| Aquaculture was closely related to the aquaculture environment.Residual bait and excreta will made the nutrient elements in the aquaculture water exceed the standard and eutrophic,resulting in the deterioration of water quality.At present,researches at home and abroad mostly focused on improving aquaculture technology and purifying aquaculture water body.Among them,the research on purification mode mainly focused on rice crab co-cropping system and intensive fish pond,the research on the three-dimensional composite ecological culture system of rice-fishery was more about the changes of water environmental factors and the physiological characteristics of rice crab.In this study,the rice-fishery integrated planting and breeding three-dimensional complex ecological culture system coupled with rice crab co-cropping and intensive fish pond(hereinafter referred to as rice-fishery complex system)in Guangming fishing village,Yinchuan is taken as the research object.The system realizes water recycling through rice-crab co-cropping system and intensive fish pond system,it is a green ecological industry model with efficient utilization of water resources and multi-level use.the collection of samples will be carried out from April to September 2021(water and soil samples will be collected at the end of April to August,water samples will be collected in mid June,mid July,mid August and mid September,and rice crab samples will be collected once in mid September),and the dynamic migration characteristics of nitrogen,phosphorus,potassium and other nutrient elements in water and soil environment are taken as the main line;The effects of systematic environmental factors on nutrient elements and their morphological transformation are explored by using four methods:correlation analysis,stepwise regression analysis,gray correlation analysis,and redundancy analysis;Through the analysis of the interception rate of nutrient elements in water and soil,the analysis of the flow of nutrient substances in the system,the construction of a prediction model for nutrient reduction and the evaluation of nutrient elements,to investigate the dynamic migration characteristics of sediment-water interface nutrients in the rice-fishery complex system,and to explore the source-sink change characteristics of nutrient elements at the sediment-water interface,so as to provide a theoretical basis for the efficient utilization of planting and breeding water body.The following results were obtained:(1)After the operation of the rice-fishery complex system,the pH,dissolved oxygen and alkalinity of the water body increased,and the salinity and permanganate index decreased.The background value of total nitrogen in intensive fish pond was 6.682 mg/L and 1.145 mg/L in September,and the background value of ammonia nitrogen was 2.139 mg/L,which was 0.092 mg/L in September,it showed a downward trend as a whole,and the contents of nitrate nitrogen and nitrite nitrogen did not change significantly;The background value of total phosphorus was 0.831 mg/L,0.108 mg/L in September,and the background value of orthophosphate was0.437 mg/L,which was 0.033 mg/L in September,which showed a decline as a whole;The background value of total potassium was 4.843 mg/L,which was 9.835 mg/L at the end of August,showing an upward trend;The background value of total nitrogen in paddy field was 5.528 mg/L,which was 1.684 mg/L in September,The background value of total phosphorus was 0.627 mg/L,and the total phosphorus in September was 0.143 mg/L,showing a downward trend as a whole;The change of total potassium content was complex and has no obvious trend.With the operation of the rice fishery complex system,the physical and chemical properties of the system water body have been improved,and the content of nutrient elements has decreased..(2)The total salt in the soil at the outlet of intensive fish pond decreased effectively.The pH was close to the background value in August,and the background value of total nitrogen was 0.964 g/kg and 0.442 g/kg in August,showing a downward trend;In August,total phosphorus and total potassium were close to the background value;The background value of ammonium nitrogen was 0.138 g/kg,which was 0.092 g/kg in August,showing a downward trend;The background value of nitrate nitrogen was 0.006 g/kg,which was 0.013 g/kg in August,with a small increase;The available phosphorus in May was relatively large,and the other months were close to the background value.The total salt in the ring ditch soil of paddy field decreased effectively,the pH increased slightly,and the background value of total nitrogen was 0.632 g/kg,which was 0.511 g/kg in August,with a small decrease;Total potassium increased slightly as a whole;Total phosphorus,available phosphorus and ammonium nitrogen showed a downward trend;The dynamic change of nitrate nitrogen is small.The total salt of paddy soil decreased effectively,the pH was close to the background value in August,the background value of total nitrogen was 0.361 g/kg and 0.409 g/kg in August,showing an upward trend as a whole;At the end of August,the total potassium was close to the background value;Total phosphorus and available phosphorus decreased slightly;Ammonium nitrogen increased slightly;Nitrate nitrogen showed a downward trend.The contents of total phosphorus and available phosphorus in the soil of the rice-fishery complex system decreased,and a small amount of total potassium accumulated.The soil of the system released some nutrient elements,but the dynamic change of nutrient elements was small.(3)The nutrient elements of rice-fishery complex system were affected by the physical and chemical indexes of water body,and the main influencing factors were alkalinity and permanganate index.Alkalinity,permanganate index,pH and water temperature had the main influence on the form transformation of nitrogen,while permanganate index,waterr temperature,alkalinity,conductivity,salinity,Chl.a and pH had the main influence on the form transformation of phosphorus.Alkalinity inhibited the rise of nutrient elements,while permanganate index and nutrient elements promoted each other.In addition,conductivity,salinity and TDS were positively correlated with nutrient elements and negatively correlated with nitrite nitrogen,Chl.a was positively correlated with nutrient elements,and water temperature was negatively correlated with nutrient elements.Therefore,the saline alkali property of rice-fishery complex system was conducive to the improvement of alkalinity and had a good inhibitory effect on the nutrient elements of water.(4)Rice-fishery complex system could effectively purify the tail water of fish pond and meet the material and energy requirements of crops and aquatic organisms.The interception rates of total nitrogen,total phosphorus and total potassium in water were 64.1%,68.0%and 41.3%respectively,indicating that the nutrient elements in water could be intercepted by energy efficiency.However,the system operates for a long time,and the interception effect of soil was not good.The interception rates of total nitrogen,total phosphorus and total potassium were-17.2%,-8.8%and 1.9%respectively,indicating that the soil released total nitrogen,total phosphorus and accumulates total potassium.In the material flow analysis,the ratio of nitrogen,phosphorus and potassium in and out of the system was 0.72:1,the ratio of output to input was 0.88:1,the utilization of nutrient elements by rice and crab was 81.6%,51.6%and 28.8%,and the surplus nitrogen,phosphorus and potassium in the system was 9.0%,46.1%and 39.2%.So the nutrient elements were transported to rice,crab and other organisms.The model showed that the nutrients decreased and nitrate nitrogen,total phosphorus and orthophosphate increased slightly with time.The rice and crab fields No.8,No.12 and No.13 of the system irrigated the Yellow River water,and the rest of the rice and crab fields used fish pond water,the evaluation of nutrient elements in May,June and August showed that after the operation of the rice-fishery complex system,the distribution of nutrient elements was more uniform,In May,it was mainly the contribution of soil nitrogen and phosphorus in the ring ditch and nitrate nitrogen and nitrite nitrogen in the ring ditch water,while the nitrate nitrogen and nitrite nitrogen in the ring ditch water decreased in June and August.In June,there were the contributions of potassium,ammonia nitrogen in the ring ditch water and ammonium nitrogen in the paddy soil.In August,the contribution of nutrient elements in the form of soil nitrogen and phosphorus increased,and the contribution of nitrogen and phosphorus in the paddy soil and orthophosphate in the ring ditch water increased.The quality of nutrient elements in the rice and crab fields irrigated with fish pond water in May is better,and the quality of No.8,No.12 and No.13 for Yellow River water irrigation in June and August was better,indicating that after the operation of the system,the nutrient element content of rice and crab fields irrigated with fish pond water was lower than that of Yellow River water irrigated rice crab field.The operation of rice-fishery complex system make the distribution of nutrient elements more diverse and uniform,and the biological utilization of nutrient elements in rice crab field with rice and crab fields irrigated with fish pond water was stronger.Rice-fishery complex system can effectively improve the water utilization capacity,provide sufficient nutrients to organisms,the saline-alkali nature of the system soil has an inhibitory effect on the rise of nutrient elements,and the bio-utilization of nutrient elements in rice and crab fields irrigated with fish pond water is stronger,indicating that the system has a good advantage in saline-alkali areas with water shortage. |
