Robert W. Howarth

Cornell University | CU · Department of Ecology and Evolutionary Biology

Seagrass meadows are known as hot spots for carbon accumulation, but there is limited field data on the variability of sediment accumulation across time and space. We developed a method to assess spatial and temporal heterogeneity in net sediment accumulation in seagrass meadows using small, inexpensive samplers, allowing for over 200 unique measur...

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 blu...

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,...

Nitrogen fixation is the process whereby molecular N2 gas is converted to reactive, biologically available forms of nitrogen. The vast majority of nitrogen on Earth is present as molecular N2, and before the advent of the agricultural and industrial revolutions, biological nitrogen fixation was the only significant process creating reactive nitroge...

Hydrogen is often viewed as an important energy carrier in a future decarbonized world. Currently, most hydrogen is produced by steam reforming of methane in natural gas (“gray hydrogen”), with high carbon dioxide emissions. Increasingly, many propose using carbon capture and storage to reduce these emissions, producing so‐called “blue hydrogen,” f...

To facilitate calculation of net anthropogenic nitrogen and phosphorus inputs (NANI/NAPI) from publicly available data sources, including county-level US census and agricultural census data, we developed the NANI/NAPI toolbox, now in its third version. NANI has been used successfully, together with climate data, to estimate riverine nitrogen fluxes...

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...

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 tim...

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 nitr...

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 bacter...

In 2019, New York State passed aggressive new climate legislation to reduce greenhouse gas (GHG) emissions and laid out major changes for how emissions are reported. One change is the inclusion of emissions from outside of the boundaries of the State if they are associated with energy use within NY; the traditional inventory considered emissions on...

Tropical forest fires have become more common due to interactions between deforestation, land clearing, and drought. Forest recovery following fires may be limited by nitrogen. Biological nitrogen fixation (BNF) is the main pathway for new nitrogen (N) to enter most ecosystems, but BNF may be constrained by other nutrients, such as molybdenum and p...

Molybdenum (Mo) is an essential trace metal that plays a central role in biological nitrogen fixation (BNF) as the cofactor in the conventional form of the nitrogenase enzyme. The low availability of Mo in soils often constrains BNF in many terrestrial ecosystems. Atmospheric sources may supply a critical source of exogenous Mo to regions with high...

Methane has been rising rapidly in the atmosphere over the past decade, contributing to global climate change. Unlike the late 20th century when the rise in atmospheric methane was accompanied by an enrichment in the heavier carbon stable isotope (13C) of methane, methane in recent years has become more depleted in 13C. This depletion has been wide...

The data presented here represent estimates of the phosphorus content of crop production, phosphorus use efficiency (PUE) and agricultural phosphorus inputs associated with it across the contiguous United States. Net Anthropogenic Phosphorus Input (NAPI) estimates and related data are also provided. Data are presented at county, sub-regional and re...

Crop N use efficiency (NUE) and P use efficiency (PUE)might be expected to exhibit different patterns across agricultural regions due to their very different environmental dynamics and management strategies. Here, following our previous work on regional patterns of NUE, we review patterns of PUE and related variables, including major inputs of P to...

Methane has been rising rapidly in the atmosphere over the past decade, contributing to global climate change. Unlike the late 20th Century when the rise in atmospheric methane was accompanied by an enrichment in the heavier carbon stable isotope (¹³C) of methane, methane in recent years has become more depleted in ¹³C. This depletion has been wide...

Agricultural production and associated environmental impacts can vary significantly because of regional differences in crops, resource use and production practices, in addition to climatic factors. Here, we review patterns of regional agricultural production, nitrogen and phosphorus use efficiency (NUE, PUE), and regional inputs of nitrogen (N) and...

Intensive agriculture represents a recent extension of green roof technology. Perceived ecosystem services provided by rooftop farming include stormwater management and the production of affordable and nutritious vegetables for local consumption. However, intensive agriculture can increase nutrient loads to surface water, yet there is little empiri...

While progress has been made in reducing external nutrient inputs to the Baltic Sea, further actions are needed to meet the goals of the Baltic Sea Action Plan (BSAP), especially for the Baltic Proper, Gulf of Finland, and Gulf of Riga sub-basins. We used the net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) nutrient ac...

In the published online version of the paper, Fig. 4 is incorrect. Corrected figure is provided below.

The separation between crop- and livestock production is an important driver of agricultural nutrient surpluses in many parts of the world. Nutrient surpluses can be symptomatic of poor resource use efficiency and contribute to environmental problems. Thus, it is important not only to identify where surpluses can be reduced, but also the potential...

All life depends on phosphorus (P), which is why it is an important crop fertilizer. Humans generally consume more P than needed and the excess ends up in sewage systems. Past management of P in fertilizer and human sewage has led to the accumulation of P in soils and sediments of lakes and streams. This accumulation is called “legacy” P because it...

[The data presented here represent estimates of the nitrogen content of crop production, nitrogen use efficiency (NUE) and agricultural nitrogen inputs associated with it across the contiguous United States. Net Anthropogenic Nitrogen Input (NANI) estimates and related data are also provided. Data are presented at county, sub-regional and regional...

National-level summaries of crop production and nutrient use efficiency, important for international comparisons, only partially elucidate agricultural dynamics within a country. Agricultural production and associated environmental impacts in large countries vary significantly because of regional differences in crops, climate, resource use and prod...

The increasing trend in riverine phosphorus (P) loads resulting from anthropogenic inputs has gained wide attention because of the well-known role of P in eutrophication. So far, however, there is still limited scientific understanding of anthropogenic P inputs and their impacts on riverine flux in river reaches along the upstream-to-downstream con...

China is undergoing a rapid transition from a rural to an urban society. This societal change is a consequence of a national drive toward economic prosperity. However, accelerated urban development resulting from rapid population migration from rural to urban lands has led to high levels of untreated sewage entering aquatic ecosystems directly. Con...

Umweltfaktoren und Ressourcen sind zwei ganz verschiedene Eigenschaften von Lebensräumen und bestimmen, wo Lebewesen existieren können. Als abiotische Umweltbedingungen oder Umweltfaktoren (engl. conditions) fasst man physikalisch-chemische Eigenschaften der Umgebung zusammen wie Temperatur, Feuchtigkeit, pH-Wert oder – in aquatischen Lebensräumen...

Die Gesetze der Thermodynamik lehren uns, dass das Universum stets auf einen Zustand größerer Entropie und geringerer Ordnung hinstrebt. Biologische Systeme sind jedoch Orte lokalisierter Ordnung: Sie werden durch eine kontinuierliche Zufuhr an Energie aufrechterhalten und wirken damit dem allgemeinen Trend entgegen. Sämtliche biologischen Einheite...

Warum variiert die Anzahl der Arten von Ort zu Ort? Und warum von Zeit zu Zeit? Diese Fragen stellen sich nicht nur Ökologen, sondern im Grunde jedem, der die Natur beobachtet und sich Gedanken über sie macht. Die Fragen an sich sind schon interessant, aber sie haben auch eine praktische Bedeutung. Wenn wir die biologische Vielfalt der Erde erhalte...

Wir haben diskutiert, durch welche Prozesse neue Arten entstehen (Abschn. 2.3) und in neue Gebiete einwandern (Abschn. 5.4 und 10.4). Und wir wissen, dass Arten lokal oder auch global aussterben können.

In diesem Kapitel liefern wir eine formale Definition für den Begriff Biogeochemie und zeigen auf, wie einige besonders bedeutende biogeochemische Kreisläufe durch anthropogene Einflüsse in globalem Maßstab verändert wurden. Laut Howarth (1984) befasst sich die Biogeochemie (engl. biogeochemisty) als Wissenschaft mit dem Einfluss der Biota auf die...

In den vorigen Kapiteln lag unser Augenmerk häufig auf Populationen einer einzigen Art. Weil wir uns klarmachen wollten, was die Abundanz und Verbreitung einer Art bestimmt, haben wir mehr oder weniger unabhängig voneinander betrachtet, welche Rolle dabei Umweltbedingungen und Ressourcen, Wanderungen, intra- und interspezifische Konkurrenz, mutuali...

In Kap. 2 haben wir deutlich gemacht, warum für dieses gesamte Buch der leicht veränderte, berühmte Ausspruch von Theodosius Dobzhansky gilt: „Nichts in der Ökologie ergibt einen Sinn, außer im Licht der Evolution“. Aber die Evolution ist mehr als nur die Grundlage der Ökologie (und der gesamten übrigen Biologie). Es gibt viele Bereiche der Ökologi...

Als Ökologen versuchen wir, die Verbreitung und Abundanz von Organismen zu beschreiben und zu verstehen. Gründe dafür können beispielsweise sein, eine Schädlingsart unter Kontrolle zu bekommen, eine gefährdete Art erhalten zu wollen oder einfach auch nur unsere Faszination von der Welt um uns herum.

Die Frage „Was ist Ökologie?“ könnten wir beantworten, indem wir uns die verschiedenen dafür vorgeschlagenen Definitionen näher ansehen und daraus die beste auswählen (Exkurs 1.1). Während sich Definitionen der Ökologie durch prägnante und präzise Formulierung auszeichnen und sich dadurch gut zur Vorbereitung auf eine Prüfung eignen, vermitteln sie...

Nach einem Beispiel für einen Prädator oder Räuber gefragt, werden die meisten Menschen spontan mit ziemlicher Sicherheit so etwas wie „Löwe“, „Tiger“ oder „Eisbär“ nennen – auf jeden Fall ein großes, gefährliches Tier, dessen Angriff für seine Beute sofort tödlich ist.

In diesem Kapitel werden wir erörtern, wie wir mithilfe der Ökologie besser verstehen können, welche Probleme das menschliche Bevölkerungswachstums, Krankheiten, die Landwirtschaft und der Ressourcenverbrauch mit sich bringen. Selbstverständlich hat alleine schon das Wachstum der menschlichen Bevölkerung Auswirkungen auf die Umwelt und die natürlic...

Nachdem wir in den vorangegangenen Kapiteln den Begriff der intraspezifischen Konkurrenz eingeführt haben, kann man sich leicht vorstellen, was mit interspezifischer Konkurrenz (zwischenartlicher Konkurrenz; engl. interspecific competition) gemeint ist: Infolge der Ausnutzung von Ressourcen oder der Interferenz durch eine andere Art leiden die Indi...

Die Erde ist von vielen verschiedenen Organismenformen bewohnt, die weder nach dem Zufallsprinzip noch gleichmäßig über die Erdoberfläche verteilt sind. Jedes im Rahmen einer Bestandserhebung untersuchte Gebiet enthält nur einen kleinen Teil der auf der Erde vorkommenden Artenvielfalt. Warum gibt es eine solche Vielfalt von Organismen? Warum sind v...

In Kap. 3 haben wir uns damit befasst, welche Auswirkungen Umweltfaktoren und Ressourcen auf einzelne Organismen haben. Nun begeben wir uns auf eine höhere Ebene und betrachten, wie sich Umweltbedingungen und Ressourcen im Zusammenspiel auf ganze Lebensgemeinschaften und Ökosysteme auswirken und wie diese Lebensgemeinschaften und Ökosysteme auf der...

Dieses Ökologie-Lehrbuch führt in leicht verständlicher Weise in die Grundlagen – von den theoretischen Fundamenten bis zu Ihren praktischen Anwendungen - ein. Durchgehend farbige Abbildungen, einfache didaktische Elemente und eine Fülle an Beispielen machen dieses Buch zu einem idealen Einstieg in die Ökologie für Studierende aller Studienabschnit...

The process of di-nitrogen (N2) fixation is widespread in nature, including in many aquatic ecosystems. In lakes, N2 fixation by planktonic cyanobacteria often contributes sufficient new nitrogen to maintain phosphorus limitation of primary production. However, it is intriguing that many estuaries and coastal marine ecosystems at salinities greater...

Human activities have increased the flow of nitrogen (N) and phosphorus (P) over much of the Earth, leading to increased agricultural production, but also the degradation of air, soil, and water quality. Here we quantify the sources of anthropogenic N and P inputs to 76 watersheds of the St. Lawrence Basin (SLB) throughout the 20th century using NA...

We estimate the emissions of the two most important greenhouse gasses (GHG), carbon dioxide (CO2) and methane (CH4), from the use of modern high-efficiency heat pump water heaters compared to the most commonly used domestic hot water systems: natural gas storage tanks, tankless natural gas demand heaters, electric resistance storage tanks, and tank...

Human activities are the main drivers of alterations of regional N cycles. With increasing population and economic development, human-induced N inputs are expected to continue to increase in the future, especially in many regions of developing countries. Because N sources vary substantially at different temporal and spatial scales and stages of eco...

Riverine phosphorus (P) levels in headwaters are a worldwide concern for environmental management due to the sensitivity of freshwater ecosystems to phosphorus loads. Here, we evaluate P in the Huai River Basin of China, a watershed with one of the highest intensities of human-activity in the world. Estimates of net anthropogenic phosphorus inputs...

We present tools for estimating regional nitrogen and phosphorus inputs to watersheds and other regions, with the aim of developing relationships between these inputs and riverine nutrient exports to coastal waters. NANI (Net Anthropogenic Nitrogen Input), first introduced by Howarth et al.1996, is calculated as the sum of oxidized N deposition, fe...

Agricultural production is critical for human survival and simultaneously contributes to ecosystem degradation. There is a need for transparent, rapid methods for evaluating the environmental impacts of agricultural production at the system-level in order to develop sustainable food supplies. We have developed a method for estimating the greenhouse...

This study provides a new approach to estimate both anthropogenic non-point-source and point-source nitrogen (N) inputs to the landscape, and determines their impacts on riverine ammonia–nitrogen (AN) flux, providing a foundation for further exploration of anthropogenic effects on N pollution. Our study site is Huai River basin of China, a water–sh...

In this study, we present data to support the hypothesis that removal of epiphytes by grazers is an important control of nitrogen fixation in temperate seagrass meadows during the summer. Previous work in West Falmouth Harbor, Massachusetts, USA, found highest rates of epiphytic nitrogen fixation in the part of the harbor (Snug Harbor) with the gre...

This study provides a new approach to estimate both anthropogenic non-point and point nitrogen (N) inputs to the landscape, and determines their impacts on riverine ammonia-nitrogen (AN) flux, providing a foundation for further exploration of anthropogenic effects on N pollution. Our study site is Huai River Basin of China, a watershed with one of...

The environmental degradation of lakes in China has become increasingly serious over the last 30 years and eutrophication resulting from enhanced nutrient inputs is considered a top threat. In this study, a quasi-mass balance method, net anthropogenic N inputs (NANI), was introduced to assess the human influence on N input into three typical Chines...

Nitrogen is an essential element for life and is the fourth most abundant element in the living biomass (by moles) after hydrogen, carbon, and oxygen. Nitrogen is in all amino acids and nucleotides, and therefore in all proteins and nucleic acids. Nitrogen is also a major component of the chitin that makes up the cell walls of fungi and the exoskel...

In this paper, we apply an established methodology for estimating Net Anthropogenic Nitrogen Inputs (NANI) to India and its major watersheds. Our primary goal here is to provide initial estimates of major nitrogen inputs of NANI for India, at the country level and for major Indian watersheds, including data sources and parameter estimates, making s...

Background/Question/Methods Nitrogen fixation is the primary source of new nitrogen to tropical forests and is exclusively performed by bacteria and archaea. While these N-fixing microorganisms are very diverse, they all share the nitrogenase enzyme, which almost always requires molybdenum (Mo). Increasing evidence in recent years suggests that Mo...

This study presents a roadmap for converting California's all-purpose (electricity, transportation, heating/cooling, and industry) energy infrastructure to one derived entirely from wind, water, and sunlight (WINS) generating electricity and electrolytic hydrogen. California's available WWS resources are first evaluated. A mix of WWS generators is...

Net anthropogenic nitrogen inputs (NANI) with components of atmospheric N deposition, synthetic N fertilizer, agricultural N fixation and N in net food and feed imports from 15 catchments in the Lake Dianchi basin were determined over an 11-year period (2000–2010). The 15 catchments range in size from 44 km2 to 316 km2 with an average of 175 km2. T...

In April 2011, we published the first peer-reviewed analysis of the greenhouse gas footprint (GHG) of shale gas, concluding that the climate impact of shale gas may be worse than that of other fossil fuels such as coal and oil because of methane emissions. We noted the poor quality of publicly available data to support our analysis and called for f...

Significance We identified a significant regional flux of methane over a large area of shale gas wells in southwestern Pennsylvania in the Marcellus formation and further identified several pads with high methane emissions. These shale gas pads were identified as in the drilling process, a preproduction stage not previously associated with high met...

Net anthropogenic nitrogen inputs (NANI) with components of atmospheric N deposition, synthetic N fertilizer, agricultural N fixation and N in net food and feed imports from 15 catchments in Lake Dianchi Basin were determined over an 11 year period (2000-2010). The 15 catchments range in size from 44 km2 to 316 km2 with an average of 175 km2. To re...

We evaluated the relative importance of dry deposition of ammonia (NH3) gas at several headwater areas of the Susquehanna River, the largest single source of nitrogen pollution to Chesapeake Bay, including three that are remote from major sources of NH3 emissions (CTH, ARN, and KEF) and one (HFD) that is near a major agricultural source. We also ex...

Human activity has greatly increased the rate of creation of biologically available nitrogen. Before the advent of the industrial revolution and the green revolution, only the natural process of bacterial nitrogen fixation created significant quantities of biologically available nitrogen, and this was balanced at the global scale by loss of this ni...

We measured metabolism rates in a shallow, nitrogen-enriched coastal marine ecosystem on Cape Cod (MA, USA) during seven summers using an open-water diel oxygen method. We compared two basins, one directly receiving most of the nitrogen (N) load ("Snug Harbor") and another further removed from the N load and better flushed ("Outer Harbor"). Both di...

We examined controls of benthic dinitrogen (N2) fixation and primary production in oligotrophic lakes in Arctic Alaska, Toolik Field Station (Arctic Long-Term Ecological Research Site). Primary production in many oligotrophic lakes is limited by nitrogen (N), and benthic processes are important for whole-lake function. Oligotrophic lakes are increa...

West Falmouth Harbor, a shallow lagoon on Cape Cod, has experienced a threefold increase in nitrogen load since the mid-to late 1990s due to input from a groundwater plume contaminated by a municipal wastewater treatment plant. We measured the exchange of nitrogen and phosphorus between the harbor and the coastal waters of Buzzards Bay over several...