What drivers control the geomorphic features and spatial arrangement and connectivity of habitat patches in the coastal zone?
Within the watersheds, there are human activities as well as internal ecosystem dynamics that drive the shape of the land- and waterscapes. Population growth in the watersheds has led to conversion of forests or agricultural lands to more suburban landscapes, accompanied by increased paving, infrastructure, and lawns.
Humans have built numerous water control structures such as dams and culverts on the streams and rivers of PIE. These structures in turn necessitated the management of anadromous fish such as river herring, and therefore construction of more structures in the form of fish ladders. Another wildlife management effort, the banning of beaver trapping, has led to a dramatic increase in the number of beaver dams constructed in the watersheds, whose impacts rivals that of the man-made dams. These structures impede, direct, and/or channelize stream flow, with obvious changes to hydrology.Because the conversion of forested landscapes to suburban ones increases the amount of paved and other impervious surfaces covering the land, it also increases runoff of water and everything it may carry, including fertilizer used to establish and maintain lawns. Water withdrawals from the watershed for municipal water supplies lower water levels, even to dryness, and in some cases transports water out of the watershed. These impacts have clear consequences for fish and other wildlife, as well as for less visible biogeochemical processes.
The cumulative effects of processes occurring in the watershed are delivered to the estuary as the mainstem rivers flow over the most downstream dams. The magnitude of the freshwater inputs varies seasonally, and is disrupted by extreme events such as floods or draughts. The tidal marshes and creeks may build or erode in response to the interplay of physical forcing with nutrient, organic matter, and sediment supply delivered from both the fresh and marine ends of the system. Human manipulation of the marshes for agriculture (salt marsh hay) or mosquito control (linear ditches) may alter ecosystem responses. We need to understand these “shaping” processes, because changes that result from their interactions , such as changes in configuration of habitats and the connections between them, affect the way the entire ecosystem functions.