WATER-RESOURCES INVESTIGATIONS REPORT 01-4153 Paul J. Friesz and John A. Colman U.S. DEPARTMENT OF THE INTERIOR Prepared in Cooperation with the Hydrology and Trophic Ecology of Walden Pond, U.S. GEOLOGICAL SURVEY MASSACHUSETTS DEPARTMENT OF ENVIRONMENTAL MANAGEMENT Concord, Massachusetts

212,000 212,500 213,000 213,500 214,000 100,000 200,000 180 220 CTW213 CTW218 CTW204 oxygen monitoring, 1997–99, and two profiles from 2000 0.05—12 EXPLANATION 300,000 Concord Carlisle (deep) EXPLANATION 220 <0.05—0.5 indicated that the May through July HOD values nearly INTRODUCTION 159 WATER TABLE—Shows altitude 900,000 MASSACHUSETTS Boston CTW206 CTW205 CTW217 were identical (0.049, 0.050, 0.051, 0.048 mg O /cm2/d, OPEN WATER 5—36 2.5—14 of water table, July 19,1999. 2 High School CTW214 Dashed where inferred. Datum Walden Pond, the deepest lake in Massachusetts, has great (deep) CTW216 1997 through 2000). These results indicate that baseline e 26—38 is sea level 220 220 0.32—0.47 m WETLANDS plu 0 50 MILES of trophic-state conditions as measured by HOD are relatively CTW227 nt 158.5 200 te WATER TABLE—Half-foot historical, naturalistic, and limnological significance as the 0.01 ex 800,000 CTW235 al contour line. Dashed where stable at present. 0 50 KILOMETERS re CTW244 152.39 a inferred. Datum is sea level ed 13—45 0.20 at 0.46 tim Septic system Long-term change in HOD-trophic state can be estimated subject of Henry David Thoreau's well-known essay "Walden: 0.14 Es CTW218 MONITORING WELL — 212,000 214,000 216,000 0.05 Alphanumeric code is local from the few historical dissolved-oxygen profiles available 0.18 identifier or, Life in the Woods" (Thoreau, 1854). Only 15 miles (mi) 180 Route 126 6.7 for Walden Pond, from 1939, 1992, 1994, and 1996 (fig.11). 1.9 CTW203 TEMPORARY WELL BEDFORD 180 200 3.1-4.9 A projected depletion line for the 1939 datum indicates that northwest of Boston, Mass. (fig. 1), Walden Pond potentially is 200 <0.05 NITRATE 200 160 dissolved oxygen in the 1939 hypolimnion may not have 200 CONCENTRATION—Bar r 153 2.5 e 160 height is proportional to nitrate been depleted if turnover occurred at the same time as in the threatened by environmental stresses common to urban lakes: a 914,000 i v R 0.39 concentration rd 0 present. The more recent historical profiles—1992, 1994, co 180 18 <0.05 ssabe on 0 NITRATE municipal landfill, septic leachate, high visitor-use rates, acid A t C 0.16 CONCENTRATION—Number 1996—indicates that depletion in those years generally was Ri CTW236 20 ve 0 154 WALDEN POND indicates nitrate concentration, r 155.44 0.06 similar to the depletion data of 1997–2000. and other contaminants from atmospheric deposition, and 18 200 in milligrams nitrogen per liter; <, less than The early profile suggests that HOD has doubled since 200 200 0.57 invasion of exotic species. Walden Pond retains clear, 160 BUILDINGS AND ROADS 1939, which implies that historical inputs of nutrients were Route 2155 200 200 0.16 less than present inputs. Of the principal sources of growth- Route 2 CTW234 Little Goose r 153.75 undegraded water because of conservation efforts that protect the ve 20 limiting phosphorus (table 1), only the swimmer source is i CONCORD 0 200 200 Pond R 0.11 CTW233 156 180 subject to anthropogenic change. Although phosphorus 912,000 M B CTW237 shore and woods surrounding the lake. Questions remain, ill 910,500 157.23 158.70 200 910,500 y rook <0.05 input in pre-recreational Walden Pond may have been low, r 180 LVW30 u 180 16 0.01-0.05 b 156.07 0 0.16 inputs may have been high in the more recent past. One however, regarding the extent of ecological changes that may ud 200 200 157 S 200 180 158.5 thousand swimmers were observed at the 1939 sampling 158.5 Route 126 already have occurred and the degree to which conservation Fairyland Walden Pond State Reservation Boundary <0.05 159 (Deevey, 1942); the Concord Herald newspaper reported on Pond 220 158 N <0.05 Area shown as figure 3 220 159 159.5 September 5, 1935, that summer Sunday afternoon crowds 200 158.5 efforts will preserve water quality in the future. Hydrologic and Little Goose 180 200 160 CTW165 RD 180 reached 25,000 at Walden Pond and that total summer Pond 158.43 O 180 Goose Pond CTW225 CTW238 159.5 NC 0 500 FEET attendance was 485,000. The relation between this apparent 0 O limnologic results from a cooperative investigation of Walden 158 159.26 C 155.24 18 unicipal Landfill long-term nutrient supply increase and plant growth is not 910,000 159 LINCOLN 0 150 METERS Walden 158.5 180 Pond between the U.S. Geological Survey and the Massachusetts Pond necessarily linear, and growth may lag behind supply. The Sandy 159 200 CONCORD Pond 156 200 CTW212 Concord M Figure 7. Nitrate concentrations in samples from observation wells near the Walden Pond State Reservation septic leach field effect of initial increases in phosphorus supply would be Department of Environmental Management are summarized in 159.64 LINCOLN decreased because of phosphorus sequestration by mineral 180 Goose and at temporary drive-point wells on the shore of Walden Pond. Estimated areal extent of the nitrate plume boundary is based LINCOLN 200 CTW240 159.5 on water-quality data and computations on ground-water flow. forms in the bed sediments followed by a larger fraction this plate report, which shows Walden Pond in relation to the 159.5 158.75 CTW242 CTW241 included in internal recycling as the sediment capacity for CTW211 158.12 158.39 CTW239 157 158.18 phosphorus became filled. To the extent that dissolved ground-water system and land use. Details of the investigation 159.24 Pond 180 oxygen in the hypolimnion became depleted, sediment- Fairhaven Bay from data collected from 1997 to 1999 (Colman and Friesz, 908,000 Trailer sequestered phosphorus would be released from iron- 200 159.80 Figure 8. The macroalga Nitella 180 180 Basemap from MassGIS digital data, 0 1/2 1 MILE grows on the bed sediment in mineral forms through reductive dissolution. The first 2001) and basic information about limnology and Walden Pond State Plane Meters, Fipszone 2001, 158.93 Park Walden Pond at depths between 1:25,000 scale 0.5 1 KILOMETER occurrence of dissolved oxygen depletion at a given level in CTW209 20 and 42 feet. The Nitella 200 CTW210 220 the hypolimnion may have been associated with a (Colman and Waldron, 1998) also are available. CTW224 158.27 biomass ties up nutrients and 158.20 158 158.64 Atmospheric substantial hypolimnetic release of phosphorus, which had Figure 1. Location and hydrologic setting of Walden Pond, Concord, Massachusetts. Thoreau Deposition generates oxygen deep in Walden Station homesite Pond. accumulated with iron over the ages. If HOD could be 158.37 200 CTW208 decreased to the level present in 1939 so that dissolved 159.10 A A’ Wyman oxygen was not depleted in the final weeks before turnover, HYDROLOGY 300 CTW226 0 180 Meadow 158.45 CTW207 18 280 then annual accumulation of phosphorus in the upper Walden Pond and the underlying and surrounding CTW221 159.45 CTW218 hypolimnetic sediments might begin again. Because some 180 220 aquifer are bordered by the Sudbury and Concord Rivers 158.14 159.38 CTW204 dissolved oxygen remains in the upper hypolimnion until 250 159.39 200 (fig. 1). Walden Pond, a kettle-hole lake with no surface CTW217 CTW214 159.40 nearly the end of stratification, the decrease of phosphorus CTW222 CTW205 CTW213 water inlet or outlet, formed at the end of the last Evaporation Precipitation Recharge 180 158.25 CTW206 input necessary to sustain aerobic conditions may not 200 159.19 NA 159.39 glaciation about 15,000 years ago by the melting of a 200 CTW214 Reservation 220 be too large. 180 159.37 0 large block of ice that broke off into glacial Lake Septic Leach Field 4 WALDEN POND 10 CTW227 CTW216 2 Comparison of Walden Pond with other seepage kettle- Water table ? 910,000 160 158.41 910,000 Sudbury from the retreating glacier. The ice block ? 20 159.38 hole lakes of eastern Massachusetts indicates the variability 150 Fine-grained 200 CTW244 260 eventually was surrounded by sorted, stratified sediments Lake-water seepage bottom sediments 30 159.38 in dissolved oxygen regimes that can develop (fig. 12). 40 ranging mainly from fine sand to coarse gravel deposited Ground-water 40 280 Thickness of the oxygenated layer in these lakes is 200 50 100 inflow by glacial meltwater (fig. 2), (Koteff, 1963). Seismic 50 STRATIFIED MIXED STRATIFIED MIXED STRATIFIED correlated inversely with nutrient inputs per area of Stratified glacial deposits 60 CTW203 reflection and fathometer data indicate that the lake and Till 60 10 159.35 0 lake surface. 70 6 60 5 30 its associated fine-grained bottom sediments extend to 20 10 50 200 55 300 Trophic Stability the till and bedrock surface in the deepest areas. Three CTW223 180 ALTITUDE, IN FEET ABOVE SEA LEVEL ABOVE SEA IN FEET ALTITUDE, 30 Bedrock 157.46 80 DEEPEST Walden Pond may have become more eutrophic, but the deep areas are defined in the lake (fig. 3); the middle 35 40 20 25 200 SOUNDING water still is clear and remains attractive to the public 160 100.1 ft. 60 50 deep area was unmapped before this investigation. The 0 30 200 90 100 0 30 (fig. 13). Does the ecological health of Walden Pond require EXPLANATION 0 1,000 FEET VERTICAL EXAGGERATION X 10 50 55 32 maximum measured depth of 100.1 feet (ft) was within 20 180 40 a decrease in nutrient input in an attempt to achieve more 2 ft of that measured by Thoreau in the winter of 1846. CONTACT LINE Dashed 0 300 METERS A’ 40 Metalimnion Epilimnion where inferred oligotrophic conditions? The answer depends on how stable 50 200 Knowledge of the water balance and the land-surface E N P O N 50 15 the present condition is. The consequences of eutro- D 159 30 L D W A 158.5 40 area contributing water to Walden Pond is needed to Figure 2. Walden Pond and fine-grained bottom sediments extend to the till and bedrock surface in deep areas. Stratified glacial CTW232 20 phication, fish kills and excessive cyanobacteria blooms, 10 DEPTH, IN FEET 60 deposits surround the lake. Water enters the lake from precipitation on the lake surface and from ground water. Water leaves the 155.18 159.5 340 understand the hydrology of the lake and to derive a 90 10 present in some eastern Massachusetts kettle-hole lakes, lake from evaporation and lake-water seepage. (Line of section shown in fig. 3.) 160 CTW230 80 LVW30 70 nutrient budget for the lake. Sources of water to Walden 157.92 158.63 likely could be prevented in Walden Pond by continued 70 160 200 Hypolimnion maintenance of dissolved oxygen in the metalimnion. An Pond include precipitation on the lake surface and 164 60 180 50 80 5 TEMPERATURE, IN DEGREES CELSIUS TEMPERATURE, oxygenated metalimnion decreases internal recycling of ground water (fig. 2). Water from precipitation infiltrates 4A 40 158.37 Water Balance 162 the permeable surficial deposits, recharges the aquifer, 30 360 90 phosphorus and provides cold, oxygenated water necessary The water balance for Walden Pond 20 0 then flows in the direction of decreasing water levels. 160 200 Boat Ramp for trout. Currently (2000) , the high, constant con- 10 180 100 without surface inflows or outflows can 200 centration of dissolved oxygen in the metalimnion is a Thus, ground-water flow does not necessarily follow 158 180 200 be expressed as 200 3/1/97 5/1/97 7/1/97 9/1/97 1/1/98 3/1/98 5/1/98 7/1/98 9/1/98 1/1/99 3/1/99 5/1/99 7/1/99 9/1/99 prominent feature of stratification in Walden Pond. land surface topography. Along steep shoreline areas Pine 11/1/97 11/1/98 ∆ 156 sloping towards Walden Pond, small quantities of S = P + GWi – E – GWo , (1), CTW231 LVW33 200 DATE The stability of metalimnetic dissolved-oxygen 154.11 158.74 154 220 Hill Figure 9. Distribution of temperature in Walden Pond, 1997—99, indicating thermal stratification during the summer and fall, and concentrations of Walden Pond likely involves the ecology overland flow may occur after intense precipitation 158 220 Fairhaven 200 155.68 ∆ Route 126 mixed conditions during winter and early spring. The temperature data were collected as vertical profiles, shown as lines of white of the macroalga Nitella, which grows only in the where S is change in lake-volume 152 WATER LEVEL IN WELL CTW165 157 events, thereby adding small amounts of water to the 240 340 MEAN GROUND-WATER ALTITUDE FOR YEARS 1965-99 240 metalimnion but in amounts that dominate plant biomass in lake. Water leaves Walden Pond by evaporation from storage; P is precipitation that falls LEVEL, GROUND-WATER 156 IN FEET ABOVE SEA LEVEL ABOVE SEA IN FEET 150 MEASUREMENT ON JULY 19, 1999 Hill 200 directly on the lake surface; GW is 155 the entire lake. Although factors presently limiting growth the lake surface and from lake-water seepage to the i CTW220 164 154 and areal extent of Nitella in the Walden Pond metalimnion ground-water inflow; E is evaporation 340 155.65 180 aquifer (fig. 2). 4B 200 320 153 A. are not completely understood, it is known that some from the lake surface; and GWo is lake- 162 152 A 159.53 0 species of Nitella can not grow in eutrophic systems, which Ground-Water Contributing Area water seepage to the aquifer (ground- No data 909,500 300 151 260 160 150 909,500 Water-table contours, surficial geology, and 280 10 16 lack light penetration below the thermocline. Substantial water outflow). The water balance for CTW243 149 200 topography were used to delineate the area contributing 158 260 151.75 320 eutrophication has occurred since the historical dissolved Walden Pond was based on average 200 148 20 14 240 147 oxygen data collection in 1939. The principal anthropogenic ground water to Walden Pond (fig. 3). The altitude and annual conditions during the 5-year 156 180 146 12 perturbation causing eutrophication is the hypothesized configuration of the water table in areas of stratified 220 30 period, 1995–99. Water-balance 154 160 145 159.5 WALDEN POND STAGE 240 LVW31 swimmer input of nutrients. Because of the long recreational glacial deposits surrounding Walden Pond were calculations based on this time period Emersons 40 10 MEASUREMENT IN JUNE, 1956 144.30 159.42 Metalimnion Epilimnion

WALDEN POND STAGE, POND STAGE, WALDEN 152 history at Walden Pond, increased nutrient input may have determined from water levels measured in 40 monitoring MEASUREMENT ON JULY 19, 1999 200 indicate that the water-residence time LEVEL ABOVE SEA IN FEET 220 50 occurred over a period of more than 100 years. Although wells and 8 ponds on July 19, 1999. The direction of 150 Cliff 8 of the lake is approximately 5 years; 300 there is insufficient HOD data between 1939 and the present ground-water flow, shown by arrows on figure 3, is 65 4C 60 therefore, inflows and outflows to DEPTH, IN FEET 6 to conclude whether the present level of eutrophication has PRECIPITATION AVERAGE perpendicular to the water-table contours. In areas of Walden Pond should reflect climatic 55 200 Thoreau FOR YEARS 1960-99 70 4 reached a new steady state, no obvious trend is evident in bedrock highs, such as Emersons Cliff and Pine Hill, 45 160 Institute conditions during this period. Ground- Hypolimnion HOD determined in recent years—1992-2000. Stability ground water flows downslope through the overlying 180 80 water outflow was calculated indirectly ANNUAL 35 2 OXYGEN, IN MILLIGRAMS PER LITER IN INCHES Heywoods would be enhanced by nutrient input decrease, which would 280 saturated till in the direction of declining land-surface 25 as a residual of the water-balance PRECIPITATION, 180 90 benefit the deep-growing Nitella. altitude because the bedrock surface is relatively 160 0 equation. There was no change in long- 1954 1956 1958 1960 1962 100 impermeable. The water-table map shows that Walden 1964 1966 term lake storage over the 1995–99 1968 1970 SUMMARY AND CONCLUSION Figure 4. Measurements of water levels1972 1974 in well CTW165 (A) and Walden Pond (B) show the EXPLANATION Pond is a flow-through lake: ground water flows into the 1976 1978 160 period based on the ground-water 1980 260 5/1/97 7/1/97 9/1/97 1/1/98 3/1/98 5/1/98 7/1/98 9/1/98 1/1/99 3/1/99 5/1/99 7/1/99 9/1/99 1982 1984 3/1/97 11/1/97 11/1/98 The water quality of Walden Pond has been protected by annual cycle of water-level declines and rises. Long-term1986 1988trends in water levels reflect trends 180 lake along its eastern perimeter, and lake water flows 1990 1992 DATE hydrograph (fig. 4A). Average in annual precipitation (C). (Lake water levels in 1956 and from19591994 to1996 1971 were collected land conservation and bank-stabilization efforts, and the 1998 Andromeda Ponds TILL AND BEDROCK—Unstippled area other than wetland or out to the aquifer along its western perimeter. The precipitation from 1995–99 was by Walden Pond State Reservation staff (Walker, 1971); precipitation data are from the water is stratified glacial deposits B. location of its ground-water contributing area. Ground water contributing area also includes Goose Pond, also a flow- 0 47.82 in/yr, which is 2.50 in. above the National Oceanic and Atmospheric Administration.) 240 Figure 10A. Distribution of dissolved oxygen in is the dominant pathway into and out of the lake and the BUILDING 10 through pond, and its contributing area. Some of the 40-year average (fig. 4C). Average Meadow Walden Pond, 1997—99 showing spring increases water-residence time for the lake is about 5 years. The water that enters Goose Pond, from ground-water inflow -20 20 and summer constant conditions in the metalimnion evaporation of 28 in/yr from the lake ROADS and summer and fall decreases in the hypolimnion. contributing area excludes nearby potential sources of from the Pine Hill area and from precipitation that falls surface was estimated by using 30 A uniform dissolved oxygen profile is restored when nutrients from the Concord Municipal landfill and a trailer ZONE OF NITELLA GROWTH 11/18/98 directly on Goose Pond, flows west out of Goose Pond regionalized pan evaporation and pan 40 the lake mixes. Lines of white dots represent park. At present, nitrogen from the Reservation septic leach -30 Local meteoric water line 220 locations of sampling points. B. Selected dissolved- into the aquifer and towards Walden Pond. coefficient measurements (Farnsworth LAND USE 50 field enters Walden Pond, but phosphorus is removed during oxygen depth profiles for 1998. The Walden Pond contributing area of 0.24 square and others, 1982). The ground-water transport. The net effect increases the nitrogen:phosphorus Open water DEPTH, IN FEET 60 9/23/98 miles (mi2) is contained mainly within the Walden Pond inflow rate to Walden Pond was ratio of inputs, a circumstance unfavorable to growth of -40 70 State Reservation boundary and other conservation land, determined by contributing-area and Wetlands 8/4/98 nuisance cyanobacteria. Walden Pond has become more Evaporation line 80 4/23/98 3/20/98 eutrophic during the past 60 years, and loses deep-water except for that area that also is part of Goose Pond and isotope mass-balance approaches. CONCORD 6/9/98 Wooded swamps dissolved oxygen. Historical and interlake comparisons of its contributing area (fig. 3). The Reservation septic LINCOLN 90 The contributing-area approach -50 plant production indicate that the trophic level of Walden leach field and the septic leach fields from residences on June 1998 to September 1999 909,000 Conservation 909,000 100 requires knowledge of the recharge rate 180 0 2 4 6 8 10121416 Pond could be decreased (dissolved oxygen increased) if privately owned land in the contributing area east of PRECIPITATION and the size of the area where ground 180 Conservation and recreation OXYGEN CONCENTRATION, IN MILLIGRAMS PER LITER phosphorus input were decreased, possibly through a Walden Pond are potential sources of nutrients to the ( Atmospheric Deposition Station ) 160 water flows directly to Walden Pond. In -60 swimmer-education program. Results of this program likely Concord Municipal landfill lake. Ground water in the Reservation leach field area MIL DEUTERIUM, IN PER DELTA GROUND-WATER INFLOW addition, the quantity of water entering 140 ( wells LVW30, LVW33, would increase the stability of the deep-growing macro alga flows westward toward the eastern shore of Walden 160 the aquifer from Goose Pond and and CTW203 ) Other 9,000 0 Nitella, which helps maintain water quality by tying up 18 Walden Pond State Reservation Boundary

Pond. Leach fields from private residences are in areas -70 0 flowing as ground water to Walden 180 A nutrients in deep plant biomass, generating metalimnetic LAKE WATER CONTOURS 8,000 10 where ground water flows directly toward Walden Pond Pond must be considered. An average ( lake surface over the east 180 dissolved oxygen at the onset of stratification, and end deep area ) 20 or indirectly by first flowing into Goose Pond. Ground recharge rate of 26.8 in. was based on 160 60 Water depth —In feet below water surface 7,000 maintaining high metalimnetic dissolved-oxygen water in the southeastern part of the contributing area -80 1939 regional estimates of Randall (1996) -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 30 concentrations during stratification. 154 Water table — Shows altitude of water table, July 19, 1999. 6,000 1999 generally flows northwest from the till-covered bedrock 140 and adjusted to account for the DELTA OXYGEN-18, IN PER MIL 180 120 Dashed where inferred. Datum is sea level 1992 40 highs, Emersons Cliff and Pine Hill. Most of the ground increased average precipitation during 160 5,000 REFERENCES CITED 140 158.5 Water table — Half-foot contour line; Dashed where 1997 water from these till-covered areas most likely enters the the 1995–99 period. The ground-water Figure 5. The isotopic composition of precipitation varied on the basis of atmospheric 50 Baystate Environmental, Inc., 1995, Study of trophic level conditions of 20 inferred. Datum is sea level 4,000 B stratified glacial deposits before discharging to Walden contribution to Walden Pond from temperature and defined a local meteoric water line (LMWL). The isotopic composition of 1 Walden Pond, Concord, Massachusetts: Massachusetts Department of ground water clustered at the low end of the LMWL and reflected the cold temperature 1994 60 Environmental Management, Division of Resource Conservation,

Pond. Northeast of Walden Pond, the Concord Municipal 3,000 2000 DEPTH, IN FEET Gull Pond 08/04/99 Goose Pond was estimated to be 20 when ground water was recharged. The isotopic composition of lake water plotted to the 111 p. landfill and a trailer park are on the north side of a BOUNDARIES 70 percent of the average annual ground- right of the LMWL, and defined an evaporation line. 1996 1998 Walden Pond 07/29/99 ground-water divide; ground water north of this divide 2,000 Colman, J.A., and Friesz, P.J., (2001), Geohydrology and limnology of water outflow because about 20 percent Walden Pond ground-water contributing area 80 Ashumet Pond 08/09/99 Walden Pond, Concord, Massachusetts, U.S. Geological Survey flows generally in the northward direction away from of the outflow perimeter of Goose Pond 1,000 Water-Resources Investigation Report 01-4137, 68 p. 90 White Pond 08/03/88 KG DO, IN HYPOLIMNION BELOW 48 FEET

00 Goose Pond ground-water contributing area

Walden Pond. compare favorably to the estimate based on the contributing- 2 lies within the contributing area of Walden Pond. No 0 Colman, J.A., and Waldron, M.C., 1998, Walden Pond, Lake-derived ground water flows towards and upgradient ground water was assumed to flow beneath or area approach. A ground-water inflow value of 58 in/yr, 180 Walden Pond State Reservation Boundary MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. 100 Massachusetts—Environmental setting and current investigations: 0 2 4 6 8 10121416 U.S. Geological Survey Fact Sheet, FS-064-98, 6 p. discharges into the Sudbury and Concord Rivers or to by-pass Walden Pond because deep areas of the lake based on the average of the δ18O and δD results (62 in/yr) MONTH/DAY A A’ GEOLOGIC SECTION DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER wetlands and streams draining into these rivers. The extend to the till and bedrock surface. The total average and the contributing-area result (53 in/yr), was used in the Deevey, E.S., Jr., 1942, A re-examination of Thoreau's Walden: The Figure 11. Dissolved oxygen (DO) content of the hypolimnion of Walden Figure 12. Comparison of dissolved-oxygen Quarterly Review of Biology, v. 17, no. 1, p. 1–11. steep water-table gradient southwest of Walden Pond is annual ground-water inflow to Walden Pond equals water-balance analysis. CTW234 MONITORING WELL —Alphanumeric code is U.S. profiles for kettle-hole seepage lakes in eastern Fairhaven 180 153.75 Geological Survey well number. Number indicates altitude Pond, which decreases from April through lake turnover in late fall. The Dincer, T., 1968, The use of oxygen 18 and deuterium concentrations in

caused by large water-level differences between Walden 180 Massachusetts during summer stratification; the 53 inches per year (in/yr) (expressed as depth of water over A summary of the water balance for Walden Pond for the of water table in feet above sea level slope of the plot versus time represents the hypolimnetic oxygen deficit. the water balance of lakes: Water Resources Research, v. 4, no. 6,

160 200 The historical August 1939 data of Deevey (1942) define a lower deficit rate profiles show a range of oxygenation in the

Pond and discharging areas—Heywoods Meadow and the lake surface). The estimated contribution from Goose 5-year period 1995–99 is shown in figure 6 partitioned on the 200 p. 1289–1306. 140 156.07 220 metalimnion. (Gull Pond data are from Portnoy

the Andromeda Ponds. 20 SURFACE-WATER SITE—Number indicates altitude of pond (line A-B) than that calculated from recent data. (1992 data are from Pond is 6 percent of this total inflow from ground water. basis of the magnitude of inflow and outflow components. 1 240 Farnsworth, R.K., Thompson, E.S., and Peck, E.L., 1982, Evaporation Bay surface in feet above sea level Massachusetts Department of Environmental Management, written and others, (2001); White Pond data are from The isotope mass-balance approach uses the stable Average inflow from precipitation and ground water totalled Walker (1988); Ashumet Pond data are from atlas for the contiguous 48 United States: U.S. Department of Water-Level Fluctuations 140 commun. (1994); 1994 data are from Baystate Environmental, Inc. (1995); Commerce, National Oceanic and Atmospheric Administration, δ18 δ about 106 in. Precipitation on the lake surface accounted for Jacobs Engineering, Inc. (2000)). Water levels in Walden Pond and the surrounding isotopes of oxygen ( O) and hydrogen ( D) that GENERAL DIRECTION OF GROUND-WATER FLOW and 1996 data are from this investigation.) Technical Report NWS 33, 26 p., 4 pls. naturally occur in water. Flows into and out of a lake and 45 percent of the inflow, whereas ground water contributed aquifer fluctuate because of seasonal and long-term 908,500 908,500 Gat, J.R., 1980, The isotopes of hydrogen and oxygen in precipitation, the lake water itself can have different isotopic signatures. 55 percent of the inflow. The proportion of inflows anchors in Fritz, P., and Fontes, J.Ch., eds., Handbook of environmental variations in recharge from precipitation. A hydrograph 212,000 212,500 213,000 213,500 214,000 These isotopic differences along with precipitation and the evaporation line for Walden Pond on figure 5, which isotope geochemistry, vol. 1, The terrestrial environment, A: New from a nearby USGS long-term observation well Base map created by using TERRAMODEL and Mass GIS DTMs, 1999, Coordinates shown as 500 meter grid, York, Elsevier, p. 21–47. Massachusetts State Plane Projection,1983 North American Datum; 1:5,000 Executive Office of Environmental Affairs (EOEA); evaporation rates can be used to determine ground-water extends from the average of the average isotopic 0 500 1000 1500 2000 FEET (fig. 4A) indicates water levels rise, in general, from Protected and Recreational Open Space data from MassGIS, 1989, Massachusetts State Plane Projection, 1983 North American Datum; Jacobs Engineering, 2000, Ashumet Pond Trophic Health Technical inflow to a lake (Krabbenhoft and others, 1990) compositions of precipitation and ground-water inflow 1:24,000 EOEA; Surficial Geology data from USGS,1964, Massachusetts State Plane Projection, 1983 North American Datum; 1:24,000 USGS; winter through early summer when recharge to the Building Footprints and Roads data from towns of Concord and Lincoln, 1999 State Plane Feet, Zone 5176, 1983 North American Datum; 1:5,000 0 100 200 300 400 500 METERS Memorandum, Volume 1: Massachusetts Military Reservation, AFC- through the lake samples. This evaporation line defines the aquifer exceeds ground-water discharge; water is avail- δ δ δ δ J23-35S18402-M17-0005, variable pagination. P(L–E(P) + E– L) GW = , (2), isotopic evolution of lake water from its source waters CONTOUR INTERVAL 10 FEET Koteff, C., 1963, Glacial lakes near Concord, Massachusetts: Article 96 able to recharge the aquifer when precipitation exceeds i δ – δ Figure 3. Walden Pond is a kettle-hole, flow-through lake. Ground water discharges into Walden Pond along its eastern perimeter GWi L (Krabbenhoft and others, 1990). Ground-water outflow NATIONAL GEODETIC VERTICAL DATUM OF 1929 in U.S. Geological Survey Professional Paper 475-C, p. C142–C144. evapotranspiration. From summer through winter, water and lake water discharges into the aquifer along its western perimeter. The area contributing ground water was delineated on the basis of (74 percent), is significantly greater than evaporation levels decline because ground-water discharge exceeds where GWi, P, and E have been defined previously and the configuration of the water table, surficial geology, and surface topography. The bathymetric map reveals three deep areas. Krabbenhoft, D.P., Bowser, C.J., Anderson, M.P., and Valley, J.W., 1990, (26 percent). Results indicate that ground water is the Estimating groundwater exchange with lakes 1. The stable isotope recharge. The annual cycle of water-level rises and δ , δ , δ , and δ are the isotopic composition of the L P E GWi dominant pathway into and out of the lake and that the mass balance method: Water Resources Research, v. 26, no. 10, declines lags climatic conditions because of the transit lake, precipitation, evaporation, and ground-water inflow, p. 2445–2453. water-residence time for the lake is 4.8 years. time for precipitation to recharge the water table through respectively. Average isotope values from water samples Table 1. Nutrient budget for Walden Pond Levine, S.N., and Schindler, D.W., 1999, Influence of nitrogen to TROPHIC ECOLOGY phosphorus supply ratios and physicochemical conditions on the unsaturated zone and because of storage within the collected from July 1998 to June 1999 represented the mers account for 34 percent of the annual nitrogen load and Large stands of Nitella have been hypothesized to intercept The primary public environmental issue for Walden Pond [Ground water, septic leach-field plume, and atmospheric sources measured directly; swimmer source estimated; other sources modified from Baystate leach field, the only substantial point source within the ground- phic, mesotrophic and eutrophic. Based on phosphorus cyanobacteria and phytoplankton species composition in the aquifer. Lake-water levels (fig. 4B) indicate a similar average isotopic values during 1995–99, except for the Environmental Inc. (1995); kg/yr, kilograms per year; N, nitrogen; P, phosphorus; kg/3 mo, kilograms per months] 27 percent of the annual phosphorus load. The percentages 2 phosphorus that might recycle from the sediments before it concerns its trophic ecology—whether urban development water contributing area (fig. 7). Nitrogen load for the plume loading, Walden Pond at 0.13 g P/m /yr is approaching a Experimental Lakes Area, Canada: Canadian Journal of Fisheries and seasonal pattern as the ground-water levels because the isotopic composition of evaporated water, which was increase to 67 and 54, respectively (table 1), during the sum- gets mixed into the water column and, through oxygen Aquatic Sciences, v. 56, p. 451–466. or high visitor attendance may have altered or will alter the Annual Summer was computed from the product of water use, an unsaturated- eutrophic state between “permissible and critical phosphorus lake is hydraulically connected to the surrounding calculated indirectly. mer. 2 generation, to reduce phosphorus recycled from the relation between plant-nutrient supplies and aquatic-plant Nitrogen Phosphorus Nitrogen Phosphorus zone loss factor, and nitrogen concentration in the septic tank. loads,” 0.084 and 0.17 g/m /yr, respectively (Vollenweider Nygaard, G., and Sand-Jensen, K., 1981, Light climate and metabolism Source of Nitella flexilis (L.) Ag. in the bottom water of oligotrophic Lake aquifer. The magnitude of fluctuations in the lake is less The isotopic compositions of precipitation, ground- Percent- Percent- Load Percent- In contrast to nitrogen, the average concentration of phospho- The growth-limiting nutrient for Walden Pond can be (1975), that apply to a lake with mean depth (42.4 ft) and sediments (Nygaard and Sand-Jensen, 1981). growth. Nutrient supplies, especially of growth-limiting Load Percentage Load N:P ratio Load N:P ratio Grane Langso, Denmark: Int. Revue Gesamt. Hydrobiol., v. 66, age of age of (kg/3 age of hydraulic residence time (4.8 yr) of Walden Pond. than in the aquifer, however, because the lake has water inflow, and lake water are plotted in figure 5. nitrogen and phosphorus, are key water-quality features of (kg/yr) of total load (kg/yr) (atomic) (kg/3 mo) (atomic) rus in the plume was not greater than that in background determined by comparison of the nitrogen-to-phosphorus Lake distribution of dissolved oxygen, indicative of plant p. 685-699. proportionally greater storage capacity than the aquifer. The isotopic composition of precipitation primarily PRECIPITATION total load sum load mo) sum load ground water. Phosphorus had been retained in the 40-ft ratio for different inputs to the average atom-to-atom ratio growth and a determinant in internal cycling of nutrients Figure13. Walden Pond swimming beach. GROUND- kettle-lake investigations because plant growth affects Background Plant-Growth Measurement Portnoy, J.W., Winkler, M.G., Sanford, P.R., Farris, C.N., 2001, Kettle varies because of changes in atmospheric temperature 66 7.7 5.5 17 27 16 4 1.4 9 27 unsaturated zone beneath the leach field and was not included required by algae (15:1; (Redfield and others, 1963). The in lakes, is a consequence of the balance among photo- Long-term variations in water levels reflect long-term (45%) WATER water clarity, determines the type and quantity of lake ground water and Dissolved Oxygen pond data atlas: paleoecology and modern water chemistry: Cape Cod storage changes in the aquifer and lake. Water levels (Gat, 1980); the precipitation samples define a local biomass production, affects the amount of summer Plume in plume load. Seventeen residences on septic leach fields were overall nitrogen:phosphorus ratio in nutrient inputs of 59, synthesis, respiration, and exchange with the atmosphere, as thermal stratification, and vertical transport of dissolved oxygen just before fall turnover likely increased the National Seashore, National Park Service, U.S. Department of ground water 260 30 ------65 15 ------Interior, 119 p. fluctuated over a range of about 11.5 ft from 1956 to meteoric water line (LMWL). The isotopic composition of OUTFLOW dissolved oxygen present in the deep water, and may even in the contributing area (fig. 3). Ground-water flow direction which was similar to the ratio in water-column measure- Whereas nutrient budgets indicate relative importance of mediated during summer by thermal stratification. Vertical oxygen into or out of the metalimnion was negligible. release of sediment phosphorus, which accumulates on Atmospheric wet 152 18 .8 3 412 38 9 .2 1 412 indicated that transport from 15 residences was toward Goose ments, indicated that nitrogen was in excess and phosphorus zonation based on thermal stratification results in temperate- Dissolved-oxygen concentrations measured during March the aerobic bed-sediment surfaces during the summer. 1999. The lowest water level was measured in early 1967 ground water varied little spatially and temporally. The (74%) affect other ecological problems, such as invasion of exotic nutrient sources, direct measures of lake trophic state such as Randall, A.D., 1996, Mean annual runoff, precipitation, and δ18 GROUND- Atmospheric dry 75 8.7 15 47 11 19 4 3.8 23 11 Pond. These residences contribute nutrients minimally to input would control the amount of plant growth. Nutrient changes in standing crops of plants or changes in dissolved zone lakes during the summer. The zones in order of and April increased in the metalimnion, indicative of Although cause and effect has not been established, these evapotranspiration in the glaciated Northwestern United States, after 4 successive years of below-average precipitation isotopic composition of ground water has lower O and species or cycling of bioconcentrating pollutants like 1951–80: U.S. Geological Survey Open-File Report 96-395, 2 sheets. δ WATER polychlorinated biphenyls (PCBs) and mercury. Nutrient Swimmers 290 34 8.7 27 74 290 67 8.7 54 74 Walden Pond, only as mediated after loss to the sediments in sources in which nitrogen is substantially in excess of the oxygen or carbon dioxide, associated with photosynthesis and increasing depth are the epilimnion (in Walden Pond 0 to substantial plant growth in this zone. After the increase, late stratification-period events preceded the only surface- (fig. 4C) resulted in a cumulative precipitation deficiency D values compared to the average annual isotopic Waterfowl 4 .5 .6 2 15 1 0 .6 4 4 supply, in turn, depends on geohydrology—sources, Goose Pond. Although nitrogen from the leach field of two res- Redfield ratio may mitigate blooms of cyanobacteria, which respiration, indicate how inputs are processed into plant 20 ft), the metalimnion (20 to 46 ft), and the hypolimnion metalimnetic dissolved oxygen concentrations remained scum-producing cyanobacteria blooms (of Anabaena) Redfield, A.C., Ketchum, B.H., and Richards, F.A., 1963, The influence of about 46 inches (in.). Two periods of high water-level composition of precipitation because precipitation INFLOW Fish stocking 6 .7 .7 2 19 2 0 .7 4 5 of organisms on the composition of seawater, in Hill, M.N., ed., The EVAPOR- amounts, and cycling of water and chemical constituents idences would enter Walden Pond directly, movement of phos- have the capability to fix nitrogen from the atmosphere. A growth in a given lake. Phytoplankton biomass, determined by (46 to 100 ft) (fig. 9). Restricted vertical mixing that results high and unchanged during the remaining six months of observed during the investigation, in late December of altitudes occurred in 1956 and 1984 following periods of recharges the aquifer from autumn to spring when Direct runoff 6.7.821610.854 Sea: New York, Wiley Interscience, v. 2, p. 26–77. (55%) phorus is unlikely because of the thick unsaturated zone and selective advantage of cyanobacteria over algae, which can chlorophyll measurements, amounted to 285 kg on a dry- from thermal stratification causes zone-specific (such as temperature stratification. Dissolved oxygen decreased in 1997 and 1998. atmospheric temperature is low. The isotopic composition ATION carried by the water. Total 858 100 32 100 59 432 100 16 100 59 Thoreau, H.D., 1854, Walden; or life in the woods, in Bode, Carl, ed., above-average precipitation. In the eastern half of long distance to the lake at their respective locations. not fix atmospheric nitrogen, is removed when nitrogen is in weight basis for Walden Pond. In addition, large stands of the metalimnetic or hypolimnetic) chemical changes, including the hypolimnion, where respiration dominated after onset of The rate of dissolved-oxygen depletion in the of lake water also varied little seasonally, which is typical The Portable Thoreau: New York, The Viking Press, 1964, Massachusetts, ground-water levels and streamflows (26%) Sources and Amounts of Atmospheric inputs were measured separately for wet and excess supply (Levine and Schindler, 1999). Cyanobacteria deep-growing macroalga Nitella grow on the bed-sediment dissolved oxygen depletion, that accrue during the entire stratification, mainly in response to decay of algal biomass, hypolimnion of Walden Pond can be measured by the p. 258–591. generally were below normal from autumn 1998 to late of deep surface-water bodies with relatively long water- blooms often form nuisance surface scums on lakes and even stratified period. that settles from the sunlit upper zones. By late fall in Plant-Nutrient Inputs inputs were dominated by three sources; ground water tions. Background nitrogen and phosphorus loads were dry deposition (collector location on fig. 3). A substantial phos- surface between depths of 20 and 42 ft (figs. 3 and 8). Nitella hypolimnetic oxygen deficit (HOD). The HOD is Vollenweider, R.A., 1975, Input-output models with special references summer 1999. Water levels in Walden Pond and the residence times (Dincer, 1968). The lake isotopic values Phosphorus and nitrogen can enter Walden Pond carried (septic leach field plume for nitrogen and ambient ground determined as the product of ground-water discharge to Walden phorus load associated with pollen fall was measured. Swim- may develop toxins; a high nitrogen to phosphorus ratio and biomass determined from weight of dried samples and percent During cold weather every year, water mixing in Walden Walden Pond, virtually all of the dissolved oxygen stored represented by the rate of change in dissolved oxygen to the phosphorus loading concept in limnology: Schweizerische surrounding aquifer during this study, however, were at plot to the right of the LMWL because evaporation causes by ground water, through direct dry or wet deposition from water for phosphorus), atmospheric deposition, and human Pond and average ground-water concentrations. A ground- mer inputs were estimated from known average composition of sources that contribute to it, such as the leach-field plume, area covered was about 5,000 kg, or more than 17 times Pond moved dissolved oxygen from the atmosphere into the below the 46-ft depth has been consumed (black zones in mass in the hypolimnion (slope of line in fig. 11). HOD is Zeitschrift Fuer Hydrologie, v. 37, p. 53–62. or above-average levels because of the large quantity of an increased enrichment of δ18O relative to δD in the lake swimmers (table 1). water plume containing nitrogen was detected in drive-point urine and assumptions about the percentage of summer Reser- may help prevent cyanobacteria blooms. water column resulting, by early spring, in near-saturation by fig. 10A). In winter, wind and surface cooling break up an integrative indicator for lake trophic state, because it Figure 6. The average annual water balance for Walden Pond the atmosphere, from birds roosting on the lake, from greater than the phytoplankton biomass. Nitella presence in Walker, E.H., 1971, Walden's way revealed: Man and Nature, stratification, and the cycle starts over. December 1971, p. 11–20. water in storage and because of the low outflow rates water. Ground-water inflow calculated with equation 2 shows that ground water is the dominant pathway into and out of parking-lot or road runoff, by fish stocking, and from Computations for ground-water nutrient inputs were div- wells along the northeast shore of Walden Pond and in observa- vation visitors that are swimmers (90 percent) and percentage Three lake terms used to indicate progressively greater lakes has been associated with clear-water conditions and later dissolved oxygen throughout (fig. 10 A and B). With spring depends on oxygen use during much of the time that the from the lake and aquifer. results in 68 in/yr for δ18O and 57 in/yr for δD, which the lake. swimmers. Estimated annual nutrient loads indicated that ided according to background and point-source contribu- tion wells immediately downgradient from the Reservation of swimmers that urinate in Walden Pond (50 percent). Swim- nutrient supply and consequent plant growth are oligotro- absence of Nitella with more turbid, eutrophic conditions. warming, the deep water was cut off from the surface by The complete depletion of hypolimnetic dissolved lake is stratified. Three years of biweekly dissolved Walker, W.W., 1988, White Pond water quality studies: Concord, Massachusetts, White Pond Advisory Committee, 28 p.

Hydrology and Trophic Ecology of Walden Pond, Concord, Massachusetts By Paul J. Friesz and John A. Colman 2001