THE HYDROGEOCHEMISTRY OF CONNECTED WATERWAYS: THE POTENTIAL OF LINKING
GEOLOGY TO FISH MIGRATIONS
1 Karin E. Limburg and 2 Donald I. Siegel
1 SUNY College of Environmental Science and Forestry, 241 Illick Hall, Syracuse, NY 13210; KLimburg@esf.edu
Department of Earth Sciences, Heroy Hall, Syracuse University, Syracuse, NY 13210
ABSTRACT: Many major North American watersheds are connected by canals and diversions, allowing fi sh migration across watersheds.
Unique geochemical “signatures” of watershed waters may be useful as natural tracers if they are incorporated into fi sh earstones
(otoliths). We tested this hypothesis by measuring concentrations of dissolved Ca, Na, Sr, Mn and Ba along the Hudson-Mohawk-Erie
Canal system, a trans-basin waterway connecting Lake Ontario to the Atlantic Ocean. The concentrations of these dissolved metals from
Adirondack (northern) tributaries were 3-350 times less than in waters from the lower Hudson River, where seawater intrusion occurs, and in the western Mohawk basin, where evaporite minerals dissolve from shales and limestones in the watershed rocks.
Of these metals, variation in concentrations of Sr, Mn, and Ba in otoliths from two Alosa aestivalis ( blueback herring) corresponded to changes in concentrations the water chemistry where the fi estuary and then westward in the Mohawk-Erie Canal drainages. The biochemical response, re fl ected by otolith metal concentrations corresponding to metal concentrations in surface water along the Mohawk-Hudson, forensically can be used to show how both invasive and native fi sh species take advantage of anthropogenically induced linkages in waterways
KEYWORDS: fi sh otoliths, microchemistry, watershed geochemistry, connected waterways, Alosa aestivalis
INTRODUCTION
The linkages between the geological and biological sciences have expanded during the past two decades with increasing interest in microbial interactions related to water-rock interactions (e.g., Bennett et al. 2000) and the response of watershed biota to environmental drivers such as acid deposition and other anthropogenic contamination (e.g.,
Likens et al. 1996). There may be an equally important linkage between geology and fi sheries science.
are readily analyzed by electron microprobes, which can quantify elemental concentrations without destroying the sample at scales < 10 m. By analyzing Sr and Ca along a transect from an otolith core to its outer edge, a detailed, fi ne-scale temporal record of where the fi sh lived in their life cycle can be obtained (Campana 1999).
Fisheries science has been revolutionized by the analysis of otoliths (ear stones) found in teleost (bony)
Otoliths are small, biogenic aragonite (CaCO
3 fi
1985; Secor et al. 1995; Fossum et al. 2000). Increasingly, microchemical constituents of otoliths are being used to interpret the environmental histories of fi shes as well.
shes.
) structures that participate in hearing and balance, and that increment on a daily and annual basis like tree rings, forming a lifelong record of age and growth (e.g. Campana and Neilson
Although much of the microchemistry work to date has exploited salinity gradients between inland, estuarine and marine waters, it is clear that geological variations within watersheds can also be re fl ected in otolith microchemistry.
For example, Bronte et al. (1996) and Brazner et al. (2004) found that suites of minor and trace elements measured in otoliths could be used to classify fi shes from different coastal wetlands and basins of Lake Superior. Kraus and Secor
(2004) found that otolith Sr:Ca in fi sh from experimentally manipulated treatments generally re fl ected aqueous Sr:Ca.
Trace elemental composition and stable isotopic ratios of oxygen in otolith aragonite can be used to identify different waters and water temperatures within which
2001b; Gillanders 2002; Kennedy et al. 2002). fi sh have lived (e.g., Patterson 1998; Campana 1999; Weidman and
Millner 2000; Campana and Thorrold 2001; Andrus et al.
2002),determine how different fi sh stocks mix or segregate
(Thorrold et al. 1998 a,b; Gillanders and Kingsford 2000), migrate (Limburg 2001; Thorrold et al. 2001), or use different habitats (Secor and Rooker 2000; Limburg et al.
In North America, numerous major watersheds and water bodies are connected by canals and diversions. Many of these connections were created in the 19 th century to improve transportation and remain today to move people and goods. They also inadvertently are pathways for nonindigenous species. For example, zebra mussels ( Dreissena polymorpha ) was introduced into Lake St. Clair near Detroit through ballast water in 1988, but spread rapidly through drainages that were connected by canals and diversions
(Grif fi ths et al. 1991). Fish can move as readily, and there is scienti fi c potential that their passage through connected waterways may be forensically recorded in their otoliths as geochemical “signatures” re fl ecting the water chemistry of different geological regions.
In particular, strontium-to-calcium (Sr:Ca) ratios are often useful proxies to identify when fi sh move from marine to freshwater because many inland waterways are Sr-depleted compared to the ocean (Limburg 1995). Sr:Ca ratios
The connected waterway system we are particularly interested in is the Hudson-Mohawk-Erie Canal system in
New York State, and its use by the blueback herring ( (( Alosa
Northeastern Geology & Environmental Sciences , v. 28, no. 3, 2006, p. 254-265.

LIMBURG AND SIEGEL aestivalis ). This fi sh is anadromous; it spawns in fresh water but then migrates to sea to mature. The blueback herring is native to major river systems along the North
American east coast, and an ideal candidate to determine if variations in its otolith chemical compositions are useful as a proxy to determine complex migration paths within interconnected waterways in New York. Blueback herring populations have increased in the Hudson River’s major tributary, the Mohawk River, which serves as the fi sh’s spawning and nursery ground. The Hudson is a tidal estuary and the seasonally varying salt front extends up-gradient approximately 100 km from the river’s mouth.
Hudson and Mohawk Rivers, had often uninterpretable lifetime patterns of otolith Sr:Ca (Limburg et al. 2001a).
Some adults had otolith Sr:Ca molar ratios around 0.001 followed, with age, by abruptly elevated levels of Sr:Ca (to about 0.003 - 0.004) typically found in anadromous fi sh migrating from fresh water to marine water. Young-ofthe-year (born that season) individuals from the Mohawk nursery ground had higher otolith Sr:Ca ratios compared to those collected in the Hudson (Limburg et al. 2001a), suggesting that fresh waters with high concentrations of Sr occur somewhere in the Mohawk River Basin or elsewhere west in the canal system. To interpret these variable Sr:
Ca, additional geochemical tracers are required better to understand geochemical changes within the waterways used by the fi sh.
Until the Erie Canal system was built during the 19 th century, the Mohawk River was historically inaccessible to fi sh migration because of an impassable waterfall at
Cohoes, NY. This system of canals now traverses New
York State and connects all major waterways and water bodies, including the Hudson River and the Great Lakes
(Fig. 1).
The water quality of the canal when it was fi rst built was poor. Flows were so sluggish that Mohawk fi sh seldom moved into it (Daniels 2001). However, blueback herring began to move from the Hudson River through the canal locks into the Mohawk River as water quality improved in the 1930s (Greeley 1935) as the canals were widened.
In 1995, several thousand blueback herring were found in the lower Oswego River, and two individuals were even caught in Lake Ontario near Oswego, NY, over 550 km from the Atlantic Ocean (Owens et al. 1998). Fifty adult blueback herring, collected in May-June 1999 from the
This paper presents the results of two synoptic surveys wherein we mapped the geochemistry of selected solutes, including Sr and Ca, in water extending from the lower
Hudson near its con fl uence with the Atlantic Ocean, through the Mohawk/Erie Canal system, and westward through the Oswego River to Lake Ontario. We also present the results of multiple trace elemental analyses (laser ablation, inductively coupled plasma mass spectrometry or LA-
ICPMS) in otoliths of two blueback herring that show different lifetime habitat use and which constitute a more robust method to characterize migrations than using Sr:Ca in otoliths alone. Our analyses demonstrate the potential for using the multi-trace elemental approach to track fi sh movements through complex networks of interconnected waterways.
Figure 1. Map of study area; approximate sampling locations shown by stars.
255

GEOCHEMICAL MARKERS AND INTERBASIN MIGRATIONS
STUDY AREA
The Hudson River is an open, tidal river for 247 km north of the ocean to the Federal dam at Troy, NY. A lock at this dam provides passageway upstream and access both to the upper Hudson River, that
Oneida River, fl fl ows south from Adirondack
Mountains, and the Mohawk River, the Hudson River’s major tributary (Fig. 1). The Mohawk River extends from Albany westward to Rome, NY, about 440 km from the Atlantic Ocean, and drains watersheds in both the
Adirondacks to the north and the Catskill Mountains to the south. The Erie Canal in Rome connects the Mohawk
River to Oneida Lake. The out fl ow of Oneida Lake, the
ows 22 km before joining the Seneca River to form the Oswego River, which in turn fl ows 40 km before discharging into Lake Ontario at Oswego, NY.
Otolith trace element analysis – Otoliths from two adult
Alosa aestivalis collected on spawning grounds near
Waterford (rkm 259) and Rome (rkm 441) respectively, were selected for trial analysis by LA-ICPMS conducted at the Department of Chemistry, Old Dominion University,
Norfolk, VA. This method is more sensitive (ppb vs parts per thousand) than wavelength-dispersive electron microprobe analysis (EMPA; see Campana 1999 for discussion of analytic methods). Based on previous Sr:Ca
EMPA results of the matching otolith from each fi sh, one fi sh was classi fi ed as an anadromous individual because the
Sr:Ca in the otolith increased rapidly at the end of the fi rst growing season, as observed in migration events (Limburg
2001, Limburg et al. 2001a), whereas the other had an ambiguous Sr:Ca otolith pro fi le (intermediate and low Sr:
Ca) and hence could not be classi fi ed as anadromous.
The bedrock geology of the Hudson River basin differs considerably from that of the Mohawk River basin and westward drainages. Brie fl y, the chemistry of the Hudson
River mostly re fl ects crystalline and clastic rocks consisting mostly of silicate and aluminosilicate minerals in the
Adirondack and Catskill Mountains, whereas Mohawk
River water chemistry re fl ects calcareous shales, limestones and dolostones deposited in a marine environment as fl at strata (Isachsen et al. 1991). Evaporitic minerals, including gypsum (CaSO
4 units.
) and rock salt are in some of the shale rock
METHODS
The otoliths were sectioned in the sagittal plane, cleaned in MilliQ-deionized water, and attached to glass slides with low-contaminant silicon glue. Blanks and standards were run prior to analysis of each otolith. Two sections of the anadromous fi sh otolith were ablated and analyzed, one from the inner portion which had been deposited during freshwater residency, and one from the marine life period. Seven sections were ablated from the unknown otolith, extending from the core area and outward toward the posterior edge (but not all the way to the outer edge; see Fig. 4). Both otoliths were analyzed for Ca, Ba, and
Mn, and these data were combined with Sr:Ca data from an earlier analysis (Limburg et al. 2001a).
Sampling
During low fl ow conditions, we sampled surface waters in two synoptic surveys (16-17 August, 2000 and 13-24
September, 2001) along a transect from the lower Hudson
River estuary at the Tappan Zee Bridge, 40 river km from the mouth (herein termed rkm) in 2000 and Croton Point
Park (55 rkm) in 2001 to Lake Ontario at Oswego, NY (Fig.
1). The year 2000 was wet, so many of the stations were re-sampled in fall 2001, when it was drier. Several major tributaries to the Mohawk River were also sampled in 2001.
Each sample consisted of approximately 100 ml of water that was fi ltered through a GFF Gelman 0.45 micron and then acidi fi ed with 1-2 ml concentrated HNO
3
.
fi lter
Water analysis – Samples in 2000 were analyzed in triplicate with a Spectrospan V Direct Current plasma optical emission spectrometer for Sr, Ca, Na, and Mn. Detection limits for all elements were ~20 µ g L -1 . Precision of analysis was within 7%, based on standard statistical characterization and analysis of known standards. Samples from 2001 were analyzed by inductively-coupled plasma optical emission spectrometry (Perkin Elmer OPTIMA 3300DV ICP-OES).
Quality controls were run after every tenth analysis. Results were rejected if the error rate exceeded 10%. Detection limits were similar.
256
Interpretation.
We calculated ratios (to Ca) of measured solutes, expressing them in mmol mol -1 according to practice and plotted them in ratio versus distance from the
Hudson River mouth to determine longitudinal trends.
RESULTS
Water chemistry – Concentrations of Ca and Sr varied widely from one end of the river transects to the other (Table
1). Ca concentrations ranged in 2000 from 2.07 mmol L -1 in the mesohaline Hudson estuary to a low of 0.48 mmol
L -1 in the tidal freshwater section of the Hudson (average in the tidal freshwater reach between rkm 100 and 229 = 0.54
± 0.03 s.d. mmol L -1 ). Ca input from the upper Hudson
(rkm 256) was 0.56 mmol L -1 , and in the lower Mohawk
(rkm 256-313) concentrations averaged 0.82 ± 0.02 mmol
L -1 . Maximum Sr concentration (0.132 mmol L -1 ) was measured at the Tappan Zee Bridge (rkm 45), declining to a fairly constant value of 0.0015 ± 0.0002 mmol L -1 in the tidal freshwater zone. Above the Troy dam, Sr coming from the upper Hudson was lower than in tidal fresh water
(0.0006 mmol L -1 ), and was higher in the lower Mohawk
(0.0028 ± 0.0002 mmol L -1 for rkm 256-313). Both Ca and Sr continued to vary upstream, with peaks around rkm
402-410, followed by declines around rkm 430-460, but increasing again west of Oneida Lake (rkm 496; Table 1).

LIMBURG AND SIEGEL
Table 1. Elemental concentrations and ratios measured along connected waterways from the estuarine Hudson River to
Lake Ontario during August 2000 and September 2001. Concentrations are in mmol L -1 .
257

GEOCHEMICAL MARKERS AND INTERBASIN MIGRATIONS
258

Strontium:calcium ratios followed a similar pattern (Table 1 and Fig. 2). In 2000, Sr:Ca was 6.4 x 10 -3
LIMBURG AND SIEGEL
(mmol mmol -1 ) in brackish water at the Tappan Zee Bridge (rkm 45) and then decreased to about 2.77 x 10 -3 in the tidal freshwater reach
(rkm 86 – 232). The open Atlantic Ocean Sr:Ca is ~ 9.2 x
10 -3 (Odum 1951). The Sr:Ca in the lower Mohawk (rkm
255-382) was of 3.4 x 10 -3 . Upstream, Sr:Ca peaked at 4.7
x 10 -3 near North Frankfort (rkm 402) and then persisted at about this ratio at least 8 km further upstream to Herkimer.
Strontium:calcium ratios then dropped to 1.0 x 10 -3 near
Rome (rkm 441; Fig. 2a).
Rome is located at the divide between the Hudson and Lake
Ontario watersheds. West of this, the inlet of Oneida Lake is a con fl uence of the Erie Canal and Fish Creek, a tributary draining southward from the Tug Hill Plateau (rkm 462,
Fig. 2a, data point drawn as a circle). Sr:Ca here was as low as at Rome (Table 1). Water leaving Oneida Lake had the highest Sr:Ca (7.8 x 10 -3 ) in the Mohawk basin and this value persisted throughout the recipient Oneida River.
This river joins with the Seneca River at Three Rivers (rkm
518) to form the Oswego River, which was also canalized and regulated as part of the New York State Canal system.
Oswego River Sr:Ca had a fairly constant 6.3 (± 0.2) x 10 -3 , re fl ected in the nearshore zone of Lake Ontario close to the river’s mouth in 2000 (5.9 x 10 -3 ).
The 2001 synoptic survey con of Sr:Ca identi fi examine their in fl fi rmed the geographic patterns
ed in the surface waters in 2000 (Fig. 2b).
Fewer data points were collected in the tidal Hudson, but more samples were collected at the mouths of tributaries to
uences. Tributary streams that have lower
Sr:Ca than the Mohawk are Schoharie Creek (Fig. 2b, box
2) and the East and West Branches of Canada Creek (Fig.
2b, boxes 3 and 4). Rivers discharging to Oneida Lake from the south have waters with high Sr:Ca (Oneida and
Chittenango Creeks, Fig. 2b boxes 5 and 6). Because 2001 was a drought year, the Oswego River discharge did not affect the nearshore zone of Lake Ontario, so the lake Sr:Ca of the lake was lower in 2001 (2.6 x 10 -3 ) than in 2000. In both 2000 and 2001, regional differences in Sr:Ca between tidal freshwater Hudson, non-tidal Mohawk, Oneida Lake, and the Oswego River were signi fi cantly different (Table
2), with Hudson < Mohawk < Oswego < Oneida in both
Figure 2. Sr:Ca ratios (mmol mol ll ) in water along the Hudson River – Lake Ontario transect, 2000 (a) and 2001 (b).
Dotted line indicates beginning of Mohawk River. Arrow points to location of Rome, NY at the Hudson/Lake Ontario watershed divide. Circular data point is the inlet of Oneida Lake. Numbered boxes indicate tributary values. Box numbers:
1 = upper Hudson River; 2 = Schoharie Creek; 3 = East Branch Canada Creek; 4 = West Branch Canada Creek; 5 =
Oneida Creek; 6 = Chittenango Creek; 7 = Seneca River.
259

GEOCHEMICAL MARKERS AND INTERBASIN MIGRATIONS
Table 2. Results of ANOVA for ratios of Sr:Ca, Mn:Ca, and Ba:Ca in connected waterways from the lower Hudson
River to Lake Ontario. Values are mmol mol -1 . Hudson includes only the tidal freshwater reach.
1996) throughout the transect, and geographic variation that was repeatable in both years (Table 1 and Fig. 3). Hudson
River Mn:Ca ratios were signi fi cantly lower than those in the Mohawk River, Oneida Lake, and its outlet river in both years (Table 2), whereas the lowest Mn:Ca ratios were in the Oswego River. Mn:Ca ratios peaked near Rome (rkm
441) to the Oneida Lake inlet (rkm 462) with the pattern repeating in 2000 and 2001. Peak values both years were
1-2 orders of magnitude higher than values in the rest of the transect. Water in the tidal Hudson River in the drier year 2001 had lower Mn:Ca, re fl ecting increased saltwater intrusion.
Barium, which was only measured in 2001, also varied spatially (Figure 3 and Table 1), with maximum concentrations (6.41 x 10 -4 mmol L -1 ) in the vicinity of
Oneida Lake. All values of Ba:Ca were signi fi cantly higher
1
(Table 2) than in marine water, about 9.9 x 10 -9 mmol mol -
(Summerhayes and Thorpe 1996). Highest ratios were found in Oneida Lake (Table 2).
Finally, sodium, a tracer of salinity, was higher in waters in the mesohaline lower Hudson River, but it was also somewhat elevated in Oneida Lake, the Oneida River, and the Oswego River from rkm 522-rkm 556 (Table 1).
Otolith microchemistry – The female fi sh captured at rkm
259 had previously been classi fi ed as anadromous based on its pattern of Sr:Ca (Limburg et al. 2001a). In the present LA-ICPMS analysis (Table 3A), the inner portion of its otolith, deposited in the fi rst season of growth, had low concentrations of Sr relative to Ca (0.59 x 10 -3 ) and moderately high Mn:Ca and Ba:Ca ratios, whereas the converse occurred in the segment of the otolith that corresponded to the next growing season (identi fi ed by optical examination of the otolith). The second growing season had a 2.7-fold increase in Sr:Ca, a 3.7-fold decline in
Mn:Ca, and a four-fold decrease in Ba:Ca. This season was identi fi ed previously as marine (Limburg et al. 2001a).
Analysis of the otolith of the male herring caught at Rome,
NY showed a strikingly different pattern (Table 3B). Sr:
Ca values fl uctuated, but none reached the values seen in the other fi sh’s otolith. Ba:Ca values were all substantially higher (range, 1.06 – 6.42 x 10 -6 ) than the 0.38 x 10 -6 value that was interpreted as marine in the anadromous fi sh.
Furthermore, Mn:Ca ratios in the Rome fi sh otolith had the highest departure from seawater (range 2.19 – 21.6 x 10 -6 ).
years.
Manganese concentrations in 2000 in river waters were higher relative to average marine values (marine concentration: 2.5 x 10 -4 µ mol L -1 , Summerhayes and Thorpe
260
The maximum value of Mn:Ca (21.6 x 10 -6 ), located in the zone of the second growth season of the Rome fi sh (i.e., the second summer of the fi sh’s life), is nearly 57 times as great as the assumed marine value from the other fi sh. In this same part of the otolith, Sr:Ca is at a minimum and Ba:
Ca is moderately elevated (Table 3B, Fig. 4).

LIMBURG AND SIEGEL
Figure 3. a) Ba:Ca from September 2001, b) August 2000 Mn:Ca, and c) September 2001 Mn:Ca molar ratios along the
Hudson River – Lake Ontario transect. Symbols as in Figure 3.
DISCUSSION
The dissolved solute concentrations in surface and ground water in the Hudson and Mohawk Rivers re fl ect the chemical compositions of the weathering rocks in their watersheds.
The tidal Hudson River passes north to south from Albany through the Hudson-Mohawk geomorphic lowland. This lowland, carved by glaciers during the Pleistocene, is mostly bordered to the east by crystalline, silicate igneous and metamorphic rocks of the Taconic Mountains, and by quartzose sandstones and conglomerates of the Catskill
Mountains to the west (Isachsen et al. 1991). These rocks chemically weather slowly and release only trace amounts of Ba and Sr from their reactive minerals, mostly feldspars
(Langmuir 1997). Surface waters in the Taconic Mountain and Hudson-Mohawk geomorphic regions that drain to the Hudson have speci fi c conductance (a measure of total dissolved solids) generally less than 500 S cm -1 (Olcott
1995), dominated by base cations and bicarbonate ions.
Strontium concentration in feldpars is very small, so Sr:Ca ratios in associated waters also are very small.
The Hudson River’s chemistry is also affected by saltwater intrusion from New York Harbor (Busby and Darmer 1970).
Strontium, Ca, and Mg concentrations in sea water are about
0.09, 9.98, and 54.49 mmol L -1 , so Hudson River water that has mixed with sea water has higher concentrations of these solutes at different ratios than are found upstream of the seawater effect, and again, Sr:Ca ratios are very low. Sea water, which has a sulfate concentration of about 21 mmol
L -1 , has negligible Ba because its solubility is low in sulfaterich waters (Drever 1988).
261
In contrast to the Hudson River, the eastwardfl owing
Mohawk River passes through the interface between the
Ontario Lowlands, also formed by glacial action, and the topographically higher Alleghany Plateau to the south
(Isachsen et al. 1991). The lowland and plateau consist mostly of marine, Lower Paleozoic age sedimentary rocks, a thick sequence of interbedded sandstones, calcareous and siliceous shales, limestones, and dolostones, deposited in shallow seas under evaporative conditions during the
Devonian period (Isachsen et al. 1991). In these settings,

GEOCHEMICAL MARKERS AND INTERBASIN MIGRATIONS
Table 3. Results of otolith microchemical analyses conducted with electron microprobe analysis (EMPA) or laser-ablation
ICP-MS (LA-ICPMS). Distance from core refers to measurement along the major posterior axis of the otolith.
trace metals, including Ba and Ba, accumulated to form nodules and laths of BaSO
4
(barite) and celestite (SrSO
4
), which since deposition, have weathered to strontianite
(SrCO
3
) and witherite (BaCO
3
Chamberlain et al. 1986).
) (Siegel et al. 1987;
Barite nodules and gypsum are in upper Devonian rocks across the entire width of the E-W drainage of the Mohawk
River (Pepper et al. 1985). Evaporite minerals dissolve faster than do silicate and carbonate minerals. Consequently, enhanced sulfate, calcium, and strontium concentrations often increase the dissolved solids concentrations in both ground water and surface water to > 1000 mg L -1 (e.g.,
Shampine 1973). The higher concentrations of these solutes as well as the different Sr:Ca in the Mohawk River and its tributaries re fl ect the contribution of dissolving evaporite minerals to the surface waters. fi sh otoliths, are excellent tracers for determining how move between habitats during their life cycles.
fi sh
Both the Mn:Ca and Ba:Ca ratios in the analyses done on the putative anadromous fi sh (Table 3A) supported its classi fi cation. The observed shifts are consistent with the differences in marine vs. the inland elemental ratios reported here from the Hudson and lower Mohawk River, and are also consistent with other otolith microchemistry studies
(e.g., Bath et al. 2000, Secor et al. 2001). The otolith from the fi sh caught in the Rome vicinity had an entirely different pattern (Table 3B), with intermediate value of Sr:Ca and elevated value of Ba:Ca and Mn:Ca compared to expected seawater-derived ratios. This combination of high and low ratios matches ratios calculated from the surface water solute concentrations in samples collected from the Rome
– Oneida inlet vicinity (rkm 441- 462).
Finally, the Mohawk River is connected arti fi cially to
Oneida Lake (Fig. 1), within which manganese nodules form. Oneida Lake is a eutrophic freshwater lake wherein manganese is released by bacterially mediated reduction from lake sediments to the water column during the summer months and concentrations of dissolved manganese can be greater than 1 mg L -1 (0.018 mmol L -1 ) (Dean et al.
1981). Taken in sum, the different water chemistries of the Hudson, Mohawk, and westward-connected waterways include natural geochemical gradients that, recorded in
The more detailed transect of Sr:Ca made with electron microprobe analysis (Fig. 4) also indicates that the
Hudson.
fi sh spent much of its life in water with higher Sr concentrations compared to Hudson River water, prior to and after spending time in the Rome vicinity. Taken together, these data suggest that this fi sh never left the waters west of the
262
Water is the major source of trace metals in fi sh otoliths, with food serving as a secondary source (Farrel and Campana

LIMBURG AND SIEGEL
Figure 4. Micrograph of an otolith from a male adult blueback herring showing core area and lines that were ablated in
ICP analyses, and a transect of Sr:Ca values measured by WDS electron microprobe analysis (EMPA) aligned to show the corresponding spatial variation (details of EMPA given in Limburg et al. 2001a). Double-headed arrow points to region of otolith where Mn:Ca values were maximal, corresponding to minimal Sr:Ca.
1996; Campana 1999). Recent experimental studies of otolith elemental uptake by several that Sr:Ca and Ba:Ca ratios in otoliths are often linearly related to their ratios in the water within which the geographical identi fi ers, also seen in fi fi sh species indicate
sh otoliths.
fi sh live
(Bath et al. 2000; Milton and Chenery 2001; but see review by Elsdon and Gillanders (2003) and Kraus and Secor
(2004) for comments on non-linear uptake relationships).
Therefore, the solute chemical gradients in the connected system of the Hudson-Mohawk-Oneida-Oswego are unique
Our preliminary results here and elsewhere (Limburg et al. 2001a; Limburg, Huang and Bilderback submitted) support the hypothesis (Owens et al. 1998) that the range of blueback herring is expanding into the Great Lakes basin
263 through arti fi cially connected waterways. An established population in the Mohawk, Erie Canal, Oneida Lake, or westward-connected rivers could be a seed source for further expansion into Lake Ontario and other Great Lakes.
On the other hand, stable isotope ratio analyses ( δ 13 C) of muscle tissue of adult fi sh found on distant inland spawning grounds are consistent with marine origin (I.R. Blackburn and K.E. Limburg, State University of New York, College of Environmental Science and Forestry, unpublished data) suggesting that these fi sh spend at least the winter prior to their spawning in the ocean. The question of the advantages obtained by fi sh from undertaking such lengthy migrations, combined with prolonged residency in freshwater habitats remote from the ocean, remains unanswered.

GEOCHEMICAL MARKERS AND INTERBASIN MIGRATIONS
Matching surface water chemistry and otolith chemistry provides a unique method to understand the ecology of fi sh populations. Our study agrees with other studies showing that the migratory movements of many species are more complex than previously assumed (Secor et al. 2000;
Limburg et al. 2001b; Thorrold et al. 2001; Kennedy et al. 2002). Synoptic surveys of elements in watersheds are routinely done for major nutrients (e.g., the U.S. Geological
Survey’s National Water Quality Assessment program) and for pollutants of concern (e.g., SO x and Hg transported or released by acid rain: Driscoll et al. 2001), but less often for minor or trace elements. We think that surveys of elemental ratios in waterways provide potential geochemical markers that can leave their marks on hard parts of fi shes such as otoliths and scales (e.g., Farrell et al. 2000; Gillanders and
Kingsford 2000; Secor et al. 2001), and in theory may be re fl ected in calci fi ed structures of other organisms, such as bivalves or crustaceans. As such, these combined markers are a powerful means to detect and interpret the history of native organisms and invasive species passing through connected waterways.
ACKNOWLEDGMENTS
We thank D. Driscoll, Z. Chen, E. Dorval, and C.M. Jones for assistance with analyses, and D. Swaney and one anonymous reviewer for their thoughtful remarks. Financial support was provided by The Hudson River Foundation,
New York Sea Grant, and the National Science Foundation
(DEB-0238121).
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