Salt marshes are highly effective carbon (C) sinks and bury more C per square meter annually than any other ecosystem. Reclamation and anthropogenic impacts, however, have resulted in extensive ...losses of salt marshes. Carbon credits can be generated and sold by restoring marshes, but only if C sequestration and net reductions in greenhouse gases (GHG) are reliably quantified. Restored marshes, however, may exhibit different patterns of GHG emissions than natural marshes and it is possible that they could temporarily become sources of N
O even in the usually N-limited estuarine environment. Research on short-term GHG flux following salt marsh restoration is limited to studies of two restored marshes which examined GHG flux more than six months after the return of tidal flooding. Here we report on a laboratory experiment in which soil cores collected from a drained agricultural marsh on the St. Lawrence Estuary were flooded with estuary water. Gas flux measurements immediately after flooding revealed small increases in N
O and CH
, but a large decline in CO
yielding, from a climatic perspective, a net cooling effect over the observation period. In addition to restoring the land's capacity to sequester C once a marsh develops, returning tidal flooding thus appears to have the added benefit of stemming large ongoing C losses. With more than 400 km
of undeveloped dykeland, Eastern Canada is well positioned to restore large sections of marsh and contribute to reducing atmospheric CO
concentrations.
We analyzed surface sediments from 23 northeast USA estuaries, from Maine to Delaware, and nine estuaries from Prince Edward Island (PEI, Canada), to determine how dinoflagellate cyst assemblages ...varied with nutrient loading. Overall the abundance of cysts of heterotrophic dinoflagellates correlates with modeled nitrogen loading, but there were also regional signals. On PEI cysts of Gymnodinium microreticulatum characterized estuaries with high nitrogen loading while the sediments of eutrophic Boston Harbor were characterized by high abundances of Spiniferites spp. In Delaware Bay and the Delaware Inland Bays Polysphaeridium zoharyi correlated with higher temperatures and nutrient loading. This is the first study to document the dinoflagellate cyst eutrophication signal at such a large geographic scale in estuaries, thus confirming their value as indicators of water quality change and anthropogenic impact.
•Dinoflagellate cyst eutrophication signal was studied in 32 NW Atlantic estuaries.•Nutrient loading is a significant predictor of cyst assemblages.•Abundance of cysts of heterotrophic dinoflagellates increased with N loading.•Indicator taxa varied regionally.
Our study of a St. Lawrence Estuary marsh reveals that, compared to native Spartina patens‐dominated vegetation, invasive Phragmites australis makes a greater contribution to soil volume and carbon ...stock (referred to as blue carbon). Phragmites' contributions to soil volume enhance marsh sustainability in face of sea level rise, and its greater contribution to soil carbon helps to reduce the atmospheric concentration of CO2. Phragmites australis (common reed) is a cosmopolitan species growing in fresh to brackish wetlands. An invasive genetic strain, introduced from Europe or Asia, has expanded extensively along the St. Lawrence River in the last few decades but has been little studied on the estuarine portion. We collected soil cores from three sites within an invasive Phragmites stand and one site within S. patens‐dominated stand in a St. Lawrence Estuary salt marsh near la Pocatiere, Quebec. We measured the bulk density, carbon content, volume, and mass of belowground organic matter in 2‐cm‐thick soil layers of three cores at each Phragmites site. Bulk density and carbon content were measured in 5‐cm‐thick soil layers of three cores at S. patens site. Results showed that soil in the Phragmites stands held 37–77% more blue carbon than in the S. patens‐dominated marsh. Based upon their diameter size, Phragmites rhizomes could be contributing 7.4–10.2 cm to the thickness in the upper 20 cm of soil. We suggest that any management of invasive Phragmites include consideration of its role in increasing blue carbon stocks and marsh resilience along with other ecosystem services.
Plain Language Summary
An aggressive invasive strain of the common reed (Phragmites australis) is widespread on the eastern coast of North America. It is rapidly spreading through salt marshes, the grassy meadows, which straddle mean sea level on the coast of Quebec's St. Lawrence Estuary. This reed is considered to degrade the value of the native salt marsh and its biodiversity by displacing native vegetation and the habitat it provides for birds and wildlife such as the Nelson's Sparrow, designated as a Species of Special Concern in nearby Maine. Our study of a St. Lawrence salt marsh, however, shows that the invasive reed can have positive effects on soil properties. We compared soils below the reed and the most common native grass, salt meadow hay (Spartina patens) and found 37–77% more carbon stored in the reed soil. Thus, growth of the reed increases the ability of salt marshes to reduce concentrations of atmospheric carbon dioxide and mitigate climate change. We measured how much the roots and rhizomes (underground stems) of the two species contributed to the soil volume and found that the reed contributed considerably more. Greater contributions to soil volume means that the elevation of the soil surface will increase faster in the reed marsh and help this tidal ecosystem to keep up with increased rates of sea level rise that will accompany climate warming. Thus, any management of the invasive reed should include consideration of its role in mitigation of climate change and marsh adaptation to sea level rise, along with other ecosystem values provided by the native vegetation.
Key Points
Phragmites australis has invaded Spartina patens‐dominated marshes of the St. Lawrence Estuary
Soils of invasive Phragmites had 37–77% greater C stocks than S. patens soils
Phragmites contributed 7.4–10.2 cm to the thickness of the top 20 cm of soil
We examined organic-walled dinoflagellate cysts from one ²¹⁰Pb-dated sediment core and 39 surface sediment samples from the northern Gulf of Mexico to determine the relationship between nutrient ...enrichment and cyst assemblages in this region characterized by oxygen deficiency. The core spans from 1962 to 1997 and its sampling location is directly influenced by the Mississippi River plume. Surface sediments were collected in 2006, 2007, 2008, and 2014 and represent approximately 1 to 4 years of accumulation. A total of 57 cyst taxa were recorded, and four heterotrophic taxa in particular were found to increase in the top section (1986–1997) of the core—Brigantedinium spp., cysts of Archaeperidinium minutum, cysts of Polykrikos kofoidii, and Quinquecuspis concreta. These taxa show a similar increasing trend with variations in US fertilizer consumption and Mississippi River nitrate concentrations, both of which increased substantially in the 1970s and 1980s. The same four heterotrophic taxa dominated dinoflagellate cyst assemblages collected near the Mississippi River Bird's Foot Delta where nutrient concentrations were higher, especially in 2014. We propose that these cyst taxa can be used as indicators of eutrophication in the Gulf of Mexico. A canonical correspondence analysis (CCA) supports this proposition. The CCA identified sea-surface nutrient concentrations, sea-surface temperature, and sea-surface salinity as the most important factors influencing the cyst assemblages. In addition, cysts produced by the potentially toxic dinoflagellates Pyrodinium bahamense and Lingulodinium polyedrum were documented, but did not appear to have increased over the past 50 years.
Conversion of wetlands by drainage for agriculture or other anthropogenic activities could have a negative or positive feedback to global warming (GWF). We suggest that a major predictor of the GWF ...is salinity of the wetland soil (a proxy for available sulfate), a factor often ignored in other studies. We assess the radiative balance of two northern salt marshes with average soil salinities > 20ppt, but with high (macro-) and low (micro-) tidal amplitudes. The flux of greenhouse gases from soils at the end of the growing season averaged 485 ± 253mgm − 2h − 1, 13 ± 30µgm − 2h − 1, and 19 ± 58µgm − 2h − 1 in the microtidal marsh and 398 ± 201mgm − 2h − 1, 2 ± 26µgm − 2h − 1, and 35 ± 77µgm − 2h − 1 in the macrotidal marsh for CO2, N2O, and CH4, respectively. High rates of C sequestration mean that loss of these marshes would have a radiative balance of − 981 CO2_eq.m − 2yr − 1 in the microtidal and − 567 CO2_eq.m − 2yr − 1 in the macrotidal marsh.
Khan, A. H., Levac, E., and Chmura, G. L. 2013. Future sea surface temperatures in Large Marine Ecosystems of the Northwest Atlantic. - ICES Journal of Marine Science, 70: 915-921.We analysed ...projections of future sea surface temperatures (SSTs) for six Large Marine Ecosystems (LMEs) of the Northwest Atlantic: the West Greenland Shelf, the Newfoundland-Labrador Shelf, the Scotian Shelf, the Northeast US continental shelf, the Southeast US continental shelf, and the Gulf of Mexico. We used state-of-the-art global climate models (CSIRO-Mk3.6, GISS-E2-R) and earth system models (CanESM2, HadGEM2-ES) and representative concentration pathways (RCPs) 8.5 and 4.5 that represent a range in possible future concentrations of atmospheric CO sub(2). Our analysis focuses on average February and August SSTs from the period 2071-2100 as the low and high temperatures of these months generally define the thermal habitat of a species. SSTs will increase in most, but not all, waters of the LMEs, and seasonality will increase in all LMEs. The difference in SSTs from the Gulf of Mexico to the Scotian Shelf may be reduced but differences will increase from the Scotian Shelf north. Although past SST changes have been greatest on the Newfoundland-Labrador Shelf, ensemble average projections indicate that the greatest future change will occur on the Scotian Shelf. The variation in future SSTs is greater among models than between RCPs, suggesting that impact studies limited to a single model may be biased.
Analysis of the spatial distribution of the dinoflagellate cyst assemblages in 19 surface sediment samples collected from 3 Buzzards Bay (Massachusetts, USA) embayments revealed the potential ...applicability of dinoflagellate cysts as biological indicators of environmental conditions in estuarine systems. Sites with the highest levels of toxic pollution and hypertrophic conditions are characterized by the lowest dinoflagellate cyst species-richness and concentrations. Among the abiotic factors influencing the distribution of dinoflagellate cysts, nutrients and toxic pollution are the major controls, as in these embayments salinity and temperature variability is low. Principal component analysis, based on the proportions of cyst taxa, indicated that cyst assemblages gradually change when moving away from the sources of nutrient pollution, sewage outfalls in particular.
An increase in greenhouse gas emissions has led to a rise in average global air and ocean temperatures. Increased sea surface temperatures can cause changes in species’ distributions, particularly ...those species close to their thermal tolerance limits. We use a bioclimate envelope approach to assess potential shifts in the range of marine macroalgae harvested in North American waters: rockweed ( Fucus vesiculosus Linnaeus, 1753), serrated wrack ( Fucus serratus Linnaeus, 1753), knotted wrack ( Ascophyllum nodosum (Linnaeus) Le Jolis, 1863), carrageen moss ( Chondrus crispus Stackhouse, 1797), and three kelp species ( Laminaria digitata (Hudson) J.V. Lamouroux, 1813; Saccharina latissima (Linnaeus) C.E. Lane, C. Mayes, Druehl et G.W. Saunders, 2006; and Saccharina longicruris (Bachelot de la Pylaie) Kuntze, 1891). We determined species’ thermal limits from the current sea surface temperatures associated with their geographical distributions. Future distributions were based on sea surface temperatures projected for the year ∼2100 by four atmosphere-ocean general circulation models and earth system models for regional concentration pathways (RCPs) 4.5 and 8.5. Future distributions based on RCP 8.5 indicate that the presence of all but rockweed ( F. vesiculosus) is likely to be threatened by warming waters in the Gulf of St. Lawrence and along the Atlantic coast of Nova Scotia. Range retractions of macroalgae will have significant ecological and economic effects including impacts on commercial fisheries and harvest rates and losses of floral and faunal biodiversity and production, and should be considered in the designation of marine protected areas.
Byers, S.E. and Chmura, G.L., 2014. Observations on shallow subsurface hydrology at Bay of Fundy macrotidal salt marshes. Hydrology is a major driver of salt marsh functions and the ecological ...services they support. Sediment saturation, and thus subsurface hydrology, affects salt marsh vegetation productivity, zonation, and survival. Subsurface hydrology influences rates of subsidence; concentrations of nutrients, organic matter, and oxygen; fluxes of the greenhouse gases methane and nitrous oxide; and sediment toxicity. Therefore, baseline knowledge of subsurface hydrology is crucial in predicting and managing change in salt marshes. Previous research on subsurface hydrology has mostly been conducted in organogenic, microtidal marshes that do not provide suitable models for minerogenic, macrotidal marshes such as those in the Bay of Fundy. In this study, we examine drivers of subsurface hydrology and compare two pairs of reference and recovering marshes with tidal amplitudes of 6 to 12 m. Measurements in PVC wells at various depths reveal differences between seasons, during the neap-spring tidal cycle, and between channels of differing depths. We suggest that soil characteristics, duration between inundation events, marsh geomorphology, and precipitation all are more important drivers of subsurface hydrology in Bay of Fundy marshes than tidal height. Our observations also indicate that subsurface hydrology generally can be restored to previously drained marshes. Bay of Fundy marshes are likely to be more ecologically resistant to rising sea level because changes in tidal heights will have a minimal effect on subsurface hydrology. Thus, restoration of the many Bay of Fundy marshes previously drained for agriculture is likely to be successful in offsetting losses expected in more vulnerable, microtidal marshes.
Efforts to address anthropogenic global climate change (AGCC) require public understanding of Earth and climate science. To meet this need, educational reforms and prominent scientists have called ...for instructional approaches that teach students how climate scientists examine AGCC. Yet, only a few educational studies have reported clear empirical results on what instructional approaches and climate education technologies best accomplish this goal. This manuscript presents detailed analysis and statistically significant results on the educational impact pre to post of students learning to use a National Aeronautics and Space Administration (NASA) global climate model (GCM). This series of case studies demonstrates that differing instructional approaches and climate education technologies result in differing levels of understanding of AGCC and ability to engage with policies addressing it. Students who learned the scientific process of climate modeling scored significantly higher pre to post on exams (quantitatively) and gained more complete conceptual understandings of the issue (qualitatively). Yet, teaching students to conduct research with complex technology can be difficult. This study also found lecture-based learning better improved recall of facts about GCMs tested by multiple-choice questions. Our findings indicate what educational systems and related technologies might provide the public with the conceptual understandings necessary to engage in the political debate over AGCC.
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