Ecohydrological Conceptualisation of the Fortescue Marsh Region
Landscape characteristics
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- Bu səhifədəki naviqasiya:
- Ecological water requirements of wetlands
- 1.3.3 Ecohydrological conceptualisation approach
- Figure 1-4: Landscape arrangement of EHUs
- Table 1-4: General attributes of landscape ecohydrological units (EHUs) in the central Pilbara region EHU Landscape position, land surface and soils
- Level of connectivity to groundwater systems Major vegetation types
Landscape characteristics The Pilbara landscape is ancient and shaped by a complex set of geomorphic and geological factors. In order to understand landscape function, it is necessary to consider landscape evolution processes and the effect these have had on the present day environment. As an example, palaeochannels are regionally significant hydrogeological features in the Pilbara that typically host a fully connected groundwater system and provide important habitats for stygofauna. Interactions between these palaeochannel features and drainages can be important for the persistence of surface and subterranean ecosystems. The poor fertility of Pilbara soils, a legacy of millennia of weathering and leaching, accentuates the importance of run-off and run-on processes for the supply of water and nutrients to vegetation. Patterns of vegetation are often related to surface geology, as mediated by the effect of geology on soil properties. Although different vegetation types may occur on different geological substrates in similar landscape position, in many cases they are likely to exhibit similar water use strategies (for example floristically different spinifex communities). Hardpans are commonly encountered within alluvial plains of the central Pilbara, comprising near surface indurated horizons which vary in thickness from centimetres to meters. Hardpans develop where there is a net moisture deficit and lack of seasonal flushing, facilitating the accumul ation and precipitation of cementing agents such as oxides of iron, aluminium and manganese , carbonates and/or silica. The process of hardpan formation can be prolonged and therefore requires stable surfaces over geological timescales. Hardpans generally have low permeability and thus may restrict the percolation of water into the underlying regolith. Major drainage systems of the central Pilbara commonly host groundwater derived calcrete. The calcrete has developed in riverine or lacustrine alluvium subject to stro ngly evaporitic conditions and fluctuating groundwater levels (Mann and Horwitz, 1979). These conditions facilitate the precipitation of calcium carbonate, where the solubility of calcite is exceeded. Varying degrees of silicification may also be exhibited, reflecting the influence of saline groundwater and silica precipitation/displacement of calcium carbonate. Some areas of calcrete occur higher in the landscape, in association with ancient drainage systems that are now dissected by more recent drainages. Carbonate precipitation remains active in spring discharge regions, such as at Millstream and Weeli Wolli Spring (Reeves et al., 2007). The Pilbara has been subject to many decades of pastoral land use, with associated land degradation issues (O’Grady, 20 04). The effects of livestock grazing, the introduction of weeds and feral animals, as well as modified fire regimes have all contributed to significant landscape changes affecting landscape ecohydrological connectivity. The spread of Buffel Grass (Cenchrus ciliaris) in riparian environments is a prime example. This species displaces native vegetation by increasing fuel loads, facilitating more frequent and intense fires and then regenerating/colonising rapidly after fire events. Such changes are expected likely to influence patterns of vegetation water use and infiltration/runoff processes. Post European settlement landscape effects are continuing with evolving rangelands management, and need to be considered when interpreting and conceptualising ecohydrological processes. Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 11 Our ref: FM-EcoConcept_v8.docx Ecological water requirements of wetlands Wetlands are permanently or persistently inundated or saturated by surface or groundwater. They may include subterranean habitats. Such areas require special attention owing to their potentially hi gh level of connectivity with other landscape elements, restricted occurrence, and propensity to support unique or unusual ecosystems. Water can converge and collect in wetlands from many different pathways. Transit times along these pathways can vary spatially and temporally in response to inputs and the physical structure of the catchment, resulting in dynamic and complex hydrological regimes (Neumann, 2013). In flat terrain where flow rates are lower, such as in lake chain systems, water is exposed for a longer time to climatic and biogeochemical processes which can alter its physicochemical properties. In steeper terrain where flow rates are greater, such as in rivers or headwater streams, there may be little modification of water properties owing to the shorter transit times. The properties of groundwater contributing to a wetland environment may similarly be modified based on residence times in aquifer systems. The level of persistence of aquatic environments has an important effect on their biotic asse mblages, and their functional importance as refuges (Davis et al., 2013). Longer hydroperiod allows more species to colonise and greater habitat complexity to develop (Boulton and Jenkins, 1998; Sheldon et al., 2002). In ephemeral wetlands the transition between wet and dry periods is important for driving biotic and abiotic exchanges, ecosystem succession processes, and maintaining ecosystem integrity (Boulton and Lloyd, 1992; Boulton and Jenkins, 1998; Junk et al., 1989). Wetland ecosystems in the central Pilbara tend to be strongly influenced by episodic, intense, rainfall events and rapid surface water movement from source areas (Pinder et al., 2010). Many surface water features, such as river pools and clay pans, are intermittent or ephemeral. The persi stence of waterbodies is dictated by flood frequency; the rate of water loss following flood events by drainage, evapotranspiration and infiltration/percolation into deep groundwater systems. Bank storage and/or perched groundwater may be important for prolonging waterbody persistence, where permitted by local area geomorphology. Different hydrological regimes associated with flooding and flow frequency, flood duration, salinity and source of water may support different species assemblages. Different stages of the hydrological regime may also be important for species life cycles, such as the utilisation of flooded wetlands by waterbirds for breeding. Permanent pools usually occur where bedrock structures impede hyporheic groundwater flow, where springs discharge groundwater or where flow has scoured pools that are sufficiently deep to encounter the watertable (Pinder et al., 2010). These wetlands are uncommon, typically supporting unusual or unique flora and fauna assemblages and potentially functioning as re fuges for a range of aquatic species. Subterranean habitats in groundwater are defined by the types of voids and interstitial spaces within host rocks and groundwater chemistry (Halse et al., 2014). Both attributes are influenced by the geology of the aquifer, the amount of landscape weathering, and local chemical and hydrological processes (Reeves et al., 2007). Connectivity with the surface influences the supply of oxygen and organic matter into subterranean ecosystems, highlighting the importance of recharge dynamics for these habitats as associated with cyclonic recharge events. Depth to groundwater is considered to constrain the complexity and abundance of stygofauna communities in the Pilbara (Halse et al., 2014). The response of stygofau na to fluctuations in the watertable is poorly understood; however, their persistence over geological time suggests they have capacity to adapt to dynamic habitat availability. 1.3.3 Ecohydrological conceptualisation approach Taking into account the ecohydrological principles discussed in Section 1.3.2, a landscape ecohydrological conceptualisation was developed through the definition of ecohydrological units (EHUs) for the study area. Each EHU represents a landscape element with broadly consistent and distinctive ecohydrological attributes (MWH, 2014). In summary the spatial definition of the EHUs is based on interpretation of land system mapping units developed by the Department of Agriculture (Van Vreeswyk et al., 2004), surface drainage networks, groundwater systems, inferred vegetation water use behaviour based on vegetation mapping (structure and dominant species) and Landsat NDVI (Normalized Difference Vegetation Index). Nine EHUs are recognised within the studystudy area as listed below: Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 12 Our ref: FM-EcoConcept_v8.docx EHU 1 Upland source areas - hills, mountains, plateaux. EHU 2 Upland source areas – dissected slopes and plains. EHU 3 Upland transitional areas – drainage floors within EHUs 1 and 2 which tend to accumulate surface flows from up-gradient. EHU 4 Upland channel zones - channel systems of higher-order streams which are typically flanked by EHU 3 and dissect EHUs 1 and 2. EHU 5 Lowland sandplains – level to gently undulating surfaces with occasional linear dunes. Little organised drainage but some tracts receive surface water flow from upla nd units. EHU 6 Lowland alluvial plains – typically of low relief and featuring low energy, dissipative drainage. EHU 7 Lowland calcrete plains – generally bordering major drainage tracts and termini, typically with shallow soils and frequent calcrete exposures. EHU 8 Lowland major channel systems and associated floodplains. EHU 9 Lowland receiving areas - drainage termini in the form of ephemeral lakes, claypans and flats. The key attributes of each EHU are further described in Table 1-4. Factors considered in the definition of EHUs included: landscape position and land surface types, including soil characteristics; landscape water balance processes; surface drainage/redistribution processes; connectivity and interactions between surface water and groundwat er systems; and major vegetation types and their water use strategies. The EHUs transition from upland to lowland environments, in a spatial arrangement hierarchy depicted in Figure 1-3 and illustrated in a landscape context in Figure 1-4. The landscape distribution of aquatic habitats, such as pools, springs and ephemeral lakes, were also considered in the definition of EHUs. These habitats are typically confined to EHUs 8 and 9, where surface and groundwater flows accumulate and surface water/groundwater interactions may occur. Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 13 Our ref: FM-EcoConcept_v8.docx Figure 1-3: Landscape hierarchy of EHUs and major water flow connectivity Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 14 Our ref: FM-EcoConcept_v8.docx Figure 1-4: Landscape arrangement of EHUs Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 15 Our ref: FM-EcoConcept_v8.docx Table 1-4: General attributes of landscape ecohydrological units (EHUs) in the central Pilbara region EHU Landscape position, land surface and soils Dominant landscape water balance processes Dominant surface drainage/connectivity processes Level of connectivity to groundwater systems Major vegetation types 1 Upland source areas - hills, mountains, plateaux. Land surface is steep and rocky. Shallow or skeletal soils with frequent bedrock exposures. Rainfall Infiltration Soil evaporation Run-off Generally short distance overland flow into dendritic drainage networks (1 st , 2 nd and 3 rd order streams). Local and regional groundwater systems are deep and not accessible to vegetation. Preferential recharge can occur as dictated by local scale geology/regolith. Hummock grasslands. Vegetation water demand met by direct rainfall and localised surface redistribution. 2 Upland source areas – dissected slopes and plains, down-gradient from EHU 1. Land surface is sloping with shallow to moderately deep colluvial soils. Rainfall Infiltration Soil evaporation Run-off Overland flow short distance into channel drainage systems (mainly 1 st to 4 th order streams). Local and regional groundwater systems are deep and not accessible to vegetation Preferential recharge can occur as dictated by local scale geology/regolith. Hummock grasslands. Vegetation water demand met by direct rainfall and localised surface redistribution. 3 Upland transitional areas – drainage floors within EHUs 1 and 2 which accumulate surface flows from up- gradient. Soils of variable depth derived from alluvium. Greater storage relative to soils in EHU 1 and 2. Inflows Infiltration Storage Evapotranspiration Surface accumulation and infiltration of flood flows (overland flows and channel breakouts). Excess volumes transferred to adjacent channels (EHU 4). Local and regional groundwater systems are deep and not accessible to vegetation. Smaller drainage floors support hummock grasslands; larger drainage floors support Eucalyptus and Acacia shrublands and woodlands. Vegetation water demand met by direct rainfall and stored soil water replenished by infrequent flood events. 4 Upland channel zones - channel systems of higher order streams (generally ≥5 th order) which dissect EHU 1 and EHU 2. Channels are high energy flow environments, subject to bed load movement and reworking. Soils of variable depth derived from alluvium including zones of deep Inflows Infiltration Storage Evapotranspiration Channel throughflow Channel beds and banks accept and store water during flow events. Large flows are transmitted down-gradient. Channels may support intermittent or persistent pools replenished by flood flows. Regional groundwater systems are deep and not accessible to vegetation. Transient or less commonly persistent shallow groundwater systems may develop beneath channels in places, as dictated by local scale geology/regolith. In rare cases these may be connected with pools. Channels are typically lined with narrow woodlands of E. victrix, A. citrinoviridis and/or other Eucalyptus and Acacia species. These are sustained by soil water replenishment from flow events. Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 16 Our ref: FM-EcoConcept_v8.docx EHU Landscape position, land surface and soils Dominant landscape water balance processes Dominant surface drainage/connectivity processes Level of connectivity to groundwater systems Major vegetation types soils. Generally high infiltration rates. In rare cases vegetation may access perched groundwater for periods of time. 5 Lowland sandplains - landform characterised level or gently undulating plains up to 10 km in extent. Deep sandy soils of aeolian origin. Uncommonly features linear dunes up to about 15 m in height. Infiltration Storage Evapotranspiration Groundwater recharge Poorly organised drainage. High rainfall infiltration and recharge. Runoff is minimal and if it does occur is generally localised, with accumulation in swales or depressions. Sandplains may receive and infiltrate inflows from channels deriving from up-gradient areas. Groundwater systems are generally deep and not accessed by vegetation. May include important zones of recharge, with associated groundwater mounding. Possibility of transient or more persistent perched groundwater at localised scales, depending on regolith characteristics. Hummock grasslands, with Acacia sp. and other shrubs, occasional mallee Eucalypts. Distinctive grassland communities relative to other EHUs. Tracts receiving run-on include Acacia and Eremophila shrublands. 6 Lowland alluvial plains – broad depositional plains of low relief. Soils typically loams, earths and shallow duplex types. Subsurface calcareous hardpans are frequently encountered. Localised surface redistribution Infiltration Storage Evapotranspiration Complex surface water drainage/redistribution patterns. Land surfaces are generally dissected by low energy channels of variable form and size. Areas of sheetflow can occur, which may be associated with banded vegetation formations. Some areas may be subject to infrequent flooding. Infiltration may be significant at local scales in association with drainage foci, These areas are likely to be correlated with relatively higher leaf area index. Groundwater systems are generally moderately deep (>10m) to deep (>20m) and not accessed by vegetation. Acacia shrublands; less commonly Hummock grasslands, Tussock grasslands or low shrublands of Bluebush/Saltbush. 7 Lowland calcrete plains – plains of low relief generally bordering major drainage tracts and termini. Shallow soils underlain by calcrete of variable thickness, which occasionally outcrops. Localised surface redistribution Infiltration Soil evaporation Groundwater recharge Complex surface water drainage/redistribution patterns. Calcrete platforms may have varying permeability. Land surfaces are generally dissected by low energy channels of variable form and size. Depth to groundwater may vary from shallow (<5 m) to deep (>20m). Preferred pathways may facilitate rapid recharge at local scale. Groundwater systems are generally not accessed by vegetation. Hummock grasslands and Acacia scrublands with occasional Eucalypts. Distinctive vegetation communities relative to other EHUs. Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 17 Our ref: FM-EcoConcept_v8.docx EHU Landscape position, land surface and soils Dominant landscape water balance processes Dominant surface drainage/connectivity processes Level of connectivity to groundwater systems Major vegetation types Generally characterised by numerous localised drainage termini. Groundwater systems in calcrete can provide important stygofauna habitat. 8 Lowland major channel systems and associated floodplains - supporting large flow volumes in flood events. Channels are high energy flow environments, subject to bed load movement and reworking. They may be physically altered by cyclonic floods. Inflows Ponding Infiltration Storage Evapotranspiration Channel throughflow Groundwater recharge Groundwater discharge (localised) Channel beds and banks accept and store water during flow events. Large flows are transmitted down-gradient. Soil water in the floodplains is replenished during flooding breakouts. Channels support transient, persistent and permanent pools. Depth to groundwater may vary from shallow (<5 m) to deep (>20m). Channels are significant recharge zones. Transient, persistent or permanent shallow groundwater systems may develop beneath channels in places, as dictated by local scale geology/regolith. These may be connected with pools in some situations. Groundwater is generally fresh. Groundwater systems can be accessible to vegetation in some situations. Evaporative discharge of shallow groundwater may occur. Inflows from up-gradient sources sustain Eucalyptus and Acacia forest and woodland vegetation communities or Tussock grasslands. Supports most of the recognised groundwater dependant vegetation communities in the central Pilbara (with the key indicator species being Eucalyptus camaldulensis, E. victrix and Melaleuca argentea). 9 Lowland receiving areas - drainage termini in the form of ephemeral lakes, claypans and flats. Deep silty and clay textured soils. Variable surface salinity (resulting from evaporites). Soils may be underlain by calcrete/ silcrete hardpans of variable depth. Inflows Ponding Infiltration Storage Soil evaporation Evapotranspiration Groundwater recharge Groundwater discharge (localised) Drainage termini receive inflows from up-gradient drainage systems. Transient to persistent ponding may occur as dictated by flooding regimes, with spillovers possible in large flooding events. Sediment accumulation and evaporative concentration of salts. Depth to groundwater may vary from shallow (<5 m) to deep (>20m). Groundwater may be fresh, brackish or saline. Groundwater systems can be accessible to vegetation in some situations. Evaporative discharge of shallow groundwater may occur. Fringed or occupied by distinctive vegetation communities such as Samphire. Regularly inundated areas may be largely devoid of vegetation. Vegetation adapted to waterlogging, flooding and salinity stressors. Potential to support groundwater dependant ecosystems (GDEs), depending on the level of surface and groundwater connectivity. However this is likely to be uncommon. Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 18 Our ref: FM-EcoConcept_v8.docx Ecohydrological Conceptualisation of the Fortescue Marsh Region Status: Final September 2015 Project No.: 83501069 Page 19 Our ref: FM-EcoConcept_v8.docx Kataloq: media media -> Uşağın fərdi psixoloji hazırlığı 20 azn ağız boşluğunun kompleks peşəkar gigiyenası 80 azn media -> Tibb xidmətinin adı media -> Әrin cәmi vә hәr bir kateqoriya üzrә mәblәği vә kredit portfelindә xüsusi çәki media -> Qeyri-standart kreditlәrin cәmi vә hәr bir kateqoriya üzrә mәblәği vә kredit portfelindә xüsusi çәkisi media -> Ramiz ƏSKƏr türk xalqlari əDƏBİyyati oçerkləRİ-1 Bakı – 2011 media -> AZƏrbaycan miLLİ elmlər akademiyasi folklor institutu qarabağ: folklor da bir tariXDİr V kitab Yüklə 12,45 Mb. Dostları ilə paylaş:
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