DISSERTATION RESEARCH: Hypoxia-induced trade-offs on zooplankton vertical distribution and community structure in freshwaters

这项研究项目的首要目标是确定湖泊和水库底层水中溶解氧(DO)浓度的变化如何影响浮游动物的行为、丰度和物种组成，以及这些变化可能如何对水质和食物网产生影响。浮游动物在淡水生态系统中扮演着关键角色；它们以浮游植物为食，浮游植物是食物网的基础，而浮游动物又被鱼吃掉。因此，浮游动物种群的变化有可能极大地改变水质和食物网。世界各地淡水生态系统中的浮游动物表现出双向垂直迁移，它们在白天迁移到湖泊或水库的底层水域，以躲避鱼类的视觉捕食和有害的紫外线(UV)辐射。在夜间，当捕食和暴露在紫外线下的风险较低时，许多浮游动物迁徙到水面以浮游植物为食。然而，人类活动正在导致全球水体底层水中DO浓度的下降。由于溶解氧减少，浮游动物白天可能停留在表层水域，不再垂直迁徙，导致丰度下降和物种组成发生变化。这项研究将与当地一家自来水公司合作进行，所有数据和结果将与管理者共享，以便为他们的水质决策提供信息。该项目将涉及在跨学科背景下培训至少两名淡水科学实验室和实地方法的本科生研究人员。此外，这项研究的结果将为在自然中心为学童创建互动和动手教育活动提供基础。该项目将整合独特的底层水(亚磁)DO浓度的全生态系统操作，对亚磁DO梯度上的水库进行跨生态系统调查，使用高频声纳观察浮游动物的垂直分布，并对浮游动物功能特征进行实验分析，以研究DO浓度的变化如何改变浮游动物的种类组成、丰度和行为。每两周一次的夏季野外调查将在五个水库进行，这些水库显示出一系列亚极磁DO浓度。其中一个水库有一个亚磁充氧系统，该系统将在实验中打开和关闭(从而控制整个生态系统规模的DO浓度)，以直接评估DO对浮游动物种群的影响。还将进行多次海底采样活动，利用声纳声学技术观察浮游动物在水柱中的垂直分布。综上所述，这些综合研究方法将从机械上确定DO浓度变化对浮游动物群落的影响，以及由此对湖泊和水库水质的影响。

The overarching goal of this research project is to determine how altered dissolved oxygen (DO) concentrations in the bottom waters of lakes and reservoirs affect zooplankton behavior, abundances, and species composition, and how these changes may have consequences for water quality and food webs. Zooplankton play a critical role in freshwater ecosystems; they feed on phytoplankton, the base of the food web, and are in turn consumed by fish. Consequently, changes in zooplankton populations have the potential to drastically alter water quality and food webs. Zooplankton in freshwater ecosystems around the world exhibit diel vertical migration, in which they migrate to the bottom waters of a lake or reservoir during the day to escape visual predation by fish and damaging ultraviolet (UV) radiation. At night, many zooplankton migrate to the water's surface to feed on phytoplankton when the risk of predation and UV exposure is lower. However, human activities are resulting in decreased DO concentrations in the bottom waters of waterbodies globally. As a result of decreased DO, zooplankton may remain in the surface waters during the day and no longer vertically migrate, resulting in decreased abundance and changes in the species composition. This research will be conducted in partnership with a local water utility, and all data and results will be shared with managers to inform their water quality decisions. The project will involve training of at least two undergraduate researchers in freshwater science laboratory and field methods in an interdisciplinary setting. In addition, results from this research will provide the basis for creating interactive and hands-on educational activities for school children at a nature center.This project will integrate a unique whole-ecosystem manipulation of bottom water (hypolimnetic) DO concentrations, a cross-ecosystem survey of reservoirs on a hypolimnetic DO gradient, high-frequency sonar to observe the diel vertical distribution of zooplankton, and experimental analyses of zooplankton functional traits to examine how changes in DO concentrations alter zooplankton species composition, abundance, and behavior. Biweekly summer field surveys will be conducted across five reservoirs that exhibit a range of hypolimnetic DO concentrations. One of the reservoirs has a hypolimnetic oxygenation system that will be experimentally turned on and off (thereby controlling DO concentrations at the whole-ecosystem scale) to directly assess the effects of DO on zooplankton populations. Multiple diel sampling campaigns will also be conducted that use sonar acoustic technology to observe the vertical distribution of zooplankton in the water column. Taken together, these integrated research approaches will mechanistically determine the effects of changing DO concentrations on zooplankton communities and resulting implications for water quality in lakes and reservoirs.