We examine the potential for diurnal variation in elevation of saltmarsh surfaces as a source of error in long-term experiments; errors particularly critical in high precision studies that employ the ...surface elevation table (SET) as a means to monitor elevations. The field study was carried out along the New Brunswick coast of the Bay of Fundy in high and low zones at three marshes with different tidal ranges. We used a total of 16 benchmark pipes and controlled for daily variability in evapotranspiration (ET), as well as timing of tidal flooding, two factors that affect soil water storage, and consequently soil volume. In six of nine trials we detected significant elevation change over periods as short as 5 d. Marsh-wide averages ranged from 1.2 to 3.0 mm, greater than the yearly increase in relative sea level in many regions. Wood Point marsh had the highest tidal range, but lowest soil organic matter content, giving its soils the lowest compressibility and little sensitivity to ET during two of three trials; the average change in elevation in Wood Point high marsh stations was 4.0 mm during the last trial. Greater differences later in the growing season (while temperature changes were minor) at Wood Point and another site suggest that plant transpiration drove changes in water storage at those sites. Significantly greater differences in elevation with lower plant cover in the third marsh suggests that evaporation drove changes in water storage there. Surface elevation change due to ET should be of greatest concern to SET users in temperate regions where there are large changes in plant biomass and variable temperatures. Variation due to plant transpiration could be reduced if yearly monitoring is scheduled before the start of the growing season.
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.
Modifications of the hydrology of the Florida Everglades began in the 1880s. Impacts due to changes in the hydrological regime, as well as nutrient enrichment are clear in the northern Everglades. ...Although these changes were more subtle in the southern Everglades, altered hydroperiods and plant communities are targeted for restoration. Identification of restoration goals requires knowledge of past conditions, but detailed vegetation surveys prior to the pre-drainage era are lacking. Palynological studies can help fill this void. Interpretations based upon pollen and plant spores alone are limited by low pollen production of the dominant marsh species and low plant diversity in the ecosystem. In some regions the occurrence of other microfossils present in palynological preparations has been used to help interpret hydrological regimes and nutrient status and here we explore that potential for paleoecological records from the Everglades.
In this study we report the distribution of various microfossils found within pollen zones identified in sediments cored from three tree islands in Shark River Slough, Everglades National Park. Using published modern pollen analogues we classified paleovegetation zones as slough, sawgrass marsh, tree island or tree island edge and documented the abundances of microfossils of algae, fungi, cyanobacteria and testate amoebae. Tree island zones, indicative of relatively short hydroperiods, were characterized by highest abundances of fungal material, testate amoebae and the base of the deposits, by the cyanobacterium,
Gloeotrichia. Much of the fungal material appears to be associated with plant roots, and the mycorrhizal
Glomus is locally abundant. The taxonomic affinity of the testate amoebae has not been determined, but some were arcellaceous forms that included charcoal particles in their tests.
Gloeotrichia also is found in marsh and slough deposits. Its occurrence in the latter probably signals minimal water depth.
Botryococcus and Zynemataceae zygospores are found in all deposits, but are less abundant in the tree island deposits. Both groups are probably part of the periphyton flora, but
Botryococcus has not been recorded in phycological studies of the Everglades. Observation of these algae in the seasonally dry Everglades is consistent with other studies where they have been reported to represent shallow, slow moving waters, but inconsistent with the assumptions of meso- or eutrophic conditions commonly made in other studies. Our observation of the alga
Botryoccocus and the meroplanktonic cyanobacterium
Gloeotrichia in the historically oligotrophic Everglades challenges their status as indicators of nutrient enrichment.
We examine rates of salt marsh accumulation in three marshes of the outer Bay of Fundy. At each marsh we selected a site in the high marsh with similar vegetation, and thus similar elevation. ...Accretion rates were estimated by 137Cs, 210Pb, and pollen stratigraphy to estimate rates of change over periods of 30, 100, and ∼170 years, respectively. These rates are compared with records from the two closest tide gauges (Saint John, New Brunswick, and Eastport, Maine) to assess the balance of recent marsh accretion and sea-level change. Averaged marsh accretion rates have ranged from 1.3±0.4 to 4.4±1.6 mm·year-1 over the last two centuries. Recent rates are similar to the rate of sea-level change recorded at Eastport, Maine, suggesting that they are in step with recent sea-level change but very sensitive to short-term variation in relative sea level. Based on the pollen stratigraphy in the marsh sediments, the marsh accretion rate was higher during the late 18th to early 19th century. Higher rates probably were due to local increases in relative sea level as a result of neotectonic activity and may have been enhanced by increased sediment deposition through ice rafting.
Surface sediment samples from 24 sites within eleven back-barrier lagoons of Rhode Island and Massachusetts (USA) contain abundant (200–6000 cysts cm
−3) and diverse (up to 40 taxa) dinoflagellate ...cyst assemblages. The lowest cyst concentrations and diversity are observed in lagoons with low salinity (<10). The pattern of spatial distribution of dinoflagellate cysts in these shallow estuarine environments is described. We assessed the relationship between the available multi-year water quality data and the composition of the dinoflagellate cyst assemblages using canonical correspondence analysis. Temperature and salinity are found to be the primary abiotic factors influencing cyst distribution in the coastal lagoons.
The ecological importance of Plantago maritima within a salt marsh on the Bay of Fundy is documented through measurements of cover, density, and biomass. During late August 1993, peak standing crops ...of Plantago were as high as 532 g m-2, and composed as much as 96% of the biomass of a stand of vegetation. Plantago is a dominant component of the marsh vegetation at an elevation just above the Spartina alterniflora-dominated low marsh, and is found as a dominant when growing in association with a number of plant species characteristic of the high marsh. We hypothesize that the existence of this community is dependent upon regular ice-shearing of Spartina patens, which would otherwise competitively exclude Plantago. This hypothesis is supported by the elevational limits of Plantago dominance and the geographical limitation of Plantago communities to portions of the northwestern Atlantic subjected to winter temperatures which average below 0°C.
We assessed the impact of nutrient additions on greenhouse gas fluxes using dark static chambers in a microtidal and a macrotidal marsh along the coast of New Brunswick, Canada approximately monthly ...over a year. Both were experimentally fertilized for six years with varying levels of N and P. For unfertilized, N and NPK treatments, average yearly CO2 emissions (which represent only respiration) at the microtidal marsh (13, 19, and 28 mmoles CO2 m-2 hr-1, respectively) were higher than at the macrotidal marsh (12, 15, and 19 mmoles m-2 hr-1, respectively, with a flux under the additional high N/low P treatment of 21 mmoles m-2 hr-1). Response of CH4 to fertilization was more variable. At the macrotidal marsh average yearly fluxes were 1.29, 1.26, and 0.77 Mmol CH4 m-2 hr-1 with control, N, and NPK treatments, respectively and 1.21 Mmol m-2 hr-1 under high N/low P treatment. At the microtidal marsh CH4 fluxes were 0.23, 0.16, and -0.24 Mmol CH4 m-2 hr-1 in control, N, and NPK and treatments, respectively. Fertilization changed soils from sinks to sources of N2O. Average yearly N2O fluxes at the macrotidal marsh were -0.07, 0.08, and 1.70, Mmol N2O m-2 hr-1 in control, N, NPK and treatments, respectively and 0.35 Mmol m-2 hr-1 under high N/low P treatment. For the control, N, and NPK treatments at the microtidal marsh N2O fluxes were -0.05, 0.30, and 0.52 Mmol N2O m-2 hr-1, respectively. Our results indicate that N2O fluxes are likely to vary with the source of pollutant nutrients but emissions will be lower if N is not accompanied by an adequate supply of P (e.g., atmospheric deposition vs sewage or agricultural runoff). With chronic fertilization the global warming potential of the increased N2O emissions may be enough to offset the global cooling potential of the C sequestered by salt marshes.
Beginning in the 17th century many Bay of Fundy marshes were diked and drained for agricultural use, but storm breaching of dikes and failure of tidal gates has returned tidal flooding to some ...marshes. We investigated two breached and undiked salt marsh pairs in the Bay of Fundy to assess the potential for recovery of these reclaimed lands and improve our knowledge about salt marsh restoration. We examined the distribution of major species with respect to elevation and compared plant cover and production of reference and recovering marshes. The vertical range of both Spartina alterniflora and Spartina patens increased with tidal range - a condition recognized for S. alterniflora, but not previously reported for S. patens. Our results reveal that S. alterniflora and S. patens are inundated less frequently than in microtidal marshes and tolerate a large variation in inundation frequency and depth. The upper portions of the S. patens zone may not be submerged by tidal waters in some years, so hydroperiod (and its associated stresses) may play less of a role in limiting the lower elevation of a species distribution in the high marsh. Our comparisons of reference and recovering diked marshes inform not only restoration activities on the Bay of Fundy, but also give a perspective on recovery trajectories of reclaimed salt marshes in general. Regionally, the broad elevation range of S. alterniflora and high sediment deposition rates impart Bay of Fundy marshes with a high resilience and prospects for success of deliberate restoration efforts are promising, without the addition of fill required for marsh restoration in some regions. While marsh loss occurs in other areas the Bay of Fundy provides an opportunity to regain this resource.
Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering carbon dioxide (CO 2 ). The carbon (C) sequestered in vegetated coastal ecosystems, ...specifically mangrove forests, seagrass beds, and salt marshes, has been termed “blue carbon”. Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long‐term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of the C sequestration value of vegetated coastal ecosystems provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosystems. Here, we identify key areas of uncertainty and specific actions needed to address them.
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