AIMS Paint Rock nutrient data (AIMS_SE_PRF_NUTR)

This study was conducted in the Paint Rock research watershed (outlet location: 34.96861724, -86.16501705) on privately owned property in Jackson County (AL, USA) as part of the Aquatic Intermittency effects on Microbiomes in Streams (AIMS) project, an NSF EPSCoR funded project (OIA 2019603). The project sought to explore the impacts of stream drying on downstream water quality across Kansas, Oklahoma, Alabama, and Idaho, integrating datasets on hydrology, microbiomes, macroinvertebrates, and biogeochemistry. The watershed drains a non-perennial unnamed tributary to Burks Creek and contains 2.97 km2 of deciduous forest in the Cumberland Plateau physiographic section. Located near Estillfork, AL, the watershed spans an elevation range from 211 to 550 m above sea level and is a tributary to the Paint Rock River (within the larger Tennessee basin). The region has a humid subtropical climate, with mean daily January and July air temperatures of 4.4°C and 25.4°C respectively, and mean annual precipitation of 1,390 mm/yr.
We collected samples every ~3 weeks from October 13, 2021, to October 1, 2024, at the outlet of our watershed (PRM01, approach 1) and seasonally at seven distributed sites (approach 2). We collected triplicate water samples for soluble reactive phosphorus (SRP; µg/L) and ammonia (NH4-N, µg/L) on each sampling occasion with a subset of samples also analyzed for nitrate/nitrite (NO3-N, NO2-N, µg/L). We collected samples at the specified location when water was present using a syringe in a well-mixed area of the stream . We then filtered water through sterile PVDF 0.45 µm syringe filters (VWR) into clean bottles following the AIMS Surface Water Chemistry SOP (Burgin 2024). For all analytes, we froze samples until analysis in the lab using colorimetric methods (APHA 2017) on an AQ300 Discrete Analyzer (SEAL Analytical, Mequon, Wisconsin, USA). We prepared and applied reagents to samples and standards of known concentrations. For SRP, reagents react to form a blue complex, the absorbance of which is measured at 880nm. Known standards were used to create calibration curves ranging from 0 μg/L to 75 μg/L with check standards run every 10. Detection limits were set at 6 μg/L. We used the phenol method for NH4-N with known standards used to create calibration curves ranging from 0 μg/L to 500 μg/L and check standards run every 10 samples. Detection limits were set at 11 μg/L. To determine NOx-N, we analyzed samples with and without cadmium reduction with known standards used to create calibration curves ranging from 0 µg/L to 1000 µg/L for NOx-N and 0 µg/L to 750 µg/L for NO2-N with detection limits set at 20 µg/L NO3-N. Differences between NOx-N and NO2-N were used to calculate NO3-N. Triplicates were inspected for outliers with mean and standard deviation reported in data.

本研究于美国阿拉巴马州杰克逊县的私有土地上的佩恩特罗克研究流域（出水口坐标：34.96861724，-86.16501705）开展，隶属于“溪流干湿交替对微生物组的影响（Aquatic Intermittency effects on Microbiomes in Streams, AIMS）”项目，该项目由美国国家科学基金会EPSCoR计划资助（项目编号：OIA 2019603）。本项目旨在探究溪流干涸对堪萨斯州、俄克拉荷马州、阿拉巴马州及爱达荷州下游水质的影响，整合了水文、微生物组、大型无脊椎动物及生物地球化学相关数据集。该流域为伯克斯溪（Burks Creek）的非常年性无名支流，流域面积达2.97平方千米，地处坎伯兰高原地貌区，覆盖落叶阔叶林。该流域位于阿拉巴马州埃斯蒂尔福克附近，海拔范围为211米至550米，属于田纳西河大流域内的佩恩特罗克河支流。该区域属亚热带湿润气候，1月和7月的日均气温分别为4.4℃与25.4℃，年平均降水量为1390毫米/年。

2021年10月13日至2024年10月1日期间，我们约每3周在流域出水口（PRM01，采用采样方案1）开展采样，并在7个分散布设的点位（采用采样方案2）开展季节性采样。每次采样均采集三份平行水样，用于测定可溶性活性磷（soluble reactive phosphorus, SRP；单位：µg/L）与氨氮（ammonia, NH4-N；单位：µg/L）；部分子集水样还额外测定了硝态氮/亚硝态氮（nitrate/nitrite, NO3-N、NO2-N；单位：µg/L）。当点位存在地表水时，我们在溪流充分混合区域使用注射器采集水样。随后依照AIMS地表水化学标准操作流程（Burgin 2024），将水样通过无菌聚偏氟乙烯（PVDF）0.45 µm针式滤器（VWR品牌）过滤至洁净瓶中。所有待测样品均冷冻保存，直至实验室采用比色法（APHA 2017）借助AQ300离散分析仪（SEAL Analytical公司，美国威斯康星州梅昆市）完成分析。我们针对样品与已知浓度的标准品配制并添加试剂。

对于SRP，试剂与待测物反应生成蓝色络合物，于880nm波长处测定其吸光度。以0 µg/L至75 µg/L的浓度梯度建立校准曲线，每10个样品插入一个质控标准样，检出限设定为6 µg/L。氨氮（NH4-N）采用苯酚法测定，以0 µg/L至500 µg/L的浓度梯度建立校准曲线，每10个样品插入一个质控标准样，检出限设定为11 µg/L。对于氮氧化物（NOx-N），我们分别对经过镉还原和未经过镉还原的样品进行分析；以0 µg/L至1000 µg/L的浓度梯度建立NOx-N校准曲线，以0 µg/L至750 µg/L的浓度梯度建立NO2-N校准曲线，检出限设定为20 µg/L（以NO3-N计）。通过NOx-N与NO2-N的差值计算得到NO3-N。对平行样进行异常值检验，最终以平均值与标准差的形式呈现数据。