A lot of data has been gathered about lentic ecosystems, such as lakes and ponds, and lotic ecosystems, such as rivers. However, there is a gap in the literature that doesn’t address ecosystems that fall somewhere in between. One example of this is in the tidal freshwater zone. Much of the time the tidal freshwater zone flows like a river, however, when the tide rises it can cause the flow of the river to stop completely and in some cases can even cause the flow to reverse. For my project, I specifically focused on sediment respiration. Most reactions happen where the sediment meets the water so the tidal freshwater zone cannot be fully understood without a full understanding of the processes occurring along this boundary.
My goal was to determine how respiration rates differ in various tidal freshwater zones of each river. In addition, I compared respiration rates in winter months to summer months. To estimate respiration rates, I measured oxygen consumption rates and porewater nutrient concentrations at these locations. I used an oxygen microsensor to create a profile of the sediment because oxygen is required for aerobic respiration and, therefore, it is a direct indicator of cellular respiration. I also analyzed the porewater to determine fluctuations in porewater nutrient concentration since these nutrients are a product of decomposition. My findings show that respiration rates increase linearly as you move downstream. In addition, I found that respiration rates were higher in summer months. When analyzing my porewater, I found a similar bell shaped curve showing ammonium concentrations to be highest in the center of the tidal freshwater zone on both rivers. The biggest factor I found that effected respiration rate was the sediment size, the smaller the sediment size, the higher the rate of respiration.
My findings were significant because they insinuate that the tidal freshwater zone is effective and efficient at removing organic matter from the water column. This is important because if the organic matter is not removed it will flow into the estuaries and tidal waters where it will promote the growth of phytoplankton and algae and eventually alter the ecosystems in these areas.
I learned more this summer than I ever could have imagined. All of the members of my lab were so patient and easy to work for. I was also very lucky to have such a fun group of people to go through my REU with. I look forward to watching my project progress with the next sampling series. A huge thanks to everyone, hasta luego!