Optimizating Functions Of Production And Decomposition Subsystems In Coupled Human And Natural Systems

With the development from agricultural civilization to industrial civilization, human activity has changed natural ecosystems, resulting in breaking original structural features, forming new fracturing production units or decomposition units, such as cropland, rangeland, plantation, city, wastewater treatment plant (WTP) and so on. In recent one hundred years, with the development of urbanization, these fracturing units coupled together to build a new coupled system:coupled human and natural systems (CHANS). In CHANS, productivity is improved, energy flow and material circulation were accelerated, multi-scale regulation from urban to regional and even global scale was strengthen. More than half of the population in the world finally have no longer concerns for food, housing problems and have the basic need to survive beyond its material comforts. In CHANS, the basic processes of production and decomposition are roughly the same with those in the natural ecosystems. Nevertheless, the producers and decomposers have changed from individual species in natural ecosystems to the complex structure with multiple function units--"organeco" in CHANS. The organeco has higher productivity than its counterparts in the natural ecosystem and has more enhanced efficient features. Currently, the structure of CHANS has just been formed; function process is not perfect, even existing big problems. On one hand, the function process of production is not enough. About12million world's people are still in hunger poverty. On the other hand, the number of decomposition organeco is far less than the number of production organeco, resulting in the accumulation of waste, making life-support systems (such as water, soil, atmosphere, etc.) contamination.In this paper, we chose production organeco and decomposition organeco as the object. We studied how to strengthen their efficiency and thus strengthen the function of the CHANS. We took China as a major research object, supplemented by data from other countries in the world as a reference. We selected grassland since its degradation had become increasingly prominent, but people in the past had insufficient attention to how to use artificial grassland to enhance its production function. Also we chose constructed wetland (CW) as a case of decomposition organeco, and with the wastewater treatment plant as a comparison reference, to study enhancing decomposition efficiency in CHANS. We compiled data-sets by both experimental data and literature data. We use material balance method, life cycle analysis, scenario analysis together to study how these two types of organeco to meet human needs. The research's content include:people's increasing livestock need for grass demanding, the current and future potential productivity of natural grassland and artificial grassland, volume of wastewater discharge in China, treatment efficient of WTP and CW, using waste nitrogen (N) for biofuel production via CW. This paper also discusses carbon (C), N flow, and C, N coupled function of the artificial grassland and CW to improve productivity in CHANS. The main conclusions are as following:1) China's population has increased1.4-fold in the past60years. Per capita consumption of beef, mutton, and milk has increased3-fold,6-fold, respectively, with the increasing development of population and consumption capability. Urbanization has led to population has increased10-fold in urban area. Per capita consumption of beef, mutton, and milk in urban has increased3-36fold. If China's population, urbanization and economic development continue to increase according to the current speed, livestock product will be needed more. The increasing livestock demand had led to lead to grassland degradation, desertification. Thus, grass supply (averagely911kg ha-1, lowest122kg ha-1) decreases, cannot satisfy total grass supply. Restoring natural grassland and utilizing available1560ha winter and summer fallow fields (could provide0.234billion tons grass), plus available0.291million tons of straw, there still exist1595.5Tg grass supply gap according to our analysis in2050.2) Artificial grassland is an important way to ease the grass gap between grass supply and demanding. Aboveground grass production in artificial grassland was averagely17275kg ha-1(highest45000kg ha-1). This number is5-32fold that of the grass production in natural grassland in China. However, the area of artificial grassland occupies only2%of China's total grassland area. If artificial grassland area will cover10%of China's total grassland (40M ha), together with forage conversion rate improving to average world level, and there only need27%of China's total grassland area for natural grassland, the balance between total grass supply and total grass demanding would be reached. Thus, the remaining63%of the grassland area, located in ecologically fragile zones will be basically to be protected, which can reduce the incidence of dust storms and improve regional and global environment.3) Biodiversity in artificial grassland is lower than that of natural grassland. Fertilizer application causes water pollution problems in artificial grassland. However, artificial grassland can supply other regulation and supporting services, such as carbon sequestration and soil fertility retention. We calculated that artificial grassland can supply net ecosystem service as high as332.7billion yuan. If63%of grassland is put under protection and restoration, those natural grassland would provide ecosystem service832.2billion yuan. Together, China's total grassland would provide1160billion yuan ecosystem service, slightly lower than ecosystem service of forest in China (1406billion yuan).4) As an important decomposition organeco in CHANS, the number of WTP has increased rapidly from266in1980s to937in2008. Wastewater treatment capability has increased more than5-fold. Wastewater treatment ratio has increased from10.3%in1980s to57.4%in2008, still lower than that in developed countries (90%). Treatment ratio for N and P can not reach the standard for surface water. Reasons are the construction and operation cost very high in China. The cost of removing1kg N was37.5to135yuan RMB, operating and maintenance costs are～0.5yuan to5.0yuan RMB removing per kg N for WTP in China.5) Recently a new wastewater treatment approach-CWs was introduced to China, as a new decomposition organeco in CHANS. The average removal rates of NH4+-N (ammonium nitrogen), TN (total nitrogen), TP (total phosphorus), COD (chemical oxygen demand), and BOD5(five day biochemical oxygen demand) are59.8%,44.3%,62.1%,73.4%, and81.8%, respectively. In addition, greenhouse gas (GHG) emission was18.5g CO2equivalent when CW treating per cubic wastewater, the number was only0.1%that of WTP. The cost of removing1kg N in a CW (13.6to70yuan RMB) was only one-third to one-half the cost of a WTP, operating and maintenance costs are～0.5yuan to5.0yuan RMB per kg N,1/7-1/27that of WTPs. Nevertheless, CWs also has disadvantages. CWs require5-10times larger land area than WTPs to remove same amount of waste N. CW treatment efficiency differs according to different hydraulic wetland types. As for NH4+-N,TN,TP,COD, vertical flow CWs are more efficient than horizontal flow and surface flow CWs. As for BOD5, horizontal flow CWs are more efficient than vertical flow and surface flow CWs. The newly developed integrated vertical flow CWs, based mainly on subsurface flow CWs, combine the advantages of vertical flow aerobic processes that stimulate nitrification with the subsurface flow anaerobic processes that promote denitrification. Thus, integrated vertical flow CWs are the most effective CW type.6) CWs can provide additional ecosystem service benefits, such as biomass production, carbon sequestration, oxygen release, reusable water supply, regional climate regulation, habitat conservation, educational and recreational usage. Moreover, biofuel production via CWs can strengthen ecosystem services. We use mass balance approach and life cycle analysis, showing the energy output, net energy balance of biomass energy yield of CWs at present reached182.3,105.4GJ ha-1. Energy output is2-8folds higher than the four current biofuel production systems (corn, soybean, switchgrass, LIHD grassland). In sum, taking Zhejiang Province as case, the total ecosystem services for CW are7840667.3yuan ha-1yr-1, much higher than forest ecosystem services (36130yuan ha-1yr-1) in this region.To sum up,using artificial grassland has improved one fold productivity, using CW can increaset the NH4+-N treatment ratio one fold higher, TN and TP treatment ratio50%higher, thus, reducing the ecological footprint in CHANS. Enhancing decomposition organeco and production organeco could improve the status of life support components.63%of natural grassland can be recovered under protection. More than90%of the wastewater treatment are thoroughly be treated. Biodiversity, amenity, educational value could be improved in total CHANS. The paradigm of using artificial grassland and CW for the improvement of ecosystem function can be impleted in other organeco. Thus, all the organeco functions in CHANS can be improved in a economic-ecological-social sustainable mode.