Carbon Dynamics and Food Chains in Coastal Environments

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Table of Contents

Abstract
Introduction
Materials and Methods
Results
Discussion
Conclusion
Works Cited

Abstract

Physical processes mediating movement of nutrients in marine ecosystems may be studied using a variety of methods. The aim of this experiment was to determine the proportion of organic matter in sediments collected from the mangrove forest (M), the salt marsh(SM) and the sandy beach (SB) using loss on ignition (LOI) method and interpret the pattern of data obtained relative to biological and physical differences in the three habitats. Duplicate samples were collected from each habitat and analyzed for % organic content. It was found that samples from salt marshes had more % organic content, followed by mangroves and finally sandy beach.

Introduction

Sediments contain organic materials such as sugars, peptides, and lipids, among others (Graham and Longmore par. 4). They are an important source of recycled nutrients, food, and energy in marine ecosystems. The “capacity of wetlands to sequester and store carbon” has provided important conservation value in a period when these unique ecosystems have become increasingly vulnerable to climatic changes due to human activities (Chmura and Hung 74). =

An accurate measurement of percentage organic matter levels is important to detect changes in carbon (and other nutrients) cycling in the ecosystem. The measurement of percentage organic content by loss on ignition is quick, cheap, and relatively accurate and is subject to limited interference from inorganic carbon. This lab report describes the results of an experiment quantifying the percentage organic content in samples drawn from Mangrove, Salty Marsh, and Sandy Beach locations.

Materials and Methods

We collected duplicate samples from each of the M, SM and SB locations. One of the two samples was treated with 1M HCL and the other unaltered. All the samples were then dried at a temperature of 105^oC to remove all moisture content and then each sample ground in a clean mortar and pestle to a fine powder. We measured about 1g of the dry samples (W_s) into pre-weighed crucibles (W_c). The crucibles were then labeled on the bottom using a pencil. The samples were heated in the muffle furnace at 550^oC for 1.5 hours, cooled and then weighed immediately. The final weight (W_f) of the crucible and sample were recorded. From the weights recorded, we calculated the % organic content of the sediment sample using the formula:

Results

HABITAT
MANGROVE		SALTY MARSH		SANDY BEACH
MEAN % CONTENT
4.52	2.49	7.01	2.86	0.81	0.64
STANDARD DEVIATION
2.503193	1.903207	3.075878	2.987307	0.498591	0.325054
VARIANCE
6.265973	3.622198	9.461028	8.924004	0.248593	0.10566

A table of the computed mean, standard deviation and variance of % OM of samples from each of the habitats are given.

A graph of % OM against the number of sample.

This figure shows the comparison between % organic content of acidic and non-acidic samples obtained from the same habitat and from three different habitats. Note the high values of % OM for the acidic samples. The % OM values of SM are the highest, followed by those of M and SB respectively.

Discussion

Change in organic carbon content in sediments may be brought about by processes and factors such as eutrophication, mineralization, high sedimentation rates, erosion, adsorption, and fresh water flow into the ocean (Graham and Longmore par. 7). To evaluate carbon stores in soil, a “conversion variable that converts percentage organic matter data into organic carbon values” is used (Craft, Seneca, and Broome 177). The method has been developed for different ecosystems.

The results support the hypothesis that coastal wetlands, like the salt marshes and mangroves, sequester environmental carbon emissions and store them as biomass and sediment. From the results, it is observable that salt marshes contain the highest percentage organic content followed by mangroves and then the sandy beach. This finding is consistent with the results obtained by Ouyang and Lee in their study of coastal marsh sediments (5059). In this study, for samples collected from the same locality, acid treated samples had more % organic content than those that were not treated with acid. Acid treatment removed CaCO₃, which could have interfered with % organic content determination.

The amount inorganic carbon present in the sediment is inversely related to the % organic content, as the removal of the mineral by acid treatment led to record-high readings of soil organic content (standard deviation of 1.931449 for M, 2.833596 for SM, and 0.584738 for SB) compared to those of untreated (1.090845 for M, 0.822663 for SM, and 0.548694 for SB). Each of the one gram of untreated samples contained both organic and inorganic carbon and on combustion, only the organic component was degraded. The inorganic part remained intact, as it is relatively stable. Conversely, the acid treated sample consisted mainly of heat labile organic matter. Heiri, Lotter, and Lemcke found that exposure time, sample size and ignition temperature affect LOI results (109). Thus, maintaining standard conditions was important in this experiment.

The salt marsh and mangrove forest recorded high % organic content perhaps due to factors such as a high vegetation cover, which acts as a home or food for biota (Polunin 78). Other possible factors include a good biogeochemical cycling and transportation of nutrients, less erosion and floods, low tides, and human activities.

Conclusion

Loss on ignition is an important method of estimating % organic matter in soil samples from a diverse range of ecosystems. The aim of this experiment was to compare the percentage organic content of sediment samples obtained from mangrove, salty marshes, and sandy beach and analyze the data obtained for comparison with data obtained in the literature review. It was found that, of the three habitats, the salty marshes contained the highest % organic content followed by the mangrove then the sandy beach, reinforcing the view that salty marshes and mangroves play a significant role as carbon sinks.

Works Cited

Chmura, Gail, and Grace Hung. “Controls on salt marsh accretion: A test in salt marshes of Eastern Canada.” Estuaries 27 (2015): 70–81. Print.

Craft, Baines, Dan Seneca, and Will Broome. “Loss on ignition and Kjeldahl digestion for estimating organic carbon and total nitrogen in estuarine marsh soils: calibration with dry combustion.” Estuaries 14.2 (1991): 175-179. Print.

Graham, Richard, and Andy Longmore. Sediment organic matter and nutrient. Web.

Heiri, Oliver, Andre Lotter, and Gerry Lemcke. “Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results.” Journal of Paleolimnology 25 (2001): 101-110. Print.

Ouyang, Xi, and Sun Lee. “Updated estimates of carbon accumulation rates in coastal marsh sediments.” Biogeosciences 11 (2014): 5057–5071. Print.

Polunin, Nicholas. Aquatic Ecosystems: Trends and Global Prospects. London: Cambridge University Press, 2008. Print.

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