for filter pollutants out of the air year-round. In addition, the increase in wind brook trout (inorganic aluminum = speed and frequency of cloud immersion also contribute to the elevational 0.200mg/L, pH = 5.0; Baldigo and increase in atmospheric deposition. On nearby Hunter Mountain, some Lawrence, 2000), the most acid exposed areas such as high-elevation forest edges can receive up to four times tolerant species in the Neversink as much deposition as the nearby lowlands (Weathers and others, 2000). River. Concentrations of inorganic Thus, there are “hot spots” of atmospheric deposition where plants, animals, aluminum and pH appear to become and soils may be exposed to extremely high pollutant loads. toxic for varying durations at most sites in the East Branch Neversink River. Concentrations of inorganic aluminum exceeded the survival FISHERIES ASSESSMENTS threshold for extended periods at severely acidified sites, such as The composition of fish communities in the Neversink watershed is typical Winnisook, but only rarely at the least of that in upland rivers of the Northeast. Species commonly observed include acidic site, Main Branch and at other brook trout, brown trout, altlantic salmon, blacknose dace, longnose dace, and minimally acidified sites West Branch, slimy sculpin. Species distribution varies with (1) water quality, which is Otter Pool, and Oasis Creek–2; fig. 9). affected by acidic deposition, and (2) physical habitat factors such as channel Differences in the severity of size and stream velocity. stream acidification appear to

12 A. SPECIES RICHNESS AND TOTAL FISH DENSITY (number of fish per square meter)

Biscuit Br. b Wildcat Mt. b Winnisook d 0.6 0.5 Slide Mt. b 0 0.2

a Otter Pool Deer Cr. c 0.7 0.1

r ve Ri

a West Branch k in Oasis Cr.-2 a 1.0 rs e er ev Riv 1.7 N nk r. rsi t B ve s Ne Oasis Cr.-1 c e W r. d B Braid-2 0.4 st 0.05 Ea Braid-1 c Main Branch a Tisons c 0.3 1.6 0.06 EXPLANATION New Hill c DEGREE OF STREAM FISH SPECIES 0.1 Upper Tisons d ACIDIFICATION brook trout 0 a East Branch b minimal 0.5 brown trout b moderate Atlantic salmon c strong blacknose dace d severe longnose dace

B. TOTAL FISH BIOMASS (grams per square meter) slimy sculpin

Wildcat Mt. b Deer Cr. c b b Biscuit Br. 5.5 Slide Mt. 5.8 4.7 3.5

Otter Pool a Winnisook d 4.9 0

r ve Ri

a k a West Branch in Oasis Cr.-2 rs 5.1 e er 15.0 ev iv N R r. k B rsin t e s ev e N . W Br st c Ea Oasis Cr.-1 a 10.1 Main Branch Tisons c 6.2 0.8 Braid-1 c d 5.4 Braid-2 FIGURE 9. Fish community characteristics at New Hill c 1.1 16 sites in the Neversink River basin, 1991- 1.0 Upper 93: A. Total fish density and species richness, Tisons d B. Total fish biomass. East Branch b 0 3.7

13 strongly affect the distribution of fish throughout the watershed. Species Fish mortality was greater during richness (total number of species) and total density of fish (number of fish per early spring and late fall than during m2) were low at strongly to severely acidified sites (fig. 9). Stream habitat other times of the year because these and changes in competition resulting from elimination of some species, however, periods had the highest frequency seemed to mitigate the negative effects of acidification on the remaining fish of severe acidic episodes. Elevated species. Features of the habitat, rather than the degree of acidification were concentrations of dissolved organic most strongly correlated with fish biomass (total weight of all fish). Large acid- carbon in stream water during fall tolerant brook trout apparently replaced smaller, and typically more numerous (after the leaves drop) increase species such as dace and slimy sculpin at strongly acidified sites, without causing the formation of organic-aluminum large changes in biomass. Though highly correlated with acidification factors, molecules that are non-toxic, and may species richness and total density were also moderately correlated with elevation, further mitigate aluminum toxicity. watershed drainage area, and water temperature.

Fish Production and Soil Calcium Acidification and Brook Trout Mortality Availability

Although pH and concentrations of aluminum appear to directly affect Although stream acidification the distribution of fish species and composition of their communities in the limits fish production in the Neversink watershed, specific factors that control the mortality of native fish Neversink watershed, several well- during acidification episodes have not been well characterized in previous buffered tributary streams in the studies. Caged, native brook trout showed increased rates of mortality in East and West Branch Neversink response to chronic and episodic acidification (Baldigo and Murdoch 1997). River provide some opportunity for Mortality for caged, young-of-the-year brook trout became significant (>20%) reproduction. Favorable water when inorganic aluminum concentrations exceeded 0.200 to 0.225 mg/L for quality, is maintained in these two or more days (fig. 10). This response may be attributable to the disruption streams even during high flows, by of regulation of ion concentrations in blood by low pH and elevated aluminum the discharge of well-neutralized, concentrations (Baldigo and Murdoch, 1997). ground water from deep sources. Chronically acidic streams such as that of the Winnisook watershed 0.425 receive little or no inputs of ground Predicted Mortality Levels water, and are therefore fishless. 0.375 Most reaches within the Neversink watershed, however, receive sufficient D, amounts of ground water to prevent

R 0.325 acidification during low flows, but 0.275 become acidified during high flows when large amounts of water move THRESHOL 0.225 100% through calcium-depleted soils directly into streams. Without large TION 0.175 50% inputs of ground water, these streams cannot support fish during their early 0.125 life-stages and provide only mediocre habitat for acid-tolerant adults.

IN MILLIGRAMS PER LITE 10% 20% 0.075 Further reductions in the diversity CONCENTRA and densities of fish communities in INORGANIC MONOMERIC ALUMINUM 0.025 the Neversink watershed are unlikely -1 14 4 9 19 24 29 if expected decreases in atmospheric EXPOSURE DURATION, IN DAYS deposition of acids continue. Fish production will remain limited by Figure 10. Estimated percent brook trout mortality as a function of chronic and episodic acidification of exposure duration and inorganic monomeric aluminum concentration. stream water, however, until the acid [Modified from Baldigo and Murdoch, 1997.] buffering ability of the soil improves.

14 SIGNIFICANT FINDINGS

Principle findings of the study were as follows: 1.Steep hillslopes and fractured bedrock result in discharge of groundwater with short subsurface residence times (less than a year) throughout the basin, although deep ground water tends to have sufficiently long subsurface residence times to neutralize acidic water. 2.Water discharging from soil into streams without contact with till or bedrock tends to be acidic and have elevated aluminum concentrations. 3.Riparian wetlands developed from discharging groundwater can lower nutrient concentrations before the water reaches the stream channel. However, because these wetlands tend to be small (less than an acre), they are unlikely to greatly reduce the release of nutrients to streams. 4.Once nitrate enters a stream channel, it can be taken up by algae and plants, or be converted to gaseous nitrogen through denitrification. High stream velocities and stream sediments with low organic matter content limit the effectiveness of these processes in the Neversink River, however. 5.Atmospheric deposition of nitrogen has probably increased the amount of nitrogen in the soil to a level at which it can no longer be fully retained by the forest ecosystem (nitrogen saturation), which results in the release of nitrogen to streams in the form of nitric acid. 6.Acid deposition has decreased the amount of available calcium (calcium not bound in rocks) in the soil to a level at which it cannot fully neutralize acidity in soil and stream water. 7.Acid deposition has decreased the numbers of fish and fish species in parts of the basin but has not strongly affected fish community biomass. Differences in the tolerance of fish species to acidified stream water resulted in the replacement of acid-intolerant species with acid-tolerant species in some acidified reaches of the basin.

MANAGEMENT IMPLICATIONS

The characteristics of the flow path of water as it of available calcium in the forest soils of the basin. is transformed from precipitation to stream water have This condition causes low pH and elevated aluminum important implications for water quality in the Neversink concentrations that often exceed toxic levels for fish, Basin. Recharge of ground water often occurs in and has degraded water quality throughout much of areas remote from the stream channel, but this water can the Neversink River. The low growth rates and discharge at the stream channel within months or less of population densities of fish communities present under entering the ground-water reservoir. In some cases, the these conditions means that the natural fishery in parts discharging water passes through a small wetland before of the Neversink River probably cannot support even a entering the stream, but in many cases it enters the stream moderate level of sport fishing. directly. A short subsurface-residence time and limited Water chemistry of the Neversink River also suggests riparian influence means that the water entering the stream the possibility of a nutrient imbalance in the forest will strongly reflect the characteristics of the recharge area. ecosystem. The relatively high concentrations of nitrate in If this recharge area is a healthy, growing forest, nutrient Neversink stream water suggest that the soils have reached concentrations will be low, but if the recharge area is nitrogen saturation. Like nitrogen, calcium is an essential affected by agriculture or a declining forest, then nutrient nutrient for tree growth, but has generally been considered concentrations could be relatively high. The traditional to be in sufficient supply in forest ecosystems. Depletion approach of using buffer strips along the stream channel to of calcium coupled with nitrogen saturation, however, may protect water quality, therefore would have limited success have resulted in a nutrient imbalance in the Neversink in a watershed such as the Neversink. Because the geology forests. This condition could potentially result in a of the Neversink River watershed is typical of the Catskill decreased tolerance of trees to stresses such as drought, Mountains, this type of hydrologic system is likely to air pollution, and insect infestations, which could lead to be common in other watersheds in the Catskill Mountain decreased forest growth and increased release of nutrients region from which New York City derives it’s water supply. to surface waters. The long-term health of the forest is Several decades of acidic deposition have led to therefore an important factor in sustaining the supply of large amounts of available nitrogen and low amounts high quality drinking water.

15 REFERENCES CITED

Ashby, J.A., Bowden, W.B., and Burns, D.A., Murdoch, P.S., Lawrence, G. B., Lovett, G. M., and Murdoch, P.S., 1998, Controls on Lawrence, G.B., and Michel, R.L., Baevsky, Y. H., 2000, Atmospheric denitrification in riparian soils 1998, The effect of groundwater deposition and watershed nitrogen in headwater catchments of a springs on NO - concentrations export along an elevational 3 hardwood forest in the Catskill during summer in Catskill gradient in the Catskill Mountains, Mountains, U.S.A.: Soil Biology Mountain streams: Water New York: Biogeochemistry, v. 50, and Biochemistry, v. 30, Resources Research, v. 34, p. 21-43. p. 853-864. p. 1987-1996. Lovett, G.M., Thompson, A.W., Baldigo, B. P., and Murdoch, P. Burns, D.A., and Kendall, C., in Anderson, J.B., and Bowser, J.J., S., 1997. Effect of stream review, Sources of NO - in 1999, Elevational patterns of sulfur 3 acidification and inorganic drainage water of two Catskill deposition at a site in the Catskill aluminum on mortality of brook Mountain watersheds differentiated Mountains, New York, trout (Salvelinus fontinalis) in the through analysis of 15N and 18O, Atmospheric Environment, v. 33, Catskill Mountains, New York: Water Resources Research. p. 617-624. Canadian Journal of Fisheries and Hall, B.R., 1997, Environment-plant Murdoch, P.S., Burns, D.A., and Aquatic Sciences, v. 54, species relationships in Lawrence, G.B., 1998, Relation of p. 603-615. groundwater seeps in the Catskill climate change to the acidification Baldigo, B. P., and Lawrence, G. Mountains of New York, M.S. of surface waters by nitrogen B., 2000. Composition of fish Thesis, State University of New deposition: Environmental Science communities in relation to stream York, College of Environmental and Technology, v. 32, acidification and habitat in the Science and Forestry, Syracuse, p. 1642-1647. Neversink River, New York: New York, 83 p. Weathers, K.C., Lovett, G.M., Likens, Transactions of the American Lawrence, G.B., Burns, D.A., G.E., and R. Lathrop, 2000, The Fisheries Society, v. 129, p. 60-76. Murdoch, P.S., and others, 1995, effect of landscape features on Brown, V.A., McDonnell, J.J., Burns, Workplan of the Neversink deposition to Hunter Mountain, D.A., and Kendall, C., 1999, The Watershed Study: U.S. Catskill Mountains, New York: role of event water, rapid shallow Geological Survey Open-File Ecological Applications, v. 10, flowpaths, and catchment size in Report 94-368. p. 528-540. summer stormflow: Journal of Lawrence, G.B., David, M.B., Lovett, Wolock, D.M., Fan, J., and Lawrence, Hydrology, v. 217, p. 171-190. G.M., and others, 1999, Soil G.B., 1997, Effects of basin size Burns, D.A., 1998, Retention of calcium status and the response on low-flow stream chemistry and NO - in an upland stream of stream chemistry to changing subsurface contact time in the 3 acidic deposition rates in the environment: A mass balance Neversink River watershed, New Catskill Mountains of New York: approach: Biogeochemistry, v. 40, York: Hydrological Processes, v. Ecological Applications, v. 9, p. 73-96. 11, p. 1273-1286. p. 1059-1072.

This report and additional earth science information can be found on the World Wide Web at: http//:ny.usgs.gov

For Additional Information Contact: Copies of this report can be purchased from:

District Chief U.S. Geological Survey U.S. Geological Survey, WRD Branch of Information Services 425 Jordan Road Box 25286 Troy, NY 12180-8349 Denver, Co 80225-0286 (518) 285-5600