Читать книгу Coastal Ecosystems in Transition - Группа авторов - Страница 16

Chesapeake Bay is a large estuary in the mid‐Atlantic region of the United States with a watershed of 166,530 km² that hosts about 18 million people. Among its many tributaries, the Susquehanna River accounts for ~50% of total riverine inputs of freshwater into CB and its tributaries and discharges directly into the head of the bay’s mainstem (Figure 1.1).

The watershed of the Susquehanna is dominated by forested areas (~65%). Agricultural and developed lands account for ~35% of the watershed but much higher proportions of nutrient inputs to CB. Major physiographical provinces in the CB watershed include Piedmont, Blue Ridge, Valley and Ridge, and Appalachian Plateau. Topographic conditions and soil permeability are variable within and among these regions. In general, steep slopes in the uplands of the Valley and Ridge contrast with gentle slopes of the Appalachian Plateau and Piedmont and flat terrain of the Coastal Plain. The ratio of watershed area to the volume of CB, an indicator of the extent to which land‐use practices in the watershed can impact water quality in the bay, is 1400 km⁻¹.

The NAS is a semi‐enclosed arm of the northeast Mediterranean Sea with sandy coasts and alluvial plains to the north and west and rugged mountains to the east. The watershed spans 110,600 km² and hosts about 20 million people. The Po River, the largest river discharging into the NAS, has a watershed that comprises 67% of the total NAS watershed and hosts large urban and industrial settlements, as well as extended areas of intensive cropping and livestock activities. Its watershed is bounded by two mountain ranges, the Apennines and Alps. In contrast to the CB, ~62% is in agriculture and developed land with only 34% forested (Malagó et al., 2019). However, with a watershed‐area/seawater volume ratio of only 174 km⁻¹ (compared to 1400 km⁻¹ for CB), the potential impact of land‐use practices on the NAS as a whole is much smaller than that for CB.