Are Earth's Estuaries Endangered More by the Local or Global Activities of Man?
Macreadie,P.I., Allen, K., Kelaher, B.P., Ralph, P.J. and Skilbeck, C.G. 2012. Paleoreconstruction of estuarine sediments reveal human-induced weakening of coastal carbon sinks. Global Change Biology 18: 891-901.
Macreadie et al. further explored this important subject by reconstructing "the sedimentary records of cores taken from two sites within Botany Bay, Sydney - the site of European settlement of Australia - to look for human-induced changes in dominant sources of detritus," where the cores "covered a period from the present day back to the middle Holocene (~6000 years) according to 210Pb profiles and radiocarbon (14C) dating."
In doing so, the five Australian researchers found that "sedimentation rates in the last 30-50 years were considerably higher than during the rest of the Holocene," and that "C:N ratios declined and began to exhibit a microalgal source signature from around the time of European settlement, which could be explained by increased nutrient flows into the Bay caused by anthropogenic activity." In addition, they report that "analysis of stable isotopic ratios of 12C/13C showed that the relative contribution of seagrass and C3 terrestrial plants (mangroves, saltmarsh) to detritus declined around the time of rapid industrial expansion (~1950s), coinciding with an increase in the contribution of microalgal sources."
As for what these findings mean, quoting Macreadie et al., "we conclude that the relative contribution of microalgae to detritus has increased within Botany Bay, and that this shift is the sign of increased industrialization and concomitant eutrophication." And in light of "the lower carbon burial efficiencies of microalgae (~0.1%) relative to seagrasses and C3 terrestrial plants (up to 10%)," they say that "such changes represent a substantial weakening of the carbon sink potential of Botany Bay," adding that "this occurrence is likely to be common to human-impacted estuaries." Once again, therefore, there exists another good example of the local water-polluting activities of man having a much greater impact on our immediate environment than our global air-enriching activities, which release CO2 into the atmosphere and thereby enhance the vegetative productivities and water-use efficiencies of Earth's terrestrial plants.
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