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One of the primary responsibilities of
the Water Resources Division of the

United States Geological Survey is to

monitor the amount and quality of waters in

our rivers, lakes, and wetlands. Hydrologists

can evaluate these important resources in the

present day, but how can they determine

what conditions were like in past decades or

even centuries? Moreover, are conditions

part of a natural cycle or caused primarily by

human activities? It is sometimes possible to

answer these questions by examining the

annual growth rings of trees (fig. 1). Each

ring can be assigned an exact year of

formation, and yearly differences in ring

widths can be used to compare past and

present conditions on a flood plain, along a

river, or within a wetland. Thus, tree rings

provide information that otherwise might be

difficult or even impossible to obtain.

Hydrology and tree growth were

investigated within a small wetland in the

Tully Valley of central New York, about 20

miles south of Syracuse. In late 1994 it was

noted that some wetland trees were dying,

and local residents reported that flow of a

small stream draining the wetland seemingly

increased and became more brackish since

the mid to late 1980s. The wetland is about 3

miles north of an extensive salt mining

operation known to have degraded local

water quality, but no effects of mining had

been confirmed previously near the wetland.

The oldest wetland trees started to grow before

theonset of mining in 1889, and thus tree-ring

studies were undertaken not only to investi-

gate recent hydrologic change within the

wetland, but also to search for evidence of

any other changes during the last 100 years.

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science fora changing world

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