Guidelines for Successful Wetland Planting Part 2 – Rehabilitation of Naturally Occuring Wetlands

TYPES OF WETLANDS
Planting sedges and water plants in constructed wetlands has already been presented (Part 1). Rehabilitation of degraded natural wetlands will be discussed here in Part 2-Rehabilitation of Natural Wetlands. Planting wetlands in STP’s and domestic greywater systems are to be discussed in Part 3. Rain gardens and detention basins will be described in the final article of the series, Part 4.

WHY RECONSTRUCT WETLANDS?
This is a big question for a small article. Generally, naturally occurring wetlands are reconstructed via revegetation because they have an identified value and are in some way degraded. Their natural vegetation has been diminished or even completely removed.
It can be easily argued that ALL wetlands have value. A wetland has values relating to one or more of the following(1):
• Uses – education, tourism, water extraction/storage
• Functions – water quality, wildlife refuge/corridor, hydrological, ecological
• Importance – national estate, nature reserve
• Significance – hosts threatened species

Causes of wetland degradation include: changed water regime including both hydrology and water quality; overgrazing; invasion of exotic pests such as European Carp and Alligator Weed and urban population growth. Wetland degradation can take the form of bare areas, weed invasion, eroded banks and limited/absence of natural wetland species. The worst case scenario may see the wetland bank morphology change and become too steep – reducing the area suitable for plant establishment to a narrow zone.

WHO RECONSTRUCTS WETLANDS?
Wetland management is a major issue(2). Reconstruction of large wetlands is generally undertaken by management authorities such as Local Councils and Government Departments for public lands and a variety of specialist consultants and wetland managers for private lands. Wetlands occurring in NSW public lands will likely have a Wetland Plan of Management (PoM) which will be an invaluable resource for any wetland works. Work on smaller wetlands may be undertaken by volunteer groups, farmers and other landowners. Generally for large scale works, much of the assessment and planning may have already been done well before the planting phase.

AIMS OF WETLAND RESTORATION
Aim(s) of a wetland revegetation project follow from its value and degradation characteristics. The most common objectives in a wetland revegetation project include:
• Introduce desirable plants to your wetland(3). This includes naturally occurring species as opposed to weeds.
• Develop a plant community that will sustain itself naturally(3 & 4). This is required if there is little sign of natural revegetation and is often related to catchment changes and weed invasion.
• Erosion control. Erosion can be caused from loss of the wetland ‘fringing’ vegetation, increased flow or a combination of both. Annual weeds and grasses, which often replace the original vegetation, have shallow root systems, which cannot prevent soil erosion(5). The tangled root mass of local native rushes, sedges, trees and shrubs are excellent for bank stabilisation.
• Creation of fauna habitat. It is important to know the specific habitat requirements of the fauna before planning the project.
• Increase flora biodiversity. It should be noted that riparian zone vegetation can be low in diversity in its pristine state5. Remember also that Australian wetlands are often dry, and if you survey the wetland only when it is dry or wet, you may get an incomplete idea about the plants it contains(3).

HABITAT ZONES
The habitat zones of natural wetlands are described in a very similar, but not the same manner to the zones of constructed wetlands (discussed in Part 1 of this series). Terminology differs largely because dry and wet cycles are a natural characteristic of Australian wetlands – more so than their constructed cousins. Natural wetland habitat zones are listed below and shown in dragram(5).
• Submergent Zone. This zone has surface water for a good proportion of the year. It includes submergent plants that grow beneath the water surface, although their leaves may float on the surface and flowering spikes may extend above the water5. This zone can be difficult to revegetate due to water depth, and is often left to revegetate naturally. Species suitable for planting in the submergent zone include Eleocharis spacelata.
• Emergent Zone. Water depth in this zone can be up to 1m in wet months of the year while only being represented by damp soil in the dry months. Dense swards of foliage should be planted in this zone, such as Baumea articulata (Jointed Twig Rush), Lepironia articulata, and Schoenoplectus validus (River Club Rush).
• Damp Zone. This area is permanently damp near the surface for most of the year. Many species including sedges and rushes can live in this zone. Examples of species to plant here include Baumea rubiginosa (Soft Twig Rush), Bolboschoenus spp, Cyperus exaltatus, Eleocharis acuta (Small Spike Rush), Philydrum langinosum (Wolly Frog Mouth), Schoenoplectus mucronatus and Phragmites australis (Common Reed).
• Ephemeral Zone/Littoral Zone. This zone surrounds the wetland edge and is the driest of all zones. It undergoes regular water level fluctuations and can be the zone of highest weed invasion. Dense plantings (6 per square metre) of sedges such as Carex appressa (Tall Sedge), Juncus usitatus (Common Rush), Juncus krausii (Sea Rush), Ficinea nodosa (Knobby Club-rush) and Gahnia species are required here.

WETLAND RESILIENCE AND THE NEED TO RE-VEGETATE
Understanding the concept of RESILIENCE is essential when deciding on the need for wetland restoration. If your wetland has limited native wetland species present, and these do not cover large wetland areas, your wetland ecosystem likely has low resilience ie limited capacity to revegetate unassisted. In this situation revegetation can be undertaken via direct seeding, transplanting or planting seedlings. The decision to plant seedlings is usually based on cost, timeframe of project, desired outcomes and availability. Many sedges and wetland species are readily available from suppliers such as Bluedale.

STEPS IN REVEGETATING DEGRADED NATURALLY OCCURRING WETLANDS
Getting the ball rolling when revegetating degraded naturally occurring wetlands can be time consuming. In natural wetlands the vegetation takes decades or even centuries to develop(3). It follows that planning to reconstruct such a system using sound planning will also take some time.

(1) Identify and Address Degradation Issues. This can be no mean feat and in many cases may have already been done for you. As already mentioned, some wetlands will have a Wetland Plan of Management (PoM) that will assist in this first step. PoMs will be available from the management authority. In many cases the degradation issues may be as simple as overgrazing or weed invasion solved by fencing or weed removal.

(2) Choose Plant Species. This also involves a level of investigation. PoMs, if available, will list the species that occur/have occurred in the past and may make planting recommendations. In the absence of a PoM, planting lists can be compiled by identifying indigenous species present at the site (including their abundance and distribution), investigating historical records, and/ or undertaking a flora survey on an area of nearby intact vegetation(5).

(3) Prepare a Planting Plan. Where to plant the chosen species will be a function of the habitat zones described above and how the species grow together naturally. Many sedges and water plants grow in large swards of the same species.

(4) Order Plants in Advance. The key to successful planting is to plan and order stock far enough in advance to ensure appropriate stock is ready at the start of the growth season(6). In some projects local provenance plant stock is specified or desired. Such plants are produced from seed growing in the local area with the aim of preserving genetic differences between species growing in different regions. Provenance plants are not readily available at specialist nurseries, including Bluedale. They can be supplied but will require a lead time of 12 – 18 months. For non-provenance plants, a 16 week period from ordering to supply is practical.

(5) Create a Planting Timetable. For provenance stock it is relevant to note that seed is generally best collected in February/March and September/October for Spring germination. August to November and February to May are the best months to encourage establishment in Southern Australia3. Planting can be difficult in wetlands full of water. The ideal water height for planting is no deeper that 2/3 of the foliage height of plants in the deepest planting zone.

(6) Mark the Planting Zones. It is vital to know final water depths so that each habitat zone will have the correct plant species. If your wetland is already full of water, this will be a relatively simple task and zones can be marked using stakes. If empty or partially so, consult the wetland design engineer or similar for advice. A detailed drawing depicting water levels may be available. For larger wetlands a survey may be required. It is notable that after planting, species frequently ‘move’ to other more suitable niches within the wetland and do not continue growing where they were first planted.

(7) Monitor Bird Activity. While undertaking preliminary site inspections, marking out and weed removal it is a good idea to monitor bird activity. Water birds are attracted to the fresh new growth of nursery stock. They can pull plants up, roots and all and cause significant losses. If there are many birds present a staged planting approach may help avoid losses, and exclusion netting should be considered. Planting larger pot sizes of 140mm will also negate damage by bird predation. Advanced ordering will be required if 140mm pots are to be used as this is not a size regularly grown by Bluedale.

(8) Treat Water Turbidity (cloudiness) OPTIONAL. You can clear muddy water using commercial clearing agents such as alum or lime – if plants establish in chemically cleared water they can help to maintain water clarity(3).

(9) Planting. With preliminary work now completed, planting can begin. Set out the plants according to their planting zones. When planting, anchor the root ball of the plant by planting it firmly into the substrate of the basin.

(10) Watering. This may be necessary for any plants not inundated by the water height at planting.

(11) Monitoring and maintenance. Monitor planting areas over coming weeks for signs of bird predation, irrigation needs and plant dislodgement. Protect plants and replace as necessary. A maintenance program will be required involving weed control and plant replacement. The Littoral Zone usually requires the most attention as weed control techniques such as mulching are not applicable.

References
(1) Swapan, Paul (2013) Chapter 5.1 The need for a Wetland Plan of Management (PoM) in Paul, S. (Ed). (2013) Workbook for managing urban wetlands in Australia. 1st edn. (Sydney Olympic Park Authority), eBook available through http://www.sopa.nsw.gov.au/education/WETeBook/, ISBN 978-0-987 4020-0-4.
(2) Sainty, Geoff (2013) Chapter 2.3 Wetland plants and wetland management in Australia. in Paul, S. (Ed). (2013) Workbook for managing urban wetlands in Australia. 1st edn. (Sydney Olympic Park Authority), eBook available through http://www.sopa.nsw.gov.au/education/WETeBook/, ISBN 978-0-987 4020-0-4.
(3) Brock, Margaret A. and Casanova, Michelle T. (2000). Are there plants in your wetland? Revegetating wetlands. LWRRDC, UNE, DLWC and EA.
(4) Nias, Deborah (2014) NSW Murray Wetlands Working Group Inc. Albury NSW. Chapter 5 Managing Wetlands. in Native Vegetation Guide for the Riverina. Charles Sturt University
(5) Water and Rivers Commission (2001). Using rushes and sedges in revegetation of wetland areas in the south west of WA. Prepared by Linda Taman. Report No. RR 8.
(6) Wong, T.H.F., Breen, P.F., Somes, N.L.G. and Lloyd S.D. (1999) Managing Urban Stormwater Using Constructed Wetlands Industry Report. Cooperative Research Centre for Catchment Hydrology. Second Edition. September 1999

Guidelines for Successful Wetland Planting Part 1 – Constructed Wetlands

TYPES OF WETLANDS

There are 4 general categories of wetland that involve planting with sedges and water plants. These include:

• Constructed wetlands which are designed to replicate natural systems
• Degraded naturally occurring wetlands
• Wetlands associated with Sewage Treatment Plants (STPs) and domestic greywater systems
• Rain gardens and detention basins

Planting sedges and water plants in constructed wetlands will be discussed in this article (Part 1). Rehabilitation of degraded natural wetlands will be presented in Part 2-Rehabilitation of Natural Wetlands. Planting wetlands in STP’s and domestic greywater systems are discussed in Part 3-Greywater Disposal Systems. Rain gardens and detention basins will be described in the final article of the series Part 4 – Rain Gardens.

THE ENGINEERING OF CONSTRUCTED WETLANDS – A CRASH COURSE

Constructed wetlands are generally designed by specialist engineers. Purposes of constructed wetlands may include one or a combination of the following: flood protection and flow control; water quality improvement; landscape/recreational amenity; and provision of wildlife habitat.

It is vital that the design purpose of a constructed wetland be considered during preparation of a planting plan. For example creating habitat for a specific bird species will likely require different plant species than a wetland installed for flood protection.

There are many engineering components that make up a constructed wetland. As with the wetland design purpose, a cursory knowledge of such components will assist in planting design. Wetland components together with appropriate species are listed below:

• Open Water Inlet Zone. This is the water entry point and is generally deep, retaining comparatively large volumes of water. Here water ponding promotes physical settlement of sediment suspended – the first phase of treatment. Ideally the open water inlet zone will include a high-flow bypass system to protect the downstream macrophyte zones from damaging floodwaters. Due to its depth, vegetation only grows on the edges of the inlet zone. Species grown here must be able to withstand sedimentation, damage by floodwaters and long periods of inundation. Tall rhizomatus water plants such as Schoenoplectus validus (River Club Rush) and Eleocharis spacelata (Tall Spike Rush) are well suited to this situation. Phragmites australis (Common Reed) also suits the open water inlet zone as it recovers rapidly from major flood events via both seeding and rhizomes.
• Macrophyte Zone. This can include any number of ‘cells’ oriented perpendicular to water flow, each with differing depths. A variety of terminology is used to describe these cells such as shallow marsh, marsh and deep marsh. These have been described well by Wong et al (1999). Each plays a different stormwater treatment role in the wetland system.
• Shallow Marsh (0-500mm). This area has only shallow inundation that regularly dries out. The ongoing wetting and drying cycle significantly influences the organic content and nutrient cycling in sediments. The plants themselves provide sites for algal epiphytes and biofilms to enhance pollutant uptake. Plants that naturally occur in ephemeral swamps/creek do well in the shallow marsh zone. Examples include Baumea rubiginosa (Soft Twig Rush), Eleocharis acuta (Common Spike Rush), Bulboscheonus fluviatilis (Marsh Clubrush), Cyperus exaltatus (Giant Sedge), Philydrum lanuginosum (Frogsmouth), and Schoenoplectus mucronatus.
• Marsh (500mm-1m). This area occasionally dries out. Its role is to maximise plant surface area and associated adhesion of particles to plant stems. Dense swards of foliage are suitable for this area, such as Baumea articulata (Jointed Twig Rush), Lepironia articulata and Schoenoplectus validus (River Club Rush).
• Deep Marsh (permanent inundation). As for the open water inlet zone, the deep marsh zone is permanently inundated and promotes sedimentation of particles. Unlike the water inlet zone however, it is usually less affected by flood damage. This zone is frequently integrated into open space due to its aesthetic appeal. The deep marsh zone supports similar plants to the open water inlet zone. Vigorous growers such as Phragmites australis (Common Reed) and Typha orientalis (Cumbungi) are best avoided in this zone as they can dominate if left unchecked.
• Littoral Zone (frequently dry). This zone surrounds the wetland edge and is the driest of all zones. It undergoes regular water level fluctuations and can be the zone of highest weed invasion. Dense plantings (6 per square metre) of sedges such as Carex appressa (Tall Sedge), Juncus usitatus (Common Rush), Juncus krausii (Sea Rush), Ficinea nodosa (Knobby Club-rush) and Gahnia species are required here.
• Habitat Island(s). An optional feature, the habitat island has areas that remain dry. They often support tall grasses, shrubs and trees.

HOW TO IMPROVE YOUR WETLAND PLANTING SUCCESS

When preparing a wetland planting plan, design should mimic natural plant occurrences. Native plants are preferable and with sufficient lead time, plants of local provenance plants can be supplied. It is notable that most sedges and water plants grow in large swards of the same species. In many cases, this is likely the result of expansion from a rhizome, competition and suitability to the water level. It follows that it is preferable to plant sedges and wetlands plants in clumps of same species for a good result. It is also notable that after planting, species frequently ‘move’ to other more suitable niches with the constructed wetland and do not continue growing where they were first planted. Wherever they end up, the water plants will continue to perform their designed function.

Bluedale recommends 8 steps to planting constructed wetlands:

(1) ORDER YOUR PLANTS IN ADVANCE Give yourself at least 16 weeks lead time, more if you require local provenance. The longer the lead time, the more mature and taller your plants will be. This will make a huge difference in planting success.
(2) Mark the planting zones. It is vital to know final water depths so that each wetland zone will have the correct plant species. If the constructed wetland is already full of water, this will be a relatively simple task and zones can be marked prior to water removal using stakes. Generally, constructed wetlands have structures such as riser outlets that provide for manual control of water level and duration of inundation. If already empty or partially so, consult the wetland design engineer or similar for advice. A detailed drawing depicting water levels may be available. For larger wetlands a survey may be required.
(3) Remove weeds. This should be done prior to planting using herbicide and/or and hand removal techniques.
(4) Monitor bird activity. While undertaking preliminary site inspections, marking out and weed removal it is a good idea to monitor bird activity. Water birds are attracted to the fresh new growth of nursery stock. They can pull plants up, roots and all and cause significant losses. If there are many birds present a staged planting approach may help avoid losses, and exclusion netting should be considered. Planting larger pot sizes of 140mm will also negate damage by bird predation. Advanced ordering will be required if 140mm pots are to be used as this is not a size regularly grown by Bluedale.
(5) Planting. With preliminary work now completed, planting can begin. Set out the plants according to their planting zones. Littoral Zone plants should be planted between the high and low level water marks. When planting, anchor the root ball of the plant by planting it firmly into the substrate of the basin.
(6) Set Water Level. If the wetland has a manual water level control device, set the water level no deeper that 2/3 of the foliage height of plants in the deepest zone. The correct level on inundation is vital. As the plants increase in height, the water level can be progressively raised until full.
(7) Watering. This will be necessary for any plants not inundated during the initial water height setting (as described above). If water has not been returned to the basin, irrigation of all the plants will be necessary until the basin refills.
(8) Monitoring and maintenance. Monitor planting areas over coming weeks for signs of bird predation, irrigation needs and plant dislodgement. Protect plants and replace as necessary. A maintenance program will be required involving weed control and plant replacement. The Littoral Zone usually requires the most attention as weed control techniques such as mulching are not applicable. If manual control of the water level is possible, weeds can be controlled by inundation.

Reference
Wong, T.H.F., Breen, P.F., Somes, N.L.G. and Lloyd S.D. (1999) ‘Managing Urban Stormwater Using Constructed Wetlands’ Industry Report. Cooperative Research Centre for Catchment Hydrology. Second Edition. September 1999