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 This archive also stores updated and unpublished estimates in the data folder 'B. Unpublished Data, Codes, and Output' that were obtained in 2014 using longer records (~ two additional years of data) and updated codes (i.e., EGRET version 2.2.0).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.

本研究摘要显示：数十年来，削减氮（N）、磷（P）与悬浮物（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）的管理措施成效，我们针对近2至30年间萨斯奎哈纳河下游水库系统（Lower Susquehanna River Reservoir System）上下游的流量归一化（flow-normalized）氮、磷、悬浮物负荷的长期季节变化趋势展开分析。

研究结果显示，营养盐与悬浮物负荷的年际及年代际变化趋势在四季中整体呈现一致规律，表明流域功能与土地利用的变化对全年各时段的营养盐及悬浮物负荷均具有相似影响。在水库系统上游，玛丽埃塔站（Marietta Station）与康内斯托加号站（Conestoga Station）的合并负荷数据显示，萨斯奎哈纳河流域的氮、磷及悬浮物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的一系列管理措施。

与之形成对比的是，自1990年代中期以来，科诺温戈水库（Conowingo Reservoir）下游区域普遍观测到悬浮物、颗粒态磷与颗粒态氮负荷呈上升趋势。我们的分析表明：其一，近2至30年来水库对这些物质的截留能力持续下降，1990年代中期以来悬浮物与磷的截留能力衰减尤为显著；其二，科诺温戈水库已接近其泥沙库容上限。

水库运行效能的这些变化将为萨斯奎哈纳河流域的日最大负荷总量（total maximum daily load, TMDL）目标达成带来全新的严峻挑战，若叠加气候变化导致的暴雨频次与强度增加，挑战将更为严峻。因此，在合理制定管控负荷要求及编制流域实施计划时，需将水库相关问题纳入考量范畴。

备注：本数据集归档对应Zhang等人2013年的研究[10.1016/j.scitotenv.2013.02.012]，其中存储的数据基于WRTDS算法4c版本生成。本归档还在‘B. 未发表数据、代码与成果’数据文件夹中存储了2014年更新的未发表估算结果，该结果基于更长的时序数据（较原研究增加约两年数据）与更新后的代码（即EGRET版本2.2.0）生成，二者最主要的差异在于边缘效应（edge effects）处理方式。