Nicholas D. Ward

Pacific Northwest National Laboratory | PNNL · Coastal Sciences Division

Temperate and tropical rivers serve as a significant source of carbon dioxide to the atmosphere(1-4). However, the source of the organic matter that fuels these globally relevant emissions is uncertain. Lignin and cellulose are the most abundant macromolecules in the terrestrial biosphere(5), but are assumed to resist degradation on release from so...

The purpose of this review is to highlight progress in unraveling carbon cycling dynamics across the continuum of landscapes, inland waters, coastal oceans, and the atmosphere. Earth systems are intimately interconnected, yet most biogeochemical studies focus on specific components in isolation. The movement of water drives the carbon cycle, and, a...

Most measurements of respiration rates in large tropical rivers do not account for the influence of river flow conditions on microbial activity. We developed a ship-board spinning incubation system for measuring O2 drawdown under different rotation velocities and deployed the system along the lower Amazon River during four hydrologic periods. Avera...

Between the land and ocean, diverse coastal ecosystems transform, store, and transport material. Across these interfaces, the dynamic exchange of energy and matter is driven by hydrological and hydrodynamic processes such as river and groundwater discharge, tides, waves, and storms. These dynamics regulate ecosystem functions and Earth’s climate, y...

Here, we examine how marine microbial communities respond when dissolved organic matter (DOM) is mobilized from coastal wetlands. Biological transformations of this DOM may increase in the presence of reactive substrates, such as algal‐derived DOM (ADOM) in the coastal zone—a process known as priming. We performed laboratory experiments examining t...

Dissolved oxygen (DO) is a key biogeochemical control in coastal systems, and its concentration and drivers vary markedly through time and space. This makes it difficult to accurately represent coastal DO and associated biogeochemical processes in models, limiting our ability to predict how these systems will respond to global change. We obtained h...

The complex interactions among soil, vegetation, and site hydrologic conditions driven by precipitation and tidal cycles control biogeochemical transformations and bi-directional exchange of carbon and nutrients across the terrestrial-aquatic interfaces (TAIs) in the coastal regions. This study uses a highly mechanistic model, ATS-PFLOTRAN, to expl...

Priming effects that stimulate increased degradation of refractory organic matter by microorganisms following fresh organic matter input is a well-known phenomenon in terrestrial environments but remains controversial in marine environments. We used a combination of chemical (gas chromatography-EI quadrupole time of flight mass spectrometry) and mo...

Relative sea level rise (SLR) increasingly impacts coastal ecosystems through the formation of ghost forests. To predict the future of coastal ecosystems under SLR and changing climate, it is important to understand the physiological mechanisms underlying coastal tree mortality and to integrate this knowledge into dynamic vegetation models. We inco...

The Tocantins River contributes ∼5% of the total flux of water to the Amazon River plume in the Atlantic Ocean. Here, we evaluate monthly variability in the composition and abundance of carbon, nitrogen, and suspended sediment in the lower reaches of the Tocantins River from 2014 to 2016. Dissolved organic carbon concentrations generally increased...

Groundwater biogeochemistry in coastal areas is spatially and temporally dynamic because fluctuations in groundwater level may cause alternate redox between distinct hydrological conditions. Recent studies have proposed connections between biogeochemistry and large-scale hydrological processes, specifically focusing on the role of redox-active comp...

Transferable and mechanistic understanding of cross-scale interactions is necessary to predict how coastal systems respond to global change. Cohesive datasets across geographically distributed sites can enable a mechanistic understanding of coastal ecosystem control points and examine how geographically transferable this knowledge is. To address th...

Inland waters are hotspots for biogeochemical activity, but the environmental and biological factors that govern the transformation of organic matter (OM) flowing through them are still poorly constrained. Here we evaluate data from a crowdsourced sampling campaign led by the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Syst...

Coastal upland forests are facing widespread mortality as sea-level rise accelerates and precipitation and storm regimes change. The loss of coastal forests has significant implications for the coastal carbon cycle; yet, predicting mortality likelihood is difficult due to our limited understanding of disturbance impacts on coastal forests. The mani...

The quality and quantity of water in the critical zone are controlled by the soil and its properties, which in turn affect the availability of nutrients as well as the growth and proliferation of microbial communities and their associated biogeochemical processes. The coastal terrestrial-aquatic interface (TAI) is a unique ecosystem where terrestri...

Large-scale experimental manipulations and coupled numerical models are used to assess the propagation of hydrological disturbances across terrestrial and aquatic interfaces. The Terrestrial Ecosystem Manipulation to Probe the Effects of Storm Treatments (TEMPEST) experiment is a manipulative experiment that uses a before-after-control-impact (BACI...

Random forests (RF) are an increasingly popular machine learning approach used to model biogeochemical processes in the Earth system. While RF models are robust to many assumptions that complicate deterministic models, there are several important parameterization decisions for appropriate use and optimal model fit. We explored the role that paramet...

The goal of this review is to provide a comprehensive overview of the magnitude and drivers of carbon cycling dynamics in the major estuaries of India. Data from a total of 32 estuaries along the Bay of Bengal (BB) and the Arabian Sea (AS) were compiled from the literature and re-analysed based on changes in season (wet vs. dry) and marine end-memb...

We present an electro-transmutation (ET) method of water purification using the Quantum Kinetic Fusor™. Electrolysis experiments were performed with residential well water and seawater coupled with two different electrode materials—stainless steel and aluminum—to test the effectiveness of ET in removing contaminants and altering the physiochemistry...

Black carbon (BC) is produced by incomplete combustion of biomass by wildfires and burning of fossil fuels. BC is environmentally persistent over centuries to millennia, sequestering carbon in marine and terrestrial environments. However, its production, storage and dynamics, and therefore its role in the broader carbon cycling during global change...

There is consensus throughout the Earth system science research community that “open data” is of critical importance. However, discoverability and accessibility are often overlooked, raising the question of how useful archived, but not easily discoverable data are. As part of evaluating databases suitable for our own research data archival, we cond...

Observations of woody plant mortality in coastal ecosystems are globally widespread, but the overarching processes and underlying mechanisms are poorly understood. This knowledge deficiency, combined with rapidly changing water levels, storm surges, atmospheric CO2, and vapor pressure deficit, creates large predictive uncertainty regarding how coas...

Increasing seawater exposure is killing coastal trees globally, with expectations of accelerating mortality with rising sea levels. However, the impact of concomitant changes in atmospheric CO2 concentration, temperature, and vapor pressure deficit (VPD) on seawater‐induced tree mortality is uncertain. We examined the mechanisms of seawater‐induced...

Sea-level rise is causing widespread tree mortality of coastal forests, with large consequences on the Earth system as a result of these forests’ importance in carbon and nutrient export. The mechanisms of mortality under these conditions are, however, poorly tested. We used wood anatomy traits, wood δ ¹³ C, and tree radial growth to retrospectivel...

Many river systems of the world are super‐saturated in dissolved CO 2 (pCO 2 ) relative to equilibrium with the atmosphere. Here we compare the coupled organic matter and pCO 2 dynamics of the world's two largest and most organic‐rich river systems. The emerging data sets for the Congo River, joint with Amazon River data, enable us to begin to thin...

De nombreux systèmes fluviaux du monde sont sursaturés en CO 2 dissous (pCO 2 ) par rapport à l’équilibre avec l'atmosphère. Nous comparons ici les dynamiques couplées de la matière organique et du pCO 2 des deux systèmes fluviaux les plus grands et les plus riches en matière organique du monde. Les nouveaux ensembles de données sur le fleuve Congo...

Methane gas plumes have been discovered to issue from the seafloor in the Puget Sound estuary. These gas emission sites are co‐located over traces of three major fault zones that fracture the entire forearc crust of the Cascadia Subduction Zone. Multibeam and single‐beam sonar data from cruises conducted in years 2011, 2018, 2019, 2020, and 2021 id...

Optical water types (OWTs) were identified from an in situ dataset of concomitant biogeochemical and optical parameters acquired in the Amazon River and its tributaries, in the Lower Amazon region, at different hydrological conditions from 2014 to 2017. A seasonal bio-optical characterization was performed. The k-means classification was applied to...

Sea-level rise is one of the most critical challenges facing coastal ecosystems under climate change. Observations of elevated tree mortality in global coastal forests are increasing, but important knowledge gaps persist concerning the mechanism of salinity stress-induced non-halophytic tree mortality. We monitored progressive mortality and associa...

Where rivers meet the sea, tides can exert a physical and chemical influence on the lower reaches of a river. How tidal dynamics in these tidal river reaches interact with upstream hydrological drivers such as storm rainfall, which ultimately determines the quantity and composition of material transferred from watersheds to estuaries, is currently...

Increasing seawater exposure is causing mortality of coastal forests, yet the physiological response associated with seawater-induced tree mortality, particularly in non-halophytes, is poorly understood. We investigated the shifts in carbon and nitrogen metabolism of mature Sitka-spruce trees that were dying after an ecosystem-scale manipulation of...

The global development of hydropower dams has rapidly expanded over the last several decades and has spread to historically non-impounded systems such as the Amazon River’s main low land tributaries in Brazil. Despite the recognized significance of reservoirs to the global methane (CH4) emission, the processes controlling this emission remain poorl...

As global climates shift, coastal systems experience changes that alter function within the tidal zone. However, it remains uncertain how changes in tidal extent and magnitude will alter coastal biogeochemical cycling. We present high‐frequency data collected in situ along two transects across a tidal creek and floodplain to capture how vertical an...

Methane (CH4) exchange between trees and the atmosphere has recently emerged as an important, but poorly quantified process regulating global climate. The sources (soil and/or tree) and mechanisms driving the increase of CH4 in trees and degassing to the atmosphere are inadequately understood, particularly for coastal forests facing increased expos...

Coastal landscapes are increasingly exposed to seawater due to sea level rise and extreme weather events. The biogeochemical responses of these vulnerable ecosystems are poorly understood, limiting our ability to predict how their role in local and global biogeochemical cycles will shift under future conditions. Here we evaluate how antecedent cond...

Increasing sea levels associated with climate change threaten the survival of coastal forests, yet the mechanisms by which seawater exposure causes tree death remain poorly understood. Despite the potentially crucial role of nonstructural carbohydrate (NSC) reserves in tree survival, their dynamics in the process of death under seawater exposure ar...

Estimations of the global carbon budget include a quantitative understanding of the evolving processes that occur along river-to-ocean gradients. However, high spatiotemporal resolution observations of these processes are limited. Here we present in situ measurements of the partial pressure of CO2 (pCO2) made through the Amazon River plume (ARP) du...

We evaluated the major pathways for methane emissions from wetlands to the atmosphere at four wetland sites in the Big Cypress National Preserve in southwest Florida. Methane oxidation was estimated based on the δ ¹³ C-CH 4 of surface water, porewater, and bubbles to evaluate mechanisms that limit surface water emissions. Spatially-scaled methane f...

Coastal shoreline forests are vulnerable to seawater exposure, the impacts of which will increase due to sea-level rise, but the long-term adaptation strategies and vulnerability of coastal forests are not well understood. We used whole-tree transpiration, leaf water potential, tree-ring width, and tree-ring δ 13 C (a proxy for intrinsic water use...

Rivers and streams represent <0.6% of the Earth's land surface but play a disproportionately large role in global biogeochemical cycles and provide locally relevant ecosystem services. However, knowledge of how rivers influence material budgets and ecosystem services has major gaps due to the lack of explicit consideration of tidally-influenced rea...

The systematic response of coastal ecosystems to inundation and salinity exposure is fundamental to their ecology and biogeochemical function. Here we observe and model freshwater-seawater interactions in a first-order stream—floodplain system where tidal access was recently restored. Subsurface flow and transport modeling were used to quantify and...

Hurricanes cause landscape-scale disturbances that affect biogeochemical cycling and water quality in coastal ecosystems. During Hurricane Irma’s passage through northern Florida, water movements driven by wind velocities up to 105 km h−1 caused a salinity peak in an estuary/blackwater river complex. Water quality was monitored across the 15 km sit...

Mitigating the environmental impacts caused by hydroelectric dams is a worldwide challenge. Aquatic ecosystems are most impacted during the reservoir filling phase, yet water quality and biogeochemical dynamics are not well-studied at this stage. Here we evaluate water quality and hydraulic parameters in the Araguari River (Amapá, Brazil) during th...

As CO2 levels in Earth’s atmosphere and oceans steadily rise, varying organismal responses may produce ecological losers and winners. Increased ocean CO2 can enhance seagrass productivity and thermal tolerance, providing some compensation for climate warming. However, the metabolic shifts driving the positive response to elevated CO2 by these impor...

The high temporal variability of the soil‐to‐atmosphere CO2 flux (soil respiration, RS) has been studied at hourly to multiannual time scales but remains less well understood than RS spatial variability. How RS fluxes vary and are autocorrelated at various time lags has practical implications for sampling and more fundamentally for our understandin...

Modifications in land-use and climate will result in shifts in the magnitude and composition of organic matter (OM) transported from wetlands to coastal waters, but differentiation between riverine and wetland OM sources in coastal areas remains a challenge. Here, we evaluate particulate and dissolved OM export dynamics in two representative estuar...

Coastal terrestrial–aquatic interfaces (TAIs) are dynamic zones of biogeochemical cycling influenced by salinity gradients. However, there is significant heterogeneity in salinity influences on TAI soil biogeochemical function. This heterogeneity is perhaps related to unrecognized mechanisms associated with carbon (C) chemistry and microbial commun...

The Belo Monte hydropower complex located in the Xingu River is the largest run-of-the-river (ROR) hydroelectric system in the world and has one of the highest energy production capacities among dams. Its construction received significant media attention due to its potential social and environmental impacts. It is composed of two ROR reservoirs: th...

Riverine dissolved organic carbon (DOC) contains charcoal byproducts, termed black carbon (BC). To determine the significance of BC as a sink of atmospheric CO2 and reconcile budgets, the sources and fate of this large, slow-cycling and elusive carbon pool must be constrained. The Amazon River is a significant part of global BC cycling because it e...

Biological processes exert important controls on geomorphic evolution of karst landscapes because carbonate mineral dissolution can be augmented and spatially focused by production of CO2 and biogenic acids from organic matter (OM) decomposition. In Big Cypress National Preserve in southwest Florida, depressional wetlands (called cypress domes) dis...