Disappearing headwaters: patterns of stream burial due to urbanization

Abstract

Headwater streams provide important ecosystem services, including clean drinking water, habitat for aquatic life, and rapid processing and uptake of nutrients, which can reduce delivery of nitrogen and phosphorus to downstream coastal waters. Despite their importance to ecosystem functioning, very little research has addressed the extent to which headwater streams are buried beneath the land surface during urbanization. We measured the occurrence of stream burial within a major tributary to the Chesapeake Bay, for streams with catchment areas ranging from 10 ha to 104 ha. We used hydrologic modeling to identify where streams should be and then calibrated a map of impervious surface area, using high-resolution aerial photography to build a stream channel decision-tree classification. We found that 20% of all streams were buried, with streams in low-residential and suburban areas outside Baltimore City exhibiting 19% burial rates. Smaller headwater streams were more extensively buried than larger streams, and this difference increased with increasing impervious surface area. Within Baltimore City, 66% of all streams and 70% of streams in catchments smaller than 260 ha (1 mi2) were buried. In this densely urbanized city, headwater streams are buried to the same extent as is dry land.