nasa-gesdisc/es-publications-researchareas huggingface dataset:
Characteristics of shoreline changes around the South China Sea from (2022)

As one of the most sensitive factors in the sealand interaction zone, the shoreline is significantly influenced by natural processes and anthropogenic activities. Monitoring long-term shoreline changes offers a basis for the integrated management and protection of coastal zones. The spatiotemporal distribution and the utilization types of shorelines had changed a lot, along with the advancement of the socioeconomics of the countries around the South China Sea (SCS) since 1980. However, the changes in shoreline characteristics for a long time around the whole SCS under anthropogenic influence remain uncertain. Using Landsat and high-resolution satellite images, this study monitored the changes in the spatial location and type of shorelines around the SCS from 1980 to 2020. Additionally, the possible reasons for the shoreline changes around the SCS were analyzed. The results showed the following: 1) the length of shorelines around the SCS maintained growth, especially in the 1990s, which increased by 734.8 km, from 28,243.8 km (1990) to 28,978.6 km (2000). 2) The proportion of natural shorelines around the SCS decreased from 92.4% to 73.3% during the past 40 years. Bedrock and mangrove shorelines disappeared most sharply by 34.2% and 21.6%, respectively. The increase of artificial shorelines was mostly driven by the expansion of constructed and aquaculture dikes. 3) The spatial location changes of most artificial shorelines can be attributed to seaward advancement, with an average advancing speed of 7.98 m/year. Of the natural shorelines, 58.4% changed in terms of their location (30.4% advancement and 28.0% retreat). Most natural shorelines around the SCS were threatened by erosion, but the extent of which was largely determined by the shorelines own stability, with less influence from the surrounding environment. Artificialization was the most prominent feature of shorelines around the SCS over the past 40 years, which was closely related to the original types of shorelines and the socioeconomic conditions of the area where they are located, and often accompanied by dramatic changes in shoreline morphology and spatial location. In addition, human interventions were not only the dominant factor in shoreline artificialization but also a major driver of natural shoreline protection.

Research areas: Land Surface/Agriculture Indicators
Long-Term Series of Chlorophyll-a Concentration in Brazilian Semiarid Lakes from Modis Imagery (2022)

By monitoring the chlorophyll a concentration (chla), it is possible to keep track of the eutrophication status of a lake and to describe the temporal dynamics of the phytoplankton biomass. Such monitoring must be both extensive and intensive to account for the short- and long-term biomass variations. This may be achieved by the remote estimation of chla through an orbital sensor with high temporal resolution. In this study, we used MODIS imagery to produce 21-year time series of chla for three strategic lakes of the Brazilian semi-arid region: Eng. Armando Ribeiro Goncalves, Castanhao, and Oros. We used data collected in 13 lakes of the region to test new and published regression models for chla estimation. The selected model was validated and applied to daily MODIS images for the three largest lakes. The resulting chla time series revealed that the temporal dynamics of the phytoplankton biomass is associated with the hydraulic regime of the lakes, with chla plummeting upon intense water renewal and keeping high during persistent dry periods. The intense rainy season of 2004 reduced the phytoplankton biomass and its effects even extended to the subsequent years. Our results encourage the exploration of the MODIS archived imagery in limnological studies.

Research areas: Water Quality, Ecosystems
Identifying ENSO-related interannual and decadal variability on terrestrial water storage (2021)

We apply two statistical techniques to satellite measurements to identify a relationship between terrestrial water storage (TWS) and El Nino-Southern Oscillation (ENSO). First, we modified and used the least-squares regression of a previous study using longer records. Second, we applied a cyclostationary empirical orthogonal function analysis (CSEOF). Although the CSEOF technique is distinct from the least-squares regression in that it does not consider proxies, each method produces two modes (decadal and interannual), showing consistency with each technique in spatial pattern and its evolution amplitudes. We also compared the results obtained by the two methods for thirty watersheds, of which five watersheds were compared with previous studies. The combination of the two modes explains the total variance in most watersheds showing the role that interannual and decadal ENSO-related signals in understanding terrestrial water storage variability. The results show that the decadal mode, along with the interannual mode, also plays an important role in describing the local TWS.

Research areas: Land Surface/Agriculture Indicators
The underappreciated role of anthropogenic sources in atmospheric soluble iron flux to the Southern Ocean (2022)

The atmospheric deposition of soluble (bioaccessible) iron enhances ocean primary productivity and subsequent atmospheric CO2 sequestration in iron-limited ocean basins, especially the Southern Ocean. While anthropogenic sources have been recently suggested to be important in some northern hemisphere oceans, the role in the Southern Ocean remains ambiguous. By comparing multiple model simulations with the new aircraft observations for anthropogenic iron, we show that anthropogenic soluble iron deposition flux to the Southern Ocean could be underestimated by more than a factor of ten in previous modeling estimates. Our improved estimate for the anthropogenic iron budget enhances its contribution on the soluble iron deposition in the Southern Ocean from about 10% to 60%, implying a dominant role of anthropogenic sources. We predict that anthropogenic soluble iron deposition in the Southern Ocean is reduced substantially (3090%) by the year 2100, and plays a major role in the future evolution of atmospheric soluble iron inputs to the Southern Ocean.

Research areas: Ecosystems
Controlling factors and impacts of river-borne neodymium isotope signatures and rare earth element concentrations supplied to the Canadian Arctic … (2022)

Determining the factors controlling the neodymium (Nd) isotopic compositions (expressed as Nd) and rare earth element (REE) concentrations of rivers is imperative to improve our understanding of the distribution of these water mass tracers in the ocean. Here we present the first measurements of <0.45 m-filtrate REE concentrations (i.e., the concentration of truly dissolved, nano-particulate and colloidal REEs passing through a 0.45 m filter, hereafter referred to as dissolved) and Nd in rivers draining into the Canadian Arctic Archipelago (CAA). Results show a large variation in both REE concentrations (Nd=[8;37,260] pmol/kg) and Nd ([32.1;15.1]) in the thirteen rivers sampled. Dissolved REE concentrations increase with increasing fractions of metamorphic rocks and ice cover in the rivers' watersheds, while Nd and PAAS-normalized REE patterns are inherited from the watershed's bedrock lithology. The four rivers draining watersheds composed of Precambrian metamorphic rocks exhibit the highest REE concentrations, the least radiogenic Nd, and shale-normalized patterns enriched in light REEs. The remaining nine rivers drain mainly or exclusively sedimentary bedrock and have lower REE concentrations, more radiogenic Nd and generally show heavy REE enrichment, with variable negative cerium (Ce) anomalies. The presence of ice sheets in the drainage area, and the ionic strength, pH, and dissolved organic carbon concentration of river water are the main factors determining riverine dissolved REE concentrations by controlling the formation and stabilization of colloids. We estimate a flow of dissolved Nd transported by Arctic rivers discharging into the CAA equivalent to the Nd flux of seawater entering the CAA. Depending on the percentage of Nd removal during mixing with seawater, the impact of river water on the Nd of seawater exiting the CAA could be modest (if 90% removal) or more significant (if 90% removal). This riverine contribution could potentially impart a climate-sensitive Nd signature to the seawater reaching Baffin Bay, with possible implications for the use of Nd in paleoceanographic reconstructions of water mass distribution.

Research areas: Ecosystems
Multi-tracer (δ18O, δD, 3H, CFCs and SF6) investigation of groundwater recharge and apparent age at the Bamenda Highlands along the Cameroon volcanic line (2020)

The Bamenda Highlands contains numerous dilute and soda springs of unknown hydrological provenance. These dilute springs are a vital source of drinking water to the inhabitants. As a contribution to water management, this study investigated the spring water recharge, residence time and sub-surface circulation using 18O, D, 3H, CFCs, SF6 and TDS. A plot of both water types along the local meteoric water line indicated the meteoric origin and rapid recharge following precipitation. Dilute springs with a 18O altitude effect of 0.27/100 m suggested recharge at different elevations. The CFC-12, CFC-11 and CFC-113 dating (complemented by 3H) showed reasonable young apparent ages of dilute springs ranging from 21 to > 52 (mean/median of 25) years and old soda springs (> 52 years). SF6 concentrations in dilute springs revealed exceptionally young ages relative to CFCs modelled ages suggesting a terrigenous enrichment of the former. Thus, groundwater dating with SF6 is unreliable in the area. Besides the old apparent ages of soda springs, their highly depleted 18O and high TDS (mean of 1396 mg/l) indicated palaeo-recharge and high waterrock interaction, respectively. In contrast, the low TDS of dilute springs (

Research areas: Land Surface/Agriculture Indicators
Importance of nutrient loading and irrigation in gross primary productivity trends in India (2020)

Investigating the effects of various environmental factors on gross primary productivity (GPP) is crucial for quantifying the carbon exchange between the atmosphere and the terrestrial vegetation for managing climate change. Although it is well known that various natural and anthropogenic factors (e.g., climate change, agricultural activities, and atmospheric CO2 concentration change) can alter GPP, their relative influences are not clearly understood in every region. In this study, we consider several factors and investigate their roles in increasing the GPP in large parts of India. We considered about three decades (1980s to late 2000s) of GPP data and use a regression based systematic approach to find out the most likely cause explaining the trends in India. This study suggests that the common suspects like CO2 and climate may have limited influence on the GPP trends in India when compared to anthropogenic influences. Our results instead support the notion that GPP trends in India are mainly shaped by agricultural activities through nutrient loading (R2=0.68) and irrigation (R2=0.1). Overall, our study reveals the potential of agricultural activities in altering the carbon budget of a region.

Research areas: Ecosystems
Advances in amazonian peatland discrimination with multi-temporal PALSAR Refines estimates of Peatland distribution, C stocks and deforestation (2021)

There is a data gap in our current knowledge of the geospatial distribution, type and extent of C rich peatlands across the globe. The Pastaza Maranon Foreland Basin (PMFB), within the Peruvian Amazon, is known to store large amounts of peat, but the remoteness of the region makes field data collection and mapping the distribution of peatland ecotypes challenging. Here we review methods for developing high accuracy peatland maps for the PMFB using a combination of multi-temporal synthetic aperture radar (SAR) and optical remote sensing in a machine learning classifier. The new map produced has 95% overall accuracy with low errors of commission (16%) and errors of omission (015%) for individual peatland classes. We attribute this improvement in map accuracy over previous maps of the region to the inclusion of high and low water season SAR images which provides information about seasonal hydrological dynamics. The new multi-date map showed an increase in area of more than 200% for pole forest peatland (6% error) compared to previous maps, which had high errors for that ecotype (2036%). Likewise, estimates of C stocks were 35% greater than previously reported (3.238 Pg in
              Draper et al. (2014)
              to 4.360 Pg in our study). Most of the increase is attributed to pole forest peatland which contributed 58% (2.551 Pg) of total C, followed by palm swamp (34%, 1.476 Pg). In an assessment of deforestation from 2010 to 2018 in the PMFB, we found 89% of the deforestation was in seasonally flooded forest and 43% of deforestation was occurring within 1 km of a river or road. Peatlands were found the least affected by deforestation and there was not a noticeable trend over time. With development of improved transportation routes and population pressures, future land use change is likely to put South American tropical peatlands at risk, making continued monitoring a necessity. Accurate mapping of peatland ecotypes with high resolution (<30 m) sensors linked with field data are needed to reduce uncertainties in estimates of the distribution of C stocks, and to aid in deforestation monitoring.

Research areas: Habitat Conversion/Fragmentation
Change in carbon flux (1960–2015) of the Red River (Vietnam) (2018)

Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 19602015. The results show that total carbon flux of the Red River averaged 2555  639 kton C year1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year1 during the 1960s to 1372 kton C year1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.

Research areas: Greenhouse Gases, Ecosystems
Satellite observed recent rising water levels of global lakes and reservoirs (2022)

Abstract
            
              Monitoring global lake/reservoir water level changes is needed to understand the global water cycle and investigate its potential drivers. The existing global water level products only cover lakes/reservoirs with large sizes (>100 km
              2
              ). Here, Ice, Cloud, and land Elevation Satellite (ICESat) and ICESat-2 altimetry data with small footprints are employed to examine global water level changes for 22 008 lakes/reservoirs greater than 1 km
              2
              . We report that 77.56% of them exhibited rising water levels over 20032021. Across the globe, 78.84% of lakes exhibit a rising water level, while the proportion for reservoirs is only 56.01%. Global lake/reservoir is estimated to experience a median water level change rate of +0.02  0.02 m yr
              1
              over 20032021, and lakes have a larger water level rise (+0.02  0.02 m yr
              1
              ) than reservoirs (+0.008  0.14 m yr
              1
              ). We detect large-scale rising water levels in the Tibetan Plateau, the Mississippi River basin, and high-latitude regions of the Northern Hemisphere. Our calculation also suggests a negative relationship between the percentage of water level rise in lakes/reservoirs and population density for global river basins (
              r
              = 0.41,
              p
              -value < 0.05) and 11 hotspots (
              r
              = 0.48,
              p
              -value < 0.05). Our result suggests that inland water level has tended to rise in recent years under natural processes while human activities (i.e. with higher population density) can balance the water level rise via reservoir regulation. We find the existing datasets underestimated global water level rise, which may be caused by the exclusion of numerous small lakes/reservoirs. Our estimated global water level change rates (that include numerous small lakes with areas of 110 km
              2
              ) can improve the understanding of global hydrological cycle and water resource management under the double pressure of climate warming and human activities.

Research areas: Land Surface/Agriculture Indicators
Can multi-strategy management stabilize nitrate leaching under increasing rainfall? (2019)

Abstract
            
              The increased spring rainfall intensity and amounts observed recently in the US Midwest poses additional risk of nitrate (NO
              3
              ) leaching from cropland, and contamination of surface and subsurface freshwater bodies. Several individual strategies can reduce NO
              3
              loading to freshwater ecosystems (i.e. optimize N fertilizer applications, planting cover crops, retention of active cycling N), but the potential for synergistic interactions among N management practices has not been fully examined. We applied portfolio effect (PE) theory, a concept originally developed for financial asset management, to test whether implementing multiple N management practices simultaneously produces more stable NO
              3
              leaching mitigation outcomes than what would be predicted from implementing each practice independently. We analyzed simulated data generated using a validated process-based cropping system model (APSIM) that covers a range of soils, weather conditions, and management practices. Results indicated that individual management practices alone explained little of the variation in drainage NO
              3
              loads but were more influential in the amount of residual soil NO
              3
              at crop harvest. Despite this, we observed a general stabilizing effect from adopting well-designed multi-strategy approaches for both NO
              3
              loads and soil NO
              3
              at harvest, which became more pronounced in years with high spring rainfall. We use the PE principle to design multi-strategy management to reduce and stabilize NO
              3
              leaching, which resulted in 9.6% greater yields, 15% less NO
              3
              load, and 61% less soil NO
              3
              at harvest than the baseline typical management. Our results make the case for applying the PE to adapt NO
              3
              leaching mitigation to increased climate variability and change, and guide policy action and on-the-ground implementation.

Research areas: Water Quality
Elevated radium levels in Nubian Aquifer groundwater of Northeastern Africa (2021)

The Nubian Sandstone Aquifer System in Northeast Africa and the Middle East is a huge water resource of inestimable value to the population. However, natural radioactivity impairs groundwater quality throughout the aquifer posing a radiological health risk to millions of people. Here we present measurements of radium isotopes in Nubian Aquifer groundwater from population centers in the Western Desert of Egypt. Groundwater has 226Ra and 228Ra activities ranging from 0.01 to 2.11 and 0.03 to 2.31 Bq/L, respectively. Most activities (combined 226Ra + 228Ra) exceed U.S. EPA drinking water standards. The estimated annual radiation doses associated with ingestion of water having the highest measured Ra activities are up to 138 and 14 times the WHO-recommended maxima for infants and adults, respectively. Dissolved Ra activities are positively correlated with barium and negatively correlated with sulfate, while barite is approximately saturated. In contrast, Ra is uncorrelated with salinity. These observations indicate the dominant geochemical mechanisms controlling dissolved Ra activity may be barite precipitation and sulfate reduction, along with input from alpha-recoil and dissolution of aquifer minerals and loss by radioactive decay. Radium mitigation measures should be adopted for water quality management where Nubian Aquifer groundwater is produced for agricultural and domestic consumption.

Research areas: Water Quality
New insights on the classification of major Amazonian river water types (2020)

Traditional water classifications for Amazonian rivers are based mainly on optical characteristics that do not fully capture their complexity. Today, an increasing amount of hydrochemical data indicates that the chemical composition of Amazonian rivers varies much more than this simple classification indicates. Revising river classification based on hydrochemical properties is proposed here. In this first comprehensive review of Amazonian river chemistry, we synthesized critical information from 168 scientific publications and distinguish unusual white, black, and clearwater rivers. It is shown the distribution of such rivers across the basin and the limitations of using generalized designations for river typologies. For example, some optically clearwater rivers draining carboniferous stripes have chemical properties similar to whitewater rivers, regardless of their high transparency. Furthermore, a clear or blackwater stream that becomes turbid because of soil erosion does not become a whitewater stream. Its hydrochemical parameters of acidity and nutrient poverty depend on the geology of the catchment area and remain relatively unaffected. These insights into Amazonian river classification provide a new understanding of their baseline limnological conditions. They have implications for sustainable management of freshwater systems and for monitoring potential impacts of large development projects and climate change on the Amazonian aquatic systems.

Research areas: Ecosystems