The fact is that numerous rooted macrophyte structures are not full of naturally strong and healthy particles and sediments and nutrients. It is because of the restriction or absence of these particles, sediments and nutrients that the study of these systems has not been as extensive and thorough as the concentration on the terrestrial structures when understanding the fate, sources and sinks of Co2 levels in the ecosystems and the plants structures (e.g., Drake and Leadley 1991). Researchers assert that "rooted macrophyte systems can be sources of CO2, Chapter 4 and other gases through microbial processing of organic matter in the sediments and direct emission from leaves" (Delaune et al. 1990).
Table 1. Total net primary production (NPP) from world systems (Modified from Valiela, 1984)
% of Total
% of Total
gC m-2 y-1
Algal Beds & reef
Estuaries (exc. marsh)
Swamp and Marsh
Lakes and Streams
Total Benthic (Aquatic Vegetation)
(i.e., algal beds, reefs, seagrasses, mangroves, swamps and marshes)
1 This is (NPP in gC m-2 y-1) x (area).
Fate of Fixed Carbon
The reason that the carbon cycle is so important to the overall global ecosystem is because change in the carbon structure can result in the overall marine structure of our planer. The researchers Borges and Gypens (2010) in their study write that the "accumulation of anthropogenic CO2 in the ocean has altered carbonate chemistry in surface waters since preindustrial times and is expected to continue to do so in the coming centuries. Changes in carbonate chemistry can modify the rates and fates of marine primary production and calcification. These modifications can in turn lead to feedback on increasing atmospheric CO2." They further write that the alterations and switches taking place in the nutrient levels and sources of the rivers can elevate the irregularity of carbon chemistry in the atmosphere. They assert that these alterations mainly occur due to the management regulation policies that have been implemented over the years. This is one aspect that influences the nutrient levels on the coastal areas more so than oceanic acidification as well irrespective of whether the influence is positive or negative (Borges and Gypens, 2010).
This is why the fate of carbon in the ecosystems is an important topic of discussion in today's era. Especially when talking the near-shore coastal structures, the carbon chemistry and structure may be affected by the loss of carbon to the coastal sediments through the regular burial or recycling processes in the systems or though the consumption of herbivores or mere transference to the shoreline to dissolve with other organic substances. All of these aspects if not controlled or managed properly can result in irregular carbon chemistry and changes that could in turn impact the nutrient levels on the coasts (Schwarz et al., 2000; Raven and Falkowski, 1999; Plus et al., 2001; Philippart, 1995a and b; Ralph et al., 2007).
The assessments of the rates of carbon burial near the coasts are again very irregular and range from the low levels of 0.2 to as high as 1 cm y-1. This ratio is common for burial in most marsh structures though. The reason for this is usually the soil and seabed near the shores is already rich in nutrients with more than 25% of the accreting substances being completely natural and organic, with the accumulation ratios of more than ca. 4 gC y-1 (Thom 1992). "Carbon sinks as peat accumulation are great in some systems on the East and Gulf coastal where marshes have been forming for 3,000-4,000 yrs" (Bricker-Urso et al. 1989). In another study the researcher explains that "other marsh systems are very new, and have little surface peat accumulation. For example, salt marshes in the Pacific Northwest are buried on the average of once every 300 yrs by ocean sediments as a result of large earthquakes and land subsidence" (Atwater 1987). Even though this subject is not analyzed in most researches, this entire process can very efficiently restructure the entire march structure near the coasts and requisition the carbon percentages in the marsh forever.
"The estimates for direct consumption through herbivore pathways and detrital pathways are not well-known in general for these systems. What is evident is that large proportions of the standing crop of these plants can be removed by animals, which shred material and/or eat the material directly" (Adam 1990).
"The loss of 59.5 km2 y-1 in the Mississippi River deltaic plain due to reduced sediment input is an extreme example of what can happen" (Britsch and Kemp 1990). An important fact to note here is higher levels and percentages of floods can initially elevate the carbon fixation levels. The overall metabolic structures and procedures can also be changed with higher flooding instances. Considering this facet, Morris and his colleagues (1990) in their respective study analyzed and exhibited a very positive and strong association between the average sea level and the aggregate yearly production of carbon. They align this higher production levels with the increased levels of floods. When specifically analyzing the areas that have experienced higher floods, like the Mississippi delta, the assessments show that there is an elevated level of benthic respiration as well as a simultaneous decrease in the aggregate production levels. There is also a heightened level of and greenhouse gas emissions in the Mississippi delta due to the higher levels of flooding (Delaune et al. 1990).
In an earlier study conducted by Andrews and Abel (1879), the researchers focused on the use of photosynthetic pathway by the seagrasses to balance and manipulated the carbon levels on the coasts. This was of interest to the researchers as findings had indicated that the ratios of the sea grass carbon isotope was similar to that present on the C4 plants as oppose to the C3 plants which had been the previous consensus. The results of the study showed that the plant called T. testudinum could very easily be categorized as a C4 plant even though its leaf structure was very different from all the other known C3 and C4 plants in the territory. Furthermore, the plant had no indications of being similar or even near the Kranz structure as that was the structure most common for C4 plants to have. The study also established that there were many freshwater submerged aquatic plants had metabolic structures that resembled the C3 structures and had characteristics similar to many seagrasses taxonomically (Andrews and Abel, 1879; see for similar results Grice et al., 1996; Hellblom and Bjork, 1999).
"Changes in the stable carbon isotope composition of Thalassia testudinum (turtle grass) leaves were measured in response to in sltu light-reduction treatments in Tampa Bay, Florida, USA," in the recent study by Durako and Hall (1992). The results of the study showed that the "leaf SI3C values of shaded T. testudinum were significantly lower than those of unshaded controls in both shallow (0.75 m below MLW) and deep (2 m below MLW) sites. Changes in leaf 6I3C were correlated with differences in the relative amount of light reaching the experimental treatments, and the magnitude of the responses increased between 1 and 3 mo after initiation of the shade treatments. Because of the close proximity of the experimental and control sites, the decrease in 6I3C in response to shading probably reflects a process (i.e. isotopic fractionation) effect rather than a source (i.e. dissolved inorganic carbon) effect." In the study they concluded that during times when the light is significantly decreased so much so that it restricts the photosynthetic rates within the T. testudinum, the carbon chemistry and production increases significantly so much so that it appears to have no limits (Durako and Hall, 1992).
In an earlier study, Abel (1984) focused on the photosynthetic carbon increase of the Thalassia hemprichii (Ehrenb) which is a very common tropical sea grass). The researcher chose to study the phenomenon of using various methodologies. The results showed that the "photosynthesis in buffered seawater in media in the range of pH 6 to pH 9 showed an exponentially increasing rate with decreasing pH, thus indicating that free CO2 was a photosynthetic substrate. However, these experiments were unable to determine whether photosynthesis at alkaline pH also contained some component due to HCO3? uptake" (Abel, 1984).
In another relevant and recent study, Beer (1997) highlighted the level and extent to which another sea grass named Zostera marina L. was capable of making use of or exploiting the compound - HCO3. The study analyzed the use of the compound as the exterior inorganic-carbon resource to perform photosynthesis. The…