8.1 Restore and enhance wetland and shoreline habitats to increase nutrient uptake and storage by plants

Key Message: Protecting, restoring and enhancing wetlands and shorelines is among the most cost-effective nutrient reduction and climate mitigation tools available to communities. New techniques for restoring wetlands, canals, ditches and shorelines to provide multiple ecosystem functions should be facilitated by public policies, regulations and outreach that expand and encourage their use.

Importance

Wetlands filter, store, and process water and nutrients, providing water quality and flood protection benefits. Coastal wetlands like mangrove forests and salt marshes occur at the critical land-water interface of the bay and its tidal tributaries. They help stabilize shorelines, buffer storm surge, and filter pollutants from land-based runoff. They also provide food and habitat for bay fish and wildlife and are critical nurseries for important recreational and commercial fish species. In addition to their role in cycling nitrogen and phosphorus, coastal wetlands store carbon in plant biomass and associated wet soils at roughly 25 times the annual rate of temperate and tropical forests (McLeod 2011). Protecting wetlands and restoring manmade ditches and altered shorelines will significantly remove and sequester nutrients and reduce harmful algal blooms.

Overview

Wetlands

Historically, freshwater and coastal wetlands in Sarasota County were degraded, fragmented and lost due to dredge and fill “land reclamation” operations to accommodate development. Land was cleared and marshes were ditched, drained, or dredged and filled to control mosquitos and make way for buildings and seawalls. The most recent shoreline habitat survey shows 55%, or 225 miles, of shoreline from Anna Maria to Venice Inlet, including upland-cut canal systems, are hardened by bulkheads and riprap (Serviss and Sauers 2003). Wetlands make up only 37% of shorelines, although areal extent of wetlands has remained relatively stable over the last 30 years because of regulation and restoration (Leverone et al., 2017).

The Sarasota Bay Estuary Program (SBEP) and Coastal & Heartland National Estuary Partnership (CHNEP) have restored several thousand acres of wetlands in Sarasota County over the last 30 years, and continue to build upon these efforts through native plantings, invasive plant removal, shoreline enhancement, habitat creation, and hydrologic restoration. SBEP, City of Sarasota, Town of Longboat Key, Sarasota County Government, and citizen volunteers have enhanced more than a mile of public shoreline at bayfront parks and preserves. For example, Sarasota County installed a series of wetlands and shoreline plantings in Red Bug Slough Preserve to enhance water quality and habitat. Design models predicted a monthly reduction in total nitrogen of 30%-68%. Other recent and planned projects include North and South Lido Key, Thaxton Preserve, Jim Neville Preserve, Phillippi Creek, Alligator Creek, Myakka Marsh, Warm Mineral Springs, and Salt Creek.

Two large regional projects slow and clean stormwater runoff using constructed wetlands. Sarasota County Government created 440 acres of wetlands and ponds to store flood waters as part of the Celery Fields Regional Stormwater Facility (CFRSF). In addition to providing flood protection to downstream neighborhoods, the Facility filters and processes nutrients before discharging stormwater to Phillippi Creek. The project also supports a world-renowned birding and recreation area. Following the CFRSF model, Sarasota County Government and the Southwest Florida Water Management District (SWFWMD) are creating wetlands and ponds to reduce excess freshwater flows to Dona Bay caused by past drainage and diversion activities. A reduction in nutrient loads to Dona Bay is expected.

Ditches and Canals

Manmade ditches and altered shorelines can be returned to a more natural state through many techniques. Strategic removal of weirs or dams placed in natural streams can improve water quality. Shorelines can be stabilized and enhanced using soil rich in organic carbon, native vegetation, and trees. If sufficient adjacent land exists, curves and bends can be added to ditches to slow waterway velocities and promote processing of nutrients and other pollutants. Snags and holes can provide refuge for fish, and fish ladders installed on water control structures to facilitate fish migration.

These features restore some natural ecosystem services, become more stable over time, and require less maintenance in the long run than typical drainage ditches. Reducing maintenance costs by enhancing ditch banks and shorelines is a current priority for the Sarasota County Stormwater Environmental Utility, CHNEP, and SBEP.

Sarasota County Government initiated an assessment of stormwater canals in the Phillippi Creek watershed in 2015 to develop recommendations for improving function and reducing long-term operation and maintenance costs. Typical maintenance involves herbicides, mowing, cleaning canals and culverts, removing obstructions, and occasionally dredging sediment. Although the outmoded practices of dredging and straightening creeks to maximize drainage or clearing and leaving bank vegetation to decay in the ditch, are still effective to prevent flooding, they are counterproductive to water quality and habitat protection. As available land for flood reduction and water quality improvement shrinks, existing land will need to serve more than one function.

The force of piped and channelized runoff causes erosion, inhibits shoreline vegetation, and degrades water quality. The Sarasota County study recommends retrofitting stormwater canals to improve flood control, water quality, and habitat with less maintenance (WEIS 2019). For example, woody vegetation in appropriate locations can stabilize banks better than existing grassy areas. It can also reduce mowing costs and increase nutrient uptake (Figure 8.1.1). Regenerative stormwater conveyance systems are another form of in-stream treatment. They consist of a series of pools and riffles with rocky surfaces above sand or gravel beds that allow for filtration and biological reduction of nutrients like nitrogen.

This technique requires additional land to create the slopes and multi-stage channels, which may limit its applicability in urban and suburban settings. During development of Palmer Ranch, the developer enhanced existing drainage ditches that were straight and narrow by flattening them with gradual 4:1 slopes more conducive to bank vegetation and maintenance. In addition, canopy trees were planted along the west side for afternoon shade and wetland plants installed along the shoreline. Strategic location of weirs elevated the water table. These changes required the developer to reserve 100 feet or more of additional land. Another 50 feet of land would have been required to meander the waterway.

Living Shorelines

In 2018, ESA Scheda and the SBEP prepared a living shoreline guidance document for homeowners, marine contractors, regulators, scientists, and coastal engineers to highlight nature-based shoreline stabilization options. The document helps guide decisions about use of a vegetated shoreline as a viable option for a particular property. More than 50 public waterfront parcels in Sarasota County have been identified as candidates for living shorelines (ESA Scheda 2018); most shorelines are candidates for seawall enhancements or hybrid living shorelines that combine natural and structural elements (Dobbs et al., 2017) (Figure 8.1.2).

Florida Sea Grant, Sarasota County’s NEST Program, SBEP, and CHNEP promote living shorelines to homeowners via presentations and brochures (Figure 8.1.3). Considering the large number of aging seawalls in the area, broad outreach about the benefits and tradeoffs of living shorelines is still needed. The Florida Fish and Wildlife Conservation Commission (FWC) recently held a 2-day course in St. Petersburg, Florida on installation of living shorelines, with CEUs for marine contractors. FWC plans similar courses across the state. The living shoreline permits issued by the U.S. Army Corps of Engineers (USACE) and FDEP have specific design standards; counties and cities need to codify and coordinate their living shoreline permit processes.

Approach

Drainage ditch enhancement

• Install local pilot projects at various scales with robust monitoring to determine nutrient removal rates and cost-effectiveness of enhancement techniques. Elements should include woody vegetation, submerged aquatic vegetation, curves and bends, and regenerative stormwater conveyance systems. USACE maintains a list of helpful resources/tools. Sarasota County Government’s Stormwater Environmental Utility is evaluating Bobby Jones Golf Course, Alligator Creek, and Phillippi Creek drainage systems for immediate opportunities.
• Convene a regional network of stormwater professionals to host workshops, webinars, and design charrettes on real projects.

Shoreline restoration

• Convene a local intergovernmental task force to develop design criteria for living shorelines and seawall enhancements. Intergovernmental coordination and agreement on design and permitting of living shorelines can facilitate progress and prevent undesirable fill material from contaminating creeks and bays.
• Expand marine contractor training in permitting, seawall removal, and living shoreline installation.
• Install living shorelines and seawall enhancements in highly visible areas as demonstration projects to familiarize the public with their look and performance (see Chapter 7.4).
• Increase educational outreach to homeowners and marine contractors about living shorelines and seawall enhancements. Target outreach based upon suitability findings of Dobbs et al., 2017.

Resources

• Living Shorelines Guidance for Sarasota Bay Watershed
• Sarasota Bay Estuary Programs Five Year Habitat Restoration Plan
• Phillippi Creek Open Channel Assessment Project

Status

Planning

Performance Measure

• Creation of a coordinated forum or working group to facilitate funding, research, and maintenance of drainage ditch enhancement projects.
• Creation of a streamlined, regionally coordinated process with accompanying education for private landowners and marine contractors to remove and replace seawalls with green infrastructure like living shorelines or seawall enhancements.
• Acres of wetland restoration or creation, miles of living shorelines created, or drainage ditches enhanced.
• Research and data on the nutrient removal rates of different ditch/shoreline rehabilitation processes and habitat restoration

Experts or Leads

Darcy Young, Sarasota Bay Estuary Program; Jennifer Hecker, Coastal & Heartland National Estuary Partnership; Tom Ries, ESA and Ecosphere Restoration Institute; Fara Ilami, FWC; Armando Ubeda, Sea Grant Agent Sarasota County; Brianna Dobbs, City of Sarasota; John Keifer, Wood Environment and Infrastructure Solutions, Inc.; John Ryan, Sarasota County Stormwater Environmental Utility; Mollie Holland, Sarasota County Neighborhood Environmental Stewardship Team

Cost Estimate

$1,000,000+

Related Activities

Chapter 7.4