Robert Howarth

Reduced light is one of the primary threats to seagrass meadows in the coming decades, with reduced light reaching the benthos due to eutrophication. We assessed a multispectral photography technique using near‐infrared photography to estimate chlorophyll content in the seagrass Zostera marina. Using near‐infrared and red wavelength cameras in the lab environment, we measured normalized difference vegetation index (NDVI) in photographs of sampled seagrass leaves. In samples taken from three different environments, we found a positive correlation between lab‐based NDVI and chlorophyll content, with variation attributable to leaf age. In samples grown under different light conditions, we found high levels of NDVI associated with lower light possibly due to seagrass photoacclimation. This method may be used in addition to existing seagrass monitoring methods to collect data on seagrass photic …

Limited availability and unwanted effects render the mineral’s future uncertain, despite its agricultural importance

My name is Robert Howarth. I am an Earth systems scientist with a BA from Amherst College and a Ph. D. from MIT and the Woods Hole Oceanographic Institution. I have been a tenured faculty member at Cornell University in Ithaca, NY since 1985 and an endowed professor at Cornell since 1993 (the David R. Atkinson Professor of Ecology & Environmental Biology). I have also served as an AdjunctSenior Scientist in the Ecosystems Center of the Marine Biological Lab in Woods Hole, MA for the past 23 years. For decades, I have worked on the consequences of global climate change, on emissions of methane from the oil & gas industry as a driver of climate change, on the production and use of hydrogen, and on alternative energy policies. I have published over 200 peer-reviewed papers, and these have been cited more than 79,000 times in other peer-reviewed literature, making me one of the most highly cited environmental scientists in the world.

My name is Robert Howarth. I am an Earth systems scientist with a Ph. D. from MIT and the Woods Hole Oceanographic Institution. I have been a tenured faculty member at Cornell University since 1985 and an endowed professor in the New York State College of Agriculture & Life Sciences at

As part of a long-term study on the effects of nitrogen (N) loading in a shallow temperate lagoon, we measured rates of N2 fixation associated with seagrass (Zostera marina) epiphytes during the summer from 2005 to 2019, at two sites along a gradient from where high N groundwater enters the system (denoted SH) to a more well-flushed outer harbor (OH). The data presented here are the first such long-term N2 fixation estimates for any seagrass system and one of the very few reported for the phyllosphere in a temperate system. Mean daily N2 fixation was estimated from light and dark measurements using the acetylene reduction assay intercalibrated using both incorporation of 15N2 into biomass and a novel application of the N2:Ar method. Surprisingly, despite a large inorganic N input from a N-contaminated groundwater plume, epiphytic N2 fixation rates were moderately to very high for a seagrass system (OH …

Our title for this editorial—the “science we need for the ocean we want”—comes from the United Nations’ Intergovernmental Oceanographic Commission [1]. We fully endorse that the future of ocean management depends on the highest quality of science that is possible. Globally, recognition is growing for the need to better protect and manage the oceans from the threats posed by climate change, ocean acidification, nutrient pollution, harmful algal blooms, overfishing, and sea-floor mining. In early March of this year, negotiators at the United Nations agreed on final language for a treaty on ocean biodiversity, building on the COP15 for biodiversity held in Montreal in December 2022. If enacted by a majority of the world’s countries, as seems likely, this treaty would create massive marine protected areas covering 30% of the ocean area by 2030. The focus is on waters beyond the territorial boundaries of nations, a …

Nitrogen (N) limitation to net primary production is widespread and influences the responsiveness of ecosystems to many components of global environmental change. Logic and both simple simulation (Vitousek and Fieldin in Biogeochemistry 46: 179–202, 1999) and analytical models (Menge in Ecosystems 14:519–532, 2011) demonstrate that the co-occurrence of losses of N in forms that organisms within an ecosystem cannot control and barriers to biological N fixation (BNF) that keep this process from responding to N deficiency are necessary for the development and persistence of N limitation. Models have focused on the continuous process of leaching losses of dissolved organic N in biologically unavailable forms, but here we use a simple simulation model to show that discontinuous losses of ammonium and nitrate, normally forms of N whose losses organisms can control, can be uncontrollable by …

Nitrogen is essential for all life, and together with phosphorus is one of the two elements most likely to limit rates of primary productivity in most inland waters. Nitrogen has many oxidation states, and a variety of processes – many of them mediated by bacteria – transform nitrogen between different inorganic compounds. The vast majority of nitrogen on Earth is present as molecular, gaseous N2. Before the advent of the industrial revolution, this N2 became biologically available only through its conversion to ammonium by bacteria capable of catalyzing this reduction, so called “nitrogen-fixing” bacteria. Over the last century, humans have greatly increased the biological availability of nitrogen through the production of synthetic fertilizer. Humans have changed the nitrogen cycle more than that of any other major element, with deleterious effects on aquatic ecosystems, human health, and climate.

In their comment on our 2021 paper “How Green is Blue Hydrogen,” Romano et al. purport to provide “a more balanced perspective on blue hydrogen, which is in line with current best available practices.” We strongly disagree. First, we categorically dismiss their presentation on methane emissions. Methane dominates the greenhouse gas footprint of blue hydrogen in our analysis, and our estimates were based on very recent, peer‐reviewed science. Romano et al., in sharp contrast, use only three sources: (1) a 2015 non‐peer‐reviewed report (which gave reasonable values, although at the low end, since based on older science, but nonetheless compatible with our paper); (2) a 2018 report from the International Energy Agency (which also gave values consistent with ours, but has been updated by the Agency in a 2022 report to give much higher values that are very consistent with ours); and (3) a value from a …

The ocean is the foundation of life and plays a key role in the Earth’s changing climate and ecosystem, but its vast span and complex workings are still far from being fully explored. Oceanography is intrinsically a multidisciplinary science, aiming at understanding the physical, biological, chemical, and geological processes in the ocean, as well as the interactions among them. More importantly, as an integral part of the multisphere Earth system, the ocean should not be studied in isolation, especially when global issues such as climate change and marine environment degradation are concerned. Understanding the interactions between the ocean and the atmosphere and between the land and the ocean is particularly critical to address these issues. In order to provide a showcase and forum for the rapidly evolving ocean and Earth system sciences, we are launching a new journal, Ocean-Land-Atmosphere …

I have carefully reviewed the draft guidance posted by the DOE on the proposed Clean Hydrogen Production Standard and offer comments below. For context, I am an Earth systems scientist with a Ph. D. from MIT and more than 40 years of post-Ph. D. experience in research and policy related to human-accelerated global change. I have been a tenured faculty member at Cornell University since 1985, have published more than 200 peer-reviewed papers that have been cited in other peer-reviewed literature more than 75,000 times, and have served on and chaired many committees and panels for the National Academy of Sciences, the International Council of Science, and the US Environmental Protection Agency. I currently serve as one of 22 members of the New York State Climate Action Council, the agency charged by law with developing the implementation plan for New York’s progressive climate law.In August of 2021, I published together with Mark Jacobson one of the only assessments of the greenhouse gas footprint of blue hydrogen (Howarth RW & Jacobson M, 2021, How green is blue hydrogen? Energy Science and Engineering 9: 1676-1687, doi: 10.1002/ese3. 956). There, we concluded that the emissions footprint of blue hydrogen under our base-case parameterization is 139 g CO2-eq/MJ. Assuming 0.286 MJ per mole of hydrogen, this is equivalent to 19.9 kg CO2-eq/kg H2. We explored several sensitivity analyses, looking at a broad range of methane emission rates, carbon dioxide capture rates, and time frames for comparing methane and carbon dioxide (ie, GWP20 and GWP100). Our bestcase scenario had a footprint of 57 g …

We examined concentrations of organic carbon, dissolved sulfides, total sediment sulfur, and stable sulfur isotope ratios in seagrass leaf tissues across a nitrogen‐enrichment gradient in a coastal marine ecosystem (Cape Cod, Massachusetts) in 2007–2010 and 2017–2019. We also measured seagrass aboveground and belowground biomass, epibiota biomass, and leaf chlorophyll content. Seagrasses were present at all sites in the former period but were lost at our most nitrogen‐impacted site (Snug Harbor) by 2011. In 2007–2010, sediment organic carbon and dissolved sulfides were highest in Snug Harbor and decreased along the gradient; leaf tissues depleted in 34S also indicated higher sulfide intrusion into seagrass tissues in more eutrophic areas. By 2017–2019, sediment organic carbon and pore‐water soluble sulfides had decreased in Snug Harbor, but had increased at the intermediate site, to levels …

Since the 1980s, the widespread use of N fertilizer has not only resulted in a strong increase in agricultural productivity but also caused a number of environmental problems, induced by excess reactive N emissions. A range of approaches to improve N management for increased agricultural production together with reduced environmental impacts has been proposed. The 4R principles (right product, right amount, right time and right place) for N fertilizer application have been essential for improving crop productivity and N use efficiency while reducing N losses. For example, site-specific N management (as part of 4R practice) reduced N fertilizer use by 32% and increased yield by 5% in China. However, it has not been enough to overcome the challenge of producing more food with reduced impact on the environment and health. This paper proposes a new framework of food-chainnitrogen-management (FCNM). This involves good N management including the recycling of organic manures, optimized crop and animal production and improved human diets, with the aim of maximizing resource use efficiency and minimizing environmental emissions. FCNM could meet future challenges for food demand, resource sustainability and environmental safety, key issues for green agricultural transformation in China and other countries.

Methane is a major driver of global warming and climate disruption, and scientists now recognize that humancontrolled methane emissions are responsible for 0.5 C of the warming observed since the 1800s, compared to 0.75 C for carbon dioxide. 1 Reducing methane emissions is critical and is perhaps the easiest way to slow the rate of global warming. 2 Unfortunately, atmospheric methane has been rising rapidly over the past decade after emissions were steady at the start of the 20th Century. 3 Many studies suggest that much of this rise may have come from increased production of natural gas, and particularly shale gas development in North America. 4Before this century, the technologies for developing shale gas did not exist, but since 2005 or so shale gas production has driven dramatically. Today, most natural gas production in the United States is from shale, and shale-gas production has accounted for most of the increase in all-natural gas production globally since 2010.3 I and others published the first analysis of how methane emissions contribute to the greenhouse gas footprint of shale gas in 2011. We used the best available data but noted the urgent need for improved measurements on methane emissions made by independent

High rates of biological nitrogen fixation (BNF) are commonly reported for tropical forests, but most studies have been conducted in regions that receive substantial inputs of molybdenum (Mo) from atmospheric dust and sea‐salt aerosols. Even in these regions, the low availability of Mo can constrain free‐living BNF catalyzed by heterotrophic bacteria and archaea. We hypothesized that in regions where atmospheric inputs of Mo are low and soils are highly weathered, such as the southeastern Amazon, Mo would constrain BNF. We also hypothesized that the high soil acidity, characteristic of the Amazon Basin, would further constrain Mo availability and therefore soil BNF. We conducted two field experiments across the wet and dry seasons, adding Mo, phosphorus (P), and lime alone and in combination to the forest floor in the southeastern Amazon. We sampled soils and litter immediately, and then weeks and …

Comments on Cayuga Lake TMDL Page 1 1 Comments on Cayuga Lake TMDL June 30, 2021 by Robert W. Howarth, Ph.D. and Roxanne Marino, Ph.D. Department of Ecology & Evolutionary Biology Cornell University, Ithaca, NY 14853 We offer these comments based on our work on nutrient pollution and water quality in aquatic ecosystems over more than 35 years, including work on Cayuga Lake and other lakes and rivers in New York. We have published over 100 papers on water quality and the source of nutrient pollution. Many of these are very highly cited in other peer-reviewed papers, and we have won awards from major professional societies (ASLO, the Association for the Sciences of Limnology & Oceanography, and CERF, the Coastal & Estuarine Research Federation) for two of our nutrient papers judged to be “transformational.” One of us (RWH) chaired a 2-year study by the National Academy of …

This special anniversary issue celebrates over 35 years of publication of the journal, Biogeochemistry. To our knowledge, Biogeochemistry is the first core journal devoted exclusively to the rapidly growing field of biogeochemistry. Since its inception, the journal has allowed many thousands of authors from different countries to communicate the growing scope, concepts, and themes of biogeochemistry. The journal has also made these research findings and perspectives accessible to global audiences and multiple generations of researchers, educators, students, environmental managers, and more. In particular, the journal has also created a unique and special home for papers analyzing the geochemistry of the Earth’s surface influenced by biological processes and human activities. Before the publication of Biogeochemistry, papers were sometimes rejected by journals for either being ‘‘too biological’’or too …

Whether net primary productivity in an aquatic ecosystem is limited by nitrogen (N), limited by phosphorus (P), or co-limited by N & P is determined by the relative supply of N and P to phytoplankton compared to their elemental requirements for primary production, often characterized by the “Redfield” ratio. The supply of these essential nutrients is affected by both external inputs and biogeochemical processes within the ecosystem. In this paper, we examine external sources of nutrients to aquatic systems and how the balance of N to P inputs influences nutrient limitation. For ocean subtropical gyres, a relatively balanced input of N and P relative to the Redfield ratio from deep ocean sources often leads to near co-limitation by N and P. For lakes, the external nutrient inputs come largely from watershed sources, and we demonstrate that on average the N:P ratio for these inputs across the United States is well …

We measured rates of nitrogen (N) fixation associated with seagrass (Zostera marina) epibiota in a nutrient-enriched lagoon (West Falmouth Harbor, Cape Cod, USA) during the peak summer season nearly every year since 2005. This research is part of a long-term ecosystem study on the effects of N pollution in a temperate coastal system; the site has a high N load in groundwater due to contamination from a municipal wastewater treatment plant. We used the acetylene reduction assay (ARA), a method widely used in many ecosystems over several decades to estimate N fixation, for the routine measurements on intact seagrass-epibiota samples taken from two sites in the harbor along the gradient from where the high N enters the system to the more well-flushed outer harbor. Samples were incubated at in-situ temperatures and a consistent light level typical of the seagrass canopy as well as in the dark, with 95 …

Molybdenum (Mo) is a key cofactor in enzymes used for nitrogen (N) fixation and nitrate reduction, and the low availability of Mo can constrain N inputs, affecting ecosystem productivity. Natural atmospheric Mo aerosolization and deposition from sources such as desert dust, sea‐salt spray, and volcanoes can affect ecosystem function across long timescales, but anthropogenic activities such as combustion, motor vehicles, and agricultural dust have accelerated the natural Mo cycle. Here we combined a synthesis of global atmospheric concentration observations and modeling to identify and estimate anthropogenic sources of atmospheric Mo. To project the impact of atmospheric Mo on terrestrial ecosystems, we synthesized soil Mo data and estimated the global distribution of soil Mo using two approaches to calculate turnover times. We estimated global emissions of atmospheric Mo in aerosols (<10 μm in …