The contribution of mangrove expansion to salt marsh loss on the Texas Gulf coast

Landscape-level shifts in plant species distribution and abundance can fundamentally change the ecology of an ecosystem. Such shifts are occurring within mangrove-marsh ecotones, where over the last few decades, relatively mild winters have led to mangrove expansion into areas previously occupied by salt marsh plants. On the Texas (USA) coast of the western Gulf of Mexico, most cases of mangrove expansion have been documented within specific bays or watersheds. Based on this body of relatively small-scale work and broader global patterns of mangrove expansion, we hypothesized that there has been a recent regional-level displacement of salt marshes by mangroves. We classified Landsat-5 Thematic Mapper images using artificial neural networks to quantify black mangrove (Avicennia germinans) expansion and salt marsh (Spartina alterniflora and other grass and forb species) loss over 20 years across the entire Texas coast. Between 1990 and 2010, mangrove area grew by 16.1 km2, a 74% increase. Concurrently, salt marsh area decreased by 77.8 km2, a 24% net loss. Only 6% of that loss was attributable to mangrove expansion; most salt marsh was lost due to conversion to tidal flats or water, likely a result of relative sea level rise. Our research confirmed that mangroves are expanding and, in some instances, displacing salt marshes at certain locations. However, this shift is not widespread when analyzed at a larger, regional level. Rather, local, relative sea level rise was indirectly implicated as another important driver causing regional-level salt marsh loss. Climate change is expected to accelerate both sea level rise and mangrove expansion; these mechanisms are likely to interact synergistically and contribute to salt marsh loss.The open access fee for this work was funded through the Texas A&M University Open Access to Knowledge (OAK) Fund

Arsenic Concentrations in Water Resources of the Choke Canyon/Lake Corpus Christi Reservoir System: Surface and Ground Waters

During the last several decades, human-related activities and populations have increased markedly along the Texas Gulf Coast, intensifying pressures on the water resources and ecosystems of this area. The Lake Corpus Christi/Choke Canyon reservoir system mitigates issues of water quantity while perturbing the quality of available fresh water resources. A driving force in the degradation of water quality is the potential loading and deposition of colloidal particles with a high affinity for trace metals and their incorporation into bedded sediments of the system. This “sequestration” may not be permanent, as redox sensitive metals (Mn, Fe, U, As and Mo) are susceptible to diagenetic remobilization due to oscillations in the hydrodynamic regime. This process may in turn result in a positive flux of metals to the water column adding a substantial stress to the aquatic environment and decreasing the quality of our freshwater supply. This research thus assessed the water quality of Lake Corpus Christi as a function of 1) tributaries and ground waters within the Nueces River basin, 2) present geochemical cycling of trace metals during temporal, spatial, and event driven oscillations of dissolved oxygen, and 3) sedimentary reservoirs in diverse sections of the lake (historic water quality as inferred from sediment cores). Water column profiles for trace metals assessed seasonal variations (summer vs. winter), an inflow event (episodic floods) and spatial distributions (oxygenated vs. stratified water column). The hypolimnetic cycling of Mn, Fe, Pb, Cr, V, Co and Ni resulted in higher enrichment factors in summer vs. winter and at the deeper station (stratified water column). The strong correlation of Pb and Mn cycling suggests diagenetic remobilization of Pb. However, the mildly reducing conditions did not entrain the cycling of As, Mo and U. Moreover, whereas Mo and U concentrations remain constant at background levels within surface waters of the whole system of study, dissolved As values in the Lower Nueces River basin (8-12 µg/L), are enriched by two orders of magnitude with respect to background levels measured in the upper basin (0.5 µg/L). The conservative behavior of As results in seasonally cycling with dilution during periods of higher inflow (winter and spring) and evapoconcentration in the summer. This contributes to the degradation of water quality and results in seasonal concentrations above the recently adopted standard for arsenic in drinking water (10 µg/L). Sediment cores encompassed the three reservoir zones: riverine, transition, and lacustrine, each with unique depositional environments. Average metal concentrations in surface sediments are below the threshold effect level (TEL) with the exception of Ni, but discrete depths indicate layers of enriched metal content. Normalized sediment profiles give further evidence of periods of enrichment and depletion of As, Co, Cu, Pb, Ni and Mn suggesting historic fluctuations in metal accumulation throughout the sediment profiles. Historical changes in material inputs to the sedimentary environments of the lake are further supported by significant changes in total organic matter and its isotopic signatures (d13C and d15N). Temporal trends, provided by the pre-reservoir conditions show decreasing values of Hg and Pb due to changes in atmospheric cycling and basinwide collection/redistribution processes. The uniform distribution of U and Mo around average sediment values suggests that the transport of these metals from upstream uranium mines has not impacted the sediments of Lake Corpus Christi. However, sedimentary peaks in As may support the selective transport and sequestration of this heavy metal due to uranium mining activities in Live Oak County. The extreme heterogeneity of As, Mo and U in ground waters suggests a mechanism for sequestration, such as sulfidization upon contact with water discharging along faults in Live Oak County enriched in H2S. The concentrations of these metals in selected ground waters are elevated well above the drinking water standards. An emphasis was placed on As because elevated levels are seen in the surface waters as well as ground waters (~10 and ~20 µg/L, respectively) . However, the ground water samples provide the first indication of enrichment in U (47 µg/L) in the Nueces River basin well above drinking water standard (30 µg/L). Sources for these selective enrichments can include both anthropogenic activities such as past mining processes and agricultural pesticide used in the drainage/aquifer basin, and natural geological inputs to ground water reservoirs

Characterization and Biodegradation of Water-Soluble Biomarkers and Organic Carbon Extracted From Low Temperature Chars

This study demonstrates that wildfires/biomass combustion may be an important source of labile pyrogenic water-soluble organic matter (Py-WSOM) in aquatic systems. Spectroscopic analysis (solid char and Py-WSOM) with Fourier transform infrared spectroscopy (FTIR) indicated that the Py-WSOM extracted from two low temperature chars (one wood, one grass) was dominated by polar moieties (-OH and C-O) derived from depolymerization and fragmentation of lignocellulose. Incubation experiments under aerobic conditions with unsterilized river water suggested that Py-WSOM and associated biomarkers may have a turnover rate of the order of weeks to months, consistent with mixing and transport conditions of riverine systems. For example, pyrogenic dissolved organic carbon (Py-DOC) had a half-life of 30-40 days. Turnover rate for the combustion biomarkers was shorter, with levoglucosan and free lignin phenols having a half life around 3-4 days and polymeric lignin components 13-14 days. The latter observations contradict earlier studies of the biodegradation of dissolved lignin and point to the need for re-assessment of lignin degradation kinetics in well-mixed riverine systems, particularly when such lignin components are derived from thermally altered plant material that may exist in a form more labile than that in highly processed riverine DOM. (C) 2013 Elsevier Ltd. All rights reserved

Limited mobility of dioxins near San Jacinto super fund site (waste pit) in the Houston Ship Channel, Texas due to strong sediment sorption

Sediments from a waste pit in Houston Ship Channel (HSC) were characterized using a number of molecular markers of natural organic matter fractions (e.g., pyrogenic carbon residues, PAHs, lignins), in addition to dioxins, in order to test the hypothesis that the dispersal and mobility of dioxins from the waste pit in the San Jacinto River is minimal. Station SG-6, sampled at the site of the submerged waste pit, had the highest dioxin/furan concentrations reported for the Houston Ship Channel/Galveston Bay (HSC/GB) system (10,000e46,000 pg/g), which translated into some of the highest reported World Health Organization Toxic Equivalents (TEQs: 2000e11,000 pg/g) in HSC sediments. Using a multi-tracer approach, this study confirmed our hypothesis that sludges from chlorinated pulps are a very likely source of dioxins/furans to this pit. However, this material also contained large quantities of additional hydrophobic organic contaminants (PAHs) and pyrogenic markers (soot-BC, levoglucosan), pointing to the co-occurrence of petroleum hydrocarbons and combustion byproducts. Comparison of dioxin/furan signatures in the waste pit with those from sediments of the HSC and a control site suggests that the remobilization of contaminated particles did not occur beyond the close vicinity of the pit itself. The dioxins/furans in sediments outside the waste pit within the HSC are rather from other diffuse inputs, entering the sedimentary environment through the air and water, and which are comprised of a mixture of industrial and municipal sources. Fingerprinting of waste pit dioxins indicates that their composition is typical of pulp and paper sources. Measured pore water concentrations were 1 order of magnitude lower than estimated values, calculated from a multiphase sorption model, indicating low mobility of dioxins within the waste pit. This is likely accomplished by co-occurring and strong sorbing pyrogenic and petrogenic residues in the waste pit, which tend to keep dioxins strongly sorbed to particles.Limited mobility of dioxins near San Jacinto super fund site (waste pit) in the Houston Ship Channel, Texas due to strong sediment sorptionpublishedVersio

Translocation of soil organic matter following reservoir impoundment in boreal systems: Implications for in situ productivity, Limnol

To evaluate the effect of reservoir flooding on carbon cycling over time, we studied sedimentary environments in three natural lakes that existed prior to impoundment and that have been incorporated in the larger lentic system of a 70-yr-old boreal reservoir in Quebec. Elemental and biomarker analyses were determined in all core intervals and three soil profiles to characterize source inputs of organic matter to sediments. Following impoundment, a twoto threefold increase in lignin concentrations (5 to 10–25 mg [10 g dry wt] �1) associated with similar decreases in selected terrigenous biomarker ratios (cinnamyl phenols: vanillyl phenols, C: V, 1.0–2.0 to 0.2–0.5; 3,5-dihydroxybenzoic acid: vanillyl phenols, 3,5-Bd: V, 0.2–0.5 to 0.1–0.2; and p-hydroxyl phenols: sum of vanillyl and syringyl phenols, P: [V�S], 0.3–0.7 to 0.1–0.4) illustrate the effect of soil erosion and subsequent translocation of surface soil organic matter (SOM) to sedimentary deposits. Using a mixing model based on mass-normalized biomarker yields in identified surface and mineral soil end-members, we show that although the proportion of mineral-derived SOM predominates in the receiving sedimentary systems during preflooding conditions (97–99 % of allochthonous inputs), translocated surface SOM increased in postflooding sediments to comprise up to 5–30 % of the total allochthonous organic matter inputs. Using a similar quantitative mixing model based on elemental C and N contents in the autochthonous and the mixed allochthonous end-members, we estimated that concomitant to the redistributio

The distribution and accumulation of mercury and methylmercury in surface sediments beneath the East China Sea

Abstract China is a massive mercury emitter, responsible for a quarter of the world’s mercury emissions, which transit the atmosphere and accumulate throughout its watercourses. The Changjiang (Yangtze) River is the third largest river in the world, integrating mercury emissions over its 1.8 × 106 km2 catchment and channelling them to the East China Sea where they can be buried. Despite its potential global significance, the importance of the East China Sea as a terminal mercury sink remains poorly known. To address this knowledge gap, total mercury and methylmercury concentrations were determined from 51 surface sediment samples revealing their spatial distribution, whilst demonstrating the overall pollution status of the East China Sea. Sedimentary mercury distributions beneath the East China Sea are spatially heterogeneous, with high mercury concentrations (> 25 ng g−1) corresponding to areas of fine-grained sediment accumulation. In contrast, some sites of fine-grained sediment deposition have significantly lower values of methylmercury (< 15 ng g−1), such as the Changjiang estuary and some isolated offshore areas. Fine-grained particles and organic matter availability appear to exert the dominant control over sedimentary mercury distribution in the East China Sea, whereas in situ methylation serves as an additional control governing methylmercury accumulation. Estimated annual sedimentary fluxes of mercury in the East China Sea are 51 × 106 g, which accounts for 9% of China’s annual mercury emissions

Climate Forecast Maps as a Communication and Decision-Support Tool: An Empirical Test with Prospective Policy Makers. Cartography and Geographic

This paper reports an empirical study of communication issues concerning climate forecasts. Students in a professional master’s degree program in environmental science and policy participated in the study as prospective policy makers. Participants viewed a set of currently issued precipitation forecast maps, and answered questions designed to assess, in the context relevant to agricultural and environmental decision making, their understanding and evaluation of the maps. Participants failed to understand some aspects of the information shown on the maps, in the current design, as the map makers intended. In particular, participants had difficulty with understanding probability forecast maps, and distinguishing probabilistic three-category forecasts and the amount of precipitation. Most participants evaluated the degree of agreement between the forecast and observation as agree only slightly or agree somewhat. More than half of the participants were not inclined to use the forecasts in agricultural decision making. Implications for improvement in design for better communication are discussed