Porewater chemistry measurements from the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx)

The Georgia Coastal Ecosystems LTER Seawater Addition Long-Term Experiment (SALTEx) is a large-scale field experiment designed to simulate saltwater intrusion in a tidal freshwater wetland to predict how chronic (Press) and acute (Pulse) salinization will affect this and other tidal freshwater ecosystems. The SALTEx experiment was initiated in 2012 and consists of 31 field plots, each 2.5 m on a side. There are three treatments (Press, Pulse, and Fresh) and two types of controls (with and without sides), each consisting of six replicates. The Press treatment plots receive regular (4 times each week) additions of a mixture of seawater and fresh river water. Pulse plots receive the same mixture of seawater and river water during September and October, which is historically a time of low flow in the river when natural saltwater intrusion occurs. The Fresh treatment plots receive regular additions of fresh river water. Treatment water is added during low tide to facilitate its infiltration into the soil, and all plots are inundated by astronomical tides at high tide. Response measurements include porewater chemistry, specifically concentrations of chloride, sulfate, sulfide, dissolved organic carbon (DOC), ammonium-N, nitrate/nitrite-N, dissolved reactive phosphorus, total phosphorus, total nitrogen, organic nitrogen, carbon:nitrogen (C:N) ratio, organic-carbon:organic-nitrogen ratio, and pH. Samples of source water were taken after collection (seawater, river water) or mixing (mixed seawater and river water in tanks) and analyzed for concentrations of dissolved reactive phosphorus, total phosphorus, ammonium-N, nitrate/nitrite-N, total nitrogen, organic nitrogen. Source water samples from 2016 and beyond also included measurements of dissolved organic carbon (DOC), carbon:nitrogen ratio, organic-carbon:organic-nitrogen ratio, chloride and sulfate.佐治亚海岸生态系统长期生态研究（Long Term Ecological Research, LTER）海水添加长期实验（SALTEx）是一项大型野外实验，旨在模拟潮汐淡水湿地中的海水入侵过程，以预测慢性（Press）与急性（Pulse）盐化作用对该湿地及其他潮汐淡水生态系统的影响。 SALTEx实验于2012年启动，共设置31个野外样地，每个样地边长为2.5米。实验包含3种处理组（Press、Pulse及Fresh）与2种对照组（带围边、无围边），每组均设6个重复样地。 Press处理组样地每周定期（每周4次）添加海水与淡水河水的混合溶液；Pulse处理组样地仅在每年9月至10月期间添加上述混合溶液，该时段为河流历史枯水期，自然海水入侵多发；Fresh处理组样地则定期添加纯淡水河水。 所有处理液均在低潮时添加，以促进其向土壤中渗透；所有样地在高潮时均会受到天文潮汐的淹没。 本实验的响应指标涵盖孔隙水化学特征，具体包括氯离子、硫酸盐、硫化物、溶解性有机碳（dissolved organic carbon, DOC）、铵态氮（ammonium-N）、硝态氮/亚硝态氮（nitrate/nitrite-N）、溶解性反应磷、总磷、总氮、有机氮、碳氮比（carbon:nitrogen ratio, C:N）、有机碳-有机氮比以及pH值。 分别在采集后（海水、河水样本）或混合后（水箱内配制的海水河水混合液）采集水源水样本，并检测其溶解性反应磷、总磷、铵态氮、硝态氮/亚硝态氮、总氮及有机氮的浓度。 2016年及之后采集的水源水样本，新增了溶解性有机碳、碳氮比、有机碳-有机氮比、氯离子及硫酸盐的检测项目。