Araphid Diatoms

Table 1 provides site description. The depth was measured at 29.9 ft. The abundance of Araphid diatoms was significantly lower than Centric diatoms (Figure 2). The average abundance of the Centric diatoms were 80 and the average abundance of the Araphid diatoms were 20 (Figure 2). There was not a constant rate for organic carbon percentage. The deepest layer showed the highest percentage of organic carbon at 47% and the lowest organic carbon percentage (23%) was found at 15cm (Figure 3). Organic carbon stored in lake sediments is mostly dependent on the amount of productivity in the lake at that time. During photosynthesis, diatoms are able to turn carbon dioxide into organic carbon which generates oxygen. However, since the shells are heavy the diatoms that die will take the carbon out of the surface waters and into the sediments. Higher rates of productivity mean more plankton and diatoms which result in a higher percentage of organic carbon stored into the sediments. Figure 2 shows that organic carbon was settling at Spanaway Lake’s bottom at much higher rates in
the past. This should mean that at this time more diatoms were present which resulted in higher rates of carbon fixation. For this experiment we did not measure the population numbers of diatoms, but we measured the relative abundance of each group/order present. The changes in organic carbon could have occurred for different reasons.
One reason the percentage of organic carbon may have changed is due to the erosion. The erosion may have caused the levels of organic carbon to decrease because of the mineral input from the runoff. It can also be that during this time, houses were being developed which meant there was a removal of terrestrial vegetation which would have reduced the input of organic to the soil and this would have reduced the carbon in the runoff (Wetzel, 2001). The terrestrial plants form much of the organic matter, the organic carbon in plant tissue is transformed by microbial utilization and degradation both at the site of growth and during transportation of runoff (Wetzel, 2001).The highest percentage of carbon is at the bottom of the sediment can be because there was more terrestrial plants and less urban development at that
time. The types of diatom that are present in a lake are dependent on their environment, and because of this they are good indicators of their aquatic environment at that time (Stevenson and Pan 1999). Centric and Araphid type diatoms were the most abundant orders found in Spanaway Lake. Figure 1 shows that centric diatom shells dominated the sediment throughout the entire sediment core. Despite fluctuations in temperature, season, and percent organic carbon, centric diatoms have remained the most abundant order of diatom within the lake.
Our results were inconclusive because it did not provide a trend when comparing diatoms and organic carbon. At each section there was a higher abundance of centric diatoms but the organic carbon was continuously changing. Future studies will need to be conducted, one possibility is looking into heavy metals. Heavy metals have been previously used to remove algae and therefore has an effect on organic carbon and this can be one reason the organic carbon is changing. Another study that can be done is to look at the levels of nitrogen and phosphorus because they can also increase or decrease algae bloom levels.