Sediment Nitrogen Cycling Progress Update


I am now halfway into my stay in Port A, and my project is coming along quite well. We spent several days in the field scoping out our test sites, practicing techniques, and, finally, collecting the sediment cores that I am studying for my research project. Tropical Storm Bill made our Mission River water chemistry field day quite the adventure, but we were still able to successfully obtain two cores from all five test sites on both rivers. I took oxygen microprofiles of the top 1-2 cm of one core for each test site on the day the cores were collected. I have just started analyzing the microprofile data, but the profiles seem to be consistent with the findings of previous studies. We also just decided to supplement my original project a bit by inputting my microprofile data and my lab mate Sierra’s sediment grain size findings into a computer program to calculate the oxygen consumption rates over depth in each core. This information will hopefully help us determine what processes are happening at the water-sediment interface.

After I took the oxygen profiles, we sectioned each core into 5 increments and collected the porewater from each section. Unfortunately, the cores we took from the Aransas River were very sandy, so we were not able to collect much porewater from some sections. Nevertheless, I am going to test the nitrate/nitrite and ammonium in as many porewater samples as I can. Right now I am still being trained on the protocol for microplate analysis of nitrate/nitrite and ammonium, but I will begin testing my samples themselves soon. We don’t quite know what to expect, especially since Southern Texas has received an unusually large amount of rain recently. We know that the nutrient concentrations in the water column were unusually low shortly before my sediment cores were collected, so my porewater samples may contain very little nitrate/nitrite and ammonium. In any case, I hope to know more soon!


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