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Historical wetlands

The Bronx River watershed in the Bronx once encompassed nearly 1000 times the area of wetland habitats it supports today. As part of an effort to “reconstruct the ecology of New York City when Henry Hudson first sailed in 1609”, Sanderson and Labruna (2005) mapped the historical ecology of the lower Bronx River Watershed. They found that approximately 27% of the land of the Bronx River watershed in the lower Bronx was wetlands (934 out of 3898 acres). This included more than 700 acres of saltwater marsh at the mouth of the river, a 184 acre freshwater wetland (“Bear Swamp”) near today’s Bronx Zoo, and more than 42 acres of riparian habitat surrounding the river. Further north in the Bronx, the other historic freshwater wetland complex, covering over a dozen acres, and readily visible on the 1897 USGS maps, was located in Woodlawn cemetery.

Wetland type Historical Current
Riparian (Acres) 89.5 *included below
Freshwater Wetland (Acres) 217.7 27.4 *
Saltwater Marsh (Acres) 716.9 5.1
Bronx River tributary wetlands (meters) 22014 234.7

Map 1: Historical and current wetlands in the Bronx.

Click on the map to download it in PDF format

What happened to the former wetlands of the Bronx River?

The natural wealth of the Bronx River watershed attracted early European traders who were drawn by the beavers that proliferated there, the good water source, and the access. In 1639, a wealthy Swede and the namesake of the Bronx, Jonas Bronck, purchased 500 acres from the Mohegan Indians. The area soon established its economic value and by the mid 1700s as many as 12 mills were in operation along “Bronck’s River.” Even so, the area remained relatively pollution free; the water was considered so “pure and wholesome” that during the 1820s and 1830s the New York City Board of Aldermen debated ways to tap into it to supply the growing city with drinking water.

By the end of the 19th century, however, the Bronx River had degenerated into what one official commission called an “open sewer” (Bronx Valley Sewer Commission Report 1896). The Bronx River valley had become an industrial corridor with very little regulation of the waterway. The construction of the New York Central Railroad in the 1840s led to a straightening of the River in the northern Bronx and Westchester and caused the first disconnection between the river and its tributaries and the depressional wetlands to the west in Woodlawn Cemetery. Smaller scale filling of wetlands such as “Bear Swamp” along the river occurred with the development of areas such as West Farms and Bronxdale and whenever a landowner wanted dry land. Large scale river straightening and filling of the floodplain and riverine wetlands took place in the 1930’s again with the construction of the Bronx River Parkway. By the 1950s, this parkway project and other ambitious infrastructure projects by Robert Moses resulted in dumping of construction rubble and debris, household waste and coal ash on hundreds of acres of salt marsh and miles of tidal tributaries along the entire coastline of the Bronx, including nearly all of the tidal marsh of the Bronx River.

While direct destruction of wetlands was occurring throughout the 19th and 20th centuries, changes upstream and in the watershed caused further loss of wetlands. In the late 1880s, most of the water in the headwaters of the river began to be diverted for New York City’s water supply as part of the New Croton Aqueduct. A dam was built to collect water in the Bronx River Reservoir and supply it to the Bronx River Pipeline. That reservoir is now known as the Kensico Reservoir. The completion of the Kensico Dam in 1915 held the upper reaches of the river in the reservoir near New Castle and may have reduced the river’s flow by one quarter. This loss of flow probably had the greatest impact on wetlands immediately downstream of the reservoir, but also contributed to the hydrologic disturbance further downstream. In the upper watershed in Westchester as well as in the Bronx, conversion of woods, meadows and wetlands to buildings and roads further disrupted the hydrologic regime by reducing infiltration to the ground water. A lower groundwater table can create drier conditions less favorable to native wetland plants. More directly, bridges and berms built on streams and over wetlands constricted and confined water flow, creating longer periods of higher water levels and greater sediment deposition that decreased biological diversity.

These changes are depicted in the maps below.

Map 2: Former Wetlands of the Bronx

The maps lay hollow polygons of historic wetlands over 2004 aerial photographs. This illustrates how most of the historic wetlands have been developed, and how contemporary wetlands are much reduced.

Click on the map to download it in PDF format

Top Right: Housing, the Bronx River Parkway and the Bronx Zoo are now located on the largest historic freshwater wetland

Bottom Right: The estuary saltwater marsh at the River’s mouth was once more than 1 mile wide. Today it is filled and developed. On the east bank is housing and Soundview Park. On the west bank are Hunt’s Point Market, shipping facilities, other industry, and housing.

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