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

岩溶含水层是人类使用的地下水的来源，是水循环的一个组成部分，可能含有各种微生物，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，将解决水文地质学和地球化学，有机物的分布和地下水群落的营养结构之间的联系。将讨论的具体问题包括水文学和地球化学如何影响化能自养和光合有机物质的时空分布以及地下水物种的利用，地下水生境中的生物多样性是否得到资源分配的支持，以及地下生境中营养结构被截断的普遍范例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部分和盐水部分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分析。初步结果表明，植物利用阳光和微生物产生的有机物质都来自无机基质的氧化还原反应，（化能无机自养生物）被无脊椎动物利用，这两种类型的有机物在含水层中分布不均，由水流控制（光合物质在补给特征附近普遍存在）和地球化学（在淡水和盐水混合的地方发生化能自养生产）。这一项目将具有重大的社会意义，因为它直接关系到水质和维持为人类使用而进行密集管理的生态系统的生物多样性。该项目还将为学生提供实地和实验室的机会，包括西班牙裔和妇女就业或注册为研究生在PI实验室。

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.