Decomposition And Nutrient Release Of Potamogeton Crispus And Their Influence On Anammox Bacteria

Submerged macrophyte is the primary productivity of aquatic ecosystem, which plays important roles in aquatic ecosystem functional structure and biodiversity. The excessive nutrients such as nitrogen and phosphorus in lakes lead to the overgrowth of submerged macrophytes. In the process of season conversion, a lot amount of submerged macrophytes decay and decompose, the nutrients re-release into the water, which results in ―secondary pollution‖ to the lakes. This process has negative effects on the aquatic ecosystem. Hence, the typical submerged plant Potamogeton crispus(P. crispus) was selected as the research object in this paper. Studying on the decomposition rate, and the releasing of nitrogen(N)、phosporus(P) when P. crispus decay; In addition, studying on the main pollutants in overlying water and sediments when the P. crispus decomposition at different initial biomass(0、10g、40g、80g), the sediments came from Jinshan lake(J), Xuanwu lake(X), Taihu lake(T), respectively; Detection of Anammox community structure, abundance, diversity and other characteristics of three groups sediments, so we can make conclusions about the influence on the nitrogen cycle when P. crispus decomposition. The main results were as follows:(1) The decomposition rate was 0.028d-1, decomposition of 50% and 95% mass needed 25 d, 107 d, respectively. The process could divide into three phases, there were fast leaching phases, moderate phases and slow decomposition phrases. The total phosporus(TP) content in the decomposition process shown trend of decrease- increase- decrease, the accumulation indexs was release. While the total nitrogen(TN) content in the trend of decrease- increase-decrease, the accumulation index was accumulation at first then release.(2) The decomposition of P. crispus had significantly effects on the overlying water. The dissolved oxygen(DO) concentration was decreased sharply at the early decomposition, then DO increase slowly. DO concentration related to the initial biomass, the more biomass, the more loss of DO. In addition, p H also declined at the early process, then increased slowly and maintained in a certain range. The content of TN, ammonia nitrogen(NH4+-N) and TP were significantly increased when the P. crispus decomposition, with the increase of initial litter biomass, the more content of TN, NH4+-N and TP were detected in overlying water. Nitrate nitrogen(NO3--N) concentration decreased in the early decomposition process, after that the content of NO3--N increased slowly.(3) P. crispus decomposition resulted in change the physical and chemical factors in sediments. The organic matter showed a trend of increase, while had little influence on p H. Moreover, the decomposition process would increase the content of TN and NH4+-N in sediments, and it related to the initial biomass. After the experiment, TN content in sediments of J, X all showed 40g>80g>10g>0g, while T showed 80g>10g>40g>0g. The decomposition of P. crispus had a complex influence on NO3--N concentration in sediments. The TP, iron/aluminum phosphate(Fe/Al-P) were increased when the decomposition of P. crispus. When experiment ended, TP in sediments showed 80g>40g>10g>0g. While the calcium phosphate(Ca-P) content was relatively stable. NH4+-N content in three group sediments had significantly negative correlation relationship with overlying water p H.(4) The decomposition of P. crispus significantly changed the Anammox community structure, abundance, diversity, and distribution. Three groups sediments Anammox abundance changed different from each other, J, X and T showed J40>J0>J80>J0, X80>X40>X0>X10, T0>T10>T40>T80, respectively. The diversity index(Shannon) and abundance index(Chao1) decreased when the experiment ended. In addition, J group Shannon had significant positive correlation with NO3--N, Chao1 had significant negative correlation with TP. T group Shannon and Chao1 had significant positive correlation with NO3--N and NO2--N. While X group diversity and abundance index had no significant correlation with environmental factors. In general, the decomposition of P. crispus would change the Anammox community structure, prompted the bacteria community structure evolving to simplification. With the increasing of biomass, Kuenenia in J sediments gradually reduced, and the proportion of Brocadia increased, Brocadia in J80 was 100%. Brocadia in X sediments was gradually reduced, while Kuenenia was increased, the proportion of Kuenenia in X40, X80 was 100%. Brocadia was dominant in T group sediments, after the decomposition, T10, T40 Brocadia accounted for 100%, however, T80 Brocadia accounted for 96.87%, Anammoxglobus/Jettenua proportion was only 3.13%.