Lake Atitlan water quality 2010-2024

Field data were collected monthly from a pelagic point identified as Weiss G (14°42’23.182” N 91°11’13.901” W), close to the lake center and with a depth of 325 m. From 2009 to early 2017, temperature (ºC) and dissolved oxygen (mg L-1) were measured monthly using a YSI 51B and YSI 85 probe that measures to 60 m depth. Additional depths were sampled by raising water to the surface with a 2.2 L opaque Van Dorn bottle and immediately reading the temperature and dissolved oxygen. From early 2017 continuous measurements were made using a RBR maestro probe that reached the lake bottom. We collected all samples for laboratory analyses with a 2.2 L opaque van Dorn bottle at 0, 5, 10, 15, 20, 30, 40, 60, 80, 100, 150, 200, 225, 250, 275, and 305 m depths, except for 2010 to 2013, when sampling was usually limited to 100 m maximum depth. For chemical analyses, we transferred samples to acid-washed 250 ml glass BOD bottles and kept them on ice in darkness until processed in the laboratory within the next 9 hours. We manually filtered samples within 9 h of collection using 25 mm diameter 0.7 µm glass fiber filters (Whatman GF/F) and then refrigerated the filtered samples at 4 ºC until analysis within 48 h of filtration. Nutrient concentrations were determined using the methods: - Ammonia (NH4+–N µg L-1) concentrations with the phenate method (detection limit (DL) = 3 µg L-1) (APHA, 2005) - Nitrate plus nitrite (NO3-–N + NO2-–N µg L-1) concentrations with the hydrazine reduction method (DL = 2 µg L-1) (Kamphake et al., 1967) - Soluble reactive phosphate (SRP) (PO4-3–P µg L-1) concentrations with the ascorbic acid reduction method (DL = 1 µg L-1) (Murphy and Riley, 1962) - Total phosphorus (TP µg L-1) with the SRP method after digestion with the method 4500-P J (APHA 2005). When concentrations were below DL, we used one-half of the DL value for statistical analysis. All recipients, as well as all glassware used, were washed with a 0.1N HCl solution, and rinsed three times with demineralized water. Acid washing followed by a triple rinse was repeated before each sample collection. Basic scripts for data analysis are included.本数据集的野外监测数据按月采自标记为Weiss G的开阔水域测点，其坐标为北纬14°42′23.182″、西经91°11′13.901″，临近湖心，水深达325米。2009年至2017年初，研究团队每月采用可测深60米的YSI 51B与YSI 85型探头，按月测定水温（单位：℃）与溶解氧浓度（单位：mg·L⁻¹）；对于更深水深的分层参数，则通过2.2 L不透明Van Dorn采水器（Van Dorn bottle）将水样提升至水面后，立即现场测量水温与溶解氧。2017年初起，改用可覆盖湖底的RBR maestro型探头开展连续监测。 研究团队在0、5、10、15、20、30、40、60、80、100、150、200、225、250、275及305米水深处，均使用2.2 L不透明Van Dorn采水器采集实验室分析所需水样，但2010至2013年的采样最大水深通常仅限100米。进行化学分析前，将水样转移至经酸清洗的250 mL玻璃生化需氧量瓶（BOD bottle）中，置于黑暗冰浴环境，并于采样后9小时内送至实验室处理。采样后9小时内，采用直径25 mm、孔径0.7 μm的玻璃纤维滤膜（Whatman GF/F）对水样进行手动过滤，随后将过滤后的样品置于4℃环境冷藏，确保在过滤后48小时内完成分析。营养盐浓度的测定方法如下： - 氨氮（NH₄⁺–N，单位：μg·L⁻¹）：采用酚盐法，检测限（DL）为3 μg·L⁻¹（APHA, 2005） - 硝酸盐与亚硝酸盐总和（NO₃⁻–N + NO₂⁻–N，单位：μg·L⁻¹）：采用肼还原法，检测限为2 μg·L⁻¹（Kamphake et al., 1967） - 可溶性活性磷酸盐（SRP，PO₄³⁻–P，单位：μg·L⁻¹）：采用抗坏血酸还原法，检测限为1 μg·L⁻¹（Murphy and Riley, 1962） - 总磷（TP，单位：μg·L⁻¹）：采用APHA 2005标准中的4500-P J法进行消解后，依照可溶性活性磷酸盐的测定方法完成检测。 当样品浓度低于检测限时，统计分析中以检测限的一半数值作为替代值。 所有采样容器及所用玻璃器皿均采用0.1N盐酸溶液清洗，随后用去离子水冲洗三次。每次采样前，均需重复上述酸洗与三次冲洗流程。 此外，本数据集附带数据分析基础脚本。