Nitrogen (N) legacy effects are widely recognized as a primary obstacle to the improvements of water quality following mitigation efforts. The exploration of long-term nutrient trajectories for nitrogen model (ELEMeNT-N) has been applied to estimate legacy effects in several watersheds globally. However, ELEMeNT-N does not account for the accumulation-release processes of nitrate within soil profile, introducing potential uncertainty in long-term simulations.

Nitrogen pollution in aquatic ecosystems, primarily from agricultural sources, presents significant environmental challenges. At the land management decision level, reducing nitrate leaching requires knowledge of nitrate loading over time and location, the complexity of which is amplified by limited data availability, especially in poorly gauged watersheds.

Reductions of nitrogen, phosphorus, and sediment loads have been the focus of watershed restoration in many regions for improving water quality, including the Chesapeake Bay. Watershed models and riverine monitoring data can provide important information on the progress of load reductions but do not always generate consistent interpretations.

Seasonal hypoxia (dissolved oxygen [DO] levels ≤ 2 mg/l) poses a severe threat to coastal ecosystems globally, including the largest estuary in the United States, the Chesapeake Bay. This V-shaped drowned river valley features shallow flanks, where the deepest waters experience persistently low DO levels typically initiated during the spring and ending in late summer or early autumn. Reports on low DO conditions in the Chesapeake Bay date back over a century.

Many coastal ecosystems have suffered from cultural eutrophication and dead zones. In the Chesapeake Bay, water quality degradation is manifested in low dissolved oxygen, poor water clarity, and decreased submerged aquatic vegetation acreage.

Many estuaries, including Chesapeake Bay, have suffered from undesirable conditions of algae blooms, poor water clarity, and low dissolved oxygen (DO). To better understand the status and trends of DO criteria attainment deficit (AD), we conducted a comprehensive assessment using monitoring data in the period of 1985–2022 and focused on the comparison of trends among 13 tidal systems.

Quantitative assessment of cropland phosphorus (P) loss via surface runoff is essential for developing effective pollution mitigation strategies. In this study, we compiled 812 datasets from 114 peer-reviewed papers for cropland P loss across China.

Oxygen depletion in coastal waters is increasing globally due primarily to eutrophication and warming. Hypoxia responses to nutrient loading and climate change have been extensively studied in large systems like the Chesapeake Bay and the Baltic Sea, while fewer studies have investigated smaller, shallower hypoxic zones.

Many agricultural watersheds rely on the voluntary use of management practices (MPs) to reduce nonpoint source nutrient and sediment loads; however, the water-quality effects of MPs are uncertain. We interpreted water-quality responses from as early as 1985 through 2020 in three agricultural Chesapeake Bay watersheds that were prioritized for MP implementation, namely, the Smith Creek (Virginia), Upper Chester River (Maryland), and Conewago Creek (Pennsylvania) watersheds.

Nutrient pollution from agriculture and urban areas plus acid mine drainage (AMD) from legacy coal mines are primary causes of water-quality impairment in the Susquehanna River, which is the predominant source of freshwater and nutrients entering the Chesapeake Bay.