Study On Variation Characteristics Of Nitrogen, Phosphorus At Sediment-Water Interface In Grass Carp Polyculture

Change of nitrogen and phosphorus in overlying water and pore-water was studied in grass carp poly-culture ponds. At the same time, the effect of feed residues, sediment thickness, temperature on release law of nitrogen and phosphorus in water-sediment interface were studied under simulated condition in laboratory. Through this study, the data of nitrogen and phosphorus cycle at water-sediment interface provide the basis for the pond-water quality management.1. Distribution features of nitrogen and phosphorus in water-sediment interface.①Overlying water, NH4+-N, NO3--N, NO2--N, TN, TP in three ponds are increasing gradually and are significantly higher than the initial value (p<0.05). The results show that nutrient content of nitrogen and phosphorus are accumulating in pond water. The quality of water contained in pond trend to depravation.②Pore-water in surface sediment (0cm-3cm), SRP concentration gradually decrease, other nutrient has not evident changing-regular. NH4+-N, SRP in pore-water are significantly higher than overlying water (p<0.05). The results show that pore-water avail to store higher concentration nitrogen and phosphorus.③Vertical distribution features of sediment nitrogen and phosphorus, NH4+-N, SRP in pore-water are decreasing with the increase of sediment depth. The interface sediment (0cm-3cm) can store high concentrition NH4+-N and SRP. The content of OM, TC, TN, TP have no obvious change during the test. The results show that the sediment accumulation of each composition was not obvious.2. The effect of feed residues on release law of nitrogen and phosphorus in water-sediment interface were studied under simulated condition in laboratory. The study took two sets of conditions, static condition (A group) and feed add condition (B group). After adding the feed, nitrate nitrogen concentration in A group is higher than B group(P <0.05), but SRP concentration in A group is lower than B group(P<0.05). At the2-14th day of experiment, NH4+-N concentration in A group is higher than B group(P<0.05). At the end of test, NH4+-N concentration in B group is higher than A group(P<0.05). NH4+-N and NO3--N release are restrained in B group at the beginning of the experiment. Nitrogen changing regulation is that increase at first, then decrease in A group, but regulation is complete opposite in B group. Feed decomposition can produce a large amount of phosphorus in B group, at the same time, SRP changing regulation increase first and then decrease.3. The effect of sediment thickness on release law of nitrogen and phosphorus were studied under simulated condition in laboratory. The study took three sets of conditions,2cm of thickness sediment (A group),6cm of thickness sediment (B group) and10cm of thickness sediment (C group). NH4+-N changing regulation is that increase at first, then decrease in all group. At the7-21th day of experiment, NH4+-N concentration in A group is lower than B group, C group (P<0.05). At the9th day of experiment, NH4+-N concentration in A group begin to decrease, but NH4+-N concentration in B group, C group begin to decrease until13th day. The results show that NH4+-N increase with the increase of sediment thickness. At the same time, sediment help maintain high concentration NH4+-N in overlying-water.4. The effect of temperature on release law of nitrogen and phosphorus were studied under simulated condition in laboratory. The study took two sets of conditions,33.9±0.94℃(A group) and22.5±1.27℃(B group). At the9th day of experiment, NO3--N, NO2--N concentration in B group is lower than A group (P<0.05). NH4+-N concentration in B group begin to decrease at13th day, but A group maintain high concentration NH4+-N. SRP concentration in A group is higher than B group (P<0.05). The results show that NH4+-N increase with the increase of overlying-water temperature.