Saltwater intrusion has particularly large impacts on karstic wetlands of the Caribbean Basin due to their porous, carbonate bedrock and low elevation. Increases in salinity and phosphorus (P) accompanying saltwater intrusion into these freshwater, P-limited wetlands are expected to alter biogeochemical cycles along with the structure and function of plant and algal communities. Calcareous periphyton is a characteristic feature of karstic wetlands and plays a central role in trophic dynamics, carbon storage, and nutrient cycling. Periphyton is extremely sensitive to water quality and quantity, but the effects of saltwater intrusion on these microbial mats remain to be understood. We conducted an ex situ mesocosm experiment to test the independent and combined effects of elevated salinity and P on the productivity, nutrient content, and diatom composition of calcareous periphyton from the Florida Everglades. We measured periphyton total carbon, nitrogen, and P concentrations and used settlement plates to measure periphyton accumulation rates and diatom species composition. The light and dark bottle method was used to measure periphyton productivity and respiration. We found that exposure to ~1 g P·m-2 ·yr-1 significantly increased periphyton mat total P concentrations, but had no effect on any other response variable. Mats exposed to elevated salinity (~22 kg salt·m-2 ·yr-1 ) had significantly lower total carbon and tended to have lower biomass and reduced productivity and respiration rates; however, mats exposed to salinity and P simultaneously had greater gross and net productivity. We found strong diatom species dissimilarity between fresh- and saltwater-treated periphyton, while P additions only elicited compositional changes in periphyton also treated with saltwater. This study contributes to our understanding of how the ecologically important calcareous periphyton mats unique to karstic, freshwater wetlands respond to increased salinity and P caused saltwater intrusion and provides a guide to diatom indicator taxa for these two important environmental drivers.

中文翻译：

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附生植物可作为咸水入侵淡水湿地的指标：来自实验操作的见解。

盐水入侵由于其多孔的碳酸盐岩基层和低海拔，对加勒比海盆地的岩溶湿地影响特别大。咸水入侵磷限制的这些淡水后，盐分和磷（P）的增加有望改变生物地球化学循环以及植物和藻类群落的结构和功能。钙质附生植物是岩溶湿地的一个特征，在营养动力学，碳储量和养分循环中起着核心作用。附生植物对水质和水量极为敏感，但盐水入侵对这些微生物垫的影响仍有待了解。我们进行了异地介观试验，以测试盐度和P升高对生产力，养分含量，佛罗里达大沼泽地钙质附生植物的硅藻和硅藻组成。我们测量了浮游植物的总碳，氮和磷浓度，并使用沉降板测量了浮游植物的积累速率和硅藻物种组成。浅色和深色瓶法用于测量植物浮游生物的生产力和呼吸作用。我们发现暴露于〜1 g P·m-2·yr-1显着增加了附生植物垫中的总P浓度，但对其他任何响应变量均无影响。盐分升高（约22 kg盐·m-2·yr-1）的垫子的总碳含量显着降低，生物量往往降低，生产力和呼吸速率降低。但是，同时暴露于盐分和磷的垫子具有更高的总生产率和净生产率。我们发现淡水和咸水处理的藻类之间的硅藻物种差异很大，而磷的添加仅引起咸水处理过的藻类中成分的变化。这项研究有助于我们理解岩溶，淡水湿地特有的对生态重要的钙质附生植物垫如何应对盐分增加和磷引起的咸水入侵，并为这两个重要的环境驱动因素提供了硅藻指示物分类的指南。