Knowledge Resource Center for Ecological Environment in Arid Area
| 项目编号 | 1015593 |
| How will reduced nitrogen loading affect temperate lake ecosystems rich in phosphorus? | |
| Moody, Eric | |
| 主持机构 | SAES - IOWA STATE UNIVERSITY |
| 开始日期 | 2018 |
| 结束日期 | 2020 |
| 资助机构 | US-NIFA（美国食品与农业研究所） |
| 语种 | 英语 |
| 国家 | 美国 |
| 中文简介 | 1190 - Limnology |
| 英文简介 | Goals / Objectives MAJOR GOALSUnderstand how legacy phosphorus in soils impacts ecosystem responses to restoration activitiesObjectives:Examine temporal trends in concentrations of nitrogen (N) and phosphorus (P) in Iowa's recreationally important lakes between 2000 (when lake monitoring program began) and 2019 (the final year of this project).Test whether lake water N:P ratio declines in response to restoration activities relative to lakes where no restoration has occurred as predicted if legacy P contributes substantial P loading even while N loading is reduced.Understand how these impacts affect the development of harmful algal blooms of Cyanobacteria in Iowa lakesObjectives:Examine temporal trends in Cyanobacteria biomass and algal community composition at the genus level in Iowa's recreationally important lakes between 2000 and 2019.Test the impacts of increasing Cyanobacteria dominance and decreasing algal N:P ratio on the performance of a keystone zooplankton grazer, Daphnia, using a combination of gradients among lakes and manipulative experiments.Project Methods EffortsI will first employ long-term water quality monitoring data collected by the Iowa State Limnology Laboratory to investigate trends in water N:P in Iowa lakes since 2000 and their impacts on algal blooms and bloom composition. Using these data, I will investigate whether algal composition within each lake covaries over time with TN:TP. I will use repeated measures ANOVA to test for temporal trends in the percent cyanobacteria and correlate effect sizes from the model with the slope in TN:TP over time among lakes. A negative correlation would indicate that steep declines in TN:TP have larger effects on increasing cyanobacterial dominance as predicted from work among lakes. In addition to these long-term data analyses, the ISU Limnology Lab will begin directly measuring microcystin concentration following the enzyme-linked immunosorbent assay (ELISA) protocol in the 130 study lakes as part of its ongoing water quality monitoring. Upon collecting these data I will then determine the extent to which historical factors such as change in TN:TP over time andGoals /or current TN:TP and algal community composition explain variation in microcystin concentrations among lakes.To investigate the impacts of shifting N:P supply on Daphnia, I will use a combination of long-term data from 130 Iowa lakes and short-term experiments using Daphnia isolated from several of these lakes along a gradient in water column N:P. As Daphnia persist in lakes with TP greater than 150 μgGoals /L in Iowa despite model predictions to the contrary (Peace et al. 2013), I will begin by analyzing the long-term data to understand what allows Daphnia persistence in P-rich lakes. In particular, I will investigate whether shifts in the N:P ratio and algal community composition control Daphnia biomass in Iowa lakes. Daphnia may maintain performance in high TP lakes if the N:P ratio remains high as well such that P is not in excess, thus I predict interacting effects of TP and N:P on Daphnia biomass. Specifically, high TP will have the largest effect on Daphnia biomass at low N:P ratios, but will have a smaller effect at high N:P ratios. Further, I predict that the slope of Daphnia biomass over time will be positively correlated with the slope of water column N:P over time among lakes.To investigate the direct and cyanobacteria-mediated effects of changing nutrient supply ratios on Daphnia traits, I will measure trait variation from paired lakes with similar N:P ratios but differences in total P concentrations averaged between 2010-2015. All lakes are sampled three times annually during the summer open water season for water chemistry, phytoplankton community composition and biomass, and zooplankton community composition and biomass as part of the Iowa State Limnology Laboratory water quality monitoring program. I will begin by collecting 50 adult Daphnia from 10 randomly selected locations around each lake and identifying them to species, measuring carapace length, measuring P excretion rates, and measuring body P content. Due to the small size of individual Daphnia, organisms will be run in groups of five for each analysis. I will collect an additional 20 individuals from each lake for genotyping at the pgi locus, at which heterozygotes outcompete homozygotes under high P conditions (Jeyasingh et al. 2009). I will then analyze whether species composition, pgi genotype frequencies, body P content, and P excretion rates vary among lakes using ANCOVA models with body size as a covariate. By comparing these responses among pairs similar in N:P ratio but varying in TP, I will thus be able to separate the effects of changing N:P ratios from the effects of variation in P concentrations.Finally, I will conduct a common garden experiment with Daphnia populations from the two lowest and two highest N:P lake-pairs. For these experiments, I will collect 30 adult Daphnia from 10 randomly selected locations around each lake from which I will then establish five clonal lines in the laboratory. As Daphnia primarily reproduce parthenogenetically, clonal lines can be established by isolating individual Daphnia, allowing them to reproduce in individual jars, isolating a single F1 offspring of each individual wild adult, and then utilizing those F2 offspring in experiments. In these experiments, Daphnia populations will be housed in 1 L mason jars filled with water filtered through a 65 μm sieve from the nearby Ada Hayden Lake. Ada Hayden Lake is a mesotrophic lake (mean TN:TP=75, mean TP=20 μgGoals /L) and will be used as a water source due to its proximity to the laboratory, relatively low TP, and to prevent any Daphnia population from being locally adapted to the local phytoplankton community. Filtering water through a 65 μm sieve will allow a natural phytoplankton assemblage as a food source while preventing any large-bodied zooplankton from entering the experimental jars. Fifteen neonate (<1 day old) F2 Daphnia from each clonal line will be raised in individual 45 mL vials and fed Ada Hayden Lake water previously fertilized with inorganic NH4NO3 (N) and KH2PO4 (P) to reach target N:P ratios of 16, 75, and 120 and a constant TP of 70 μgGoals /L following Lee et al. (2017). Water and seston N:P ratios as well as microcystin concentrations of each treatment will be verified using the same protocols used in the lake monitoring program and measured weekly throughout the experiment. This experiment will require a large number of individual Daphnia (1800 total), but the relatively short generation times and high fecundity of Daphnia make this experiment feasible. Treatments will last for 21 days, the approximate natural lifespan of Daphnia. Each neonate will be photographed through a microscope with a scale bar at the beginning and end of the experiment to calculate growth rate as change in body length. After 21 days I will also measure variation in body percent P and P use efficiency as well as genotype all clonal lines at the pgi locus following the protocols of Jeyasingh et al. (2009). I will then test for effects of source populationEvaluationBy combining the availability of long-term lake monitoring data and my own experiments, I hope to maintain a high level of research productivity throughout my post-doctoral tenure at Iowa State University. My goal is to submit two lead-author papers per year during my fellowship as well as two additional co-authored papers per year. Further, I plan to present the results of my work in at least one major environmental science conference per year such as the Society for Freshwater Science (SFS), Association for the Sciences of Limnology and Oceanography (ASLO), and the Ecological Society of America (ESA). My progress in meeting these goals will be assessed during annual progress evaluations conducted by my post-doctoral supervisor, Dr. Grace Wilkinson. |
| 英文关键词 | daphnia ecological stoichiometry eco-evo dynamics zooplankton |
| 来源学科分类 | 1190 - Limnology |
| 资源类型 | 项目 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/356104 |
| 推荐引用方式 GB/T 7714 | Moody, Eric.How will reduced nitrogen loading affect temperate lake ecosystems rich in phosphorus?.2018. |
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