Data associated with Long-term seasonal trends of nitrogen, phosphorus, and suspended sediment load from the non-tidal Susquehanna River Basin to Chesapeake Bay

From the study abstract: Reduction of nitrogen (N), phosphorus (P), and suspended sediment (SS) load has been a principal focus of Chesapeake Bay Watershed management for decades. To evaluate the progress of management actions in the Bay's largest tributary, the Susquehanna River, we analyzed the long-term seasonal trends of flow-normalized N, P, and SS load over the last two to three decades, both above and below the Lower Susquehanna River Reservoir System. Our results indicate that annual and decadal-scale trends of nutrient and sediment load generally followed similar patterns in all four seasons, implying that changes in watershed function and land use had similar impacts on nutrient and sediment load at all times of the year. Above the reservoir system, the combined loads from the Marietta and Conestoga Stations indicate general trends of N, P, and SS reduction in the Susquehanna River Basin, which can most likely be attributed to a suite of management actions on point, agricultural, and stormwater sources. In contrast, upward trends of SS and particulate-associated P and N were generally observed below the Conowingo Reservoir since the mid-1990s. Our analyses suggest that (1) the reservoirs' capacity to trap these materials has been diminishing over the past two to three decades, and especially so for SS and P since the mid-1990s, and that (2) the Conowingo Reservoir has already neared its sediment storage capacity. These changes in reservoir performance will pose significant new kinds of challenges to attainment of total maximum daily load goals for the Susquehanna River Basin, and particularly if also accompanied by increases in storm frequency and intensity due to climate change. Accordingly, the reservoir issue may need to be factored into the proper establishment of regulatory load requirements and the development of watershed implementation plans. Note: This data archive for Zhang et al. (2013) [10.1016/j.scitotenv.2013.02.012] stores data that were obtained based on the WRTDS algorithms, version 4c. This archive also stores updated and unpublished estimates in the data folder 'B. Unpublished Data, Codes, and Output' that were obtained in 2014 using longer records (~ two additional years of data) and updated codes (i.e., EGRET version 2.2.0). The most important differences relate to the handling of edge effects.

本研究摘要表明：数十年来，削减氮（N）、磷（P）与悬浮泥沙（SS）负荷始终是切萨皮克湾流域（Chesapeake Bay Watershed）管理的核心要务。为评估该海湾最大支流萨斯奎哈纳河（Susquehanna River）的管理行动进展，我们分析了过去2至30年间，下萨斯奎哈纳河水库系统上下游的流量归一化氮、磷、悬浮泥沙负荷的长期季节变化趋势。

研究结果显示，营养盐与泥沙负荷的年际及年代际尺度变化趋势在四季中整体呈现相似模式，这意味着流域功能与土地利用的变化对全年各时段的营养盐及泥沙负荷均存在相似影响。在水库系统上游，玛丽埃塔站与康内斯托加站的合并负荷数据表明，萨斯奎哈纳河流域的氮、磷、悬浮泥沙负荷整体呈下降趋势，这大概率可归因于针对点源、农业面源及暴雨径流源头的一系列管理措施。

与之形成鲜明对比的是，自20世纪90年代中期以来，科诺温戈水库（Conowingo Reservoir）下游的悬浮泥沙及颗粒态磷、氮负荷普遍呈上升趋势。我们的分析得出两点结论：其一，水库对这些物质的截留能力在过去2至30年间持续下降，尤以1990年代中期以来的悬浮泥沙与磷负荷截留能力下降最为显著；其二，科诺温戈水库已接近其泥沙存储容量上限。

水库功能的这些变化将为萨斯奎哈纳河流域达成总最大日负荷（total maximum daily load, TMDL）目标带来全新的重大挑战，若叠加气候变化导致的暴雨频次与强度增加，这一挑战将更为严峻。因此，在制定合规性负荷要求与流域实施计划时，需将水库相关问题纳入考量范畴。

注：本数据存档对应Zhang等人（2013年）的研究[10.1016/j.scitotenv.2013.02.012]，其中存储的数据均基于WRTDS算法4c版本生成。本存档的“B. 未发布数据、代码与输出”数据文件夹中还包含2014年基于更长时间序列（约增加两年观测数据）与更新后的代码（即EGRET版本2.2.0）生成的更新版未发布估算结果。两者最主要的差异体现在边缘效应处理环节。