As water-quality challenges intensify, the widely used Weighted Regressions on Time, Discharge, and Season (WRTDS) method offers an adaptable and practical framework for global water-quality science and management.

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Efforts to constrain the negative environmental impacts of excess nitrogen (N) and phosphorus (P) are costly and challenging, due in part to inconsistent reporting of nutrient sources at temporal and spatial scales relevant for local decision making.

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Vegetated buffer strips (VBS) are widely used to mitigate agricultural non-point source pollution yet reported retention efficiencies vary considerably across different landscapes. We synthesized 409 observations extracted from 91 peer-reviewed publications to evaluate critical determinants of VBS retention efficiency for agricultural runoff, focusing specifically on total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS).

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River water quality degradation is a prevailing problem in coastal China with intensifying human-nature interaction. However, the spatial and temporal dynamics of water quality and their drivers remain poorly understood.

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Low dissolved oxygen (DO) conditions pose a persistent threat to aquatic life in coastal ecosystems. In Chesapeake Bay, DO criteria are used to evaluate restoration progress, but traditional assessment methods—such as binary pass/fail outcomes and attainment deficit metrics—can obscure important spatial and temporal variability across tidal segments.

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Many waterbodies undergo nutrient decline, called oligotrophication, globally, but a comprehensive dataset to understand ecosystem responses is lacking. The OLIGOTREND database comprises multi-decadal chlorophyll a and nutrient time series from rivers, lakes, and estuaries with 4.3 million observations from 1894 unique measurement locations. The database provides empirical evidence for oligotrophication responses with a spatial and temporal coverage that exceeds previous efforts.

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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.

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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.

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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.

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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.

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