Robert R Twilley

Louisiana State University | LSU · Department of Oceanography and Coastal Sciences (DOCS)

Tidal wetlands can be a substantial sink of greenhouse gases, which can be offset by variable methane (CH4) emissions under certain environmental conditions and anthropogenic interventions. Land managers and policymakers need maps of tidal wetland CH4 properties to make restoration decisions and inventory greenhouse gases. However, there is a misma...

Loss-on-ignition (LOI) has been widely used to estimate soil organic carbon (OC) content for coastal wetland soils, owing to recent interest in ‘blue carbon’ systems. Comparatively less attention has been paid to soil nutrient retention, specifically total nitrogen (TN), despite being a historically limited resource that influences C cycling and aq...

Mangroves are one of the most carbon‐dense forests on the Earth and have been highlighted as key ecosystems for climate change mitigation and adaptation. Hundreds of studies have investigated how mangroves fix, transform, store, and export carbon. Here, we review and synthesize the previously known and emerging carbon pathways in mangroves, includi...

Tidal marshes store large amounts of organic carbon in their soils. Field data quantifying soil organic carbon (SOC) stocks provide an important resource for researchers, natural resource managers, and policy-makers working towards the protection, restoration, and valuation of these ecosystems. We collated a global dataset of tidal marsh soil organ...

Hurricanes are one of the most common natural events that disturb estuarine and coastal wetlands along the Gulf of Mexico. The episodic and energetic events of hurricanes modify wetland hydrodynamics, sedimentation, and vegetation structure, which can impact the connectivity of coastal deltaic floodplains in processing riverine nutrients. Hurricane...

Unlabelled: The use of loss on ignition (LOI) measurements of soil organic matter (SOM) to estimate soil organic carbon (OC) content is a decades-old practice. While there are limitations and uncertainties to this approach, it continues to be necessary for many coastal wetlands researchers and conservation practitioners without access to an elemen...

Deltaic wetlands in coastal Louisiana are experiencing widespread changes in vegetation dynamics and distribution due to rising sea level and long-term modifications in hydrology and sediment supply. Using field and remote sensing data, we investigated how aboveground biomass (AGB) and C stocks change in response to seasonality along salinity and s...

Land loss in the Mississippi River Delta is due to the human-altered sediment budget, yet the relative contributions of building dams, levees and extracting subsurface resources are unknown. Here, using numerical models, we show how each cause contributed to the land loss crisis in Barataria Basin within the Mississippi River Delta. Before human in...

Deltaic floodplains are highly vulnerable to relative sea level rise (RSLR) depending on the sediment supply from river channels that provides elevation capital as adaptation mechanism. In river channels where levees have restricted sediment supply to coastal deltaic floodplains, river sediment diversions have been proposed as a restoration strateg...

Mangroves are known for large carbon stocks and high sequestration rates in biomass and soils, making these intertidal wetlands a cost-effective strategy for some nations to compensate for a portion of their carbon dioxide (CO 2 ) emissions. However, few countries have the national-level inventories required to support the inclusion of mangroves in...

Coastal river deltas are centers of surface water nitrate processing, yet the mechanisms controlling spatio‐temporal patterns in nutrient variability are still little understood. Nitrate fluctuations in these systems are controlled by complex interactions between hydrological and biogeochemical drivers, which act together to transport and transform...

We measured benthic fluxes of dissolved nutrients in subtidal sediments and intertidal soils associated with river-pulse events from Mississippi River via the operation of a river diversion structure at Caernarvon, LA. Experiments measuring benthic fluxes in subtidal habitats were conducted during the early spring flood pulse (February and March) e...

Increasing nitrate (NO3−) loading in rivers due to agricultural fertilization alters benthic nitrogen (N) cycling and shifts coastal wetlands from being a net source to net sink of reactive N. Heterotrophic N2 fixation that converts N2 to reactive N is often assumed negligible in eutrophic ecosystems and excluded in coastal N budget evaluations. We...

Nitrate (NO3–) enrichment in rivers over the last four decades has potentially shifted how coastal ecosystems process nitrogen (N). Shifts in N dynamics may be particularly significant in coastal deltaic floodplains when sediments are inundated during river flood stage as this may change the fate of NO3– transported to the coastal ocean. We evaluat...

Aim Mangrove wetlands span broad geographical gradients, resulting in functionally diverse tree communities. We asked whether latitudinal variation, allometric scaling relationships and species composition influence mangrove forest structure and biomass allocation across biogeographical regions and distinct coastal morphologies. Location Global....

The Wax Lake Delta (WLD) is an actively prograding delta in the Mississippi River Delta Plain that is otherwise experiencing widespread degradation and submergence of its coastal wetlands. The WLD is actively accumulating mineral and organic sediment that increases soil surface elevation, changing emergent wetland communities as the young delta dev...

Hydrology is a critical driver controlling mangrove wetlands structural and functional attributes at different spatial and temporal scales. Yet, human activities have negatively affected hydrology, causing mangrove diebacks and coverage loss worldwide. In fact, the assessment of mangrove water budgets, impacted by natural and human disturbances, is...

International efforts to restore degraded ecosystems will continue to expand over the coming decades, yet the factors contributing to the effectiveness of long‐term restoration across large areas remain largely unexplored. At large scales, outcomes are more complex and synergistic than the additive impacts of individual restoration projects. Here,...

Located at the mouth of large rivers, coastal deltaic floodplains are important ecosystems for trapping sediment and removing excess nitrogen introduced to the river through agricultural and urban runoff. Hydrological connectivity (the percent of river channel water interacting with floodplain wetlands), water age (the time elapsed since water ente...

Rising sea levels have increased flood risk in coastal communities on both the east and west coasts of the USA. The goal of this analysis is to approximate flood defense costs from cyclonic flooding as a partial means to evaluate the resilience of coastal communities. Storm surge models were previously constructed via an established approach to rep...

We tested the hypothesis that benthic fluxes will increase spatially in a coastal deltaic floodplain as sediment organic matter increases in response to developing hydrogeomorphic zones along a chronosequence of the active Mississippi River Delta. A continuous flow-through core system was used to incubate intact sediment cores from three hydrogeomo...

Storm surge models are constructed to represent the Louisiana coastal landscape circa 1850, 1890, 1930, 1970, 1990, 2010, 2030, 2050, 2070, 2090, and 2110. Historical maps are utilized to develop models with past landscapes while a continuation of recent landscape trends is assumed for future models. The same suite of meteorological wind and pressu...

Aboveground biomass (AGB) plays a critical functional role in coastal wetland ecosystem stability, with high biomass vegetation contributing to organic matter production, sediment accretion potential, and the surface elevation's ability to keep pace with relative sea level rise. Many remote sensing studies have employed either imaging spectrometer...

Mangroves are considered one of the most productive ecosystems in the world with significant contributions as carbon sinks in the biosphere. Yet few attempts have been made to assess global patterns in mangrove net primary productivity, except for a few assumptions relating litterfall rates to variation in latitude. We combined geophysical and clim...

We present here an integrated analysis of coastal deltaic floodplains in the active Atchafalaya Coastal Basin coupled to downstream deltaic estuaries to review how ecosystem properties self-organize around fluvial processes during river re-occupation as part of the delta cycle. The flood pulse of the river is critical to providing autogenic feedbac...

The deposition of suspended sediment is an important process that helps wetlands accrete surface material and maintain elevation in the face of sea level rise. Optical remote sensing is often employed to map total suspended solids (TSS), though algorithms typically have limited transferability in space and time due to variability in water constitue...

The co-evolution of wetland loss and flood risk in the Mississippi River Delta is tested by contrasting the response of storm surge in coastal basins with varying historical riverine sediment inputs. A previously developed method to construct hydrodynamic storm surge models is employed to quantify historical changes in coastal storm surge. Simplifi...

Management and restoration of coastal wetlands require insight into how inundation, salinity, and the availability of mineral sediment and nutrients interact to influence ecosystem functions that control sustainability. The Mississippi River Delta, which ranks among the world's largest and most productive coastal wetland complexes, has experienced...

The Louisiana coastal landscape comprises an intricate system of fragmented wetlands, natural ridges, man-made navigation canals, flood protection and oil and gas infrastructure. Louisiana lost approximately 1,883 square miles (4,877 sq km) of coastal wetlands from 1932 to 2010 including 300 square miles (777 sq km) lost between 2004 and 2008 due t...

Because mangroves store greater amounts of carbon (C) per area than any other terrestrial ecosystem, conservation of mangrove forests on a global scale represents a potentially meaningful strategy for mitigating atmospheric greenhouse‐gas (GHG) emissions. However, analyses of how coastal ecosystems influence the global C cycle also require the mapp...

The extensive coastal wetlands in Mississippi River Delta represent the seventh largest deltaic floodplain in the world, contributing to many services that sustain the economies of the region. Subsidence, sea level rise, saltwater intrusion, wave action from storms, and sediment depletion have contributed to chronic wetland losses, converting veget...

Because mangroves store greater amounts of carbon (C) per area than any other terrestrial ecosystem, conservation of mangrove forests on a global scale represents a potentially meaningful strategy for mitigating atmospheric greenhouse‐gas (GHG) emissions. However, analyses of how coastal ecosystems influence the global C cycle also require the mapp...

Much of the previous research on coastal deltaic land building has focused on the planform delta dimensions; whereas this research focuses on shifts in vertical elevation and deltaic island edge cross-sectional morphology in relation to a proposed conceptual model of deltaic island edge morphological development. This study was conducted using data...

Global-scale variation in mangrove ecosystem properties has been explained using a conceptual framework linking geomorphological processes to distinct coastal environmental settings (CES) for nearly 50 years. However, these assumptions have not been empirically tested at the global scale. Here, we show that CES account for global variability in man...

The exposure time is a water transport time scale defined as the cumulative amount of time a water parcel spends in the domain of interest regardless of the number of excursions from the domain. Transport time scales are often used to characterize the nutrient removal potential of aquatic systems, but exposure time distribution estimates are scarce...

This chapter focuses on the net primary productivity and carbon (C) dynamics of mangrove wetlands as related to the potential to sequester atmospheric C in above- and belowground biomass and in the soil. We discuss the large variation in ecosystem properties across different coastal environmental settings and pay particular attention to global patt...

Future conditions of coastal Louisiana are highly uncertain due to the dynamic nature of deltas, climate change, tropical storms, and human reliance on natural resources and ecosystem services. Managing a system in which natural and socio-economic components are highly integrated is inherently difficult. Sediment diversions are a unique restoration...

Deltas are globally important locations of diverse ecosystems, human settlement and economic activity that are threatened by reductions in sediment delivery, accelerated sea level rise, and subsidence. Here we investigated the relative contribution of river flooding, hurricanes and cold fronts on elevation change in the prograding Wax Lake Delta (W...

Wetland dominated estuaries serve as one of the most productive natural ecosystems through their ecological, economic and cultural services, such as nursery grounds for fisheries, nutrient sequestration, and ecotourism. The ongoing deterioration of wetland ecosystems in many shallow estuaries raises concerns about the contributing erosive processes...

This book presents a comprehensive overview and analysis of mangrove ecological processes, structure, and function at the local, biogeographic, and global scales and how these properties interact to provide key ecosystem services to society. The analysis is based on an international collaborative effort that focuses on regions and countries holding...

Old growth mangroves in existing protected areas store more carbon than restored forests or plantations. Carbon storage in such forests has economic value independent of additionality, offering opportunities for policy makers to ensure their maintenance, and inclusion in climate change mitigation strategies. Mangrove forests of the Everglades Natio...

Deltaic landscapes, such as the Mississippi River Delta, are sites of extensive conversion of wetlands to open water, where increased fetch may contribute to erosion of marsh edges, increasing wetland loss. A field experiment conducted during a storm passage tested this process through the observations of wave orbital and current velocities in the...

River deltas all over the world are sinking beneath sea-level rise, causing significant threats to natural and social systems. This is due to the combined effects of anthropogenic changes to sediment supply and river flow, subsidence, and sea-level rise, posing an immediate threat to the 500–1,000 million residents, many in megacities that live on...

Aim We developed a set of statistical models to improve spatial estimates of mangrove aboveground biomass ( AGB ) based on the environmental signature hypothesis ( ESH ). We hypothesized that higher tidal amplitudes, river discharge, temperature, direct rainfall and decreased potential evapotranspiration explain observed high mangrove AGB . Locati...

We examined the role of reactive iron (FeR) in preserving organic carbon (OC) across a subaerial chronosequence of the Wax Lake Delta, a prograding delta within the Mississippi River Delta complex. We found that ∼15.0% of the OC was bound to FeR, and the dominant binding mechanisms varied from adsorption in the youngest subaerial region to coprecip...

Belowground biomass is thought to account for much of the total biomass in mangrove forests and may be related to soil fertility. The Yela River and the Sapwalap River, Federated States of Micronesia, contain a natural soil resource gradient defined by total phosphorus (P) density ranging from 0.05 to 0.42 mg cm−3 in different hydrogeomorphic setti...

River water entering estuaries affects the physical and chemical environment at irregular intervals creating a highly dynamic aquatic habitat. Phytoplankton are important primary producers in estuaries that respond quickly to their changing environment. Over a 12-month period, the phytoplankton response was examined in terms of biomass, abundance,...

The world's coastal deltaic wetlands are threatened by relative sea level rise. Protecting these ecosystems requires understanding deltaic growth and few studies have focused on how vegetation influences this growth. Here we explore the ecogeomorphic evolution of Wax Lake Delta (WLD) using a remote sensing database consisting of 1083 Landsat 5 and...

Considering the challenge that the economic, social and ecological systems face -in order to know and mitigate the global climate change-, evidences of the functional structure of mangroves ecological system are presented revisiting the hypothesis presented by Yáñez-Arancibia et al. (1998), and revised latter by Yáñez-Arancibia et al. (2010): “the...

Given the significance of natural and built assets of the Gulf of Mexico region, the three states of Alabama, Louisiana, and Mississippi, leveraged their unique partnerships, proximity, and significant prior investments in cyberinfrastructure (CI) to develop the Northern Gulf Coastal Hazards Collaboratory (NG-CHC). This collaboratory was establishe...

Nutrient biogeochemistry associated with the early stages of soil development in deltaic floodplains has not been well defined. Such a model should follow classic patterns of soil nutrient pools described for alluvial ecosystems that are dominated by mineral matter high in phosphorus and low in carbon and nitrogen. A contrast with classic models of...

Considering the challenge that the economic, social and ecological systems face -in order to know and mitigate the global climate change-, evidences of the functional structure of mangroves ecological system are presented revisiting the hypothesis presented by Yanez-Arancibia et al. (1998), and revised latter by Yanez-Arancibia et al. (2010): "the...

Frente al desafío que enfrentan los sistemas económicos, sociales y ecológicos de la zona costera, se presentan evidencias de estructura funcional del sistema ecológico de manglar, revisitando la hipótesis planteada por Yáñez-Arancibia et al. (1998) y revisada más adelante por Yáñez-Arancibia et al. (2010): “los manglares como hábitat forestado crí...

Recent studies suggest that coastal ecosystems can bury significantly more C than tropical forests, indicating that continued coastal development and exposure to sea level rise and storms will have global biogeochemical consequences. The Florida Coastal Everglades Long Term Ecological Research (FCE LTER) site provides an excellent subtropical syste...