Wetland Cores Research Articles

Pre-hispanic wetland irrigation and metallurgy in the South Andean Altiplano (Intersalar Region, Bolivia, XIVth and XVth century CE)

The high-altitude Andean Altiplano has been subject to abrupt climate changes during the Holocene. The resulting impact on the hydrological cycle has obliged ancient societies to adapt and develop strategies to face droughts and sustain agropastoral activities. Here, we present the results of archaeological prospections together with the biogeochemical characterization of a well-dated core collected at Saitoco wetland in the arid southern Altiplano (Intersalar Region, Bolivia). Archaeological survey allowed the mapping of a network of channels collecting water from the surrounding mountains to the wetland, and the presence of small copper mines and metallurgical installations. Traces and major element concentrations and accumulation rates, together with elemental and isotopic characterization of organic matter (OM) (i.e., Corg and δ13Corg) in the wetland core have been used to document the evolution of the landscape in relation to climatic and anthropogenic pressure. While OM, bromine (Br), selenium (Se) and mercury (Hg) data were used to assess the variability of precipitations during the Late Holocene (4.2 ka BP to the present), local and regional mining activities have been reconstructed through the variations of lead (Pb), copper (Cu), and antimony (Sb). Our results show an abrupt change in OM composition during the 14th and 15th century CE, characterized by an abrupt shift in δ13Corg synchronous with a rise in Br, Se and Hg, testifying for the waterlogging of the wetland during a known arid period in the region. This change is attributed to anthropogenic transformation of the landscape through the irrigation of the wetland by channeling streams from the surrounding mountains. At the same time, a mining pollution signal was recorded supporting local Cu mining and metallurgy. The mining signal then reached its maximum values during the Inca and Colonial periods, which matches with reported enhanced mining activities in the region. From the colonial era onward, the wetland progressively dried up, likely resulting from the abandonment of the site. Through the combination of a biogeochemical record and archaeological prospections, this study provides evidences that societies of the arid Intersalar region have transformed their landscape and developed wetland irrigation and mining during the arid 14th and 15th century CE Period.

Modelling hydrological strength and alteration in moribund deltaic India.

The Ganga-Brahmaputra moribund deltaic floodplain region hosted many socio-ecologically precious freshwater wetland ecosystems experiencing hydrological alteration. The present study aimed to model hydrological strength (HS) to show the spatial difference and account for the degree and direction of hydrological alteration of Indian moribund deltaic wetland in three phases e.g. (1) phase I (1988-1997), (2) phase II (1998-2007) and phase III (2008-2017). Three key hydrological parameters, such as Water Presence Frequency (WPF), water depth, and hydro-period were considered for hydrological strength modelling using two ensemble Machine Learning (ML) techniques (Random Forest (RF) and XGBoost). Image algebra was employed for phasal change detection. Hydrological strength models show that around 75% of the wetland area was lost in-between phases I to III and the loss was found more intensive in moderate and weak HS zones. Existing wetland shows a clear spatial difference of HS between wetland core and periphery and river linked and delinked or not linked wetlands. Regarding the suitability of the ML models, both are acceptable, however, the XGBoost outperformed in reference to applied 15 statistical validation techniques and field evidence. HS models based on change detection clarified that more than 22% and 55% of the weak HS zone in phases II and III respectively were turned into non-wetland. The degree of alteration revealed that about 40% of wetland areas experienced a negative alteration during phases I to II, and this proportion increased to 63% in between phases II to III. Since the study figured out the spatial nature of HS, degree and direction of alteration at a spatial scale, these findings would be instrumental for adopting rational planning towards wetland conservation and restoration.

Early onset of summer monsoon during the Mystery Interval (17.5–14.5 ka BP) in the East Asian Summer Monsoon area: Evidence from leaf alkane δ2H

Exploring the seasonal atmospheric processes involved with hydroclimate changes of the East Asian Summer Monsoon (EASM) during the Mystery Interval (MI, 17.5–14.5 ka BP) will enhance understanding of the EASM climate system. Here we report on the δ2H values of leaf wax n-alkanes (δ2Halk) in a wetland core retrieved from southern China. These values are relatively negative during the MI, contrasting to positive excursion recorded by stalagmite δ18O in nearby caves during the same period. Considering the overlap of the primary synthesis time of leaf waxes in deciduous woody plants and periods of precipitation δ2H alteration in the EASM (late spring to early summer), we interpret the relatively negative signal of δ2Halk in the wetland core as the early onset of summer rainfall during the MI. The early onset of summer rainfall was likely due to the early northeastward shifting of the Western Pacific subtropical high due to the low land-sea thermogradient between the Qinghai-Tibet Plateau and the West Pacific Ocean.

The Project ArAGATS Kasakh Valley Archaeological Survey, Armenia: Report of the 2014–2017 Seasons

During four field seasons spanning 2014 through 2017, Project ArAGATS (Archaeology and Geography of Ancient Transcaucasian Societies) expanded our long-term research on the origins and development of complex political systems in the South Caucasus with a comprehensive study of the upper Kasakh River valley in north-central Armenia. The Kasakh Valley Archaeological Survey employed both systematic transect survey of 43 km2 and extensive satellite- and drone-based reconnaissance to accommodate the complex topography of the Lesser Caucasus and the impacts of Soviet-era land amelioration. Though our survey was animated by questions related to the chronology and distribution of Bronze and Iron Age fortifications and cemeteries, we also recorded Paleolithic sites stretching back to the earliest human settlement of the Caucasus, Early Bronze Age surface finds, and historic landscape modifications. Concurrent to the survey, members of the ArAGATS team carried out test excavations at select settlement sites and associated burials, and a series of wetland core extractions, with the goals of affirming site occupation sequences and setting them within their environmental context. This report provides an overview of the results of these multidisciplinary activities.1

Spatial and Temporal Variations of Nitrogen and Phosphorus in Surface Water and Groundwater of Mudong River Watershed in Huixian Karst Wetland, Southwest China

When considering the factors affecting the spatial and temporal variation of nitrogen and phosphorus in karst watersheds, the unique karst hydrogeology as an internal influencing factor cannot be ignored, as well as natural factors such as meteorological hydrology and external factors such as human activities. A watershed-scale field investigation was completed to statistically analyze spatial and temporal dynamics of nitrogen and phosphorus through the regular monitoring and collection of surface water and shallow groundwater in the agricultural-dominated Mudong River watershed in the Huixian Karst Wetland over one year (May 2020 to April 2021). Our research found that non-point source pollution of nitrogen (84.5% of 239 samples TN > 1.0 mg/L) was more serious than phosphorus (7.5% of 239 samples TP > 0.2 mg/L) in the study area, and shallow groundwater nitrogen pollution (98.3% of 118 samples TN > 1.0 mg/L) was more serious than surface water (68.6% of 121 samples TN > 1.0 mg/L). In the three regions with different hydrodynamic features, the TN concentration was higher and dominated by NO3−-N in the river in the northern recharge area, while the concentrations of TN and TP were the highest in shallow groundwater wells in the central wetland core area and increased along the surface water flow direction in the western discharge area. This research will help improve the knowledge about the influence of karst hydrodynamic features on the spatial patterns of nitrogen and phosphorus in water, paying attention to the quality protection and security of water in karst areas with a fragile water ecological environment.

Predicting wetland area and water depth of Ganges moribund deltaic parts of India

Wetland area and depth of wetland in the moribund Ganges delta of India is simulated and predicted up to 2037. Normalized Difference Water Index (NDWI) map from 1987 to 2017 is used for predicting the same. Artificial Neural Network (ANN) based Cellular Automata (CA) simulation is used to predict wetland area and exponential adaptive smoothing and least square regression are used to predict wetland depth. The result shows 17–18% of wetland area may lose their existence in the upcoming two decades. Water depth of large wetlands area is likely to be reduced by 45–50% in both seasons and small fragmented marginal wetlands are going to be dried out in the next twenty years. Large wetland and wetland core area is safer than smaller and fringe wetland. Considering the socio-ecological importance policy should be taken and the result could help to define plan sustainably.

Natural archives of long-range transported contamination at the remote lake Letšeng-la Letsie, Maloti Mountains, Lesotho

Naturally accumulating archives, such as lake sediments and wetland peats, in remote areas may be used to identify the scale and rates of atmospherically deposited pollutant inputs to natural ecosystems. Co-located lake sediment and wetland cores were collected from Letšeng-la Letsie, a remote lake in the Maloti Mountains of southern Lesotho. The cores were radiometrically dated and analysed for a suite of contaminants including trace metals and metalloids (Hg, Pb, Cu, Ni, Zn, As), fly-ash particles, stable nitrogen isotopes, polycyclic aromatic hydrocarbons (PAHs) and persistent organic pollutants such as polychlorinated biphenyls (PCBs), polybrominated flame retardants (PBDEs) and hexachlorobenzene (HCB). While most trace metals showed no recent enrichment, mercury, fly-ash particles, high molecular weight PAHs and total PCBs showed low but increasing levels of contamination since c.1970, likely the result of long-range transport from coal combustion and other industrial sources in the Highveld region of South Africa. However, back-trajectory analysis revealed that atmospheric transport from this region to southern Lesotho is infrequent and the scale of contamination is low. To our knowledge, these data represent the first palaeolimnological records and the first trace contaminant data for Lesotho, and one of the first multi-pollutant historical records for southern Africa. They therefore provide a baseline for future regional assessments in the context of continued coal combustion in South Africa through to the mid-21st century.

Research On Wetland Ecological Planning Of Jiukenghe Reservoir In Zhaoqing

The article takes Zhaoqing Jiukenghe Reservoir as the research object. According to the land use planning of Zhaoqing City, the rural construction around the Jiukenghe Reservoir in Dinghu District of Zhaoqing and the development of the Jiulong Lake tourist area have caused potential pollution threats to the water source protection area. This paper mainly uses GIS ecological planning methods to study the analysis of wetland development potential of water sources, formulate wetland protection plans, delineate wetland core protected areas, restore wetland ecosystems, delineate ecological buffers, and cultivate wetland conservation forests. It also needs to control pollution sources in village construction and tourism practices, cultivate multi-level natural landscapes of aquatic plants, provide good habitats and breeding habitats for wild animals and plants, enhance water purification and water conservation functions, and create ecological landscapes in natural countryside.

Holocene climate dynamics derived from pollen record of Jiulongchi wetland in Fanjing Mountain, southwest China

An alpine wetland core was obtained to a depth of 4.0 m from the Fanjing Mountain in southwest China. Sections of the core were dated with 14C data obtained with high resolution mass spectrometry (AMS), and Holocene climate changes were inferred by categorizing predominant tree and fern vegetation identified from pollen and spore counts at various core depths. The temperature increased during 11.9–8.0 cal ka BP, and the warmest period was during 8.0–4.6 cal ka BP. Then, it gradually became cooler during the late Holocene. Our temperature estimates were in good agreement with the previous studies of the Holocene temperature in the Asian monsoon areas. There were two relatively wet periods of 10.7–8.0 cal ka BP and 4.6–2.6 cal ka BP. There was an asynchronous precipitation trend in the south, north and southwest China, which was probably due to the different monsoon impacts. In East Asian summer monsoon (EASM) area, the monsoon precipitation gradually transgressed northward during the early to middle Holocene and regressed southward during the late Holocene. Our results will be useful to improve the understanding of the coherent spatio-temporal patterns of climate evolution in EASM region in China.

Understand the resilience and regime shift of the wetland ecosystem after human disturbances

Wetland protection and restoration are important for human's sustainable development, and assess the resilience and regime shift of wetland ecosystem under human disturbances is necessary for this purpose. Geochemical records, including nitrogen (N), phosphorus (P), heavy metals and polycyclic aromatic hydrocarbons (PAHs) from seven wetland cores dated by 210Pb and 137Cs analysis were used to identify the historical background of human disturbances on wetlands in the Sanjiang Plain. We also carried out paleoecological analysis (including plant macrofossils and diatoms) in one core (Honghe wetland) to reconstruct the successions of wetland ecological communities. The resilience and regime shift of ecosystem were evaluated based on autocorrelation and the Sequential t-test analysis of regime-shifts algorithm. Our results show that enrichment factors (EFs) of N, P and heavy metals (Cu, Zn, Pb etc.), and the concentrations of PAHs experienced slight increases from the 1920s but dramatic increases from the late 1970s. The dominant species of plant community began to change from Drepanocladus aduncus to Carex lasiocarpa from the late 1970s, and the diatoms began to change from wet-indicator to dry-indicator species from the 1950s in Honghe wetland. The regime shift of the wetland ecosystem occurred around 1990 CE, which due to a drop in water level caused by human activities, such as wetland drainage for the reclamation and the excessive use of groundwater for irrigation purpose, rather than climate moisture variations. There is a time gap between the severe disturbances and regime shift due to the stronger resilience of wetland ecosystem. The ecological characteristics (e.g. water level, biological compositions, and EFs of nutrient elements and heavy metals) of Honghe wetland before the late 1970s (release phase) were used as reference conditions for wetland restoration.

Studies on pollen deposition pattern in relation to modern vegetation of flood prone region in Assam, India

This paper presents a palynological dataset on Pashumara Wetland and Ranga Reserve Forest to differentiate flooded and non–flooded area in relation to existing vegetation in Assam. Study reveals that the palynoassemblage in Pashumara Wetland is an admixture of arboreal local and extra–local taxa and not fully matches with present vegetation. The various pollen distributions were observed in continuation to study sites and confirmed that pollen deposition pattern in wetland depends on parent plant growth, flood activity and surrounding vegetation. Presence of broken pollen is indicative of long distance transportation under a fluvial environment. The palynoassemblage of Ranga Reserve Forest located in non–flooded area to display modern pollen and vegetation relationship and identification of local arboreal taxa in the region. The main forest elements include Syzigium, Lagerstroemia and Emblica in the palynoassemblage are suggestive of presence of tropical deciduous forest under warm and humid climate. Pollen clumps in the palynoassemblage signifies their local origin and entomophily. This generated palynodata could be precisely utilized to distinguish flooded and non–flooded area and to interpret palaeovegetation and past climate changes in relation to palaeoflood episodes by the analysis of wetland core from the region and to correlate other tropical flood prone region of the globe.

Holocene development of mountain wetlands within and outside of landslide in the Hachimantai volcanic group, northeastern Japan

In warm and humid, tectonically active regions like Japan, landslides are an important influence on the development of mountain wetlands, but data bearing upon the relationship of Quaternary landslides to wetland development are scarce. We used lithological analysis, 14C dating, tephra age data, and carbon contents of wetland cores to compare the evolution of four wetlands, one (the Oyachi wetland) within a landslide area transformed by mass movement and three (the Appi Highland wetlands) outside of a landslide area, in the heavy snowfall region of the Hachimantai Mountains of northeastern Japan. Evidence from the Oyachi wetland shows that its transition from peatland to forest was interrupted at about 5500 cal BP by slope movement leading to the development of a lake that was drained by streams at about 3300 cal BP, after which a peatland environment has persisted until the present. We suggest that the evolution of this type of wetland is primarily influenced by landslide movements and stream dissection rather than climate change. In the Appi Highland wetlands, peatlands appeared much later, around the time of the To-a tephra fall in 915 AD, during the Medieval Warm Period, and have persisted with little change until the present. We suggest that the development of mountain wetlands outside of landslide areas is primarily related to climate changes rather than topographic changes. Sediment analyses of mountain wetlands within landslide areas may be useful for tracing the development of Quaternary landslides and subsequent topographic changes that may have implications for biodiversity in mountainous regions.

Evolution of the alluvial fans of the Luo River in the Weihe Basin, central China, controlled by faulting and climate change - A reevaluation of the paleogeographical setting of Dali Man site

The Luo River is located in the southern part of the Chinese Loess Plateau and the northern part of the Weihe Basin, in Central China. In the basin it flows proximal to the site of the Luyang Wetland core, which is an important archive of climate change over the past 1 Myr in this region. In this paper, the contribution of the Luo River to the sedimentary record is analyzed by reconstructing the evolution of this river during the Middle to Late Pleistocene. It is argued that an alluvial fan of the Luo River has contributed to the sedimentary archive until approximately 200–240 ka. From this moment onwards, the fan became incised and terraces began to form. The formation of a new alluvial fan further downstream led to the disconnection of the Luo River from the Luyang Wetland core site. We propose that this series of events was caused by the displacement of an intra-basinal fault and the resultant faulting-forced folding, which caused increased relative subsidence, and thus increased sedimentation rates at the core site. Therefore, a complete sediment record in the ‘Luyang Wetland’ was preserved, despite the disconnection from the Luo River.The chronology of the fans and terraces was established using existing age control (U-series, ESR, OSL, pIRIR290 and magnetic susceptibility correlation), and through correlation of the loess-paleosol cover to marine isotope stages. Based on sedimentological characteristics of the fluvial sequence, we suggest that incision of the Luo River occurred in two steps. Small incisions took place at transitions to interglacials and the main incision phases occur at the transition from an interglacial to glacial climate.Due to the incision, basal parts of the oldest Luo River alluvial fan are exposed, and it is in one of these exposures that the famous Dali Man skull was retrieved. This study shows that the Dali Man did not live on a river terrace as previously thought, but on an aggrading alluvial fan, during wet, glacial conditions.

Kinetics of heterotrophic biomass and storage mechanism in wetland cores measured by respirometry

Although oxygen uptake rate has been widely used in activated sludge for measuring kinetic and stoichiometric parameters or for wastewater characterization, its application in constructed wetlands (CWs) cores has been recently proposed. The aim of this research is to estimate the kinetic and stoichiometric parameters of the heterotrophic biomass in CW cores. Respirometric tests were carried out with pure carbonaceous substrate and real wastewater. Endogenous respiration was about 2 gO2 m(-3) h(-1) (per unit of bed volume), while the kinetic parameters obtained for COD oxidation were very high (maximum rate per unit of bed volume of 10.7-26.8 gCOD m(-3) h(-1)) which indicates high biodegradation potential in fully aerobic environment. Regarding to stoichiometric parameter, the maximum growth yield, Y(H), was 0.56-0.59 mgCOD/mgCOD, while the storage yield, Y(STO), was 0.75-0.77 mgCOD/mgCOD. The storage mechanism was observed in CW cores during COD oxidation, which leads to the transformation of the external soluble substrate in internal storage products, probably as response to intermittent loads applied in CW systems, transient concentrations of readily biodegradable substrate and alternance of feast/famine periods.

Simple methods for evaluating accommodation space formation in coastal wetlands

Land-surface subsidence and erosion are the principal processes that form accommodation space in interior coastal wetlands when they are converted to open water. The relative contribution of subsidence and erosion to wetland loss can be estimated by comparing elevations and vertical offsets of stratigraphic contacts that are correlated between adjacent sediment cores. Accommodation-space measurements assume that wetland-sediment thicknesses and the elevation of stratigraphic contacts were originally nearly uniform over short horizontal distances (tens to hundreds of meters). The accommodation space attributable to erosion equals the difference in wetland-sediment thickness between wetland cores and adjacent open-water cores taken at formerly emergent wetland sites. The accommodation space attributable to subsidence equals the elevation difference of a stratigraphic marker correlated between the two cores using the wetland core as the reference standard. Together, subsidence plus erosion at an open-water core location equals the accommodation space created by land loss, which is the difference between the adjacent emergent wetland elevation and the existing water depth.

Habitat and hydrological–hydrochemical characteristics of the Agras wetland (Northern Greece)

The Agras wetland located in the Prefecture of Pella, Macedonia, North Greece, is a semi-artificial wetland that was created as a reservoir by the Public Power Corporation (PPC) in 1950. The wetland quickly turned into an important natural resource for the whole area. Partly due to European legislation (Birds Directive 79/409/EEC, Habitats Directive 92/43/EEC and Water Framework Directive 2000/60/EEC) and partly to its recognized environmental and local economic value, the state designated the wetland as a Special Protection Area (SPA) and proposed its inclusion into the European Natura 2000 Network (Limni Agra, GR1240004). The aim of this paper was to study and relate the important biotic and abiotic factors of the wetland, and to assess the human impact on its functions, through the establishment and operation of a baseline monitoring system. The ecological research shows that the wetland's core area comprises an impressive mosaic of eight land-use categories and seven natural vegetation types. Notable differences in spatial distribution of specific hydrochemical parameters were observed. Water level fluctuation along the wetland indicates a unique evolutionary pattern that resembles neither a lake nor a river system. Overall, a fair relationship between hydrochemistry, hydrodynamics, habitats and human interventions is substantiated.

Reconstructing high-magnitude/low-frequency landslide events based on soil redistribution modelling and a Late-Holocene sediment record from New Zealand

A sediment record is used, in combination with shallow landslide soil redistribution and sediment-yield modelling, to reconstruct the incidence of high-magnitude/low-frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part. Eleven sediment cores were obtained from a dune-impounded wetland at Te Henga, west Auckland, northern New Zealand. Sediment stratigraphy and chronology were interpreted by radiocarbon dating, foraminiferal analysis, and provisional tephrochronology. Gradual impoundment of the wetland began c. 6000 cal yr BP, coinciding with the start of a gentle sea-level fall, but complete damming and initial sedimentation did not begin until c. 1000 cal yr BP. After damming, four well-defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores. For interpreting the sediment pulses, a physically based landslide model was used to determine spatially distributed relative landslide hazard, applicable at the catchment scale. An empirical landslide-soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material, sediment delivery ratio and the impact on total catchment sediment yield. Sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back-analysis of modelled sediment yield output. In general, at least four major high-magnitude landslide events, both natural and intensified by forest clearance activities, occurred in the catchment upstream of Te Henga Wetland during the last c. 1000 years. The spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard. The magnitude of the sediment pulses represented in the wetland can be back-calculated to critical rainfall thresholds representing a shallow landslide model scenario.