Wetland Restoration with Hydrophytes: A Review

Abstract

Restoration cases with hydrophytes (those which develop all their vital functions inside the water or very close to the water surface, e.g., flowering) are less abundant compared to those using emergent plants. Here, I synthesize the latest knowledge in wetland restoration based on revegetation with hydrophytes and stress common challenges and potential solutions. The review mainly focusses on natural wetlands but also includes information about naturalized constructed wetlands, which nowadays are being used not only to improve water quality but also to increase biodiversity. Available publications, peer-reviewed and any public domain, from the last 20 years, were reviewed. Several countries developed pilot case-studies and field-scale projects with more or less success, the large-scale ones being less frequent. Using floating species is less generalized than submerged species. Sediment transfer is more adequate for temporary wetlands. Hydrophyte revegetation as a restoration tool could be improved by selecting suitable wetlands, increasing focus on species biology and ecology, choosing the suitable propagation and revegetation techniques (seeding, planting). The clear negative factors which prevent the revegetation success (herbivory, microalgae, filamentous green algae, water and sediment composition) have to be considered. Policy-making and wetland restoration practices must more effectively integrate the information already known, particularly under future climatic scenarios.

Keywords: aquatic phanerogams; charophytes; constructed wetlands; floating macrophytes; natural wetlands; planting; revegetation; sediment transfer; seeding; submerged macrophytes; transplanting.

Figure 1

(a) The number of records obtained in the Web of Science (WoS) search for wetland restoration by countries (*except for the African continent) (notice the logarithmic scale). (b) The number of records in the WoS with the keywords: (restoration AND macrophyt*) AND (submerg* OR floatin*) AND (wetlan* OR shallow lak*) AND “country”, for the countries that showed more than 60 records in the previous search (graph (a)). (c) Number of records for the countries of graph (b) now with the keywords: (restoration AND macrophyt*) AND (submerg* OR floatin*) AND (wetlan* OR shallow lak*) AND (plantin* OR seedin* OR reveget* OR transplant*) AND “country”. Searches made in March 2021.

Figure 2

(a) Seed bombs with Typha seeds prepared by students with the supervision of the managers of Tancat de la Pipa wetland (Albufera de València Natural Park, Spain; photographs: Lourdes Ribera); (b) examples of M. spicatum, S. pectinata and the charophyte Chara vulgaris ready to be planted in the field without any kind of holder; (c) example of M. spicatum with the root-sediment system in a peat pot ready to be planted in the field; (d) fragments of hydrophytes with a stone to serve as “anchor” to be thrown inside enclosures (see Figure 2c) (S. pectinata, M. spicatum, C. submersum and C. vulgaris).

Figure 3

(a) Tanks of hydrophyte cultures produced indoors, now acclimatizing in the field before being planted in Tancat de la Pipa wetland (Albufera de València Natural Park, Spain; photographs: Ximo Fernández. (b) Exclosures to plant hydrophytes using the method shown in Figure 2d; the exclosure is almost 100% covered with the grown submerged macrophytes (the thin ropes in the upper part try to avoid grazing by herbivorous birds). (c) Exclosures to plant hydrophytes that are being enlarged successively to get wider coverages (photographs taken from [84]).

Figure 4

(a) Distribution of the native genera of submerged macrophytes (and charophytes) used for revegetation in wetlands; (b) the most used native species of submerged macrophytes for revegetation in wetlands. (c) Distribution of the native genera of floating-leaved and free-floating species used for revegetation in wetlands. (d) Percentage of the floating-leaved and free-floating native species used for revegetation in wetlands.