Brief Environmental Description of Marshes

• Marshy areas, esp. in area of confluence of Tigris and Euphrates are underlain by a clay layer, about 3 meters below surface. That’s what keeps surface water from infiltrating into the ground water table.
• Groundwater below the clay layer is very saline, and not useful for any irrigation purposes (get figures on salinity). So if brackish water or irrigation return flows are used to sustain a new type of marsh, there would be no damage to the groundwater table because of the impermeability of the clay layer, and the saline groundwater beneath.
• There are a few vestigial marshes in the Al Hammer and Central area that survive, year-to year. It is not known what the salinity is nor how the vegetation has been altered to adapt to the new hydrologic regime.
• Long term data collected before 1970 (and before large-scale reclamation of the Central Marshes altered the overall basin salt balances) suggest that the original marshes in the Central region underwent salinity variation of between 900ppm during flood season, to 3,000 ppm during droughts. This should be considered the "normal" natural salinity variation for that area, although it probably was already affected by upstream agricultural drainage and soil salinization.
• Groundwater from Baghdad southward is naturally very saline up to a depth of 800m. It gradually improves northward, so that about 100 km north of Baghdad, groundwater is routinely used for agricultural irrigation and drinking water.
• Originally, many irrigation projects dealt with "reclamation" of marginal lands, as well as marshes, for the purpose of agriculture. That reclamation scheme included the construction of a drainage system for collection and conveyance of saline water draining off the crop fields after an irrigation application. It is essentially a dual canal system – fresh water for irrigation, and a return flow system of saline runoff. The soils and groundwater of virtually all arid and semi-arid areas of the world are saline. Most "reclamation" projects today, however, that are undertaken for the Ministry of Irrigation focus on construction of drainage systems and not expansion of agricultural land.
• Previously, irrigation return flows were simply returned to the main irrigation canals and mixed with fresher water for dilution. As one progressed from north to south, the irrigation waters got progressively more saline, and resulted in reduced crop yields, and accelerated salinization of soils. The large drainage canal, called _________________, is designed to carry the highly saline (___ppm) irrigation return flows to the Persian Gulf.
• It is possible to reconfigure the drainage system somewhat to serve as the supply brackish water for a new type of estuarine marsh in the areas that were formerly freshwater. Brackish water marshes are ecologically just as productive as freshwater marshes. Only difference is the type of biota. Advantage is there will always be a supply of brackish water to sustain the marsh. Estuarine species typically can survive a wide range of salinity – from freshwater spring flood flows to drought conditions.