s2ary
09-10-2007, 06:47 PM
Salt Panne Development
Perennial or open water pannes and pools are formed by a number of different processes.
• Natural Formations with multiple interconnected pools are usually formed as drainage features in the low marsh. (Panne Complexes) As the marsh rose up from the mud flat the sub-watershed was small and bowled allowing the gentle flow to meander around vegetation. This is why most naturally forming panne complexes are associated with the terminus portions of channels.
• Upland depressions (Vernal Pools) submerged with sea level rise can form huge panne complexes, but again the constant erosive forces of filling and draining the complexes ensures that a tide channel is closely associated with the panne system. When flood tides reach the panne after an extended neap tide cycle, evaporation has lowered the water levels in the panne. Because the water inside the panne is lower than the water outside the panne, water from outside the panne rushes in to fill the panne. Over time erosion caused by the rushing water erodes a channel into the panne.
• Peat blocks removed by ice caking are often associated with isolated small pannes.
• Long-term surface deposition of foreign materials can smother marsh vegetation causing a depression in the marsh surface.
Temporal or vegetated pannes are usually formed by;
• Peat blocks removed by ice caking.
• Long-term surface deposition of foreign materials can create depressions that are wet during portions of a monthly tide cycle. If the dry portions of the tide cycle are more than a few weeks of the monthly tide cycle vegetation can persist in the panne.
• Localized surficial drainage patterns can also case an area to be wetter than the surrounding marsh.
The current understanding is that Pannes cycles are dictated by approximately 15-20 year cycles based on sulfide accumulation.
• Over a period of years hydrogen sulfate accumulation increases in a panne complex. As the accumulation increases it negatively effects plant growth. As the marsh plants begin dying, the area between the panne complex and the associated channel or rill the frequency and water volume of tidal exchanges into the panne complex increases. During this period of rejuvenation, sulfur toxicity in the panne complex is flushed out or reduced. As the favorable growing conditions return, the plants slowly close the opening between the channel and the panne complex. During this period the pool depth and surface area may only vary by 6 inches or less. But because the range of high tide is only 4 feet, a six inch decrease in elevation results in approximately a 25% frequency increase in tidal exchange.
• Another one of the processes in the sulfur cycle is an increase of Sulfuric acid which can lower the pannes pH. Altered pH levels can negatively affect panne productivity as well.
Perennial or open water pannes and pools are formed by a number of different processes.
• Natural Formations with multiple interconnected pools are usually formed as drainage features in the low marsh. (Panne Complexes) As the marsh rose up from the mud flat the sub-watershed was small and bowled allowing the gentle flow to meander around vegetation. This is why most naturally forming panne complexes are associated with the terminus portions of channels.
• Upland depressions (Vernal Pools) submerged with sea level rise can form huge panne complexes, but again the constant erosive forces of filling and draining the complexes ensures that a tide channel is closely associated with the panne system. When flood tides reach the panne after an extended neap tide cycle, evaporation has lowered the water levels in the panne. Because the water inside the panne is lower than the water outside the panne, water from outside the panne rushes in to fill the panne. Over time erosion caused by the rushing water erodes a channel into the panne.
• Peat blocks removed by ice caking are often associated with isolated small pannes.
• Long-term surface deposition of foreign materials can smother marsh vegetation causing a depression in the marsh surface.
Temporal or vegetated pannes are usually formed by;
• Peat blocks removed by ice caking.
• Long-term surface deposition of foreign materials can create depressions that are wet during portions of a monthly tide cycle. If the dry portions of the tide cycle are more than a few weeks of the monthly tide cycle vegetation can persist in the panne.
• Localized surficial drainage patterns can also case an area to be wetter than the surrounding marsh.
The current understanding is that Pannes cycles are dictated by approximately 15-20 year cycles based on sulfide accumulation.
• Over a period of years hydrogen sulfate accumulation increases in a panne complex. As the accumulation increases it negatively effects plant growth. As the marsh plants begin dying, the area between the panne complex and the associated channel or rill the frequency and water volume of tidal exchanges into the panne complex increases. During this period of rejuvenation, sulfur toxicity in the panne complex is flushed out or reduced. As the favorable growing conditions return, the plants slowly close the opening between the channel and the panne complex. During this period the pool depth and surface area may only vary by 6 inches or less. But because the range of high tide is only 4 feet, a six inch decrease in elevation results in approximately a 25% frequency increase in tidal exchange.
• Another one of the processes in the sulfur cycle is an increase of Sulfuric acid which can lower the pannes pH. Altered pH levels can negatively affect panne productivity as well.