Background/Question/Methods The Chesapeake Bay, in mid Atlantic USA, like many coastal regions of the world, has become highly eutrophic and in some areas anoxic over the last century.  This ecological degradation has led to a collapse of the fish and shellfish economy.  The Bay drains a large watershed which historically has been largely agricultural.  Additionally, heads of tributaries have served as ports for transport of materials.  Most recently, urban and suburban development has led to increased impervious surfaces and changes in flow patterns of water and materials. The question is the extent to which these different activities contributed to the downfall of a diverse ecosystem and rich economy.
Results/Conclusions Using sediment cores collected throughout the estuary, the history of land use and fluxes of materials that flowed into the estuary have been reconstructed for a few hundred to several thousand years.  Prior to European colonization, the landscape was almost entirely forested, consisting of a mosaic of different forest species on different geologic/soils substrates.  Following colonization, 300 years ago, the mosaic changed from one of different forest types to forested and non-forested patches.  As most of the land was converted to agriculture, the landscape pattern became obscured.  The ratio of arboreal to non-arboreal (excluding ragweed) to ragweed pollen in sediment cores records changes in the percentage of land in forest and in agriculture.  In the 1600s and into the early 1700s less than 20% of the land was farmed.  During this time, sediment and nutrient influxes into the estuary were slightly higher than in pre-colonial time, but still remained low.  During the late 1700s and into the 1800s, about 40 to 50% of the land was in agriculture.  Coincident with these changes on the land, sedimentation increased from two to tenfold, as did influxes of nutrients from fertilizers as well as metals.  In the late 1800s and into the early 1900s, 80% of the land was agricultural.  Sediment and nutrient influxes increased accordingly.  Eutrophication and anoxia of the Chesapeake Bay began at approximately the time 40% of the land was under cultivation and when small farms separated by forest patches were being replaced by large commercial operations. Imported guano, phosphates and other sources of nutrients were used to increase crop production.  Later, with the introduction of synthetic nitrogen, the estuarine ecosystem  changed from a benthic system to a pelagic-microbial system and the fish and shellfish economy was greatly diminished.