Agricultural land use is typically associated with high stream nutrient concentrations and increased nutrient loading to lakes. For lakes, evidence for these associations mostly comes from studies on individual lakes or watersheds that relate concentrations of nitrogen (N) or phosphorus (P) to aggregate measures of agricultural land use, such as the proportion of land used for agriculture in a lake’s watershed. However, at macroscales (i.e., in hundreds to thousands of lakes across large spatial extents), there is high variability around such relationships and it is unclear whether considering more granular (or detailed) agricultural data, such as fertilizer application, planting of specific crops, or the extent of near‐stream cropping, would improve prediction and inform understanding of lake nutrient drivers. Furthermore, it is unclear whether lake N and P would have different relationships to such measures and whether these relationships would vary by region, since regional variation has been observed in prior studies using aggregate measures of agriculture. To address these knowledge gaps, we examined relationships between granular measures of agricultural activity and lake total phosphorus (TP) and total nitrogen (TN) concentrations in 928 lakes and their watersheds in the Northeastern and Midwest U.S. using a Bayesian hierarchical modeling approach. We found that both lake TN and TP concentrations were related to these measures of agriculture, especially near‐stream agriculture. The relationships between measures of agriculture and lake TN concentrations were more regionally variable than those for TP. Conversely, TP concentrations were more strongly related to lake‐specific measures like depth and watershed hydrology relative to TN. Our finding that lake TN and TP concentrations have different relationships with granular measures of agricultural activity has implications for the design of effective and efficient policy approaches to maintain and improve water quality.

中文翻译：

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农业土地利用的粒度措施在宏观上对湖泊氮和磷的影响不同。

农业土地利用通常与高浓度的溪流养分和增加的湖泊养分含量有关。对于湖泊，这些关联的证据主要来自对单个湖泊或流域的研究，这些研究将氮（N）或磷（P）的浓度与农业土地利用的总体度量联系起来，例如湖泊流域中用于农业的土地比例。但是，在宏观尺度上（即，在很大空间范围内成百上千个湖泊中），这种关系存在很大的可变性，目前尚不清楚是否考虑更细化（或更详细）的农业数据，例如肥料施用，特定作物的种植或近流作物种植的程度，将改善预报并有助于了解湖泊养分驱动因素。此外，目前尚不清楚氮和磷的湖与这些措施之间是否具有不同的关系，以及这些关系是否会因地区而异，因为先前的研究已经使用农业综合措施观察到了地区差异。为了解决这些知识差距，我们使用贝叶斯分层建模方法研究了美国东北部和中西部地区928个湖泊及其流域中农业活动的粒度度量与湖泊总磷（TP）和总氮（TN）浓度之间的关系。我们发现，湖泊的总氮和总磷浓度都与这些农业措施有关，特别是近流农业。农业措施与湖泊总氮含量之间的关系在区域上的差异大于总磷。反过来，TP浓度与特定于湖泊的措施（如相对于TN的深度和流域水文学）之间的相关性更强。我们的发现，湖泊中总氮和总磷浓度与农业活动的粒度度量有不同的关系，这对设计有效和高效的政策方法以维持和改善水质具有重要意义。