Quantifying climate variability and regional anthropogenic influence on vegetation dynamics in northwest India.

To explore the spatio-temporal dynamics and mechanisms underlying vegetation cover in Haryana State, India, and implications thereof, we obtained MODIS EVI imagery together with CHIRPS rainfall and MODIS LST at annual, seasonal and monthly scales for the period spanning 2000 to 2022. Additionally, MODIS Potential Evapotranspiration (PET), Ground Water Storage (GWS), Soil Moisture (SM) and nighttime light datasets were compiled to explore their spatial relationships with vegetation and other selected environmental parameters. Non-parametric statistics were applied to estimate the magnitude of trends, along with correlation and residual trend analysis to quantify the relative influence of Climate Change (CC) and Human Activities (HA) on vegetation dynamics using Google Earth Engine algorithms. The study reveals regional contrasts in trends that are evidently related to elevation. An annual increasing trend in rainfall (21.3 mm/decade, p < 0.05), together with augmented vegetation cover and slightly cooler (-0.07 °C/decade) LST is revealed in the high-elevation areas. Meanwhile, LST in the plain regions exhibit a warming trend (0.02 °C/decade) and decreased in vegetation and rainfall, accompanied by substantial reductions in GWS and SM related to increased PET. Linear regression demonstrates a strongly significant relationship between rainfall and EVI (R2 = 0.92), although a negative relationship is apparent between LST and vegetation (R2 = -0.83). Additionally, increased LST in the low-elevation parts of the study area impacted PET (R2 = 0.87), which triggered EVI loss (R2 = 0.93). Moreover, increased HA resulted in losses of 25.5 mm GSW and 1.5 mm SM annually. The relative contributions of CC and HA are shown to vary with elevation. At higher elevations, CC and HA contribute respectively 85% and 15% to the increase in EVI. However, at lower elevations, reduced EVI is largely (79%) due to human activities. This needs to be considered in managing the future of vulnerable socio-ecological systems in the state of Haryana.

Spatio-temporal variability of physico-chemical variables, chlorophyll a, and primary productivity in the northern Arabian Sea along India coast.

The present study attempts to understand the seasonal and spatial variations in the physico-chemical (temperature, pH, salinity, dissolved oxygen, and nutrients) and productivity characteristics of the northern Arabian Sea off the Indian coast. Samples were collected from four different sites off the Veraval coast. The values of the physical and chemical variables were higher during the summer season, whereas nutrient concentrations were high during the winter season due to the maturity of intake nutrients during post-monsoon and winter convective mixing during the northeast monsoon. The dissolved oxygen (DO) concentration was strongly and positively correlated with the net primary productivity (NPP) and chlorophyll a (Chl-a) content to support productivity along the region. Dissimilarity in study variables was observed between the inshore and offshore locations. Principal component analysis revealed a strong relationship between nutrients and productivity variables (Chl-a and NPP). Nutrient levels were high at inshore sites, which can be attributed to the heavy nutrient load from land-based anthropogenic activities and impact due to natural processes like water mixing, sedimentation, and wave activities. Nutrients were strongly and positively correlated with the productivity variables, i.e., Chl-a and NPP. Chl-a positively correlated with NPP (r = 0.90), which indicates that it is a principle productivity pigment in the marine ecosystem.

Alterations in hydrological variables and substrate qualities and its impacts on a critical conservation reserve in the southwest coast of India.

The present study investigated the long-term fluctuation in the hydrological and substrate variables at different habitats of Kadalundi-Vallikkunnu Community Reserve (KVCR) over the last decade. We hypothesize that natural impact represented by climate change and long-term impact from anthropogenic activities including industrialization and intensified agricultural practices have a direct effect on the natural hydrological cycle and the quality of coastal shores and thus can be a reason for coastal habitat and wildlife degradation. Results indicate a significant degradation in nutrient and organic matter concentration in the sediment and dramatic increase in nutrient concentration, salinity, temperature, and pH in the water. Sediment and water degradation can be one of the important factors affecting the structural quality and biodiversity of the region. Therefore, having long-term monitoring data can be useful to plan and design management and conservation strategies to protect local biodiversity and ecosystem.

Distribution of Aureococcus anophagefferens in relation to environmental factors and implications for brown tide seed sources in Qinhuangdao coastal waters, China.

Brown tides caused by Aureococcus anophagefferens have occurred along the Qinhuangdao coastline in the Bohai Sea (BS) in recent years. Little is known about the spatio-temporal distribution of A. anophagefferens, particularly its profile distribution and the effects of environmental controls. In this study, four surveys were conducted in Qinhuangdao coastal waters during the brown tide from June to July 2013; another survey was conducted to cover a larger region in the BS in May 2016. Temperature, salinity, nutrients, and chlorophyll a were analyzed; and the density of A. anophagefferens was detected by a sensitive qPCR method. The intensive brown tide only occurred in Qinhuangdao inshore waters at temperatures ranging from 21.5 to 23.2 °C and relatively high salinity (> 29). Redundancy analysis indicated that the low dissolved inorganic nitrogen limited the growth of other pico- and nano-algal species; high dissolved organic nitrogen and low inorganic nutrients were suitable for the development of brown tides in Qinhuangdao coastal waters, which also contained a thermocline during the brown tide. At the early stage of the brown tide, a high abundance of A. anophagefferens appeared at the bottom of offshore waters characterized by low temperature and high salinity. The A. anophagefferens cells were speculated to originate from water mass located in a depression between the central ridge and the Qinhuangdao coastal area. In brief, this study reported the spatio-temporal variation of brown tides based on the abundance of A. anophagefferens and environmental forces and implied that A. anophagefferens could be transported from the bottom of offshore waters to promote brown tides in inshore waters of Qinhuangdao.

Spatial-temporal variation of Aureococcus anophagefferens blooms in relation to environmental factors in the coastal waters of Qinhuangdao, China.

The brown tides occurring in the coastal scallop cultivation area of Qinhuangdao, China, in recent years are caused by Aureococcus anophagefferens and significantly impact the scallop industry and the marine ecosystem in this region. Long-term investigations of phytoplankton and hydrological variables in the Qinhuangdao sea area were conducted in this study to understand the spatial-temporal variations of A. anophagefferens in relation to environmental factors. Samples were collected during twelve cruises from July 2011 to December 2013 and were analyzed for the temperature, salinity, dissolved oxygen (DO), nutrients and phytoplankton pigments. All diagnostic pigments of A. anophagefferens, such as chlorophyll c3 (Chl c3), Chl c2, 19'-butanoyloxyfucoxanthin (But-fuco), fucoxanthin (Fuco), and diadinoxanthin (Diad), were detected in the surface water by using high-performance liquid chromatography (HPLC). The highest concentrations of But-fuco (5.64 µg L-1), Fuco (37.94 µg L-1) and chlorophyll a (Chl a, 17.25 µg L-1) occurred in different seasons and sampling sites. The A. anophagefferens bloom (as indicated by But-fuco) usually expanded from the south to the north of the Qinhuangdao sea area, close to scallop-culturing regions. The bloom unusually starts in May, reaches its peak in June and almost disappears in August, with the temperature ranging from ca. 19 °C to 23 °C. The redundancy analysis (RDA) indicated that relatively high salinity (>29) and low inorganic nutrients were suitable for the development of the A. anophagefferens bloom. The ratios of diagnostic pigments to Chl a were not constant during different cruises and generally obeyed two different linear relationships, thus indicating the co-occurrence of the blooms of A. anophagefferens and other species, such as Minutocellus polymorphus. In summary, our work reports the long-term variation of A. anophagefferens blooms based on diagnostic pigments and environmental controls, which may provide more insights into the formation mechanisms of the brown tide in this region.

Vertical variations of soil water and its controlling factors based on the structural equation model in a semi-arid grassland.

Soil water content (SWC) of a vertical profile plays an important role in the soil-plant-atmosphere continuum system through eco-hydrological process, which was controlled by multiple factors. Previous studies ignored soil water from a systematic perspective because of the lack of suitable methods to deal with interrelated factors. We developed a meta-model based on structural equation model (SEM) to identify the factors contributing to soil water, and the interactions among these factors, in a semi-arid grassland system. The model was based on the hypothesis that soil water is affected by hydrological variables (precipitation: P, evapotranspiration: E and underground water: GW), vegetation (vegetation coverage: VC and above ground biomass: AGB), and soil parameters (soil organic matter: SOM and bulk density: BD). E and AGB decrease soil water content, while VC and SOM help to retain soil water content. The proportion of explained variation in soil water increased with depth due to increasing stability. The most important contributors were AGB (r∂ = -0.15) and VC (r∂ = 0.39), and their contributions were opposite because their mechanisms differed. The accumulation of AGB in the growth season consumed soil water through root uptake. The contribution of AGB increased with depth, inferring that grassland species are xerophytes with deep roots to access soil water during drought. Coverage positively contributed to soil water, but its influence decreased with depth because its main effects (intercepting rainfall and providing shade) were at the surface. This systematic perspective of how hydrological, vegetation, and soil properties affect soil water will be useful to guide the management of semi-arid grasslands.