Received Nov 15; Accepted Feb 8. To view a copy of this license, visit http: However, few studies have focused on determining when anthropogenic influences on wetland began through sedimentary archives. To fill this critical gap in our knowledge, combustion sources and emission intensities, reconstructed via black carbon BC and polycyclic aromatic hydrocarbons PAHs were analyzed in two wetlands in the Sanjiang Plain in Northeast China. By combining previous sedimentary and archaeological studies, we attempt to date the beginning of intensive anthropogenic influences on the Sanjiang Plain.
Our results showed that BC deposition fluxes increased from 0. An upward trend was apparent during the last years. Before cal yr BP, human activities were minor, such that the wetland ecosystem in the Sanjiang Plain before this period may represent the reference conditions that for the recovery of these wetlands.
As the human population increased after cal yr BP, combustion sources changed and residential areas became a major source of BC and PAHs.
In this way, the wetland ecosystem gradually became more heavily influenced by human activities. The historical conditions of an ecosystem that have been influenced by subsequent human activities—and the remaining information associated with these ecosystems—can be used to inform modern ecosystem management and restoration approaches 1.
Paleoenvironmental records can be used to reconstruct and understand the condition of these ecosystems e. Paleoenvironmental records provide a useful tool for identifying baseline conditions for ecosystem recovery. Identifying the period when human activities began to influence the ecosystem is the first step in determining the baseline conditions that are necessary for ecosystem restoration. The Sanjiang Plain, located in Northeast China, has records of human activity dating to the early Holocene epoch 4.
Human population in this area increased Heilongjiang Province from 20, in cal yr BP to 1. As the human population has grown, the influence of human activities on wetland ecosystems on the Sanjiang Plain has undoubtedly increased, presumably increasing the extent of wetland ecosystems that have been destroyed 7.
Thus, identifying the period when human activities began to influence wetland ecosystems of the Sanjiang Plain and reconstructing these baseline conditions using paleoenvironmental records is critical. Black carbon BC , which is produced by the incomplete combustion of fossil fuels or biomass, is widespread in the environment and influences biogeochemical processes in ecosystems 8.
Fossil fuel combustion emitted 4. As an important component of atmospheric aerosols, BC has an impact on global climate change 11 and on the transport of persistent organic pollutants POPs 12 , After being retained in the atmosphere for a few days 14 , BC is deposited in the landscape and can be stored in the soil carbon pool for several thousand years Previous studies have focused on investigating BC concentrations and historical deposition fluxes in forest soils 16 , marine sediments 17 , lake sediments 18 , and loess These studies have suggested that the historical trend of BC deposition fluxes is related to climate change 20 or the degree of BC produced by anthropogenic sources This approach therefore is suitable for reconstructing the historical intensity of combustion source emissions.
Thus, investigating historical fluctuations in BC deposition in wetland systems and the factors that influence these fluxes is critical. In addition, the climate of the Sanjiang Plain has changed dramatically during the Holocene epoch.
This climatic variability has likely affected the frequency and intensity of wildfires 24 and therefore may have influenced deposition fluxes of BC. Analyses of BC in wetland sediments can therefore be used to study the patterns and drivers of past combustion intensive i. Polycyclic aromatic hydrocarbons PAHs are organic pollutants prevalent in the sediments of freshwater environments PAHs are co-emitted with BC and are produced by similar historical combustion sources This relationship is a useful tool for diagnosing the sources of PAHs Once in the water-sediment system, PAHs can bind to suspended particulate matter and can be easily transported to surface sediments Based on the diagnostic ratios of PAHs in sedimentary archives, the sources of these combustion products can be identified, and the degree of influence of human activities on ecosystems can be evaluated.
In addition to identifying modern combustion sources, historical sources of PAHs have already been reconstructed in sedimentary environments successfully Therefore, these diagnostic ratios are suitable for investigating the historical types of combustion sources and can serve as indirect indicators for identifying the historical sources of combustion in wetland sediments. We used these data to reconstruct variation in combustion emissions by BC deposition fluxes and diagnose historical types of combustion sources using the diagnostic ratios of PAHs during the Holocene epoch.
Based on these results, we assessed the degree to which historical human activities have influenced BC and PAH deposition in wetland ecosystems of the Sanjiang Plain. By combining our data with previous sedimentary studies from this region and historical documents from the Heilongjiang Province, we aimed to determine the period when human activities began to influence wetland ecosystems in the Sanjiang Plain.
The identification of this period will allow the characterization of the baseline conditions necessary for future wetland conservation practices. To compare the HXZ wetland with the DFH wetland, which only extends to cal yr BP, we chose the last 10, years to examine the historical trend in black carbon and the late Holocene epoch last years for determining the types of combustion sources in this study.
The sedimentary rates obtained by the age-depth model were similar in different sections of the two profiles: Mean accumulation rate in the DFH profile was 2. In the DFH profile, the dry bulk density in surface sediments was 0. This value increased with increasing depth, reaching a stable value of approximately 1. The dry bulk density in the HXZ profile increased from 0.