Global groundwater decline

UC Santa Barbara Assistant Professors Scott Jasechko and Debra Perrone recently published a paper analyzing data from 170,000 monitoring wells and 1,693 aquifer systems across over 40 countries, showing that globally, there is extensive and rapid groundwater level decline, particularly in dry regions with large-scale croplands. 

The researchers compiled groundwater level data by delineating aquifer systems across the globe and performing a literature review of local published studies. Statistical analyses of groundwater level trends included Theil-Sen regression slopes, which estimate the slope of linear relationships between two variables. This type of regression was ideal because it is not sensitive to outliers and allowed the team to compare trends between the late 20th and early 21st centuries from a large data set. They found that, compared to 1980 to 2000, about 30% of aquifer systems had experienced accelerated groundwater-level declines between 2000 and 2022. Despite many previous publications discussing groundwater scarcity and unsustainable groundwater withdrawals, few touch on the potential for aquifer recovery. The study highlighted the recovery of depleted aquifers, finding that in about half of the analyzed aquifer systems, groundwater-level declines have slowed and show potential for aquifer recovery. This research suggests that aquifer depletion is not necessarily inevitable and can be reversed, despite the fact that rapidly rising groundwater levels are rare. The study also acknowledged its various limitations such as data availability; analysis can only be done on areas from which existing data is available. In addition, results are based on annual averages, while groundwater levels can vary between seasons. Climate variability is another factor that can influence recent groundwater levels compared to the late twentieth century. Another question the researchers are currently investigating is how climate change affects groundwater levels and subsequently how to predict groundwater levels in certain areas. 

Metabolic Imaging

When studying metabolism-related diseases, it is critical to use metabolic imaging to understand and study”metabolic heterogeneity,” or the differences between metabolic activities among cells. Metabolic heterogeneity can affect many aspects of human health and plays a role in diseases such as neurodegenerative disorders, diabetes and cancer. Although much progress has been made to study these processes, current imaging methods have limitations and are often used to study model organisms that lack practical significance to humans. To address this, UCSB researchers at the Kosik Lab developed an imaging platform that involves the mapping of lipid metabolism in human-derived cultures at the single-cell level. Optical photothermal infrared (O-PTIR) microscopy, as it is called, features high resolution and is compatible with fluorescence imaging.

In the study, researchers utilized an azide-tagged infrared probe to detect newly synthesized lipids. Experiments involving human-relevant model systems such as human-induced pluripotent stem cells and human brain organoids — artificially grown organ tissue — were performed. Lipid metabolism was observed in various cell types and mutations, over time and with differentiation stages. Findings suggested that neurons in brain organoids had a considerable reduction in lipid metabolism function in comparison to astrocytes, a type of non-neural central nervous system cell. The researchers compared the O-PTIR method with other single-cell metabolic imaging methods such as optical metabolic imaging (OMI). Compared to O-PTIR, OMI is more challenging to adapt to other metabolic pathways such as that of cholesterol. In further research, the team intends to improve the O-PTIR platform system, including by performing experiments with a greater number of cells to detect more subtle heterogeneity.

Shark Fishing Mortality

Overfishing has long posed a threat to many aquatic species, including sharks, whose populations have steadily declined due over the past decade. Researchers at UCSB recently co-published a paper discussing mortality rates of sharks across the globe even after widespread protective legislation has been put in place. This legislation intended to reduce shark bycatch from pelagic tuna fisheries and prevent shark finning, a lucrative practice in which sharks’ fins are removed before the animals are released back into the ocean. The study of spatial and temporal trends in shark fishing mortality and its link to legislative regulation had not been done before. The researchers found that between 2012 and 2019, total shark fishing mortality increased from at least 76 to 80 million sharks. In addition, the mortality of sharks in coastal waters increased by 4% whereas mortality decreased by 7% in pelagic fisheries.

In this study the researchers took a synthetic approach by compiling available data published or reported by fisheries, countries and regional fishery management organizations (RFMOs). Specifically, they studied global patterns of shark fishing mortality and compared them to regulations put in place at that time. Areas of high shark fishing mortality were shown to be in coastal environments including the Atlantic coast, West Africa, the North Indian Ocean and the Coral Triangle. A decrease in mortality in pelagic fisheries was related to the introduction of RFMO regulations which banned the retention, or harvesting, of certain threatened species. Although finning regulations have been adopted, they have not been shown to reduce shark mortality. The findings suggest that instead of finning, shark fishing has become more concentrated on small coastal species that are not protected by regulations. However, some regional shark fishing and retention bans, such as the RFMO regulations, have shown success. Nevertheless, the researchers provide evidence that shark fishing regulations need to be expanded and that conservation efforts should be pursued to protect these threatened species.

A version of this article appeared on pg. 10 of the Feb. 1, 2024 print edition of the Daily Nexus.