Wetlands in the Mesopotamian Plain in southern Iraq were extensively drained in the 1990s. Re-flooding of drained areas commenced in 2003, and included parts of the Central marsh between the Euphrates and Tigris Rivers. New vegetation in the re-flooded areas of the Central marsh was studied in 2006. Most of the wetland plant species and communities widely distributed prior to drainage have reappeared, but there were some species and communities that did not re-establish. Aboveground plant biomass is recovering in some communities, but in most of the new communities, biomass and diversity were low. Postflooding sites were characterized by higher concentrations of chloride and bicarbonates in surface water and higher percent organic matter in sediment than those prior to drainage. Comparisons among the three study sites in the re-flooded areas and those between pre-drainage and postflooding sites suggests that differences in water quality, including more saline conditions in the re-flooded wetlands, might be hindering the biomass recovery. The water source being limited to only the Euphrates River, a much more subdued seasonal fluctuation in the quantity of water input and output, and inputs of contaminated waters appear to be responsible for the delay in vegetation recovery in the Central marsh.
Gross primary production (GPP) is a fundamental ecosystem process that sequesters carbon dioxide (CO2) and forms the resource base for higher trophic levels. Still, the relative contribution of different controls on GPP at the whole-ecosystem scale is far from resolved. Here we show, by manipulating CO2 concentrations in large-scale experimental pond ecosystems, that CO2 availability is a key driver of whole-ecosystem GPP. This result suggests we need to reformulate past conceptual models describing controls of lake ecosystem productivity and include our findings when developing models used to predict future lake ecosystem responses to environmental change.
Climate changes are predicted to influence gross primary production (GPP) of lakes directly through warming and indirectly through increased loads of allochthonous coloured dissolved organic matter (cDOM) from surrounding landscapes. However, few studies have investigated this combined effect. Here we tested the effects of warming (elevated 3℃) and cDOM input (three levels of humic river water addition) on GPP in autumn (2 months including open water and ice‐covered periods) in experimental pond ecosystems. The cDOM input decreased whole‐ecosystem GPP at natural temperature conditions mainly as a result of lower benthic GPP not fully counteracted by an increase in pelagic GPP, while warming increased whole‐ecosystem GPP due to a positive response of mainly pelagic GPP at all levels of cDOM input. Warming delayed autumn ice cover formation by 2 weeks but did not affect light availability in the water column compared to ambient ice‐covered treatments. Gross primary production during this period was still affected by warming and cDOM. The results stress the importance of accounting for multiple climate drivers and habitats when predicting lake GPP responses to climate change. We conclude that climate change may shift whole‐ecosystem GPP through different responses of habitat‐specific GPP to increasing cDOM inputs and warming.
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