Change of NDVI of Different Types of Vegetation and the Responses to Climate Change in Zhalong Wetland

[Objective] The aim was to explore response characters of NDVI of different types of vegetation to climate change. [Method] Based on NDVI data acquired by SPOT/VGT and meteorological data of five meteorological stations during 19982011, the change trend of NDVI and the relevant correlation with meteorological factors were analyzed in the research area. [Result] NDVI of different types of vegetation in Zhalong wetland kept increasing, especially after 2004. Of the vegetations, NDVI was of significant positive correlation with average temperature, average minimum temperature, average maximum temperature, rainfall and average relative humidity in a ten-day period （P 0.01）. In addition, NDVI responses are of different characters to meteorological factors. The responses of NDVI of vegetations were of lag phase to meteorological factors in Zhalong wetland. Specifically, the lag phase of ten-day average temperature and ten-day average minimum temperature was 10-20 d; the lag phase of ten-day average maximum temperature was 20 -30 d; the lag phase of ten-day rainfall was 20 d; the lag phase of ten-day averager relative humidity was 0-10 d. [Conclusion] The research provides references for further exploration of vegetations’ responses to climate change and formulation of vegetation protection and utilization under background of climate change.

Effects of Climatic Change on Evapotranspiration in Zhalong Wetland,Northeast China

Evapotranspiration （ET） process of plants is controlled by several factors. Besides the physiological factors of plants, height, density, LAI （leaf area index）, etc., the change of meteorological factors, such as radiation, temperature, wind and precipitation, can influence ET process evidently, thus remodeling the spatial and temporal distribution of ET. In order to illuminate the effects of meteorological factors on wetland ET, the ET of Zhalong Wetland was calculated from 1961 to 2000, the statistical relationships （models） between ET and maximum temperature （Tmax）, minimum temperature （Tmin）, precipitation （P） and wind speed at 2m height （U2） were established, and the sensitivity analysis of the variables in the model was performed. The results show that Tmax and Tmin are two dominating factors that influence ET markedly, and the difference of rising rate between Tmax and Tmin determines the change trend of ET. With the climatic scenarios of four General Circulation Models （GCMs）, the ET from 2001 to 2060 was predicted by the statistical model. Compared to the period of 1961-2000, the water consumption by ET will increase greatly in the future. According to the scenarios, the rise of Tmax （about 1.5℃ to 3.3℃） and Tmin （about 1.7℃ to 3.5℃） will cause an additional water consumotion of 14.0%- 17.8% for reed swami）. The ecological water demand in Zhalong Wetland will become more severe.

SPATIAL DISTRIBUTION OF NUTRIENTS OF SHALLOW LAKE IN THE ZHALONG WETLAND

The Zhalong wetland,a Ramsar listed wetland in China,which is located in the lower reaches of theWuyu’er River,perennially takes in lots of nutrient input of N and P from around the catchment.Nutrient substanceswere especially accumulated in the shallowlakes owning to the low-lying topography.The Xianhe Lake,where is loca-ted in buffer zone of the Zhalong wetland reserve,was chosen as our target area.The spatial variation of nutrient sub-stances in the shallow lakes was discussed and its influence factors were pointed out.The results showed that nitrogenand phosphorus in the wetland water existed mainly in the form of organic ones.The concentration of total nitrogen(TN)ranged from 0.65 mg/L to 10.64 mg/L and total phosphorus(TP) ranged from 0.013 mg/L to 0.052 mg/L.Ratio ofN/P was between 25.6 and 206.5.The water quality of the Xianhe Lake has been contaminated and is in heavy eutroph-ication.Total P has been acting as the major limiting factor.The distribution pattern of nitrogen and phosphorus in wet-land water showed characteristics of internal release except for the stream mouth area.There,the vertical distributions ofnitrogen and phosphorus nutrients were from both exterior source and internal release,and was mainly influenced by ex-terior source during flood period.Strong hydrodynamic disturb contributed to nitrogen and phosphorus nutrients suspen-ding and releasing in the sediments.The nutrients distribution in the water varied independent on regional changes ofdifferent frequency of hydrodynamic disturb.Mineralization and denitrification might be promoted in high frequency hy-drodynamic disturb area.In growing period,the absorption ofPhragmitesto nutrients was an important mechanism of nu-trients descending and spatial variation in the shallow lake.

Simulation and evaluation of the water purification function of Zhalong Wetland based on a combined water quantity-quality model

The water purification function of natural wetland systems is widely recognized,but rarely studied or scientifically evaluated.Extensive studies have been carried out by various international wetland research communities to quantify the water quality improvement ability of the natural wetlands,in order to maintain such ability and wetland ecological health.This study aims to evaluate the purification function of Zhalong Wetland in China for removing total nitrogen(TN) and phosphorus(TP),based on ex-situ experiments and the development of a combined water quantity-quality model.Experiments and model predictions were carried out with different input TP and TN concentrations.Statistical analyses demonstrated that the relative errors between model simulations and experimental observations for TN and TP were 8.6% and 12.4%,respectively.With water retention time being maintained at 90 d,the removal rate of these pollutants could not reach the required Grade V standards,if the inflow TN concentration was over 42 mg L-1,or the input TP concentration was over 14 mg L-1.The simulation results also demonstrated that,even with Grade V quality standard compliance,when the water inflow from surrounding industries and agriculture lands into Zhalong Wetland reaches 0.3×10 8 m 3 a-1,the maximum TN and TP loads that the reserve can cope with are 1.26×10 3 t a-1 and 0.42×10 3 t a-1,respectively.Overall,this study has produced a significant amount of information that can be used for the protection of water quality and ecological health of Zhalong Wetland.

Evaluation of the carbon sequestration of Zhalong Wetland under climate change

Wetland ecosystems are crucial to the global carbon cycle.In this study,the Zhalong Wetland was investigated.Based on remote sensing and meteorological observation data from 1975-2018 and the downscaled fifth phase of the coupled model intercomparison project(CMIP5)climate projection dataset from 1961-2100,the parameters of a net primary productivity(NPP)climatic potential productivity model were adjusted,and the simulation ability of the CMIP5 coupled models was evaluated.On this basis,we analysed the spatial and temporal variations of land cover types and landscape transformation processes in the Zhalong Nature Reserve over the past 44 years.We also evaluated the influence of climate change on the NPP of the vegetation,microbial heterotrophic respiration(Rh),and net ecosystem productivity(NEP)of the Zhalong Wetland and predicted the carbon sequestration potential of the Zhalong Wetland from 2019-2029 under the representative concentration pathways(RCP)4.5 and RCP 8.5 scenarios.Our results indicate the following:(1)Herbaceous bog was the primary land cover type of the Zhalong Nature Reserve,occupying an average area of 1168.02±224.05 km^(2),equivalent to 51.84% of the total reserve area.(2)Since 1975,the Zhalong Nature Reserve has undergone a dry-wet-dry transformation process.Excluding several wet periods during the mid-1980s to early 1990s,the reserve has remained a dry habitat,with particularly severe conditions from 2000 onwards.(3)The 1975-2018 mean NPP,Rh,and NEP values of the Zhalong Wetland were 500.21±52.76,337.59±10.80,and 162.62±45.56 gC·m^(2)·a^(-1),respectively,and an evaluation of the carbon balance indicated that the reserve served as a carbon sink.(4)From 1975-2018,NPP showed a significant linear increase,Rh showed a highly significant linear increase,while the increase in the carbon absorption rate was smaller than the increase in the carbon release rate.(5)Variations in NPP and NEP were precipitation-driven,with the correlations of NPP and NEP with annual precipitation and summer precipitation being highly significantly positive(P<0.001);variations in Rh were temperature-driven,with the correlations of Rh with the average annual,summer,and autumn temperatures being highly significantly positive(P<0.001).The interaction of precipitation and temperature enhances the impact on NPP,Rh and NEP.(6)Under the RCP 4.5 and RCP 8.5 scenarios,the predicted carbon sequestration by the Zhalong Wetland from 2019-2029 was 2.421(±0.225)× 10^(11) gC·a^(-1) and 2.407(±0.382)× 10^(11)gC·a^(-1),respectively,which were both lower than the mean carbon sequestration during the last 44 years(2.467(±0.950)× 10^(11) gC·a^(-1)).Future climate change may negatively contribute to the carbon sequestration potential of the Zhalong Wetland.The results of the present study are significant for enhancing the abilities of integrated eco-meteorological moni-toring,evaluation,and early warning systems for wetlands.

Partitioning of vertical water loss in reed swamp wetlands:Theory,research and application

This paper proposes an on-site monitoring system for evaporation （Ew） and evapotranspiration （ET） in wetlands called the Compensation Evapotranspiration Observation System. Considering the characteristics of wetlands environment and emergent plants, the vertical flux of water loss in wetlands can be separated using the system based on compensation principle. A comparison research on water loss through ET in reed （Phragmites australis） stands between Zhalong wetland and Baiyangdian wetland was carded out in 2004-2009. In Baiyangdian wetland, the ET rates from three reed stands with different leaf area indexes were measured. The results show that annual ET in Zhalong wetland was 739-886 mm during study period. Comparatively, annual ET of the three reed stands in Baiyangdian wetland was 970-1117 mm, 1261-1452 mm and 1759-2035 ram, respectively. The ET rates in Baiyangdian were stronger than in Zhalong because of the effects of geography and climate characteristics. Moreover, seasonal dynamic changes and influence factors of transpiration-acting factor from the two wetlands were also analyzed. It is indicated that the transpirafion-actng factor can be affected by geographic location, aboveground biomass, plant growth and climate conditions.