[Spatial Diffusion Mechanism Underlying Peri-urban Cropland Heavy Metal Contamination in the Black Soil Region].

The spatial diffusion mechanism underlying cropland heavy metal contamination in a complex peri-urban environment provides a crucial basis for controlling soil contamination from the source and also for ensuring the quality of black soil croplands. However, previous studies have struggled to locate the contamination sources or trace their diffusion trajectories in space. In this regard, representative peri-urban croplands in the black soil region were selected as a case, and soil As, Pb, Hg, and Cd were deemed as the main research objects. Moreover, an affinity propagation algorithm and spatial autocorrelation regression were adopted to measure the contamination patterns and identify the major determinants, in an attempt to reveal how heavy metals are diffused in the peri-urban cultivated area. The results indicated that ① the average concentrations of soil As and Cd were 39.35 mg·kg-1 and 0.183 mg·kg-1, respectively, which exhibited heavier accumulation in the study area. The Nemerow index indicated that there were 52.38% of croplands indicating slight contamination. ② The affinity propagation algorithm identified three potential sources with a similar impact extent for As, which were situated in the typical cultivated area. Both of the two identified potential sources for Pb were situated in close proximity to Fanjiatun Town. The diffusion patterns for Hg and Cd were complex, particularly for the latter, of which the potential sources were scattered in multiple places. ③ The spatial lag model indicated that the distributions of As and Cd were mainly controlled by the intensive agriculture in peri-urban areas, among which As was related to the application of herbicide and Cd was related to the distribution of protected agriculture. Pb was mainly influenced by urbanization and industrialization, whereas Hg was found to be associated with the migration conditions of the soil. However, the regulating function provided by either croplands or their nearby environment did not play an important role in determining the diffusion patterns of heavy metals. The present study enriches the theory and methods for the spatial analysis of cropland heavy metal contamination and is significant for controlling contamination from the source in peri-urban croplands in the black soil region.

Cultivated land multifunctionality in undeveloped peri-urban agriculture areas in China: Implications for sustainable land management.

The spatial planning and sustainable management of peri-urban cultivated land are key aspects of national development in many countries because of the continuing expansion of urban areas and deterioration of agro-ecosystem services. Detailed geo-informational investigation of cultivated land multifunctionality and the spatial interactions and dependencies of these multiple functions is required to inform the currently weak theoretical framework of multifunctionality at the peri-urban scale. Accordingly, the objective of this study was to construct a comprehensive methodology to identify and evaluate cultivated land multifunctionality in a spatial context. Geochemical data were used to measure cultivated land multifunctionality. We evaluated two main functions-the productive function and the ecological function-of an undeveloped peri-urban agriculture (PUA) area in the northern fringe of Changchun City in the black-soil region of northeastern China. For the ecological utilization of PUA areas, tradeoff and synergy analyses of cultivated land multifunctionality and coordinated development under complex land-use patterns were measured using a bivariate local Moran's I method. Results reveal considerable spatial heterogeneity in the two functions, with hotspots or coldspots being found in the PUA area. The productive function presents a less pronounced decreasing trend along the rural-to-urban gradient compared with the ecological function. Tradeoffs and synergies between the productive function and the ecological function occur mainly in the northern (more rural) part of the PUA area, where the spatial spillover effect of urbanization is relatively low. Cultivated land functions are strongly affected by urbanization-induced land-use types, and the coordinated areas of the productive function are generally consistent with those of the ecological function. According to these results, we delineate nine zones of multifunctionality in the studied PUA area. Given the importance of harmonizing cultivated land multifunctionality to manage limited land resources in a sustainable way, application of the GIS- and geochemistry-based multifunctionality evaluation scheme proposed in this study should be used to guide peri-urban spatial planning and land-use management and inform the policy arena concerning the transition of land use in urban peripheries.

[Risk Zoning of Heavy Metals in a Peri-urban Area in the Black Soil Farmland Based on Agricultural Products].

Agricultural products are a primary pathway for humans to accumulate heavy metals (HMs) via the soil-crop system and should therefore should be included as a crucial part of the food security in our country. Given that previous studies on protection zoning for preventing farmland HM pollution rarely considered agricultural products as a basic element, this study attempted to establish a zoning system for farmland HM prevention, which was based on the perspective of agricultural product pollution. We subsequently took a representative peri-urban area in the black soil region, which was provided with a higher risk of being polluted, as an empirical case. The results indicated that:① the comprehensive quality index of agricultural products (IICQAP) was 1.09, illustrating only a mild HM pollution, with Pb and Ni having the highest accumulation levels; ② the human health risk index (QHI) was 0.61, showing no risk for human health; and ③ the designed zoning method revealed 89.45% of the farmlands to be risk-free at the moment and 10.55% of the farmlands to be under low risk of HM pollution in agricultural products. According to the zoning results, we suggested prioritized protection and an early-warning strategy, respectively, and further recommended prevention methods such as accumulation intervention, crop restructuring, and in-situ passivation. The results served to enrich the theoretical basis for preventing farmland HM pollution, to reinforce the management standards for agricultural products in the black soil region, and also to build a differentiated urban-rural farmland protection system.

Reclamation of Cultivated Land Reserves in Northeast China: Indigenous Ecological Insecurity Underlying National Food Security.

The competition for land resources created by the need for food security and ecological security is intensifying globally. To resolve the issue of land scarcity in agriculture following rapid urbanization, China implemented its requisition-compensation balance policy of cultivated lands in 1997, the introduction of which consumed numerous areas of land, such as river shoal and bare land, through reclamation. Moreover, these reclaimed and newly cultivated lands were mainly distributed in the northern part of China. Most previous studies of this subject have only examined the overall balance of cultivated lands in well-developed regions, and there is a lack of knowledge about the indigenous gains and losses before and after reclamation in important areas such as northeast China. Therefore, this study selected two representative county-level units in northeast China as the study area to analyze the conversion of cultivated land reserves during 1996-2015, evaluate the performance of reclaimed cultivated lands in terms of quality and productivity and calculate reclamation-induced changes in ecosystem service value. The results indicated that by 2015 only 16.02% of the original cultivated land reserves remained unconverted; nearly 60% were reclaimed as cultivated lands and over 20% were converted to other land resources. River shoal and ruderal land were the primary resources for cultivated lands compensation, and marsh, bare land and saline-alkaline land were found to be converted the most thoroughly. The gain of 23018.55 ha reclaimed cultivated lands were of relatively inferior quality and lower productivity, contributing approximately 4.32% of total grain output. However, this modest gain was at the expense of a 768.03 million yuan ecosystem services loss, with regulating services and supporting services being undermined the most. We argue that even if northeast China continues to shoulder the responsibility of compensating for a majority of cultivated land losses, it still needs to carefully process reclamation and introduce practical measures to protect indigenous ecosystems, in order to better serve the local residents and ensure prolonged food security with sustainability.