Thorhaug, Anitra , Harlem, Peter .
The long-term monitoring of persistent restored seagrass beds in urban-impacted Biscayne Bay: Urban sewage vs. causeway dredge and fill.
Intensive development of Northern Biscayne Bay between 1900 and 1980 resulted in nine Causeways (using bay bottom sediment including seagrasses), creating linear borrow pits and navigable channels, and isolated holes, purpose-built navigation channels (USACE Intracoastal Waterway, Port of Miami channel) cutting the bottom into segments, with spoil islands, marinas including sub-channels. Before 1930, borrow activity focused on filling barrier islands and mainland mangrove swamps, expanding existing islands and the residential creation of new islands, resulting in pits below the photic zone. 40% percent of the original bottom was dredged or filled (Harlem, 1979). Urban sewage was released into the inner Bay for many decades. Bottom sediments are typically fine quartz sand intermixed with calcium carbonate grains, much of which is biogenic, over submerged Miami Limestone (oolitic). Mangrove peat margins formed the majority of the barrier island western shore as well as smaller scattered deposits on the mainland. We discuss one portion of a larger project to restore the endemic SAV to Biscayne Bay commencing in 1976 (Thorhaug, 1976) during the first community Bay restoration project. From 1977-1984, two degraded sites were restored by two differing techniques. We compare persistent seagrass bed results from 1.) the planting in 1978 consisting of a shallow causeway site (0.2 to 1.4m) filled with sediment plus rock dredged from adjacent seagrass bottoms, and 2.) in 1984,a deeper site ( 1.1-2 m) wherein decades of sewage dumping, plus intracoastal channelization to the east had decimated seagrass. Manually planting with three species Thalassia testudinum, Halodule wrightii (beaudetti) and Syringodium filiforme planted by seeds and plugs at site1 and site 2 by sprigs. Persistent beds (34y and 28y,respectively) from the original restoration plantings occurred at each site. A diagnostic ecohistory, including the geological, construction, and restoration and ecology is described and compared between sites for 2 yr and 2011 metrics of seagrass monitoring, differences in depth,turbidity, and intermediate observations of persistence. Known physiological factors the seagrass restoration efforts overcame include persistent turbidity ,urban runoff, high energy events (storms, strong currents), annual wind events aligned to high fetch, as well as numerous anthropogenic factors. Post-planting monitoring of the restored sites shows that ecological services of sediment stabilization plant and animal communities have returned to these meadows. Harlem, Peter Wayne. (1979) Aerial Photographic Interpretation of the Historical Changes in Northern Biscayne Bay, Florida:1925-1976. Sea Grant Tech. Bull. No. 40, Florida Sea Grant, 151 p.
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1 - Yale University, School of Forestry and Environmental Studies, 370 Prospect St, New Haven, ct, 06511, usa
2 - Florida International University, Southeast Environmental Research Laboratories, Miami, Fl , 33199, usa
Presentation Type: Oral Paper:Papers for Topics
Date: Tuesday, July 10th, 2012
Time: 11:30 AM