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Semelhante a Saline Groundwater Dependent Ecosystems, Eyre Peninsula, South Australia - Peri Coleman
Semelhante a Saline Groundwater Dependent Ecosystems, Eyre Peninsula, South Australia - Peri Coleman (20)
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Saline Groundwater Dependent Ecosystems, Eyre Peninsula, South Australia - Peri Coleman
- 1. 1 Saline Groundwater Dependent Ecosystems:Saline Groundwater Dependent Ecosystems: A look at some West Coast habitats and organismsA look at some West Coast habitats and organisms October 2013
- 2. 2 Salt lakes, sabkhas and dolinesSalt lakes, sabkhas and dolines
- 3. 3 Doline:Doline: The WhirlpoolThe Whirlpool Thank you to Sharie Detmar at DEWNR for the use of these photographs
- 4. 4 Salt lake:Salt lake: Seagull LakeSeagull Lake
- 5. 5 Current hydrology & geomorphologyCurrent hydrology & geomorphology
- 8. 8 An introduction toAn introduction to some specificsome specific inhabitants ofinhabitants of dolines, salt lakes anddolines, salt lakes and sabkhassabkhas
- 9. 9 BMC’sBMC’s
- 10. 10 Beach rock seepage communitiesBeach rock seepage communities
- 11. 11 Tecticornia flabelliformisTecticornia flabelliformis (fan or(fan or bead samphire)bead samphire)
- 12. 12 What is theWhat is the T. flabelliformisT. flabelliformis niche?niche? • Soil type • Soil moisture • Soil salinity • pH and gypsum tolerance
- 13. 13 MeetMeet Coxiella glauertiCoxiella glauerti (resurrection snail)(resurrection snail)
- 14. 14 A unique behavioural response to aridityA unique behavioural response to aridity
- 15. 15 A small diversion on the topic of rarityA small diversion on the topic of rarity Rarity per se does not relate to threatening processes. “Rare” may mean a naturally tiny population, or it may mean a large population in a small and very specific habitat. By definition, plants with small populations or narrow distributions are more vulnerable to threatening processes and so in Australia we classify plants as: Rare: a taxon which is rare within Australia but not facing any identifiable threat Endangered: a taxon in serious risk of disappearing in the wild within 10-20 years Vulnerable: a taxon not presently endangered but at risk over 20-50 years
- 16. 16 Threats to GDE’s and speciesThreats to GDE’s and species
- 19. 19 Sea level rise…Sea level rise…
- 21. 21 What is being done to improve things?What is being done to improve things? • One-on-one talks with West Coast Councils about the vulnerability of these habitats and possible other sources of saline water for road building (tourists need good roads) • Workshops with West Coast people to help them • Recognise different samphire species • Recognise saline GDE’s and value them • Develop monitoring programs for vulnerable habitats • Inclusion of the West Coast marine-influenced GDE’s into the new Temperate Saltmarsh Ecological Community that has recently been granted EPBC Act protection
Notas do Editor
- Linear chains of sink holes, canyons, caves, weathered pavements and wetland basins occur between Streaky Bay and Drummond Point. The phenomenon is restricted to those areas where Pleistocene limestone forms the seafront of the coast. During the Pleistocene glacial periods, with lower sea-levels, the exposed limestones would be subject to karst (solution holes and cracks) development. With glacial melting, and the transgression inland of a rising sea, marine waters would flood back into these permeable limestone areas. With stabilisation of sea level 5-6000 years ago, the majority of these low lying areas have become separated from the sea by huge windblown dunes of sand. Regardless of this separation from the sea, where land behind the dunes is/was lower than the final Holocene sea level, the head differential allows seawater to seep into the terrestrial environment, providing seawater to sustain the wetland. In the SE of South Australia, where such dune ridges are currently eroding away, some similar salt lakes look to be in imminent danger of being reconnected to the sea and becoming embayments. In the Eyre Peninsula there are three commonly found features that are expressions of this geomorphology: dolines, salt lakes and sabkhas, and they often co-occur. We will have a quick look at each…
- Basically, dolines are holes in the ground, dissolved out of the parent limestone, and often filled with water. There are permanent freshwater dolines across the Eyre Peninsula and Nullarbor. The string of coastal dolines near Streaky Bay and Sceale Bay are fed by groundwater that seeps from the sea, and discharge through a series of interconnected dolines that overflow into the nearby Caltapanna Wetlands, so these small cliff-sided pools maintain a marine salinity. The Whirlpool is located north of Seagull Lake just adjacent to the Caltapanna Wetlands on the Streaky Bay to Baird’s Bay Road. While the dolines contain many common salt lake invertebrates, quite a number of species of invertebrates in these springs are of marine origin . How they got there is something of a mystery. While entry as adults through the coastal dunes is almost an impossibility, it is just possible some arrive as larvae through distinct voids under the dunes. In this case you would expect all the dolines to have a similar assemblages. That is not the case. A more acceptable explanation of origins is from when the sea level was slightly higher and low lying land in hollows such as Seagull Lake, Caltapanna and the dolines were connected directly to the ocean. Where a marine habitat has survived as doline springs of marine water entering a landscape a little below present sea level, the maritime species have also survived. Each spring system has a unique combination of marine species according to the luck of survival - each spring has differences in depth and volume, flow rate, temperature etc. Larger, more permanent springs (such as the Seagull Lake Spring and Paddy’s Vent) have more species than the smaller ones. The Whirlpool had the least species as it is quite small. As the water in this spring is salty, it was seen as an ideal source of construction water for local road building programs.
- Only a little further south on the same rod, you find Seagull Lake. Seagull Lake itself has an interesting history. It probably started as a marine embayment formed during the marine intrusion more than 6000 YBP, which could have extended further inland to encompass the present Caltapanna wetlands to the east. Early on in its evolution a transgressive sand sheet blocked the expansion to the east. This would have established a distinct eastern shore and occluded the lake from the present inland wetlands (point this out on aerial). More importantly, a spit would have built across the western opening to the bay effectively separating the inlet from the ocean. Given the plentiful supply of sand along Sceale Bay and the lack of an inflowing stream into Seagull Lake to provide extra water to scour the entrance, this occluding spit would soon have built into a beach and then eventually into the massive frontal dunes there today, that exceed 30m high (point this out on aerial). This process appears to have been replicated in several places along the western side at Eyre Peninsula, eg at Lake Sheringa. At places where there is no sand supply, mainly facing south, the bays formed by the marine intrusion have remained open eg at Baird Bay. Interestingly there are beaches and dunes at the lake’s eastern end that indicate much higher water levels than experienced now. It is likely the high beach and small dunes on the eastern shore are remnants of beaches and dunes built while the lake was still connected to the sea. Wind driven waves during high tides would have built them higher than high tide level. The present lake level during the winter of 2012 was close to mean sea level. High Spring tides would be about 1 to 1.3 m above this and with wind driving waves would easily account for beaches at 1.6-1.75 m. The dunes behind this beach would have commenced as beaches but with lake level lowering due to tidal attenuation associated with occlusion of any opening to the sea through the western spit, a lower beach lakeside of these dunes would have formed. This is the beach that is preserved today. Once the opening to the sea had closed, there would be no more high beach building.
- Water sources for this lake are complex. The massive dune and limey deposit system along the western shore and bordering Sceale Bay, permits filtered sea water through it to appear as a major spring in the doline to the far southwest corner of the lake (point it out). This and direct rainfall (meteoric water) are the major sources of water for the lake, which holds some water year round. Smaller water sources include a perched lens of meteoric freshwater (derived from rainfall) in the large western dunes, that discharges to the north-western shore of the lake as a diffuse flow (point it out), and a discharge of groundwater from the Robinson Groundwater Basin flowing especially from the south and east (point it out). Water leaves the lake only via evaporation, which is high in this arid area. As evaporation only removes freshwater, the salts (common salt, and assorted calcium precipitates) and any sediments all accumulate in the lake body. Wind action pushes the loose material around and it is starting to form spits and islands that are segmenting the lake into separate basins. This is the fate of lakes – they have a distinct life span – they are formed when some blockage traps water in a depression, they bloom into life (be it short in the case of puddles, or eons long in the case of huge deep lakes like Baikal in Russia), then they gradually sediment up and eventually become a marsh, wide riverine flat or other more terrestrial wetland. Seagull Lake is well along on the long journey to becoming a sabkha, although this may be delayed by the sea level rise we are seeing as a result of global warming…
- Sabkha is a transliteration of the Arabic word for a salt flat. Sabkhas are supratidal, forming along arid coastlines and are characterized by evaporitecarbonate deposits with some siliciclastics. Sabkhas form subaerial, prograding and shoaling-upward sequences that have an average thickness of a meter or less. The accepted type locality is along the coast of the Persian Gulf in the United Arab Emirates. What does that all mean? They are found in arid areas. Hence the formation of evaporites like carbonate, gypsum and salt. They are recent, geologically speaking, and are located adjacent to and hydrologically contiguous with, the sea. The resulting water table in sabkhas varies from being congruent with the surface to being shallowly located just below the surface. Wind is an important feature, both in cutting areas that are lower than sea level off from tidal inundation and in deflating the surface of the sabkha itself. The combination of wind with seasonal surface inundation gives rise to beach lines and cuspate spits that gradually give rise to multiple basins across the sabkha. The Yanerbie Wetlands are a typical coastal sabkha or salt flat, lower than sea level, cut off from the sea to the north at Tractor Beach by a small dunefield and at the south by the massive White Dunes of Yanerbie. The surface is dry for much of the year, becoming impassably wet and slippery with just a small amount of rain. Vegetation and bare areas occur in patterns across the surface of the sabkha dependent on the balance of water sources and underlying chemistry…
- The dark blue colour represents where the soil water is essentially fresh. The colour lightens as it becomes more saline. At relatively low salinities Ferric oxides and calcium carbonates start to precipitate when they discharge near the surface, as “beach rock”. Gypsum (calcium sulfate) precipitation starts to occur when there are more than 155g/L of total dissolved salts. Where this occurs underground in the sabkha muds, the gypsum forms a “fragipan” or fragile hard pan, between 20-50 cm below the surface. The brine continues to evaporate, and at about 300g/L common salt starts to form on the surface of the sabkha. Where each of these precipitates occurs depends on the interplay of the intruding marine sourced waters, the relatively fresh groundwaters, direct rainfall, discharge of meteoric waters from dune water lenses and the evaporation from the surface. The mosaic of chemico-hydrologic conditions is the main controlling feature for the biological inhabitants…
- Just a quick introduction only – there is a whole world of scientific endeavour that I could go into about each of these, but for this presentation I just want do show you that even the most hostile looking habitats have their own special denizens, with a little more detail provided for two species that are currently facing challenges to their existence on the Eyre Peninsula…
- The cyanobacterial mats or benthic microbial communities common in sabkhas, saltlakes and dolines mean they are a significant carbon sink, and indeed they are a major source of oil and gas hydrocarbons in the Middle East. These BMC’s (benthic microbial communities) may be in layers buried within the sediments, or they may be present on the surface as ‘algal polygons’ or “mats” or as structures like thrombolites, or even as the microbial pennies found at the doline feeding Seagull Lake. Where BMC’s form on the lake or sabkha surface as a mat they help to bind the sediments together and also fix nitrogen, so they are an integral part of developing the hostile sabkha surface so that it can support the more complex tracheophyte plant species.
- This is a microhabitat at Seagull Lake that was too small to map, but was a really interesting find… Where groundwater seeps up through the beach rock along the southern side of the lake, filamentous algal mat communities form small ‘caps’ over the seeps. This looks like a filamentous green algae but it is really made up of chains of the golden diatom, Achnanthes brevipes . Under the cap of algae a range of marine invertebrates can be found, using the cap as a refugium from dehydration during the period when lake levels are low. Some fauna species were found both here and elsewhere in the lake during this survey, like the polychaete worm Scoloplos cylindrifer and the janarid isopod Ianiropsis n sp.. Other species were only found under the algal caps during the summer survey. The salt lake snail ( Coxiella striata ) was one of these, but is present in the main lake during winter. The pinky orange shells of dead adult specimens are present washed up on beaches right around the lake. A minute snail ( Hydrococcus brazieri ) was found associated with Coxiella under the algal caps, but is recorded nowhere else in the lake.
- This is a dwarf samphire. It is not a bushy species, with relatively little branching. It is the only samphire we know that is deciduous, dying back in cold weather, when it looks like little dead sticks. The plant is bright apple green in summer, making it easy to spot. It turns reddish when it gets cold, before dying back. The flower heads are distinctive with fan shaped bracts under each group of flowers. The prickly yellow seed is also distinctive. This species is listed as Vulnerable under the Commonwealth EPBC Act.
- The vegetation associations on sabkhas are zoned, and reflect the soil types and the groundwater chemistry. The following looks at the preferences of T. flabelliformis and the two species found most often in association with it or growing in nearby patches: Tecticornia flabelliformis (fan samphire) likes: • a mineral soil dominated by clay • can tolerate a range of moisture, preferring almost saturated conditions • tolerates high salinity • tolerates high pH • gypsiphile that grows above gypsum fragipans Tecticornia halocnemoides (grey samphire): • thrives on anything from sandy to clay soils • prefers slightly drier soils • tolerates high salinity but not as high as T. flabelliformis • prefers slightly lower pH than T flabelliformis • tolerates rain-leached gypsum substrates (eg gypsiferous sands on beaches and beach ridges) but rarely found above gypsum fragipans on playa (conditions too wet) Sarcocornia quinqueflora: • will grow on peaty, shelly, sandy and clay dominated soils • prefers saturated soils • will tolerate a wide range of salinity from a bit higher than marine down to brackish • prefers a lower pH than either T flabelliformis or T halocnemoides • does not grow above gypsum fragipans, grows commonly on carbonate beaches, less often on gypsiferous beaches The interplay of all these factors constrains the distribution of each species, and small differences in water sources, climate effects and groundwater connectivity have surprisingly large effects on this delicately balanced system. We will look further at this in the section on threats, but having introduced you to a groundwater dependent plant species, I am now going to introduce you to a GD animal species.
- According to most sources, Coxiella glauerti is restricted to Western Australia, but obviously it never read the sign on the border, because here it is in Yanerbie Wetlands and Seagull Lake in western Eyre Peninsula. This salt lake snail is NOT the common Coxiella striata that is found in most SA salt lakes – that’s the little one that washes up in pink drifts on the beaches at Seagull Lake. The resurrection snail is larger and more heavily built, white when live and grey when dead. These snails have opercula and this, along with a unique behavioural method of aestivation allows them to survive on the arid sabkha surfaces.
- To survive the long dry season, the snails gather together in ‘plates’ and then each snail BACKS the pointy end of its shell into the ground. They pack in closely together and then each animal retreats down into the deepest part of its shell and pulls its ‘front door’ (operculum) in after itself. By grouping together the snails present a large white surface that reflects heat away from them. The animals are sitting in the damp soil, and because the groundwater table is so close, cooling moisture is being drawn up past them to evaporate from the sabkha surface. They sit, as it were, in air conditioned comfort until the wet season brings them a skin of surface water and they wake up. The factors required to make this a successful strategy would seem to include: • that there be sufficient snails present that they can easily clump together in a plate without having to travel very far looking for a group and that the plates be large enough that the few snails on the outer edge that are most at risk of desiccation should not be a significant portion of the number of snails in the plate, • that the water table be sufficiently close to the surface that the air conditioning effect will work and • that the surface of the playa is not disturbed so the plates are not damaged or broken up. As with the fan samphire, the conditions for the snails’ continued existence are based on a very fine balance.
- Fan Samphire occurs in rare, but often populous, colonies on very specific habitats (coastal sabkhas have a distinctly limited occurrence, and inland salt lake occurrences appear to be relatively rare). It is currently classed as Vulnerable. As a result of its specific physical and chemical requirements colonies are often separated from neighbouring colonies by a considerable distance, leading to suggestions that the species may comprise a number of genetically very different groups (Shepherd, pers com).
- I mentioned earlier how these habitats are finely balanced mosaics that depend on tight chemico-hydrological parameters, so it is hardly surprising that the biggest threat is…
- HYDROLOGY, HYDROLOGY, HYDROLOGY Really, there are other threats, but this one is the biggie and it comes in several flavours. If you change the hydrology there will be rapid consequences. Extraction of water for use as construction water for road building as is apparent here at Yanerbie sabkha will drop the water table across the entire sabkha. It you look closely at the photo you can see the gypsum layers under the sabkha surface. Now that the atmospheric oxygen can reach the exposed substrate you can also see the development from potential to actual acid sulfate soils (the yellow colour is jarosite). The adjacent population of Tecticornia flabelliformis was all limp from dehydration when we visited the site in late summer and large plates of resurrection snails were dead. Sabkha surfaces are often slightly bowl-shaped and the water table near the edge of the pan may be further from the surface. If the water table is artificially lowered by extraction of water, you may see the impacts on the snails first in a ring around the edge of the pan. The plates of snails in the middle of the pan may be the last to fail. This kind of action, where extraction of water from under a sabkha puts an entire local population of a Commonwealth protected species at risk is actually a “controlled action” under the EPBC Act. Mind you, the snails have no similar level of protection... At The Whirlpool, the doline was also pumped for water. While the marine inflow managed to refill the hole with water overnight each time it was pumped, the relict marine invertebrate populations were all gone. Should pumping cease and the spring be left alone in the future, some degree of recovery will occur with saltlake plants and invertebrates and visually it will look OK, but it will be without its relict marine invertebrates. Should the spring be used again as a water resource, it again will be visually impaired BUT of greater concern is that the connected Paddy’s Vent within the wider Caltapanna Wetlands will be affected.
- Interrupting groundwater connectivity by putting compacted tracks across sabkhas has been responsible for destroying large numbers of T. flabelliformis at Arno Bay on the Eyre Peninsula, and Port Parham on Gulf St Vincent. As well, the mounded dirt washes onto the sabkha, sometimes raising the surface level sufficiently for Tecticornia halocnemoides to replace the fan samphire.
- Sea level rise is the opposite hydrological extreme. As sabkhas are just above, at, or even below, current sea level, any increase in sea level increases the height of the water table. And the increased inundation with seawater has a profound impact on the soil chemistry. When sabkhas dry out, are flooded with freshwater, or receive more rain, the gypsum present in the soil and surface tends to resist dissolution. We say it is ‘sparingly soluble’ in water. This is why the plant that tends to replace T flabelliformis in those situations is T halocnemoides , which tolerates gypsum in drier, slightly lower salinity situations. But when seawater inundates areas with gypsum evaporites, the gypsum dissolves. It seems counter-intuitive that saltier water can dissolve gypsum easier than freshwater can, but it is so. It is called the ionic strength effect and relates to the ionic charges of the electrolytes. You can prove this for yourself at home by attempting to dissolve a known weight of gypsum in freshwater and in seawater… The upshot is, with additional seawater, at first the T. flabelliformis does very well but as the gypsum layer dissolves and the salinity becomes more regularly marine or weaker, Sarcocornia quinqueflora can invade. As it is a mat plant, it rapidly takes up all available space and the T. flabelliformis disappears. The photographs show the impact of SLR at Torrens Island sabkha where a rapid amount of local relative sea level rise has affected a fan samphire sabkha. The driest, landward part of the sabkha is showing signs of erosion of the benthic microbial community that holds the surface together and provides nitrogen for the Tecticornia , but the plants themselves are flourishing with the additional inundation. The upper photo shows the main central sabkha of the island that is now almost completely vegetated with Sarcocornia .
- There are other threats to these groundwater dependent ecosystems. These mainly relate to disturbance and grazing. ORV tracks, dumping, grazing animal tracks all break up the benthic microbial communities, loosen and dislodge the ‘plates’ of Coxiella glauerti , and damage individual plants of Tecticornia flabelliformis . Selective grazing of the fruiting heads of T. flabelliformis (which are salty/sweet) by fallow deer has resulted in its extirpation from one sabkha in the River Light delta north of Adelaide.