I went to a session about freshwater diversity and stable isotope studies. I was hoping to get good information about stable isotopes and how we can use them for my senior thesis...and that I did! The first talk was an introduction to a huge study conducted by IPY Canada on arctic char. Dr. Jim Reist presented an overview on char biodiversity, taxonomy and adaptability to changing climatic conditions. Char consist of 5-22 species (depending on if you are a lumper or a splitter) with 2 major groups separated by environment (lacustruine or riverine). They are only found in waters above 45N even though they can be either anadromous (migratory) to estuarine areas or static. Jim claims that there is a greater diversity in the young char than previously thought. What was originally small and large forms, his group found a new small benthic form. The larger form is of a higher trophic level than both the small and benthic form. He found that the juvenile forms prefer non-glaciated streams as increased temperature promotes faster growth rates, and provides a means of possible predatory escape. More on the temperature effect was covered a few lectures later. The next lecture was a more detailed one about char migration and their effect on coastal lakes. Interestingly, char can choose whether to be anadromous or sympatric. If anadromous, they rear for 3-5 years in freshwater then move to estuarine or marine environments returning only to spawn. It is important to not that sympatric arctic char and lake trout do not coexsist. Because arctic char are mostly iteroparous (don't die after spawning), they return to freshwater every fall and return to saltwater in the spring. Associated with this migration, is a nutrient spike. The question is: where does the nutrient come from? Salt-, or freshwater uptake? The author examined this by tracking delta S34,delta C13, and delta N14 isotopes in the flesh of the char. The amount of sulfur isotopes would indicate the amount of salt water nutrients uptaken by the char. The Carbon isotopes indicate a more litoral source of nutrient. The nitrogen would give the trophic level of the fish. What was found is that 99% of the nutrient uptake by anadromous char was marine. The nitrogen isotopes reflect a food web were the lake trout prey on juvenile char. It was also found that mercury levels are inversely related to condition of the char. Climate change may affect the migration patterns of the char which may affect the nutrient uptake, but more work is needed to determine that.
The next talk was by Michael Powers about using otoliths to determine temperature of the environment at various times in juvenile chars' life. Oxygen is uptaken by the fish and passed into the blood stream. Some oxygen is precipitated in the otolith (earbone) of the fish as CaCO3. This carbonate forms rings much like tree rings. These rings can be analyzed for their O18:O16 ratios, which is directly related to the environmental O ratios. This ratio can then be plugged in to a fractionation equation (Storm-Suke et al, 2007 for char) to determine the environmental temperature. He seperated the groups based on temperature and compared the growth rates. He found that in the cold water conditions there was a trend in growth that showed warmer conditions within the cold group promoted higher growth rates. In the warm water group, he found no growth trends meaning temperature does not effect growth after a certain point, but instead is dependent entirely on metabolism and nutrient intake. I later asked Michael about whether the methods could be applied to foraminifera and he referred me to some classic isotope work on forams and assured me it could as long as the CaCO3 was not involved in metabolism (which it is not).
The next talk by Jane Godiksen played off of Mike Powers research involving O-18 to O-16 ratios in predicting paleotemperatures, except she took it one step further and developed a fractionation equation specific to each species of char and applied it to the interpretation. She separated otoliths of the same species to different temperatures and from that plotted the ratios of each in their relations to their respective temperatures. From that, he found that the fractionation equation was not linear as simplifiers would have you believe. She claims that in order to have a good study of theses ratios, species specific fractionation equations need to be used.
After the char people, Frank Wronga introduced another huge study put together by IPY Canada which developed predictive models for freshwater nutrient flux. This model was made public so that the average person can help in the data collecting. In doing this the model improved flux monitoring as well as outreach to the not northern community. Joseph Culp presented some of their findings and predictions. They found that thermokarst for the most part: increases dissolved carbon, organic carbon, nitrate, phosphorus, sedimentation and scouring. It also significantly alters flow regime. The project looked at freshwater rivers trending from the south to the north of Canada and measured water chemistry, sediment transport, biodiversity of invertebrates and algae, nutrient and biomass. As one expects, water temperature decreases northward and with this decrease, are decreases in bioactivity, growth rates, production and specialist species. Joseph found that the nutrients in all rivers are low, with phosphate as the limiting reagent throughout. Algal biodiversity and abundance decreased northward. Invertebrate density decreases northward with a rapid decrease to 0 in mayflies, with this decrease in overall biodiversity northward is associated decrease in decomposition rates.. The chlorophyll producers are dominated by diatoms throughout. Joseph also looked at food web sources and found that O-carbon sources move landward as you go north.
The next talk was not that good and was not timed well as he skipped over his results to save time lol. It was by Nikolaus Gahter and looked at tundra lakes and the effect of permafrost melt on them. There are three types of tundra lakes: unslumped lakes, slumped lakes and secondarily developed slumped laked. Slumped lakes form when permafrost melts and clears out pore space and the lake walls collapse. These slumped lakes can redeveloped to form secondarily developed slumped lake. The talk was quite strange as he switched gears halfway and talked about these fish he found in a series of supposed fishless lakes. Then he ran out of time before the "so what" topic.
The final talk was a study on how algae responds to changing climate. The talk was by Nadia Slovania and looked at the holocene. We then see a decrease in diatoms and organic carbon as well as no vegetation in association with the younger dryas, where temperatures were lower than. Soon after we begin to see an increase in diatoms, tree pollen and leaves found in lakes. This is reflected of the passing younger Dryas, and a warming of overall temperatures. The research is important because it shows how one can use pollen, diatoms and plant life as a proxy for temperature change in paleoenvironments.
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