Rietvlei Wetland Reserve


The Rietvlei Wetland Reserve is a nature reserve situated in Table View, Western Cape, South Africa. It is managed by the City of Cape Town's Environmental Resource Management Department.
The Rietvlei Wetland Reserve forms part of the greater Table Bay Nature Reserve.

Background

Rietvlei is considered as the most important area for waterbirds in the region and is recognized as an Important Bird Area by BirdLife International. Official recognition of its importance to biodiversity by the South African government was first afforded in 1984, when it was established as a Nature Area. This was followed by its declaration as a Protected Natural Environment in 1989, and the establishment of the Rietvlei Wetland Reserve in 1993. The first formal management plan for the reserve was developed in 1994, and this has served to guide management activities to the present.

History

The most obvious and dramatic human-induced modification at Rietvlei was the dredging of the entire north-west section between 1974 and 1976. Seawater was pumped into the pans to facilitate the operation and a vast area was dredged to a depth of. The ecological consequences were profound and irreversible. A sizable portion of Rietvlei's shallow ephemeral pans was changed into a permanent deep-water lake, which resulted in a total change in ecological character for this portion of the system.

Features

Visitor facilities

Rietvlei Wetland Reserve offers various user activities, including several types of water sport recreation, bird watching, picnic, fishing and outdoor environmental education opportunities. The Rietvlei Education Centre hosts a range of environmental education programmes and utilises the two bird hides and the short footpath for field excursions.
The Milnerton Aquatic Club leases an area of land inside the nature reserve from where they promote windsurf, sail, power- and radio-controlled boating. The Southern African Foundation for the Conservation of Coastal Birds manages a rehabilitation facility at Rietvlei.

Habitats

A range of natural and semi-natural habitats exist in this fluctuating wetland, which floods in winter and dries out in summer when the estuary mouth closes. These habitats include shallow marine waters, estuarine waters, sand/shingle shores, tidal mudflats, saltmarshes, coastal brackish saline lagoons, rivers, streams and creeks, permanent freshwater lakes and permanent and seasonal freshwater marshes and pools.

The Diep estuary

The Diep River flows through the Rietvlei wetland and the Milnerton Lagoon, which together have generally been considered to comprise the Diep estuary. If the contour above mean sea level is used as the estuary delineation, then the Diep estuary entirely encompasses the Rietvlei Wetland Reserve. The Diep River has its origins in the Riebeek Kasteel Mountains north-east of Malmesbury from where it flows for about south-west towards Cape Town before entering the sea at Milnerton, some north of the Port of Cape Town. It has one major tributary, the Mosselbank, which drains the northern slopes of the Durbanville Hills. Other tributaries include the Swart, Groen, Klein, and Riebeeck, with the Klapmuts being a tributary of the Mosselbank. The total size of the catchment is 1,495 km2 or 154,347 hectares.

Biodiversity

Birds, amphibians, reptiles and mammals

A total of 173 species have been recorded at Rietvlei, of which 102 are waterbirds and 76 are present regularly. Breeding has been confirmed for 23 waterbird species and is suspected for a further 13 species. The high diversity of waterbirds is due to the wide range of wetland habitats present and the proximity of Rietvlei to the ocean, which allows both freshwater and coastal species to exploit the system. Fluctuating water-levels are intrinsic to Rietvlei's biological value. During peak floods, swimming birds of deep, open water abound. Birds of marshy habitats replace these as the water recedes, and waders exploiting shallow mudflats occur in great abundance just prior to the wetland drying up. Rietvlei has been ranked as the sixth most important coastal wetland in South Africa for waterbirds, and it supports an average of 5,550 birds in summer; during good years, however, numbers are boosted above 15,000. Phoenicopterus minor, a species of global conservation concern, occurs at the site, but not in globally significant numbers.
; Updated from South African Biodiversity Database as species present on site on 2011/01/10
; Indigenous - rare and endangered
  1. Anthropoides paradiseus
  2. Circus ranivorus
; Indigenous
  1. Acrocephalus gracilirostris
  2. Actitis hypoleucos
  3. Alcedo cristata
  4. Alopochen aegyptiacus
  5. Anas capensis
  6. Anas erythrorhyncha
  7. Anas hottentota
  8. Anas smithii
  9. Anas sparsa
  10. Anas undulata
  11. Anhinga rufa
  12. Apus affinis
  13. Ardea cinerea
  14. Ardea goliath
  15. Ardea melanocephala
  16. Ardea purpurea
  17. Bostrychia hagedash
  18. Bradypterus baboecala
  19. Bubulcus ibis
  20. Burhinus vermiculatus
  21. Calidris alba
  22. Calidris canutus
  23. Calidris ferruginea
  24. Calidris melanotos
  25. Calidris minuta
  26. Cercotrichas coryphoeus
  27. Ceryle rudis
  28. Charadrius hiaticula
  29. Charadrius marginatus
  30. Charadrius pallidus
  31. Charadrius pecuarius
  32. Charadrius tricollaris
  33. Chlidonias leucopterus
  34. Columba guinea
  35. Corvus albus
  36. Egretta alba
  37. Egretta garzetta
  38. Egretta intermedia
  39. Elanus caeruleus
  40. Estrilda astrild
  41. Euplectes orix
  42. Falco rupicolus
  43. Fulica cristata
  44. Gallinago nigripennis
  45. Gallinula chloropus
  46. Haematopus moquini
  47. Haliaeetus vocifer
  48. Himantopus himantopus
  49. Hirundo albigularis
  50. Hirundo rustica
  51. Larus cirrocephalus
  52. Larus dominicanus
  53. Larus hartlaubii
  54. Limosa lapponica
  55. Macronyx capensis
  56. Megaceryle maximus
  57. Merops apiaster
  58. Microcarbo africanus
  59. Microcarbo coronatus
  60. Milvus migrans
  61. Motacilla capensis
  62. Netta erythrophthalma
  63. Numenius arquata
  64. Numenius phaeopus
  65. Nycticorax nycticorax
  66. Oxyura maccoa
  67. Pelecanus onocrotalus
  68. Phalacrocorax capensis
  69. Phalacrocorax lucidus
  70. Philomachus pugnax
  71. Phoenicopterus minor
  72. Phoenicopterus ruber
  73. Platalea alba
  74. Plectropterus gambensis
  75. Plegadis falcinellus
  76. Podiceps cristatus
  77. Podiceps nigricollis
  78. Porphyrio madagascariensis
  79. Pternistis capensis
  80. Recurvirostra avosetta
  81. Rostratula benghalensis
  82. Spilopelia senegalensis
  83. Sterna balaenarum
  84. Sterna bergii
  85. Sterna caspia
  86. Sterna hirundo
  87. Sterna sandvicensis
  88. Sterna vittata
  89. Tachybaptus ruficollis
  90. Tadorna cana
  91. Thalassornis leuconotus
  92. Threskiornis aethiopicus
  93. Tringa glareola
  94. Tringa nebularia
  95. Tringa stagnatilis
  96. Vanellus armatus
  97. Vidua macroura
; Alien
  1. Anas platyrhynchos
  2. Columba livia
  3. Numida meleagris
; Updated from South African Biodiversity Database as species present on site on 2011/01/07
  1. Amietia fuscigula
  2. Amietophrynus pantherinus
  3. Strongylopus grayii
  4. Strongylopus grayii grayii
  5. Tomopterna delalandii
  6. Xenopus laevis
; Updated from South African Biodiversity Database as species present on site on 2011/01/13
  1. Acontias meleagris
  2. Afrogecko porphyreus
  3. Bradypodion pumilum
  4. Chersina angulata
  5. Lycodonomorphus rufulus
  6. Meroles knoxii
  7. Naja nivea
  8. Pelomedusa subrufa
  9. Pseudaspis cana
  10. Scelotes bipes
  11. Trachylepis capensis
  12. Trachylepis homalocephala
  13. Typhlosaurus caecus
; Updated from South African Biodiversity Database as species present on site on 2011/01/10
; Indigenous
  1. Aonyx capensis
  2. Felis caracal
  3. Galerella pulverulenta
  4. Herpestes ichneumon
  5. Hystrix africaeaustralis
  6. Mus minutoides
  7. Myosorex varius
  8. Raphicerus campestris
  9. Raphicerus melanotis
; Alien
  1. Canis lupus familiaris
  2. Felis silvestris catus

    Invertebrates and fish

multiply rapidly after winter flooding and disappear in summer as the water dries up. In the estuary there is a range of salinities, resulting in a diverse community of zooplankton. The invertebrate fauna is a vital food source for birds and fish, the most abundant fish in the wetland being Liza richardsonii.
; Updated from South African Biodiversity Database as species present on site on 2010/12/31
; Indigenous
  1. Anguilla mossambica steinitzi
  2. Caffrogobius nudiceps
  3. Galaxias zebratus
  4. Lithognathus lithognathus
  5. Liza richardsonii
  6. Mugil cephalus
  7. Rhabdosargus globiceps
; Alien
  1. Cyprinus carpio
  2. Gambusia affinis

    Plant communities

Five distinctive wetland plant communities occur: perennial wetland, reed-marsh, sedge-marsh, open pans and sedge pans. The perennial wetland is characterized by scant aquatic vegetation, dominated by Ruppia, Potamogeton and Enteromorpha. The reed-marsh is dominated by Phragmites, invaded in places by Typha. The sedge-marsh is dominated by Bolboschoenus and Juncus. The open pans are sparsely covered in macrophytes, consisting mainly of Limosella and Salicornia, and the sedge pans are dominated by Bolboschoenus in summer and Aponogeton and Spiloxene in winter.
; Updated from South African Biodiversity Database as species present on site on 2011/02/02
; Indigenous
  1. Alternanthera sessilis
  2. Amellus tenuifolius
  3. Ammophila arenaria
  4. Arctotheca populifolia
  5. Arctotis hirsuta
  6. Arctotis stoechadifolia
  7. Athanasia dentata
  8. Atriplex semibaccata~
  9. Bolboschoenus maritimus
  10. Brunsvigia orientalis
  11. Carissa macrocarpa
  12. Carpobrotus acinaciformis
  13. Carpobrotus edulis
  14. Ceratophyllum demersum~
  15. Chasmanthe aethiopica
  16. Chrysanthemoides incana
  17. Chrysanthemoides monilifera
  18. Cladoraphis cyperoides
  19. Conicosia pugioniformis~
  20. Cynanchum africanum
  21. Cynodon dactylon
  22. Cynosurus echinatus
  23. Cyperus textilis
  24. Dasispermum suffruticosum
  25. Didelta carnosa~
  26. Ehrharta longiflora
  27. Ehrharta villosa~
  28. Euclea racemosa
  29. Ferraria crispa
  30. Ficinia indica
  31. Ficus natalensis~
  32. Gladiolus griseus
  33. Grielum grandiflorum
  34. Helichrysum niveum
  35. Helichrysum patulum
  36. Hermannia pinnata
  37. Hermannia procumbens~
  38. Indigofera complicata
  39. Ischyrolepis eleocharis
  40. Juncus kraussii~
  41. Kedrostis nana~
  42. Lavatera arborea
  43. Lemna minor
  44. Limonium equisetinum
  45. Limonium scabrum~
  46. Lolium multiflorum
  47. Lolium rigidum
  48. Ludwigia adscendens diffusa
  49. Lycium ferocissimum
  50. Lythrum salicaria
  51. Malva parviflora~
  52. Metalasia muricata
  53. Moraea flaccida
  54. Moraea miniata
  55. Morella cordifolia
  56. Myoporum tenuifolium
  57. Nylandtia spinosa
  58. Olea capensis
  59. Olea europaea africana
  60. Othonna coronopifolia
  61. Passerina ericoides
  62. Pelargonium gibbosum
  63. Persicaria lapathifolia
  64. Phragmites australis
  65. Phylica ericoides~
  66. Pistia stratiotes
  67. Plantago coronopus
  68. Plecostachys serpyllifolia
  69. Psoralea repens
  70. Rhus crenata
  71. Rhus glauca
  72. Rhus laevigata
  73. Rhus lancea
  74. Rhus lucida~
  75. Romulea tabularis
  76. Rumex crispus
  77. Rumex lativalvis
  78. Ruschia macowanii
  79. Ruschia tumidula
  80. Salicornia meyeriana
  81. Salvia africana-lutea
  82. Sarcocornia capensis
  83. Sarcocornia natalensis~
  84. Sarcocornia pillansii~
  85. Schoenoplectus scirpoides
  86. Senecio burchellii
  87. Senecio halimifolius
  88. Sideroxylon inerme~
  89. Sparaxis bulbifera
  90. Sporobolus virginicus
  91. Stenotaphrum secundatum
  92. Tetragonia decumbens
  93. Tetragonia fruticosa
  94. Tetragonia spicata
  95. Thamnochortus spicigerus
  96. Thinopyrum distichum
  97. Trachyandra filiformis
  98. Triglochin bulbosa
  99. Typha capensis
  100. Xanthium strumarium
  101. Zantedeschia aethiopica
  102. Zygophyllum morgsana
; Alien
  1. Acacia cyclops
  2. Acacia saligna
  3. Avena sativa
  4. Azolla filiculoides
  5. Commelina benghalensis
  6. Cortaderia selloana
  7. Eichhornia crassipes
  8. Eucalyptus lehmannii
  9. Lolium perenne
  10. Paspalum vaginatum
  11. Pennisetum clandestinum
  12. Schinus terebinthifolius

    Threats

The effects of the nearby Century City Development on Blouvlei, which used to support a large heronry holding 12 breeding species, is cause for considerable concern. Most of these birds used to forage at Rietvlei and would contribute substantially to the large numbers of birds occurring here. The effects on this breeding area will probably result in fewer birds visiting the Rietvlei area. Other threats to the wetland include siltation, which results from erosion, and pollution and eutrophication from fertilizers, pesticides, sewage works, stormwater run-off and livestock manure. Petroleum factories and suburban areas on the margin of the system also pose problems. Vast areas of the mudflats and salt marsh have been smothered by thick mats of non-native grasses, notably Paspalum vaginatum, resulting in habitat loss for waders, the most diverse and abundant community of waterbirds at Rietvlei. Other non-native species, including stands of Acacia saligna, are being cleared from large areas around the margin of the wetland.