Nitrogen is a key pollutant and is the key ingredient behind eutrophication which is an up and coming problem for numerous marine sources. It has been shown from numerous other studies that parameters such as ph, dissolved oxygen etc affect nitrogen release levels from sediments. Key to this study it has been shown that DO (dissolved oxygen) is an important factor affecting the nitrogen cycle in the aquatic systems.
This study performed in Aidong Ruan et al. (2009) looked at sediment from a lake in Nanking, the lake was called Lake Xuanwu. The authors wanted to see whether by having altered oxygen conditions compared to the norm whether this would affect the nitrogen transforming bacteria number and activity, to back up the past studies results and conclusions.
The method used was that the sediment was collected, and then prepared and kept at a constant ph and moisture content to avoid any other reasons why the experimental conditions occurred. The sediment was then put under one of four different oxygen supply levels. These conditions were either; oxygen saturation, aerobic condition, anoxic condition, and an anaerobic condition, with the highest DO value of 0.70mg L, and the highest being 8.60 mgL, the other 2 were intermediate values, with the aerobic being 6mgL and the anoxic being just 2 mgL of oxygen supplied. Then the levels of aerobic heterotrophic bacteria, ammonifying bacteria and nitrifying bacteria were counted and compared.
The results from this showed that from all of the conditions used the highest levels of denitrifying bacteria was in the anoxic sediment conditions during the whole experiment. And the lowest was in the fully saturated oxygen condition, showing quite clearly that when dissolved oxygen is high enough it is very beneficial to the environment, not only because it provides more oxygen to the species within, but also because it reduces the nitrogen bacteria levels and so would most probably reduce the eutrophication levels, helping all aspects of the water source.
The enhanced oxygen supply also inhibited the activities of urease,nitrate reductase and nitrite reductaes in the sediments, and there was a positive corellation between the activity of protease and DO concentration within the sediments.
From this the conclusions made were that Key groups of nitrogen transforming bacteria and enzyme activities in sediments developed in response to dissolved oxygen, and that oxygen inhibits the "bad" bacteria in this situation, which proves beneficial all round for the reasons mentioned above.
This study is very interesting, and possibly suggests that where eutrophication occurs oxygen could just be pumped in to reduce these effects and help the biodiversity, the benefits of this study are that should eutrophication and nitrogen bacteria become a problem there is a solution known, or at least a rough suggested method to it.
The url for the paper is below:
Reference:
Aidong Ruan , Ruo He , Shengyou Xu & Tao Lin (2009): Effect of dissolved oxygen on nitrogen purification
of microbial ecosystem in sediments, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and
Environmental Engineering, 44:4, 397-405
Hi Oliver, I was wondering about a few points mentioned about this paper:
ReplyDeleteIf the enzymes linked with the metabolism of denitrifying bacteria were inhibited with enhanced oxygen levels, does that mean that the bacteria found another metabolic substrate in order to survive (just at lower abundances)?
Also, although increasing oxygen does appear to reduce the quantity of denitrifying bacteria, the solution proposed does seem a little far-fetched. I have not looked into how one would go about maintaining oxygen levels in water, however logical seems to suggest that the oxygen will most likely not remain dissolved without a constant supply being pumped in, considering the concentration gradient created by this will cause the oxygen to diffuse into the environment. This could be highly costly, not do mention the effect on other organisms found in the waters! How did the researchers go about maintaining a constant level in this paper?
Thanks
It doesnt say they switch to another substrate it states that the urease activity alters, under the difference conditions thus in my eyes meaning that this activity can account for the decrease in nitrifying bacteria. And yes as briefly mentioned in the review to maintain the oxygen it would need to be probably pumped in constantly, thus leading to a weigh up between financial input and environmental output sort of thing, and the way they kept the oxygen levels constant for each scenario was by having a closed circuit which contained a pvc container, and then to get the scenarios they either pumped in oxygen at a certain rate to keep the levels constant or added nitrogen if they needed to change the oxygen saturation levels.
ReplyDeleteHope this helps
Ollie.