Constructed in the 1930s, these sewage ponds were used up until the 1960s, at which point they were abandoned. Over the next two decades, the ponds gradually filled in.
Native salt marsh vegetation began to recolonize the edges, but it remained sparse and never the filled in ponds themselves. Thus, in the 1980s, access was limited to the site to keep it preserved and in 1979-1980, Spartina foliosa plugs were transplanted to the sewage lagoon. The Spartina colonization was successful and the plants have continued to thrive.
Goal:
To investigate methods for restoring and enhancing salt marsh vegetation in disturbed habitats.
Description:
Alteration 1:
Storm induced river flooding is known to reduce soil salinity and cause extreme sedimentation, which can encourage spartina colonization if it raises the mudflat elevations. From October 2, 1979 to September 17, 1980, the conditions and soil salinity fluctuations encouraged the growth of spartina and seed germination.
Experiment:
Spartina patches were sorted into three experimental groups for testing. Some patches were given nothing (control), some were fertilized with nitrogen, and some were covered with tiles to test drainage effects. There was no significant difference between the plot groups, which may be attributed to poor seasonal timing, a small measurement period, or already nitrogen saturated soil from nutrient rich sediments and flooding.
Alteration 2:
Spartina seedlings were transplanted to the west side of the ponds, which had previously been lacking in vegetation. Of the 66 cores that contained spartina shoots, 18 survived. Next, 20 clumps raised from seeds were planted at 1 m intervals and covered with aviary wire to minimize grazing, which was a major cause of mortality in the first round of planted shoots.
The next seedling transplant garden tested for transplant shock differences in fresh, brackish, and sea water. 29 clumps were raised for seedlings with 313 shoots total, and were randomly planted at 1m intervals adjacent to the first seedling transplant. These new shoots were also covered with wire cages. No significant difference was seen between the transplants within the different water types.
In the transplant garden from mature S. foliosa, 100 shoots were placed along the tidal creek on the south end of the lagoon. Of these, nearly 100% survived and expanded.
The successful establishment of 840 Spartina plants outside range of existing stands indicates that the species was limited by dispersal over the sewge ponds.
Spartina clones are known to retain sediment, which creates a positive feedback loop. In other words, sedimentation encourages spartina colonization, which in turn encourages more sedimentation. This is a known cause of habitat conversion, creating more areas for salt marsh vegetation and shorebird feeding.
Monitoring studies done in 1979 and 1980 indicated that some patches of the spartina were established from seed, one of the first documented instances of Spartina establishment from seed in San Diego county.
Timeline:
-Sewage evaporation ponds constructed (1930’s)
-Sewage ponds abandoned (1960’s)
-66 cores transplanted (1979)
-Census records 33 patches of Spartina on edge of sewage lagoon (June 29, 1979)
-9 experimental transplant gardens established (June 18, 1980)
– Census shows 103 separate Spartina patches total (July 11, 1980)
-100 Spartina shoots transplanted along tidal creek near south end of sewage lagoon (June 19, 1980)
-20 clumps raised from seeds transplanted (August 5, 1980)
– 2nd seedling transplant garden established (October 13, 1980)
– Census shows 100% survival (October 28, 1980)
-Access limited and Spartina plugs transplanted into the southern pond (1980/81)
-Heavy winter storms and sedimentation (Winter 1993)
-Spartina clones number over 80 (1997)
-Major sediment accretion (1997-1998 ENSO)
-Current Projects: n/a
Bibliography/Sources:
Nordby, C., Zedler, J., Williams, P., Boland J. “Coastal Wetlands Restoration and Enhancement.” U.S. Department of the Navy- Wildlife and Natural Resource Office. November, 1980
Ward, Kristen M. “Episodic colonization of an intertidal mudflat by cordgrass (Spartina foliosa) at Tijuana Estuary” San Diego State University. 2000
Personal Contact: John Boland