Dissertation Research: Ecosystem scale abiotic and biotic drivers of food web structure in deep phreatic aquifers

喀斯特含水层是供人类使用的地下水来源，是水循环的一个组成部分，可能包含多种微生物、无脊椎动物和脊椎动物群落。许多岩溶含水层受到地下水开采和污染的威胁，但对其群落结构、生态系统功能或生物地球化学循环的了解相对较少。这项研究，在得克萨斯州中南部的爱德华兹含水层，将解决水文地质和地球化学之间的联系，有机物质的分布，和地下水群落的营养结构。具体问题将包括水文和地球化学如何影响化学自养和光合有机质的时空分布以及地下水物种的利用，地下水栖息地的生物多样性是否得到资源分配的支持，以及地下水栖息地截断营养结构的流行范式是否得到同位素数据的支持。这些问题将通过在含水层的淡水和咸水部分进行跨地球化学梯度取样来解决。方法将包括地下水的无机和有机地球化学特征，地球化学数据的地理空间分析，稳定同位素分析和无脊椎动物的形态计量学分析。初步结果表明，植物利用阳光和微生物从涉及无机底物的氧化还原反应中获得能量所产生的有机物都被无脊椎动物利用，并且这两种有机物在含水层内分布不均匀。受水的运动（光合作用物质在补给特征附近普遍存在）和地球化学（淡水和咸水混合的地方发生的化学岩石自养生产）的控制。该项目将具有重大的社会意义，因为它直接关系到水质和生态系统中生物多样性的维持，这些生态系统是为人类使用而集中管理的。该项目还将为学生提供实地和实验室的机会，包括在PIs实验室工作或注册为研究生的西班牙裔和女性。

Karst aquifers are sources of groundwater for human use, are an integral component of the water cycle, and may contain diverse microbial, invertebrate, and vertebrate communities. Many karst aquifers are threatened by groundwater extraction and contamination, but relatively little is known about their community structure, ecosystem function, or biogeochemical cycling. This research, on the Edwards Aquifer of south-central Texas, will address links between hydrogeology and geochemistry, the distribution of organic matter, and the trophic structure of groundwater communities. Specific issues that will be addressed will include the ways that hydrology and geochemistry affect the spatial and temporal distribution of chemolithoautotrophic and photosynthetic organic matter and utilization by groundwater species, whether biodiversity in groundwater habitats is supported by resource partitioning, and whether the prevailing paradigm of truncated trophic structure in subsurface habitats is supported by isotopic data. These issues will be addressed by sampling across geochemical gradients in the freshwater and saline portions of the aquifer. Methods will include inorganic and organic geochemical characterization of groundwater, geospatial analysis of geochemical data, stable isotope analyses, and morphometric analyses of invertebrates. Preliminary results show that organic matter produced both by plants, using sunlight, and by microbes that derive energy from redox reactions involving inorganic substrates (chemolithoautotrophs) is utilized by invertebrates, and both types of organic matter are distributed unevenly within the aquifer, being controlled by the movement of water (photosynthetic matter being prevalent near recharge features) and geochemistry (chemolithoautotrophic production occurring where fresh and saline groundwaters mix). This project will have substantial societal importance because it directly relates to water quality and the maintenance of biodiversity in ecosystems that are intensively managed for human use. The project also will provide field and laboratory opportunities for students, including Hispanics and women employed or enrolled as graduate students in the PIs laboratory.