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We investigated processes contributing to periodic acidification events in headwater streams of Nee Soon Forest Catchment (NSFC) in Singapore by monitoring hydrochemical changes in response to rainfall inputs. Stream chemistry response to most rainfall events was characterized by decreases in pH from means ranging from 5.1 to 5.3 to below 4.8–5.0 and corresponding increases in specific electrical conductivity from baseflow values of 15–30 to 50–80 μS cm−1, indicative of low-total dissolved solids in stormflow. The decreases in pH in the streams, which are typically acidic year-round, were related to occasional highly acidic rainfall inputs (pH ~4.05) and likely the flushing of organic acids into the stream by shallow subsurface flow interacting with surface litter and/or organic-rich soil horizons. The interaction of rainwater runoff with organic matter in the soil matrix possibly alters the chemical composition of stormflow, influencing pH. Decomposition of instream organic matter also reduces stream water pH. Leaching experiments revealed that the overland flow passing through organic matter and A horizon material has the potential to lower stream water pH by approximately a half unit or more, in part, by flushing nitrates that were produced by microbial decomposition of organic matter and/or precipitated sulphur that enterred the forest by wet or dry atmospheric deposition. The observed periodic acid events are a natural phenomenon in the stream system in this urban environment because of naturally acidic rainfall and granitic soils with low buffering potential. However, acid events are likely amplified in frequency and magnitude by anthropogenic pollution emissions of sulphur and nitrogen species (e.g., SO2 and NOx) from local and regional sources that lower rainfall pH. Although, acid runoff events are typically short-lived (

Root water uptake (RWU) strategies shape climate-vegetation feedbacks and ecosystem productivity. A fundamental relationship between RWU strategies and evolutionary histories (phylogeny) of trees, however, remains poorly understood. Establishing a phylogenetic basis for tree RWU, particularly groundwater use, could improve their representation in terrestrial biosphere models (TBMs) that are crucial for understanding hydrologic and ecosystem responses to climate perturbations. We explored possible phylogenetic bases for tree RWU using two independent data sets: (a) observed root and local groundwater depths representing 502 tree species, and (b) groundwater, soil, and xylem water isotopic evidence for groundwater uptake representing 412 species. Maximum rooting depths (RDMAX), the ratio between RDMAX and mean water table depth (WT) (RDMAX/WT), and isotopic evidence of groundwater uptake showed significant phylogenetic signals, suggesting that tree RWU strategies are more similar among closely related species. Our findings may be used to parameterize species-level RWU in TBMs, particularly for data-poor regions.

We investigated submarine groundwater discharge (SGD) in a volcanic coastal area that hosts the world's most biodiverse reefs. Measurements of 222Rn activity in coastal seawater, a tracer for groundwater, indicated prevalent SGD. In areas where seawater 222Rn activity was generally higher, we discovered hydrothermal springs emitting acidic waters (pH~5.4-6.0) and venting magmatic CO2 which brought local pCO2 levels up to 95,000 ppm. The collection of vents raised CO2 and lowered pH over 1-2 km of coastline. The hydrogen and oxygen isotope composition of water and chloride concentration revealed that the springs discharge recirculated seawater mixed variably with terrestrial groundwater. Shallower springs and porewater have a higher proportion of terrestrial groundwater than deeper springs, which emit mostly recirculated seawater. This suggests that different SGD mechanisms are present. The SGD could be contributing to the evolution and function of the biodiverse ecosystem but it also represents myriad pathways for contamination. Plain language abstract Groundwater flow from land to sea could have important coastal impacts but usually is unrecognized. Delicate reefs may be particularly sensitive to groundwater inputs. Yet, few studies have made connections between groundwater and reefs. We investigated submarine groundwater in a volcanic coastal area that hosts the world's most biodiverse reefs. By measuring 222Rn activity in seawater as a tracer for groundwater, we found that groundwater discharge is prevalent throughout the coast. In areas where seawater 222Rn activity was higher, we discovered hydrothermal springs emitting acidic waters (pH~5.4-6.0) and venting volcanic CO2 which brought local pCO2 levels up to 95,000 ppm. The collection of vents raised CO2 and lowered pH over 1-2 km of coastline. The composition of water samples indicate that the springs discharge recirculated seawater mixed variably with terrestrial groundwater. Shallower springs and porewater from the seabed have a higher proportion of terrestrial groundwater than deeper springs, which emit mostly recirculated seawater. These waters also interact more with the aquifer matrix. Because different mechanisms of groundwater flow from land to sea are taking place, the groundwater flow could be contributing to the evolution and functioning of the ecosystem. However, groundwater also represents potential pathways for contamination released from land.

“Banks won't give a mortgage loan to someone who is only going to be in the country for 1 year,” declared the real estate agent. His remark shocked me. I was a tenure-track faculty member at the time, but I was deemed unworthy to receive a line of credit because of my visa situation. I'm a citizen of the Philippines, and the visa that my U.S. institution obtained for me had to be renewed each year. So, on paper it looked as though I only had permission to be in the country for 1 year. My wife and I encountered many such hurdles because of my visa—and they ultimately drove me to quit my faculty position and leave the country. ![][1] ILLUSTRATION: ROBERT NEUBECKER > “Don't sign … until you know that you'll have what you need in your new country.” In hindsight, I didn't take the visa application process seriously enough when I was negotiating my job offer. I was so excited about landing a tenure-track position that I didn't take time to think through what kind of visa and accommodations I would need to make my personal life work. I also assumed that the university had a system in place to deal with foreign hires. I said yes to the job offer and signed on the dotted line. The first sign of trouble came when I tried to buy a house in our new city. I had moved there ahead of my wife and 1-year-old daughter so that I could look for a neighborhood where we could settle down. But as the real estate agent predicted, mortgage lenders didn't want to gamble on someone with a 1-year visa. I signed a lease for an apartment instead. After my wife joined me, we needed a car because our sprawling community didn't have a strong public transportation system. But we had trouble securing credit for that, too. In the end, we had to put down more than $3000 as a down payment. The third, and final, straw came when my wife wanted to return to her work as a nurse after her maternity leave. Prior to our move, she had obtained a license to practice nursing in the United States. But she couldn't apply for jobs because of legal restrictions associated with my visa. That left her feeling frustrated and isolated, unable to establish a professional life in a new country. Stress ran high in our small one-bedroom apartment. The logical fix to our problems was for me to secure permanent residency status, otherwise known as a green card. But that just brought more problems. I pleaded with my department chair, dean, and provost to support my green card application. But it took 6 months for the university to agree to sponsor my application, and I didn't know how long the review and approval process would take on top of that. Exasperated by the entire ordeal, I applied for jobs in countries that I thought would be more supportive of foreign workers and their families. I was offered a faculty job in the Netherlands and, within 3 months, my family and I moved across the Atlantic. That was 1 year ago, and we've been much happier ever since. My wife, who is allowed to work in the Netherlands, is completing a course toward a nursing certification while our daughter, now 3 years old, is at government-subsidized day care. We are renting a nice house and are looking for one to buy. And we've been helped by a government policy that grants a 30% tax exemption for foreign hires for a period of 5 years. I'm glad we've ended up where we are. But when I look back, I wish that I'd been more prepared and proactive when negotiating my first faculty position. I could have asked the university to apply for a multiyear visa—which, I later learned, is what human resources staff had done for other faculty hires. I could have also requested a guarantee that the university would sponsor my application for permanent residency within a certain period of time and would pay for some immigration-related expenses, such as green card application fees. I hope that other immigrant scientists take heed from my tale. If you land a job, don't sign on the dotted line until you know that you'll have what you need in your new country. [1]: /embed/graphic-1.gif

The importance of mangrove-derived material in sustaining coastal food webs (i.e. the Outwelling Hypothesis) is often invoked in support of mangroves conservation. Biogeochemical cycling, particularly nitrogen (N) and phosphorus (P) in mangrove ecosystems, however, is poorly understood because of high spatial heterogeneity and temporal variability of sources, sinks, and transformation pathways. Here we show that the distribution of N and P are intimately related to vegetation distribution and seasonality. We examined the dynamics of N and P in sediments and in a tidal creek of the Can Gio Mangrove Forest, Vietnam. Our objectives were to (1) determine the spatial distribution of dissolved inorganic nitrogen and phosphorus in the mangrove forest along a Rhizophora-Avicennia-mudflat transect; and (2) identify the respective inputs and transformation pathways of N and P in the water column via 24-h time series measurements in a tidal creek. Sediment porewater had N-NH4+ and N-NO3− concentrations

The ecohydrological separation hypothesis has generated considerable scientific interest and debate in ecohydrological studies, and it assumes there exist two water pools in subsurface water, one of which is soil water used by plants and the other is that supplied to groundwater. Although this hypothesis has been tested in several humid sites, a further test in arid and semiarid conditions is still needed. Based on the isotopic ratios in different water bodies collected during a 2-year field work, the hypothesis was tested in a drier zone located in the Qilian Mountains of the northeastern Tibetan Plateau in order to investigate whether this separation phenomenon existed in a drier climate, and whether this may be a common characteristic or an exception. The results suggested that the hydrological separation does not necessarily exist and may not even be determined by stable isotopes; there is a clear need to more precise experimental methods.