Quantitative Assessment In The Impacts Of Human Activities On Net Primary Productivity Of Wetlands In The Northeast China

Net primary productivity (NPP) is an important ecological parameter for wetlandecosystem function. Quantitatively distinguishing the effects of climatic changes andhuman activities on NPP is the key to wetland conservation, restoration, and managementunder the background of global changes. Northeast China, a major distribution of wetlandsin China, had an obvious changed wetland NPP due to the disturbances of human activities.Taking the wetlands in Northeast China as the study object, this paper aims to develop aquantitative assessment in the impacts of human activities on wetland NPP by the means offiled observations, model simulation, analyzes of remote sensing (RS) and geographicinformation systems (GIS).Based on the data of wetland distribution in2000and2010, landscape patterns anddynamic characterizes of wetland in Northeast China were analyzed. Wetland potential netprimary productivity (PNPP) and actual net primary productivity (ANPP) were estimatedby using the CASA model and MODIS products, and then validated by field observationsfor examining its spatial patterns and temporal dynamics. Furthermore, the influences fromchanged area of wetlands on ANPP were analyzed. A human activities relative influencecontribution index (RICI) for the unchanged wetland in spatial distribution was establishedby the PNPP and ANPP. Spatiotemporal dynamics of RICI during2000-2010were theninvestigated. In addition, the differences in impacts of human interference on wetland NPPat different spatial scales were discussed. Consequently, the effects of human activities onwetland NPP were quantitatively assessed from the two aspects of changed and unchangedwetland in spatial distribution. Through the above studies, this paper hopes to improve theunderstanding in carbon budget of wetland ecosystems, and to provide scientific basis forthe management, protection, and restoration of wetlands. The basic conclusions are drawnas follows:(1) Landscape pattern and change characteristics of wetlands in Northeast ChinaWetlands in Northeast China, dominating with riverine and lake wetlands, have apparentgeographical features due to the climatic variations and varied human disturbances, andrelate to regional geomorphology. Wetlands in important wetland distribution regions alsohave evident differences in landscape features and wetland coverage ratio. A largerlandscape aggregation degree is found in the Greater Khigan Mountains and larger landscape fragmentation in the Liaohe Basin.Areas of wetlands in2000and2010in Northeast China are6.93×104km2and6.72×104km2, respectively. And the coverage ratio of wetlands in2000and2010are5.6%and5.4%, respectively, which is higher than the mean level of that in China. The largestwetland patch with an area of2.4×103km2locates in the Zhalong Wetland in SongnenPlain. Although good effects of protection and restoration on wetlands are found inNortheast China, the wetland degradation is still severely. The wetlands in Northeast Chinadegraded by3.15%from2000to2010, with an increased area of3443km2and loss area of5629km2. The loss rate of area loss is198km2per year and whole wetland coverage ratiodecreased0.2percentage points. The Songnen Plain has the largest loss of wetland, andSanjiang Plain has the largest decrease in coverage ration of wetlands, while Liaohe Basinhas the largest increase in landscape fragamentation of wetlands.(2) Estimation and analysis of wetland potential net primary productivity (PNPP) andactual net primary productivity (ANPP)Based on the MODIS products, the CASA model integrating VPM and TEM models wasemployed to estimate and analyze the PNPP and ANPP. There are remarkablecharacteristics in spatial pattern of PNPP and ANPP. PNPP is mainly influenced bytemperature, and PNPP has apparent difference in spatial pattern with ANPP due to thevarious human activities. A decreased trend was observed in PNPP and ANPP during2000-2010. Variation in ANPP is evidently larger than that in PNPP based on the standarddeviation. Human activities have resulted in a NPP loss of91.8gC·m-2·yr-1.(3) Quantitatively assessment in the impacts of human activities on wetland NPPWetland ANPP in Northeast China had a loss of1.34Pg C·yr-1because of the changedwetlands area from2000to2010. All the four wetland important distribution regions havedecreasing ANPP, while Songnen Plain have the largest changes in ANPP with a loss of0.61Pg C·yr-1. The conversion between wetlands and croplands led to an ANPP loss of0.77Tg C·yr-1.Owing to the economic development and urban construction, conversionbetween wetlands and build-up lands resulted in an ANPP loss44.3Gg C during2000to2010.Effects of human activities on the NPP of unchanged wetland in spatial distribution arevaried clearly in Northeast China. The RICI have obvious spatial heterogeneity andgeographical features. Larger RICI values are mainly distributed in Songnen plain and Hulun Buir. Mean value of RICI in the whole Northeast China is0.108. Human activitiesstill play negative roles in wetlands at the scale of Northeast China, which resulted insignificant decreases of wetland NPP. The RICI in Northeast China varied between0.074and0.153from2000to2010, and exhibited slowly increasing trend. This indicates that thehuman disturbances on wetland NPP are still enhancing. Although periodic process inwetland conservation was achieved, habitit quality of wetlands in Northeast China stillcontinued to decrease.(4) Spatial differences in impacts of human activities on wetland NPP at different studyscalesMean values and annual dynamics of RICI, as well as its spatial differences wereinvestigated at the scale of wetland important distribution region. Results show that notabledifferences of effects of human activities on wetland were observed among the fourwetland important distribution regions. The largest mean value of RICI (0.278) during2000-2010was found in Liaohe Basin. Meanwhile, slowly decrease of RICI was found inSongnen Plain. This suggests that there is a gradually reduced anthropogenic influence onwetland NPP and good conservation and restoration of wetlands in Songnen Plain.Increasing RICI from2000to2010indicates serious human disturbances in other threewetland important distribution regions.Important wetland natural reserves with larger RICI value than zero suggests thatnegative disturbances from human activities still existed in those reserves and the protectefficiency needs to be improved. The strongest interferences from human were observed inthe Dalai Lake Wetland Natural Reserve among the international important wetlands with aRICI of0.495, which indicate more attentions need to be paid in this reserve. Small RICIvalues were observed for wetlands in Nanweng River Natural Reserve locating in thenorthern mountainous areas, which are correlated with less population and humanaccessibility. Decreased annual RICI trends for wetlands in Zhalong, Honghe, Shuangtaiheestuary natural reserves reflect the improved conservation on wetlands in those reserves,especially in Zhalong wetlands. On the contrary, increasing trends of RICI values (i.e.positive RICI change slope) were observed in the other seven wetland nature reserves,suggesting increased human disturbances and requiring more conservation efforts.